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     

Hydration of Portland cement with additions of calcium sulfoaluminates

The effect of mineral additions based on calcium aluminates on the hydration mechanism of ordinary Portland cement (OPC) was investigated using isothermal calorimetry, thermal analysis, X-ray diffraction, scanning electron microscopy, solid state nuclear magnetic resonance and pore solution analysis. Results show that the addition of a calcium sulfoaluminate cement (CSA) to the OPC does not affect the hydration mechanism of alite but controls the aluminate dissolution. In the second blend investigated, a rapid setting cement, the amorphous calcium aluminate reacts very fast to ettringite. The release of aluminum ions strongly retards the hydration of alite but the C–S–H has a similar composition as in OPC with no additional Al to Si substitution. As in CSA–OPC, the aluminate hydration is controlled by the availability of sulfates. The coupling of thermodynamic modeling with the kinetic equations predicts the amount of hydrates and pore solution compositions as a function of time and validates the model in these systems.     

Influence of Portland cement composition on early age reactions with metakaolin

The reactivity of two metakaolins, which vary principally in their surface area, and Portland cements of varying composition were examined via isothermal calorimetry for pastes at water-to-cementitious materials ratio of 0.50 containing 8% cement replacement by weight of metakaolin. Both metakaolins examined appear to have a catalysing effect on cement hydration. Calorimetry showed accelerated hydration, a slight increase in cumulative heat evolved during early hydration, and - for some cements examined - apparently an increased intensity of the heat evolved, particularly during the period typically associated with hydration of calcium aluminates. The higher surface area metakaolin had a greater effect. It is proposed that the presence of metakaolin may enhance dissolution of cementitious phases and/or provide additional, well-dispersed sites for nucleation of hydration products, in addition to increasing the early age concentration of solubilized aluminium (due to metakaolin dissolution). The increased intensity of some of the calorimetry data also suggests that some additional exothermic reactions are occurring, which may be related to an increased reactivity of calcium aluminate phases in the cement as well as the reaction of the metakaolin. This effect is apparently increased as the cement equivalent alkali content increases.     

Interaction between ettringite and a polynaphthalene sulfonate superplasticizer in a cementitious paste

It has been recognized that the interaction between a superplasticizer and C3A is crucial when controlling the rheology of Portland cement grouts, mortars and concretes. In spite of the fact that a great deal of research has been done to understand the exact nature of this interaction using different experimental techniques, there is not yet a clear understanding of all the basic principles which command that interaction. In an attempt to cast some complementary light in the type of interactions developed between C3A, Portland cement and a polynaphthalene sulfonate superplasticizer in the presence of calcium sulfate, the rheological behavior of a particular cementitious system in which only calcium aluminates or calcium sulfoaluminates hydrated phases could be formed has been studied. This study has shown that superplasticizer molecules are not only adsorbed on unhydrated cement phases but also and perhaps more on some of their hydrates. This adsorption on the hydrates slows down drastically or even stops the growth of ettringite germs. However, when all the initial superplasticizer molecules have been consumed normal growth of ettringite resumes. This interaction between superplasticizer molecules and ettringite can be used to explain the important water consumption in the early stages of mixing as well as the never answered question: where are all the superplasticizer molecules in a hardened concrete.     

油井水泥浆流变模型研究进展

油井水泥浆的流变性是水泥浆配方设计的核心及安全施工的前提。本文就国内外水泥浆流变模型、计算方法、流变特性及其主要影响因素（温度和压力）进行了综合评述。最后提出了水泥浆配方流变学设计的试验操作流程。     

Stress from crystallization of salt

The thermodynamic and kinetic factors influencing crystallization pressure are reviewed for cases including capillary rise and evaporation, cyclic wetting and drying, and hydration of cement. Under equilibrium conditions, where the crystal is surrounded by a film of solution, high stresses are expected only in small pores, but when that film is discontinuous (as may occur during drying), high stresses can arise even in large pores. High crystallization pressure requires a substantial supersaturation of the pore liquid. In the case of sodium sulfate, supersaturation results from the difference in solubility between the anhydrate and decahydrate phases; for ettringite, supersaturation may develop following the cooling from elevated temperatures. During the hydration of Portland cement, crystallization pressure may result from the growth of ettringite and/or calcium hydroxide.     

