EFFECT OF CARBON FIBER REINFORCED POLYMER RETROFITTING ON RECYCLED BRICK AGGREGATE CONCRETE COLUMN

Abstract

Most old structures in Bangladesh are found to be made of poor-quality materials, lowstrength concrete (about 17 MPa), and brick aggregate because of the acute scarcity of natural stones in the early days. Moreover, some of them were constructed without proper compliance with the existing codes, and the updated building code demands a more stringent design philosophy. Hence, strengthening the structures to comply with the recent design guidelines becomes an issue of utmost significance. The study examined the feasibility of using CFRP jacketing to retrofit inferior-quality columns in Bangladesh. In this study, one-third scale columns made of low-strength recycled brick aggregate concrete (17 MPa and 10 MPa), with square and rectangular shapes having dimensions of 150 mm x 150 mm x 950 mm (kl/r = 21.94, l/h = 6.33) and 150 mm x 225 mm x 950 mm (kl/r = 14.63, l/h = 4.22), respectively are tested. Columns are evaluated to find out the effect on axial capacity, moment capacity, dilation, ductility, and toughness with discrete and continuous CFRP confinement under eccentric loading. Columns of similar sizes with no CFRP confinement are also tested under concentric and eccentric loading to compare their behavior. One square column having no transverse reinforcement was tested to observe the effect of confinement by tie bars. The results indicate that CFRP wrapping enhanced the axial capacity, moment capacity, deformation responses, ductility, and toughness of the columns. It is observed that the discrete and continuous wrapping increased the axial capacity of a column by at least 27% and 49%, respectively, and the corresponding moment capacity increased by at least 32% and 54%. The confined compressive strength (f’cc) of the concrete cylinders increased by a minimum of 41% and 91%, respectively, due to adding one and two CFRP layers. The ACI 440.2R-17 code is not recommended for FRP systems for concrete with compressive strength (f'c) less than 17 MPa, but a minimum of 65% higher compressive strength is found for a lower strength (10 MPa) concrete. Thus, the ACI 440.2R-17 code can be conservatively used to predict the capacity of a CFRP-confined recycled brick aggregate concrete column.