Design of High Volume CFBC Fly Ash Based Calcium Sulphoaluminate Type Binder in Mixtures with Ordinary Portland Cement.

Peeter Paaver,Oliver Järvik,Kalle Kirsimäe

doi:10.3390/ma14195798

Peeter Paaver, Oliver Järvik + Show 1 more

Open Access

https://doi.org/10.3390/ma14195798

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Journal: Materials	Publication Date: Oct 3, 2021
Citations: 3	License type: CC BY 4.0

Affiliation: University of Tartu, Tallinn University of Technology

Abstract

Growing concerns on global industrial greenhouse gas emissions have boosted research for developing alternative, less CO2 intensive binders for partial to complete replacement of ordinary Portland cement (OPC) clinker. Unlike slag and pozzolanic siliceous low-Ca class F fly ashes, the Ca- and S-rich class C ashes, particularly these formed in circulating fluidised bed combustion (CFBC) boilers, are typically not considered as viable cementitious materials for blending with or substituting the OPC. We studied the physical, chemical-mineralogical characteristics of the mechanically activated Ca-rich CFBC fly ash pastes and mortars with high volume OPC substitution rates to find potential alternatives for OPC in building materials and composites. Our findings indicate that compressive strength of pastes and mortars made with partial to complete replacement of the mechanically activated CFBC ash to OPC is comparable to OPC concrete, showing compared to OPC pastes reduction in compressive strength only by <10% at 50% and <20% at 75% replacement rates. Our results show that mechanically activated Ca-rich CFBC fly ash can be successfully used as an alternative CSA-cement type binder.

Highlights

Production of ordinary Portland cement (OPC) emits a large fraction, about 8%, of the anthropogenic greenhouse gases [1]
The reduction of the carbon dioxide emissions in cement clinker production and the development of low‐carbon binders have become the priorities of the cement industry
Fly‐ash‐based binders are considered as viable alternatives to CO2‐extensive cement clinker systems, the use of waste ash produced in circulating fluidised bed com‐

Summary

Introduction

Production of ordinary Portland cement (OPC) emits a large fraction, about 8%, of the anthropogenic greenhouse gases [1]. Calcium sulphoaluminate (CSA) and Ca-sulphoaluminate-belite (CSA-C2S) cements are increasingly coming into focus as sustainable, less CO2 intensive alternatives to OPC [3,4,5,6,7,8]. CSA cements exhibit mechanical-chemical properties similar or even exceeding that of the OPC—e.g., in terms of rapid strength development, low shrinkage and chemical durability—that has allowed their use in different construction applications replacing or along with OPC [5,9,10,11], and in geotechnics for weak soil stabilisation [12,13]. CSA cements are composed mainly of ye’elimite [C4A3-Ca4 (AlO2 ) SO3 )], belite (C2S—dicalcium silicate), and gypsum (CaSO4 2H2 O), and the main hydration products providing the cementation are ettringite (C6A2H26Ca6 Al2 (OH) (SO4 )3 ·26H2 O) and nanocrystalline Al(OH) , depending on the ye’elimite to belite and calcium sulphate ratio, monosulphate, C–S–H gel-like phase, strätlingite and/or hydrogarnet can form [8,14,15,16]

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