Concrete Special Spec.pdf

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5.1 CONCRETE MATERIALS AND MIXES

5.1.2 Materials

5.1.2.1 Portland Cement Add the following to item 1:

1a. The chloride content shall not exceed 0.1% when tested in accordance with Clause 4 of BS EN 196-2.

1b. The heat of hydration shall not exceed 290 kJ/kg at 7 days when tested in accordance with BS EN 196.

1c. The acid soluble alkali level measured as (Na2O+0.658 K2O) shall not exceed 0.6% by weight determined in accordance with BS EN1962.

1d. For any type of cement, the following physical & mechanical test shall also be included:

Consistency in accordance with BS EN 196-3

Setting time in accordance with BS EN 196-3

Soundness in accordance with BS EN 196-3

Compressive Strength BS EN 196-1

1e. The compressive strength of the cement when tested at 28 days according to BS EN 196 shall be at least 42.5 MPa.

The test results shall meet the following mechanical and physical requirements given as characteristic values:

Strength Class

Compressive Strength MPa Initial Setting Time

minutes

Soundness (expansion)

mm Early Strength Standard Strength

2 days 7 days 28 days

32.5 N - 16.0 32.5 52.5 75

10

32.5 R 10.0 -

42.5 N 10.0 42.5 62.5 60

42.5 R 20.0 -

52.5 N 20.0 - 52.5 45

52.5 R 30.0 -

Add the following after item 4:

5. Any consignment not used within two (2) months from the date of manufacture will not be allowed to be used in the works.

6. Approval of cement does not relieve the Contractor of the responsibility to produce concrete of the specified strength.

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5.1.2.2 Silica Fume

Delete item 2 and replace with the following:

2. Microsilica from each furnace and type of base metal shall be type tested to the requirements of ASTM C 1240 including its optional requirements. Type testing shall be conducted at least once every three years.

2a. In addition the material delivered to the project site shall be tested at the frequency stipulated in ASTM C1240. The test results shall conform to the requirements of ASTM C1240 as well as the following:

Properties Value

SiO2 Min. 85%

Free Carbon Max. 3%

Bulk density Max. 600 kgs/m3

Chloride Max. 0.2 %

Other metals Report as assayed

2b. Batch test certificates shall be provided for each consignment delivered to the site.

5.1.2.5 Aggregates


1a. Except as may be modified hereunder the aggregate (fine and coarse) for all types of concrete shall comply in all respects with BS 882 "Concrete aggregates from natural sources".


2a. Before any material from a particular source is used, the Contractor shall obtain representative samples of fine and coarse aggregates and carry out the necessary tests and analyses to show that the samples comply with the Specification. During the progress of the works, the grading and chemical characteristics may be checked at frequent intervals.

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Add the following to Table 5.1.2.1 and Table 5.1.2.2

Table -5.1.2.1a : Limits for Physical, Chemical And Mechanical Properties of Aggregates for Concrete

S No. Test Test Methods Permissible Limits

Fine Coarse

1. Light weight pieces ASTM C123 max.0.5% max.0.5%

2. Water absorption ASTM C128 ASTM C127

max.2.3% max.2.0%

3. Specific Gravity (Apparent) ASTM C128 ASTM C127

min.2.60 min.2.60

4. Partially crushed faces of coarse aggregate with at least one crushed face.

Hand Picking and Visual Inspection

Method

100%.

5.

Acid soluble Chlorides, Cl

BS 812 Part 117,

Appendix C

For reinforced concrete made with SRPC cements

max.0.03% max.0.01%

OPC & MSRPC cements max.0.03% max.0.02%

For mass concrete made with SRPC cements

max.0.03% max.0.02%

OPC & MSRPC cements max.0.03% max.0.04%

For prestressed concrete & steam cured structural concrete

max.0.03% max.0.01%

6.

Mechanical strength

10% fines value BS 812 Part 111

- min100KN

Impact value BS 812 Part 112

- max.30%

7. Drying Shrinkage BS 812 Part

120 max.0.05%

8.

