CORRELATION OF HARDENED CONCRETE TEST METHODS AND RESULTS

A laboratory investigation was conducted (a) to determine compressive, tensile, and shear strength parameters of several concrete mixtures, (b) to evaluate the test methods utilized, and (c) to correlate the results obtained. Six- by twelve-in. concrete test specimens were cast from four different concrete mixtures using the two types of aggregate (limestone and natural) and two cement factors (4 and 6 bags per cu yd). Compressive, tensile (diametral compression), and three types of direct shear strength tests were conducted on air-dried specimens, and triaxial tests were conducted on specimens representing three different moisture conditions. The shear strength determined by the Mohr envelope of failure for the triaxial tests most closely approximates the pure shear strength of concrete. The direct shear tests have inherent discrepancies in the methods and equipment that cast doubts on the results obtained through their use. The strength of concrete kept moist until time of test is lower than that of concrete that has been allowed to air-dry. The beneficial effects of angular aggregate as compared to rounded aggregate balance the detrimental effect of the higher water-cement ratios required for equal consistency. (Author)