Effect of ultrafine slag and metakaolin blend on the properties of high-strength dry-mix concrete for potential application in concrete masonry unit production

This study aimed to develop a high-strength and low-Portland cement content dry-mix concrete with properties important for concrete block masonry unit manufacturing. First, the effect of six aggregate gradations on the compressive strength of dry-mix concretes made with a commercial Portland/Portland limestone cement was studied. Then, the aggregate that provided the highest strength was selected to prepare a dry-mix concrete that contained 50% of that cement together with an ultrafine granulated blast furnace slag (UFS) and a locally available medium-grade metakaolin (MK). Another binder that contained commercial slag combined with MK was also considered for comparison. The concretes were tested for the compressive strength, water absorption, permeable voids volume, bulk electrical resistivity, and freeze–thaw resistance. Results showed that the concrete incorporating MK–UFS achieved a 28-day compressive strength of ∼70 MPa, while that with MK–slag reached ∼56 MPa. The concrete with MK–UFS also exhibited reduced water absorption and improved freeze–thaw resistance.