Macro- and Microstructural Investigations on Strength and Durability of Pumice Concrete at High Temperature

The strength and durability performance of concretes incorporating 0–40% of finely ground pumice as cement replacement (by mass) subjected to high temperatures up to 800°C is described. The strength properties were assessed by unstressed residual compressive strength, while durability was investigated by crack pattern observations, the rapid chloride permeability test (RCPT), mercury intrusion porosimetry, microhardness testing, and differential scanning calorimetry. The results of RCPT revealed that concrete durability deterioration commences at temperatures that are lower than those at which compressive strength deterioration commences. Such a loss of durability can be explained by a weakened interfacial transition zone between the hardened cement paste (hcp) and aggregate and by the concurrent coarsening of the hcp pore structure. When pumice is included, an improvement of fire resistance was observed, as characterized by the higher residual compressive strength and improved durability. Pumice concrete showed good performance with a higher residual strength, higher chloride resistance, and higher resistance against deterioration, particularly at temperatures below 600°C as compared to the control normal Portland cement concrete. The improved performance of pumice concrete can be attributed to the substitution of pumice for cement, which leads to refinement of the pore structure and a lower quantity of calcium silicate hydrate. The deterioration of both strength and durability of pumice concrete increased with the increase of temperature up to 800°C due to a substantial reduction in residual strength and increase in pore volume and pore diameter. The serviceability assessment of pumice concrete after a fire should therefore be based on both strength and durability considerations.