This paper investigates ultimate strength of lightweight concrete specimens: cubes, cylinders, and prisms wrapped by different layers CFRP respect to several curing periods. The specimens were prepared and tested under compressive and flexural loading at the ages of 7 days and 28 days with varying confinement levels (from unconfined; 0L to double-layer of CFRP, i.e., 2L). The results showed that all three factors: confinement level, specimen geometry and curing age had a significant effect on both compressive strength as well as flexural strength. Indigenous soft soil was wrapped with various CFRP wraps to study the change in failure mode from brittle to ductile with an increase in confinement and two-layer WR-CFRPs exhibited the maximum gains in compressive and flexure-up to 48% compressive, 380% of flexural strength when compared with unconfined specimens. Cylindrical samples prove always more pronounced strengthening effect than cubes, probably because of having a more even stress field and less influence to the corner effects. Besides, the confinement effect became more significant when specimens were left to cure for 28 days, highlighting initiation of concrete maturity requirement for best CFRP development. The findings indicated that early-age confinement (7-day, 2L) achieved strength equal or superior to shear-critical fully cured unconfined specimens, and confirmed the potential of CFRP in emergency repair and retrofitting. However, the ultimate strengths were the best when using both multi-layer CFRP confinement and full curing. These results highlight the synergistic relationship between geometry optimization, curing regimen and advanced fiber reinforcements in enhancing the structural response of lightweight concrete structure.
This paper deals with the behaviour of waste pozzolanic materials, such as fly ash (FA), ground granulated blast furnace slag (GGBS), rice husk ash (RHA) and burnt brick powder (BBP)-based geopolymer concrete (GPC) under a repeated freezing and thawing cycles. The study focuses on the impact of curing regimes (24 h, 48 h, 7 d and 28 d) and exposure to 25 and 35 F-T cycles on the mechanical and durability characteristics of GPC. In recent literature, analytical and numerical work has shown that micro-crack evolution and interconnected pores dictate the degradation of strength under cyclic freezing but limited experimental data are available for waste-based GPC systems. The concretes were mixed into specimen and cured at $60^{\circ}\text{C}$ in an oven for 24 h and tested according to standard F-T testing (ASTM C666). It was found that the loss in strength up to 35 cycles did not go beyond 18 %, and residual compressive strength was higher than 80% of original one, passing durability criteria according to ASTM C666 or EN 12390-9. The relationship between the strengths in compression and tensile strength, both of F-T aged and natural samples, were roughly linear ( $R^{2}\approx0.85).$ Deeper potassium hydroxide activation and the enrichment of RHA and BBP in the AC enhanced the porosity while decreasing the mass yields, as compared with previous results. These findings demonstrate the potential uses of waste-based geopolymer concretes as environmentally friendly and frost-resistant substitutes for ordinary Portland cement in construction in sub-arctic environment.