硫铝酸盐水泥混凝土流变性与微观结构分析

本文研究了工程上常用的聚羧酸、氨基磺酸盐、萘系高效减水剂(FDN)与硫铝酸盐水泥(SAC)的浆体流变性以及改善方法,即利用某无机缓凝剂有效控制硫铝酸盐水泥的凝结时间,增粘剂解决浆体流动度较大时造成的板结、泌水问题。同时用SEM和压汞法对硫铝酸盐混凝土和普通硅酸盐混凝土的微观结构进行了分析,总结了硫铝酸盐水泥混凝土的部分特点。     

化学外加剂在低水泥浇注料中的作用机理与应用分析

分析了在低水泥浇注料中,由于微粉粒子在水中产生电离、吸附和晶格取代等现象导致其表面荷电形成双电层结构、微粉粒子产生絮凝的现象;阐述了化学外加剂对微粉粒子的分散作用机理,即DLVO理论和HVO理论;分别介绍了萘系(FDN)、脂肪族、氨基磺酸盐系、聚羧酸系高效减水剂的具体作用机理;分析了在低水泥浇注料中三聚磷酸钠、六偏磷酸钠、柠檬酸钠、密胺树脂、聚丙烯酸钠、氨基磺酸盐、聚羧酸系高效减水剂等化学外加剂的应用现状。认为聚羧酸系高效减水剂具有较好的减水效果,其生产与应用研究将越来越广泛和深入。     

减水剂在水泥与粉煤灰表面的吸附行为研究

为了揭示水泥与粉煤灰对减水剂的竞争吸附规律,采用分光光度法研究了SMF、FDN和ASP三种减水剂在此两种颗粒表面的吸附行为.结果表明,三种减水剂在胶凝颗粒表面的吸附均符合Langmuir等温吸附方程,属单分子层吸附.吸附量顺序均为:SMF>FDN>ASP.20℃时,SMF、FDN、ASP减水剂在水泥表面的饱和吸附量分别为12.95、11.35、3.83mg/g,而在粉煤灰表面的饱和吸附量则分别为3.15、2.86、1.10mg/g,表明水泥对减水剂的吸附强于粉煤灰对减水剂的吸附.减水剂在胶凝颗粒表面的吸附动力学也遵循Lang-muir吸附速率方程,SMF、FDN在水泥表面的平均吸附速率大于在粉煤灰颗粒表面的平均吸附速率,而ASP在两种胶凝颗粒表面的吸附速率较为接近.研究表明SMF、FDN将优先吸附在水泥颗粒表面,而ASP在水泥和粉煤灰表面的吸附选择性不高.     

天然高分子基混凝土减水剂研究进展

混凝土外加剂已成为混凝土第5大组成部分,其中减水剂应用最为广泛。当前,以石油化工产品为原料的多种传统减水剂会造成环境污染。为适应绿色混凝土发展的需要,开发基于可再生资源的绿色化混凝土外加剂成为必然趋势。文中综述了天然高分子基混凝土减水剂的研究进展,包括纤维素基减水剂、淀粉基减水剂,其他多聚糖高分子基减水剂等,并一步展望了减水剂研究的发展方向。     

硫铝酸钙改性硅酸盐水泥应用研究进展

硫铝酸钙改性硅酸盐水泥熟料兼具硅酸盐水泥熟料和硫铝酸盐水泥熟料的优良性能,同时该种水泥熟料对粉煤灰等火山灰类材料具有超强的活性激发效果,这使得硫铝酸钙改性硅酸盐水泥具有广阔的应用前景。主要概括了硫铝酸盐改性硅酸盐水泥的性能及水化特性,综述了该种水泥与不同矿物掺合料的复合性能以及与化学外加剂的适应性,提出了硫铝酸钙改性硅酸盐水泥存在的问题及改善措施。     

水泥混凝土外加剂与水泥适应性探讨

在混凝土、砂浆或净浆的制备过程中,掺入不超过水泥用量5％（特殊情况除外）,能对混凝土、砂浆或净浆的正常性能要求而改性的一种产品,称为混凝土外加剂。混凝土外加剂的开发应用,使混凝土逐渐朝绿色高性能混凝土方向发展。然而混凝土外加剂与水泥之间有时存在不相适应的状况,影响了外加剂的应用效果和混凝土的性能。本文从混凝士外加剂、水泥等方面入手,对水泥混凝土外加剂与水泥适应性的影响因素及使用过程中应注意的问题进行了探讨。     

