Properties of blended cements with thermally activated kaolin

Kaolin, one of the materials of major importance for the ceramic and paper industry, is also used in the construction industry as a raw material for the production of white cement clinker and, in the form of metakaolin, as an artificial pozzolanic additive for concrete. Metakaolin is a vital component of high-performance and architectural concrete; however, its application in regular concrete is very limited due to relatively high production costs. This report evaluates the performance of a low-cost metakaolin-based additive called thermally activated kaolin (TAK), in cement. Due to its pozzolanic properties and the densification of cement matrix, the application of TAK provides a 15% improvement of the compressive strength. It was shown that TAK of optimal quality can be manufactured by the thermal treatment of raw kaolin with 74% of kaolinite at 750 °C without the intermediate beneficiation stage. The application of a developed approach can significantly reduce production expenditures and make the application of such an additive feasible even in regular-grade cement and concrete.     

Study of the hydration process of quaternary blended cements and durability of the produced mortars and concretes

This study aims to clarify the effect that blended cements with four components have on the hydration process and durability of concrete. Therefore, blended cements with two different proportions of high calcium fly ash, natural pozzolan and limestone have been produced and have been compared with CEM I. Compressive strength was measured at different ages and the hydration kinetics was studied by means of proton nuclear magnetic resonance (NMR-H). Furthermore, the above mentioned cements have been used to produce mortars and concretes and their durability have been determined. The aspects of durability that has been determined are: pore size distribution by means of NMR-H and mercury intrusion porosimetry, penetration of chlorides, carbonation and resistance to sulfates attack. The conclusion of the present study is that quaternary blended cements can perform as well as CEM I cement as far as compressive strength are concerned and they produce durable mortars and concretes.     

Sodium sulfate attack on plain and blended cements

This paper presents an investigation into the sodium sulfate resistance of three portland cements of various compound compositions and 24 blended cements produced by replacing 10%, 20%, 30% and 40% of these cements with a fly ash and a natural pozzolan. Sulfate expansion of mortar specimens was evaluated using ASTM C1012 test procedure. No acid titration was made to change pH of the sulfate solution. In addition to 5% sodium sulfate concentration prescribed in the standard, 18 selected cements were also exposed to sodium sulfate of 3% concentration. A mathematical expression was developed to estimate the sulfate susceptibility of cements regarding their C₃A, C₃S/C₂S ratio, mineral additive content as well as concentration of sulfate solution.     

Sulfate resistance of blended cements containing fly ash and rice husk ash

In this paper, the sulfate resistance of mortars made from ordinary Portland cement containing available pozzolans viz., fly ash and ground rice husk ash (RHA) was studied. Class F lignite fly ash and RHA were used at replacement dosages of 20 and 40% by weight of cement. Expansion of mortar prisms immersed in 5% sodium sulfate solution and the change in the pH values of the solution were monitored. The incorporation of fly ash and RHA reduced the expansion of the mortar bars and the pH values of the solutions. RHA was found to be more effective than fly ash. Examination of the fractured surface of mortar prisms, after a period of immersion, by scanning electron microscopy confirmed that sulfate attack of blended cement mortars was restricted owing to the reductions in calcium hydroxide and C/S ratio of the C–S–H gel in the blended cement mortar. In comparison to Portland cement mortar, less calcium sulfate and much less ettringite formations were found in the mortars made from blended cement containing RHA. The amounts of calcium sulfate and ettringite found in the blended cement mortar containing fly ash were also small but were slightly more than those of RHA mortar. Up to 40% of Portland cement could be replaced with these pozzolans in making blended cement with good sulfate resistance.     

Sulfate resistance of plain and blended cements exposed to magnesium sulfate solutions

This study was conducted to evaluate the performance of plain and blended cements exposed to magnesium sulfate solutions with varying sulfate concentrations for up to 24 months. Four types of cements, namely Type I, Type V, Type I plus silica fume, and Type I plus fly ash, were exposed to five magnesium sulfate solutions with sulfate concentration of 1%, 1.5%, 2.0%, 2.5%, and 4.0%. The sulfate-resistance was evaluated by visual examination, and measuring reduction in compressive strength. Maximum deterioration, due to sulfate attack, was noted in Type I cement. The performance of Type V, Type I plus silica fume and Type I plus fly ash cements was not significantly different from each other. The enhanced sulfate-resistance noted in the Type I cement blended with either silica fume or fly ash indicates the usefulness of these cements both in sulfate and sulfate plus chloride environments.     

