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The use of silica fume as a partial replacement for Ordinary Portland Cement provides a wide variety of benefits, such as reduced pressure on natural resources, reduced CO2 footprint, and improved mechanical and durability properties. The formation of more stable crystallographic phases in the hardened cement paste can promote resistance to concrete attacks. However, using coarse silica fume may result in lower expenses and shorter workdays. In this work, coarse silica fume was used as a partial replacement of cement, by weight, at 3%, 5%, and 7%, and it was used as limestone filler at different particle sizes. The size of coarse silica fume used was 238 μm. The microstructural, compositional analysis, and crystalline phase content of mixed cements at different ages were evaluated. The addition of coarse silica fume and limestone promoted pore refinement of the composites and increased the calcium and silica content. The filling effect of fine limestone and coarse silica fume particles, as well as the formation of CSH gel, was found to be the main reason for the densified microstructure. The contributions of combined coarse silica fume and limestone improve the stability of CSH gels and pozzolanic reaction.

Portland cement production is an energy-intensive process that releases carbon dioxide into the atmosphere. To reach carbon neutrality by 2050, it would be necessary to implement innovative measures in the cement industry to deliver carbon neutrality. In this respect, it is striking that the new cement types made with high contents of industrial by-products will act as a lever to combat climate change. Accordingly, the purpose of this study is to assess coal–ash blended cements in light of climate change mitigation. In particular, ground coal bottom ash could be considered as a novel constituent for common cement production. The performance of these coal–ash mortars was assessed by measuring pozzolanic reactivity, mechanical strength gain, and microstructural characteristics. Mortars were made with 10%, 25%, or 35% of coal ash (fly ash and/or bottom ash). Therefore, by considering an emission intensity factor of 830 kgCO2/kg of clinker, a reduction in carbon dioxide emissions for all coal fly ash cements is expected, which will be about 83 kgCO2/kg of cement, 208 kgCO2/kg of cement, and 290 kgCO2/kg of cement, respectively. Ground coal bottom ash presented similar characteristics to the coal fly ash. Consequently, ground coal bottom ash is a promising Portland cement constituent with properties comparable to coal fly ash, and its increased usage can contribute to the climate change mitigation.

This work presents the results of the partial substitution of Portland cement (PC) by natural fluorite (NF) and calcined fluorite (CF) in mortars, at 10%, 25% and 40%. To meet these objectives, a sample of fluorite was initially studied by XRD, SEM and Raman Spectroscopy (RS). A chemical quality analysis (CQA) and a chemical pozzolanicity test (CPT) at 8 and 15 days were carried out in a second stage to establish the pozzolanic properties of the investigated sample. Finally, a mechanical compressive strength test (MCST) at 7, 28 and 90 days was carried out on specimens made up with PC/NF and PC/CF mixes, at a ratio of 10%, 25% and 40%. XRD, SEM and RS results indicated fluorite as the major mineralogical phase. The CPT and CQA showed an increase in the pozzolanicity of the samples from 8 to 15 days. The MCST showed an increase in compressive strength from 7 to 90 days for both PC/NF and PC/CF specimens. The results obtained establish that fluorite produces positive effects in the mortar and contributes to the gain of mechanical strength over time, being a suitable material for the manufacture of cements with pozzolanic addition with a reduction of CO2 emissions, and by reducing the energy costs of production.

The purpose of this paper is to establish some correlations between the main technical parameter with regard to the cement-based materials technology, the 28-day compressive strength, and ultrasonic pulse velocity of standard mortar samples cured at three different conditions—(i) under water at 22 °C; (ii) climatic chamber at 95% RH and 22 °C; (iii) lab ambient, 50% RH, and 22 °C—and after five curing periods of 1, 2, 7, 14, and 28 days. Good correlations for each curing conditions were obtained. All the positive linear relationships showed better R2 than exponential ones. These findings may promote the use of ultrasonic pulse velocity for the estimation of the 28-day compressive strength of standard Portland cement samples within the factory internal quality control.