Potential reactivity, Note 2 Of Aggregates, Chemical Method Of Cement-Aggregate Combination

ASTM C289 Innocuous Innocuous

ASTM C227 6 month expansion 0.10 %

maximum

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Delete item 5 (i) and replace with the following:

Table- 5.1.2.2a Frequency of Routine Tests on Aggregates

S No. Tests Frequency

1. Grading - BS EN 933-1 Per 1,000m3 Concrete

2. Material finer than 0.075 mm - BS EN 933-1 or ASTM C117

- do -

3. Clay lumps and Friable Particles - ASTM C 142

Per 4,000m3 Concrete

4. Organic impurities ASTM C 40 Per 20,000m3 Concrete

5. Water absorption - ASTM C128/C127 - do -

6. Specific Gravity - ASTM C128 /C127 - do -

7. Shell content - BS EN 933-7 - do -

8. Particle shape BS 812 Section 105 Part 105.1.& Section 105 Part 105.2

- do -

9.

Acid soluble chlorides, Cl Qualitative-BS 812 Part 117 Appendices A/B

Per 10,000m3 Concrete

Quantitative-BS 812 Part 117 Appendix C

Each 12 concrete days if result is more than 75% of the limit and each month if result is less than 75% of the limit.

10. Acid soluble sulphates, SO3 - BS EN 1744-1

Per 10,000 m3 or each 24 concrete days if result is more than 75% of the limit & each 2 months if result is less than 75% of the limit which ever is less.

11. Soundness, Mg SO4 (5 cycles) ASTM C88

Each 48 concrete days or 20,000 m3 whichever is less

12.

Mechanical Strength

10% Fines or impact value - BS 812 Parts 111, 112

Each 30 concrete days or 10,000 m3 whichever is less

Los Angeles abrasion - ASTM C 131/C 535 - do -

13. Moisture variation in sand - by Oven dried method

Twice daily

14. Drying Shrinkage BS 812 Part 120

At the start of the project and whenever there is a change in the source of supply

15.

Potential Reactivity: of aggregates (ASTM C 295, C 289) of Carbonate (ASTM C 586) of Cement aggregate combination (ASTM C 227)

At the start of the project and whenever there is a change in the source of Supply

16 Light weight pieces test (ASTM C 123) Per 20,000 m3

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9. The results of these tests shall be submitted to the Engineer and his approval shall be obtained before any of the material is used in the works. Part of each sample will be required for concrete trial mixes and part shall be retained for comparison with subsequent deliveries.

10. Sampling for testing and analysis shall be carried out, where applicable, in accordance with BS 812 Part 102

11. The maximum size of the aggregate shall not be larger than 1/5 of the narrowest dimension between sides of the member for which the concrete is to be used and not larger than 3/4 of the maximum clear distance between reinforcing bars.

12. Beach sand shall not be permitted for use in concrete mixes.

13. Unless otherwise authorized by the Engineer coarse aggregate shall be delivered to site in separate sizes according to the maximum specified aggregate size for each grade of concrete.

14. Aggregate shall be tested for petrographic analysis. The petrographic analysis report shall include the recommendation on the possibility of using aggregate in the production of concrete.

15. Fine Aggregate shall be clean sharp natural and/or crushed sand complying to the grading requirements of BS 882 Zone C or M. The Contractor shall mechanically wash aggregate to remove salts and other impurities in order to meet the requirement specified.

16. Coarse aggregate shall be prepared as single sized aggregate and blended to produce normal size grading. The combined grading shall be within the appropriate grading limits given in BS 882. However, in no case shall materials passing the 0.075mm, sieve exceed three (3) percent by weight of the combined aggregate.

17. Aggregates that are deleteriously reactive with the alkalis in the cement in an amount sufficient to cause excessive expansion of concrete shall not be used.

17.1: Aggregates may initially be assessed for its reactivity in accordance with ASTM C289 and if potential reactivity is indicated, then mortar bar tests in accordance with ASTM C227 shall be carried out.

17.2: If the Petrography report determines the aggregate as silicate type, the aggregate shall be tested for alkali silica reactivity. If the aggregate is defined as carbonate type, the test shall be conducted for alkali carbonate reactivity. The test results shall show that the aggregate is not deleterious for use in concrete.

5.1.2.6 Water

Add the following item after item 1:

1a. The mixing water should be clear, apparently clean and free from matter harmful to concrete in its fresh or hardened state. Potable water can be used. Water shall be tested for physical and chemical properties and meet the requirements of BS EN 1008.

1b. Water for curing concrete shall meet the requirements of BS EN 1008 and not contain impurities in sufficient amounts to cause discoloration of the concrete. Sources of Water shall be maintained at such depth and the water shall be withdrawn in such a manner as to exclude silt, mud, grass and other foreign matter.

