Carbonation Processing and Strength Evolution of Portlandite-Based Cementing Systems | AIChE

Carbonation Processing and Strength Evolution of Portlandite-Based Cementing Systems

Authors 

Sant, G. - Presenter, University of California, Los Angeles
Mehdipour, I. - Presenter, Laboratory for the Chemistry of Construction Materials (LC2), UCLA
La Plante, E., University of California, Los Angeles
Falzone, G., University of California, Los Angeles
Pilon, L., University of California, Los Angeles
Neithalath, N., Arizona State University
Innovative binders based on portlandite (Ca(OH)2) compositions have the potential to take up carbon dioxide (CO2), e.g., from flue gas streams, and form calcium carbonate compounds which offer cementitious attributes. But, carbonation processing of such materials requires elaboration of how complex pore networks, and water saturation therein affect CO2 transport and uptake. Therefore, this paper elucidates how the creation of air-filled porosity resulting from processing conditions regulates CO2 mineralization and carbonation strengthening in portlandite-enriched cementing formulations. Toward this end, the relation between processing and carbonation kinetics are elucidated and linked to strength development and microstructure evolution resulting from in situ CO2 mineralization and subsequent pozzolanic reaction. In general, the extent of air-filled porosity scales with carbonation kinetics so long as a critical liquid water saturation (Sw,c) is exceeded; below which carbonation is sharply hindered. It is also shown that the formation of hydration products strongly hinders carbonation by: (i) decreasing the CO2 transport properties, and, (ii) reducing the exposed surface area of carbonatable reactants through surface coverage. Finally, the extent of carbonation is correlated with strengthening vis-à-vis uncarbonated systems that utilize traditional silicate cement hydration. An unprecedented level of strengthening – of ≥ 3.5x – is achieved for dry-cast (carbonated) portlandite mortars. On the basis of these concepts, the processing-carbonation kinetics relations in portlandite-enriched cementing systems enable exploiting prehydration, in situ CO2 mineralization, and pozzolanic reaction, featuring enhanced early- and later-age strength development. These outcomes offer new insights that are needed to create novel pathways for utilizing in situ CO2 mineralization as a means for designing carbonate-based, CO2 sorbing cementing agents for construction applications.