Modified blended limestone-Portland cement binders: Evaluation of 4 different sodium silicates

One-part blended cements with 65% limestone and 35% Portland cement (PC) were activated by 3-8%wt. of four powdered sodium silicates of different modulus SiO2/Na2O = 1-3.26. Pastes were cured at 20 degrees C for 180 days in dry and underwater conditions. The use of moduli <3.26 promoted quick setting and low strength of the pastes. The use of modulus = 3.26 showed the best results in terms of workability, underwater stability and compressive strength higher than a reference non-activated blend; the evolution of pH, rate of heat liberation and setting times were similar among the activated and non-activated blend, indicating that the hydration of PC was not strongly altered by the activator and that other favorable reactions took place. Microstructural characterization showed that the developed strength was favored by reactions of the sodium silicate with portlandite from the Portland cement and limestone, as well as by the condensation of C-S-H and silica gel.