Chemical and mechanical activation of hybrid fly ash cement

Abstract

Hybrid fly ash cement is a binder with a composition between that of pozzolanic fly ash cement and alkali-activated fly ash cement. Its production requires less cement clinker than ordinary Portland cement, facilitating a much-needed reduction in the carbon dioxide footprint related to the production of high-clinker-containing cement. Research on activation methods is required to overcome the low early age strength and slow strength development in hybrid fly ash cements. In this study the activation of a South African siliceous fly ash (70%) for use along with Portland cement (30%) in a hybrid alkaline binder was investigated. Both chemical (the addition of sodium sulfate) and mechanical (milling) activation of fly ash was studied. The aim of this work was to develop a better understanding of the characteristics of compressive strength development of hybrid fly ash cement mortars over an extended curing period of up to a year. The results indicated that the combination of mechanical and chemical activation (sodium sulfate) can be considered a viable solution to improving early strength and slow strength development, so that hybrid cements are able to comply with the strength requirements of the BS EN 197 cement specification.

Portland Versus Alkaline Cement: Continuity or Clean Break: “A Key Decision for Global Sustainability”

“…For example, and to mention just a few cases: ✓ Alkaline activation (with salts such as carbonates, sulphates, silicates, etc.) of mixtures of blast furnace slag (AAS), fly ash and small proportions of clinker, at room temperature, can achieve compressive strengths of more than 40 MPa (more than enough for most of the applications in architecture and civil engineering) ( Donatello et al, 2013 ; Garcia-Lodeiro et al, 2013a ; Martauz et al, 2016 ; du Toit et al, 2018 ). ✓ For synthetic glasses, depending on the CaO content and the activation conditions, it is possible to generate materials with compressive strengths of between 10 and 60 MPa ( Buchwald, 2012 ; Garcia-Lodeiro et al, 2016a ; Ruiz-Santaquiteria et al, 2016 ).…”

“…✓ Alkaline activation (with salts such as carbonates, sulphates, silicates, etc.) of mixtures of blast furnace slag (AAS), fly ash and small proportions of clinker, at room temperature, can achieve compressive strengths of more than 40 MPa (more than enough for most of the applications in architecture and civil engineering) ( Donatello et al, 2013 ; Garcia-Lodeiro et al, 2013a ; Martauz et al, 2016 ; du Toit et al, 2018 ).…”

“…One-part AABs can be prepared with any of the precursors analyzed in sub-section 2.2, although according to the literature blast furnace slag, fly ash and calcined clay are the ones most commonly used ( Peng et al, 2017 ; Hajimohammadi et al, 2018 ). Similarly, any of the solid activators described in sub-section 2.3 and others not cited hereunder can be used to prepare such cements ( Abdollahnejad et al, 2019 ; Alahrache et al, 2016 ; Askarian et al, 2018 ; Askarian et al, 2019 ; du Toit et al, 2018 ). From the industrial standpoint, manufacture of these products calls for installing a mill (in the simplest case) or a comprehensive facility similar to the ones in place in PC plants with thermal processing functions for industrial-scale production of the flyglass precursor.…”

Machine-Learning-Aided Prediction of Flexural Strength and ASR Expansion for Waste Glass Cementitious Composite

“…According to the previous findings, the Na2SO4 reacts with Ca(OH)2 to generate gypsum and NaOH [60,61]. The gypsum further reacts with the aluminate in cement to generate ettringite (AFt), and NaOH participates in the reaction with Ca(OH)2 and WGP (or fly ash) to produce the additional gels [62,63]. This results in more hydration products compacting the WGP mortar structure and improving the flexural strength.…”

Characterisation of the Hydration Products of a Chemically and Mechanically Activated High Coal Fly Ash Hybrid Cement

“…The hybrids produced consist of 70% siliceous coal fly ash and 30% Portland cement. In turn this may aid to develop a better understanding of the improved mortar compressive strength characteristics of a hybrid coal fly ash cement hydrated for up to a year, which was investigated and published in previous work [24].…”