Comparison of the retarding mechanisms of zinc oxide and sucrose on cement hydration and interactions with supplementary cementitious materials

Sucrose and zinc oxide (ZnO) are effective cement hydration retarders. The goal of this study was to provide a new look into the ZnO cement hydration mechanism and to investigate impacts of various supplementary cementitious materials (SCMs) on retardation behavior of ZnO and sucrose. Changes in the pore solution composition and reaction kinetics were measured for cementitious systems with ZnO or sucrose that contained rice straw ash (RSA), wheat straw ash, silica fume, metakaolin, and fly ash. Among the SCMs used, RSA dramatically suppressed ZnO and sucrose retardation. Experimental results indicated that the mechanism by which ZnO retards hydration reaction could be nucleation and/or growth poisoning of C-S-H. Reduced retardation of paste samples containing RSA was attributed to the ability of RSA to provide nucleation sites for C-S-H precipitation. This study provides a better understanding of the interaction between SCMs and cement hydration retarders essential in predicting retarder–dose effects.     

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.     

硅灰、偏高岭土对矿渣-粉煤灰微珠胶凝材料性能的影响

首先通过改变粉煤灰微珠掺量,确定满足快速修补要求的矿渣-粉煤灰微珠胶凝材料基体的最佳配比,再调节偏高岭土、硅灰掺量,研究其对复合胶凝材料凝结时间、力学性能和水化机理的影响。研究发现,偏高岭土对凝结时间的改变较硅灰更敏感。通过化学结合水测试,分析了不同硅灰和偏高岭土掺量对矿渣-粉煤灰微珠胶凝材料水化反应程度影响的原因。力学实验结果表明：矿渣-粉煤灰微珠胶凝基体复合掺加5%硅灰（质量分数）+15%偏高岭土（质量分数）,试块2 h抗压强度为11.5 MPa、28 d抗压强度达到75.2 MPa,且呈现缓慢递增的趋势。     

Use of recycled copper slag for blended cements

Copper slag is a by‐product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition‐containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry     

海水环境下矿物掺合料对硫铝酸盐水泥的水化影响

研究了海水环境下掺入硅灰、粉煤灰、矿渣对硫铝酸盐水泥抗压强度、化学收缩和水化产物的影响规律.结果表明:当硅灰的掺量为2.5%时,水泥浆体的抗压强度比空白组高.矿渣掺量为10%的水泥浆体28 d抗压强度明显超过掺入硅灰和粉煤灰时的强度,60 d强度高于空白组.掺入2.5%硅灰后,水泥浆体的化学收缩增大;在水化早期,粉煤灰和矿渣的火山灰活性很低,导致水泥浆体的化学收缩降低.掺入10%硅灰加快了硫铝酸盐水泥3 d水化反应,钙矾石生成量增多,水泥浆体早期强度比掺其它掺合料有所提高,但体积过快膨胀会破坏其内部结构,对水泥浆体的强度发展不利.     

蒸汽养护条件下复合水泥胶凝材料的优化匹配

利用XRD、SEM、TG/DSC、MIP等测试方法,对常压高温蒸汽养护下矿渣和粉煤灰等不同组成的复合胶凝材料物理性能及水化特性差异进行研究.结果表明,85℃常压蒸养条件下水泥水化产物与标准养护下基本相同,但水化产物数量有大幅提高,且有少量C9S6H18和钙矾石(AFt)稳定存在.辅助胶凝材料的适宜匹配,使水泥石结构较致密,蒸养强度较高.少量硅灰的掺加,有利于优化水泥石结构,促进蒸养条件下水泥石强度发展.     

粉煤灰/硅灰复合掺合料对水泥净浆性能的影响

研究了水泥标准稠度用水量、粉煤灰掺量、硅灰掺量、粉煤灰与硅灰双掺对水泥净浆性能的影响.结果表明,硅灰使水泥净浆需水量明显增加,粉煤灰、硅灰双掺可克服单掺粉煤灰早期强度低的缺点,短期内能提高水泥净浆的抗压强度.     

