Sintered Bottom and Vitrified Silica Ashes Derived from Incinerated Municipal Solid Waste as Circular Economy-Friendly Partial Replacements for Cement in Mortars

Sintered bottom ash (SBA) and vitrified ash (VA) derived from the incineration of municipal solid waste (MSW) at 1200 °C were used in this study as replacements for Type 2 Portland cement (CEM-II) based mortars. This approach negates the need to send them to landfill, benefits the circular economy and contributes towards the decarbonisation of cementitious construction materials in response to international net zero carbon emission agendas. The material (physico-chemical) characteristics of VA and SBA were analysed before being used as partial replacements for CEM-II in mortars, whereby compressive strength (CS) was the primary criterion for assessing engineering performance. VA and SBA replaced CEM-II at dosages of 10%, 25% and 50% based on their high inorganic and pozzolanic contents; whereby the 10% and 25% replacements did not compromise mortar strength. The alkalinity and pozzolanic properties of SBA collectively indicated it has greater potential as a cementitious material over VA, which possessed a neutral pH. The 28-day CS recorded for mixtures containing 25% VA and 10% SBA were 13.74 MPa and 11.77 MPa, respectively compared with 17.06 MPa for CEM-II control samples. The use of 2% additional water in 25% SBA mortar designs improved strength further, indicating that SBA’s water retention properties permitted further hydration and strength development with curing. Microstructural, mineralogical and infrared spectroscopy analyses indicated that these strengths were owed to the formation of silicate-based hydration products. The outcomes from this study highlight that SBA has potential for replacing CEM-II and VA as a filler in cementitious mortar. Graphical Abstract: [Figure not available: see fulltext.]</p

Is sustainability certification for biochar the answer to environmental risks?

Biochar has the potential to make a major contribution to the mitigation of climate change, and enhancement of plant production. However, in order for biochar to fulfill this promise, the industry and regulating bodies must take steps to manage potential environmental threats and address negative perceptions. The potential threats to the sustainability of biochar systems, at each stage of the biochar life cycle, were reviewed. We propose that a sustainability framework for biochar could be adapted from existing frameworks developed for bioenergy. Sustainable land use policies, combined with effective regulation of biochar production facilities and incentives for efficient utilization of energy, and improved knowledge of biochar impacts on ecosystem health and productivity could provide a strong framework for the development of a robust sustainable biochar industry. Sustainability certification could be introduced to provide confidence to consumers that sustainable practices have been employed along the production chain, particularly where biochar is traded internationally