Creep of geopolymer and Portland cement pastes due to high temperature exposure

![CDATA[Geopolymer is a new class of binder based on aluminosilicates and purported to be an environmentally friendly alternative to ordinary Portland cement (OPC) based binder, and can potentially replace OPC in concrete making. Chemical structure of geopolymer has been widely reported to have incredible resilience to high temperature exposures, up to 700ºC. In these temperatures, OPC decomposes to little or no strength. However, strong resistance to elevated temperatures, such as fire exposure, requires more than chemical stability. High temperature creep plays an important role in relieving stresses created due to uneven temperature expansions, and in concretes, to accommodate the thermal incompatibility between aggregates and pastes. In OPC concretes, this property, known as Transient Thermal creep’ (TTc), plays a major role in providing fire resistance. In this investigation, geopolymer samples were prepared using Class F fly ash and sodium silicate and sodium hydroxide as activators. The OPC samples were prepared with a water/cement ratio of 0.4. Strengths of OPC and geopolymer pastes are 66 MPa and 63 MPa, respectively. Creep (TTc) of geopolymer and ordinary Portland cement (OPC) based pastes due to high temperature exposures were measured at elevated temperatures up to 550ºC. At temperatures below 250ºC, geopolymer showed a significantly higher creep (TTc) than OPC paste. In the range of 250-550ºC, geopolymer did not show any pronounced increase in transient creep while OPC paste developed significant transient creep. The investigation also measured compressive strengths and elastic modulus of geopolymer and OPC samples while the samples were kept at temperatures up to 550ºC. At 550ºC, geopolymer‘s hot strength increased to 108 MPa, whereas the OPC slightly reduced to 62 MPa. At 550ºC, the elastic modulus of geopolymer increased by 40%, whereas the OPC has little change in its elastic modulus. The paper also reports thermal expansion/shrinkage of the samples up to 550ºC. Thermal gradient within the sample plays an important role in the results; hence attention must be paid to the size of samples as they can significantly affect the results.]]