Utilization of beet molasses as a grinding aid in blended cements

This paper investigates the viability of using beet molasses as a grinding aid for blended cements with high volumes of mineral admixtures. Different ratios of beet molasses (0.01–0.05% by weight of cement) were added into a blended cement containing 41% of fly ash and GBFS. The influence of beet molasses on performances of blended cement was studied by comparing with one commercially available, triethanolamine-based grinding aid (TA). The results show that when comparing with the blank cement mixture, the cement containing 0.02–0.03% molasses shows a higher compressive strength at 3 days and 28 days, even exceeding the TA mixture. The improved microstructure of the molasses modified cement paste was also demonstrated by the pore structure and SEM measurements. These improvements are attributed to the better particle size distribution induced by the addition of molasses, indicating the potential application of beet molasses as a good grinding aid.     

Freeze–thaw resistance of blended cements containing calcined paper sludge

This work deals with the frost resistance of blended cements containing calcined paper sludge (source for metakaolin) as partial Portland cement replacements. Freeze–thaw tests were performed on blended cement mortars containing 0%, 10% and 20% waste paper sludge calcined at 650 °C for 2 h. Cement mortar specimens were exposed to freezing and thawing cycles until the relative dynamic modulus of elasticity fell below 60%. The performance of the cement mortars was assessed from measurements of weight, ultrasonic pulse velocity, compressive strength, mercury intrusion porosimetry and SEM. Failure of the control cement mortar occurred before 40 freeze/thaw cycles, while cement mortar containing 20% calcined paper sludge failed after 100 cycles. After 28 and 62 freezing and thawing cycles, cement blended with 10% and 20% calcined paper sludge exhibited a smaller reduction in compressive strength than the control cement.     

掺多元复合矿物外加剂高性能混凝土耐久性

指出矿物外加剂的复合化是配置高性能混凝土的良好途径,尤其在提高混凝土耐久性方面,发挥了明显的效应,从抗渗性能、抗冻融性能、抗硫酸盐侵蚀性能、抗碳化性能和抵抗碱—集料反应能力等方面,阐述了粉煤灰、矿渣与硅灰多元复合矿物外加剂高性能混凝土的耐久性。     

A study of the permeability and acid attack of corn cob ash blended cements

The durability of concrete made with corn cob ash (CCA) blended cement was investigated in this study. Permeability and chemical attack involving H₂SO₄ and HCl were the key parameters considered. Nine classes of CCA blended cements were employed with the CCA content ranging from 0% to 25%. The 0% CCA replacement involved the use of normal ordinary Portland cement and it served as the control. The water absorption of blended cement concrete was performed using 100 mm cube specimens of mix proportions 1:1½:3, 1:2:4 and 1:3:6 with 0.5, 0.6 and 0.7 water-to-binder ratios, respectively. The chemical attack test was carried out using 50 × 50 × 15 mm mortar specimens of mix proportions 1:1, 1:2 and 1:3 with water-to-binder ratio ranging between 0.26 and 0.29. The results indicated that the use of CCA blended cement reduces the water absorption of concrete specimens. Optimal reduction occurred at 10% CCA replacement for 1:1½:3 and 1:2:4 mix proportions and at 15% CCA replacement for 1:3:6 mix proportion. The resistance to chemical attack was improved as the addition of CCA up to 15% replacement level, caused a decrease in permeability and reduction in weight loss due to reaction of the specimens with HCl and H₂SO₄ acid water.     

