Influence of alkali on the sulphate resistance of ordinary portland cement mortars

The work described here indicates that the alkali content of an ordinary portland cement (opc) has an influence on the sulphate resistance of mortars made with it. Some criteria regarding the relationships between the C₃A, SO₃ and Na₂O eq contents of an opc to minimise or prevent sulphate expansion of mortars made with it, are suggested.     

Compressive strength studies on portland cement mortars containing fly ash and superplasticizer

The effects of two super water-reducing admixtures on the compressive strengths and elastic moduli of portland cement mortars containing fly ash were determined. The results show that the effectiveness of the chemicals for improving the strengths of mixtures in which portland cement is partially replaced by fly ash decreases with an increase in the percentage of ash. Increased strength can be nil or too low to justify the additional expense associated with the chemicals. The mixtures did exhibit normal stress-strain relationships: the elastic moduli were related to the ultimate compressive strengths in the usual manner. The results are based on mixes with equal workabilities.     

Superplasticized portland cement: production and compressive strength of mortars and concrete

This paper deals with the effect of intergrinding different percentages of a naphthalene-based superplasticizer with Portland cement clinker and gypsum on the fineness of the product, and on the water requirement and the compressive strength of the mortars made with the superplasticized cement. The properties of the fresh and hardened concrete made with the superplasticized cements were also investigated. The results showed that the intergrinding of a given amount of a naphthalene-based superplasticizer with Portland clinker and gypsum reduced the grinding time required for obtaining the same Blaine fineness as that of the control Portland cement without the superplasticizer. The water requirement of the mortars made with the superplasticized cements was similar to that of the mortars made with the control Portland cements when the same amount of the superplasticizer was added at the mortar mixer; for a given grinding time and a Blaine fineness of 4500 cm²/g, the mortars made with the superplasticized cement had higher compressive strength than those made with the control Portland cement. For a given grinding time or Blaine fineness of cement ≥5000 cm²/g, the slump loss, air content stability, bleeding, autogenous temperature rise, setting times, and compressive strength of the concrete made with the superplasticized cements were generally comparable to those of the concrete made with the control Portland cements when the superplasticizer was added at the concrete mixer.     

Polymer-Impregnated mortars I. Effect of polymer state on mechanical behavior

Mortar specimens were impregnated with methyl methacrylate, n-butyl acrylate, styrene, and crosslinking agents in various combinations. After polymerization of the monomers in situ, studies of mechanical properties such as Young's modulus and compressive strength were made. In one experiment, various ccpolymers of methyl methacrylate and n-butyl acrylate were prepared and tested as a function of temperature. Excellent reinforcement was obtained with any combination of monomers as long as the resulting polymer was at a temperature below its glass transition temperature. This suggests that the modulus of the reinforcing polymer is crucial, glassy behavior being required. The addition of crosslinking agents such as TMPTMA increased the high temperature strength, however.     

Effect of carbon fibres on the mechanical properties and corrosion levels of reinforced portland cement mortars

The changes in mechanical properties of portland cement mortars due to the addition of carbon fibres (CF) to the mix have been studied. Compression and flexural strengths have been determined in relation to the amount of fibres added to the mix, water/binder ratio, curing time and porosity. Additionally, the corrosion level of reinforcing steel bars embedded in portland cement mortars containing CF and silica fume (SF) have also been investigated and reinforcing steel corrosion rates have been determined. As a consequence of the large concentration of oxygen groups in CF surface, a good interaction between the CF and the water of the mortar paste is to be expected. A CF content of 0.5% of cement weight implies an optimum increase in flexural strength and an increase in embedded steel corrosion.     

Belite in portland cement

An X-ray diffraction pattern of β-belite is found on the basis of computer-calculated X-ray diffraction analyses of samples obtained by treating cement clinker with salicylic acid-methanol solutions. The method described also permits detection of high-temperature belite modifications in some of the samples.     

Some further evidence on a specific effect of silica fume on the pore structure of portland cement mortars

SEM observations are reported on silica fume-Ca(OH)₂ crystals-water mixture which give evidence of a mechanism of almost complete dissolution of the Ca(OH)₂ crystals with remnent voids corresponding to the initial crystals shapes. These observations could be related to the recently observed appearance of a coarse pore family in the 1–2 μm size range in hydrated silica fume mortars.     

Composition of portland cement belites

Electron microprobe techniques using modern energy-dispersive detectors allow rapid elemental analyses of suitable flat specimens. An analysis of some 200 belite grains from a wide range of commercial cement clinkers gives a statistical insight into the compositional variations within this important cement phase. These variations are discussed in terms of current lattice substitution schemes and their importance from a product viewpoint.     

Composition of high manganese portland cement

Two portland cements, each containing over 0.6 percent Mn₂O₃, are compared. ASTM potential compound compositions are almost identical but early strengths differ significantly. Strength differences are due to differences in C₃A contents as determined by x-ray diffraction and by correcting compound composition to allow for manganese in the ferrite phase.     

