硅酸盐水泥水化热的研究及其进展

硅酸盐水泥水化硬化过程中会释放大量的水化热,由此而产生的温度应力是导致混凝土出现裂缝的一个主要原因,对大体积混凝土的影响更为显著。因此,水泥混凝土水化热的研究长期以来受到国内外水泥和混凝土科学家及建筑工程界的重视。本文在总结前人关于水泥水化热研究方面提出的一些理论计算公式的基础上,综合分析了影响水泥水化热的因素,介绍了国内外关于水泥水化放热模型的最新研究进展以及水泥生产中降低水化热的技术措施。     

纳米C-S-H对水泥水化、硬化浆体孔结构及混凝土强度的影响

通过水化热测试、化学结合水含量测试、X射线衍射分析、压汞测试及强度测试研究了合成的纳米水化硅酸钙(n-C-S-H)对水泥水化过程、硬化水泥浆孔结构及混凝土强度的影响。结果表明:n-C-S-H显著加速了水泥早期水化,提升了水泥在12～24 h龄期的水化程度,从而显著提高混凝土12～24 h龄期的抗压强度,24 h以后对强度提升效果逐渐减小。3 d以后n-C-S-H对混凝土强度发展没有明显的促进作用,1.5%掺量下混凝土强度反而较空白样有所降低;加入n-C-S-H的硬化水泥浆在12 h～3 d龄期内相比空白水泥浆临界孔径降低,凝胶孔孔隙率提高,毛细孔孔隙率降低。n-C-S-H改变了C-S-H凝胶的生成方式,使其原本从水泥颗粒表面析出变为了从孔溶液中析出,显著减小了毛细孔孔隙率,同时增加了凝胶间孔的体积。这种多核生长的方式导致水化产物结构疏松,从而导致基体强度略微降低。因此,在相同水化程度时,掺有n-C-S-H的混凝土抗压强度略低于空白混凝土。     

水化热抑制剂对水泥-粉煤灰胶凝材料水化和混凝土性能的影响EI北大核心CSCD

探究了水化热抑制剂(TRI)对水泥-粉煤灰胶凝材料水化过程和混凝土性能的影响。通过改变粉煤灰在胶凝材料中的占比和水化热抑制剂的掺量,观察了胶凝材料的水化过程以及混凝土的绝热温升、力学性能和干燥收缩特性。胶凝材料的水化热测试结果表明,在含有粉煤灰的胶凝材料中,水化热抑制剂降低胶凝材料的放热速率峰值、延后放热峰出现时间的作用更加明显。硬化浆体的相组成和微观结构测试表明,水化热抑制剂对胶凝材料水化程度的抑制主要发生在7 d前。混凝土试验结果表明,水化热抑制剂会放缓混凝土的绝热温升速率,降低粉煤灰混凝土的早期强度并增加干燥收缩。     

水化热抑制剂对水泥-粉煤灰胶凝材料水化和混凝土性能的影响

探究了水化热抑制剂(TRI)对水泥-粉煤灰胶凝材料水化过程和混凝土性能的影响。通过改变粉煤灰在胶凝材料中的占比和水化热抑制剂的掺量,观察了胶凝材料的水化过程以及混凝土的绝热温升、力学性能和干燥收缩特性。胶凝材料的水化热测试结果表明,在含有粉煤灰的胶凝材料中,水化热抑制剂降低胶凝材料的放热速率峰值、延后放热峰出现时间的作用更加明显。硬化浆体的相组成和微观结构测试表明,水化热抑制剂对胶凝材料水化程度的抑制主要发生在7 d前。混凝土试验结果表明,水化热抑制剂会放缓混凝土的绝热温升速率,降低粉煤灰混凝土的早期强度并增加干燥收缩。     

SO3含量对含三异丙醇胺水泥水化的影响

通过水泥胶砂强度试验、水化热(hydration heat)测量、硬化水泥浆体的热分析(TGA)、X射线衍射分析(XRD)及定量X射线衍射分析(QXRD)、微观形貌扫描电镜(BSE)观察,研究了不同SO3含量对含三异丙醇胺(triisopropanolamine,TIPA)硅酸盐水泥胶砂强度、水化进程和水泥浆体微观结构的影响.结果表明:SO3含量提高有助于提高含三异丙醇胺水泥的早期强度;水化热分析结果表明在含TIPA水泥中额外加入SO3后,水泥水化反应速率增大,水化3 d累积放热量增加,水化程度更大,且AFt-AFm的转化过程受到抑制;与含TIPA水泥水化相比,额外SO3掺量为0.6％时,硫酸盐促进整个硅酸盐相(C3S+C2S)的早期水化生成更多的Ca(OH)2(CH)参与C4AF的水化,在一定程度上促进其反应生成更多的AFt;外掺SO3生成的水泥石更致密.     

