【作者】 魏风艳；

【导师】 许仲梓； 吕忆农；

【作者基本信息】 南京工业大学 ， 材料学， 2005， 博士

【摘要】 本课题得到国家重点基础研究发展规划973—“高性能水泥制备与应用的基础研究”资助,课题编号（2001CB610706）。 建筑业的可持续发展已成为国民经济发展的一个重大问题。充分利用工业废渣作为矿物掺合料进行高性能水泥基材料的研制符合我国可持续发展战略,是水泥基材料进一步发展的根本课题。矿物掺合料的掺入,使水泥基体系成分复杂,影响水泥水化产物的形貌、化学组成、结构及其稳定性,也会对水泥混凝土的耐久性产生影响。目前研究表明混合材对碱-硅酸反应（ASR）有很好的抑制作用,但对混合材抑制ASR机理的认识需进一步完善。混合材抑制ASR的作用,不同研究者均着重强调混合材对混凝土中碱和Ca（OH）₂的作用。主要包括混合材对碱的物理稀释、吸附,与Ca（OH）₂的火山灰反应减少甚至消除体系中Ca（OH）₂等方面。却忽视了火山灰反应生成的大量低Ca/Si的C-S-H凝胶在抑制ASR中的作用。 研究高性能水泥基材料中低Ca/Si的C-S-H凝胶形成及其在抑制ASR中的作用机理是本论文的主题。在研究高性能水泥基材料水化产物Ca（OH）₂数量变化,以及高性能水泥基材料对ASR抑制作用的基础上,研究了主要水化产物C-S-H凝胶的形貌、化学组成和结构变化,以及高性能水泥基材料中碱的溶出规律,提出了低Ca/Si的C-S-H凝胶能够“固化”体系中大量的碱,减少碱与活性集料反应的机会,而起到抑制ASR的作用。进一步研究C-S-H凝胶的化学组成和结构变化与C-S-H凝胶持碱能力之间的关系,从材料本征特性提出混合材抑制ASR的新机理。研究工作取得如下进展: 研究了高性能水泥基材料水化产物Ca（OH）₂数量、分布、形貌变化以及高性能水泥基材料对ASR的抑制效果。结果表明,随粉煤灰掺量增加,水泥石中Ca（OH）₂含量因二次火山灰反应的发生而明显降低,Ca（OH）₂含量的变化在一定程度上反映了火山灰反应程度。粉煤灰掺量达到30%和45%时,砂浆棒几乎不发生膨胀,表明粉煤灰对ASR有显著的抑制效果。 利用SEM/EDS和TEM/EDS对高性能水泥基材料水化产物C-S-H凝胶的化学组成研究发现,随粉煤灰掺量增加,二次火山灰反应生成的C-S-H凝胶的Ca/Si明显降低,且C-S-H凝胶中结合碱的数量增大,表明低Ca/Si的C-S-H凝胶能够“固化”孔溶液中大量的碱,减少可发生ASR的有效碱量。 高性能水泥基材料和普通水泥基材料中碱的溶出规律对比研究结果表明,未掺矿物掺合料的水泥基体系,在38℃、100%R.H.条件下养护至4个月的整个反更多还原

【Abstract】 This thesis is sponsored by the National Basic Research Program of China "973" —"Fundamental Research on the Manufacture and Application of High Performance Cement" （No. 2001CB610706）.The sustainable development of construction industries has been one of the very important issues of national economy. It is the basic thesis for further development of cement-based materials to make the best use of industry wastes as mineral admixtures to manufacture high performance cement-based materials （HPCM） and it accords to the strategy of national sustainable development. The morphology, chemical composition, structure and stability of hydration products, as well as the durability of cement and concrete are influenced in HPCM system with the adding of mineral admixtures. The use of mineral admixtures as partial replacement for Portland cement in concrete is an effective means for controlling expansion due to alkali-silica reaction （ASR）, however, the mechanism has not been clearly understood. Most researchers have put emphasize on the interaction mineral admixtures with alkali and Ca（OH）₂, i.e. adsorption and dilution of alkali by mineral admixtures and the secondary pozzolanic reaction reducing the content of Ca（OH）₂, while ignoring the effect of lower Ca/Si ratio C-S-H gel produced by secondary pozzolanic reaction on ASR.The purpose for this thesis is to investigate the formation of lower Ca/Si ratio C-S-H gel and its mechanism in controlling ASR in HPCM system. Based on the study of evolvement of Ca（OH）₂ in HPCM system and the suppressing effect of HPCM system on ASR, the morphology, chemical composition and structure of C-S-H gel in HPCM system and the alkali released from HPCM were studied. It is proposed that the increased alkali-binding capability of the low Ca/Si ratio C-S-H gel can significantly reduce the alkali available for reactive aggregate, resulting in the suppression of ASR. The relationship between the chemical composition and structure of C-S-H gel and its alkali-binding capability was further studied. A new mechanism of mineral admixtures in suppressing ASR is proposed from the essential characteristic of materials. The progresses are as follows:The effect of mineral admixture on the content, distribution and morphology of Ca（OH）₂ and the effect of HPCM system on ASR were studied. Results indicate thatthe content of Ca（OH）2 in paste decreased significantly by secondary pozzolanic reaction with the increase of fly ash. Ca（OH）2is an index of the degree of pozzolanic reaction to a certain extent. Fly ash has strongly preventive effect on ASR. There was almost no expansion in mortar bars when the content of fly ash reached 30% and 45 %.The chemical composition of C-S-H gel is determined by TEM/EDS and SEM/EDS. Results showed that with the increase of fly ash, the Ca/Si ratio of C-S-H gel produced by secondary pozzolanic reaction decreased significantly and more alkali （NaOeq.） was retained in C-S-H gel.Comparative study on the alkali release from HPCM and ordinary Portland cement （OPC） system found that about 80% of alkali in OPC system was released after curing for 4 months at 38°C 100% R.H., while a much lower alkali release from HPCM system, at about 20% of total alkali. It indicates that the hydration products from HPCM have a stronger capability in retaining alkali than OPC system. The result was also confirmed by TEM/EDS analysis.The alkali-binding capability of C-S-H gel is determined by its chemical composition and structure. The structure of C-S-H gel was analysed by FT-IR and 29Si MAS NMR. It was found that the average length of [SiC?4]4" tetrahedron chains increased. More acidic silanol （Si-OH） bonds and broken bonds caused by the loss of bridging [SiO,*]4" tetrahedron exist in the HPCM system. Na+ and K+ ions can reacted with Si-OH and provide electrical neutrality with the net negative surface charge on C-S-H gel. Furthermore, the surface force caused by the high specific surface area of C-S-H gel can attract more Na+ and K+ on the surface of C-S-H gel, resulting in high alkali-binding capability of the low Ca/Si ratio C-S-H gel.In view of above results, a new controlling mechanism of mineral admixture on ASR was proposed. Low Ca/Si ratio C-S-H gel formed by secondary pozzolanic reaction has excellent alkali-binding capability. It plays an important rule in reducing the available alkali for reactive aggregate and suppressing ASR.更多还原