The Physical Microstructure of Reactive MgO Cement Pastes Subjected to High CO_2 Concentration

【Author】

Liwu Mo;Daman K.Panesar;

【Abstract】

<正>Reactive MgO cement(RMC) is a low-carbon cementing material,which is usually prepared by mixing a relatively large amount of reactive MgO,industrial wastes and a relatively small amount of Portland cement.In contrast to conventional cement,RMC gains its mechanical properties as a result of carbonation reactions.This study investigates RMC mixtures which consist of 20-40%reactive MgO,0-40%slag and general use Portland cement,subjected to 99.9%concentration of CO_2 curing.The microstracture is characterized based on various tests including:DVS(Dynamic Vapor Sorption),SEM(Scanning Electronic Microscope) and BSEM(Back-scattered Electronic Microscope).Based on the results,the carbonation mechanism is discussed Results indicated that,the carbonation of C-S-H leads to the formation of amorphous CaCO_3 as well as SiO_2 gel,which slightly increases the volume of meso-pores ranging from O-11nm as well as the corresponding specific surface area.In addition to MgCO_3.3H_2O,a large amount of inter-connected round shape Mg-Ca-bearing carbonates were formed due to carbonation of RMC,which contributed to the densiftcation of cement pastes.The carbonation of RMC probably proceeds mainly through the crystallization in the supersaturated solution containing both Ca~(2-) and Mg~(2-) in the RMC pastes when subjected to CO_2 curing. Originality Reactive MgO cement(RMC) can gain similar or superior mechanical performance,in comparison to conventional concrete,after carbonation owing to the formation of carbonates.The mechanical properties of RMC i.e.microhardness,compressive strength are closely related to the morphology of carbonates as well as the pore structures.Since under normal condition with relatively low concentration of CO_2,the carbonation of RMC is extremely slow,this study employs high concentration of CO_2,99.9%,to accelerate the carbonation.This study aims to characterize the pore structure by using Dynamic Vapour Sorption(DVS) method and investigate the morphology of carbonates formed in RMC pastes after exposure to the high concentration of CO_2 via SEM and BSEM.The investigation of microstructure of carbonated RMC pastes provides useful information for understanding the properties as well as the accelerated carbonation mechanism of RMC.

【Keywords】

reactive MgO;;carbonation;;microstructure;;CO_2 curing;;carbonate

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