低水化热水泥浆用微胶囊型热控材料制备及应用

基于天然气水合物低温、高压及电解质条件下的分解特性,以常规波特兰油井水泥为基料,外掺入微胶囊型热控材料(PCM-1),制备了一种低水化热水泥浆体系。采用自研半绝热测试实验设备对水泥浆体系早期水化过程中的温度进行了连续测量,以水泥浆体系最高温度(T_m)及最大水化温升(Tr)表征了PCM-1对水泥浆体系水化热的控制效应。结果表明,PCM-1的含量15%时(以水泥的质量为基准,下同),该水泥浆较纯水泥浆的水化最高温度下降了22.3℃,最大水化温升下降了23.6℃;24 h及48 h水化热分别下降了7.68×10~4 J及7.28×10~4 J。微胶囊能够有效地控制水泥浆的水化温升及水化热,大幅降低了深水水合物层的固井风险。     

水化热调控剂与氧化镁复掺对混凝土抗裂行为的影响

为了研究氧化镁膨胀剂与水化热调控剂复掺对混凝土抗裂性能的影响,探讨水化热调控剂的作用机理,开展了单掺氧化镁及水化热调控剂与氧化镁复掺对混凝土水化热、绝热温升、限制膨胀率、体积变形、自收缩、弹性模量及微观结构的影响研究。结果表明:水化热调控剂可显著改变水泥水化放热历程,净浆抑温率可达31.2%,随入模温度升高,抑温效果增强;水化热调控剂可激发氧化镁的水化,促进膨胀能的释放,随养护温度提升,作用效果更显著;水化热调控剂可改变混凝土温升历程,特别是降低混凝土早期水化热释放速率;水化热调控剂与氧化镁复掺可降低混凝土自收缩,当水化热调控剂掺量为0.2%和0.4%(质量分数)时,混凝土收缩值分别减少了84 με和54 με;水化热调控剂会导致混凝土早龄期弹性模量降低,但对长龄期弹性模量影响不大;水化热调控剂对水泥水化历程、水化产物生成及微观结构密实程度的改变是提高混凝土抗裂性能的根本原因。     

水泥水化热测试方法研究进展与趋势

水泥水化硬化过程中会释放出大量热量,由此产生的热应力是导致混凝土结构中产生裂缝的原因之一。目前,水泥水化热的测试方法主要分为溶解热法、直接法和等温量热法。本文在总结前人关于水泥水化热测试方法研究的基础上,介绍了国内外对水泥水化热测试的最新研究进展。     

矿渣粉、高钙灰及其改性材料对水泥早期水化进程的影响

通过水泥化学收缩和水化热测试方法研究了矿渣粉、高钙灰和脱硫石膏、煅烧脱硫石膏、硫酸钠等改性材料对水泥浆体早期水化进程的影响,同时与不同试样的早期强度进行对比分析.50%的矿渣粉和高钙灰替代水泥后显著降低塑性阶段的化学收缩和早期强度,但对硬化后的化学收缩影响不大,矿渣粉与高钙灰按照适当比例复合对降低塑性阶段化学收缩的作用更明显,有利于降低塑性开裂;脱硫石膏和元明粉对早期化学收缩影响不大.矿渣粉、高钙灰替代50%水泥后明显降低第2放热峰并增加1个第3放热峰,纯矿渣粉的第3放热峰较高,复掺20%高钙灰后第3放热峰降低并且出现时间延后,复掺30%高钙灰使第2放热峰也降低,水化热显著减少;脱硫石膏或煅烧脱硫石膏延缓水化反应进程而对总体反应程度影响不大;水化热实验结果显示硫酸钠促进早期水化反应的作用明显.结果表明:采用20%高钙灰替代矿渣粉对早期水化程度和初始结构建立影响不大,脱硫石膏或煅烧脱硫石膏作激发材料能够分散早期的集中放热而对总体水化进程影响不大;水化热对水化过程的反映比化学收缩更清晰和更准确.     

矿渣对阿利特-硫铝酸钡钙水泥硬化浆体结构和性能的影响

通过对水泥浆体凝结性能、力学性能和孔结构的测定,结合扫描电镜分析和差热-热重分析,研究了矿渣掺量对阿利特-硫铝酸钡钙水泥浆体硬化浆体结构和性能的影响.结果表明:随着矿渣掺量的增加,水泥的凝结时间延长,水化热减少,早期抗压强度下降.但其后期抗压强度已接近或超过了纯水泥的抗压强度,掺入矿渣对水泥的后期抗压强度影响不大.硬化水泥浆体中的Ca(OH)2含量随水化龄期的延长而增加,并随矿渣掺量的增加而降低.矿渣的活性效应和填充效应有效地改善了硬化水泥浆体的微观结构和孔结构,从而使水泥的力学性能有所提高.     

核电站主体工程用水泥的生产

核电站核岛是常规岛混凝土工程用水泥的特点是：要求早，后期强度高，标准偏差小，水化热低，干缩率低，杂质含量和有害成分含量少，为满足核电站混凝土主体工程对水泥的质量要求，在生产水泥的过程中应采取的相应措施。     

Application of a microwave impulse technique to the measurement of free water content in early hydration stages of cement paste

A microwave impulse method is designed and employed to the monitoring of residual moisture content in early hydration stages of cement paste. Complementary experiments consisting in determination of the times of beginning and end of setting and of the course of bending strength, compression strength, Young's modulus and hydration heat production during the early hydration period are performed in order to find possible correlation between the measured moisture changes, development of mechanical parameters and hydration heat release. It is observed that the fastest decrease of residual moisture content roughly agrees with the early stages of the hardening process, i.e., with the time period between the end of setting and the moment when first measurable values of mechanical parameters are obtained.     

