Papers by Author: Xiao Xin Feng

Abstract: The building mortar was prepared with iron mine tailing sand substituted for natural sand, and the effect of tailing sand on the performances of mortar, such as consistency, stratification, density and strength, was investigated. The results show that it is feasible to prepare building mortar with iron mine tailing sand. The sediment percentage in tailing sand has relatively large effect on the fluidity of mortar, and the tailing sand should be washed with water before being used. When the mortar with low W/C ratio is prepared, a proper amount of water-reducing admixture should be used to adjust the stratification of mortar into the right range. The density of the mortar mixture can meet the requirement of the standard in China. The building mortars with different strength grade and different use can be prepared by adjusting the mixture proportion.

Abstract: The effects of Al₂O₃ and Al(OH)₃ on expansion due to alkali-silica reaction (ASR) were tested by using Accelerated Mortar Bar Test and through prolonging the curing age, and the ffect was compared with silicon fume and fly ash. The results show that ASR can be inhibited effectively by proper content of silicious admixtures within 14 days, but can not in long term, while it can be inhibited by proper content of Al₂O₃ and Al(OH)₃ not only within 14 days but also in long term. The composite of silicious admixtures and aluminous admixtures has synergetic effect on inhibiting ASR, and there exists a value of Al₂O₃/SiO₂ with which ASR is suppressed best. For the composite, ASR is suppressed mainly by silicious admixtures in early age and mainly by aluminous admixtures in long term.

Abstract: Concretes of C30 and C60 were prepared with iron mine tailings as fine aggregate and coarse aggregate and with natural sand and common crushed stone separately. The drying shrinkage of concretes cured under the natural condition in the laboratory was tested. The results showed that whether C30 or C60 the drying shrinkage of concrete prepared with iron mine tailings was a little smaller than that of concrete with natural sand and common crushed stone. It was also found that whether the concrete with iron mine tailings or the concrete with natural sand and common crushed stone the drying shrinkage of C60 concrete was larger than that of C30 concrete.

Abstract: Through accelerating the hydration by heighening the curing temperature, the effect of the hydration of the unreacted cement in the hardened mortar with low W/C on the long-term strength was investigated. The results show that in the hardened mortar with low W/C, there exists a lot of unreacted cement at the age of 28 days, and when these cement particles hydrate again at the long age, it is disadvantageous to the long-term strength of the mortar. Moreover, the lower the W/C, the lower the hydration degree at the earlier age, and the more disadvantageous to the development of strength at the long age.

Abstract: The binding of sodium and potassium into cement paste influences the performance of concrete: for example, alkali balances between solid and paste constituents and pore fluid affect the potential for alkali aggregates reaction. However, quantification of the binding potential into paste solids has proven to be difficult, although much empirical data are available from pore fluid analyses. In this study, single-phase homogeneous C-S-H phases have been prepared at Ca: Si molar ratios (C/S) of 1.8, 1.6, 1.3, 1.0 and 0.8 and reacted with four alkali hydroxide concentrations, both NaOH and KOH, between 10 and 300 mM. A steady-state alkali partition is attained in less than 4d at 20°C by flame emission spectroscopy and the ξ potential of C-S-H and C-A-S-H gel unreacted and reacted with alkali hydroxide are measured. The results indicate：alkali binding into the C-S-H and C-A-S-H gel improves as its C/S decreases；Al3+ has been introduced to form C-A-S-H gels, and the influence of Al3+ on alkali sorption properties was determined: the replacement of Si4+ by Al3+ and Na+ or k+ markedly increases alkali binding and decreases the ξ potential of gel；the more Ca:Si ratio，the less alkali binding, the more ξ potential of gel.

Abstract: The mechanism of using mineral admixtures in concrete for suppressing alkali-silica reaction has been studied through analyzing pore solution and observing the surface of aggregates in mortar bars with scanning electron microscope (SEM). The results show that when mineral admixtures are used in the concrete, not only the alkali concentration in the pore solution can be reduced, but also the diffusion of alkali ions from the outside of concrete to the inside can be prevented, and the diffusion of alkali ions from the pore solution to the surface of the aggregates can also be prevented. Thus the attack of alkalis to aggregates is reduced, and the alkali-silica reaction is suppressed.