大掺量磷渣硅酸盐水泥的试验研究

研究了磷渣比表面积、磷渣掺量、窑灰掺量和激发荆对四个水泥体系物理性能的影响.结果表明:配置高掺量磷渣硅酸盐水泥,磷渣细度应控制在比表面积500m2/kg左右为宜;15%的窑灰掺量对磷渣水泥后期强度有显著的提高,特别是在磷渣掺量较大的情况下,平均增长率可达到20%以上;硫酸钠对磷渣水泥3d强度有一定的提高,对28d强度影响不大;在磷渣窑灰复掺水泥体系中,硫酸钠均不同程度提高了体系的3d和28d强度.     

Chemical shrinkage of portland cement pastes

Chemical shrinkage of normal Portland cement pastes (0.4 ≤ w/c < 0.8) has been measured at 20°C and of pastes with w/c = 0.5 furthermore at 35, and 50°C by means of measuring the volume change of samples of cement paste during the hydration. A small increase in the chemical shrinkage at “infinite time” was found at increasing water-cement ratio. The influence of the temperature was found to be twofold: Increasing temperature caused an increasing rate of the development of chemical shrinkage and a decrease of the chemical shrinkage at “infinite time”.Earlier studies of chemical shrinkage of Portland cement paste are also reported.     

钢渣-矿渣-粉煤灰复合硅酸盐水泥

1 前言 GB12958-1999《复合硅酸盐水泥》国家标准已颁布实施。物检中发现:采用多种活性混合材料复合比掺单一混合材的水泥有更好的强度优势,具有优良的物理力学性能。复合硅酸盐水泥作为通用水泥品种之一,被广泛用于工业及民用建筑施工。 笔者根据当地的资源条件,利用水淬电炉钢渣、粒化高炉矿渣及干排粉煤灰,在黄石市秀山水泥厂成功研制出早强高的“钢渣、矿渣、粉煤灰复合     

Electron microprobe analysis of portland cement clinkers

Using modern electron microprobe techniques, we have undertaken a detailed composition analysis of all the major phases in portland cement. A preferential incorporation of certain elements into either alites or belites is confirmed, and compared to existing ideas on alite decomposition. In addition the composition data are discussed in terms of solid-solutions existing in the various phases; in particular there is evidence of a further solid solution in the interstitial phase between C₃A and the alumino-ferrites.     

An X-ray diffraction analysis of portland cement

This method describes a quantitative determination of the major phases in cement or clinker. In addition, well defined ferrite and aluminate diffraction patterns are obtained which lend themselves to crystallographic evaluation. After initial grinding, the cement sample is split. One portion is used for the determination of silicates and the other is treated with maleic acid to remove the silicate phases for closer examination of aluminates and ferrites.     

Alkali compounds in Nigerian portland cement clinkers

Four out of the six Nigerian Portland cement clinkers contain alkali bearing compounds in the form of either single or double sulphates. An attempt has been made to identify these compounds and derive their compositions from SEM-EDXA study.     

Reactions between methanol and portland cement paste

The paper concerns the suitability of methanol replacement as a method for drying cement paste specimens prior to microstructural examination. Thermogravimetric tests on both cement paste and calcium hydroxide which were soaked in methanol for various periods show that methanol alters sample composition by reacting to form a carbonate-like product. Also, some of the methanol is found to remain with the solid at temperatures above 300°C. It is concluded that until more is known about the interaction between methanol and the cement paste constituents, the correct interpretation of test results of methanol treated specimens is likely to be very difficult.     

Strength of autoclaved portland blast furnace cement

The optimum autoclaving conditions for Portland blast furnace cement of 35% slag content, in the absence as well as in the presence of fine quartz, have been investigated. It was found that maximum strengths were developed in an autoclaving period of 4 h at 230 lb/in²; the strength values obtained for vibrated mortar cubes were 470 kg/cm² for 1 : 3 (W) cement–standard sand mix, and 904 kg/cm² for 1 : 0.5 : 2.5 cement–fine sand–standard sand mix. Strength values for various autoclaving pressures and times are given.     

Effect of chloride solutions on portland cement

Expansion of hardened normal Portland cement in chloride solutions exceeded that in distilled water, but specimens made of ground cement-clinker were not appreciably affected by the presence of chloride ions. Addition of chloride ions to sulphate solutions caused increased expansion of cement pastes, but the combined effect of chloride and sulphate ions was less than that of the sum of the separate components. Magnesium and calcium chloride were more aggressive than sodium and potassium chloride. In chloride solutions, richer cement pastes were more strongly expanded than poorer ones, in contrast to their behaviour in sulphate solutions. The results are interpreted in terms of the rates of formation of calcium chloroaluminate, the effect of chloride ion on sulphoaluminate crystallisation, slight variations in composition of the chloride phase and leaching of some of the reaction products.     

Utilization of phosphogypsum in portland cement industry

Disadvantages associated with the presence of impurities in phosphogypsum can be overcome when, instead of adding it directly to portland cement as a set-retarding additive, it is added to the raw mix before clinkering. Due to the mineralizing action of phosphogypsum, the clinker can be made at a substantially reduced temperature. Cements made by grinding a clinker containing 2 percent SO₃ derived from phosphogypsum did not need any further retardation and possessed high early strength characteristics.