International Concrete Abstracts Portal

This study comprehensively investigates the development of ambient-cured self-consolidating geopolymer concrete (SCGC) based on the chemical composition of binders and alkaline activators. Five factors of the chemical composition of binders and alkaline activators, each with four levels, are used to evaluate and optimize the workability and compressive strength of the high-strength SCGC. The designed SCGC mixtures provided sufficient workability properties and compressive strength between 28 and 70.3 MPa (4061 and 10,196 psi). It was found that the SCGC mixture with a binder content of 600 kg/m3 (37.4 lb/ft3), a CaO/(SiO2 + Al2O3) mass ratio of 0.55, an Na2O/binder mass ratio of 0.11, an SiO2/Na2O mass ratio of 1.2, and an Na2O/H2O mass ratio of 0.35 was the optimum mixture, which achieved a slump flow of 770 mm (30.3 in.), 28-day compressive strength of 70.3 MPa (10,196 psi), and final setting time of 80 minutes. The CaO/(SiO2 + Al2O3) ratio in binders, binder content, and Na2O/binder mass ratio have been found to be the most influential factors on the workability and compressive strength of ambient-cured SCGC. Microstructural analysis of SCGC mixtures showed that the increase in the CaO/(SiO2 + Al2O3) ratio promoted the formation of calcium- aluminate-silicate-hydrate (C-A-S-H) gels and enhanced the compressive strength by filling voids and creating a compact and dense microstructure.

Despite the advantageous features of earthen construction for sustainability, certain limitations arise, notably the time-intensive nature of the construction process. Some efforts have been made to achieve self-consolidating earth concrete (SCEC) by overcoming the presence of fine particles to achieve adequate rheology. The impacts of cement, metakaolin, and limestone filler on dry flowability characteristics, rheology, workability, and compressive strength of self-consolidating earth paste (SCEP) mixtures were assessed in this study. The investigated mixtures were proportioned with different clay compositions and polycarboxylate ether (PCE), with and without the initial addition of sodium hexametaphosphate (NaHMP) as a clay dispersant. It was revealed that the addition of NaHMP and metakaolin to the mixtures consisting of finer clay particles significantly increased the static yield stress, build-up index, critical shear strain, and storage modulus evolution. Finally, the contribution of dry flowability characteristics of the powders to the rheological properties of the SCEP mixtures was investigated to facilitate the selection process.

The challenges of deterioration and increasing maintenance costs in steel-reinforced concrete railway sleepers emphasize the urgent need for innovative, durable, and sustainable alternatives. This study evaluated the shear strength of precast concrete sleepers prestressed with basalt fiber-reinforced polymer (BFRP) rods, using normal self-consolidating concrete (NSCC) and fiber-reinforced self-consolidating concrete (FSCC). Seven full-scale specimens, each 2590 mm (8 ft, 6 in.) in length and prestressed to 30% of the tensile strength of BFRP rods in accordance with the Canadian Highway Bridge Design Code (CHBDC), were tested to assess cracking loads, ultimate strength, bond behavior, and failure mechanisms. All tests were conducted in accordance with the American Railway Engineering and Maintenance-of-Way Association (AREMA) guidelines. The results indicate that all specimens met AREMA design load requirements without visible cracks or slippage based on a train speed of 64 km/h (40 mph), annual traffic of 40 MGT (million gross tons), and sleeper spacing of 610 mm (24 in.). Comparative analysis using CSA S806-12 (R2021) design standard and ACI 440.4R-04 (R2011) design guide revealed that predictions based on CSA S806-12 (R2021) were less conservative than those from ACI 440.4R-04 (R2011) for the shear strength of BFRP prestressed sleepers. The BFRP rods exhibited excellent tensile performance, with minimal prestress losses, and their sand-coated surface ensured efficient load transfer by preventing slippage and enhancing the bond strength. FSCC specimens demonstrated delayed cracking, enhanced crack control, and ductility compared to NSCC specimens. These findings highlight the potential of BFRP prestressed concrete sleepers, particularly when combined with FSCC, as a sustainable solution for railway infrastructure, emphasizing the need for a design code refinement for BFRP applications.

Limited research work has been done so far on fibrous self-consolidating concrete (FSCC) columns reinforced with fiber-reinforced polymer (FRP) bars under axial compressive load. This paper presents an experimental study of innovative FSCC columns reinforced with basalt FRP (BFRP) bars. The main objectives of this study included investigating the compression behavior and failure mechanisms of full-scale circular FSCC columns reinforced with BFRP bars and ties. In addition, analyzing the impact of using synthetic fibers on the peak capacity and pseudo-ductility of the BFRP-FSCC columns was considered. For this study, a total of eight columns were tested under concentric load, and the test variables were the longitudinal reinforcement ratio, transverse reinforcement ratio, and reinforcement and concrete types. Test results revealed that the FSCC column reinforced with BFRP bars and the FSCC column reinforced with steel bars had similar behavior and failure modes. The compression failure in the concrete controlled the ultimate capacity of specimens. Lastly, adding fibers improved the specimens’ peak load, post-peak behavior, and pseudo-ductility under axial compression load.

This study investigated the serviceability behavior and strength of polypropylene fiber (PF)-reinforced self-consolidating concrete (PFSCC) beams reinforced with glass fiber-reinforced polymer (GFRP) bars. Five full-scale concrete beams measuring 3100 mm long x 200 mm wide x 300 mm deep (122.1 x 7.9 x 11.8 in.) were fabricated and tested up to failure under four-point bending cyclic loading. Test parameters included the longitudinal reinforcement ratio (0.78, 1.18, and 1.66%) and PF volume (0, 0.5, and 0.75% by concrete volume). The effect of these parameters on serviceability behavior and strength of the test specimens is analyzed and discussed herein. All the beams were evaluated for cracking behavior, deflection, crack width, strength, failure mode, stiffness degradation, and deformability factor. The test results revealed that increasing the reinforcement ratio and PF volume enhanced the serviceability and flexural performance of the beams by effectively restraining crack widths, reducing deflections at the service and ultimate limit states, and decreasing residual deformation. The stiffness exhibited a fast-to-slow degradation trend until failure for all beams, at which point the beams with a higher reinforcement ratio and fiber volume evidenced higher residual stiffness. The cracking moment, flexural capacities, and crack width of the tested beams were predicted according to the North American codes and design guidelines and compared with the experimental ones. Lastly, the deformability for all beams was quantified with the J-factor approach according to CSA S6-19. Moreover, the tested beams demonstrated adequate deformability as per the calculated deformability factors.