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Concrete in saline or coastal settings exposed to freezing temperatures is frequently affected by coupling actions of sulfate assault and freeze–thaw degradation, reducing the service life of concrete structures significantly. This study conducted an accelerated freeze–thaw cycle test in pure water and Na2SO4 solution with a mass proportion of 5% to examine the coupling impact of sulfate freeze–thaw on the frost resistance of composite limestone powder (CLP) concrete. Combined with SEM and XRD methods, the performance degradation mechanisms of composite limestone powder (CLP) concrete in coupling sulfate freeze–thaw conditions were analyzed with a microscopic point of view. The findings demonstrated that limestone powder has a filling effect but the activity is low. When the content is 10~20%, the chemical response is higher than the physical response. The pozzolanic effect of fly ash and slag can improve the pore structure and improve the compactness of concrete. The "superposition effect" of limestone powder, fly ash, and slag can improve the frost resistance of CLP concrete. The scenario of salt freezing cycles has negative effects that are worse than those of water freezing cycles on the antifreeze performance of CLP concrete, including apparent morphology, mass loss, relative dynamic modulus of elasticity, and compressive strength. Sulfate's activation effect boosts slag's activity effect, which significantly promotes the antifreeze performance of concrete subjected to salt frozen cycles over water frozen cycles. The freeze–thaw damage model of CLP concrete under coupling sulfate freeze–thaw is established through theorem analysis and experiment statistics, laying a theoretical framework for the popularization and use of this concrete. [ABSTRACT FROM AUTHOR]

The tightly spliced truss-reinforced plate-honeycomb flat beam is a novel type of composite beam, with the advantages of high rigidity, high bearing capacity, and ease of construction. In this study, on the basis of the performance in bending tests, the numerical analysis method is used to study the influence of the honeycomb hole–height ratio, and section height on the bearing capacity of the honeycomb composite flat beam. On this basis, the simplified method to calculate the ultimate bending capacity of the new honeycomb composite flat beam was proposed. The research results show the failure modes of the specimens are mainly divided into two states, including the deflection exceeding the limit and the concrete flange plate separating from the steel beam. The tightly spliced truss-reinforced plate-honeycomb flat beams have good ductility, of which the average value reaches 8.2. The simplified method proposed in this article for calculating this type of honeycomb composite beam has an error of less than 10% in terms of bending bearing capacity, which has advantages over the double T-shaped steel method. The calculation method and design suggestions proposed in this study provide a basis for the research and application of this type of composite flat beam. [ABSTRACT FROM AUTHOR]

In the process of service, reinforced concrete structures have to bear both load and multi-environmental factors. The deterioration of reinforced concrete beams is critical to the durability, safety, and sustainability of reinforced concrete structures. The main aim of the present research is to determine the degradation mechanism of reinforced concrete beams subjected to sustained loading and multi-environmental factors. Reinforced concrete beam specimens were prepared, loaded and then exerted multi-environmental factors. At the end of each degradation period, the degradation of concrete (chemical contents of concrete beam surfaces, carbonation depth, compressive strength and maximum cracks) and the corrosion of steel bars (corrosion ratio and tensile strength) were continuously measured. Moreover, degraded reinforced concrete beams were flexural loaded in four-point bending failure tests. The degradation mechanism of reinforced concrete beams subjected to sustained loading and multi-environmental factors was analyzed. Thus, this study can promote a comprehensive understanding of reinforced concrete beams subjected to sustained loading and multi-environmental factors. [ABSTRACT FROM AUTHOR]

Because of the existence of beams, columns, shear walls, and other structural components, the external wall of a building is often composed of two parallel structures, wherein one is a concrete structure and the other is made of bricks. Therefore, to determine the economical thermal insulation thickness of an external wall, one can not only consider a single structure. Mathematical models of economical thermal insulation thickness considering and not considering the effect of non-homogeneity of external walls were established based on the method of life-cycle cost. The economical thermal insulation thickness and economic benefits of a building wall in Beijing that is composed of two parallel structures with EPS thermal insulation were comparatively analyzed. The comparisons were carried out with two different heat sources and three different concrete structure-to-external wall ratios. The results show that non-homogeneity of external walls have a considerable influence on the economical thermal insulation thickness and economic benefit of an insulating external wall. The economical thermal insulation thickness under the consideration of non-homogeneity of external walls will become thicker. However, the increase in life-cycle cost is not significant, whereas the increase in life-cycle saving is very significant, and the payback period becomes shorter. The effectiveness of the investment and the energy efficiency revenue without consideration of the effect of non-homogeneity of external walls are underestimated. Thus, a method that considers this effect can obtain more reasonable economical insulation thicknesses and economic benefits. [ABSTRACT FROM AUTHOR]

The interfacial bonding behavior of textile reinforced concrete (TRC)-confined concrete and corroded steel bars was studied by central pull-out testing using three types of specimens (not strengthened, strengthened after corrosion and strengthened before corrosion). The results show that without the TRC constraint, the ultimate bond strength between the concrete and corroded steel bar decreases with increasing corrosion ratio, especially after the concrete cracks due to reinforcement corrosion, at which point the ultimate bond strength rapidly decreases. However, the ultimate bond strength of the specimens strengthened after corrosion can be three times greater than the strength of the specimens not strengthened when the concrete cracks due to reinforcement corrosion. For the specimens strengthened before corrosion, the TRC strengthening layer effectively limits the decrease in the ultimate bond strength between the corroded steel bars and concrete, which results in specimens with a high interfacial bond strength at high corrosion ratios. Thus, compared to the other two types of specimens, this case comparatively yielded the best results. Finally, for all three types of specimens and according to the experimental data, a calculation model of the ultimate bond strength was established considering changes in the corrosion ratio. [ABSTRACT FROM AUTHOR]

When the energy saving rate of existing residential buildings renovation is determined, the thermal performances of external walls, windows, and roof interact with each other. Therefore, it is necessary to study the determination of economical insulation thickness of building envelopes considering the interaction among building envelope performances. The objective function and its bound of envelope thermal performance optimization in the energy-saving renovation of existing residential buildings in severe cold and cold zones in China were established. It is the conditional extremum problem and can be solved through Lagrange’s method of multipliers to determine the economical insulation thickness of external walls and roofs simultaneously. The method is proved to be feasible by an existing residential building in Beijing. When the same window types are selected, the energy-saving renovation program of the building envelope determined by the Lagrangian optimization method can produce the minimum investment in insulation, minimum investment payback period, and the largest net present value (NPV) of the life cycle. [ABSTRACT FROM AUTHOR]