Abstract
The compressive mechanical response of ultra-high-performance concrete (UHPC) surpasses that exhibited by the types of concrete for which the ASTM C39 compressive strength test and ASTM C469 compression modulus of elasticity test were developed. When attempting to complete these tests on UHPC, one will likely face challenges related to both the required load rate of 35 psi/s (0.25 MPa/s) and the cylinder end preparation requirements. Compression strength test durations for concretes with compressive strengths up to and exceeding 29 ksi (200 MPa) can be excessively long. Common cylinder end preparation techniques are not acceptable because of the high strength of the concrete, resulting in the requirement that the cylinder ends be ground to a plane, parallel finish. Researchers at the U.S. Federal Highway Administration are developing solutions to these challenges. Research on the compressive strength of UHPC has demonstrated that the strength determined through the use of an ASTM C109 type of test on concrete cubes is very similar to the strength reported with ASTM C39 tests on cylinders. Thus cubes, which do not require end preparation, can be used as a surrogate for cylinders. A separate study investigating the effect of increasing the load rate during cylinder compressive tests to 150 psi/s (1 MPa/s) was also completed. In this testing program, 400 cylinders with strengths between 18 and 30 ksi (124 and 200 MPa) were tested at a range of load rates. The strength and modulus of elasticity increases resulting from the load rate increase were observed to be minimal.
