STRUCTURAL AND DURABILITY PERFORMANCE OF SUSTAINABLE FIBER-REINFORCED CONCRETE UTILIZING RECYCLED CONCRETE POWDER AND BASALT FRP BARS.

Abstract

Recycled concrete powder (RCP), obtained from further processing of construction and demolition waste (CDW), presents an abundant material and holds promise as an alternative to conventional supplementary cementitious materials (SCMs), which may have limited availability. In all phases of this dissertation, recycled aggregate concrete (RAC) mixes incorporated a 50% replacement ratio of natural coarse aggregates (NCA) with recycled concrete aggregates (RCA), aiming to enhance sustainability by conserving natural resources. The dissertation comprised three phases. In the first phase, the reliability of sustainable concrete, incorporating RCP as a partial substitute for ordinary Portland cement (OPC), was assessed by examining the mechanical and durability properties over various curing durations. Modifications were made to the sustainable concrete by adding ground granulated blast furnace slag (GGBFS) to improve durability and basalt fibers (BF) to enhance mechanical properties. The first phase investigated various parameters, including aggregate type, binder composition, and the addition of BF at a 0.75% fiber volume fraction 𝑉𝑓. The second phase focused on investigating the bond durability of basalt fiber-reinforced polymer (BFRP) bars embedded in a proposed fiber reinforced green recycled aggregate concrete (FGRAC) under severe environmental conditions. FGRAC incorporated a ternary blend of 15% RCP, 15% GGBFS, and 70% OPC, along with 0.75% 𝑉𝑓 of BF. A total of 57 pullout specimens were prepared to explore the influence of aggregate type, binder composition, BF addition, environmental conditions, and seawater immersion duration. Additionally, an analytical model was proposed to better represent the experimental bond-slip response of the tested pullout specimens compared to the widely used analytical models. A 50-year service life prediction model was developed to assess the extent of improvement in bond strength retention for BFRP bars embedded in FGRAC compared to those embedded in respective concrete without BF or in 100% OPC-based RAC. In the third phase, the shear behavior of large-scale concrete beams reinforced with BFRP longitudinal bars, BFRP stirrups, and structural fibers was evaluated. The investigation included studying the effect of aggregate type, binder composition, reinforcement ratio, stirrup spacing, addition of structural fibers, and types of structural fibers, including BF and steel fibers (SF). Additionally, a prediction equation was proposed for the shear capacity of concrete beams reinforced with fiber reinforced polymer (FRP) bars, FRP stirrups, and BF.