He Xingyang

Microstructure and Composition of Hydration Products of Ordinary Portland Cement with Ground Steel-making Slag

The effect of ground steel-making slag on microstructure and composition of hydration products of ordinary Portland cement (OPC) was investigated by mercury intrusion porosimetry (MIP), X-ray diffraction (XRD) and differential thermal analysis (DTA). Results show that ground steel-making slag is a kind of high activity mineral additives and it can raise the longer-age strength of OPC mortar. The total porosity and average pore diameter of OPC paste with ground steel-making slag increase with the increase of the amount of ground steel-making slag replacing OPC at various ages, while after 28 days most pores in OPC paste with ground steel-making slag do not influence the strength because the diameter of those pores is in the rang of 20 to 50 nm. The hydration mechanism of ground steel-making slag is similar to that of OPC but different from that of fly ash and blast furnace slag. The hydration products of ground steel-making slag contain quite a lot of Ca(OH)2 in long age.

Influences of a New Admixture MX on Concrete Durability

The performance of concrete with a new admixture MX was studied by using the freeze-thaw cycle, permeability and chemical attack test. The experimental results show that MX improves the durability of concrete. Within the optimum proportion ranges from 0.1% to 1%, the compressive strength of concrete after freeze-thaw is increased by 20%–50%, and Young’s modulus can be increased by 3.76–5.64 times. The strength and weight loss of concrete with 0.4% MX are respectively decreased by 28% and 60% after hydrochloric acid attack. The strength and weight loss of concrete with 0.4% MX are decreased by 5%–20% after sulfuric acid and sodium sulfate attack. The permeability of concrete with 1% MX at 28 days can be decreased by more than 30%. The investigation of the negative temperature property of MX and analysis on concrete composition and microstructure by MIP reveal that the heat conduction is resisted and the freezing procedure of solution in concrete pore is retarded due to the adding of MX. Moreover, the pore structure of concrete with MX is improved, thus improving the durability. Based on this study, a resistance model of MX to block the heat and mass transference was proposed, and the mechanism of durability improvement of concrete with MX was explained.

Surface modification and model of glassy cementitious materials

Basic theory of surface modification about glassy cementitous materials is presented. At the same time modified glassy cementitous materials were manufactured by means of point activation and disperse and grind aid according to technology of mechanical-chemistry. This theory about surface modification has been proved by some experimental results such as SEM, size distribution, fluidity of the paste, physical-mechanical properties of the hardened paste and heat of the hydration. The particle size of modified fly ash is tending to become smaller and the shape of microfine particles seems a ball; strength of modified glassy cementitous materials and ordinary portland cement compound paste has a obvious increment and fluidity of the paste also has a noticeable improvement; surface modification also can accelerate the formation of paste structure to a certain degree. Besides a model about the interactive mechanism of modified glassy cementitous materials and ordinary portland cement is put forward.