Abstract
This contribution discusses the carbon capture and utilization (CCU) approach based on CO2 mineralization of cement paste from recycled concrete as new approach to capture CO2 and significantly contribute to the reduction in CO2 emissions associated with cement production. The current literature suggests that all CO2 released from the decomposition of limestone during clinker production can be sequestered by carbonation of the end-of-life cement paste. This carbonation can be achieved in a few hours at ambient temperature and pressure and with a relatively low CO2 concentration (< 10 %) in the gas. The carbonation of cement paste produces calcite and an amorphous alumina-silica gel, the latter being a pozzolanic material that can be utilized as a supplementary cementitious material. The pozzolanic reaction of the alumina-silica gel is very rapid as a result of its high specific surface and amorphous structure. Thus, composite cements containing carbonated cement paste are characterized by a rapid strength gain. The successful implementation of this CCU approach relies also on improved concrete recycling techniques and methods currently under development to separate out the cement paste fines and such. Full concrete recycling will further improve the circular utilization of cement and concrete by using recycled aggregates instead of natural deposits of aggregates. Although the feasibility of the process has already been demonstrated at the industrial scale, there are still several open questions related to optimum carbonation conditions and the performance of carbonated material in novel composite cements.
Highlights
The use of concrete has been growing continuously in the 20th and 21st centuries
A solution based on carbonation of the cement paste from old demolished concrete and its application as an supplementary cementitious material (SCM) has been described as a novel carbon capture and utilization process
Recent studies indicate that the process of enforced carbonation of cement paste can be conducted under mild conditions and may be upscaled to an industrial scale
Summary
The use of concrete has been growing continuously in the 20th and 21st centuries. Today, concrete is the most widely used man-made material and the most important material of our built environment [1]. Lu et al [29] and Zajac et al [30,31,32,33] have applied CO2 mineralization to modify the recycled cement paste into a new supplementary cementitious material (SCM) These exploratory studies show that most of the CO2, originally released by limestone calcination during clinker production, can be sequestered by carbonation of the RCP, provided that the paste is separated from the sand and aggregates. The method is schematically illustrated, and it relies on improved concrete recycling where the fines rich in cement paste are partly separated out from sand and coarser aggregate These fines are wet carbonated, producing a new material that can be utilized in the production of new composite cements [33]. The carbonated alumina-silica gel is characterized by a faster pozzolanic reaction as compared to fly ashes
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