This paper presents the results of an experimental study conducted to evaluate the effect of curing conditions on the properties of normal and high strength concrete (NSC and HSC) with and without pre-wetted lightweight aggregates (LWAs). Cylinder specimens were drilled out from square concrete slabs subjected to four curing regimes (i.e. standard, water, natural and sealed curing) respectively, and then tested to obtain the compressive strength after 60 days. Three discs cut along the height direction of cylinder specimens (top, middle and bottom) were used to orderly measure the ultrasonic pulse velocity (UPV), open porosity, water absorption and splitting tensile strength. Afterwards, the comprehensive evaluation index, i.e. relative curing efficiency (RCE), was proposed based on the testing results above to quantitatively assess the effect of curing conditions on the physical properties of concrete. The experimental results indicated that curing conditions significantly influence the strengths and durability-related properties of NSC and HSC. The linear correlation can be obtained between sorptivity and open porosity of concrete under various curing conditions. Furthermore, in terms of the RCE analysis, the durability-related properties are more sensitive to the curing conditions than strengths for NSC and HSC.

Both the hardening process and formation of microstructure of concrete are significantly influenced by the curing condition. The capillary absorption of concrete is closely related to the structure and distribution of the pores within the material. This paper presents an experimental study on the influence of four curing conditions, i.e., standard curing, natural curing, water curing, and sealed curing, on the capillary absorption of normal concrete. Compressive strength tests on the cylinder specimens that are core drilled from concrete slabs are carried out. The "pie" samples cut from three different locations along the height direction of cylinder specimens are then conducted to measure the ultrasonic pulse velocity (UPV) and porosity, which quantitatively characterize the internal state of concrete after 28 days initial curing. In order to realize the continuous observation of water absorption testing, an improved gravimetrical test setup for measuring the sorptivity (the rate of water absorption) of concrete is designed to investigate capillary absorption of the "pie" samples. The experimental results indicate that the curing condition has an important influence on compressive strength, ultrasonic pulse velocity, and porosity of concrete. The temperature and relative humidity are the key factors to ensure strength development during the curing procedure and to determine the internal pore structure and the compactness of concrete. For the same curing conditions, the cumulative water content, sorptivity, and porosity of concrete gradually decrease with the increase of distance from the surface, but the ultrasonic pulse velocity reverses.

In order to enhance the large-scale and high-quality application of limestone powder (LP) and phosphogypsum in the construction industry. Therefore, this paper mainly studies the effect of LP on the physical and mechanical properties of phosphogypsum-based composites, and clear the mechanism of action from the micro level. Based on the results, the conclusions were as follows: LP has the effect of reducing the standard consistency water requirement and shortening the setting time of fresh phosphogypsum-based composites slurry; LP can increase the bulk density and reduce 24-hour water absorption of hardened phosphogypsum-based composites matrix; In addition, the strength of the matrix increases first and then decreases with the increase in the amount of LP and the recommended amount of LP is 5%-10%. Microscopic tests have shown that when the amount of LP is less than 10%, it can effectively reduce the porosity, refine the pore size, and play the role of a dense hardened matrix. In addition, the appropriate amount of LP particles can be adsorbed on the surface of dihydrate crystals, increasing the bonding force between the crystals, which is conducive to increasing the strength of the composite matrix.

Water penetration into concrete is one of the main factors to cause the deterioration of structures and chloride-induced reinforcing steel corrosion. External sustained mechanical loadings can substantially change the internal pore-structure of concrete and then lead to microcracks, which play a critical role in the durability of concrete because of the provision of additional pathways for aggressive agents (such as chloride ions, sulfate, oxygen, carbon dioxide etc.) to ingress into concrete. This paper presents an experimental investigation into capillary absorption of unsaturated concrete subjected to sustained compressive loading. In order to realize the couple of loading and water absorption process, the hollow cylinder specimens were loaded to different compressive loading levels, and simultaneously tested by an improved device for cumulative absorbed water measurement to conduct a series of water absorption experiments. The focus of this paper is to analyze the experimental results and quantify the influence of external loading and load-induced microcracks on the water absorption of concrete. According to unsaturated flow theory of concrete, the functional relationship with the stress level and sorptivity, which can characterize the tendency of concrete to absorb and transmit water by the capillary mechanism, is reasonably proposed for analyzing the effect of different compressive loading levels on water transport properties. The experimental results indicated that with the increase of applied compressive stress, the rate of capillary absorption of load-damaged concrete initially decreases, and with a further increase in stress level, one markedly increases.