Alkali activated metakaolin with high limestone contents – Statistical modeling of strength and environmental and cost analyses. (February 2020)

• Record Type: Journal Article
• Authors: Perez-Cortes, Pedro; Escalante-Garcia, J. Ivan
• Is Part Of: Cement & concrete composites. Volume 106(2020)
• Publication Date: 2020-02
• Subjects: Geopolymer -- Alkali activated cements -- Limestone -- Metakaolin -- Surface response method -- Sustainability; Composite-reinforced concrete -- Periodicals; Concrete -- Periodicals; Composite materials -- Periodicals; Composites de ciment -- Périodiques; Béton -- Périodiques; Composites -- Périodiques; Béton léger -- Périodiques; Cement composites; Composite materials; Composite-reinforced concrete; Concrete; Lightweight concrete; Periodicals; Electronic journals; 620.135
• DOI: 10.1016/j.cemconcomp.2019.103450
• Languages: English
• ISSNs: 0958-9465

Abstract

Abstract: Alkaline binders of metakaolin (MK) and limestone (LS) are promising sustainable cementitious new alternatives; however, systematic studies are required to understand them to take them to industrial level. This study presents the modeling and optimization of strength using the surface response method of such binders with up to 80%LS and molar ratios of Na/Al = 0.5–1.86 and Si/Al = 1.81–3.13. A quadratic model (R-squared = 94.31%) indicated an optimal formulation of 32.32%LS, Na/Al = 1.34 and Si/Al = 2.96 with a predicted, and experimentally corroborated, 28-day strength of 70 ± 3.9 MPa, which was higher than references of 100%MK and blended Portland cement (BPC). The microstructural features were in agreement with the high strength. The analyses of cost, CO2 -emissions and energy demand indicated pastes of 100%MK are better than BPC only regarding CO2 -emissions, while blends with %LS>32.12% were better in all indicators relative to both of the former. As limestone is abundant, cheap, reduces alkali demand and do not require calcination, these binders are actually sustainable. Highlights: Alkaline binders of metakaolin with high limestone contents were statistically studied. The use of limestone reduced the water demand and the amount of alkalis. These are advantageous in strength, environmental impact and cost relative to Portland cement. The limestone load and Na/Al and Si/Al ratios, and their interactions, affected the strength. Optimized predicted and corroborated binders of 60%limestone reached ∼63 MPa at 28-day.