Chapter Twelve: Design Standards and Specifications

1 Chapter Twelve: Design Standards and Specifications

1.1 1.1 Design Standards

A Standard is a limit of the measure of quality of a product prepared for judgement and compliance by an authoritative agency, professional or a recognized body. According to �(Business Dictionary, 2020)� Standards can be classified as:

Government or statutory agency for standards and specifications enforced by law, Proprietary standards developed by a firm or organization and placed in public domain to encourage their widespread use, and Voluntary standards established by consultation and consensus and available for use by any person, organization, or industry.

Once established, standards (like bureaucracies) are very difficult to change or dislodge. Standards that apply for water supply and sanitation projects will be from Tanzania Bureau of Standards, for construction works British standards shall be used.

A list of institutions whose standards are recommended to be used in design is shown below;

1. Tanzania Bureau of Standards,
2. British Standards (BS),
3. American Society for Testing and Materials (ASTM)
4. Deutsches Institut für Normung (DIN);
5. German institute for standardisation,
6. American Association of State Highway and Transportation Officials (AASHTO),
7. European Standards(ES),

Table 12.1 describes standard codes of practice and relevant area for application construction works.

1.1.1 Table 12.1 Common Standards Used in Water Projects

No	Name	Institution	Use of standard
1	BS 8110 of 1997	British Standards	Code of practise for design and construction
2	BS 812 : Part 2 : 1995	British Standards	Testing aggregates- Methods of determination of density
3	ISO 1167-1 Part 1	International Standards (ISO)	Thermoplastics pipes, fittings and assemblies for the conveyance of fluids — Determination of the resistance to internal pressure
4	SO 1452-2 Part 2	International Standards	Thermoplastics pipes, fittings and assemblies for the conveyance of fluids — Determination of the resistance to internal pressure
5	BS 6399 : Part 1 : 1996	British Standards	Code of practice for dead and imposed loads
6	BS 1377-9: Part 9: 1990	British Standards	Methods of test for Soils for civil engineering purposes: In-situ tests
7	DIN 1048	Deutsches Institut fürNormung	Quality tests of concrete
8	DIN 4226	Deutsches Institut für Normung	Concrete aggregates; definitions, sizes, quality requirements and testing
9	DIN 15018	Deutsches Institut für Normung	Steel construction; basis for design and performance, calculations

For projects with requirements that are not covered by recommended standards, the designer should seek approval from the Tanzania Bureau of Standards.(TBS)

1.2 1.2 Specifications

Specifications is a detailed description of how work is to be performed or requirements to be achieved, dimensions to be met, materials to be used, standards to be followed and tests carried out for the product to meet acceptance criteria.

Specifications are normally drafted by the client to suit the need for a particular work, for the purpose of construction of water projects standard specifications have been prepared for various woks as follows:

• Standard Specifications for Civil Works,
• Standard Specifications for Electrical works,
• Standard Specifications for Mechanical works and
• General Specifications.

These documents can be downloaded from Ministry’s Website customized to fit the needs of particular works.

1.3 1.3 Materials

1.3.1 1.3.1 Building Materials

Building material is any material used for construction purposes such as materials for structures. wood, cement, aggregates, metals,sand, bricks, concrete, clay are the most common type of building material used in construction.The choice of these is based on their cost effectiveness for building projects or the designer also guards the designed facilities against corrosive compounds or chemicals.. Construction materials ranges from aggregates, sand, cement, wood, steel, e.t.c.

1.3.2 1.3.2 Materials Testing

Before materials are used for construction works, it is imperative for the contractor or the PE to conduct appropriate tests as per applicable standards indicated above. The following are the minimum tests proposed to be conducted on various construction materials.

1.3.2.1 1.3.2.1 Aggregates

Test of aggregates explained below includes both fine and coarse aggregates.

1.3.2.1.1 Flakiness indextest

Flaky particles are those whose least dimension is 0.6 times lesser than the mean size. Thickness of these particles are comparatively smaller than the other two dimensions. Maximum allowable limit of the flaky particles in the mix is 30%. If it exceeds this value then the mix is considered unsuitable for construction purpose. Flakiness index is the percentage by weight of flaky particles in a sample. The flakiness index is calculated by expressing the weight of flaky particles as a percentage of the total weight of the sample , test procedure is as outlined in BS – 812 ,1995 .

1.3.2.1.2 Elongation index test

Elongated particles are particles having length considerably larger than the other two dimensions, also one dimension is 1.8 times greater than the other two dimensions. Maximum allowable limit of the flaky particles in the mix is 30%. If it exceeds this value then the mix is considered unsuitable for construction purpose.

Elongation index is the percentage by weight of elongated particles in a sample. The elongated Index is calculated by expressing the weight of elongated particles as a percentage of the total weight of the sample, test method is expalined in BS – 812 ,1995

Flaky and elongated particles lower the work ability of concrete mixes due to high ratio of surface area to volume. The presence of flaky and elongated particles also may cause inherent weakness in concrete with possibilities of breaking down under heavy loads.

1.3.2.1.3 Abrasion (Los Angeles Abrasion Test)

Abrasion test is the measure of aggregate toughness and abrasion resistance on crushing, degradation and disintegration. Test for abrasion is conducted based on BS 812: Part 113: 1990.

