Portland cement versus hybrid cement and geopolymers: performance at high temperatures

This paper reports on a comparative study of the mechanical performance at high temperatures of a commercial Portland cement (CEM I 42.5 (OPC)), a hybrid cement (CEM HYC = 30% clinker + 32.5 % BFS + 32.55 % FA + 5 % alkaline activator) and a geopolymer (fly ash-activated with waterglass solution). Two types of mechanical tests were conducted on samples made of each of these three cementitious systems: i) high-temperature mechanical tests to determine mechanical strength and ii) post-thermal treatment tests to evaluate residual strength after two hours of exposure to temperatures ranging from 400 °C to 1000 °C. Differential thermo-gravimetric (DTA)/TG, X-ray diffraction and Hg porosimetry were applied to track the mineralogical and microstructural variations taking place in the materials. The results of these tests were correlated to the observed mechanical behaviour. The results from the three binders have provided new ideas about the relationship between the elemental composition of materials and high-temperature performance. This relationship will be an important factor to take into account when determining the high-temperature performance of future cements and concretes