The frequency of testing for the materials shall be as follows:

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Table5.1.2.3 Frequency of Routine Testing:

ITEM Sampling Method

Test Method

Test Frequency Rate

a. Cement - as per BS EN 196

BS EN 196-7

BS EN-196

Each 5000m3 of concrete poured.

b. Steel

Deformed Steel Bar as per BS 4449

BS 4449 BS 4449 3 Specimens per each size 100 tons.

Strand as per ASTM A416 if needed

ASTM A416 ASTM A370

1 Specimen per each size 18 ton

c. Concrete

Air content, as per BS EN 123501-7

BSEN 12350-1

BSEN 12350-7

Once at the time of mix design of concrete or as directed by the Engineer.

Flexural strength of Prism as per BS EN 12390-5

BSEN 12350-1

BSEN 12390-5

Once at the time of mix design of concrete or as directed by the Engineer.

Bleeding as per ASTM C232

BS EN 12350-1

C 232 One at the time of mix design of concrete or as directed by the Engineer.

Splitting Tensile Strength of Concrete Cylinder as per ASTM C-496 & others

BS EN 12350-1

C-496 One at the time of mix design of concrete or as directed by the Engineer.

Depth of Water Penetration (BS EN 12390 P-8)

BSEN 12350-1

BS EN 12390-8

Each 200m3 of particular grade of structural concrete or as directed by the Engineer.

ISAT as per BS 1881-p-208

BS EN 12350-1

BS 1881 - 208:1996

Each 500m3 of particular grade of structural concrete or as directed by the Engineer.

Rapid chloride permeability

BS EN 12350-1

ASTM C 1202

Each 200m3 of a particular grade of structural concrete or as directed by the Engineer.

Slump test - as per BS EN 12350-2

BS EN 12350-1

BS EN 12350-2

From each transit mixture load arrived at site

Concrete Mix Design (Mixing and Sampling in the lab) as per BS 1881, Part 125 & In Site (Sampling) as per BS EN 12350-1

All mixes are to be designed once for verification and approval.

d Kerbs-as per BS 7263

BS EN 1339 BS EN 1339

3 Samples to be taken from each batch of up to 1000 kerbs in whole consignment

e. Water BS EN 1008 BS EN 1008

One Sample per every week of production of concrete or as agreed by the Engineer

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5.1.3 CONCRETE MIXES 5.1.3.1 Design Mixes Add the following after item 1:

1a. Structural concrete shall have a service life of at least 100 years.

5.1.3.3 Reports


1a. Approval for concrete mixes shall only be given after submissions and the results of the site trial are found to be satisfactory. Approval will not be given on the strength of documentary submissions only.

1b. Each mix of concrete must be given a unique identification number which shall be cross referenced in all documents concerning the mix.

1c. Submissions for each mix of concrete must be made during the mobilization period. The submission shall comparatively outline the properties required by the specification and either the actual mean properties of the mix proposed obtained statistically from previous production batches or the target values assigned for production. The submission must contain the total chlorides and sulphates based on cementitious content, total aggregate grading together with a graphical illustration, the aggregate cement ratio by volume, the hydrated cement % by volume, the fineness modulus, the nominal aggregate size distribution by weight percentage, the total % passing 75 m, wet mixing time, distance from plant to site and estimated delivery time. A sample copy of the approved batching plant computer printout shall be enclosed.

1d. The specification stipulates limits for properties in the form of minima-maxima. These limits must not be construed as targets to achieve. The designer must aim for a target mean for each property to attain the quality of concrete required.

1e. A site trial mix in the form of a dummy placement must be conducted in accordance with Appendix 2.1 of these Specifications to determine the properties of the fresh and cured concrete proposed. In addition the site trial will enable assessment of The Contractors ability to perform formwork and rebar construction, quality checks, placement and curing tasks.

Site Trial

Various Parameters and abilities need to be assessed during the site trial and shall include the following but not limited to:

Slump reduction over time.

Increase of concrete temperature over time.

Transporting cubes from the site to an approved independent laboratory.

The correlation between strength and durability values of 28-day wet cured cubes and 7-day wet cured structure.

The Contractors ability to construct leak free formwork.

The Contractors ability to provide shaded and suitable areas for sampling and cube making.

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The Contractors ability to place, compact and cure the concrete.

