Abstract
Due to the low hydration activity and poor volume stability, extensive steel slag utilization is restricted. In this paper, the hydration process and microstructure of alkali-activated materials with steel slag as a cementitious material and fine aggregate were studied. The phase composition and micro-morphology of hydration products were measured using XRD, NMR and SEM. The response relationship between microstructure and mechanical properties during hydration was revealed. The results show that the main hydration products of the alkali-activated steel slag powder-granulated blast furnace slag powder cementitious system are Ca(OH)2 and calcium aluminosilicate hydrate (C-A-S-H) gel. With the progress of hydration, the amount of calcium silicate hydrate (C-S-H) gel and the average molecular chain length increase, Al[4]/Si decreases, while C/S increases first and then decreases, and the structure of cement paste becomes much more compact. The interface between steel slag sand and cement paste is denser than that of river sand, since the hydration occurs on the surface of steel slag sand, which leads to the formation of C-A-S-H gel and Ca(OH)2. As a result, the compressive strength of concrete prepared by steel slag sand is higher than that of river sand with the same mix proportion.
Highlights
Steel slag is mainly composed of impurities in steelmaking charge, slagging materials, eroded furnace linings and oxides of many elements formed by oxidation in the furnace charge [1,2]
There is no obvious interface between mortar cement paste and steel slag sand when steel slag sand is used as a fine aggregate in samples cured for 28 days from Figures 12 and 13
There is no obvious interface between mortar cement paste and steel slag sand when steel slag the amount of calcium silicate hydrate (C-S-H) (C-A-S-H) gel increases, and other substances are wrapped up and sand is used as a fine aggregate in samples cured for 28 days from Figures 12 and 13
Summary
Steel slag is mainly composed of impurities in steelmaking charge, slagging materials (limestone, iron ore, dolomite, etc.), eroded furnace linings and oxides of many elements formed by oxidation in the furnace charge [1,2]. Steel slag has certain cementitious activity and is often used as a mineral admixture to replace part of cement. Hisham Qasrawi et al [14] used steel slag with high stability to replace part of ordinary river sand as an aggregate to prepare concrete. Steel slag powder contains f-CaO, active RO phase and other components, which will produce volume expansion in the process of a hydration reaction [9,16,17,18], compensating the shrinkage of concrete and reducing or even replacing the use of an expansion agent in concrete [19]. The phase composition and micro-morphology of hydration products were analyzed by XRD, NMR and SEM, and the hydration development process was discussed, revealing the corresponding relationship between microstructure and macroscopic properties It would provide a theoretical basis for the large-scale and high value-added utilization of steel slag
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