Experimental investigation of effect of admmixture on concrete strength and frost-resistance
The influence of admixture on concrete strength and frost-resistance was analyzed by using the mercury intrusion method and the rapid frozen-thaw method under the condition of the same water/binder ratio in this paper. The results showed that the intensity of the concrete with single doped compound mineral admixture is slightly lower than the normal concrete's in concrete 28-days strength experiment when the fixed water/binder ratio is 0.38, but the extent of the concrete strength growth is bigger, and maybe exceed the normal concrete's at the late period of the whole session. It also could be found that the concrete strength added single air entraining agent is lower, particularly the strength of the concrete double mixed with compound mineral admixture and air-entraining agent is lowest. In term of the pore structure, the porosity rate of concrete can be lower and the harmful hole is decreased as well as the less-harmful hole and no-harmful hole are increased when the compound mineral admixture is mixed. The porosity rate will increase, closed pore and less-harmful hole will enhance by a wide margin if the admixture of air entraining agent is added. Moreover, the pore size distribution of concrete becomes reasonable if these two substances are admixed at the same time. From the aspect of frost-resistance, the concrete with co-doped compound mineral admixture and air-entraining agent is best, the concrete with uni-doped air-entraining agent is better secondarily and the concrete with compound mineral admixture alone is just slightly better.
Comparison of measured and calculated permeabilities for hardened cement pastes
Abstract The experimental and calculated permeabilities of hardened cement pastes were compared. Experimental data for water permeability was obtained from the work of Nyame and Illston in 1980 on neat pastes with water-to-cement ratios ( w c ) between 0.23 and 1.0. Mercury intrusion porosimetry (MIP) and impedance spectroscopy (IS) measurements were performed on equivalently prepared specimens. Then the Katz-Thompson relation was used to calculate permeability. Calculated results track well with experimental data as a function of time, with the experimental value of permeability slightly higher at most times. The correlation between experimental and calculated permeabilities, at all times, are within 1.5 orders of magnitude. The largest differences occurred at late times for the samples with low w c ratio. This calculated permeability is quick, relatively simple and appears to give reasonable results when compared to conventional water intrusion methods.
Permeability versus conductivity for porous media with wide distribution of pore sizes.
Using recent results on random resistor networks, we derive the relation between the permeability and the conductivity of liquid-saturated porous materials, presumably exact in the limit of a wide distribution of pore sizes. This relation also applies to some continuum percolation models, and the range of its universality is discussed. Some discrepancy is found with the previous anlaysis of Katz and Thompson [Phys. Rev. B 34, 8179 (1986)]. Mechanisms are proposed to recover agreement with their experiments. The pore-size parameter \ensuremath{\Lambda} characterizing surface effects is computed.