聚羧酸系减水剂在预拌混凝土中常见问题及分析

聚羧酸系减水剂作为一种新型的外加剂,具有减水率高、保塑性能好、水泥适应性强、混凝土收缩小等优点,但在掺入预拌混凝土的使用过程中,由于各种原因,引起混凝土的质量问题,合理选用使用原材料,提高聚羧酸类减水剂在预拌混凝土中的应用。     

有机膦酸类化合物在混凝土工程中的应用及缓凝机理研究进展

通过掺加具有水化热抑制作用的外加剂来降低胶凝体系的水化放热量及放热速率是减少混凝土中温度裂缝的重要措施。相对于葡萄糖酸钠和糖钠等常用缓凝材料,有机膦酸类化合物对硅酸盐水泥具有更为有效的水化热抑制作用和缓凝作用。过去几十年,有机膦酸类化合物在国外常被作为缓凝材料应用于工民建、油田固井和一些有特殊要求的混凝土工程中。在我国,有机膦酸类化合物主要应用在油田固井混凝土工程中,近年来在越来越多的工民建混凝土工程中也有所应用,但是其应用范围仍然十分有限。有机膦酸类化合物具有以下特征:(1)在一定掺量范围内可大幅降低硅酸盐水泥的水化放热速率和放热量,改善硅酸盐水泥水化放热过程;(2)有机膦酸类化合物对水泥熟料含量的变化不敏感,与硅酸盐水泥、聚羧酸减水剂和萘系减水剂均具有较好的适应性;(3)在一定掺量范围内,有机膦酸类化合物可改善混凝土拌合物性能,提高混凝土长期力学性能;(4)有机膦酸类化合物的主链结构具有高温稳定性,适用温度达200℃以上,在高温环境下其对硅酸盐水泥仍具有较强的缓凝作用。有机膦酸类化合物对硅酸盐水泥水化的影响较复杂,目前硅酸盐水泥缓凝机理尚不十分明确。不同学者对此持有不同的观点。其中一种观点认为:有机膦酸类化合物首先促进水泥中Ca~(2+)溶解,在富铝层表面促进水泥矿物水化,进而促进铝酸三钙(C_3A)的水化;接着与水泥中Ca~(2+)结合,在硅酸三钙(C_3S)表面形成半透水的稳定螯合物,抑制C_3S的水化,从而抑制水泥的进一步水化。而另一种观点认为:有机膦酸类化合物有效抑制了钙矾石凝胶向晶体转变的成核和生长过程,并认为延缓钙矾石晶体的生长是导致硅酸盐水泥缓凝的主要原因。本文从有机膦酸类化合物在混凝土工程中的应用着手,总结了有机膦酸类化合物对硅酸盐水泥水化动力学的影响以及缓凝机理的研究进展。基于此,为进一步扩大有机膦酸类化合物在混凝土工程中的应用范围,提出了应进一步研究有机膦酸化合物对混凝土力学性能、体积稳定性、热力学性能和耐久性能的影响,同时应进一步研究有机膦酸类化合物对硅酸盐水泥水化动力学的影响及缓凝机理。     

碱式硫酸镁水泥的研究进展及性能提升技术

碱式硫酸镁水泥(Basic magnesium sulfate cement,BMSC)是一种以外加剂技术为核心的新型镁质胶凝材料,主要由轻烧氧化镁、不同结晶水的硫酸镁、矿物掺合料与化学外加剂一起混磨而成,使用时与普通硅酸盐水泥一样加水拌和即可。碱式硫酸镁水泥具有氯氧镁水泥轻质、快凝、高强、耐磨的优点,且不易吸潮反卤。BMSC的主要水化产物5Mg(OH)_2·MgSO_4·7H_2O相(5·1·7相)的溶解度仅为0.034 g/100 g水,与硅酸盐水泥基本处于同一量级,远低于氯氧镁水泥,在建筑保温材料等领域可以广泛取代氯氧镁水泥。碱式硫酸镁水泥的抗折强度约为同强度等级硅酸盐水泥抗折强度的2～3倍,且其耐久性能、护筋性能与普通硅酸盐水泥相当。同时,BMSC混凝土具有较大的刚度和良好的抗震性能,其抗弯拉及抗冲击荷载性能均优于同等级普通硅酸盐水泥混凝土,尤其是开裂荷载比同强度、同配筋的普通混凝土大10%,因此其在结构工程领域也有良好的应用前景。更重要的是,用于制备碱式硫酸镁水泥的轻烧氧化镁的煅烧温度较低,使BMSC满足了建筑节能和环境保护的要求,有望成为未来核心高性能生态友好型水泥,具有巨大的发展潜力。本文概述了碱式硫酸镁水泥的性能特点,综述了其制备方法及水化过程,对比分析了碱式硫酸镁水泥、氯氧镁水泥和硫氧镁水泥的微观结构与性能的差异,阐明了镁质原料中α-MgO的含量和活性、α-MgO/MgSO_4及H_2O/MgSO_4的配料物质的量比、化学外加剂种类及掺量对碱式硫酸镁水泥微观结构及性能的影响。在此基础上,从原料及制备工艺等方面提出了进一步提升碱式硫酸镁水泥性能的措施,并展望了碱式硫酸镁水泥未来的研究方向。     

