Shrinkage and strength development of alkali-activated fly ash-slag binary cements: Fid-Bau Portal

Shrinkage and strength development of alkali-activated fly ash-slag binary cements

Hojati, Maryam / Radlińska, Aleksandra

Highlights•Shrinkage characteristics of different alkali-activated fly ash-slag binders were evaluated.•Utilization of higher-pH sodium silicate activator mitigated autogenous and drying shrinkage.•Strength development and setting time properties of different binary binders were measured.•Addition of larger amount of slag to binary binder led to a quicker set, higher strength and stiffness.•Activating by higher-pH sodium silicate solution resulted in a slower setting, higher strength and stiffer matrix.

AbstractThis paper evaluates the effect of fly ash and slag proportions and the type of activating solution on shrinkage and strength development of alkali-activated binary fly ash-slag mixtures (mortar and paste), cured at room temperature. Three different volumetric ratios of slag/fly ash were considered: 10%, 15%, and 20%. Two activators with different pH and modulus, n=(SiO2/Na2O)mol were utilized. The liquid to solid volume ratio of all binders was maintained at 0.75. The results showed that while the addition of slag significantly shortens the time of setting (up to 178min), and increases the compressive strength (up to 93%) and bulk modulus (up to 43%), it also results in higher autogenous shrinkage, but smaller mass loss during drying. Measured drying shrinkage of mixtures with various slag contents was similar, likely due to counteracting effects of binder stiffness and degree of saturation. Fly ash-slag binders activated at higher pH exhibited larger chemical shrinkage, but lower autogenous (up to 21%) and drying shrinkage (up to 47%) magnitude.