Study On Middle Or Low-Strength Steel Slag Anti-cracking And Impermeable Concrete

Though the application of the middle or low-strength mass concrete has been used widely in the crossing river tunnel and the anchor of bridge, there have been very serious phenomena of buildings cracking and leakage in many old concrete constructions and even recent concrete constructions. So, it is very important to enhance the quality of concrete anti-cracking and impermeable property.This paper analyses the problem of concrete cracking and leakage, and set up the model of the middle or low-strength steel slag anti-cracking and impermeable concrete (ACIC) on the base of the analysis. The four principles of water permeable resistance character, volume stability character, toughness and anti-chemical corroded character have been put forward for raw materials selection and durability design of ACIC, ACIC is designed by the theory of composite material and the theory of fiber-reinforced, and two series of ACIC, such as fly ash series and steel slag series, have been manufactured by means of mineral admixture, hybrid fiber and chemical admixture. Hydrating heat, macro-mechanics quality, durability and microstructure of the ACIC have been researched.The result of macro-quality experiments show: mineral admixtures markedly slow the hydrating velocity of cement slurry, decrease and delay the hydrating max-temperature, in which steel slag is more effective; expansive agents compensate concrete shrinkage, enhance the concrete dense degree, strengthen the interfacial layer between fiber and cement matrix and improve the physical mechanics qualities of ACIC; minimal admixtures markedly improve the concrete workability property, increase the concrete later intensity & density and the capability of anti-chemical attack and anti-permeability; hybrid fiber reinforces the toughness of obviously ACIC by the means of anti-cracking effect of fiber with different sizes and different properties in the corresponding construction levels. The toughness experiment of ACIC shows: minimal admixtures are not helpful to the concrete toughness, but hybrid fiber can enhance the limit energy of concrete deterioration, the compressive and tensile strengths and toughness index, which improves the ACIC toughness. The expansive experiment shows steel slag cancompensate the concrete shrinkage during a long time and hybrid fiber restrains the concrete shrinkage. The impermeability experiment under the conditions of high hydraulic pressure in long time shows that the impermeability grade of ACIC is further beyond P40 and that the steel slag series of ACIC is better than the fly ash ones.The process of structure formation of ACIC is studied by means of XRD, SEM and so on. Meanwhile, the cause and mechanism of the ACIC compensating shrinkage have been analyzed, and the composition, structure and the rule of durability influence of ACIC have also been proved up. It is showed by test that the expansive agent hydrates to create a greet deal of ettringite (AFt), which is of pin stick shape and put up complex structure; the mineral admixture leads to the thinning of pore size of cement paste, compact of hydration product phase, improvement of interface transition between aggregate and cement stone, which results in the improvement of anti-cracking and impermeable quality of ACIC.