Microstructure of Dry Mortars without Cement: Specific Surface Area, Pore Size and Volume Distribution Analysis

The evolution of the microstructure of the wastepaper sludge ash-based dry-mortar mixtures is characterized. Mixtures have been prepared with a large volume of wastepaper sludge ash (WSA) and ground granulated blast-furnace slag (GGBS) as a binder matrix mixed with water. Two ratios of water/binder (w/b) = 0.5 and 0.6 were selected. Both of these two industrial by-products are well-known as supplementary cementitious materials in the construction industry and they constitute a convenient replacement for cement. A series of these dry mortars for two ratios w/b were activated by three different chemical activators. They were placed in 4 × 4 × 16 cm3 molds and then compacted at the same compaction energy of 600 kN·m/m3. The influence of water quantity, compaction level and activators on the microstructure of these mortars was investigated by measuring the specific surface area, pore size and volume. Different series of samples have been compared in terms of adsorption/desorption hysteresis and pores network. The influences of water quantity and energy level were first discussed on non-activated dry mortars and this analysis led to the selection of an optimal energy for the comparative study of activated dry mortars. A significant difference in behavior was observed between the studied activators in terms of specific surface area, adsorption property and pore distribution. Then, the microstructure of the three activated dry mortars is observed and analyzed considering the two w/b ratios, the mechanical strength obtained and the type and dosage of activator used. Dry mortars show micropores regardless the quantity of water and the dosage of activator.