| Slag is widely used in the modern concrete field as a kind of mineral admixtures. Studies on reinforcement mechanism of slag in concrete mainly embodied in three aspects,including micro-aggregate effect, micro-crystals nucleus effect and activity effect. Micro-aggregate effect makes structure of concrete the most compact, micro-crystals nucleus effect decreases the size of harmful crystal in ITZ, activity effect increase content of gel. And all the three effects reinforce compactness of concrete. This paper focuses on slag chemical composition and study the role of slag hydration products, especially LDHs type in resistance to sulfate erosion. Achievements in this paper will explore new approaches for concrete anti-corrosion technology.Pure slag vitreous of which chemical composition can be controlled was prepared by high temperature melting- water quench cooling method based on the three-dimensional network structure theory. The relationship between chemical composition of slag and morphology, type and quantity of hydration products is studied. Content of LDHs type hydration products is proportional to the content of magnesium in slag. Sulfate erosion resistence of complex binder with fly ash, slag and clinker experienced dry-wet cycle in sodium sulfate solution was studied. Microscopic mechanism is analyzed utilizing XRD, SEM and XEDS. Studies have shown that:1) Vitreous with very small amounts of silicate mineral crystal is obtained by a mixture of CaO, SiO2, Al2O3 and MgO through high temperature melting and water quench cooling, which is called water quench vitreous of which chemical composition is designed by calculation of raw material ratio. Water quench vitreous is used to imitate blast-furnace slag. Number of non-bridging oxygen can be used as the evaluation index of activity of synthetic slag, due to its reflection of polymerization degree of vitreous network structure. Activity of slag is not only affected by the vitreous polymerization degree, but also had a great deal with its fineness.2) Main hydration products of water quench vitreous is C-S-H gel and Mg-Al type hydrotalcite(a kind of LDHs). With the improvement of magnesium content of slag, the content of LDHs hydration products increases, and not altered obviously after 28 day ages.3) Sulfate erosion resistance of complex binder with water quench vitreous is better than that of control group. With the time of dry-wet circulation increase, specimen showed an expansion after shrinkage, quality of specimen decreased after increased, water absorption continue to rise, while the strength continue to decrease.4) Compared with alkali-activated slag, Mg-Al type hydrotalcite in hydration product of complex binder with fly ash, slag and clinker is not easily observed due to its less content and coexist with C-S-H gel. Content of Ca(OH)2 decrease when cementitious material is under attack with sulfate, and the product of sulfate erosion is mainly needle-stick like ettringite(AFt). |
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