Fresh concrete:

Test for workability ( Slump test)

IS 1199 specifies various test for workability . They are

Slump test

Compaction Factor test.

Flow table test

Vee-Bee time.

The most commonly used workability test in the field the slump test is described below.

Apparatus

Slump mould with bottom diameter 20 cm , Top diameter 10 cm and Height 30 cm

Base plate for fixing the mould

Tamping rod 16mm dia 600 mm long.

Steel scale.

Test procedure:

Sampling:

From Mixers: At least three approximately equal sample increments totaling to 0.02 m3 shall be taken from a batch during concrete discharge and each sample increment shall be collected by passing a clean shovel in to the stream of concrete.

From concrete at the time and place of deposition:

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For low temperature conditions and retarded mixes the initial penetration may be deferred for an elapsed time of 4 to 6 hours, and perhaps longer.

Not less than 6 penetration resistance determinations made in each rate of hardening and the time interval between penetration resistance .

Calculation:

Calculate the penetration resistance in N/mm2 (kgf/cm2) as the force required to cause a 25 mm depth of penetration of the needle divided by the area of the bearing surface of the needle.

The range of properly conducted trial by the same operator shall not exceed 84 minutes.

The average setting time for the two sets of tests each consisting of three similar batches shall not depart more than 20 minutes for the average of the two.

For each of the variable and conditions of concrete as specified the results from each of the three or more rate of hardening test shall be plotted separately, showing penetration resistance Kg/cm2 as the ordinate and elapsed time in hours and minutes as abscissa.

Where 35 kg/cm2 and 1 hour are represented by not less than 13

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Measure the height of clay , silt layer. Calculate the percentage of clay and silt in the total sand layer.

Normally clay and silt content in natural sand should not exceed 10 percent by volume. The allowable limits of material passing 75 micron sieve for natural sand and crushed sand specified.

Sieve Analysis of sand:

Sand consist of material mostly between 4.75 mm and 150 microns sizes. Sand may be naturally available or manufactured by crushing and pulverizing . Sieve analysis of sand is done to findout the size of particles present in it and the uniformity of grading. Sand based sieve is classified into four zones (refer table 12 ). Sand conforming zone I is the coarsest variety and conforming to zone Iv is the finest variety.

The sieves required for doing sieve test for sand are 4.75 mm, 2.36 mm, 1.18mm, 600 microns, 300 microns and 150 microns.

Procedure for doing sieve analysis is as follows.

Sieve the sand progressively starting from the biggest sieve , namely 4.75 mm .

Note down the weight of sand retained in each sieve respectively.

Calculate the percentage of sand retained in each sieve and also the cumulative percentage retained on each sieve.

Calculate the cumulative percentage of sand passing through each