Effect of construction joints on the modulus of rupture

Abstract

The purpose of this study is to correlate the compressive strength (fc) of concrete to the modulus of rupture (R) for a non-reinforced test beam with a construction joint placed at the center. The testing was performed according to the ASTM standards. The current ACI code suggests a formula for the correlation of R to fc, given that the concrete specimen is monolithic (no joints). Given the fact that no concrete structure is built without the use of construction joints, whether planned or un-planned, an engineer would definitely benefit from an equation that could relate the flexural strength of concrete (modulus of rupture) in function of its compressive strength. In addition to that, it would also prove useful to know how much flexural strength is being reduced in the existence of a construction joint. The aim of this paper is to show that the amount of flexural strength reduced in the presence of a construction joint is not as significant as most engineers believe. Due to that belief, most engineers tend to add tremendous amounts of steel reinforcement at the joints to compensate for this reduction. Hopefully, a better understanding of the effects of a construction joint on the modulus of rupture will assist structural engineers in their design calculations, thus reducing the amount of steel reinforcement at the joints, which in turn will lead to ultimate cost savings on a large-scale project. This is what value engineering is all about.