Development of eco-friendly binder using metakaolin-fly ash–lime-anhydrous gypsum

This paper presents the properties of a cementless mortar developed to produce eco-friendly building material without carbon dioxide emissions and with various beneficial effects. The binder used in this mortar was developed by the reaction of inorganic minerals fly ash (FA), lime (L) and activated kaolin clay, which is rich in silica and alumina. The Metakaolin (MK) was prepared by thermal activation of kaolin clay for 3 h at 750 °C. The ratio of FA:MK:L was 30:40:30 mass%. Anhydrous gypsum was added as a chemical activator in varying proportions of 0, 2.5, 5, 7.5 and 10% by weight of the binder. The mortar was prepared using a binder:sand ratio was of 1:1.5 mass% and a water/binder ratio of 0.50. The mortar specimens were cured at 20 °C for 24 h in their moulds and then demoulded. The demoulded mortar specimens were cured at room temperature up to 28 days. Compressive strength and apparent density of the hardened mortar specimens were systematically measured. On the basis of the test results, it was concluded that the activator addition of 10% had an appreciable influence on the compressive and flexural strength. The compressive and flexural strength increased by 56% and 45% more than that of the control mortars at 28 days of hydration. It was also concluded that the microstructure of the binder contain a cross link of hydration products and exhibits dense morphology.

► We studied properties of a cementless and eco-friendly binder for masonry mortar.
► Binder was developed using fly ash, lime, activated kaolin clay and gypsum.
► Binder with 5–10% gypsum satisfies minimum strength requirements of masonry mortar.
► Addition of 10% gypsum had significant effect on compressive & flexural strengths.
► Microstructure of binder exhibits dense morphology.