电阻率法研究矿物掺合料对水泥早期水化的影响

进一步开发利用矿物掺合料潜在的水化活性一直受到关注。有文献表明：水泥浆体的早期水化与其电阻率有着一定的关系．但用电阻率法对水泥浆体早期水化研究较少。基于此，本文研究了掺矿物掺合料浆体的水化过程，并采用一种新型仪器——非接触式电阻率测量仪。试验还通过强度测试和XRD作了定量和定性的分析。结果表明：电阻率曲线不仅表现了掺不同矿物掺合料的浆体的水化过程，也表现了不同矿物掺合料的活性的大小。强度试验和XRD对矿物掺合料的活性作了进一步的证实。     

Sulfate attack and reinforcement corrosion in plain and blended cements exposed to sulfate environments

The extensive use and addition of mineral admixtures and the recent modifications in the physicochemical characteristics of portland cements have introduced a large number of variables that need to be addressed. Furthermore, the effect of cations associated with sulfate ions on these variables is inconclusive and extensively debated in the literature. On the other hand, the exposure of many reinforced concrete structures to sulfate-bearing environments has brought attention to the role of sulfate ions in the corrosion of reinforcing steel. Unfortunately, there is very little data on this aspect. The following subjects are addressed: (i) the effect of sulfate cation type on strength and expansion; (ii) the role of sulfate ions in reinforcement corrosion; (iii) the role of plain and blended cements in both sulfate attack and reinforcement corrosion; and (iv) a comparison of the performance of concrete made with the above-cited cements with that of small (25 mm cube) cube mortar specimens.     

Effect of initial curing on chloride ingress and corrosion resistance characteristics of concretes made with plain and blended cements

This paper reports the results of an experimental study conducted to evaluate the effect of initial curing conditions on the chloride ingress characteristics of concretes made with plain and four different blended cements. In addition, the corrosive behavior of steel bars embedded in plain and blended cement concretes were studied through half-cell potential measurements. A total of ten different concrete mixtures having water–cement (w/c) ratios of 0.65 and 0.45 were cast and tested. Test specimens were subjected to three different initial curing conditions, namely uncontrolled, controlled, and wet before exposure to high chloride environment. The research variables included cement type (i.e., plain and blended cements), w/c ratio, and initial curing condition. The results indicated that the initial curing condition had pronounced effects on the related properties: in particular, the most prominent effects were observed on blended cement concretes, which performed extremely well when initially cured in wet conditions. Inadequate or poor initial curing practice resulted in remarkably lower chloride penetration resistance for both plain and especially blended cement concretes.     

Properties of blended sulfoaluminate belite cement

The subject of the study was the possibility of the blending of sulfoaluminate belite (SAB) cement by means of various pozzolanas. The results obtained show that it was possible effectively to modify the properties of SAB cement by means of granulated blast furnace slag, fly ash, and silica fume, and the properties of materials based on these blends. Interesting properties from practical viewpoints of these materials was their compressive strength. As it is very well known, this is by the blending used to decrease. From a viewpoint of the acceptable compressive strength decrease, for SAB cement blends well-found portions of pozzolana with the values of approximately 5–15% seem to be optimal. This range was significantly lower than well-found portions of pozzolanas with values of approximately 20–40% for Ordinary Portland Cement (OPC) blends. The main cause was the fact that unique sources of calcium hydroxide needed for pozzolanic reaction in SAB was only β–C₂S compared to OPC having two sources of calcium hydroxide — the hydration of C₃S and β–C₂S. Therefore, the amount of calcium hydroxide for the pozzolanic reaction in the SAB cement blends was significantly lower. That was why the lower portions of pozzolanas in SAB cement blends were suitable.     

Effect of blended cements produced with natural zeolite and industrial by-products on alkali-silica reaction and sulfate resistance of concrete

In this study, influence of blended cements produced with different types of pozzolans on alkali-silica reaction (ASR) and sulfate resistance of concrete was investigated. For this reason, natural zeolite (clinoptilolite), fly ash (FA), and ground granulated blast furnace slag (GBFS) were used in different types of blended cement production. According to the mechanical performance of these blended cements, ASR and sulfate resistance experiments were carried out to obtain the durability performance of these cements. The length changes and microstructure investigations of the mortar specimens with different types of blended cements showed that zeolite, FA, and GBFS had reduced ASR and sulfate damages when compared with ordinary CEM I 42.5 reference specimen.     

