CONCRETE, REINFORCEMENT, FORMWORK AND JOINTS

1 CONCRETE, REINFORCEMENT, FORMWORK AND JOINTS

1.1 General

This section covers all requirements concerning concrete, reinforcement and formwork . For clarity, this section is divided into four sub-sections as follows:

1.2 Concrete

1.3 Reinforcement

1.4 Formwork

1.5 Joints

The sub-sections are complementary to each other and shall be read accordingly.

1.6 Concrete

1.6.1 Scope

This sub-section covers the supply of materials for concrete, design of concrete mixes, quality control of concrete, mixing, transporting, placing and curing of concrete and testing of water retaining structures.

1.6.2 Organisation of Concrete Production at the Site

At the commencement of the contract, the Contractor shall submit for the approval of the Engineer a method statement detailing with regard to the requirements of this Specification his proposals for the organization of concreting activities at the site.

The method statement shall include the following items: •Plant proposed;
•Layout of concrete production facility;
•Proposed method of organization of the concrete production facility;
•Quality control procedures for concrete and con¬crete materials;
•Method of transport and placing of concrete;
•Striking times for formwork and procedure for temporary support of beams and slabs.

1.6.3 Test Certificates

Unless otherwise directed by the Engineer, manufacturer's test sheets shall be supplied with each consign¬ment of cement and admixture certifying compliance with the relevant standard.

The Contractor shall also submit to the Engineer certificates of calibration for the weighing and dispensing equipment on the concrete batch mixing plant.

The Contractor shall also submit to the Engineer certified test results for all tests carried out on aggregate, water, fresh concrete and hardened concrete, all as specified.

In case of doubt, new tests shall be executed at the Contractor' s expense.

1.6.4 Aggregate Samples

Before work on trial mixes of concrete is commenced, the Contractor shall submit for approval samples 50 kg in weight of each aggregate, which he proposes to use. The source of each aggregate shall be clearly marked on the container of each sample.

Certified test results demonstrating compliance with relevant quality standard shall be submitted at the same time. Samples approved by the Engineer shall be preserved at site for reference.

1.6.5 Record of Concreting

An accurate and up to date record showing dates, times, weather and temperature when various sections of the works were concreted shall be kept by the Contractor and shall be available for inspection by the Engineer.

The Contractor shall also record the results of all concrete tests and shall identify these results for the parts of the works of which the sampled material is representative.

The Contractor shall submit to the Engineer, not more than twenty-four hours in arrears, a daily return for each grade of concrete of the number of batches mixed, the number of batches and total volume of concrete placed, the number of batches wasted or rejected and the weight of cement used.

The return shall also include specific details of each location in the works where concrete was placed, together with the grade of concrete, total volume of concrete placed and the number of batches used for each location.

1.6.6 Concrete Mixes

At the commencement of the works the Contractor shall design a mix for each grade of concrete, which will be required for use in the works and shall submit full details of the mix designs to the Engineer for his approval. Each mix design shall be according to the requirements of the Specification.

1.6.7 Construction Joints And Lifts

The Contractor shall submit to the Engineer for his approval, as soon as is practicable after the acceptance of his tender and not less than three weeks before the commencement of concreting, drawings showing his proposals for placing concrete on which the position of all construction joints and lifts shall be shown.

No concreting shall be started until the Engineer has approved the method of placing, the positions and form of the constructions joints and the lifts. The construction joints shall be located so as not to impair the strength of the structure. Rebates, keys or notches shall be formed and water stops inserted as the Engineer may require. The position of construction joints and the size of formwork panel shall be so coordinated that where possible the line of any construction joint coincides with the line of a formwork joint, and that in any case all construction joint lines and formwork joint lines appear as a regular and uniform series.

For all exposed horizontal joints and purposely inclined joints, a uniform joint shall be formed with a batten of approved dimensions to give a straight and neat joint line.

1.6.8 Cement

All cement used on the work shall be standard brand Portland cement from a single approved source conform¬ing to the requirements of Portland cement class PZ 25-NW or class PZ 35-L (DIN 1164). The source of cement shall not be changed without prior approval of the Engineer.

The cement shall be tested for soundness in accordance with the relevant DIN standards. Cement used in the works for structural parts underground shall be sulphate-resisting Portland cement unless otherwise specified or agreed with the Engineer.

The Contractor shall provide from each consignment of cement delivered to site such samples as the Engineer may require for testing. Any cement which is, in the opinion of the Engineer, lumpy or partially set shall be rejected and the Contractor shall promptly remove such cement from the site. Cement, which has been stored on the site for more than forty days, and cement, which in the opinion of the Engineer is of doubtful quality, shall not be used in the works unless it is retested and the test results show that it complies in all respects with the relevant standard.

1.6.9 Storage of Cement

Immediately upon arrival at the site, cement shall be stored in silos designed for the purpose or in dry weather-tight and properly ventilated structures with floors raised 500 mm above ground level with adequate provision to prevent absorption of moisture. Insulation shall be provided to prevent the temperature of the cement exceeding 770C. As a minimum cement storage silos shall be painted with a light reflecting material.

All storage facilities shall be subject to approv¬al by the Engineer and shall be such as to permit easy access for inspection and identification. Each con¬signment of cement shall be kept separately and the Contractor shall use the consignments in the order in which they are received.

Cement of different types and from different sources shall be kept in clearly marked secure storage facilities. Cement delivered to the site in drums or bags provided by the supplier or manufacturer shall be stored in the unopened drums or bags until it is used in the works.

Any cement in drums or bags, which have been opened on the site, shall be used immediately or shall be disposed of.

1.6.10 Aggregates

Aggregates shall be hard, durable and clean and shall not contain deleterious materials in such form or quantity as to adversely affect the strength of concrete.

Aggregates for concrete shall be obtained from an approved source, and shall conform to the requirements of DIN 1045 and DIN 1084, and shall be washed clean.

Sampling and testing of aggregates shall be carried out in accordance with the requirements of the appropriate clause of DIN 4226.

The aggregates to be supplied shall not give rise to any alkali reaction with the cement, weather silica or carbonate. Potential reactivity or otherwise of aggregates shall be determined in accordance with ASTM C 289.

In addition, the soluble chlorides and sulphates content of the aggregates shall be such that the concrete mix as a whole complies with the specified limits of salt content. Tests for chlorides and sulphates and for potential alkali reaction shall be carried out when required by the Engineer.

1.6.11 Storage of Aggregates

The Contractor shall provide means of storing the aggregates at each point where concrete is made such that:
•each normal size of coarse aggregate and fine aggregate shall be kept separate at all times;
•contamination of the aggregates by the ground or other foreign matter shall be effectively prevented at all times;
•each heap of aggregate shall be capable of draining freely.
•aggregates are to bekept as cool as possible by shading and provision of water sprinkling if required.

The Contractor shall ensure that graded coarse aggregates are tipped, stored and removed from store in a manner that does not cause segregation.

Wet fine aggregate shall not be used until, in the opinion of the Engineer, it has drained to a constant and uniform moisture content, unless the Contractor measures the moisture content of the fine aggregate continuously and adjusts the amounts of fine aggregate and added water in each batch of concrete mixed to allow for the water contained in the fine aggregate. If necessary to meet the requirements of this clause, the Contractor shall protect the heaps of fine aggre¬gate against inclement weather.

1.6.12 Water

Water for washing of aggregates and for mixing concrete shall be in accordance with DIN 4030 and DIN 1045 and shall be clean and free from objectionable quantities of organic matter, alkali, salts and other impurities.

When required by the Engineer, the Contractor shall take samples of the water being used or which it is proposed to use for mixing concrete and test them for quality1 including determining the concentration of sulphates and chlorides, which shall be such that the concrete mix as a whole complies with the specified limit for salt content.

The Contractor shall ensure that sufficient quantities of water for production and curing are available on the site at all times.

1.6.13 Admixtures

At the Contractor's opinion, or at the request of the Engineer, but in either case at the expense of the Contractor, an admixture may be added to the concrete to control the set, effect water reduction and increase workability. Such admixture may be either a hydroxylated carboxylic acid type or a ligning-sulphonate type but shall contain no calcium chloride. The required quantities of cement shall be used in the mix regardless of whether or not any admixture is used. The quantity of admixture used and the method of mixing shall be in accordance with the manufacturer's instructions. Use of admixture is to be avoided whenever possible.

Admixtures shall not be used unless the Engineer has given his prior approval in writing for each instance. Both, the amount added and the method of use shall be to the approval of the Engineer who shall also be provided with the following information:
•the typical amount added and the detrimental effects, if any, of an increase or decrease in this amount;
•the chemical name(s) of the main active ingredient(s) in the admixture;
•whether or not the admixture leads to the entrainment of air when used at the amount the manufacturer recommends.

Any approved admixture shall fulfil the test requirements of the Institut fur Bautechnik (IfBt) in West Berlin, Edition No. 3, February 1984 or equivalent.

When more than one admixture is used in a concrete mix, the compatibility of the various admixtures shall be ascertained by standard tests and certified by the manufacturers.

1.6.14 Calcium Chloride

The use of calcium chloride in concrete will not be permitted.

1.6.15 Test Equipment

The Contractor shall furnish all equipment and materials necessary for collecting samples and carrying out field laboratory tests on materials for concrete and on fresh and hardened concrete. Laboratory equipment shall be housed in a suitable laboratory building on the site, which shall also incorporate space for storage of field test equipment and for curing of concrete test cubes in an orderly manner so that they are readily accessible for testing on the due date. The Contractor shall also furnish all weights, containers and other equipment necessary for testing the weigh-batching equipment for concrete materials and the dispensers for admixtures.