硫铝酸盐水泥混凝土力学性能影响因素分析

本文研究了水灰比,掺和料及其复合（矿渣：粉煤灰=2：1复掺）、引气剂对硫铝酸盐水泥（SAC）混凝土各龄期抗压强度的影响,并与普通硅酸盐水泥混凝土（OC）进行了对比,结果表明：水灰比的增加．引气剂和掺和料的掺入都会使混凝土的早期,后期强度明显降低,但是,对于普通硅酸盐水泥混凝土,由于显著的二次水化作用,在一定的掺量范围内,掺和料的加入使混凝土的早期强度降低,但后期强度增长甚至超过未加掺和料的混凝土。     

聚羧酸系减水剂在客运专线工程中的应用研究

介绍聚羧酸系减水剂在满足铁路客运专线高性能混凝土综合性能方面的能力和特点,分析了工程应用中使用聚羧酸系减水剂存在的一些问题。提出解决聚羧酸系减水剂与水泥的相容性问题以及保持聚羧酸系减水剂本身质量稳定性是目前该减水剂应用的关键。     

A study of the combined influence of condensed silica fume and a water reducing admixture on water demand and strength of concrete

In recent years condensed silica fume has been acknowledged as one of the most effective pozzolans ever added to concrete. Properly used in adequate amounts and combined with a water reducing admixture, many important qualities of concrete are achieved or secured. The principle of dosage of water reducing admixture adopted in this combination has been to dose a quantity proportional to the amount of silicate fume. The positive effect on concrete strength from this combination of admixtures has been described as an “efficiency factor” for 1 kg silica fume between two to five when the efficiency of 1 kg cement is the unit. This study shows first that the dosing principle used until now is contradicted by experimental evidence and secondly that the water reducing admixture (lignosulfonate) used in the experimental series studied is responsible for 60% or more of the strength gain at 28 days, whereas the silica fume has to be credited for less than 40%. A more correct “efficiency factor” can then be calculated.     

大掺量粉煤灰复合水泥物理性能与混凝土性能

大掺量粉煤灰复合水泥混合材的组合方式对水泥的物理性能会产生影响 ,同时水泥的混凝土性能也会随之有明显的改善     

Application of factorial models to predict the effect of anti-washout admixture, superplasticizer and cement on slump, flow time and washout resistance of underwater concrete

The anti-washout underwater concrete posses different properties from conventional underwater concrete. When an anti-washout admixture is mixed with concrete, the viscosity of the concrete is increased and its resistance to washout is enhanced. Superplasticizer ensures enough concrete fluidity to spread readily in place without vibration. A factorial design was carried out to mathematically model the influence of three key parameters on slump, flow time measured by Orimet and mass loss by washout of underwater concrete. The parameters considered in this investigation were the dosage of cement, the concentrations of anti-washout admixture and superplasticizer. All mixes were made with 0.43 water/cement ratio which correspond a typical underwater concrete. The proposed models are valid for concretes with cement dosage ranging between 420 kg/m³ to 520 kg/m³ and the concentrations of anti-washout admixture and superplasticizer varying between 0.02%–0.13% and 0.4%–1.8%, by mass of cement, respectively. Test results of the models indicated that the slump is highly affected, in order of importance, by dosage of cement and the dosage of superplasticizer, then by the concentration of anti-washout admixture. The mass loss by washout is influenced, in order of significance, by the concentration of anti-washout admixture, the dosage of cement, the concentration of superplasticizer and the interaction between the dosages of cement and anti-washout admixture. The flow time is affected, in order of importance, by the dosage of cement, the concentration of superplasticizer and the interaction between these parameters. This model can be used as a tool to facilitate the test protocol required to optimise the underwater concrete.     

