Concrete Quality Control

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© Dr. Mohamed Abdallah El-Reedy Email:elreedyna@gmail.com The mould for the slump test is a cone, 305mm (12in) high. It is placed in a smooth surface with smaller opening at the top. It filled with concrete in three layers. Each layer is tamped 25 times with a standard 16 mm (5/8 in) diameter steel rod, rounded at the end, and the top surface is stuck off by means of screening and rolling motion of the tamping rod. The mould must be firmly held against its base during the entire operation; this is facilitated by handles or footrests braze to the mould. Immediately after filling, the cone is slowly lifted, and the unsupported concrete will now slump. The decreases in the height of the center of the slumped concrete is measured to the nearest (1/4 in), 5mm. In order to reduce the influence of the friction on the slump variation, the inside of the mould and its base should be moistened at the beginning of every test, and prior to lifting of the mould the area immediately. The test must be comply with ASTM C 143-78. Slump Test

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© Dr. Mohamed Abdallah El-Reedy Email:elreedyna@gmail.com Flow Table Test This test is comply with BS1881part 105 of 1984 and DIN 1048 part I The slump cone is placed centrally on the table.The slump cone is filled with concrete in two equal layer each layer tamped lightly 10 times with the wooden bar. After 30 sec. The cone is slightly raised. The table-top raised by the handle and allowed to fall 15 times in 15 seconds. The conc. diameter is measured in two directions parallel to the table edge. The arithmetic mean of the two diameter will be the flow measurement in mm. 400 mm indicate medium workability and 500 mm high workability

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© Dr. Mohamed Abdallah El-Reedy Email:elreedyna@gmail.com Three types of compression test specimens are used: cubes, cylinders, and prisms. Cubes are used in Great Britain, Germany and many other countries in Europe. Cylinders are the standard specimens in the Unites States, France, Canada, Australia and Newzeland. In Scandinavia tests are made on both cubes and cylinders. The tendency nowadays, especially in research is to use cylinders in preference to cubes, but before comparing the two types of specimens the various tests should be considered in detail. Compression Tests

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© Dr. Mohamed Abdallah El-Reedy Email:elreedyna@gmail.com The standard cylinder is 6 in diameter, 12 in long ( 150 by 300 mm) and is cast in a mould generally made of steel or cast iron. The cylinder specimens are made are compacted either in three layers using a 16 mm diameter rod or in two layers by means of an immersion vibrator. Details of procedure are prescribed in ASTM Standard C192-76. Cylinder Test

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© Dr. Mohamed Abdallah El-Reedy Email:elreedyna@gmail.com After top surface of the cyliner has been finished by means of trowel, the cube is stored undistributed for 24 hours at a temperature of 18 to 22 º C and relative humidity of not less than 90 percent. At the end of this period the mould is stripped and the cylinder is further cured in a water at 19 to 21º C . The test is generally performed at 28 days but it also perform additional test at 3 and 7 days. In compression test, the cylinder is placed with the faces in contact with the platens of the testing machine, i.e. the position of the cube when tested is at right angles to that as-cast. The load on the cylinder should be applied at a constant rate of stress equal to 15 MPa/min(2200psi/min). Cylinder Compressive Tests

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© Dr. Mohamed Abdallah El-Reedy Email:elreedyna@gmail.com Compressive Strength Machine Specifications The machine must be comply with ISO 4012 The crushing load for sample not be less than 1/10 machine measurement range The accuracy for the crushing load is 1 % The steel plate for Rockwell no. 55 and the hardening thickness not less than 5 mm The dimension of the plate loading more than the sample dimensions

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© Dr. Mohamed Abdallah El-Reedy Email:elreedyna@gmail.com Regular Mistakes Finish the test without complete sample failure. No proof aggregate with maximum aggregate size not reasonable to the sample dimension ( max. aggregate size 40 with cube 15 cm length). No contstant loading rate. In good conditions sample for 30 N/mm2 take 1 minute, any increasing in loading rate will give you higher results

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© Dr. Mohamed Abdallah El-Reedy Email:elreedyna@gmail.com ACI Evaluation and Acceptance of Concrete No single test strength ( average strength of two cylinder from a batch) shall be more than 500 psi below the specified compressive strength fc’ 2500 psi for a specific 3000 psi concrete. The average of any three consecutive test strengths must be equal or exceed the specific compressive strength, fc`

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© Dr. Mohamed Abdallah El-Reedy Email:elreedyna@gmail.com EC Evaluation and Acceptance of Concrete The result of compressive strength for any cube test must be not less than the characteristic strength. The difference between the higher cube strength to the lower cube strength for single test must be not higher tan 15% of the average test.

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© Dr. Mohamed Abdallah El-Reedy Email:elreedyna@gmail.com Steel Bar Test 2 samples for the same diameter for each deliver has weight less than 50 ton. 3 samples for the same diameter for each deliver has weight equal to or more than 50 ton. Avoid increase temperature to the sample. Load test must be increase gradually. The result of any bars must not be less than 95% of the values in the following table. The ratio between the tensile strength and yield strength must not be less than 1.1 in mild steel and 1.05 in H.G.S.

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Concrete in Hot Climate :

© Dr. Mohamed Abdallah El-Reedy Email:elreedyna@gmail.com Cracks caused by evaporation can be very deep, range in width between 1mm to 3mm and can be wide short or as long as 1m. a drop in the ambient related humidity encourages this type of cracking so that in fact the causes of it appear to be rather complex. According to the ACI, the risk of plastic cracking is result of the following combinations of temperature and relative humidity: 41º C (106 F) and 90 % 35 º C (90 F) and 70% 24º C (75 F) and 30 % Concrete in Hot Climate

Concrete in Hot Climate :

© Dr. Mohamed Abdallah El-Reedy Email:elreedyna@gmail.com Concrete in Hot Climate There are a number of remedial measures that can be taken. the cement content should be kept as low as possible so that the heat of hydration does not unduly aggravate the effects of high ambient temperature. The temperature of the fresh concrete can be lowered by pre-cooling one or more ingredients of the mix. For instance, ice can be used instead of some of the mixing water, but it is essential that the ice melt completely before the mixing has been completed. The cooling of the aggregate is more difficult and, because of the low specific heat of stone, less effective. The temperature of concrete delivered at site in hot weather should be as low as possible; an upper limit of 29 º C (85º F) is often specified.

Concrete Quality Control

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Concrete in Hot Climate :

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