Objective and Significance: –
The aggregate crushing value gives a relative measure of the resistance of an aggregate to crushing under a gradually applied compressive load. With aggregate of aggregate crushing value 30 or higher, the result may be anomalous, and in such cases the ten percent fines value should be determined instead. Crushing value is strength of the aggregates against crushing load. Aggregates undergo crushing in road construction and road operation work. If it gets crushed easily then road quality decreases accordingly. So Crushing value test is very important to so.
To determine crushing value of aggregates using aggregate crushing mould apparatus.
Aggregate Crushing Mould: –
15-cm diameter open-ended steel cylinder, with plunger and base-plate, of the general form and dimensions and a straight metal tamping rod. For measuring the sample, cylindrical metal measure of sufficient rigidity to retain its form under rough usage and of the following internal dimensions: Diameter 11.5 cm and Height 18.0 cm
Compression Testing Machine: –
Sieves: – 12.5 mm, 10.0 mm and 2.36 mm
Weight Scale: – To measure sample weight.
i) The aggregates passing through 12.5mm and retained on 10mm IS Sieve are oven-dried at a temperature of 100 to 110 Degree C for 3 to 4hrs.
ii) The cylinder of the apparatus is filled in 3 layers, each layer tamped with 25 strokes of a tamping rod
iii) The weight of aggregates is measured (Weight ‘A’).
iv) The surface of the aggregates is then levelled and the plunger inserted. The apparatus is then placed in the compression testing machine and loaded at a uniform rate so as to achieve 40t load in 10 minutes. After this, the load is released.
v) The sample is then sieved through a 2.36mm IS Sieve and the fraction passing through the sieve is weighed (Weight ‘B’).
vi) Two tests should be conducted
Results and Calculations: –
Aggregate Crushing Value = (B/A) X 100
where A = weight of oven-dried sample
B = weight in ‘g’ of fraction passing through 2.36 mm sieve.