| Alkali-activated binding material is a new kind of building materials, which has high early strength, and excellent performance in frost resistance. Alkali-activated binding material has been received increasing attention for the reason that it uses solid wastes as its main raw materials, which can save energy and resources. However the behavior of easy cracking under dry condition and insufficient research on durability restrict its wide application. Researches show that alkali-activated binding material concrete has a quick speed of carbonation, for the reason carbonation can reduce pH of pore solution, which may increase the risk of damage caused by rusting of the steel bar. Concrete on service may suffer from the attack of sulfate from sea water and underground water. Due to the alkali-activated binding material does not contain calcium hydroxide, its magnesium sulfate erosion resistance ability is poor. Whether the above problems can be overcome is a key point of the application of alkali-activated concrete.Based on slag as main raw materials, this paper mainly studies the alkali content, curing age, activator type, on the influence of carbonation depth of alkali-activated slag(AAS)concrete. The hydration products, carbonation product and their morphology of AAS paste made by different activator are analyzed. Crack resistance, volume stability, porosity, the non-evaporation water content, the influence of carbonization depth was studied when addition active MgO in AAS system. Analyzes the hydration products, carbonation product and their morphology of AAS paste mixed with MgO. And put forward the improvment mechanism of MgO. Studied influence of alkali content, activator type, content of MgO on the resistance of concretes when immersed in Na2SO4 and MgSO4 solution, analyses the changes of compressive strength and weight, the change of products of AAS paste under MgSO4 solution with different MgO content. Main research results are as follows:(1)Extend curing time can improve the carbonation resistance of concrete. High alkali content of concrete, carbonate slower in the early age, faster than low alkali content in late age. Using NaOH as activator(AASN), carbonation depth is less than sodium silicate at 28 and 56 d. Hydrotalcite can be observed in the products of AASN paste. After carbonation AASN generated grain huge gaylussite, while nahcolite growth after carbonation when use sodium silicate. After carbonization concrete strength has a slightly increase, with a little decline compared with the blank sample.(2)Increase the reactivity of MgO, accelerate its hydration rate and improve the performance of AAS crack resistance. Under the condition of natural curing, when mixed with 3% MgO, the volume stability and resistance to chloride ion permeability of concrete is best.(3)Adding MgO into AAS paste, reduce its water absorption, and enhance the content of non- evaporation water. With the increase of MgO content, the carbonation resistance of concrete increases. The hydration of MgO almost finished and the content of hydrotalcite-like incresed when adding 3% MgO in AAS at 28 d. The products after carbonation is natron when adding MgO, then transform to nahcolite in late age.Hydrotalcite-like can absorb CO2, will decomposed when carbonate seriously. The residual MgO can be directly involved in the carbonation reaction. Adding MgO delayed the decomposition of C-S-H gel and promoted the formation of aragonite.(4)After soaking in Na2SO4 and MgSO4 solutions, wet weight of concrete have no obvious change, dry weight increased with immersion time extended. Using Na2SO4 and MgSO4 during the test have slightly effects on compressive strength. |
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