Investigation of blended cement hydration by isothermal calorimetry and thermal analysis

Hydration of portland cement pastes containing three types of mineral additive; fly ash, ground-granulated slag, and silica fume was investigated using differential thermal analysis, thermogravimetric analysis (DTA/TGA) and isothermal calorimetry. It was shown that the chemically bound water obtained using DTA/TGA was proportional to heat of hydration and could be used as a measure of hydration. The weight loss due to Ca(OH)₂ decomposition of hydration products by DTA/TGA could be used to quantify the pozzolan reaction. A new method based on the composition of a hydrating cement was proposed and used to determine the degree of hydration of blended cements and the degree of pozzolan reaction. The results obtained suggested that the reactions of blended cements were slower than portland cement, and that silica fume reacted earlier than fly ash and slag.     

海水和矿物掺合料对硫铝酸盐水泥砂浆性能的影响

本文研究了不同拌和水以及海水拌和时粉煤灰和硅灰掺量对硫铝酸盐水泥(SAC)砂浆力学性能和表观孔隙率以及净浆凝结时间、化学收缩、孔溶液pH值和氯离子结合能力等的影响,并通过XRD、SEM和EDS分析水泥水化产物和微观结构。结果表明,海水能加快SAC早期水化并提高其早期强度,但后期强度和淡水拌和时无明显差别。粉煤灰和硅灰均会延长SAC凝结时间,对早期抗压强度不利,而掺加质量分数为5.0%和7.5%的硅灰能提高SAC砂浆28 d抗压强度。硅灰掺量增加时会提高用水量和表观孔隙率,降低流动性,使水泥化学收缩增大,降低净浆pH值且减少氯离子结合量;粉煤灰能够提高砂浆流动性,减少水泥化学收缩,但掺量越大对SAC砂浆抗压强度和抗折强度越不利,掺质量分数为10%的粉煤灰可小幅提高氯离子结合量且减小表观孔隙率。     

Supplementary cementitious materials for mitigating degradation of kraft pulp fiber-cement composites

Kraft pulp fiber reinforced cement-based materials are being increasingly used where performance after exposure to environmental conditions must be ensured. However, significant losses in mechanical performance due to wet/dry cycling have been observed in these composites, when portland cement is the only cementitious material used in the matrix. In this research program, the effects of partial portland cement replacement with various supplementary cementitious materials were investigated. Binary, ternary, and quaternary blends of silica fume, slag, Class C fly ash, Class F fly ash, metakaolin, and diatomaceous earth/volcanic ash blends were examined for their effect on the degradation of kraft pulp fiber-cement composite mechanical properties (i.e., strength and toughness) during wet/dry cycling. After 25 wet/dry cycles, it was shown that binary composites containing 90% slag, 30% metakaolin, or greater than 30% silica fume did not exhibit any signs of degradation, as measured through mechanical testing and microscopy. Ternary blends containing 70% slag/10% metakaolin or 70% slag/10% silica fume were also effective in preventing degradation. A reduction in calcium hydroxide content and the stability of the alkali content due to supplementary cementitious material addition were shown to be primary mechanisms for improved durability.     

Alkali release characteristics of blended cements

This paper presents results of an experimental program conducted to investigate the capacity of hydration products of different cementing materials to retain “bound” alkalis when the alkalinity of the surrounding solution drops. The study covered paste samples containing high-alkali Portland cement and various levels of silica fume and/or fly ash. The results showed that the ability of the hydration products of cement-fly ash systems to bind alkalis is a function of the CaO content of the fly ash, the binding increasing as the calcium content decreases. High-alkali fly ashes (Na₂O_e > 5.0% and CaO in the range of 15% to 20%) showed considerable amounts of alkali contributed to the test solutions. Silica fume does not have a high capacity to retain alkalis in its hydration products; however, ternary blends containing silica fume and fly ash have excellent capacity to bind and retain alkalis.     