1.6.16 Proportioning in General

Concrete shall be composed of cement, aggregates, admixtures and water. These materials shall be of the qualities specified. The exact proportions in which these materials are to be used for different parts of the work shall be determined by the Contractor in accordance with all requirements given in DIN 1045 and submitted to the Engineer for review prior to use in the work. In general, the mix shall be designed to produce a concrete capable of being deposited so as to obtain maximum density and smoothness of surface. The proportions shall be changed whenever necessary or desirable in the opinion of the Engineer.

1.6.17 Water-Cement Ratio and Compressive Strength

The minimum compressive strength and cement contents of concrete shall be not less than required in the appropriate DIN standard. The Engineer may order the cement contents for any class of concrete to be increased over the quantity specified in the tabulation if he determines that such increase is necessary to obtain the required strength. Such increased quantities of cement, if so ordered, shall be furnished by the Contractor at no additional cost to the Employer. The maximum water-cement ratio shall be 55 litres of water per 100 kilograms of cement.

1.6.18 Limits Of Salt Content

No concrete shall contain more than the following total quantities of substances expressed as percent-ages by weight of cement:
For all mixes:
•total chlorides 0.6 % (as Chloride ions)
•total acid soluble sulphate 4.0 % (as S0₃ ions)

Tests shall be carried out in accordance with the appropriate DIN standards.

1.6.19 Consistency

The quantity of water entering into a batch of concrete shall be in accordance with DIN 1045, just sufficient, with a normal mixing period, to produce a concrete which, in the judgement of the Engineer, can be worked properly into place without segregation and which can be compacted by the vibratory methods herein specified to give the desired density, un-permeability and smoothness of surface. The quantity of water shall be changed as necessary, with variations in the nature or moisture contents of the aggregates, to maintain uniform production of a desired consistency. The consistency of the concrete in successive batches shall be determined by tests in accordance with DIN 1048. The slumps to be used will be determined by the Engineer for the various parts of the work but in general they shall be <40 cm>.

1.6.20 Mix Design

The Contractor shall submit to an independent laboratory, approved by the Engineer, samples of coarse and fine aggregate and cement proposed to be used in the work. From analyses and tests of the samples furnished, the laboratory shall design a concrete mix to meet each of the strength requirements and slumps specified. The laboratory shall also prepare two (2) test cylinders of each design mix from the samples furnished and test one at 7 days and one at 28 days. Three (3) copies of test results and mix designs shall be submitted to the Engineer for approval. All costs for furnishing samples mix design and testing shall be at the expense of the Contractor.

1.6.21 Trial Mixes

As soon as the Engineer has approved each of the concrete mix designs, three batches of concrete for each grade shall be made at site under full-scale production conditions using the same mixing time and handled by means of the same plant, which the Contractor proposes to use in the works.

The proportions of cement, aggregates and water shall be carefully determined by weight in accordance with the Contractor's approved mix design and sieve analyses shall be made in accordance with DIN 4226 of fine aggregate and of coarse aggregate used.

The amount of cement and of each separate size of aggregate entering into each batch of concrete shall be determined by direct weighing equipment furnished by the Contractor and approved by the Engineer. The quantity of water entering the mixer shall be measured by a suitable water meter or other measuring device of a type approved by the Engineer and capable of measuring the water in variable amounts within a tolerance of three percent.

The slump of each batch of each trial mix shall be determined immediately after mixing by the method described in DIN 1048 and not be outside the limits specified in clause 3.2.20.

In accordance with DIN 1048 three test cubes from each of the three batches shall be made by the Contractor in the presence of the Engineer from each trial mix. The cubes shall be made, cured, stored and tested at 28 days after manufacture in accordance with the method described in DIN 1048. If the average value of the compressive strength of the nine cubes taken from any trial mix is less than the target mean strength used in the mix design or if any individual cube test result falls below 85 % of the target mean strength, the Contractor shall re-design that mix and make a further trial mix and set of test cubes.

A full-scale test of the workability of each trial mix of each grade of concrete shall be made by the Con-tractor in the presence of the Engineer. The trial mix of each grade of concrete shall be batched, mixed and then transported a representative distance in the manner that the Contractor proposes to batch, mix and transport the concrete to be placed in the works. After discarding the first batch so made, the concrete from later batches shall be placed and compacted in trial moulds both for reinforced and mass concrete with dimensions typical of the works in accordance with the procedures described in later clauses, the sides of the moulds being capable of being stripped without undue disturbance of the concrete placed therein. The sides of the moulds shall be stripped after the concrete has set and the workability judged by the surface appearance and compaction obtained. If the workability test shows that the required workability is not attained for any trial mix for any grade of concrete, the trial mix shall be re-designed by the Contractor and a further full scale workability test undertaken for that trial mix.

The re-design of the concrete mixes and the making and testing of trial mixes of concrete shall be repeated for each grade of concrete until trial mixes of concrete have been established which meet the specified requirements and have the required workability as demonstrated in the full scale workability test described above.

If at any time during the construction of the works the Engineer approves a change in the source of cement of aggregate or if the grading of the aggregate alters to such an extent that the fraction of aggregate retained on any sieve cannot be maintained within five percent of the total quantity of fine and coarse aggregate when adjusted as specified for sampling and testing of aggregates, then further trial mixes of concrete shall be made, tested and approved for use.

1.6.22 Material Batching

All cement used in the manufacture of concrete shall be measured by weight with an approved weighing device. For concrete of grades more than B 10, the fine aggregate and the several nominal sizes of coarse aggregate shall be measured singularly or cumulatively by weight using weigh-batching machines.

For concrete of grade B 10, the fine and coarse aggregate shall be measured separately either by weight using weigh-batching machines or by volume in gauge boxes.

Weigh-batching machines shall provide facilities for the accurate control and measurement of the aggregates either singularly or cumulatively and shall be capable of immediate adjustment by semi-skilled operators in order to permit variations to be made to the mix. All weigh dials shall be easily visible from the place at which filling and emptying of the hoppers is controlled.

Every concrete mixing machine shall be fitted with a device to measure added water by weight and shall be so constructed that the water inlet and outlet valves are interlocked so that either one of them cannot be opened unless the other is fully closed. The weighing device shall be provided with an overflow with a cross-sectional area at least four times that of the inlet pipe and with its discharge point clear of the mixing plant. The entire water system shall be maintained free of leaks at all times and the measuring device shall be fitted with a drain pipe which allows the full quantity of water being measured to be drained off for checking the measurement. The outlet arrangement of the measuring device shall be such that between five and ten percent of the water enters the mixer before the other materials and a further five to ten percent of the water enters the mixer after the other materials. The remainder of the water shall be added at a uniform rate with the other materials. The water measuring device shall be readily adjustable so that the quantity of water added to the mixer can, if necessary, be varied for each batch.

Where volume batching is permitted by the Specification, gauge boxes shall be soundly constructed of timber of steel to contain exactly the volume of the various aggregates required for one batch of each mix. They shall have closed bottoms and shall be clearly marked with the mix and the size of the gauge box for fine aggregate, an allowance shall be made for the bulking of the fine aggregate due to the average amount of moisture contained in the stockpiles on the site. Before the Contractor shall put any gauge box into use on the site, he shall obtain the approval of the Engineer of the size and construction of such gauge box. Any admixtures, which may be used, shall be measured separately in calibrated dispensers.

All mixing and batching plants shall be maintained free of set concrete or cement and shall be clean before commencing mixing. The accuracy of calibration of any weighing plant, water measuring plant and admixture dispenser shall be checked before carrying out trial mixes, before mixing concrete for inclusion in the works, after each service or adjustment to the mixing plant, and in any case at least once per month.

1.6.23 Mixing Concrete

All concrete shall be mixed in accordance with DIN 1045 with batch mixers in accordance with DIN 459 The mixing of each batch shall continue not less than 1.5 minutes after all materials, including water, are in the mixer.

Hardened concrete or mortar shall not be permitted to accumulate on the inner surfaces of the mixer. Re-tempering, i.e. remixing with the addition of water to concrete that has been partially hardened, will not be permitted.

On commencing work with a clean mixer, the first batch shall contain only half the normal quantity of coarse aggregate to compensate for the adhesion of the other materials to the drum.

1.6.24 Ready-Mixed Concrete (optional)

Ready-mixed concrete shall not be used in any part of the works without the Engineer's written approval, which may be withdrawn at any time.

The Contractor shall satisfy the Engineer that ready mixed concrete complies with the Specification in all respects, and that the manufacturing and delivery resources of the proposed supplier are adequate to ensure proper and timely completion of each concreting operation.

The specified requirements as to the sampling, trial mixing, testing and quality of concrete of various grades shall apply equally to ready-mixed concrete.

Any additional facility, which the Engineer may require for the supervision and inspection of the batching, mixing and transporting of ready-mixed concrete shall be provided by the Contractor at his own expense.

