Performance of natural clinoptilolite zeolite in the cementitious materials: A comparative study with metakaolin, fly ash, and blast furnace slag

Different pozzolanic materials possess different chemical and mineralogical compositions and could show different performances in the blended hydrated cementitious materials. In the present study, the performance of natural clinoptilolite zeolite, a popular silica-alumina-based natural pozzolanic material in recent times, was investigated to compare with other commonly available silica-alumina (metakaolin) and silica-calcium (blast furnace slag, and Class C-fly ash) enriched pozzolanic materials in the blended cementitious system. The performance was evaluated on fresh (workability), hydration (setting time and chemical shrinkage), and mechanical (compressive strength) properties of hydrated cementitious materials. Thermogravimetric analysis (TGA) was accomplished to measure the pozzolanic activities of all respective pozzolanic materials. The water absorption, porosity, and chloride ion penetrability of concrete via surface resistivity were measured as the transport properties. For the durability properties, drying shrinkage and the alkali-silica aggregate reaction (ASR) of mortars were investigated. Results revealed that the addition of clinoptilolite zeolite reduced the workability but accelerated the setting time of hydration compared to other pozzolanic materials. Zeolite particles increased the volume of chemical shrinkage compared to other pozzolanic materials due to the particle packing effects. The addition of zeolite led to decreasing the compressive strength due to relatively slow pozzolanic activity compared to the other pozzolanic materials as measured by the TGA analysis. Zeolite blended samples had a similar water absorption and porosity compared to the metakaolin, slag, and fly ash blended samples. All pozzolanic materials were equally effective in reducing the drying shrinkage, while zeolite particles attributed to the internal curing capacity. Overall, clinoptilolite zeolite exhibited excellent resistance to chloride-ion penetrability due to the finer pore size, and a reduction in deleterious expansion due to ASR through cation exchange compared to slag and fly ash particles.