Strength estimation of concrete masonry units using stress-wave methods

Solid concrete masonry units (CMUs) are rapidly replacing burnt clay bricks in the construction industry, especially in the southern regions of Asia. In developing countries, the plants producing CMUs lack effective quality control for the fabricated units. They rely on destructive tests, such as those described by ASTM C140, to demonstrate compliance with compressive strength criteria. Such destructive testing is expensive and is, therefore, performed on a limited scale. A previous study concluded that a surface hardness based nondestructive test (NDT) method (rebound hammer test) is not reliable and that ultrasonic pulse velocity (UPV), which is a stress wave propagation based method, can be a useful tool for strength estimation of CMU (Sajid et al., 2016). This study compares the performance of the UPV test with that of the resonant frequency test, another stress wave propagation based method, to evaluate the compressive strength of concrete specimens. The specimens are made with materials, mixture proportions and compaction similar to those of solid CMUs. The statistical models show that the resonant frequency test is more reliable compared with the UPV test for evaluating strength of concrete for masonry units.