低热硅酸盐水泥水化及性能研究现状

低热硅酸盐水泥因水化热低而被大量应用于高等级大体积混凝土工程以降低温度应力给结构带来的开裂风险。此外,高温下强度增长稳定的特点决定其能在高热施工环境发挥作用,优良的体积稳定性有利于解决混凝土结构开裂问题,较高的后期强度和优良的抗侵蚀性能适合用于高性能混凝土的制备。本文从水化、性能等角度出发,分析了低热硅酸盐水泥在水化调控、水化产物及微观结构、性能优化等方面存在的部分问题,总结了低热硅酸盐水泥高温耐受、抗侵蚀、体积稳定等性能特点,提出了低热硅酸盐水泥在严酷环境、高热环境中的应用展望。     

超硫酸盐水泥净浆的酸性侵蚀劣化机制

本文对比研究了超硫酸盐水泥(SSC)与硅酸盐水泥在盐酸侵蚀条件下的力学性能变化规律,探讨了SSC的酸性侵蚀劣化机制。测试了SSC净浆试件正常养护后在盐酸溶液以及清水中抗压强度的变化,并计算了抗压强度保持率;采用X射线衍射(XRD)、扫描电子显微镜(SEM)和热重分析(TG-DTG)等微观测试方法分析了SSC在盐酸侵蚀下水化产物种类和数量的变化,并探究了其微观结构的演化过程,分析了劣化机理。结果表明：不同于硅酸盐体系,SSC体系主要水化产物为钙矾石和水化硅酸钙;与硅酸盐水泥相比,SSC在酸中具有较高的抗压强度保持率和更好的抗酸性侵蚀性能;盐酸侵蚀SSC后,SSC主要水化产物均被分解,体系中存在二水石膏和大量的二氧化硅胶体,而硅酸盐水泥体系中则存在大量的二氧化硅胶体。     

Improved chloride binding stability for hydration products of calcium aluminates by phosphorus modification

Improved chloride binding stability for calcium aluminate cements is proposed by the doping of phosphorus. Phosphorus-modified aluminates clinker has an improved chloride binding stability compared to pristine aluminates, ordinary Portland cement and sulfur-modified calcium aluminates, as verified by experimental observation. The existence of the newly found phosphorus-modified Friedel's salt (PFS) accounts for the excellent chloride binding stability, which was understood by density functional theory calculations. Local density of states of the valence band minimum is predominantly localized around P atoms in the PFS, but evenly distributed in the Friedel's salt (FS). The frontier band energy of the partial density of states on Cl and O elements in the PFS is lower than that in the FS by 0.21 and 0.05 eV, respectively. This makes the PFS more stable than the FS salt to ionic attack.     

磷渣对硅酸盐水泥的缓凝机理

在对已有的磷渣缓凝机理进行分析的基础上,通过实验对他们的论点进行了质疑,提出了吸附机理,即在硅酸盐水泥水化初期形成的半透水性水化产物薄膜对磷渣颗粒的吸附,导致这层薄膜致密性增加,从而导致离子和水通过薄膜的速率下降,引起水化速度降低,最终导致缓凝,并运用这个观点分析了磷渣比表面积与P,F含量不同对凝结时间的影响机理.     

Oil well cement slurries II. Adsorption behaviour of dispersants

The adsorption of naphthalene sulfonate formaldehyde condensate (NSFC) on the surface of cement particles has been measured for slurries based on different class G oil-well cements and is correlated to their rheological properties. The influence of the order of addition on the adsorption and the resulting slurry rheology is shown and discussed. The conditions for the reversibility and irreversibility of NSFC adsorption are discussed. The amount of NSFC adsorbed has been monitored versus time of hydration at 25°C and 85°C. The retarding side effect of this oligomer on the hydration of a cement slurry is described and a mechanism of action proposed.     

石膏掺量对高阿利特水泥防腐抗渗性能的影响研究

研究了石膏掺量对高阿利特水泥抗海水侵蚀和抗渗性能的影响,并与普通水泥进行了比较。利用XRD、SEM—EDS等测试方法对水泥水化产物的物相组成和形貌进行分析、观察;用压汞法对水泥硬化浆体的孔结构进行了分析。结果表明,石膏掺量对高阿利特水泥硬化浆体的致密性有较大影响,进而影响水泥砂浆的抗海水侵蚀性能,石膏的适宜掺量为5％,在此掺量下高阿利特水泥的抗蚀系数达1．01,而普通水泥的抗蚀系数仅为0．87,高阿利特水泥的有害孔较少,总孔隙率较低,抗渗性能得到较大改善。     

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。     

水泥浆粉去除废水中铅离子效果及行为研究

水泥浆粉含有可吸附重金属离子的成分,可作为吸附剂来处理重金属离子废水。本文利用硅酸盐水泥制备了不同水化龄期的水泥浆粉来处理含Pb²⁺废水,通过X射线衍射仪、同步热分析仪、电感耦合等离子体发射光谱仪等测试方法,研究了水泥浆粉龄期、浆粉用量、Pb²⁺浓度、pH值、温度、时间对Pb²⁺去除效果及吸附行为的影响。结果表明,水泥浆粉对废水中的Pb²⁺去除率普遍大于80%。在35 ℃、pH=2、吸附时间200 min时,0.04 g水灰比为0.50、水化龄期为60 d的水泥浆粉对初始浓度为700 mg/L的Pb²⁺溶液的Pb²⁺去除率为96.06%,吸附容量为336.22 mg/g。水泥浆粉对Pb²⁺的吸附热力学符合Freundlich吸附等温模型,吸附动力学符合拟一级动力学模型。     