The Contractors ability to perform quality control.

1f. Each class of concrete (shown on the drawings) is denoted by its 28 days characteristic cube strength and the maximum size of aggregate. Preliminary laboratory tests shall be carried out to determine mixes that satisfy the specification with the approved materials.

1g. The Contractor shall carry out as many trial mixes at his own cost, as may be necessary to demonstrate that the mix design, site tasks and curing procedure adopted will produce concrete of the specified properties.

1h. When the mix has been approved, variations shall not be made in the proportions, type or the source of the constituent ingredients, or in the size and grading classification of the aggregate without the consent of the Engineer. A new submission shall be made by the Contractor in the event any change in the approved parameters.

1i. Samples shall be tested to determine the following properties of mixes proposed for initial field tests:

I. Bleeding in accordance with ASTM C232 (non-vibrating) shall not exceed 0.5% for structural concrete.

II. Drying shrinkage in accordance with BS EN 1367 shall not exceed 0.05 % for structural concrete.

III. Air content if applicable BS EN 12350

IV. Workability to BS EN 12350

V. Chloride permeability shall be less than 2,000 coulombs for structural concrete, when tested in accordance with ASTM C-1202.

VI. Water Permeability test results according to BS EN 12390-8 shall not exceed 10mm for concrete contain microsilica and 25mm for concrete does not contain microsilica.

VII. Fresh and hardened concrete densities to BS EN 12350 and BS EN 12390 respectively.

VIII. Compressive strength to BS EN 12390

1j. If the minimum maximum values are not complied with, the proposed mixes shall be rejected.

1k. All costs connected with the preparations of trial-mixes and the design of the job-mixes shall be borne by the Contractor.

1l. The average compressive strength of the trial mixes shall exceed the specified characteristic strength by a margin of 1.64 times the standard deviation measured from the validated production history of the specific mix from the concreting plant, except that no standard deviation less than 3.5 N/mm2 shall be used as a basis for designing a mix.

1m. The average ASTM C 1202 permeability shall be below the specified value by 500 coulombs.

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1n. Statistical data: Where there is no validated statistical data existing for the specific mix design submitted for approval, The Engineer shall assign estimated mean strengths based on the trial mix and to the following table:

No. fck,cube or

fc,cube [N/mm2]

Minimum Margin [N/mm2]

Estimated Target Mean [N/mm2]

Lower limit of range [N/mm2]

1 < 30 + 9 Trial mix mean

less 4 Trial mix mean

less 8

2 30 + 9 Trial mix mean

less 4.5 Trial mix mean

less 9

3 40 +10 Trial mix mean


less 10



less 12



less 14

1o. The mean strength shall not be computed from a mixture of different mix designs.

1p. The estimated mean strengths shall be replaced with the actual mean strength once at least 40 results from 40 separate loads made over at least 30 days is available. The target strength to aim for shall be the actual mean and not the minimum strength stipulated in the specification. The producer must maintain a register of product data obtained from production batch tests for each mix design as follows.

Arithmetic mean

Minimum

Maximum

Standard Deviation

Count

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5.1.3.4 Concrete Classes

Delete Table 5.1.3.1 and replace with the following:

Concrete Class

Maximum Aggregate Size (mm)

Range of Cement Content (kg/m3)

Microsilica (Percentage of Cement Weight) -%

Maximum Free

Water/Cement Ratio

Characteristic 28-Days Cube

Strength CCS (N/mm2)

Characteristic 28-Days Cylinder Strength

CCS (N/mm2)

50/20 MS 7 20 370 - 400 7 0.40 50 40

45/20 MS 7 20 350 - 380 7 0.40 45 36.5

40/20 MS 7 20 345 - 370 7 0.40 40 32

50/20 20 425-500 - 0.45 50 40

45/20 20 425-475 - 0.45 45 36.5

40/20 20 350-450 - 0.45 40 32

37/20 20 330 - 350 - 0.42 37 30

35/20 20 320 - 330 - 0.42 35 29

30/20 20 300 - 400 - 0.5 30 24

25/20 20 250 - 275 - 0.5 25 20

16/20 20 230 - 250 - 0.5 15 13

Note: Concrete Classes are defined based on the Characteristic 28 Days Cube Strength CCS (N/mm2)

5.1.3.7 Water Cementitious Materials Ratio

Delete item 1 and replace with the following:

1. The water cementitious ratio shall be determined in accordance with BS EN 206.

1a. The water cementitious ratio of structural concrete shall not exceed 0.4

1b. The water cementitious ratio of blinding concrete shall not exceed 0.5

5.1.3.8 Slump Limits


1a. The slump of the concrete with microsilica shall be at least 100mm and for normal concrete shall be at least 75mm. The maximum slump for normal concrete is 120mm. There is no upper limit for the slump of concrete with microsilica. However, the concrete shall not show any sign of segregation during placement. The slump for piling concrete shall be 180mm minimum.

