Study of Microstructure, Crystallographic Phases and Setting Time Evolution over Time of Portland Cement, Coarse Silica Fume, and Limestone (PC-SF-LS) Ternary Portland Cements

Abstract

The use of silica fume as a partial replacement for Ordinary Portland Cement provides a wide variety of benefits, such as reduced pressure on natural resources, reduced CO2 footprint, and improved mechanical and durability properties. The formation of more stable crystallographic phases in the hardened cement paste can promote resistance to concrete attacks. However, using coarse silica fume may result in lower expenses and shorter workdays. In this work, coarse silica fume was used as a partial replacement of cement, by weight, at 3%, 5%, and 7%, and it was used as limestone filler at different particle sizes. The size of coarse silica fume used was 238 μm. The microstructural, compositional analysis, and crystalline phase content of mixed cements at different ages were evaluated. The addition of coarse silica fume and limestone promoted pore refinement of the composites and increased the calcium and silica content. The filling effect of fine limestone and coarse silica fume particles, as well as the formation of CSH gel, was found to be the main reason for the densified microstructure. The contributions of combined coarse silica fume and limestone improve the stability of CSH gels and pozzolanic reaction.

Carbonation Resistance of Ternary Portland Cements Made with Silica Fume and Limestone

“…This finding confirms the positive effect of the pozzolanic reaction of the silicon oxide present in the silica fume and the calcium oxide formed in the cement hydration [ 39 ]. This reaction leads to a denser structure [ 34 ]. However, the worst performance was found in the sample with the highest content of limestone (20%), H7L20-0-0 and H5L20-0-0, independently of the silica fume content (7% and 5%, respectively).…”

“…This estimation is compared to the carbon dioxide uptake estimated by the Tier 1 methodology (dashed line green in Figure 1) defined and calculated in reference [7]. Accordingly, a ternary cement made with Portland cement clinker, limestone powder, and a third cement constituent, for example, coarse silica fume, can be a promising construction product due to the good experience [34,44], the adequate availability of the constituents, and the low environmental impact.…”

“…Blended cements with a high content of Portland cement constituents, other than clinker, will contribute to the drawdown of carbon dioxide emissions and, therefore, the negative environmental impact of Portland cement production. In an attempt to produce low-carbon and cost-effective blended cements, new formulations are currently being investigated [ 34 ]. Zeraoui et al [ 35 ] studied ternary binders (Portland cement-ground granulated blast-furnace slag-flash-calcined sediment) and reported that 10% flash-calcined sediment plus 40% ground granulated blast-furnace slag can replace 50% of Portland cement.…”

“…Accordingly, a ternary cement made with Portland cement clinker, limestone powder, and a third cement constituent, for example, coarse silica fume, can be a promising construction product due to the good experience [ 34 , 44 ], the adequate availability of the constituents, and the low environmental impact.…”

“…Ground limestone is already being used worldwide in Portland cement, providing some characteristics to the cement depending on its particle size distribution (PSD) and its content in the blended cement, i.e., dilution, filler, nucleation, and chemical effects [ 34 ].…”