PERCOLATION AND PORE STRUCTURE IN MORTARS AND CONCRETE

The cement paste in concrete and mortar has been shown to have a pore size distribution different than that of plain paste hydrated without aggregate. For mortar and concrete, additional porosity occurs in pore sizes larger than the plain paste's threshold diameter as measured by mercury intrusion. Based on the assumption that these larger pores ar e essentially present only in the interfacial zones surrounding each a ggregate, an experimental program was designed in which the volume fra ction of sand in a mortar was varied in a systematic fashion and the r esultant pore system probed using mercury intrusion porosimetry. The i ntrusion characteristics were observed to change drastically at a crit ical sand content. Similar results are observed for a series of mortar specimens in which the cement paste contains 10% silica fume. To bett er interpret the experimental results, a hard core/soft shell computer model has been developed to examine the percolation characteristics o f these interfacial zone pores. Using the model, interfacial zone perc olation in concretes is also examined. Finally, the implications of in terfacial zone percolation for transport properties and durability of mortar and concrete are discussed.