Papers by Author: Xiu Sheng Tang

Abstract: The effects of the ratio of magnesium to phosphorus (Mg/P) on the compressive strength, bond strength, drying shrinkage and pH value of magnesium phosphate cement (MPC) were investigated. The results show that the consistent effect of the ratio of Mg/P on compressive strength and bond strength, as the ratio increases, the strengths are both first increased and then decreased, and the best ratio is 3:1. For setting time and drying shrinkage, the effects of the ratio of Mg/P are both obvious. Mainly manifested as the increase of the ratio, all of them show a decreasing trend. And the setting time can be shortened by 78%, furthermore, 28d the maximum drying shrinkage rate can be reduced by 29%. The effect of the ratio of Mg/P on pH value is mainly that when the ratio increases, the time of the inflection point of pH value is obviously advanced, and their final pH value is close.

Abstract: The effects of borax on the setting time, compressive strength, bond strength, drying shrinkage and pH value were investigated for potassium magnesium phosphate cement (MKPC). The results show that with the increase of borax dosage, the setting time is gradually extended, both compressive strength and bond strength are greatly decreased, the drying shrinkage rate is increased. Especially high dosage of borax, the extension of setting time is more obvious. Compared with that without borax, when the dosage of borax is 12.5%, setting time can be prolonged by 214.8%.The influence of borax dosage on the time-dependent effect of compressive strength shows that when the dosage of borax is 2.5%~5.0%, compressive strength increases rapidly from 4h to 1d, and increases relatively slowly from 1d to 3d. When borax dosage is less than 2.5% or higher than 5%, the law of time-dependent effect of compressive strength is the opposite. Compared to borax prior to magnesia addition, the pH value of the system is larger and the time of inflection point is advanced when borax and magnesia are mixed together at the same time. The increase of borax dosage can reduce the pH value of the system, and decrease the rising rate of pH value, at the same time the required time when the final pH value is relatively stable is longer.

Abstract: Because the setting time of magnesium phosphate cement (MPC) was too quick, its further application was restricted. Influence factors about magnesium phosphate cement setting time are summarized and the influence laws are studied in the paper. The results show that with the increase of phosphorus to magnesium ratio (P/Mg) or boron to magnesium ratio (B/Mg), the setting time is both obviously prolonged. The effect of water to binder ratio (W/C) on the setting time of MPC has an optimal point. As the specific surface area increases gradually, the setting time of MPC is greatly shortened. Although fly ash has effect on setting time of MPC, the effect is very small. At the same time, the setting time is closely related with environmental temperature, the pH value of the system and mixing volume.

Abstract: Sulfate attack of cementitious materials is closely related to the essential properties of cementitious materials and erosive environments. Therefore, the foundation of service life prediction model becomes very difficult and complicated. In this paper, the temperature and concentration of an erosive solution were taken into account in lab accelerating test, the service life prediction model of sulfate attack based on equivalent time and damage variable was founded by using Arrhenius equation, the concept of maturity, Fick’s law and the theory of damage mechanics. Dynamic elastic modulus value change, and/or mass change, and/or compressive or flexural strength change, et al. can be used as damage variable to show the evolving process of sulfate attack in concrete in this prediction model, and certain changed rate was considered as the damage critical value in concrete in terms of the standard or references or test results. To estimate the possible service life of concrete structures in sulfate attacking condition by lab accelerating test according to this prediction model, it will be benefit to guide the selection of raw materials and design of durability in concrete.

Abstract: To improve structure durability of Cao’e River Floodgate in China, durability and lifetime prediction of high-volume ground granulated blast-furnace slag (GGBS) concrete were investigated. Chloride ion permeability was analyzed with nature soaking method and RCM method. High-volume GGBS concrete had better capability to resist chloride ion penetration with lower diffusion coefficient of chloride ion than ordinary Portland concrete (OPC) had. Experiment of steel-bar corrosion in dry-wet environments proved that high-volume GGBS concrete had better performance to protect steel-bar than OPC had. In the sulfate solution, high-volume GGBS mortar bars only produced small expansion which was 40% of that of Portland cement mortar bars. The performance of frost resistance of high-volume GGBS concrete was favorable. GGBS debased the capability of carbonation resistance. Lifetime prediction illuminated high-volume GGBS concrete was beneficial to extended project lifespan. The results show that high-volume GGBS concrete can solve the facing durability problem of Cao’e River Floodgate.

Abstract: To protect circumstance and improve of structure durability of Cao’e River floodgate, high volume industrial residue concrete (HVIRC) was prepared, and its mechanical property and durability were studied systematically. 10% of fly ash and 40% of ground granulated blast-furnace slag was used to replace 50% of cement in HVIRC. HVIRC had better anti-carking ability with larger tensile strength, larger ultimate tensile strain, larger tensile-compressive strength ratio and smaller elastic modulus-to-strength ratio. Dry shrinkage rate of HVIRC was similar with that of ordinary Portland concrete (OPC). HVIRC had higher compactness with smaller gas diffusion coefficient and relative permeability coefficient. Expansion caused by alkali-silica reaction reduced greatly by using high volume industrial residue and alkali-silica reaction was controlled markedly. HVIRC had better property of chloride ion penetration resistance with low effective diffusion coefficient. HVIRC could protect steel-bar from premature corrosions. Properties of sulfate resistance and frost resistance of HVIRC were also favorable. It’s proved that high volume industrial residue can enhance greatly mechanical property and durability of concrete and HVIRC can be used in Cao’e River floodgate.

Abstract: Performing the superposition effect of multi-elements mineral admixtures, high performance concrete (HPC) with 3% of silicon fume, 20% of fly ash and 40% of ground granulated blast-furnace slag (GGBS) was prepared, and its physical and mechanical properties and durability were studied systematically. The compressive strength and tensile strength of HPC are better than those of ordinary concrete. HPC has high compactness with smaller gas diffusion coefficient and relative permeability coefficient. Adding volume stabilizer and controlling the contents of SO3 in the GGBS and volume stabilizer at 3%, can reduce dry shrinkages effectively. Large mount of mineral admixture was used to make the concentrations of K+ and Na+ in the pore solution and the expansion caused by alkali-silica reaction depress greatly. So the alkali-silica reaction gets controlled markedly. The effective diffusion coefficient of chloride ion is 1.96×10-12 m2/s, which means HPC has a favorable chloride ion penetration resistance. After 15 times of wet-dry cycle, the rates of the rust area and quality loss of the reinforcing steel bars in HPC are only 4.1% and 0.05% respectively, so HPC has better performance of steel protection. The mortar bar did not expand in corrosive sodium sulfate solution, and it means HPC has better performance of sulfate resistance. The performances of frost resistance and carbonation resistance of HPC are also favorable. It’s proved in tests that the superposition effect of multi-elements mineral admixtures can enhance the physical and mechanical properties and durability of concrete greatly.