Measurement of compressive strength and rebar parameters of reinforced concrete in buildings in Nairobi, Kenya

摘要

Concrete is a widely used material in the construction of commercial and residential buildings. It is very strong under compression but relatively weak in tension. Rebar are cast into concrete to enable the concrete structures to carry the tensile loads. The strength of the concrete, and the rebar cover, location and diameter are critical for the durability of the concrete structures especially those that are subject to degrading environment during their service life. This study reports measurements of concrete compressive strength using a laboratory pre-calibrated Schmidt/rebound hammer, and rebar diameter, location and cover using a Profometer 5+. Laboratory calibration involved prepared 36 cubes of concrete specimens composed of 6 grades of cement mixtures each replicated 6 times. The compressive strengths of all the cubes were measured using a Denison Compressive Testing Machine. Data obtained from hammer measurements were plotted against related Denison data and a calibration equation generated using least square fitting at a correlation coefficient of 0.8. Accuracy of Profometer was also established to within <10% by measuring casted specimens of reinforced concrete blocks of specified parameter. The two instruments were then used to obtain in situ measurements of existing reinforced concrete blocks in a selected building successfully. The method proved to be fast and inexpensive and is therefore a necessary asset in Kenya.