Repair Mortars and New Concretes with Coal Bottom and Biomass Ashes Using Rheological Optimisation

The objective of the present work is to analyse the potential of using non-classical additions in concrete and mortar compositions such as coal bottom ash (BA) and biomass ash (Bio), as partial replacing binder of ordinary Portland cement. It is intended to deal with production of these type of wastes and its accumulation and contribute to the minimisation of carbon and embodied energy in construction materials. The aim is to identify the concrete and mortars formulation types where it is possible to get more benefit by incorporating BA and Bio. Based on the optimisation of the rheological properties of cement-based materials, mortars with repair function and concrete compositions were developed including 0%, 10%, 15% and 20% of BA and Bio as cement replacement. An assessment of the evolution of relative concrete compressive strength was calculated as a function of the relative solid volume fraction of several concretes. BA compositions present low resistance to high flow rates, increasing the ease of placement and vibration. BA seems to present more filler and pozzolanic effect when compared with Bio. BA mortars fulfil the compressive strength and stiffness requirements to be used as repair mortars, allowing the replacement of 15% or 20% of cement by an industrial waste. This by-product is able to work in the development of the mortar and concrete microstructure strength adopting a much more sustainable solution for the environment.