1.6.25 Preparing for Concreting

For the preparation of concreting, the following shall apply:
•Each surface shall be thoroughly wetted by sprinkling, prior to the placing of any concrete, and these surfaces shall be kept moist by frequent sprinkling up to the time of placing concrete thereon. The surface shall be free from standing water, mud and debris at the time of placing concrete.
•Concrete surfaces upon or against which concrete is to be placed, where the placement of the old concrete has been stopped or interrupted so that, in the opinion of the Engineer, the new concrete cannot be incorporated integrally with that previously placed, are defined as construction joints. The surface of horizontal joints shall be levelled with a wooden float to provide a reasonably smooth surface. A surface consisting largely of coarse aggregate shall be avoided. Except where the drawings call for joint surfaces to be painted, the joint surfaces shall be cleaned of all laitance, loose or defective concrete and foreign material. Such cleaning shall be accomplished by sandblasting followed by thorough washing. All pools of water shall be removed from the surface of construction joints before the new concrete is placed. After the surfaces have been prepared to the satisfaction of the Engineer, all approximately horizontal construction joints shall be covered with a layer of mortar approximately 25 mm thick. The mortar shall have the same proportions of cement and sand as the regular concrete mixture, unless otherwise directed by the Engineer. The water-cement ratio of the mortar in place shall not exceed that of the concrete to be placed upon it and the consistency of the mortar shall be suitable for placing and working in the manner hereinafter specified. The mortar shall be spread uniformly and shall be worked thoroughly into all irregularities of the surface and wire brooms shall be used where possible to scrub the mortar into the surface. Concrete shall be placed immediately upon the fresh mortar.
For construction joints refer to items 3.5.1 and 3.5.2.
•When the placing of concrete is to be interrupted long enough for the concrete to take a set, the working face shall be given a shape by the use of forms or other means, that will secure proper union with subsequent work, provided that construction joints shall be made only where approved by the Engineer.
•No concrete shall be placed until all formwork, installation of reinforcement and parts to be embedded and preparation of surfaces involved in the placing have been approved by the Engineer. All surfaces of forms, reinforcement and embedded items that have become encrusted with dried grout from concrete previously placed shall be cleaned of all such grout before the surrounding or adjacent concrete is placed.
Where specified and elsewhere as ordered by the Engineer, the excavated surfaces shall be prepared as specified under concrete protection.

1.6.26 Exclusion of Water

No concrete shall be placed in any water structure until all water entering the space to be filled with concrete has been properly cut off or has been diverted by pipes or other means and carried out of the forms, clear of the work. No concrete shall be deposited under water without the explicit permission of the Engineer and then only in strict accordance with his directions, nor shall the Contractor, without explicit permission, allow still water to rise on any concrete until the concrete has attained its initial set. Water shall not be permitted to flow over the surface of any concrete in such manner and at such velocity as will injure the surface finish of the concrete. Pumping or other necessary dewatering operations for removing groundwater will be subject to the approval of the Engineer.

1.6.27 Transporting and Placing

Concrete shall be conveyed from the mixer to its place in the works as rapidly as possible by methods which will prevent segregation or drying out and ensure that the concrete is of the required workability at the time of placing.

Concrete, which upon or before placing is found not to conform to the requirements specified herein, shall be rejected and immediately removed from the works. Concrete which is not placed in accordance with these Specifications, or which is of inferior quality as determined by the Engineer shall be removed and replaced by and at the expense of the Contractor. Unless agreed otherwise with the Engineer, no concrete shall be placed except in the presence of the Engineer. Concrete shall not be placed when unsuitable heat of wind conditions will prevent proper placement and curing as determined by the Engineer. Prior to placing any concrete, the Contractor shall give the Engineer 24 hours written notice.

Concrete shall not be dropped through reinforcement steel or into any deep form, whether reinforcement is present or not, causing separation of the coarse aggregate from the mortar on account of repeatedly hitting rods or the sides of the form as it falls, nor shall concrete be placed in any form in such a manner as to leave accumulation of mortar on the form surfaces above the placed concrete. In such cases, some means such as the use of hoppers and, if necessary, vertical ducts of canvas, rubber or metal shall be used for placing concrete in the forms in a manner that it may reach the place of final deposit without separation.

In no case shall the free fall of concrete exceed 1.5 m below the ends of ducts, chutes or buggies. Concrete shall be uniformly distributed during the process of depositing and in no case after depositing shall any portion be displaced in the forms more than 2 m in horizontal direction. Concrete in forms shall be deposited in uniform horizontal layers not deeper than 60 cm and care shall be taken to avoid inclined layers or inclined construction joints except where such are required for sloping members. Each layer shall be placed while the previous layer is still soft. The rate of placing concrete in forms shall not exceed 1 m of vertical rise per hour.

All ends of chutes, hopper gates and all other points of concrete discharge throughout the Contractor's conveying, hoisting and placing system shall be so designed and arranged that concrete passing from them will not fall separated into whatever receptacle immediately receives it. Conveyor belts, if used, shall be of a type approved by the Engineer. Chutes longer than 15 m will not be permitted. Minimum slopes of chutes shall be such that concrete of the specified consistency will readily flow in them. If a conveyor belt is used, it shall be wiped clean by a device operated in such a manner that none of the mortar adhering to the belt will be wasted. All conveyor belts and chutes shall be covered. Sufficient illumination shall be provided in the interior of all forms so that the concrete at the places of deposit is visible from the deck or runway.

Concrete shall be placed and compacted before the initial set has occurred and, in any event, not later than 45 minutes from the time of mixing. When pneumatic placers are used, if the end of the placer pipe is not equipped with an energy-absorbing device, it shall be kept as close to the work as practicable. Mortar or water used at the beginning or end of a run shall be discharged outside the formwork. When pumps are used, the end of the supply pipe shall be kept immersed in the concrete during placing to assist compaction. Mortar and water used at the beginning or end of a run shall be discharged outside the formwork

The order of placing concrete in all parts of the work shall be subject to the approval of the Engineer. In order to minimize the effects of shrinkage, the concrete shall be placed in units as bounded by construction joints. The placing of units shall be done by placing alternate units in a manner such that each unit placed shall have cured at least 7 days before the continuous units are placed, except that vertical walls shall not be placed until the wall footings have cured at least 14 days and the corner sections of vertical walls shall not be placed until all the adjacent wall panels have cured at least 14 days. The surface of the concrete shall be level whenever a run of concrete is stopped. To ensure a level, straight joint on the exposed surface of walls, a wood strip at least 20 mm thick shall be tacked to the forms on these surfaces. The concrete shall be carried about 13 mm above the underside of the strip. About one hour after the concrete is placed, the strip shall be removed and any irregularities in the edge formed by the strip shall be levelled with a trowel and all laitance shall be removed.

1.6.28 Concreting in hot Weather

Care shall be taken to prevent rapid drying of newly placed concrete. When the ambient temperature in the forms is more than 300C or when so directed, the temperature of the concrete as placed shall not exceed 300C.

To achieve this, the Contractor shall provide sun shades over stockpiles of aggregate, cement silos, mixing water tanks and pipelines and in addition, shall carry out the first and as necessary others of the following procedures (preferably pouring concrete at night) which shall be submitted to the Engineer for approval:
•Cool the mixing water and replace part of the water by chipped ice. The ice shall be completely melted by the time mixing is completed.
•Spray clean cool water over the aggregate stockpiles. The Contractor shall carry out regular tests on the aggregates to ensure that concentrations of sulphates or chlorides do not rise to unacceptable levels and to ensure that moisture content determinations allow for such spraying.
•Shade or wet the outside of the formwork.
•Apply a fine moisture (fog) spray of clean cool water to shaded areas immediately prior to placing concrete.
•Pour concrete at night.
The fresh concrete shall be shaded as soon as the surface of fresh concrete is sufficiently hard. Concrete placement will not be permitted, if in the opinion of the Engineer, the Contractor does not have proper facilities available for placing, curing and finishing the concrete in accordance with these Specifications.

1.6.29 Compaction

As concrete is placed in the forms or in excavations, it shall be thoroughly settled and compacted, throughout the entire depth of the layer which is being consolidated, into a dense, homogenous mass, filling all corners and angles, thoroughly embedding the reinforcement, eliminating rock pockets, and bringing only a slight excess of water to the exposed surface of concrete during placement.

For compaction the Contractor shall use power driven internal type vibrators supplemented by hand spading and tamping, except as otherwise approved by the Engineer. The vibrators shall at all times be adequate in number, amplitude and power to compact the concrete properly and quickly throughout the whole of the volume being compacted. For each three vibrators in operation one standby vibrator shall be readily on hand. Care shall be used in placing concrete around water stops. The concrete shall be carefully worked by rodding and vibrating to make sure that all air and rock pockets have been eliminated. Where flat-strip type water stops are used, the concrete shall be worked out under the water stops by hand, making sure that all air and rock pockets have been eliminated.

Vibrators shall be inserted into the uncompacted concrete vertically and at regular intervals. Where the uncompacted concrete is in a layer above freshly compacted concrete, the vibrator shall be allowed to penetrate vertically for about 100 mm into the previous layer. In no circumstances shall vibrators be allowed to come into contact with the reinforcement or formwork nor shall they be withdrawn quickly from the mass of concrete but shall be drawn back slowly so as not to leave voids. Internal type vibrators shall not be placed in the concrete in a random or haphazard manner nor shall concrete be moved from one part of the work to another by means of the vibrators.

The duration of vibration shall be limited to that required to produce satisfactory compaction without causing segregation. Vibration shall on no account be continued after water or excess grout has appeared on the surface.

1.6.30 Attendance of Steel Fixer and Carpenter

During the concreting of all reinforced concrete including prestressed concrete, a competent steel fixer and carpenter shall be in attendance on each concreting gang and shall ensure that the reinforcement, formwork and embedded fittings including form-work and reinforcement spacers are kept in position as work proceeds.

