The effect of jaw's curvature on Brazilian tensile strength of rocks

This paper investigates the effect of the jaw's curvature, also known by contact angle and jaw arc central angle (2 alpha), of the Brazilian test apparatus on indirect tensile strength of various rock types. That's why, ten rock samples including limestone, marble, skarn, granite, diorite, and granodiorite were collected from some quarries in different provinces of Iran. Petrographic, mineralogical and textural investigations were performed using thin section analyses. Physical properties of the selected rock samples namely dry and saturated unit weights, porosity, water absorption, and specific gravity were determined for the rock samples. In addition, Brazilian tensile strength at different 2 alpha angles (i.e., 2 alpha = 0 degrees, 10 degrees, 15 degrees, 20 degrees, 45 degrees, and 60 degrees) were determined for the rocks in the laboratory. Results show that the parameter for the rocks is between 3.81 MPa at 2 alpha=0 degrees and 54.76 MPa at 2 alpha=60 degrees. This means that Brazilian tensile strength increased with increasing 2 alpha angle from 0 degrees to 60 degrees. Also, it was found that the highest change rate of the Brazilian tensile strength occurs in range of 2 alpha=15 degrees-30 degrees for most studied rock samples. In some tested samples, the parameter is decreased only at 2 alpha=60 degrees. The values of Brazilian tensile strength of the rocks tested by flat and standard jaws are near to each other.