Carbonate-bonded construction materials from alkaline residues

Peter Nielsen,Mieke Quaghebeur,Giulia Costa,Ruben Snellings,Renato Baciocchi

doi:10.21809/rilemtechlett.2017.50

Abstract

Accelerated carbonation is a rapidly developing technology that is attracting attention as it uses CO2 as a binder to make construction materials. Originally stemming from geochemical and environmental research into CO2 sequestration or waste remediation, accelerated carbonation has been developed into a technology that enables to transform alkaline precursors into products that meet technical requirements for use as aggregates or shaped blocks. Alkaline precursors can be manufactured from primary resources or derived from industrial residues: a.o. metallurgical slags, incineration ashes and concrete recycling residues are prone to carbonate under controlled conditions. Moist carbonation of shaped Ca-silicate rich precursors at elevated curing temperature and CO2 concentration or pressure has delivered the most promising results so far. This letter presents an overview of current accelerated carbonation approaches to make carbonate bonded construction materials from alkaline residues. The general carbonation mechanism is explained and two application routes are exemplified: i.e. production of lightweight aggregates and compact blocks by accelerated moist carbonation.

Highlights

Among low carbon cements, by far the greatest CO2 reduction potential is offered by cements that sequester CO2 as solid carbonates as part of their solidification process [1,2]
In case carbonation is desirable kinetic barriers that slow down the natural carbonation process need to be overcome by applying elevated temperature and CO2 concentrations in curing chambers or autoclaves
By optimizing the particle packing and compacting pressure EAF steel slag compacts (300x100x50 mm) were produced with compressive strengths up to 134 MPa after carbonation and that complied to environmental leaching limit regulations [18]

Summary

Introduction

By far the greatest CO2 reduction potential is offered by cements that sequester CO2 as solid carbonates as part of their solidification process [1,2]. In case carbonation is desirable kinetic barriers that slow down the natural carbonation process need to be overcome by applying elevated temperature and CO2 concentrations in curing chambers or autoclaves. Chemicals such as NaOH can be added to accelerate and enhance the process even further [7]. In principle similar mechanisms apply for carbonation of different precursors, this review will focus on Ca(Mg) silicate based precursors, mainly because most recent progress was made in this area. The carbonation mechanism, potential precursors and examples of specific product developments are treated

Carbonation mechanisms

Precursors and CO2

Case 2

Findings

Conclusions and perspectives