1b. Workability shall be assessed by the following tests the requirements for which shall be as specified elsewhere in the documents.

Slump test shall be performed according to BS EN 12350-2

Compaction factor shall be performed according to BS EN 12350-4

Vebe time shall be performed according to BS EN 12350-3

Flow test shall be performed according to BS EN 12350-5

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5.1.3.13 Adjustments to Concrete Mixes


1a. If the maximum aggregate size is 10mm, the maximum cementitious content stipulated for each class of concrete may be increased by up to 20kg/m3. For 40 mm aggregates the cement content may be decreased by 30 kg/m3.

1. The Contractor shall use Microsilica for structural concrete in any environment with a requirement for concrete permeability of a maximum of 2000 coulombs (ASTM C 1202).

5.1.3.15 Permeability Tests


2a. In view of the large variation of permeability values obtained with the ASTM C 1202 test, the target for the value at a trial mix shall be the maximum of [2000 minus 500] Coulombs unless validated production data exists for the population statistic for a specific mix design which shows it to be different. The population shall consist of at least 40 specimens from different batches with data for the range of values, the standard deviation, the population mean and a graphical frequency distribution.

The water permeability when tested in accordance with BS EN 12390-8 shall not exceed 10mm for structural concrete.

5.1.4 Construction Requirements

5.1.4.4 Quality Control and Testing

Add the following to item 1:

1a. The testing shall be either performed by the approved independent agency or at the site laboratory in the presence of the Engineer or his representative.

5.1.4.5 Quality Control Testing on Fresh Concrete

Add the following after item 1 (v)

1(vi). The testing of fresh concrete and the making of cubes must be performed by qualified technicians. Cubes made on site shall be prepared on a level, hard surface in a mobile or fixed shaded hut complying to BS EN 12390. The molds shall be checked to conform to BS EN 12390. The Cubes shall be protected from evaporation losses immediately after making by encasing each cube with Hessian and a plastic bag. The cube in its mold shall be transported to the vicinity of the curing tank not earlier than 12 hours but not later than 36 hours from its making and de-molded. The de-molded cubes shall be instantly immersed in a temperature controlled curing tank. The cube shall be protected from damage and drying out during transportation.

1(vii). The producer is prohibited from handling the cubes or transporting them to the laboratory once they have been made. The Consultant shall be the custodian of the cubes till they have been tested. Cubes must be tested in an approved independent laboratory or at the site laboratory where the tests are supervised and witnessed by the Engineers representative. They shall not be tested in the producers laboratory.

1(viii). A sample for test cubes shall mean two sets, each of three cubes taken from a spot sample.

1(ix). A sample of concrete shall be taken at random on eight separate occasions during the first five days of using a mix at least one sample being taken each day. The standard

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deviation shall be calculated from at least 40 individual cube results each representing separate batches of each concrete mix produced by the same plant under the same conditions of mixing. Thereafter one sample shall be taken at random for each class of concrete in accordance with the Clause on Quality Control of these Specifications. The sampling rate for the ASTM 1202 and BS EN 12390-8 permeability tests shall be 1 sample every 200m3 for each test.

1(x). In addition to the above requirements, at least one sample shall be taken from each individual structural unit even the quantity is less than 200 m3, or part of a unit, when the latter is the product of a single placement.

1(xi). From each sample three cubes shall be made for testing at 28 days and three for testing at 7 days.

1(xii). The frequency of sampling may be required to be varied if directed by the Engineer.

1(xiii). The procedures shall be repeated when materials or design mixes are changed.

1(xiv). A test result for a sample shall mean the mean of three cubes forming the sample set. Each individual result in the sample set shall be within 15% of the mean result. In the event that any individual result fails to comply with the closeness requirements, the non complying result shall be discarded from the mean calculation and the mean shall be derived from the remaining results from the two cubes. The number of total accumulated results below the specified characteristic compressive strength should not be more than one and no result should fall below the characteristic strength minus 3 N/mm3. The average compressive strength test result of the cubes in a sample set when tested at 28 days shall not be less than the design characteristic 28 day cube compressive strength.

