Dilation Effects in FRP-Confined Square Concrete Columns Using Stone, Brick, and Recycled Coarse Aggregates

The axial capacity enhancement of square plain concrete columns due to fiber-reinforced polymer (FRP) wrap is measured through experiments as a function of the fundamental dilation property of the parent concrete. To this end, unconfined (control) and FRP-confined concrete column specimens made using stone, brick, recycled stone, and recycled brick aggregates having their own dilation properties were subjected to uniaxial compression. The dilation effect measured using the digital image correlation technique (DICT) was observed to have a distinct relation with the concrete modulus of elasticity resulting from the coarse aggregate unit weight and absorption capacities. Relations between the strengthening ratio and strain enhancement ratio with the actual confinement ratio were plotted to measure the confinement effectiveness coefficients and strain enhancement coefficients using a redefined confining pressure model. The measured coefficients are found to be distinctly lower for brick and recycled aggregate concretes than for stone aggregate concrete. This confirms the necessity of using a revised set of coefficients to estimate the effective confinement in columns of aggregates that exhibit a greater dilation property in concrete. (C) 2015 American Society of Civil Engineers.