1.6.31 Curing of Concrete

All concrete shall be cured by protecting the surface from the effects of sun shine, drying winds, and rain, running water or mechanical damage for a continuous period of four days when the cement used in the concrete is sulphate resisting Portland cement. The production shall be applied as soon as practicable after completion of placing by one or more of the following methods:
Method 1: Wooden forms shall be wetted immediately after concrete has been poured and shall be kept wet with water until removed. If forms are removed within 14 days of placing the concrete, curing shall be continued in accordance with the applicable method.

Method 2: The surface shall be covered with burlap mats which shall be kept wet with water for the duration of the curing period, until the concrete in the walls has been placed. No curing compound shall be applied to surfaces cured under method 2.

Method 3: The surface shall be covered with moist earth not less than 4 hours, not more than 24 hours, after the concrete is placed.

Method 4: The surface shall be sprayed with a liquid curing compound which will not affect the bond of paint to the concrete surface. It shall be applied in accordance with the manufacturer's instruction at a maximum coverage rate of 5 square metres per litre in such a manner as to cover the surface with a uniform film which will seal thoroughly. The curing compound shall be as approved by the Engineer.

Where the curing compound method is used, care shall be exercised to avoid damage to seal during the curing period. Should the seal be damaged or broken before the expiration of the curing period, the break shall be repaired immediately by the application of additional curing compound over the damaged portion.

Wherever curing compound may have been applied by mistake to surfaces against which concrete subsequently is to be placed and to which it is to adhere, said compound shall be entirely removed by wet sand-blasting just prior to the placing of new concrete. Where curing compound is specified, it shall be applied within 2 hours after completion of the finish of unformed surfaces, and within 2 hours after removal of forms on formed surfaces. Repairs required to be made to formed surfaces shall be made within the said 2 hour period provided, however, that any such repairs which cannot be made within the 2 hour period shall be delayed until after the curing compound has been applied. When repairs are to made to an area on which curing compound has been applied, the area involved shall first be wet-sandblasted to remove the curing compound. Liquid curing membranes (d) shall not be used on class U 1 surfaces where laitance is to be removed and aggregate exposed to provide a satisfactory bond for placing further concrete or mortar screeds or on surfaces where the Engineer is of the opinion that the appearance of the concrete surface will be affected.

1.6.32 Care and Repair of Concrete

The Contractor shall protect all concrete against injury or damage from excessive heat, lack of moisture, overstress, or any other cause until final acceptance by the Engineer. Particular care shall be taken to prevent the drying of concrete and to avoid roughening or otherwise damaging the surface. Any concrete found to be damaged, or which may have been originally defective, or which becomes defective at any time prior to the final acceptance of the com¬pleted work or which departs from the established line or grade, or which for any other reason does not conform to the Specifications, shall be satisfactorily repaired or removed and replaced with acceptable concrete at the Contractor's expense.

1.6.33 Finish of Concrete Surfaces

Workmanship in formwork and concreting shall be such that concrete shall normally require no making good, surfaces being perfectly compacted, smooth and with no irregularities. Concrete surfaces for the various classes of unformed and formed finishes shall in any event never exceed the maximum permitted tolerances, which shall be as shown in the table below except where expressly, stated otherwise in the Specification. Surfaces shall be free from fins, bulges, ridges, offsets, honeycombing, or roughness of any kind, and shall present a finished, smooth, continuous, hard surface.

Tolerances for line, level, irregularities and dimension shall in accordance with DIN 18201 and DIN 18202. Irregularities shall be tested by means of a straight template for plane surfaces or its suitable equivalent for curved surfaces, the template being 4.0 m long.

Maximum tolerance (mm) in accordance with DIN 18202.
Class of Finish Required Grade of Accuracy according to DIN 18202
U1 A
U2 B
F1 A
F2 B
F3 C

1.6.34 Unformed Surfaces

Finishes to unformed surfaces of concrete shall be classified as U1 or U2, "spaded1' or "bonded concrete" or such other special finish as may be particularly specified. Where the class of finish is not specified, the concrete shall be finished in class U1.

Except as otherwise provided herein, unformed top surfaces of concrete shall be brought to a uniform surface and worked with suitable tools to a smooth-wood-f bat finish. Excessive floating of surfaces while the concrete is plastic will not be permitted. All surfaces shall be placed monolithically with the base slab. Dusting of dry cement and sand on the concrete surface to absorb excess moisture will not be permitted.

Floor slabs and exposed tops of walls and curbs shall be finished in class U2. At the Contractor's opinion, the above-mentioned floor slabs may be finished with a power float after screeding. Subse¬quent to the afore-mentioned finish, all sloping surfaces of floor slabs shall be lightly broomed to provide a skid-resistant surface.

1.6.35 Treatment of Surface Defects

As soon as forms are removed, all exposed surfaces shall be carefully examined and any irregularities shall be immediately rubbed or ground in a satisfactory manner in order to secure a smooth, uniform, and continuous surface. Plastering or coating of surfaces to be smoothed will not be permitted. No repairs shall be made until after inspection by the Engineer, and then only in strict accordance with his directions. Concrete containing voids, holes, honeycombing, or similar depression defects, shall be completely removed and replaced. All repairs and replacements herein specified shall be promptly executed by the Contractor at his own expense. Holes left by tie-rod cones shall be reamed with suitable toothed reamers so as to leave the surfaces of the holes clean and rough. These holes shall then be repaired in an approved manner with drypacked mortar. Holes left by form typing devices having a rectangular cross section, and other imperfections having a depth greater than their least surface dimension, shall not be reamed but shall be repaired in an approved manner with dry-packed mortar.

All repairs shall be built up and shaped in such a manner that the completed work will conform to the requirements of the Engineer using approved methods which will riot disturb the bond, cause sagging, or horizontal fractures. Surfaces of said repairs shall receive the same kind and amount of curing treatment as required for the concrete in the repaired section.

Prior to filling any structure with water, any cracks that may have developed shall be chiselled to a V-shape and filled with construction joint sealant conforming to the recommendation of the sealant manufacturer.

1.6.36 Building-in Pipes and Plant

Wherever possible, pipes and other items of plant passing through concrete structures shall be installed and connected to the remainder of the pipework system to ensure proper fit, and shall be built into the structure as work proceeds.

Where this procedure is impossible due to programme or other requirements, holes shall be formed for the items of plant to allow them to be built in later after complete installation of the plant. In no case shall individual pipes of a complicated pipework system including flanged joints be built into concrete structures before accurate fit of the whole system can be checked after complete installation. Where holes are formed these shall be of size and shape sufficient to permit proper placing and compaction of concrete or grout. The surface of the holes shall be treated to produce a "bonded" surface before installation of plant.

Before building-in commences the plant shall be adequately supported in position to prevent movement or damage during building-in.

Concrete used for building-in shall be of the same grade as concrete of the member into which the plant is being built, except that the mix shall also incorporate an approved expanding additive used in accordance with the manufacturer's instructions. Concrete, mortar and grout shall be carefully placed and compacted around the plant to avoid damaging or moving the plant.

1.6.37 Puddle Flanges and Pipe Supports

Puddle flanged fittings for building into the walls may be of the single flanged type. Where the single-flanged type is used it shall be positioned so that the puddle flange is in the centre of the wall. Where the double-flanged type is used it shall be positioned so that the outside face of each flange is flush with the face of the wall. Pipe support blocks shall be provided by the Contractor where necessary in chambers to support the pipe adequately, both during and after construction. The Contractor shall be entirely responsible if damage is caused to pipes because of his failure to provide adequate supports. Support blocks shall be made from B 25 concrete or a higher grade.

1.6.38 Corrosion Protection Requirements

Pipe, conduit, dowels and other ferrous items required to be embedded in concrete construction shall be so positioned and supported prior to placement of concrete that there will be a minimum of 5 cm clearance between said items and any part of the concrete reinforcement. Fixing of embedded steel members at major reinforcement will not be permitted. Fixing may be performed by welding at distribution bars or additional bars.

1.6.39 Precast Concrete

Precast concrete units shall be obtained from an approved manufacturer or prepared by special skilled employees and shall be true to dimension and shape, with true arises and with perfectly smooth exposed faces free from surface blemishes, air holes, crazing or other defects, whether developed before or after building-in. The concrete shall comply in every respect with the provisions of the contract whether such units are manufactured on the site or obtained from other manufacturers.

All cement, aggregate and other materials for precast concrete units with faces, which are exposed, wither internally or externally shall be from the same sources throughout. Exposed surfaces of the units shall be uniform in colour and in texture.

Formwork and unformed surfaces for precast concrete units shall comply generally with the accuracy grade "C” according to DIN 18202. Squareness and twist shall be as follows:
•Squareness: When considering the squareness of a corner, the longer of the two adjacent sides being checked shall be taken as the baseline and the shorter side shall not vary in its distance from the normal so that the differences between the greatest and the shortest dimension exceeds 6 mm. When the nominal angle is other than 90 degrees, the included angle between the check lines shall be varied accordingly
•Twist: Any corner on any nominally' plane surface shall not be more than 6 mm from the plane containing the other three corners.

The positions of individual connecting bolts, bolt holes, projecting steel and other devices in any associated grade (e.g. the joint of two precast units) shall be within 3 mm of their true position in the group in which they are cast. The location of any such group shall be within 6 mm of its true position in the unit in which it is cast, provided that such deviation does not adversely affect the proper assembly of the whole structure.

The Contractor shall submit to the Engineer for approval full details of his proposed method of carrying out all operations connected with the manufacture and assembly of precast concrete structural members, including:
•a description of the types of casting bed, mould and formwork for the various type of members;
•the procedure for concrete casting and the method of curing the concrete;
•the procedure for transporting, handling, hoisting and placing of each type of precast structural member; •full details of temporary supports necessary to ensure adequate stability during erection, due account being taken of construction loads, including wind.

