The Effect Of Subsequent Moist Curing On The Hydration Of Cement In Concrete After CO₂Curing

Carbon dioxide (CO2) is the dominant greenhouse gas resulting from manyanthropogenic activities, mainly combustion of fossil fuels. One of the strategies tomitigate CO2emissions is considered to be carbon dioxide capture and storage (CCS).The current storage methods include enhanced oil recovery, underground geologicalstorage, disposal in deep oceans, and ex situ mineral carbonation of abundant metaloxide minerals such as olivine, serpentinite and wollastonite. CO2curing of concretecan be used as a mineral sequestration method with the advantage of producing avalue-added concrete product. During CO2curing of concrete, it is CO2that reactswith cement. After the reaction, the CO2is stored as a solid calcium carbonate inconcrete construction products.This paper’s achievements mainly focused on the effect of subsequent moistcuring on the properties and microstructure of concrete:By researching the effect of remaining w/c ratio on CO2curing process of the dryand hard concrete, it was found that the remaining w/c ratio was the key factor to gainthe best CO2curing degree and compressive strength. Excessive water in freshcompacted specimens or concrete blocked the pores and prevented the penetration ofcarbon dioxide. On the other hand, lack of water inside concrete had negative effectson reaction, since the CO2curing reaction needed water as solvent.According to the temperature curve, its peak temperature preceded others whenthe remaining w/c was about0.16~0.20, which was very proper for the carbonationreactions.Main products and micro mechanism of specimen before and after CO2curingprocess with advanced testing measures such as TG and IR were investigated. Theexperiment results showed that during the CO2concrete curing process, mainsubstances reacting with CO2were cement clinkers, and the reaction products aftercuring were calcium carbonate and silica gel. The specimen with higher CO2curingdegree produced carbonates with better crystallinity. After CO2curing, the totalporosity and portion of capillary pore (50-1000nm) of concrete decreased evidently.Effect of subsequent moist curing on the compressive strength andmicrostructure of concrete with w/c ratio of0.11,0.18and0.25were investigated.The result showed that with the prolonging of curing time, the compressive strengthincreased continuously. The compressive strength increased fast in the concrete with w/c ratio of0.25, though its final strength was lower than the blank one. According tothe SEM micrographs and EDS analysis, the main products during moist curing wereetteringite, C-S-H gel and calcium monocarbonaluminate hydrate.Effect of subsequent moist curing on the microstructure of mortar with w/c ratioof0.11,0.18and0.25were investigated. The study found out that during thesubsequent hydration, the calcite forming during CO2curing reacted with C3A andformed calcium monocarbonaluminate hydrate. Meanwhile, the Ca(OH)2was notdetected due to its reaction with silica gel. It also can be found that the porosity ofmortar decreased after subsequent hydration and the pore structure in the mortarspecimens with w/c ratio of0.25developed better.