Effect of construction joints on the splitting tensile strength of concrete

AbstractThe purpose of this study is to experimentally correlate the compressive strength (f′c) of concrete to the splitting tensile strength (T) for plain concrete in the existence of a construction joint, and formulate an empirical equation relating T to f′c. Both the American Concrete Institute code (ACI 318-08 (ACI Committee 318, 2008)) and the American Society for Testing and Materials (ASTM (ASTM Standard C496, 2002; ASTM Standard C192/C192M, 2002; ASTM Standard C39/C39M, 2005; ASTM Standard C617, 2002)) provide the testing methods and standards, as well as the applicable theoretical and experimental formulas for the correlation between T to f′c for concrete specimens, which are monolithic, indicating that the specimens lack any construction joints. Providing a useful reduction factor in the splitting tensile strength of concrete due the existence of a construction joint is essential. It is a well known fact that construction joints are used in every concrete structure, which indicates that engineers would definitely benefit from an equation that could relate the splitting tensile strength of concrete in function of its compressive strength.The results suggest that the reduction in the splitting tensile strength in the presence of a construction joint is not as much as most engineers tend to believe. Due to that belief, most engineers tend to overdesign for steel reinforcement at those joints to compensate for this reduction. The objective of the study is to better the understanding of the effects of a construction joint on the splitting tensile strength. Thus provide an empirical equation to assist engineers in their design calculations, therefore reducing the amount of steel reinforcement at the construction joints. Thus also leading to cost saving on projects

The effect of concrete vertical construction joints on the modulus of rupture

The purpose of this study is to experimentally correlate the compressive strength (f′c) of concrete to the modulus of rupture (fr) for plain concrete beams with a vertical construction joint placed at their center. The ACI code provides a formula for the correlation of fr to f′c, but with the provision that the concrete specimen is monolithic (no joints). It is well known 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 modulus of rupture of concrete as a function of its compressive strength. A better understanding of the effects of construction joints on the modulus of rupture will assist engineers in making rational decisions on how to deal with vertical construction joints, which in turn will lead to ultimate cost savings on large-scale projects. In this study, seven different concrete mix designs were used. From each concrete mix, six plain concrete beams were poured, half of which were monolithic and the other half with a vertical construction joint at the beam center. Four cylinders per design mix were casted for the purpose of obtaining the mix compressive strength. The experimental results indicate that for monolithic beams, the ACI Code always underestimates the modulus of rupture, whereas in the presence of a vertical construction joint, the conducted experiments yield a significant loss in the modulus of rupture of concrete that varies between 24% and 83%. Thus, there is a clear justification for providing dowels at construction joints in order to assure continuity in strength over joints in plain concrete

The effect of construction joints on the flexural bending capacity of singly reinforced beams

The main purpose of conducting this study is to determine the difference in the bending capacity between a singly reinforced monolithic beam and a singly reinforced beam with a construction joint at the beam center, for a range of different compressive strength (f’c) of concrete. Testing was conducted according to applicable ASTM standards. During humongous construction projects, it is very rare to build a concrete structure without instigating the use of construction joints, whether by design or by de facto forces. On site, the construction supervisor would contemplate whether one could relate the bending capacity of the concrete beam with the use of accidently imposed construction joint. Thus it is very essential to determine the effect the construction joint has on the flexural bending capacity of the concrete. Provided are charts to account for the loss in the bending capacity of singly reinforced beam in the existence of a construction joint for a specific concrete compressive strength