Papers by Author: Ming Shu Tang

Abstract: Replacement of steel fiber by scrap tires wire as shielding agent in cement-matrix composites was discussed in this paper. The electromagnetic shielding effectiveness (SE) of cement based composites materials containing FeCuNbSiB amorphous alloy powder and scrap tires wire were measured with coaxial planar－spectrum analyzer method. Results show scrap tires wire can effectively enhance the SE of cement composites in tested frequency range. The shielding effectiveness at 1.5GHz is 14.1 dB at a scrap tires wire content of 1.3 vol.% in cement paste. The SE of composites that simultaneously contain scrap tires wire and FeCuNbSiB powder is higher than singly use these shield agents.

Abstract: In order to improve dimensional stability of cementitious materials, synergistic effect of shrinkage reducing admixtures (mixture of glycol ethers and siloxane, SRA) and MgO-based expansive agent (MEA) burned at 850 °C, 950 °C, 1050 °C and 1200 °C for 1 h on the deformation of cement paste was investigated while being cured in water of 20 °C, 40 °C and 60 °C, sealedly by polyethylene sheet at 20 °C, 40 °C and 60 °C as well as in simulated using environment. The results illustrated that combined use of SRA and MEA (burned at 850 °C and 950 °C) could compensate the shrinkage of cement paste effectively, and MEA also could make up for the shortage of SRA whose shrinkage-reducing ratio decreased at later age. In the simulated using environment, the paste both with SRA and MEA (burned at 850 °C and 950 °C) was in micro-expansion condition, and the average deformation increased slowly till 240d, and the deformation amplitude reduced to the half of the control sample. Then hydration of MEA in the present of SRA was examined by gravimetry. The results indicated that the presence of SRA retarded the hydration of MEA, but with prolonged curing, the hydration degree of MEA with or without SRA tended to be the same.

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.

Abstract: This paper discusses the sulfate resistance and frost of mass hydraulic concrete which containing fly ash, superplasticizer and a novel MgO-bearing expansive agent (HNM), at same time, the mechanisms and processes of sulfate attack on it have been proposed. Results showed that using a water/binder ratio of 0.48 in RCC containing 50 % fly ash and 8 % HNM a durability factor of over D300 can be achieved and sulfate resistance may be improved slightly.