Determining the “apparent” activation energy of concrete: Ea—numerical simulations of the heat of hydration of cement

The “apparent activation energy” of concrete—E_a—is usually determined by means of mechanical or calorimetric tests. This parameter, which characterises the sensitivity of concrete hydration processes to temperature, is required for estimating the compressive strength of concrete at early age by the “method of equivalent age.” The major aim of this paper is to show how numerical simulations of released heat under adiabatic conditions could be an alternative to experiments for determining E_a. The simulation model—the CHAL program—which is developed here, is based on the kinetic model of Avrami-Erofeev. The coupling by temperature between the different chemical reactions of the main anhydrous components of cement is taken into account by using the Arrhenius' law. The model leads to a better understanding of the polymineral characteristic of cement as regards heat of hydration and E_a determination. The “apparent” nature of E_a and its dependence on hydration degree can be underlined.     

Experimental study and numerical simulation on the formation of microstructure in cementitious materials at early age

The formation of microstructure in early age cement paste and concrete was examined with an ultrasonic experimental set-up. Research parameters included the influence of curing temperature (isothermal curing at 20, 30 and 40 °C), water/cement ratio (0.40, 0.45 and 0.55) and amount of aggregate. In parallel with the experiments, the cement hydration model HYMOSTRUC was utilized to simulate the formation of the microstructure. In this study, the cement paste was considered as a four-phase system consisting of water, unhydrated cement, hydration products and that part of the hydration product that causes the contact between the hydrating cement grains (so called “bridge volume”). A correlation has been found between the growth of bridge volume calculated with the model and the changes in the pulse velocity. It is believed that ultrasonic pulse velocity (UPV) measurements can represent a valuable tool to investigate the development of the microstructure at early age.     

水泥细度对早龄期碾压混凝土综合抗裂性的影响(英文)

水泥水化热与比表面积和化学组成有关,但是相对于调整水泥的化学组成来说,通过减小水泥的比表面积来降低水泥水化热要容易得多。为了探索水泥比表面积与碾压混凝土抗裂性能的关系,采用相同熟料磨制了3种细度的水泥,研究了水泥细度对水化热、胶砂强度的影响,以及对混凝土的工作性、力学性能(抗压强度、抗拉强度和抗拉弹性模量)、极限拉伸值、绝热温升等性能的影响;同时,采用温度–应力试验机,评估了在100%约束和近似绝热条件下水泥细度对早龄期碾压混凝土综合抗裂性能的影响。结果表明:水化热与比表面积成线性关系,降低水泥比表面积是降低混凝土温升的有效、便捷的措施;粗磨水泥提高了碾压混凝土的工作性,降低了混凝土的抗压强度和弹性模量,但混凝土极限拉伸值没有明显变化;温度–应力试验表明,随着水泥比表面积的降低,混凝土第二零应力温度更低,粗磨水泥碾压混凝土综合抗裂风险更低。     

Modelling elasticity of a hydrating cement paste

Concrete is a complex multi-scale composite involving multi-physics processes. As it is the only evolving component of concrete, the cement paste has a major influence on the mechanical properties of concrete at early age. This paper focuses on the increase of the elastic properties of a cement paste during its hydration. The homogenization theory for disordered media is used in order to estimate the evolution of the effective elastic moduli of the hydrating paste. The morphological model refers to two types of C-S-H (calcium silicate hydrates, main hydration products of Portland cements) distinguished by many authors: inner products or high density C-S-H build up layers surrounding the anhydrous particles, while the outer products or low density C-S-H play the role of a porous matrix.The simulations of the effective Young's modulus at late age during hydration and at the end of hydration prove to be in excellent agreement with the experimental results available in the literature.     

高铁用高性能矿物掺合料对混凝土性能的影响

以高速铁路为工程背景,试验研究了高性能矿物掺合料对水泥水化热及混凝土工作性能、力学性能和耐久性能的影响。试验结果表明:高性能矿物掺合料能够显著提高水泥净浆的早期水化热及混凝土试块的抗压强度、抗氯离子渗透性能和抗冻性能。     

Effect of fly ash on the kinetics of Portland cement hydration at different curing temperatures

This paper describes the effect of fly ash on the hydration kinetics of cement in low water to binder (w/b) fly ash-cement at different curing temperatures. The modified shrinking-core model was used to quantify the kinetic coefficients of the various hydration processes. The results show that the effect of fly ash on the hydration kinetics of cement depends on fly ash replacement ratios and curing temperatures. It was found that, at 20 °C and 35 °C, the fly ash retards the hydration of cement in the early period and accelerates the hydration of cement in the later period. Higher the fly ash replacement ratios lead to stronger effects. However, at 50 °C, the fly ash retards the hydration of the cement at later ages when it is used at high replacement ratios. This is because the pozzolanic reaction of the large volumes of fly ash is strongly accelerated from early in the aging, impeding the hydration of the cement.