矿物超细粉对水泥浆体化学收缩的影响研究

通过笔者自行设计的化学收缩测量装置分别对掺硅灰、磨细矿渣、超细粉煤灰的水泥浆体化学收缩进行了测定。结果表明，硅灰的掺入增大了水泥浆的化学收缩；磨细矿渣的掺入使水泥浆体的化学收缩稍有增长，但不十分明显；而超细粉煤灰则可以较好地抑制水泥浆体的化学收缩。对掺矿物掺合料的水泥浆体强度的测试结果从另一个角度论证了化学收缩是由水化引起的，即水化程度的大小反映了化学收缩的大小。     

海工高性能混凝土用复合胶凝材料的试验研究

在调查分析海工混凝土工程实例的基础上，试验研究了硅酸盐水泥中掺入矿粉、粉煤灰、硅灰等混合材料对海工混凝土性能的影响。研究结果表明，在硅酸盐水泥中掺加矿粉、粉煤灰、硅灰等混合材料可以改善海工混凝土的综合性能。矿物混合材料的复合掺入比单独掺入能更好地改善混凝土抗Cl^-侵蚀性能。海工专用复合胶凝材料生产时宜尽可能地采用多种混合材料。     

硅灰掺量对免烧粉煤灰陶粒性能的影响

以粉煤灰为原料,辅掺硅灰制备了碱激发免烧陶粒。采用筒压强度试验、吸水率试验、含泥量试验、磨破率试验、耐腐蚀试验、X射线衍射仪和扫描电子显微镜试验,系统地研究了硅灰掺量对陶粒性能的影响。结果表明,3 d、7 d、14 d龄期时,随着硅灰掺量增加,粉煤灰陶粒的筒压强度呈逐渐增加趋势,磨破率与吸水率呈逐渐下降趋势,耐腐蚀性能也得到提高。当硅灰掺量为15%和20%(质量分数)时,龄期为14 d时,陶粒的筒压强度分别达到19.43 MPa和20.37 MPa。由微观分析知,适量的硅灰掺量可以提高粉煤灰的水化程度,增加陶粒结构密实性,但当掺量达到15%~20%时,水化程度有所减弱。     

钾基碱性电解水对粉煤灰混凝土性能的影响

碱性电解水具有高活性、强碱性、强离子性和吸附性等优点。利用碱性电解水作为拌合水制备不同取代率的粉煤灰混凝土,系统研究碱性电解水对粉煤灰混凝土的工作性能、力学性能和抗氯离子渗透性能的影响,并结合X射线衍射仪(XRD)、扫描电镜(SEM)和差热分析试验(TG/DTA)分析碱性电解水混凝土的水化产物及微观结构形貌。结果表明:碱性电解水能够促进混凝土中水泥早期水化反应,改善混凝土的工作性能,除了生成更多的C-S-H凝胶体和Ca(OH)₂等水化产物外,还生成了钾长石,降低了孔隙率,提高结构密实度,改善了混凝土的力学性能和抗渗性能;同时,碱性电解水在一定程度上可以激发粉煤灰的早期活性效应,使得粉煤灰玻璃体网络结构加速断裂,粉煤灰中的SiO₂和Al₂O₃大量溶出与混凝土中的水化产物Ca(OH)₂发生二次反应,生成更多的硅酸钙和铝酸钙等胶凝性产物。相较于普通自来水混凝土,当粉煤灰取代率为20%和30%(质量分数)时,碱性电解水混凝土的56 d抗压强度分别增长了8.7%和3.5%。     

