The aim of this study was to determine the effect of finely ground filler on the properties of slag-alkali binder based on blast furnace slag. An aqueous solution of sodium silicate and caustic soda (aqueous solution of NaOH) was used as a hardening activator with an alkali modulus (weight ratio SiO2/Na2O) equal to 1.0 and 0.5. The results showed that the introduction of Reftinskaya GRES fly ash into the binder instead of ground blast furnace granulated slag causes an increase in the initial setting time, but does not affect the final setting time. No cracking was detected during hardening in mixtures containing fly ash, provided that a complex based on sodium silicate and an aqueous solution of NaOH was used as a hardening activator. The introduction of alkali into the sodium silicate solution helps to reduce the silicate modulus (the mass ratio of SiO2/Na2O) and reduce the formation of shrinkage microcracks due to the formation of a homogeneous structure and the formation of fly ash and the formation of sodium hydroaluminosilicate (H-A-S-N).

Keywords: cement paste, ground granulated slag, fly ash, hardening activator, setting time, shrinkage, microcracks

The aim of the study was to determine the effect of the amount of alkaline hardening activator on the geopolymer binder consisting of ground blast furnace slag and fly ash. Ground blast furnace slag with fly ash was activated with sodium silicate (SN) at different contents of alkali solution (A). The results showed that an increase in the alkali activator content (SN:A = 5%:3% → 15%:4%) promotes an increase in the strength of concrete over the entire time interval of monitoring the strength gain. The addition of fly ash affected an increase in the compressive strength of concrete samples from 16 to 18% relative to the compositions without fly ash. Micro cracking is manifested in the compositions of geopolymer concretes without fly ash, activated by a sodium silicate solution at a higher silicate modulus. The reduction of the silicate modulus CH led to less microcrack formation and a more uniform structure, and the introduction of fly ash into the concrete mixture helps to eliminate internal stresses and the formation of microcracks on the surface of concrete samples.

Keywords: by-products, blast furnace slag, alkaline hardening activators, fillers, performance properties, strength, water absorption, development driver