Papers by Keyword: Maximum Intensity Projection (MIP)

Abstract: For water filled porous materials, the difference between the relaxation time of molecules at the pore surface and the relaxation time of molecules in the bulk fluid can be interpreted by a fast diffusion model. With this model, the nuclear magnetic resonance (NMR) can be applied to investigate the microstructure of cement pastes. The cement pastes we tested are two series, one is of same water to cement ratio (w/c=0.4) at different curing time (7d, 28d and 90d), the other is of different water to cement ratio (w/c=0.3, 0.4 and0.5, respectively) at the same curing day. Comparing results by NMR method with those by mercury intrusion porosimetry (MIP) shows that NMR is a convenient and nondestructive way to probe pore distribution of cement pastes.

Abstract: The method of the second intrusion mercury in MIP was used to investigate the pore characteristics of hardened cement paste with w/c ratio 0.23, 0.35 and 0.53, respectively, in order to research the quantitative relationship between transport properties and pore characteristics in cement-based composite materials. The results show the second intrusion mercury could well determine the effective pore structure parameters, and effective porosity accounts for 25% to 50% of total porosity in cement paste. At the same time, the existence of the first and second peak in pore size distribution curves is confirmed by MIP, such as, the first peak in hardened cement paste with water to cement ratio 0.53 is very distinct, however, with the decrease of water to cement ratio, the first peak gradually disappears. The pore diameter corresponding to the first and second peak is critical pore diameter of capillary pore and gel pore, respectively.

Abstract: Inorganic salts are important admixtures usually used in cold weather concrete. As research basic of influence of salts on concrete durability, effects of inorganic salts on pore structure of cement paste were studied in this paper, and possible implications of concrete property with pore structure was also analyzed. Pore structure of paste added CaCl2, NaCl, Na2SO4, NaNO2, Ca(NO3)2 and Ca(NO2)2 curing for 3 days and 28 days were tested through mercury intrusion porosimetry (MIP). The results showed that no matter 0.3 or 0.5 water-cement ratio, the pores whose diameter <50nm in paste with salts increased at 3 days, which was harmful for the control of concrete shrinkage and cracking at early age. Adding Ca (NO3)2 increased coarse pores (>200nm) of paste at 3 days, but these coarse pores turned into fine pores and reduced significantly at 28 days. Adding NaCl and Na2SO4 into cement paste raised coarse pores with size>1000nm at 3 days and 28days, which were harmful for the pore structure.