Abstract
In this study, we replaced 30% of the cement with steel slag to prepare binding material; additionally, small amounts of CaCO3 and CaSO4·2H2O were added. This was done to study the compound effect of CaCO3 and CaSO4·2H2O on the strength of steel slag-cement binding materials. The hydration degree of the steel slag cementitious material was analyzed by XRD, TG and SEM. The results showed that the optimum proportions of CaCO3 and CaSO4·2H2O were 3% and 2%, respectively. Compared with the steel slag-cement binders without adding CaCO3 and CaSO4·2H2O, the compressive strength increased by 59.9% at 3 days and by 17.8% at 28 days. Acting as the nucleation matrix, CaCO3 could accelerate the hydration of C3S. In addition, CaCO3 was involved in the hydration reaction, generating a new hydration product, which could stably exist in a slurry. Meanwhile, CaSO4·2H2O could increase the number of AFt. The compound effect of CaCO3 and CaSO4·2H2O enhanced the intensity of steel slag-cement binding materials and improved the whole hydration behavior.
Highlights
Steel slag is a by-product in steel production, which makes up approximately 10~15% of crude steel output 1
This synergy is mainly because the presence of CaCO3 can inhibit the conversion of ettringite (AFt) into the single type sulfur aluminate (AFm) 19, since CaCO3 reacts with C3A, generating a single carbon aluminate (Ca4Al2O6·CO3·11H2O); when CaSO4·2H2O consumption has finished, the remaining C3A in system that is intended for amount of ettringite (AFt) to react will reduce relatively, as a result of inhibiting the conversion from AFt to Afm, improving the strength of the complex binder
1) CaCO3 can act as the crystal nucleus of hydration products, and contribute to accelerating the hydration of C3S, thereby increasing the early strength of the composite binder
Summary
Steel slag is a by-product in steel production, which makes up approximately 10~15% of crude steel output 1. 70% of China’s steel slag is converter steel slag, the chemical and mineral composition of which is similar to that of Portland cement clinker with gelling properties. This steel slag has great potential for application in cement. Steel slag can show good cementitious behaviors with a chemical excitation agent and using the steel slag to replace part of cement can prepare gelling materials that satisfy the mechanical properties and durability of the specific requirements. To increase the application of steel slag as a mineral admixture for binding materials, it is necessary to weaken its negative effect on the strength and enhance its ability to improve the hydration behavior of cementitious
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