1.3.2.1.4 Organic Impurities Test

Sand should be checked for presence of organic impurities such as decayed vegetation, humus, and coal dust as these affect the quality of concrete. Test for organic impurities should be conducted as per. BS 812: Part 4: 1976

1.3.2.1.5 Aggregate Crushing value (ACV) test

Aggregate crushing value test on coarse aggregates is a relative measure of the resistance of an aggregate crushing under gradually applied compressive load.Method for determination of Aggregate Crushing Value (ACV) is the Code: BS 812 Part 110, 10% finer test

The 10 per cent Fines Aggregate Crushing Value (10 % FACT) is determined by measuring the load required to crush a prepared aggregate sample to give 10 per cent material passing a specified sieve after crushing. Test procedure is outline as per code BS 812: 1990 Part III.

1.3.2.1.6 Impact resistance value (AIC) test

The aggregate impact resistance value is a measure of resistance to sudden impact or shock, this value may differ from resistance to gradually applied compressive load. The procedure of Aggregate impact resistance value is provided in code BS 812 : Part 112 : 1990

1.3.2.1.7 Grading – sieve analysis test

This is classification of a coarse-grained soil  based on the different particle sizes it contains. This aspect is important as it indicates the comprehensibility properties, shear strength and hydraulic conductivity. The standard gradation and sieve analysis test is: BS 812: Section 103.1: Sieve Analysis of Fine and Coarse Aggregates

1.3.2.1.8 Absorption test

Water absorption is a measure of the porosity of the aggregates, it gives an indication of the strength of the aggregates. When more water is absorbed, the aggregates is more porous in nature and generally considered unsuitable unless found to be acceptable based on strength, impact and hardness tests. The standard method for Testing aggregates to water absorption test is according to BS 812-120:1989.

1.3.2.1.9 Specific gravity test

The specific gravity of aggregate is the ratio of its mass to that of an equal volume of distilled water at a specified temperature. The standard method for Testing aggregates to determine the density is BS 812 : Part 2 : 1995

1.3.2.1.10 Chemical content (pH,Chloride and Sulphate)Test

This test aims at establishing permissible levels of chlorides and sulfates in aggregate, high levels of chemicals may result in deterioration of concrete by corrosion of steel reinforcement. Corrosion of steel affects serviceability and strength of concrete structures. The test to determine the content of chemicals in aggregates is conducted as per BS 812-Part 117 & 118:1988

1.3.2.2 1.3.2.2 Water

1.3.2.2.1 Impurities Test

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 TBS adopts the new standards that are under review as of know, the Tanzanian standards will be adopted.

1.3.2.2.2 Chemical content such as Chloride,pH values, Sulphate

Samples of the water being used or which is proposed to be used for mixing concrete shall undergo testing for quality to determine 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. Chemical content in water may be determined through procedure explained in the code APHA 21st:2005 / ICP OES.

1.3.2.3 1.3.2.3 Cement

1.3.2.3.1 Setting time Test

The settling time is the time required for cement to convert from a plastic paste to a non-plastic and rigid mass. The cement settling time is determined through procedures explained in the AASHTO T 131 and ASTM C 191: Time of Setting of Hydraulic Cement.

1.3.2.3.2 Comprehensive Strength Test

The comprehensive strength of cement is the measure of the strength it provides to the mix after it has hardened .The test enables one to identify the quantity of cement required and how much strength it will provide. The comprehensive strength of cement is a basic data needed for mix design. Cement, basically identified by its comprehensive strength as grade 53 grade, 43 grade, 33 grade of cement. The test procedure to is as per code of practice BS EN 196-1:2005.

1.3.2.4 1.3.2.4 Concrete Works

Tests conducted for concrete includes

1.3.2.4.1 Slump test

Concrete slump test or slump cone test is done to determine the work ability or consistency of concrete mix prepared in the laboratory or at the construction site when undertaking concreting. Concrete slump test should be carried out from batch to batch to check the uniform quality of concrete during construction.The slump test is carried out as per procedures mentioned in ASTM C143 in the United States, and EN 12350-2 in Europe.

1.3.2.4.2 Comprehensive strength test:

Comprehensive strength of concrete is the measure of the Comprehensive strength which is the ability of the material or the structure to carry the loads on its surface without any cracks or deflection. Standard testing methods for Compressive Strength of Cylindrical Concrete Specimens is carried out using the procedure as stated in the American Society for Testing Materials ASTM C39/C39M.

1.3.2.4.3 Concrete voids Test.

This test method is related to the susceptibility of the cement paste portion of the concrete to damage by freezing and thawing. The test estimates the likelihood of damage of concrete due to cyclic freezing and thawing .The parameters of the air-void system of hardened concrete can be determined by the procedures described in the code AASHTO T 269.

1.3.2.5 1.3.2.5 Steel

1.3.2.5.1 Tensile strength

The tensile strength of steel is the measure of maximum amount of stress that can be taken before failure. Tensile strength should be conducted as per standards methods as provided in code of practise DIN 15018 or BS449 (1978/1984).

1.4 1.4 Soil Test

1.4.1 1.4.1 Methodology of conducting Soil Investigation for borehole and test pit

There are several methods of soil investigation for engineering purposes.

1. Borehole drilling method

This method used to collect soil materials from underneath by using Rig machine,heavy duty hand auger and light set hand auger.The diameter of the borehole is ranging from 150mm to 180mm depending the size of the bit to be used.During drilling, the following aspects should be observed:

• Visual soil classification and texture should be recorded,
• Water table shoul be observed and recorded,
• Depth which includes collection of soil materials at difference depth depends on the changing of soil materials to be recorded.
• Labelling of soil at each depth and soil clasification
• Collection of soil materials and keep in plastic bags to avoid moisture content
• Soil logging or profile should be shown as below table