Papers by Author: Li Wu Mo

Abstract: The resistance to sulfate attack of mortars containing 0%, 20%, and 40% of fly ash cured in 5 wt. % sodium sulfate solution at 20°C was investigated in this paper. Visual appearance, cracking analysis, velocity of ultrasonic wave and length change were applied to evaluate the sulfate resistance of mortars. The phases and microstructure of the reaction products due to sulfate attack were examined by XRD and SEM, and the pore structure of the mortars was analyzed by MIP. The effects of fly ash on the sulfate attack of mortars were analyzed. Results indicated that the addition of fly ash improved the resistance of sulfate attack significantly, this probably contributed to the pozzonlanic reaction of fly ash.

Abstract: Blended expansive agents consisting of MgO and CaO were prepared by calcining the mixtures of dolomite and magnesite. The mineral phases and microstructures of expansive agent were examined by XRD and SEM. The expansion properties of cement pastes containing 5% and 6% of expansive agent as well as the microstructure of hydrated expansive agent in cement paste were investigated. Results indicated that the contents of MgO and CaO in the blended expansive agent could be adjusted by changing the mix proportion of dolomite and magnesite. All the cement pastes containing expansive agent produced rapid expansion. At the same addition dosage, irrespective of curing temperature, expansive agent containing higher content of MgO produced greater expansion in cement pastes, particularly at late age, which probably ascribes to the relatively slow hydration of MgO.

Abstract: Shrinkage compensating by the expansion generated by the hydration of expansive additive is one of the important measures to improve the dimensional stability of cement-based materials. Due to the slow hydration of MgO, it may cause delayed expansion in cement and thus has been used as an expansive additive to compensate thermal shrinkage at late age in mass concrete. The relationship among the microstructure, activity and expansion properties of MgO-type expansive additive (MEA) has not been clearly demonstrated, though many researches have been focused on its expansion mechanism and expansion properties. So the industrial production and application of MEA depend much on empirical methods. Three different types of MEA are produced by calcining magnesite at 900°C, 1100°C, and 1300 °Cfor 1h in an electrical furnace. The specific surface area, activity, inner pore structure, microtopography and expansion properties of the MEA have been investigated. Results show the effect of calcination temperatures on the expansion properties of MEA results from the changes in its microstructure, specific area, and thus the activity. High calcination temperature causes growth in MgO grain, decrease in specific area and surface defects of MgO, and hence the reduction of the activity value, inducing slow hydration rate and thus delayed expansion. This study will provide a platform for well understanding various activity and expansion properties of MEA produced under different temperatures.