All tendons, duct forming devices, anchorages and other components shall be kept free of mud, oil (except water soluble oil applied for protection), paint, retarders, loose rust or other foreign matter. They shall be placed with a tolerance of  3 mm in concrete dimensions of 300 mm or less or  6 mm in concrete dimensions over 300 mm.

The bearing surfaces between anchorages and concrete shall be normal to and concentric with the tendons and the line of action of the prestressing force.

1.6.40 Installation of Precast Concrete Units

At all stages and until completion of the work, precast members shall be adequately protected to preserve all permanently exposed surfaces, arises and architectural features. The protection shall not mark or otherwise disfigure the concrete.

All units shall be laid, bedded, jointed and fixed in accordance with the lines, levels and other details shown on the approved drawings.

Dry-pack mortar jointing for packing shall consist of one part by volume ordinary Portland cement and two and a half parts by volume of fine aggregate passing a 1 mm sieve. The mortar shall be mixed with only sufficient water to make the material stick together when being moulded in the hands. The mortar shall be placed and packed in stages, wherever possible from both sides of the space being filled, using a hardwood stock hammered until the mortar is thoroughly compacted.

Any precast concrete structural member which is found to be cracked, damaged or otherwise inferior in quality either before or after erection, shall be rejected and replaced by the Contractor at his own expense.

1.6.41 No-Fines Concrete

No-fines concrete shall be used in sub-soil drainages. The grading of the coarse shall be:
•not less than 95 % by weight passing a 16 mm DIN sieve (DIN 4187);
•not more than 5 % by weight passing a 8 mm DIN sieve (DIN 4187).

The proportion of aggregate, cement and water shall be determined by trial mixes by the Contractor starting with a cement : aggregate particles ratio of one to eight by volume. The trial mix shall be considered suitable when all the aggregate particles are coated with a film of cement grout. The water content shall be just adequate to ensure that the cement paste completely coats the aggregate. The concrete when placed shall contain no layers of laitance. No-fines concrete shall not be mixed by hand. Vibration shall not be used to compact the concrete. Three test cubes of non-fines concrete shall be made of each trial mix. The minimum crushing strength of the chosen mix shall be 3 N/mm2 at 28 days.

1.6.42 Precast Concrete Products

Precast concrete products shall be constructed in accordance with DIN standards being hydraulically pressed where possible.

The concrete shall comply in every respect with the provisions of the contract, whether such products are manufactured on the site or obtained from other manufacturers.

1.6.43 Concrete For Benching

Concrete benching in manholes and works structures shall consist of class B 25 concrete unless otherwise specified. It shall be placed with low workability to the approximate shape required and, while still green, shall be finished with not less than 50 mm of class B 25 concrete to a steel trowelled finish and to the contours indicated on the drawings.

1.6.44 Air-Entrained Concrete

Concrete for those structures where required shall include an approved air-entraining agent capable of producing a 5 % air-entrainment with a tolerance of 0.5 %. The mix shall be purposely designed, having regard to the nature and grading of use aggregate and air-entraining agent being used.

The Engineer reserves the right, at any time, to sample and test the air-entraining agent used in the works. Preference shall be given to the use of air-entraining agents which can be administered in fixed calibrated amounts through a dependable mechanical dispenser or cachet, and which are added to the mixing water. No air-entraining agent shall be used in the works without the written approval of the Engineer.

1.6.45 Pumping Concrete

Where pumping of concrete is permitted, no relaxation of the requirements of this Specification will be permitted. Particular attention shall be paid to the proper grading of aggregates to prevent bleeding and/or segregation during the pumping operations. The inclusion of water-reducing additives or other materials, including flyash, to improve the flow characteristics of the concrete will only be permitted where it can be shown that they do not adversely affect the concrete either in the plastic phase or in the finished work.

1.6.46 Sampling and Testing of Aggregate

The Contractor shall sample and carry out mechanical analysis of the fine aggregate and each nominal size of coarse aggregate in use, employing the method described in DIN 4226 at least once in each week when concreting is in progress and at such more frequent intervals as the Engineer may require. The grading of all aggregates shall be within specified limits and should the fraction of aggregate retained on any sieve differ from the corresponding fraction of aggregate in the approved mix by more than 5 % of the total quantity of fine and coarse aggregate, the Engineer may instruct the Contractor to alter the relative proportions of the aggregates in the mix to allow for such differences.

1.6.47 Sampling and Testing of Concrete

The Contractor shall provide the equipment necessary to determine the compacting factor of freshly mixed concrete at each place where concrete is being made and shall determine the compacting factor of the freshly mixed concrete by the method described in DIN 1048 on each occasion that a set of test cubes is made and not less than once a day or as the Engineer may direct.

For each grade of concrete, works test cubes shall be made whenever required by the Engineer but not less frequently than as follows unless otherwise particularly specified:
•for concrete of grade more than B 10: one set of cubes per 25 m3 or part thereof concreted per day;
•for concrete of grade B 10 and less: one set of cubes per 10 batches or part thereof concreted per day. Each set of cubes (six cubes per set) shall be made from a single sample taken from a randomly selected batch of concrete. Three cubes shall be tested 7 days after manufacture and three cubes 28 days after manufacture when requested by the Engineer and addi¬tional set of cubes shall be made for testing three days after manufacture.

Test reports shall be submitted to the Engineer in duplicate.

1.6.48 Compliance with Specified Requirements

The concrete shall be deemed satisfactory provided that: •The average 28 days strength determined from any group of four consecutive test cubes exceeds the specified characteristic strength by not less than 5 N/mm2 for grade B 10 concrete and 7.5 N/mm2 for grades more than B 10 (or one-half of the current margin for any grade where a reduced margin has been approved by the Engineer for that mix design);
•Each individual test result is greater than 85 % of the specified characteristic strength. If only one cube result fails to meet the second requirement, that result may be considered to represent only the particular batch of concrete from which the cube was taken, provided that the average strength of the group satisfies the first requirement.

If more than one cube in a group fails to meet the second requirement or if the average strength of any group of four consecutive test cubes fails to meet the first requirement then all the concrete in all the batches represented by all such cubes shall be deemed not to comply with the strength requirements.

1.6.49 Non-Compliance

When the average strength of four consecutive test cubes fails to meet the first requirement, no further concrete from that mix shall be placed in the work and the Contractor shall establish the cause of the failure and apply such remedies as are necessary. The Contractor shall demonstrate by trial mixes and test cube results that the revised mix is in accordance with the specified requirements.

The Contractor shall, within 24 hours of the date of test, make proposals for agreement with the Engineer about action to be taken in respect of any concrete represented by test cubes which fail to meet either of the requirements. These proposals may include, but shall not be limited to, cutting and testing cores. Concrete which is ultimately found not to comply with any of the requirements of the Specification shall be rejected and shall be broken out and replaced or otherwise dealt with as agreed with the Engineer at the expense of the Contractor.

Furthermore, the Engineer may order additional cement added to the mix immediately. The mixes used may also be changed whenever, in the opinion of the Engineer, such change is necessary or desirable to secure the required workability, density, impermeability, surface finish and strength, and the Contractor shall be entitled to no additional compensation because of such changes.

1.6.50 Cutting and Testing of Core Samples

As and where directed by the Engineer cylindrical core specimens of 150 mm nominal diameter shall be taken normal to the face of the hardened concrete for the purposes of examination and testing. The procedure for drilling, examination, measurement and testing for comprehensive strength shall be in accordance with DIN 1048. Prior to preparation for testing, the specimen shall be made available for examination by the Engineer. If the crushing strength of the specimen deter-mined in accordance with DIN 1048 is less than the characteristic strength at 28 days for the grade requirements in other respects, the concrete in that part of the works of which it is a sample shall be considered not to comply with the specified requirements.

1.6.51 Inspection Procedures

Before any lift of concrete is placed, the Contractor shall carry out an inspection to ensure that all preparations are complete, including the provision of the necessary equipment and personnel and shall ensure that sufficient materials are available to complete the works proposed.

After completion of this inspection, the work shall be offered for inspection by the Engineer, sufficient time being allowed for inspection and correction of any defects. No concrete shall be placed until the Engineer has inspected and approved the surfaces upon which the concrete is to be placed, the formwork and the reinforcing steel.

The Contractor shall institute a "pour card" system in which a card is made out for each lift of concrete and is initialled by the Contractor and Engineer indicating that the inspections have been carried out. The "pour card" shall include spaces to identify the concrete being placed and to signify completion of the inspections by the Contractor and Engineer of the following items:
•preparation of surface on which concrete is to be placed;
•formwork;
•reinforcement
; •ready for concrete placing;
•inspection after removal of formwork (any remedial work shall be agreed and noted);
•curing procedures;
•completion of remedial work (if any).

1.6.52 Concrete Protection System

All structural concrete in contact with the ground shall be protected by one of the methods specified below. Unless otherwise specified, in-situ concrete surfaces which are to be protected shall have either U2 or F2 finish as appropriate.

Prefabricated membrane tanking: The membrane shall be performed consisting of 1.5 mm thick rubber/bitumen compound formulated for use in hot climates, backed with 0.3 mm thick PVC sheet. The membrane shall adhere with watertight joints to itself at overlaps and to concrete surfaces prepared with suitable priming compound. The membrane and primer shall be applied in accordance with the manufacturer’s instructions to horizontal, inclined and vertical surfaces.

