Abstract
The mechanical performance of a hybrid cement containing 48 % fly ash, 48 % mineralised belite clinker, 1.5 % gypsum and 2.5 % Na2SO4 was analysed and the hydration products were identified. The findings showed that the newly designed cement met European standard EN 197-1 compositional, mechanical and setting time requirements (cement type IVB). The hydration products forming in this blended ‘alkaline-belite’ cement (as it was determined through XRD, 29Si and 27Al MAS NMR and electron microscopy) consisted in a mix of cementitious gels: C-(A)-S-H and N-(C)-A-S-H, which interacted and over time evolved toward the latter with no detriment to the mechanical strength developed by the cement.
Highlights
The CO2 emissions due to Portland cement production are environmentally problematic mainly due to the very high volume of demand for cement in view of concrete needs in the world
Belite (Chatterjee, 1996; García-Díaz et al, 2011; Stanek and Sulovský, 2015), alkaline and hybrid alkaline cements (Deschner et al, 2012; García Lodeiro et al, 2013, 2016) are among the binders studied as alternatives to the traditional Portland cement
The heat of hydration released by the belite clinker fraction, in conjunction with the presence of the Na2SO4, sufficed to alkali-activate the fly ash, affording the system good initial mechanical behavior
Summary
The CO2 emissions due to Portland cement production are environmentally problematic mainly due to the very high volume of demand for cement in view of concrete needs in the world. Portland cement production is continuously increasing at global level and there exists a general agreement to consider Portland cement responsible of 7–8% of the total emissions of carbon dioxide in the world (Scrivener et al, 2018a). The use of alternative fuel, the addition of minerals to Portland cement, the inclusion of mineralizers and fluxes in the raw mix, along with the development of alternative binders, are some of the sustainable solutions envisaged today by the cement industry and the scientific community (Lothenbach et al, 2011; Zhang et al, 2012). Due to the low hydraulic activity of the SCMs, blended cements usually show delayed setting times and low early mechanical strength development, which is limiting the replacement of clinker by SCMs in the cement (Lothenbach et al, 2011). It is quite probable that future will lead to us to a combination of those options above mentioned like the most effective choice
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