The effects of hydroxypropyl methyl cellulose ether, starch ether, bentonite, and redispersion emulsoid powder on the working and mechanical properties of fresh dry-mixed mortar were studied. The results show that hydroxypropyl methyl cellulose ether has the greatest impact on the consistency and water retention of ordinary dry-mixed mortar and that redispersion emulsoid powder reduces the water action and starch ether has essentially no effect on water retention. It also shows that the time of mortar condensation when mixed with hydroxypropyl methyl cellulose ether is the longest, followed by redispersion emulsoid powder and bentonite. Starch ether can slightly, but not obviously, extend the setting time of cement mortar. Hydroxypropyl methyl cellulose ether has the greatest impact on the mechanical properties of ordinary dry-mixed mortar, followed by redispersion emulsoid powder, starch ether, and bentonite. As the water retention increases, the setting time of the mortar also increases. The use of water as a thickening material has a retarding effect on the mortar, increases the water-retention rate, and increases the retarding effect. Moreover, increasing the content of the chemical admixtures decreases the strength of cement mortar.

To improve the deformation and energy dissipation capacities of conventionally reinforced coupling beams with low shear span to beam depth ratios, a new method for seismic retrofitting coupling beams using carbon-fibre-reinforced polymer (CFRP) composites is proposed and studied. Experiments are conducted to test four large-scale coupling beams with identical geometries and reinforcement layouts but with different retrofitting schemes. The effects of the arrangement of CFRP sheets and CFRP anchors on the seismic behaviour in terms of strength, stiffness, ductility, energy dissipation capacity and failure modes are evaluated. The study indicates the proposed retrofitting technique is well suited to improving the seismic behaviour of low-slenderness coupling beams in moderate seismic zones. The use of CFRP U-wraps can significantly improve the deformation and cumulative energy dissipation capacities of coupling beams while the beam stiffness can remain nearly constant. By using diagonal CFRP sheets, the strength, stiffness and energy dissipation capacity of coupling beams can be increased. The delamination of CFRP U-wraps can be delayed by using CFRP anchors, but sufficient insertion depth of the anchors is required to avoid their pull-out failure.

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.

To study the impact of limestone powder (LP) fineness on the physical and mechanical characteristics of concrete, a total of 88 sets of LP concrete mixtures were designed, in which the LP content (0~35% of the mass of cementitious materials), LP-specific surface area (350–1000 m²/kg), and water–binder ratio were used as testing factors. The experimental and theoretical approaches were performed to study the physical (slump) and mechanical properties (compressive strength and bond-slip behaviors with steel bars) of LP concrete. Secondly, the compressive activity index (CAI) was introduced as a measurement for quantifying the compressive activity of LP. The results indicate an optimal improvement in the physical and mechanical properties of LP concrete when the LP content is equal to or less than 15% and the specific surface area is equal to or less than 600 m²/kg. An increase in LP content will result in a drop in the bond strength between concrete and steel bars; in contrast, an increase in LP-specific surface area will enhance the bond strength. Furthermore, CAI can better reflect the role of LP in concrete, which provides a theoretical basis for the application of LP in concrete.