1(xv). If the above criteria are not satisfied, the unit represented by the sample is questionable and the following actions may be instructed as appropriate:

Cutting and testing cores from placed concrete

Load-testing relevant structural units

Cutting out and replacing defective concrete

1(xvi). If the range of individual cube strengths made from the same sample exceeds 15% of the mean, then the method of making, curing and testing cubes shall be checked. In the event of a sample having a range exceeding 20%, then the result shall be unacceptable and the Engineer may order any of the following actions:

Improving quality control

Cutting and testing cores from placed concrete

1(xvii). Structural Concrete shall be tested for durability properties by conducting permeability tests as specified herein and when directed by the Engineer.

1(xviii). Permeability tests in accordance with BS EN 12390-8 shall be carried out. The maximum acceptable penetration at 28 days shall be 10mm for concrete using microsilica as ingredient and 25mm for concrete produced without using microsilica.

1(xix). 100 mm cores shall be tested to ASTM C 1202 Chloride permeability. The maximum acceptable value shall be 2000 Coulombs.

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5.1.4.6 Quality Control Testing on Hardened Concrete


1a. In the event core testing is required, the Contractor shall cut cores from locations identified by the Engineer and test them to BS EN 12350 and 12390.

1b. In the event the test specimens for durability tests (water permeability test and RCPT) fail to meet the specification, three cores from the structure shall be tested and the test results shall meet the Contract specification requirements.

1c. The cost of cutting and testing cores and any resultant delay shall be borne by the Contractor regardless of whether the permeability of the deposited concrete proves to be satisfactory or not.

1d. Where the permeability test results found by testing the three cores taken from the structure is confirmed as not complying with the permeability requirements, then the Engineer may instruct that further cores be cut and tested in order to determine the full extent of the defective concrete and further investigations to be carried out.

1e. Defective concrete shall be cut out and replaced or alternative remedial action shall be taken, as directed by the Engineer. The cost of such work and any resultant delay shall be borne by the Contractor.


8. When instructed by the Engineer concrete shall be tested for drying shrinkage and wetting expansion, for which 75x75mm prisms shall be prepared and tested in accordance with BS EN 12350 and 12390 or BS6073 Part 1 Appendix D. The maximum acceptable limits shall be:

Drying Shrinkage: 0.05%

Wetting Expansion: 0.03%

9. Cubes may be required and trials carried out to determine stripping times for formwork, the duration of curing and to check testing and sampling errors.

10. The air content of air-entrained concrete shall be determined (ASTM C231) for every 200m3 each batch produced until consistency has been achieved, when required by the Engineer. The maximum value shall not exceed 2%.

11. Tolerances in Proportioning Materials per load (not per batch) shall be as follow:

Cement: Measurement for proportioning all cement shall be accurate to within one (1) percent throughout the range of use. In the case of bagged cement only full bags, undamaged or unbroken will be permitted.

Water: The mixing water shall be measured by weight or by volume. In either case the measurement shall be accurate to within one (1) percent throughout the range of use.

Aggregate: The aggregates shall be measured by weight to accuracy within two (2) percent through-out the range of use.

Admixtures: Admixtures shall be measured by volume if in liquid form and by weight if solid. The measurement shall be accurate to within 3.0% throughout the range of use.

12. The Contractor shall be responsible for the performance of all concrete mixes used in the works. The mix proportions selected shall produce concrete that is sufficiently workable and finishable for all uses intended and shall conform to the requirements of the drawings and all other requirements of this Specification.

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Add the following after item 5.1.4.6

5.1.4.7 Mixing Concrete

1. Concrete shall be wet batched from a fully automatic computer controlled plant whether it is ready-mixed or site-mixed. The plant shall have been audited and approved by the Engineer for supply to the Works. Dry batching will only be allowed by the Engineer in exceptional circumstances where the delivery of wet concrete is not feasible due to transportation time.

The audit by the Engineer shall cover the following areas:

Quality system and control

Storage, handling and control of constituent ingredients

Fully computerized automatic plant and equipment

Calibration

Control of batching operations

Control in delivering concrete

Testing laboratory

Qualified experienced personnel

2. All ingredients in the concrete must enter the system through the weigh scales or volumetric devices. All weights must be automatically logged and printed by the plant computer. Every ingredient must be weighed through the computer controlled automatic weighing system and printed in the printout.

