Strength and durability performance of high-strength concrete modified with hybrid natural pozzolanic materials

This study investigates the potential of hybrid natural pozzolanic materials, namely pumice and scoria powder, as partial cement substitutes in high strength concrete (HSC). By incorporating these materials at varying percentages (10%, 15%, 20%, 25% and 30% of cement weight) alongside a consistent superplasticizer dosage of 1.6%, the compressive strength, split tensile strength and Scanning electron microscopy analysis along with durability through strength loss after 30 days in sulfuric acid were tested. Compressive strength tests were used to evaluate performance at 28 days, and strength loss was measured after 30 days of exposure to sulfuric acid. The microstructure of the samples was examined using scanning electron microscopy. The findings showed that the HSC mixes HSC0, HSC10, HSC15, and HSC20 had respective compressive strengths of 63.02, 64.44, 62.07, and 60.30 MPa. Pozzolanic activity was responsible for the improved performance at subsequent curing stages. The addition of pozzolanic elements enhanced acid resistance, with strength losses of 8.25%, 9.87%, and 12.93% for HSC0, HSC10, and HSC25, respectively. Notably, HSC0 had a denser calcium-silicate-hydrate (C-S-H) matrix. The results show that adding pumice and scoria to high-performance concrete as sustainable additives can have positive effects on durability and strength. Even though adding 20% pozzolanic material does not increase strength beyond 10%, it may still be taken into consideration for certain uses where other advantages like sustainability or the idea of green concrete are more important.