养护制度对混凝土微结构形成机理的影响进展

Review on the Microstructure Formation Mechanism in Concrete Material Under Different Curing Regimes

养护制度是影响混凝土微结构形成的关键因素,进而决定了混凝土的性能。早在20世纪60年代,国内外学者就尝试通过控制养护温度或湿度来改善混凝土的性能,但由于控制变量的单一性,其对混凝土性能的提升效果有限。随着现代混凝土技术的发展,同时控制养护温度、湿度,甚至压力的蒸汽养护与蒸压养护应运而生。蒸汽养护和蒸压养护主要通过生成大量高密度C-S-H凝胶来为混凝土提供强度,且随着蒸压养护的持续,C-S-H凝胶向强度高、密度大的托勃莫来石转变,促进混凝土强度进一步增长。然而,蒸汽养护与蒸压养护在快速提高混凝土强度的同时,也会使混凝土产生孔隙率增大、孔径粗化及界面过渡区性能变差等问题,从而影响混凝土的长期耐久性。为此,常采用降低水胶比、掺加矿物掺合料、延长养护时间、二次养护等措施,来改善蒸汽养护与蒸压养护混凝土的界面过渡区性能和孔隙结构,从而提升混凝土微结构的稳定性。本文在综述标准养护、蒸汽养护和蒸压养护对混凝土水化产物的组成与形貌、界面过渡区和孔隙结构影响的基础上,归纳了不同养护制度下改善混凝土界面过渡区和孔隙结构的有效措施,分析了不同养护制度提升混凝土微结构稳定性的作用和机理,以期为混凝土养护制度的选择提供参考。最后,指出了不同养护制度下超高性能混凝土微结构形成与演变研究的不足。

Curing regime is the key factor that affects the microstructure formation in concrete and further determines the performance of this material.As early as the 1960s,scholars at home and abroad started to improve the concrete performance through the variation of curing temperature and humidity.However,due to the singleness of this variable,its improvement on the concrete performance is limited.With the advent and deve-lopment of modern concrete technology,curing techniques such as steam and autoclaved curing emerges,which meet the requirement to simultaneously control the curing temperature,humidity and even pressure.Steam curing and autoclaving can promote the rapid growth of concrete strength,meeting the early strength requirement in engineering and reducing the construction period.At the micro-level,steam curing and autoclaving can accelerate the C-S-H gel formation in concrete,which contributes to its strength development at the macro-level.After longer time in autoclaved curing environment,C-S-H gel in concrete can transform to tobermorite crystals with high-strength and density,which further improves the mechanical strength of concrete.However,during the fast strength growth for concrete in steam and autoclaved curing,it also undergoes the problem of large porosity,increa-sing number of micro-cracks and decreasing performance in the interface transition zone,which could affect the long-term durability of concrete.By the measures of decreasing water to binder ratio,adding mineral admixtures in cement-based material,prolongating curing time and exerting secondary curing,the performance of interfacial transition zone and pore structure in concrete can be improved,thereby improving the microstructural stability of concrete under steam or autoclaved curing.This paper reviews the influence of curing regime(standard curing,steam curing and autoclaved curing)on the composition and morphology of hydration products,interfacial transition zone structure and the pore structure in concrete material.Based on the review,effective measures to improve the interfacial transition zone and pore structure of concrete have been concluded and the mechanisms for these measures to improve the microstructural stability of concrete under different curing regime have been analyzed,which can provide references for the selection of curing regime for concrete.Finally,the deficiency in the microstructure formation and evolution of ultra-high performance concrete(UHPC)under different curing regimes have been summarized.