After the blinding concrete has hardened, the membrane shall be applied, bitumen face downwards, and shall extend at least 200 mm beyond the outer limits of the structure. As soon as the membrane has been applied and before any reinforcement or structural concrete is placed, the membrane shall be covered by a sand/cement screed 50 mm thick, extending over the whole area of the base of the structure. The membrane projection of 200 mm shall be temporarily protected with a layer of board as specified below to prevent mechanical damage.

Alternatively a purpose made rock-proof non-compressible board may be used instead of screed if approved by the Engineer.

After the concrete structure has been constructed up to ground level and curing is completed, the surfaces, which will be in contact with the ground, or as detailed otherwise on the approved drawings, shall be primed with the material supplied by the membrane manufacturer. The vertical membrane shall be bonded onto the projection of the base membrane and terminated in a chase at the top completed with a rubber bitumen seal. Fillets and reinforcing strips shall be used.

Completed areas of vertical membrane shall be protected from mechanical damage during backfill operations by 12 mm thick cardboard, fibreboard or chipboard secured with suitable adhesive, or by concrete blockwork. Made-in-place membrane tanking:

As an alternative to prefabricated membrane tanking on horizontal surfaces, the Contractor may propose to design, supply and install a made-in-place membrane of bitumen asphalt concrete laid on a tack coat placed on clean original ground.

The bitumen asphalt concrete shall comprise bitumen or asphalt and coarse and fine aggregates. The Contractor shall demonstrate to the Engineer that, testing by trial and by experience, that made-in-place membrane tanking exhibits characteristics which are in all respects equal to or better than prefabricated membrane tanking. The system shall be:
•waterproof during life of protected structure;
•robust during preparation for concreting;
•flexible in differential settlement;
•incompressible under weight of structure.
Made-in-place membrane tanking may be used in place of blinding concrete provided that the Contractor shall also have demonstrated to the Engineer the practicability of this system by testing, by trial and by experience.

Vertical or sloping concrete surfaces shall be protected by prefabricated membrane tanking as specified which shall overlap and adhere in made-in-place membrane tanking over a width of 200 mm. Bituminous latex emulsion:

This material shall only be used as an alternative to membrane tanking where the Engineer has specifically agreed that satisfactory membrane tanking cannot be carried out.

The emulsion shall be a rubber-rich bituminous emulsion suitable for use in hot climates and capable of building up a film with minimum dry thickness of 1.0 mm, which is impermeable to water penetration and possessing a high degree of flexibility.

A priming mixture shall be made by thoroughly mixing the part emulsion with 6 parts fresh water. Coats other than priming coat shall not be diluted.

Application rates shall be as follows:
Surface Coat Application rate (m/litre)
Horizontal 1st (priming) 7
2nd 1
3rd 1.5

Vertical 1st (priming) 7
2nd 2
3rd 2
4th 2
or as necessary to build up a minimum dry film thickness of 1.0 mm. Overcoating shall take place as soon as the previous coat has dried. Immediately the final coat has been applied to vertical surfaces, bituminised building paper shall be applied to the fresh emulsion and pressed into close contact over the whole area of the protection.

Horizontal and vertical surfaces shall be protected from mechanical damage during subsequent construction work by screed or boarding as specified for membrane tanking.

Polyethylene sheet: 250 micron polyethylene sheet shall be placed against vertical or sloping surfaces of excavated ground before placing concrete directly against such surfaces. Backfilling with sand against protected surfaces shall be carried out in such a manner that the protection is not damaged. Nevertheless, if such damage occurs, the damage shall be made good to the satisfaction of the Engineer.

1.6.53 Concrete Protection Procedures

Details of concrete protection shall be shown by the Contractor on the working drawings. Such details shall include corners, overlaps, brick or board protection and details for curved faces, etc. Concrete protection Systems proposed for use in the works shall be demonstrated by the Contractor to the Engineer for approval before submission of preliminary working drawings showing use of such systems in the works.

1.6.54 Machinery Bases and Grouting In

Bases to take machinery and associated pipework shall be finished to class F 2 or U 2, as appropriate to the dimensions shown on the approved drawings or as ordered by the Engineer. The mounting surface of the base shall be steel floated to true and level planes.

The structural concrete on which the bases are to be erected shall be prepared by hacking and cleaning off. Bases shall be tied to the structural concrete with vertical reinforcement. Horizontal reinforcement will also normally be provided at the level of the pockets for the holding down bolts.

Bolt pockets and lead-ins for grout shall be formed by means approved by the Engineer. Polystyrene formers will not be permitted. Where expand metal is used as a former it shall be left in. When the machinery has been erected the bolt pockets shall on approval of the Engineer be completely filled using a mixture of 2 parts of sulphate resisting cement to 3 parts sharp sand by volume with sufficient water to form a thick creamy consistency.

The machinery will be run under the supervision of the Contractor and witnessed by the Engineer after the grout has hardened. When so directed the Contractor shall complete the grouting operation by filling the space between the top of the concrete and the underside of the machinery base plate.

1.6.55 Test for Watertightness of Water-Retaining Structures

Water-retaining structures for water supply purposes shall satisfy the following tests for watertightness, before any external rendering or other finishes are applied (if any).

The water for testing shall fill the first 1.25 m and be filled as quickly as supply permits. Between this and top water level the rate of filling shall not exceed a steady rate of 300 mm per 24 hours unless otherwise directed. After filling to top water level no further water shall be introduced for 7 days and the structure shall satisfy the test if at the end of this week no leakage is apparent and the water level does not drop more than 3 mm plus an allowance for evaporation during the last 48 hours. Throughout the 48 hour period the water level shall be recorded every 4 hours by means of two hook and vernier gauges approved by the Engineer and sited as directed by him. In addition to the foregoing visible leakages will not be accepted.

Following satisfactory completion of the tests the structures shall be disinfected in accordance with DVGW working sheet W291.

1.7 Reinforcement

1.7.1 Scope

This Specification covers detailing, fabricating, supplying and placing of reinforcing steel and acces-sories for all cast in place and precast concrete. The Contractor shall be entirely responsible for the correctness of bar schedules before arranging for the supply, cutting and bending of steel reinforcement.

1.7.2 Submissions

The following submissions are required by this Specification:
(1) Test certificates Manufacturer’s test certificates for each delivery of reinforcing steel. Each certificate shall show the country of origin and test. Welding procedure tests.
Welder qualification tests.

(2) Data Manufacturer's data on accessories and mechanical couplings.

(3) Drawings All reinforcement drawings and bending schedules prepared by the Contractor.

1.7.3 Steel Reinforcement

Steel for reinforcement shall be of the following kinds in accordance to DIN 488 and DIN 1045.
• Type - IG - untreated plain round mild steel bars 220/340 GU
• Type - IR - untreated deformed round mild steel bars 220/340 RU
• Type - IIIU - untreated deformed round high yield steel bars 420/500 RU
• Type - IV G - welded hard drawn steel wire and other cold worked high bond barfabric500/550 GK

1.7.4 Accessories

The Contractor shall supply all accessories such as reinforcing steel supports, hold-downs, spreaders, hangers, tie wire and all other incidentals necessary to complete an acceptable installation of all concrete reinforcement. All accessories shall be of steel with the exception of spacers to maintain concrete cover to reinforcement against formed or blinded surfaces which shall be of concrete of same texture, colour and composition as cast-in-place concrete. Concrete spacers shall be in the form of a truncated cone or pyramid and shall be used with the larger face towards the reinforcing steel. The smaller face of a truncated cone or pyramid shall have minimum dimension of 50 mm.

1.7.5 Dowels

Dowel shall be of the same size and spacing as bars with which they are lapped. Unless otherwise noted, the lap and embedment shall be 64 times bar diameter minimum of each. Dowels shall be wired or otherwise held in position. Dowels shall be installed prior to placing concrete. They shall not be placed into freshly placed concrete.

1.7.6 Detailing

Steel reinforcement shall be as shown on the approved drawings. The Contractor shall be responsible for checking the drawings before cutting and bending reinforcement. When any information relating to reinforcement is missing or apparently incorrect, the Contractor shall remedy the missing or incorrect information to the approval of the Engineer.

1.7.7 Cutting and Bending of Reinforcement

Bars shall be cut and bent in accordance with the provisions of DIN 1045. All bending shall be done cold with the use of an approved bending machine. Rebending of bars will not be permitted. Cut and bent bars shall be bundled and labelled for positive identification with the drawings and bending schedules, until they are incorporated into the work.

1.7.8 Storage of Reinforcing Bars and Fabric

The Contractor shall stack separately and label different types of reinforcement for positive identi-fication. Steel reinforcing bars shall be kept clean and shall be free from pitting, loose rust, mill scale, oil, grease, earth, paint, or any other material, which may impair the bond between the concrete and the reinforcement.

Reinforcing steel shall be stored and fabricated under cover on wooden or concrete supports such that the steel is elevated from the ground surface by a minimum of 150 mm.

1.7.9 Storage of Prestressing Wire and Bars

In addition to complying with the above storage requirements, the Contractor shall ensure that pre-stressing wire and bars are protected from mechanical damage by storing on time supports above a concrete slab, and shall ensure that during storage the wire and bars are kept properly coated with water soluble oil inside protective wrappings.

1.7.10 Fixing of Reinforcement

All reinforcement shall be securely and accurately fixed in positions shown on the approved drawings using approved spacer blocks or chairs. All intersections of bars shall be secured by using suitable clips or annealed iron wire, the ends being turned into the body of the concrete. The Contractor shall ensure that all reinforcement is maintained in position at all times, particular care being taken during placing of concrete.