低温(10℃)-干湿循环下水泥砂浆抗硫酸盐侵蚀试验研究

在低温(10 ℃)-干湿循环双重环境下,对不同水灰比不同胶凝材料方案的水泥砂浆试件的抗硫酸盐侵蚀性能进行了试验研究,其中水灰比采用0.5和0.36,胶凝材料分别为普通硅酸盐水泥、中抗硫酸盐硅酸盐水泥和在普通硅酸盐水泥中分别掺入15%矿粉+1%硅灰和15%矿粉+3%硅灰.结果表明:在低温(10 ℃)-干湿循环双重条件下,既存在化学侵蚀又存在物理侵蚀,但是以物理侵蚀为主;通过降低水灰比或者使用抗硫酸盐硅酸盐水泥能显著提高砂浆抗硫酸盐侵蚀性能;在不同的水灰比下,复掺矿粉和硅灰会得到不同的效果,在低水灰比时能提高抗硫酸盐侵蚀的性能,在高水灰比时反而会降低抗硫酸盐侵蚀的性能.     

粉煤灰海工高性能混凝土的应用研究

针对粒化高炉矿渣粉和硅灰存在的缺陷。研究采用粉煤灰替代粒化高炉矿渣粉配制混凝土,进而观察其力学性能、抗氯离子渗透性以及胶凝材料的水化热。研究结果表明,所配制的混凝土能满足海工高性能混凝土高耐久性的需要,粉煤灰替代粒化高炉矿渣粉胶凝材料具有较低的水化热,有利于大体积混凝土的施工。     

基于灰色系统理论的磷建筑石膏基胶凝材料组分优化设计研究

以云南磷石膏为主要原料制备磷建筑石膏基胶凝材料.通过应用灰关联分析法分析磷建筑石膏基胶凝材料的组分(复合硅酸盐水泥、普通硅酸盐水泥、矿渣硅酸盐水泥、硅灰、粉煤灰、磷建筑石膏)对其绝干抗压强度的影响,确定了掺合料最佳组合为粉煤灰、矿渣硅酸盐水泥、硅灰;并运用多目标智能加权灰靶决策模型综合考虑抗压强度、抗折强度、初凝时间、终凝时间、软化系数、孔隙率六个指标,确定了其最佳配合比.试验表明:当粉煤灰:矿渣硅酸盐水泥:硅灰:磷建筑石膏的配合比为6%:5%:3%:86%时,其综合性能最好,绝干抗压强度为14.11 MPa,抗折强度为2.58 MPa,初凝时间为16 min,终凝时间为43 min,软化系数为0.51,孔隙率为23%.     

新型混凝土表面防护材料的研究

以纳米SiO2、硅灰、粉煤灰作为矿物掺和料对水泥基材料进行改性,形成混凝土表面防护层.利用RCM法测定氯离子扩散系数,并通过SEM、XRD、DSC等手段研究改性水泥基材料的水化产物组成及微观结构,分析改善机理.结果表明:混凝土表面砂浆防护层能将混凝土抗氯离子侵蚀能力提升56.75％,并且这种提升效果随着粉煤灰、硅灰、纳米SiO2的掺入更加明显,且其提升能力依次增加;粉煤灰依靠其微集料效应及填充效应,增强了水泥石的密实程度;纳米SiO2、硅灰依靠其火山灰活性促进水泥的水化并产生二次水化,进而提升抗氯离子侵蚀能力.研究结果说明了利用无机矿物掺合料对水泥基材料进行改性形成防护层可明显提升混凝土的抗氯离子侵蚀能力,为进一步研究无机混凝土表面防护体系提供了研究基础.     

矿物掺合料对机制砂砂浆性能的影响

研究了在相同水灰比与流动度情况下,单掺或复掺硅灰及不同地区粉煤灰等矿物掺合料对机制砂砂浆流动性、强度的影响,并与标准砂砂浆进行了比较。结果表明、与标准砂相比,机制砂砂浆需水量大、保水性差、易泌水,但具有增强作用;硅灰引起机制砂砂浆流动性减小、减少泌水、增进强度。水灰比相同时,随掺量灰增大,机制砂砂浆流动性增大,不同龄期下砂浆抗压强度均下降。复掺硅灰与粉煤灰可提高机制砂的强度。上海与贵州两地的粉煤灰品质基本相同,对砂浆性能的影响也基本相同。