A study on the hydration rate of natural zeolite blended cement pastes

Natural zeolite is a type of mineralogical material containing large quantities of reactive SiO₂ and Al₂O_3. It is widely used in the cement industry in China as a cement blending material. Like other pozzolanic materials such as silica fume and fly ash, zeolite contributes to concrete strength mainly through the pozzolanic reaction with Ca(OH)₂, Thus, the pozzolanic reactivity of this type of material in comparison with other pozzolans is of much interest. This paper presents experimental results on the compressive strength, degree of pozzolanic reaction, and porosity of zeolite modified cement pastes. These results are compared with those obtained from similar blended cement pastes prepared with silica fume and fly ash replacements. Based on the experimental results, it can be concluded that natural zeolite is a pozzolanic material, with a reactivity between that of silica fume and fly ash. Generally, in blended cement pastes with a lower water-to-cementitious materials ratio, the natural zeolite contributes more to the strength of the pastes. But in the pastes with a higher water to cementitious ratio and a lower cement replacement level it undergoes a higher degree of reaction.     

Sulfate resistance of plain and blended cements exposed to wetting–drying and heating–cooling environments

Exposure conditions significantly affect the resistance of cements to sulfate attack. This article investigates the sulfate resistance of ordinary portland cement (OPC), sulfate resistant portland cement (SRPC), and blended cements with different proportions of natural pozzolan and Class F fly ash when subjected to different exposure regimes. Plain and blended cement mortar specimens were stored under three different conditions: (i) continuous curing in lime-saturated water, (ii) continuous exposure to 5% Na₂SO₄ solution at room temperature, and (iii) cyclic exposure to 5% Na₂SO₄ solution at room temperature in which the cycles consisted of wetting–drying and heating–cooling. The sulfate resistance of cements was evaluated by measuring the reduction in compressive strength and length change of mortar specimens up to one year of exposure. This study revealed that the performance of blended cements under sodium sulfate solution at room temperature was better than that of SRPC with a 3.6% C₃A content when the length change was considered. However, for the structures exposed to sulfate attack and cycles of wetting–drying and heating–cooling, SRPC was found to perform better than blended cements when the compressive strength losses were considered.     

Combined effect of mineral admixtures with superplasticizers on the fluidity of the blended cement paste

The new concrete often incorporates several organic and mineral admixtures which interact with the various constituents of the cements and cause some problems of hardness and workability. In the present study, limestone cement (C1) and pozzolanic cement (C2) were used to make cement paste with two types of superplasticizer; SP1 based on polynaphthalene sulphonate (PNS); and SP2 based on resins melamines (PRM). Marsh cone test was adopted to check the combined effects of the following factors on the fluidity namely the type of cement, the type and the dosage of the superplasticizer, the type and the replacement rate of the mineral admixture and the water–cement ratio (W/C). The results of this work show that limestone cement presents a high fluidity with low loss after 1 h relatively to the pozzolanic cement within the saturation proportioning. Superplasticizer SP1 constitutes an incompatibility case when it is mixed with cement containing high C₃A or alkali content such as C2 cement. Also, limestone powder is found to be the best mineral admixture when it replaces a part of cement, where more fluidity is exhibited caused by the dilution effect.     

Strength and drying shrinkage properties of self-compacting concretes incorporating multi-system blended mineral admixtures

Drying shrinkage can be a major reason for the deterioration of concrete structures. The contraction of the material is normally hindered by either internal or external restraints so that tensile stresses are induced. These stresses may exceed the tensile strength and cause concrete to crack. The present study investigated compressive strength and particularly drying shrinkage properties of self-compacting concretes containing binary, ternary, and quaternary blends of Portland cement, fly ash (FA), ground granulated blast furnace slag (GGBFS), silica fume (SF), and metakaolin (MK). For this purpose, a total of 65 self-compacting concrete (SCC) mixtures were prepared at two different water to binder ratios. It was observed that drying shrinkage lessened with the use of FA, GGBFS, and MK while incorporation of SF increased the drying shrinkage.     

矿物外加剂对氯氧镁水泥水化放热特性的影响

以青海察尔汗盐湖水氯镁石部分热解产物作为镁水泥原料,采用内掺法掺入不同矿物外加剂(粉煤灰、硅灰及矿渣),进行水化热试验.试验结果表明:3种矿物外加剂均能降低热解镁水泥水化热,其中粉煤灰降低效果最好;矿物外加剂掺量越大,热解镁水泥水化热值降低越大.本试验为镁水泥中掺加粉煤灰、硅灰及矿渣降低水化热值、减少温度对体积稳定性的...