Mechanical properties and microstructure of slag and fly ash alkali-activated lightweight concrete containing miscanthus particles

To improve the early age strength of miscanthus-based composites, alkali-activated binders (ground granulated blast furnace slag and fly ash: AASF) were investigated against Portland cement. The impact of miscanthus content on strength development was assessed at three levels of aggregate to precursor binder mass ratio (0.27, 0.43 and 0.76). For the same aggregate to binder ratio, AASF mixes developed compressive strengths exceeding 1.3 MPa at 5% strain, seven times higher than those obtained with Portland cement, with the bulk density values measured in the range of 910–1070 kg/m³. However, these values for vegetal concretes remain lower than non-vegetal concretes of similar apparent densities such as those made with polystyrene aggregates. The analysis of the microstructure of AASF composites indicates a strong interfacial transition zone, showing microstructural features that suggest the achievement of a complete reaction.