Search Results (2)

To promote the application of recycled concrete in construction engineering, the flexural behavior of ultra-high toughness cement-based composite (UHTCC) materials and recycled concrete composite beams was investigated in this study. Recycled aggregates were used in the production of both recycled UHTCC (R-UHTCC) and recycled concrete. A total of 10 beams were manufactured and tested under four-point bending load. The primary design parameters included concrete strength grade, R-UHTCC layer height, stirrup spacing in the pure bending section, and tensile reinforcement ratio. The effects of these parameters on the failure mode, crack width, load-midspan deflection response, ductility, load-tensile reinforcement strain response, and flexural capacity of the beams are discussed. The results indicate that limiting the use of R-UHTCC to a specific height range within the tensile zone of the beams can yield superior flexural properties compared to using R-UHTCC across the full section. The R-UHTCC and recycled concrete composite beams demonstrated good crack resistance, load-deflection response, and ductility. Compared to the R-UHTCC layer height and stirrup spacing, the influences of concrete strength and tensile reinforcement ratio on the flexural behavior of the composite beams are more significant. The maximum increase in flexural capacity and ductility index was 18.8% and 67.3%, respectively, as the concrete strength grade increased from C30 to C70. The flexural capacity increased by 64.6% as the longitudinal reinforcement ratio increased from 0.258% to 3.68%. Furthermore, a stiffness calculation method based on the effective moment of inertia was proposed and validated through experimental results. The research findings provide a theoretical and design basis for the application of R-UHTCC and recycled concrete composite beams in engineering. Full article

The purpose of this research is to investigate the durability damage law for ultrahigh toughness cementitious composites (UHTCCs) under freeze–thaw environments and impact resistance. In this study, UHTCCs with fiber length-to-diameter ratios of 5/30, 8/30, 12/20, 12/30 and 12/48 were tested for impact resistance and freeze–thaw cycles. The freeze–thaw cycle process and impact resistance process for UHTCC are comprehensively analyzed and evaluated in terms of mass loss, compressive strength loss, relative dynamic elastic modulus loss and impact resistance number. The freeze–thaw damage prediction model for the relative dynamic elastic modulus of the UHTCC is established based on the regularity of the measured data for the relative dynamic elastic modulus of UHTCC and also on the GM(1,1) power model. The accuracy and reliability of the GM(1,1) power model is analyzed using the relative error, absolute correlation degree, mean variance and probability of small errors. According to the evolution law of the impact resistance number of the UHTCC, the impact damage prediction model for UHTCC is established based on the Weibull distribution model, and the accuracy of the model is analyzed by using the decision coefficient R². The results show that UHTCC has high durability performance, and the durability performance of UHTCC at a length-diameter ratio of 12/48 is optimal. The freeze–thaw damage evolution model and impact damage evolution model established in this research are sufficiently realistic, the average relative error of the GM(1,1) power model is less than 5%, and the coefficient of determination R² of the Weibull distribution model is greater than 0.93, which effectively reflects the damage development process for concrete under freeze–thaw and impact environment with high fitting accuracy. Full article