3. Constituent ingredients shall not be added to the ready mixed wet concrete once the agitator or truck has left the loading bay at the mixer.

4. Delivery of the concrete load shall be accompanied by the approved batch plant computer printouts. The printouts shall be for each individual batch as well as for the load. The computer printouts shall have the details including but not limited to project name, client name, consultant name, contractor name, location, structure details, mix id, grade of concrete, weight of ingredients, variation between the mix design and actual quantity in percentage, mixing time, time of mix started, time of mix finished, water cement ration, etc.

5. The mixing time of concrete with microsilica shall be at least 60 seconds and that for the normal concrete is 30 seconds.

6. Mixers which have been out of use for more than 30 minutes shall be thoroughly cleaned before any fresh concrete is mixed.

7. The method of discharge from the mixer shall be such as to cause no segregation whether partial or otherwise of the concrete materials.

8. The aggregates shall be stored under shade on hard and leveled platforms. Storage of aggregates and sand directly on the ground will not be allowed.

9. The Contractor shall ensure that the constituent materials of the concrete are sufficiently cool to prevent the concrete from stiffening in the interval between its discharge from the mixer and compaction in its final position. Precautions shall include the shading of aggregate stockpiles and the use of chilled water.

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10. The Concrete shall be carried in purpose-made agitators, operating continuously, or truck mixers. The concrete shall be compacted and in its final position within 90 minutes of the introduction of cement to water or damp or wet aggregates, unless a longer time is agreed by the Engineer. The time of such introduction shall be recorded on the batch plant printout note together with the weight of the constituents of each mix and other parameters printed by the computer and as approved.

11. When truck mixed concrete is used, water shall be added under the supervision, either at the Site or at the central batching plant as agreed by the Engineer but in no circumstances shall water be added in transit.

12. Unless otherwise agreed by the Engineer, truck mixer units and their mixing and discharge performance shall comply with the requirements of ASTM C 94.

13. Re-mixing of concrete which has commenced to set shall not be allowed and in no case shall such concrete be used in the Works.

14. All nominal sized aggregates shall be kept in separate identified stockpiles from which samples can be collected and tested as specified.

15. The addition of water to wet batched concrete delivered to site from a concrete plant shall not be permitted. Concrete delivery vehicles shall not be fitted with means of direct delivery of water into the drum.

5.1.4.8 Minimum Test Requirements for Concrete

1. Unless the Engineer otherwise directs, the testing program conforming to the applicable procedures set out in the relevant ASTM and BS specifications shall include at least the tests specified below. Samples for compressive strength tests shall be taken as specified in the Table below with a minimum of one sample taken every day that the mix is used. A sample consists of 6 cubes, 3 to be tested at 7 days and 3 at 28 days. Additional cubes may be taken as directed by the Engineer.

Structure Type Sampling to Represent a

Volume of m3

Critical structures e.g. masts, cantilevers, columns 10

Intermediate structures e.g. beams, slabs, bridge decks 50

Heavy concrete construction e.g. breakwaters, solid rafts 100

For each component of the structure (such as pier, abutment etc.), permeability samples shall be tested in accordance with these Specifications for permeability compliance.

5.1.4.9 Provisions for Equipment at Site

1. The Contractor shall provide and maintain the equipment listed in the table below on site for the Engineer's use during the contract period.

S No. Description

1 2mm Sieve to BS EN 933-2

2 150mm standard molds for test cubes and accessories

3 Standard slump cones and accessories

4 Lab grade glass thermometer 0-500 degree C

5 Tape measures (readability 1mm)

6 Portable anemometer

7 Hygrometer (with humidity chart)

8 Spirit Level

! ! " # ! $

% & % % ' ( %

5.1.6 Basis of Payment


1a. No separate payment will be made for the material including shutter and labor used in the preparation of architectural finish for the structures as shown in the Drawings or as required by the Engineer. The cost for architectural finish shall be considered as included in the rate of Concrete for the relevant item in the Bill of Quantities. The architectural finish shown in the Contract Drawing is indicative only. It may be modified during the tenure of the Contract as required by the Engineer.

Documents

Concrete Special Spec.pdf