Incorporation of Waste Materials into Portland Cement Clinker Synthesized from Reagent-Grade Chemicals

In this study, the feasibility of using waste materials to manufacture Portland cement was investigated. Reagent-grade chemicals were used to synthesize a Portland cement clinker with a tightly controlled composition. Then, calcium oxide-bearing waste materials, specifically fly ash and blast furnace slag, were combined with the reagent-grade chemicals. The synthetic cements were characterized using X-ray diffraction, scanning electron microscopy, and isothermal calorimetry. Results show that Portland cement can be successfully synthesized by replacing reagent-grade chemicals with up to 40% fly ash and 60% slag incorporation. These synthetic cements possess early-age hydration behavior similar to a commercial Type I/II Portland cement.     

Filler cement: The effect of the secondary component on the hydration of Portland cement: Part 2: Fine hydraulic binders

In Part 1 of this paper, it was shown that enhanced hydration was achieved by blending a fine non-hydraulic filler into an ordinary Portland cement. This enhancement was considered to be a particle size effect and associated with the presence of fine particles of filler which provided the additional nucleation sites. The filler, rutile, had a variable cement equivalence and reached a maximum value of 0.9kg/kg after hydration had proceeded for three days. In this second part, the same Portland cement was blended seperately with latent hydraulic binders (two pulverized fuel ashes and a ground granulated blastfurnace slag, a Lurgi slag and a volatilized silica). The apparent overall reactivity of these binders was seen to have two components, the first being the particle size effect with its influence on the hydration of the Portland cement and the second the inherent hydraulicity of the secondary material.     

The hydration of Portland cement,C3S and C2S in the presence of a calcium complexing admixture (EDTA)

The effect of EDTA, a calcium chelating agent, on the early hydration of Portland cement, C₃Sand β-C₂S has been studied by solution analysis and electron microscopy. EDTA is a retarded of cement hydration. Under normal conditions of hydration, the silica levels in solution are very low (<0.05 M) but in the presence of EDTA an initial flush of silica appears in the bulk aqueous phase. On continued hydration, following the saturation of EDTA with calcium, the appearance of ‘free’ calcium causes precipitation of C-S-H gel from the bulk solution and changes in microstructure of the colloidal gel around clinker particles in C₃S and β-C₂S pastes are observed. The action of EDTA as a retarding admixture is explained in terms of the membrane model of cement hydration.     

纳米氧化铝对硅酸盐水泥浆体流变、水化和硬化强度的影响

本文研究了纳米氧化铝(NA)对硅酸盐水泥浆体的早期流变性、中期水化特性和后期力学性能的影响,并且分析了三个阶段之间参数的相关性。结果表明,NA的掺入增大了新拌水泥浆体的屈服应力和塑性黏度,且当NA掺量范围为3%~5%时,屈服应力和塑性黏度最大增幅均超过110%。在水泥浆体中掺入NA明显改变了硅酸盐水泥早期的水化放热速率和放热量,并且使得浆体在各龄期的抗压强度和抗折强度有所增长。对于该复合胶凝体系,早期的水化放热量与流变参数呈指数增长的变化趋势,而放热峰值速率与抗压强度则存在近似线性的函数关系。     

水泥-石灰石粉浆体流变经时行为研究

研究了水泥-石灰石粉浆体流变参数随水化时间的变化,采取RHEORIAB QC型旋转黏度计测定水泥-石灰石粉浆体流变,采用Herschel-Bulkley模型拟合浆体曲线得到相关流变参数,分别利用Roussel和Philippe提出的模型对水泥-石灰石粉浆体的动态屈服应力和稠度进行拟合。结果表明：水泥浆体动态屈服应力比石灰石粉浆体小,稠度比石灰石粉浆体大;水泥-石灰石粉浆体动态屈服应力、稠度随水化时间线性增大,随石灰石粉掺量增加,增大速率线性减小,其初始动态屈服应力线性增大,初始稠度按二次抛物线先增大后减小。     

碳酸化对普通硅酸盐水泥水化性能的影响

通过控制加水量来调节普通硅酸盐水泥的碳酸化程度。通过对硬化浆体水化产物的种类及含量进行分析,研究了在不同的加水量下,碳酸化对普通硅酸盐水泥水化性能的影响。结果表明：在加水量为0.2%～7%的范围内,碳酸化增重率由0.133%增至6.8%;普通硅酸盐水泥经碳酸化后,生成CaCO3晶体颗粒;f-CaO的含量由1.584%下降至0.198%;随着碳酸化增重率的增大,碳酸化水泥的标准稠度用水量由0.28增至0.42;碳酸化降低了普通硅酸盐水泥3 d、28 d抗压强度,尤其对3 d抗压强度影响更为明显;碳酸化生成的CaCO3易与水泥中的C3A反应生成碳铝酸钙;碳酸化抑制普通硅酸盐水泥的早期水化,但对后期水化影响较小。