Hybrid geopolymer-cement coating mortar optimized based on metakaolin, fly ash, and granulated blast furnace slag

Abstract

The use of wastes for new binders aims to reduce the environmental impact caused by the manufacture of Portland cement (PC) given the advance of urbanization. In this work, the main effects of the use of Geopolymer Cement (GC) in partial replacement to PC in mortars for coating were investigated. The GC was obtained from mixtures of industrial wastes, fly ash (FA), granulated blast furnace slag (GBFS), and metakaolin (MK), activated by a solution composed of alkaline sodium silicate (SS) and potassium hydroxide (KOH). The factors used for the experimental planning were the cement replacement content, T (10, 30, and 50%, by weight) and the aggregate-cement ratio, A/C (6.11, 6.90, and 7.69, by weight). Some properties were evaluated initially: consistency, compressive strength, durability (sulfate attack) and microstructural analysis (SEM, XRD, DSC, and TG). For optimized mixture and reference were tested: consistency, setting time, the heat of hydration, water retention, compressive strength, flexural tensile strength, tensile bond strength, dimensional variation, water absorption, voids content, elastic modulus, and thermal conductivity. The results are promising for the use of GC in mortars. The optimized mortar reached values of compressive strength and flexural tensile strength of 5.65 MPa and 1.73 MPa, respectively. The results showed the feasibility of using as eco-friendly mortar for internal and external coating, or as a mortar to repair degraded coatings. Hybrid mortars did not show good performance for attack by sulfates.

Keywords

• Coating mortars
• Geopolymer cement
• Granulated blast furnace slag
• Fly ash mortar
• Metakaolin