【作者】 黄磊；

【导师】 阎培渝；

【作者基本信息】 清华大学 ， 土木工程， 2020， 博士

【摘要】 由于担忧混凝土的碱骨料反应,以及对水泥与外加剂的相容性和混凝土开裂敏感性的不利影响。近年来对于水泥中的碱含量限制较为严格。这对于充分利用低品位的原料不利,无助于水泥工业的可持续发展。由于现代水泥和混凝土组分和性能的变化,碱在水泥水化过程中的作用机理需要诚信审视,给予充分而全面的了解,以便合理使用不同碱含量的水泥。本论文使用不同厂家生产的不同碱含量的硅酸盐水泥熟料,外掺一定量的硫酸钾,制备了一系列碱含量在较大范围变化的硅酸盐水泥,系统研究了碱对于水泥水化过程的影响。重点关注了不同碱含量的水泥的水化动力学、水化速率和水化产物、浆体孔溶液组成及其影响因素;还对碱含量对于水泥与外加剂的相容性、水泥强度发展规律的影响进行了研究。根据不同厂家生产的硅酸盐水泥熟料分析结果,熟料中碱含量高会抑制C₃S晶体的发育。熟料不同矿相中碱的分布存在明显差异,K的偏析更严重。水泥熟料中的硫酸碱在水泥拌水后迅速溶出,在10 min后浓度趋于稳定。K离子溶出率远高于Na离子。水泥熟料中的硫碱比越高,碱的溶出率越高。水泥中可溶性碱的溶出直接改变孔溶液组成,通过对相关物质饱和度的影响,改变C₃A与C₃S的溶解,CSH的沉淀及CH与AFt的生成。高碱含量抑制了水泥熟料中C₃A的溶解与AFt的生成,促进了C₃S的溶解与CH的生成,提升了水泥的早期水化程度。随着碱含量的增加,对CSH的影响由对其生长速率的促进转变为同时对成核的促进,对应着水泥水化反应的加速和诱导期的缩短。高碱含量对水泥与聚羧酸减水剂的相容性产生不利影响。碱含量增加改变了浆体孔溶液组成,提升了水泥浆体的Zeta电位,导致部分聚羧酸减水剂吸附于硅酸盐相表面的扩散层,难以有效发挥吸附-分散作用。孔溶液中的SO₄^2-与聚羧酸减水剂在铝酸盐相表面的竞争吸附,进一步抑制了聚羧酸减水剂的吸附-分散作用的发挥。低C₃A水泥与聚羧酸减水剂的相容性对碱含量的变化更为敏感。从水泥基材料工作性的角度出发,对低C₃A水泥碱含量的控制应引起特别注意。对于低碱水泥,适量的外掺碱能延缓浆体微结构的形成,延缓水泥凝结。外掺碱（K碱）含量较高时,形成钾石膏晶体,促进浆体凝结。高碱含量在早龄期能促进浆体孔隙结构细化,使水泥强度提高;但在后期无助于硬化浆体的孔隙结构优化与水泥强度发展。更多还原

【Abstract】 Due to concerns about the alkali aggregate reaction of concrete,the adverse effects on the compatibility of cement and additives as well as on the cracking sensitivity of concrete,the content of alkali in cement is restricted strictly in recent years.This goes against the full use of low-grade raw materials and the sustainable development of the cement industry.Because the compositions and properties of cements and concretes vary greatly recent years,the effecting mechanism of alkali on the hydration process of cement needs to be examined renewedly and recongnized comprehensively,for a reasonable use of cements with different alkali content.In this thesis,Portland cement clinkers with different alkali content produced by different manufacturers were used,a certain dosage of potassium sulfate were added to prepare a series of Portland cements with a large range of alkali content.The influence of alkali on cement hydration process was studied systematically.The thesis focuses on the hydration kinetic,hydration rate,hydrates and pore solution composition of cements with different alkali content,as well as their influenced factors.Moreover,the influence of alkali content on the compatibility of cement and additives,the development law of cement strength were studied.According to the analysis results of Portland cement clinkers produced by different manufacturers,high alkali content in clinker depress the development of C₃S crystal in clinker.The distributions of alkali in different mineral phases of clinkers are different,the segregation of K is more significant.The alkali sulfates in the cement clinkers dissolve rapidly after the mixing of cement and water,the concentrations of alkali metal ions tend to be stable after 10 minutes.The dissolved ratio of K is much higher than that of Na.The higher the ratio of sulfur to alkali is,the higher the dissolved ratio of alkali in cement is.The dissolution of soluble alkali in cement changes the composition of pore solution directly,influences the dissolution of C₃A and C₃S,the precipitation of CSH and the formation of CH and AFt through its effect on the saturation of related substances.High alkali content in cement depresses the dissolution of C₃A and the formation of AFt,promotes the dissolution of C₃S and the formation of CH,and leads to a higher hydration degree of cement paste at early age.With the increase of alkali content,the effect on the precipitation of CSH changes from promoting its growth rate to promoting its nucleation simultaneously,which corresponds to the acceleration of cement hydration reaction and the shortening of induction period.High alkali content has an adverse effect on the compatibility of cement and polycarboxylate superplasticizer.The alkali addition increases zeta potential of cement paste,resulting in some of the polycarboxylate superplasticizer is adsorbed onto the diffusion layer on the surface of silicate phase,which restrains its adsorption-dispersion effect.Moreover,the competitive adsorption of SO₄^2-in pore solution and polycarboxylate superplasticizer on the surface of aluminate phase restrains the adsorption-dispersion effect of polycarboxylate superplasticizer ulteriorly.The compatibility of cement with low C₃A content and polycarboxylate superplasticizer is more sensitive to the change of alkali content.The moderate increase in alkali content in cement delay the setting of cement with low alkali content.The large increase in alkali content（K-base）lead to the formation of syngenite crystal in the paste,promoting the setting of cement.High alkali content can promote the refinement of the pore structure of the hardened paste and improve the strength of cement in early age,but it is not conducive to the optimization of the pore structure of the hardened paste and the strength development of cement in later age.更多还原