Evaluation of early-age compressive strength of geopolymer concrete masonry units

This paper presents the results of the experimental study on the early-age (1-day) compressive strength of geopolymer concrete masonry units (GCMU). The binder was a combination of ground granulated blast furnace slag (or simply slag) and fly ash with ratios of 3:1 and 1:1. It was activated using an alkaline solution consisting of sodium silicate and sodium hydroxide at a mass ratio of 1.5. Additional water was added to selected mixes to enhance the castability and compactability. The effect of the mix design parameters on the early-age compressive strength of GCMU was investigated. Results showed that an increase in the binder-to-aggregate ratio increased the compressive strength by up to 57%. Similarly, increasing the alkaline solution-to-binder and slag-to-fly ash ratios led to 4 and 3.5 times higher compressive strengths, respectively. Meanwhile, additional water had a negative impact on the compressive strength of GCMU, decreasing it by up to 74%. Still, it was possible to obtain a 1-day compressive strength of 36 MPa for a GCMU having a binder-to-aggregate ratio of 1:5, slag-to-fly ash ratio of 3:1, and solution-to-binder ratio of 0.4. Such results provide evidence of the ability to utilize geopolymer concrete in the field of masonry construction.