Concrete cover to reinforcement shall be as specified in the table below. Correct concrete cover to reinforcement shall be maintained with the aid of approved spacer pieces. Reinforcement in slabs shall be maintained in position by means of chairs at 90 cm centres maximum. Reinforcement in walls with two layers of reinforcement shall be maintained in position by using 6 mm U or Z-shaped spacers at 180 cm centres maximum.

No part of the reinforcement shall be used to support formwork, access ways, working platforms, or the placing equipment or for the conducting of an electric current. Welding of reinforcement is subject to the Engineer' s permission.

1.7.11 Concrete Cover

Except as otherwise shown on the approved drawings reinforcement shall be installed with clearance coverage in centimetres as follows:
• All surfaces in contact with water or placed against soil 5.0 cm
• Underside of slabs over water in enclosed conduits and beams and columns not exposed to soil or water 4.0 cm
• Surfaces exposed to air and all interior surfaces in pipe galleries and dry rooms 3.0 cm

1.7.12 Tolerances

Tolerances in placing reinforcement shall be: • for members 60 cm or less in depth  0.5 cm
• for members more than 60 cm in depth  1.5 cm

1.7.13 Inspection and Testing

When required by the Engineer, the Contractor shall take samples from reinforcement delivered to site and shall arrange for the samples to be tested by an approved testing agency. Test certificates from that agency shall be submitted to the Engineer.

The Engineer or his authorized representative may require witnessing such testing and also routine testing at the manufacturer's works.

The Contractor shall be responsible for all checking and inspection of reinforcement before preparations for placing concrete are offered for inspection by the Engineer.

1.7.14 Straightening

Reinforcing steel shall not be straightened or rebent in a manner that will injure the material. Bars with kinks or bends not shown on the drawings shall not be used.

1.7.15 Approval by Engineer

In no case shall any reinforcing steel be covered by concrete until the amount and position of the reinforcement have been checked by the Engineer and his permission given to proceed with concreting.

1.8 Formwork

1.8.1 Scope

This section covers the supply, erection and removal of formwork, the finishes to be attained and the remedial action to be taken to the finished concrete after removal of formwork.

1.8.2 Submissions

When required by the Engineer, the Contractor shall submit calculations and designs for formwork including layout of panels, before fabrication has commenced.

1.8.3 General

Formwork shall be constructed of timber, sheet metal or other approved material. The Contractor shall also furnish all struts, braces and ties to withstand the placing and vibrating of concrete and the effects of weather.

Except as otherwise expressly approved by the Engineer, all material brought on the job site as forms, struts or braces shall be new material. All forms shall be smooth surface forms and shall be of good quality.

For each class of finish the Contractor shall provide sample panels to the satisfaction of the Engineer. If the sample panels do not meet the requirements, the Contractor shall perform new samples. Sample panels shall be not less than 0.30 m thick and about 2 m2 in area. All surface finishes of constructed concrete shall be equal to the sample panels approved by the Engineer.

1.8.4 Form Ties

Form ties for use in water-retaining structures shall incorporate a diaphragm not less than 50 mm diameter welded to the mid point of the tie, designed to prevent water passing along the tie.

Form ties with integral waterstops shall be provided in a cork or other suitable means for forming a conical hole to ensure that the form tie may be broken off back of the face of the concrete. The maximum diameter of removable cones for rod ties, or of other removable form tie fasteners having a circular cross section, shall not exceed 40 mm and all such fasteners shall be such as to leave holes of regular shape for reaming. Holes left by the removal of fasteners having a circular cross section, shall not exceed 40 mm and all such fasteners shall be such as to leave hole of regular shape for reaming. Holes left by the removal of fasteners from the ends of snap-ties or form ties shall be reamed with suitable toothed reamers so as to leave the surfaces of the holes clean and rough before being filled with mortar. Wire ties for holding forms will not be permitted. No form-tying device or part thereof, other than metal, shall be left embedded in the concrete, not shall any tie be removed in such manner as to leave a hole extending through the interior of the concrete member. The use of snap-ties which cause spalling of the concrete upon form stripping or tie removal will not be permitted. If steel panel forms are used, rubber grommets shall be provided where the ties pass through the form in order to prevent loss of cement paste. Where metal rods extending through the concrete are used to support or to strengthen forms, the rods shall remain embedded and shall terminate not less than 50 mm back from the surface in the case of reinforced concrete and 150 mm in the case of unreinforced concrete.

1.8.5 Number of Forms

A sufficient number of forms of each kind shall be provided to permit the required rate of progress to be maintained. Whenever, in the opinion of the Engineer, additional forms are necessary to maintain the progress schedule, such additional forms shall be provided by the Contractor at his own expense. The design and inspection of concrete forms, false work and shoring shall comply with the applicable standards.

1.8.6 Design

The Contractor shall be responsible for the adequacy and safety of formwork.

All forms shall be true in every respect to the required shape and size, shall conform to the established alignment and grade, and shall be of sufficient strength and rigidity to maintain their position and shape under the loads and operations incident to placing and vibrating the concrete. Suitable and effective means shall be provided on all forms for holding adjacent ends of panels and section rightly together and in accurate alignment so as to prevent the formation or ridges, fins, offsets, or similar surface defects in the finished concrete. Plywood, 15 mm and greater in thickness, may be fastened directly to studding if the studs are spaced close enough to prevent visible deflection marks in the concrete. The forms shall be tight so as to prevent the loss of water, cement and fins during placing and vibrating of the concrete. Adequate clean-out holes shall be provided at the bottom of each lift of forms. The size, number and location of such clean-outs shall be subject to the approval of the Engineer.

On formwork to external faces which will be permanently exposed, all horizontal and vertical form-work joints shall be so arranged that joint lines shall form a uniform pattern on the face of the concrete. The Contractor shall make up the formwork from standard sized manufactured formwork panels, the size of such panels shall be approved by the Engineer before they are used in the construction of the work. The finished appearance of the entire elevation of the structure and adjoining structures shall be considered when planning the pattern of joint lines caused by formwork and by construction joints to ensure continuity of horizontal and vertical lines.

Concrete construction joints will not be permitted at locations other than those shown on the approved drawings, except as may be approved by the Engineer. When a second lift is placed on hardened concrete, special precautions shall be taken in the way of the number, location and tightening of ties at top of the old lift and bottom of the new to prevent any unsatisfactory effect whatsoever on the concrete. Pipe stubs and anchor bolts shall be set in the forms where required.

Unless otherwise shown, exterior corners in concrete members shall be provided with 20 mm x 20 mm chamfers. Re-entrant corners in concrete members shall not have fillets unless otherwise shown.

1.8.7 Vertical Surfaces

All vertical surfaces of concrete members shall be formed, except where placement of the concrete against the ground is called for on the drawings or explicitly authorized by the Engineer. Permission for placing concrete against trimmed ground in lieu of forms will be granted only for members of comparatively limited height and where the character of the ground is such that it can be trimmed to the required lines and will stand securely without caving or sloughing until the concrete has been placed.

1.8.8 Formed Surfaces - Class of Finish

Finishes to formed surfaces shall be classified as Fl, F2 or F3 as finish specified in elsewhere. Where the class of finish is not specified the concrete shall be finished to class F2.

1.8.9 Erection of Formwork

All formwork shall be soundly constructed, firmly supported, adequately strutted, braced and tied to withstand the placing and vibrating of concrete and the effects of weather. Formwork shall not be tied to or supported by reinforcement.

Faces of formwork in contact with concrete shall be free from adhering foreign matter, projecting nails and the like, splits or other defects, and all form-work shall be clean and free from standing water, dirt, shavings, chippings or other foreign matter. Joints shall be sufficiently watertight to prevent the escape of mortar or the formation of fins or other blemishes on the face of the concrete.

All exposed exterior angles on the finished concrete of 90 degrees or less shall be given 20 mm by 20 mm chamfers.

Formwork shall be provided for the top surfaces of sloping work where the slope exceeds 15 degrees from the horizontal (except where such top surface is specified as spaded finish) and shall be anchored to enable the concrete to be properly compacted and to prevent air being trapped.

Formwork in contact with the concrete shall be treated with a suitable non-staining mould oil prior to reinforcement and concrete placement to prevent adherence of the concrete except where the surface is subsequently to be rendered.

Care shall be taken to prevent the oil from coming in contact with reinforcement or with concrete at construction joints. Surface retarding agents shall not be used unless approved by the Engineer. Where ties are built into the concrete for the purpose of supporting formwork, the whole or part of any such supports shall be capable of removal so that no part remaining embedded in the concrete shall be nearer than 50 mm from the surface in the case of reinforced concrete and 150 mm in the case of unreinforced concrete. Holes left after removal of such supports shall be neatly filled with well rammed dry-packed mortar. Openings for inspection of the inside of the formwork, for the removal of water used for washing down and for placing concrete shall be provided and so formed as to be easily closed before or during placing concrete. Before placing concrete all bolts, pipes or conduits or any other fixtures which are to be built in shall be held fast by fixing to the formwork or otherwise. Holes shall not be cut in any concrete without prior approval of the Engineer.

