Objective: For the assessment of the aggregate crushing value of coarse aggregate.
The aggregate crushing value provides a subjective measure of the resistance of the aggregate crushing in the pressure of the progressively smeared compressive load. When the aggregate crushing value is 30 or greater the outcome can be irregular and in those kind of circumstances the ten percent fines value has to be assessed in its place.
Apparatus
- Steel cylinder 15 cm diameter with base plate and plunger
- Straight metal tamping rod 16mm diameter and 45 to 60cm long rounded at one of the ends
- An equilibrium of volume ability of 3 kg readable and precise to one gram.
- Dial gauge
- IS sieves of sizes 2.36mm, 10mm, and 12.5mm.
- A machine for compression testing.
- Cylindrical metal measure of adequate firmness to maintain its shame even under rough utilization and of 11.5cm diameter and 18cm height.
Sampling
The coarse total passing 12.5mm IS sieve and reserved on a10mm. IS sieve and is exposed to the heated temperature of 100 to 110°C for approximately 4 hours and refrigerated in just room temperature.
The total volume of aggregate has to be in a such a way that the density of material in the cylinder, after conduction of the process of tamping as defined below should not exceed 10cm.
The suitable volume might not be found suitably by the process of filling the cylinder.
Calculate and assess in three layers of nearly equal density, with each one of the layer being tamped at least 25 times with the help of the tamping rod and lastly leveled off with the utilization of the tamping rod as straight edge, with very delicate care being taken in the cases of the feebler resources so that the particles are not exposed to the circumstances of breaking. The mass of the material including the test sample which has to be assessed (weight A) and the similar weight of sample should be undertaken for the for the repetition of the process.
Procedure
(i) at first, keep the cylinder in the position on the base plate and measure its weight. (W)
(ii) Now, keep the specimen in 3 layers, each one of the layer being exposed to minimum of 25 strokes with the utilization of the tamping rod, however, delicate care has to be undertaken so that the weak materials will not break the particles and then once again measure it.
(iii)Properly even out the surface of the measured aggregate meticulously and connect the plunger so that it is positioned in a parallel position on the even surface, once again meticulous care being taken to safeguard that the plunger does not cause any kind of jam in the cylinder.
(iv)Now position the cylinder with plunger on the top of the loading platform of compression testing machine.
(v) Put load at a uniform rate so that it leads to the total load of 40T being applied in under 10 minutes.
(vi) Suspend the load and detach the substance from the cylinder.
(vii) Meticulously filter the material with 2.36mm IS sieve, we have to be very careful in order to get rid of the fines.
(viii)Measure the weight of fraction passing through the IS sieve (W2).
Calculations
The proportion of the mass of the fines created to the mass of aggregate specimen in each test has to be articulated in the form of percentage, the outcome being chronicled to the initial decimal place.
W2= Total crushing value = (W2x100) / (W1-W)
W2 = The total weight of the fraction passing through the suitable sieve
W1-W =Weight of surface dry sample.
The mean of two conclusions to closest whole number refers to the total crushing value.
Result
The aggregate crushing value of the given sample=