Studies On Relationship Of Carbonation With Hydration Of Steel Slag And Cement

The steel slag is waste generated in the steel refining process, with the development ofChina’s steel industry, the total amount of steel slag inceases rapidly. The chemical compositionof steel slag is complex and unstable, which contains f–CaO and f–MgO which result in badsoudness, therefore steel slag not been widely used. CO₂storage research mainly concentrateson the plant storage, marine storage and curing a variety of mineral storage.The study usingsteel slag and portland cement as raw materials for carbonation results in stored CO₂,generating a certain amount of CaCO₃, and explores the relationship between carbonation andhydration of steel slag and protland cement.The main contributions of this thesis are as follows:By ethanol–ethylene glycol titration, salicylic acid–methanol extraction and analyzingXRD patterns, TG–DTG curves, SEM photographs and hydration characteristics before andafter carbonation steel slag show that diffraction peaks intensity of f–CaO, C₂S and C₃S aredecreased, and the content of free–CaO decreases from3.92%to1.11%, and silicate phasecontent decreases from47.06%to14.38%after carbonating steel slag, which show thatf–CaO and silicate phase involve in the carbonation reaction. Carbonating steel slag generates15.95%CaCO₃which size is <1μm cube particles, soliding solution of Mg²⁺, and thedecomposition temperature is667℃. These show that generating CaCO₃is at a higher energystate; Carbonation promotes steel slag early hydration, but inhibits the late hydration.By analyzing activity index, hydration characteristics and XRD patterns, TG–DTGcurves and SEM photographs of hardened paste before and after carbonation steel slag showthat hydration properties of composite with carbonated steel slag are determined by thecontent of CaCO₃generated in carbonation and silicate in carbonated steel slag; CaCO₃generated in carbonation promotes the hydration of C₃S in the composite cementitiousmaterials, which reacts with C₃A in hardened paste generating calcium carboaluminatehydrate, and promotes generation of AFt and inhibits the transformation of AFt to AFm.Steel slag hydrates a certain time and is carbonated. By analyzing CO₂mass gain andXRD patterns of different hydration time steel slag and carbonated steel slag show that certain hydration time can promote the carbonation reaction, but hydration time is not easy for toolong, otherwise reduces the specimen carbonative effect.By ethanol–ethylene glycol titration, and analyzing mechanical properties and XRDpatterns, TG–DTG curves, SEM photographs and hydration characteristics before and aftercarbonation clinker and portland cement show that the f–CaO content decreases andgenerating cuboidal CaCO₃grain which size is <1μm after carbonating portland cement andclinker; The degree of carbonation increases with increasing water content; The generatingCaCO₃shell coats in surface of portland cement and clinker particles, which hindering themcontact with water to inhibit the early hydration. But generating CaCO₃involves in hydrationreaction, so carbonation has smaller effect on the post-hydration of portland cement andclinker.By designing orthogonal experiment to study carbonation process of portland cement.We composite carbonated cement with uncarbonated cement in1:1ratio to test mortarstrength. By analyzing hydration characteristics of pure cement, carbonated cement andcomposite cement, XRD patterns and SEM photographs of hardened paste show that theoptimal carbonation condition is water content is0.2%, CO₂gas pressure is0.2MPa,carbonation temperature is25℃and carbonation time is30min; Water content andcarbonation temperature have a significant influence on3d compressive strength ofcomposite, but the larger influence of water content;3d and28d compressive strength ofcomposite is higher than that of pure cement, and the strength level increases from42.5to52.5; Generating CaCO₃promotes the early hydration of portland cement; Hardened pastegenerates calcium carboaluminate hydrate and precipitates CaCO₃grain which size is1μm.