High strength fiber reinforced one-part alkali activated slag/fly ash binders with ceramic aggregates: Microscopic analysis, mechanical properties, drying shrinkage, and freeze-thaw resistance

Abstract

One-part alkali-activated binders, also known as the “just-add-water” concept, have received great attention due to their advantages over two-part alkali-activated binders. By avoiding the use of dangerous alkali solutions, these binders are easier to both handle and transport. Ground granulated blast furnace slag is one of the side streams, which can be used in one-part alkali-activated binders to reach high compressive strength at an early age. However, using slag alone has some disadvantages, including a fast setting time and a large drying shrinkage, narrowing the application of these mix compositions and causing crack formation, respectively, thus shortening service life. Fly ash can be used in one-part alkali-activated materials to partially substitute for slag in order to both minimize drying shrinkage and prolong the setting time. Moreover, ceramic waste can be used as a replacement for normal sand, which is great achievement in terms of developing environmentally friendly alkali-activated materials exclusively from side steam. This paper presents new research on the effects on the fresh and hardened-state properties of one-part alkali-activated mortars of replacing up to 80% of slag with fly ash. These properties were characterized by the initial and final setting time, the strength development (compressive and flexural), and the drying shrinkage. Microstructural analyses (SEM/EDS, XRF, TGA/DTG) justified the results. Moreover, different fiber contents and combinations were used to reinforce the developed one-part alkali-activated slag/fly ash mortars to increase the strength, further reduce the drying shrinkage, and improve the freeze/thaw resistance.The results showed that fly ash and fibers can reduce the drying shrinkage and prolong the setting time. The weakened mechanical properties caused by decreasing the amount of slag are still adequate to let the composite slag/fly ash material be considered in construction applications.