Research on mechanical properties and hydration mechanism of alkali-activated sintered brick powder

The discarded sintered bricks account for about 50% of the total amount of urban construction waste, its improper and rampant disposal cause significant damage to the environment.In order to seek a new way of resource utilization of waste sintered bricks, the waste sintered brick powder was used as raw material, water glass and NaOH were used as composite alkaline activators to prepare alkali-activated cementitious materials.The influences of sodium silicate modulus and Na2O content on the mechanical properties of alkali-activated sintered brick powder were studied, and the hydration mechanism of alkali-activated sintered brick powder was revealed by applying hydration heat, X-ray diffraction and scanning electron microscopy.The results showed that the compressive strength of alkali-activated sintered brick powder increased first, and decreased with the increasing of the sodium silicate modulus and Na2O content.The 28 d compressive strength reached the maximum level up to 1.70 MPa when the sodium silicate modulus was 1.8 and the Na2O content was 3.0%,which could be used as supplementary cementing materials.With the decreasing of sodium silicate modulus or the increasing of Na2O content, the induction period of hydration reaction of alkali-activated sintered brick powder slurry was extended, and the appearance of the second exothermic peak during the acceleration period was delayed.The total heat release increased first and decreased with the decreasing of sodium silicate modulus, and increased with the increasing of Na2O content.During the micro structure evolution of the alkali-activated cementitious materials, when the sodium silicate modulus and the Na2O content were too high or low, the formation of the hydration product, i.e.N-A-S-H gel would be blocked, and the porosity increased, which would affect the growth of the samples compressive strength.