Microcracking and Behavior of High-Strength Concrete Subject to Biaxial Tension-Compression Stresses.

Research at The University of Texas has been conducted to determine the properties and micro-cracking behavior of high-strength concrete subjected to biaxial tension-compression stresses. Static tests and microcrack mapping was performed on 35 specimens which consisted of 5-in. square x 12-in. thick plates cut from concrete beams. Tests were performed in a biaxial test machine developed at The University of Texas. The primary variables studied were the discontinuity and ulitimate stress levels at each stress ratio. The microcrack patterns and total crack lengths at various pre-and post-discontinuity stress levels were mapped and recorded. Results indicated that even small amounts of tensile stress reduced stress reduced the ultimate compressive strength of the specimens dramatically. The uniaxial strength of the plates was 75 percent that of standard 4-in. x 8-in. cylinders when both were tested at 172 days after casting. Youngs modulus of elasiticity was found to be 3 percent higher for specimens loaded in tension than compression. Keywords Biaxial tests, High strength, Concrete microcracking,