Performance of cementitious and slag-fly ash blended geopolymer screed composites: A comparative study

This study investigates the potential use of geopolymer (GP) composites for screed applications complying with BS 8204 requirements. Different cementitious (CM) and GP screed mixtures were prepared with varying the liquid-to-binder ratio, binder-to-sand ratio, and type of sand. The fresh and mechanical properties were evaluated by testing the flowability, flow retention, density, setting time, compressive and flexural strengths, drop impact resistance, and pull-off and slant shear bond strengths. Test results showed that the fresh properties of GP screeds were relatively inferior to those of CM counterparts; however, the strength development rates and resistance against the impact of GP screeds were higher, reflecting their capability to accelerate operation works without the use of moist curing that is normally required for cement-based materials. The sand content was increased in GP screeds without compromising the superior mechanical and bond properties. Screed mixes made with crushed sand at a binder-to-sand ratio of 1:7, and the solution-to-binder ratio of 0.60 complied with Category B, while screed mixes made with dune sand at a binder-to-sand ratio of 1:2 and the solution-to-binder ratio of 0.55 complied with Category A of BS 8204. An increase in the binder-to-dune sand ratio to 1:3 did not affect the classification of the screed composites, while decreasing the solution-to-binder ratio shifted the material to Category B. Such data can be of interest to contractors and engineers aiming to replace Portland cement and crushed sand with GP-based mixtures containing dune sand for screed applications, leading to an enhanced sustainability of the construction industry.