Abstract
Cement-based materials decay with exposure to aggressive agents, a development that raises infrastructure operation and maintenance costs substantially. This paper analyses the inclusion of ultrafine construction and demolition (UC&DW) and biomass-fuelled power plant (BA) waste as pozzolanic additions to cement in pursuit of more sustainable and eco-respectful binders and assesses the durability of the end materials when exposed to seawater, chlorides (0.5 M NaCl) or sulphates (0.3 M Na2SO4). The effect of adding silica fume (SF) at a replacement ratio of 5% was also analysed. Durability was determined using the methodology proposed by Koch and Steinegger, whilst microstructural changes were monitored with mercury intrusion porosimetry (MIP), X-ray diffraction (XRD) and scanning electron microscopy (SEM) for a fuller understanding of decay processes. According to the findings, the new blended cements containing 20%UC&DW + 10%BA or 20%UC&DW + 20%BA + 5%SF resist the attack by the aggressive media studied, with a 56-d corrosion index of over 0.7. The composition of the reaction products generated with the attack is essentially the same in OPC and the SCM-bearing materials. The results show that the optimal replacement ratio for SCM is 30%.
Highlights
The decline in flexural strength values of the water-soaked cement and the materials exposed to seawater, sodium chloride (0.5 M NaCl) or sodium sulphate (0.3 M Na2 SO4 ), was an indication that the effect of the dilution resulting from the lower amount of clinker present in new blends M1 and M2 was greater than the effect of the pozzolanicity of this type of SCMs (UC&DW and biomass-fuelled power plant (BA))
The following conclusions can be drawn from this study
Pastes bearing 30% (20% UC&DW + 10%BA) SCMs exhibit 10% lower flexural strength than OPC and those with 45% (20%UC&DW + 20%BA + 5%silica fume (SF)) supplementary cementitious materials 11% lower strength than the 56-d water-soaked pastes
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Pozzolanic SCMs in particular favour durability due to their effect on pore system refinement and reduction of pore solution alkalinity and portlandite content in cement matrices [4,6] In addition to those technical advantages, the use of SCMs carries social and environmental benefits associated with lower natural resource consumption and the valorisation of industrial byproducts, as well as a significant decline in CO2 emissions. Further to research on mechanical behaviour, GRC has no adverse effect on new eco-cement performance at low replacement ratios (≤7%), whereas masonry ultrafines induce no significant decline in compressive or flexural strength at percentages of up to 25%. Another line of research that has evoked considerable interest, as noted earlier, is the valorisation of agroforestry waste as an SCM. The variations in pore size distribution detected with mercury porosimetry were explored
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