International Concrete Abstracts Portal

A capsule phase-change material (CPCM) was synthesizedusing n-tetradecane as the core, expanded graphite as the shell,and ethyl cellulose as the coating material through a controlledassembly process. The results demonstrate that the infiltration ofn-tetradecane significantly enhances the density of the expandedgraphite, while the ethyl cellulose coating effectively preventsthe desorption and leakage of the liquid phase-change materialduring phase transitions. As a result, the CPCM exhibits a compactstructure, chemical stability, and excellent thermal stability. Theincorporation of this CPCM into cement-based materials endowsthe material with an autonomous heat-release capability attemperatures below 5°C. When the CPCM content reaches 20%,the thermal conductivity of the cementitious matrix increases by24.66%. Moreover, the CPCM significantly improves the freezing- and-thawing resistance of the cement-based materials, reducingthe compressive strength loss by 96% and the flexural strengthloss by 65% after freezing-and-thawing cycles. This CPCM fundamentally enhances the frost resistance of cement-based materials, addressing the issue of freezing-and-thawing damage in concrete structures in cold regions.

It is well known that the estimates of most shear capacity prediction models for reinforced concrete (RC) components are of high dispersion due to their elaborate failure mechanisms and elusive material variability. A probability prediction model is more appropriate for estimating the shear capacity of RC members than a deterministic prediction model. Therefore, this study proposed a probabilistic model to evaluate the shear capacity of RC T-beams and employed a Bayesian-Markov chain Monte Carlo (MCMC) approach to determine the posterior parameter in the shear strength prediction model by Bayesian updating. The analysis results indicate that the probabilistic model achieves minimal variance, offering the most accurate predictions that closely match test data compared with other prediction models. The shear capacity of a T-beam increases with changes in flange width and flange height ratio, but remains constant once beyond a certain level. The shear capacity varies rapidly when the shear-span ratio (λ) is less than 2.5 or larger than 4.0 due to a notable shift in the failure mechanism. Besides, the shear capacity raises linearly by increasing the characteristic value of stirrups (ρvfyv).

This paper presents the torsional behavior of hollow reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) U-wraps. Test parameters involve variable wall thickness in the section and the width and spacing of the externally bonded CFRP sheets. An experimental program is conducted with 27 beams (three unstrengthened and 24 strengthened) to examine their capacities, shear flows, and force distributions when incorporating a ratio of 0.27 to 0.46 between the areas of the hollow and gross cross sections. The stiffness and capacity of the test beams are dominated by the wall thickness, and the effectiveness of CFRP strengthening becomes pronounced as the void of the beams decreases. The presence of CFRP redistributes internal shear forces in the cross section, which is facilitated by narrowing the spacing of the U-wraps. The effective zone of CFRP retrofit is positioned near the outer boundary of the strengthened section. Regarding crack control, multiple discrete U-wraps with narrow spacings outperform wide U-wraps with enlarged spacings. While the location of a shear-flow path is dependent upon the wall thickness, the width of the U-wraps controls the effective shear-flow area of the beams. The size of the void is related to the stress levels of internal reinforcing components, including yield characteristics. Transverse stirrups are the principal load-bearing element for the unstrengthened beams; however, the reliance of the stirrups is reduced for the strengthened beams because the U-wraps take over portions of the torsional resistance. Through a machine learning approach combined with stochastic simulations, design recommendations are proposed.

This study investigates the feasibility of utilizing a hybrid combination of recycled steel fibers (RSF) obtained from scrap tires and manufactured steel fibers (MSF) in concrete developed for pavement overlay applications. A total of five concrete mixtures with different combinations of MSF and RSF, along with a reference concrete mixture, were studied to evaluate fresh and mechanical properties. The experimental findings demonstrate that the concretes incorporating a hybrid combination of RSF with hooked-end MSF exhibit comparable or higher splitting tensile strength, flexural strength, and residual flexural strength to that of concretes containing only hooked-end MSF, straight MSF, and RSF. This enhanced mechanical performance can be ascribed to the multiscale fiber reinforcement effect that controls different scales (micro to macro) of cracking, thereby providing higher resistance to crack propagation. The concretes containing only RSF show lower splitting tensile strength, flexural strength, and residual flexural strength compared to concrete solely reinforced with straight MSF or other steel fiber-reinforced concrete (SFRC) mixtures due to the presence of various impurities in the RSF, such as thick steel wires, residual rubber, and tire textiles. Interestingly, blending RSF with hooked-end MSF overcomes these limitations, enhancing tensile strength, flexural strength, and residual flexural strength, while significantly reducing costs and promoting sustainability. Lastly, the findings from the pavement overlay design suggest that utilizing a hybrid combination of RSF with hooked-end MSF can reduce the design thickness of bonded concrete overlays by 50% compared to plain concrete without fiber reinforcement, making it a practical and efficient solution.

This research investigates the impact of using washed waste fines (WWF), a byproduct from ready-mixed concrete (RMC) plants, as a partial replacement for natural sand in concrete. Cylindrical (100mm x 200mm) and cubic mortar specimens (50mm x 50mm x 50mm) were created with 20% WWF substitution. Hardened properties such as compressive strength, tensile strength, UPV, and durability parameters such as chloride migration coefficient and carbonation coefficient were evaluated. The study also examined the microstructure of concrete using a Scanning Electron Microscope (SEM). Results showed that incorporating WWF enhanced both the hardened and durability properties of concrete, increasing compressive strength by 25% compared to the control case. Additionally, WWF decreased the non-steady-state chloride migration and carbonation coefficients, indicating improved durability. SEM analysis revealed a denser microstructure, and WWF incorporation reduced the permeable porosity and absorption capacity of concrete.