Significance of Porosity Measurements on Blended Cement Performance


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Title: Significance of Porosity Measurements on Blended Cement Performance

Author(s): R.F. Feldman

Publication: Special Publication

Volume: 79


Appears on pages(s): 415-434

Keywords: blended cements; cal cium hydroxides; c strength; density (mass/volume) ; durability; fly elasticity; porosity; quartz; sslags; temperature. ompressive ash; modulus of

Date: 5/1/1983

Normal portland cement mixed separately with two types of fly-ash and ground quartz to produce blends containing 35 per cent additive and a mix containing 70 per cent slag were cured in water at 21, 35 and 55'C at a w/c = 0.45. After 2, 7, 14, 28, 90, 180, 365 and 550 days, Ca(OH)2 content, pore size distribution, compressive strength, Young's modulus and microhardness of the products were determined. Density and porosity were measured by mercury intrusion, helium pycnometry and methanol saturation. Mortars were also prepared using these blends. After curing for 15 or 240 days they were exposed to a salt solution containing 27.5% CaC12, 3.9% MgC12, 1.8% NaCl and 0.1% NaHCO3. The porosities of the hydrated blends were higher when measured by mercury intrusion and had a higher percentage of fine pores. Densities of the products calculated from these pore measurements gave more realistic values. Higher temperatures increased the early rate of reaction of the cement, then retarded it, but the acceleration period was extended for the cement blends. Factors responsible for durability were found to be pore volume above 88 nm diam and Ca(OH)2 content.