Formulation of low clinker blended cements and concrete with enhanced fresh and hardened properties

Federica Boscaro,Marta Palacios,Robert J Flatt

doi:10.1016/j.cemconres.2021.106605

Abstract

Blended cements appear as the most promising way to massively produce cements with reduced environmental footprints. However, considering the generally lower early mechanical performance of highly blended cements, chemical admixtures are increasingly relied upon to increase early strength. However, in many cases this can negatively impact other properties as rheology and durability.This paper proposes an approach to formulate low clinker cements and concrete using moderate alkali activation or gypsum to enhance early and long-term compressive strength, without inducing excessive alkali-silica reaction (ASR) expansion. It examines blended cements containing burnt oil shale along with limestone and fly ash or slag as supplementary cementitious materials. It optimizes the combination of polycarboxylate ether (PCE) superplasticizers with the strength enhancers. Along with the use of Ca(NO3)2 to drive PCE adsorption, this provides good rheology control, increased early and long-term compressive strength, as well as acceptable ASR expansion in cements with only 50% clinker.

Highlights

Portland cement production is responsible for about 5–8% of manmade CO2 emissions [1]
This may be related to the lower solubility of gypsum in com parison with Na2SO4, that would lead to a lower concentration of sulfate ions in solution, which may compete with polycarboxylate ether (PCE) on being adsorbed onto cement surfaces
In the present paper we presented a straightforward approach to formulate low clinker cements and concrete in presence of multiple chemical admixtures

Summary

Introduction

Portland cement production is responsible for about 5–8% of manmade CO2 emissions [1]. One of the most effective solutions to sub stantially reduce its environmental footprint is clinker replacement with supplementary cementitious materials (SCMs) [2]. Much research has been conducted on identifying new sources of SCMs [3], on combining several types of SCMs and on investigating their effects on cement and concrete properties [4]. This led to the development of new binders among which calcined clay limestone cements (LC3) represent a prom ising solution [5]. Common SCMs show slower reactivity than alite, which results in lower early compressive strength of highly substituted binders [6]. The use of chemical admixtures is gener ally seen as an essential vector to increase the performance of low clinker cements and concrete [7]

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Methods

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Discussion

Conclusion