自密实混凝土工作性研究

本文主要介绍了自密实混凝土的定义。就流动性而言,自密实混凝土属于宾汉姆（Bingham）模型,成型好坏与混凝土塑性黏度η有关。高效减水剂、砂率、矿物掺合料、水胶比和胶凝材料的用量对自密实混凝土的工作性能有显著的影响。     

膨胀剂和钢管侧限对混凝土徐变应变的影响

为了研究不同膨胀剂质量分数和钢管侧限对混凝土徐变应变的影响,共进行了12组有、无钢管侧限的混凝土徐变试验。结果表明:加载龄期到480天的试验试件中,有钢管侧限的混凝土徐变应变约是无钢管侧限徐变应变的0.175~0.181倍,钢管侧限大大降低了混凝土的徐变应变。同时进行了三种不同质量分数膨胀剂(质量分数分别为4%、8%和12%)的混凝土徐变试验。结果表明:无论有、无钢管侧限的混凝土结构,膨胀剂质量分数对混凝土徐变应变的影响关系为:质量分数4%时,结构徐变应变均最大;质量分数为8%时,结构徐变应变次之;质量分数为12%时,结构徐变应变最小。通过钢管侧限对混凝土的套箍效应计算分析表明,在混凝土结构加载应力相同情况下,有钢管侧限的混凝土结构应力比小于无侧限的混凝土结构应力比;钢管侧限对混凝土的侧向约束增加,限制了混凝土纵向变形;随着应力比的减小,结构徐变变形减小。同时应用扫描电镜二次电子成像分析膨胀剂的作用机制得出:水泥浆中膨胀剂水化产生粗棒状、互相交叉的三硫型硫铝酸钙(AFt)结晶体,填充在原来被溶液占据的小孔里,使水泥石更密实。     

Concrete carbonation in arid climate

Fifty-four different concrete mixes were exposed to hot arid weather in Kuwait to monitor their extent of carbonation. Various parameters affecting carbonation such as water/cement ratio, cement content, type of cement, type and dosage of admixture, water-curing period, type of coating, and the addition of silica fume or pulverized fuel ash were investigated. For many of these variables, the carbonation depth and rate constant (K) are reported for an exposure period of 8.6 years. The results show that the water/cement ratio is one of the main factors affecting carbonation. The values of (K) ranged from 2.1 to 7.8 as the water/cement ratio increased from 0.45 to 0.8. Concrete made with white Portland cement carbonated less than ordinary or sulphate resisting cements. Two curing compounds were effective in reducing carbonation while two coating materials prevented carbonation after eight years of exposure.     

Prediction of setting for admixture modified mortars using the VCCTL

The time at which Portland cement concrete transitions from a viscous suspension of particles to a rigid interconnected matrix is commonly referred to as “time of set” and is a critical parameter when placing concrete structures. Use of chemical admixtures in concrete for water reduction or acceleration of hydration alters setting behavior; laboratory quality control testing is required to define the altered setting behavior. Use of the Virtual Cement and Concrete Testing Laboratory (VCCTL) for prediction of early age concrete behavior has been limited to plain portland cement concrete. Direct modeling of kinetic and thermodynamic behavior for admixture modified concrete remains challenging.An indirect method to simulate admixture alteration of set is proposed. Hydration simulations are time calibrated using heat of hydration curves obtained from admixture bearing pastes. Simulation results are compared to mortar setting tests, with agreement in certain cases falling within standard specified precision values.     

Effect of gypsum type on properties of cementitious materials containing high range water reducing admixture

In this study, the effect of cement gypsum type on properties of the properties of cement paste, mortar and concrete mixtures containing high range water reducing admixture (HRWR) was investigated. Two different types of cement prepared from the same clinker but containing either calcium sulfate hemihydrate or dihydrate as retarder were used. The fresh and hardened (compressive strength and drying-shrinkage) properties as well as static and dynamic rheological behavior of the mixtures were investigated. Compared to the mixtures containing dihydtate, the fresh and rheological properties of mixtures were negatively affected when cement-containing hemihydrate was used. However, hemihydrate utilization had a positive influence on the early compressive strength. The adverse effects on fresh properties were more significant in paste mixtures. These negative effects decreased in the mortar and concrete mixtures. The presence of hemihydrate in cement was found to increase the drying-shrinkage.     

Effects of chromium(VI) reducing agents in cement on corrosion of reinforcing steel

During the production of cement it is necessary to add a reducing agent that converts soluble hexavalent chromium into trivalent chromium. This paper explores effects of iron(II) sulphate reducing agents, namely monosulphate and heptahydrate, as cement admixtures, on corrosion of concrete reinforcement. Accelerated corrosion tests of reinforcing steel have been performed in pore solutions simulating concrete prepared using either CEM I or CEM II type cement, with addition of various concentrations of iron(II) sulphate reducing agent. All of the test results indicate corresponding tendencies and point towards the potential for iron(II) sulphate to foster or accelerate corrosion of the reinforcement. The results of this study indicate an immediate need for a more detailed research, especially in concrete as a more realistic corrosion environment, of the application of iron(II) sulphate as a reducing agent in cement.