Time-dependent material properties and reinforced beams behavior of two alkali-activated types of concrete

This paper presents an experimental study on the development of material properties over time (up to around 2 years) and the structural behavior of reinforced beams, for two types of alkali-activated concrete (AAC). Compressive strength, flexural strength, tensile splitting strength, elastic modulus, and flexural behavior of reinforced beams are investigated. Tested material properties of AAC are compared with the properties of conventional concrete, as predicted by Eurocode. For the mixes of AAC and the conventional concretes with the same 28 days compressive strength, flexural and tensile splitting strength at 28 days are found to be similar, whereas the elastic moduli of AAC mixtures is up to 30% lower than those of conventional concrete. Related to the long term behavior, after 28 days moist-curing and subsequently exposing AAC specimens to laboratory conditions (50% RH/20°C), a reduction of flexural strength, tensile splitting strength and elastic modulus, is observed. Structural behavior of the reinforced AAC beams in four-point bending test seems not to be affected significantly by the observed decrease in material properties, and is found to be similar to that of conventional concrete beams. The acquired results indicate that the observed decrease of material properties over time might be related to drying (moisture loss). However, more research is needed to understand the phenomenon, especially related to the aimed structural application and safe upscaling of AAC.