1.8.10 Maintenance of Forms

Forms shall be maintained at all times in good condition, particularly as to size, shape, strength, rigidity, tightness and smoothness of surface. Forms, when in place, shall conform to the established alignment and grades. Before concrete is placed, the forms shall be thoroughly cleaned. The forms' surfaces shall be treated with a non-staining mineral oil or other lubricant approved by the Engineer. Any excess lubricant shall be satisfactorily removed before placing the concrete. In addition, all forms shall be given a preliminary oil treatment by the manufacturer or shall be oiled by the Contractor at least two weeks in advance of their use. Care shall be exercised to keep oil off the surfaces of steel reinforcement and other metal items to be embedded in concrete. Forms may be re-used if in good condition and if approved by the Engineer.

Light sanding between uses shall be required wherever necessary in the opinion of the Engineer to obtain uniform surface texture on all exposed concrete surfaces. Exposed concrete surfaces are defined as surfaces, which are permanently exposed to view. In the case of forms for the inside wall surfaces of hydraulic structures, unused tie rod holes shall be covered with metal caps or shall be filled by other methods approved by the Engineer.

1.8.11 Removal of Formwork

Formwork shall be so designed as to permit easy removal without resorting to hammering or levering against the surface of the concrete.

The period of time elapsing between the placing of the concrete and the striking of the formwork shall be as approved by the Engineer after consideration of the loads likely to be imposed on the concrete and shall in any case be not less than the period stated in DIN1045.

The Contractor shall be held responsible for any damage arising from removal of formwork before the structure is capable of carrying its own weight and any incidental loading.

1.8.12 Building in Plant

The Contractor shall erect all formwork, struts and other temporary work to enable plant to be built in, and such formwork shall be designed to allow placing of the concrete, mortar or grout so as to fill the voids completely, and to enable air to escape from any cavities during filling. The formwork shall be sealed against pipework and other items of plant to prevent leakage of grout. Formwork shall be supported independently of all plant and pipework. The Contractor shall use such templates and moulds as are necessary to achieve the accurate positioning of such items as penstocks and access cover.

1.8.13 Inspection and Testing

Before concrete is placed against any formwork, the formwork shall be inspected by the Contractor and offered for inspection and approval by the Engineer.

If a “pour-card” system is in operation, the card shall be signed by the Contractor and submitted to the Engineer with the request for inspection of the formwork.

1.9 Joints

1.9.1 Construction Joints

A construction joints is defined as a joint in the concrete introduced for convenience in construction at which special measures are taken to achieve subsequent continuity without provision for further relative movement.

Concrete placed to form the face of a construction joint shall have all laitance removed and the large aggregate exposed prior to the placing of fresh concrete.

The laitance shall wherever practicable be removed when the concrete has set but not hardened by spraying the concrete surface with water under pressure or brushing with a wire brush sufficient to remove the outer mortar skin and expose the large aggregate without being disturbed. Where the laitance cannot be removed due to hardening of the concrete, the whole of the concrete surface forming the joint shall be treated by high pressure water jet, sand blasting, use of a needle gun or a scaling hammer to remove the surface laitance.

1.9.2 Performance of Construction Joints and Lifts

General Bonding shall be required at all joints in walls, except where otherwise shown or specified. Concrete next to waterstops shall be placed in accordance with below. Construction joint sealant Where required, construction joints in floor slabs shall be formed with grooves which shall be filled with a construction joint sealant. The materials used for forming the grooves shall be left in the grooves until just before the grooves are cleaned and filled with joint sealant. After removing the form from the grooves, all laitance and fins shall be removed and the grooves shall be sandblasted. The grooves shall be allowed to become thoroughly dry, after which they shall be blown out, immediately thereafter, they shall be primed and filled with the construction joint sealant. The primer used shall be supplied by the same manufacturer supplying the sealant. No sealant will be permitted to be used without a primer. Care shall be used to completely fill the sealant grooves. Areas designated to receive a sealant fillet shall be thoroughly cleaned, as outlined for the grooves, prior to application of the sealant. The sealant shall be two-pack polyurethane polymer designed for bounding to concrete which is continuously submerged in water. No material will be acceptable which has an unsatisfactory history as to bond or durability when used in the joints of hydraulic structures. Prior to ordering the sealant material, the Contractor shall submit to the Engineer for approval sufficient data to show general compliance with the specification requirements. The material shall meet the following requirements: • Work life 45-90 mins. time to reach “A” hardness (at 250C, 200 gr quantity) 20 hrs max. • Ultimate hardness 20-40 shore "A' • Tensile strength1 16 kg/cm2 mm. • Ultimate elongation 400 5 mins. • Tear resistance: 120 kg per cm of thickness Alternatively a two-pack polysulphide may be used as a sealant. Certified test reports from the sealant manufacturer on the actual batch of material being supplied indicating compliance with the above requirements shall be furnished to the Engineer before the sealant is used on the job. The primer and sealant shall be placed strictly in accordance with the recommendations of the manufacturer, taking special care to properly mix the sealant prior to applica-tion. Before any sealant is placed, the persons carrying out the work shall be carefully instructed as to the proper method of application. All sealant shall cure at least 7 days before the structure is filled with water. Waterstops Materials and manufacture Central waterstops shall have 10 mm thick webs and be extruded from an elastomeric polyvinylchloride compound containing the necessary plasticisers, resins, stabilizers and other materials necessary to meet the requirements of these Specifications. No reclaimed or scrap material shall be used. The waterstop manufacturer shall furnish to the Engi¬neer current test reports and a written certifica¬tion that the material to be supplied meets the following physical requirements: Unit Value Physical property (sheet material): Tensile strength mm (kg/cm2) 120 Ultimate elongation mm (%) 350 Stiffness in flexure mm(kg/cm2) 28 28 Accelerated extraction: Tensile strength mm (kg/cm2) 105 Ultimate elongation mm (%) 300 Finished waters top: Tensile strength mm (kg/cm2) 100 Ultimate elongation mm (%) 280 Splices and joints Prior to use of the waterstop material in the field, a cross section sample of a fabricated waterstop of each size or shape to be used shall be submitted to the Engineer for approval. These samples shall be fabricated so that the material and workmanship represent in all respect the fittings to be furnished under this contract. When tested, they shall have a tensile strength across the joints equal to at least 42 kg/cm2. Field splices and joints shall be made in accordance with the waterstop manufacturer's instructions using a thermostatically controlled heating iron. Flat-steel waterstops For flat-steel waterstops the thickness shall be less than 5 mm. Adequate means shall be provided for anchoring the waterstop in concrete. In placing flat-steel waterstops in the forms, means shall be provided to prevent them from being folded over by the concrete as it is placed. Horizontal waterstops shall be held in place with continuous supports to which the top edge of the waterstop shall be tacked. Vertical waterstops shall be held in place with light wire ties at 45 cm centres which shall be passed through the edge of the waterstop and tied to the two curtains of reinforcing steel. In placing concrete around waterstops, concrete shall be worked under the waterstops by hand so as to avoid the formation of air and rock pockets. 4.5.3 Movement Joints Generally Movement joints for expansion and contraction shall be constructed in accordance with the details and to the dimensions shown on the approved drawings or where otherwise ordered by the Engineer and shall be formed of the elements specified. The Contractor shall pay particular attention to the effects of climatic extremes about the works on any material which he may desire to use in any movement joints and shall submit for approval by the Engineer his proposals for the proper storage handling and use of the said materials having due regard to any recommendations in this connection made by manufacturers. Waterstops shall conform to the requirements specified elsewhere. Waterstops shall be incorporated into all expansion and contraction joints in units which retain or exclude liquids. Different types of waterstop material shall not be used together in any complete installation. Waterstops shall be fabricated into the longest practical units at the supplier's works and shall be continuous throughout the structure below highest water level. Intersections and joints shall be factory made where possible. Waterstops shall be carefully maintained in the position and supported on accurately profiled stop boards to create rigid conditions. Joint filler shall be either cork/bitumen joint filler or cellular joint filler. Cork/bitumen joint filler shall be waterproof and rot proof and shall not extrude as a result of compression. Cork joint filler shall compress to less than 50 % of its original thickness with immediate recovery to 80 % or more of its original thickness. Cellular joint filler shall be used only for joints of low horizontal loading and shall be a preformed low compression joint filler made from foam rubber. Cellular joint filler shall recover to its original thickness after each loading and unloading. The joint filler shall be fixed to the required dimensions of the joint cross section and shall provide a firm base for the joint sealer. Where the depth of joint between the concrete surface and the waterstop does not exceed 500 mm, a filler shall be placed in single depth sections. Sealing of movement joints shall be carried out only when adjacent concrete surfaces are perfectly dry and as long after the concrete has been set as possible. Immediately before the application of the joint sealer the groove protection batten shall be removed in such lengths as represent a single day's work for sealing the joints. The joint grooves shall be cleaned, adequately primed and filled with approved sealer strictly in accordance with the manufacturer's instructions and on joints of 25 mm and larger with a shape factor of 2:1 (width to depth). On permanently exposed areas of structures joint sealing is to be carried out with the aid of masking tape to form neatly defined surface limits to the sealer. 4.5.4 Sliding Planes Sliding planes on the concrete and joint blinding layers shall consist of a bitumen sand mixture 1 to 4 by volume spread evenly 3 mm thick over the carpet coat or of building paper either of which shall be applied immediately before the structural floor is concreted and shall be at all times suitably pro¬tected. Where building paper is used the concrete formation carpet shall be finished with a steel trowel to give a smooth surface. Sliding joints shall consist of two layers of purpose made preformed plastic membrane which when in contact shall give a coefficient of friction of not more than 0.2 when subjected to a load of 270 Kg/m2. Where formed in concrete structures the lower joint bedding surface shall be steel float finished to a smooth true surface.