Enduring performance of alkali-activated mortars with metakaolin as granulated blast furnace slag replacement

In the construction industries worldwide, improving the materials durability and achieving sustainability are the main goal. Owing to their excellent strength performance various alkaliactivated binders can be one of the alternative solutions to the polluting traditional cement. Currently, ground blast furnace slag (GBFS) is the major base material used in the alkali-activated binders. High drying shrinkage and low resistance to sulfuric acid attack affect negatively the durability performance and life span of alkali-activated paste, mortars, and concretes made from GBFS. Thus, a series of alkali-activated mortars (AAMs) were designed with various contents (5, 10, 15, 20 and 25, mass%) of metakaolin (MK) as GBFS replacement to improve their strength performance. In addition, the strength and durability performance of the designed mixes were compared with the control mixture prepared using 100% of GBFS. The impact of varying MK level on the long-term performance such as compressive strength, porosity, resistance to sulfuric acid attacks, wet-dry cycles, drying shrinkage, and carbonation were evaluated. Various recommended standards were followed to cast the specimens in different shapes (cubes, cylinders, and prisms) and sizes. Mortar containing 10% of MK as GBFS replacement showed the highest compressive strength (63.4 MPa) at 28 days of curing age. Furthermore, the inclusion of MK as GBFS replacement was shown to improve the AAMs durability performance wherein the drying shrinkage was reduced and the resistance to aggressive environments was increased. The specimens containing 5% and 10% of MK revealed a lower porosity and carbonation depth compared to the control specimen. It was concluded that the proposed AAMs due to their long-term stability can be the sustainable and potential substitutes to the traditional construction materials.