Influence of organic admixtures on the rheological behaviour of cement pastes

The rheological properties of cementitious pastes used to proportion Self-Consolidating Concretes (SCC) have been examined, in particular, the influence of High range water reducing admixture (HRWRA) with that of Viscosity Modifying Admixtures (VMAs) have been compared. HRWRAs are known to have dispersing effects on the cement particles through steric and/or electrostatic repulsion, while the effects of VMAs are expected to stabilise the paste by increasing the viscosity of the aqueous solution. Both transient and steady state rheological behaviour of the cementitious pastes proportioned with different dosages of HWRA and VMA were considered. Experimental results show that the influence of VMAs on rheological properties is actually minor compared to that of HRWRAs. These results are discussed in the framework of rheology of concentrated suspensions.     

Influence of mineral admixtures on the alkali-aggregate reaction

Different mineral admixtures were used as cement replacements to study the alkali-aggregate reaction between quartzite and cement paste. The experimental program included expansion measurement of the mortar-bar specimens, observation of the microstructure, and analysis of the gel composition. Two Portland cements with different alkali contents were used to prepare mortar bars containing different amounts of natural pozzolan, fly-ash, and slag. Three natural pozzolans with different alkali contents were also utilized to assess the effect of their alkalies on the mortar expansion. The results indicate that not all gels are equally expansive and that mineral admixtures change the composition of the gel. The double layer theory is used to explain the expansion results of the mortar bars containing different levels and types of mineral admixtures. As this theory predicts, the experimental results show a strong negative correlation between expansion and the charge fraction of bivalent cations in the gel.     

有机接枝改性凹凸棒石对磷吸附性能的影响

有机接枝可以改善凹凸棒石粉末在吸附中的流失现象,但同时接枝反应也会影响凹凸棒石对磷的吸附效率。为了降低这一影响,对改性凹凸棒石进行接枝试验,研究不同接枝工艺对接枝产物吸附除磷效果的影响。结果表明,当丙烯酰胺、N,N′-亚甲基双丙烯酰胺、碳酸氢钠、改性凹凸棒石的质量分别为0.7、0.04、1、1 g,无水乙醇、5%过硫酸钾和水的用量分别为5、1和7 mL时,有机接枝凹凸棒石吸附剂除磷率能达到92%,是未接枝时的93.8%,吸附容量达到4.6 mg/g。     

复合反应器中高浓度有机废水对硝化作用的影响

选用悬浮球形填料作为复合生物反应器的填料,研究有机物去除和硝化作用。研究显示,将进水COD质量浓度从400 mg/L逐渐增加到2 000 mg/L,进水NH3-N质量浓度维持在30 mg/L~45 mg/L运行20天,随着COD质量浓度的逐渐增高,NH3-N的去除率从82%左右降低到-25.9%,硝化反应能力呈逐渐减小的总体趋势。     

复掺混合材水泥流变性及其与高效减水剂相容性的研究

根据工厂实际情况设计混合材正交配比水平,通过Marsh时间和水泥净浆流动度实验,比较复掺矿渣、粉煤灰、石灰石对水泥流变性的影响,发现粉煤灰对浆体流变性的影响最大;并从中挑选流变性较好的几组试样,测试其与高效减水剂的相容性,得出最佳配比.即当掺入0.6%的萘系高效减水剂时,最佳复掺混合材配比为矿渣21%,粉煤灰3%,石灰...     

Influence of calcium concentration in the washing liquor on detergency performance of linear alkylbenzene sulfonate

The effect of the concentration of linear alkylbenzene sulfonate (LAS) on soil removal efficiency at various water hardnesses was studied. The present investigation indicates that: (i) For each LAS concentration, a calcium ion concentration interval exists, defined by 0.78<(Log(LAS)/Log(Ca))<0.85, where the detergency reaches a maximum; (ii) 24 h after having been prepared, the solutions present either clear solutions (water appearance), milky solutions (without precipitate in the bottom of the bottle), or clear solutions with precipitate in the bottom of the bottle. The milky solutions correspond to the defined interval. The solutions where the relationship LAS/Ca is defined are located, surprisingly in a precise zone of the LAS-calcium solubility diagram. The study has been carried out with and without ionic strength buffering, and the addition of electrolyte moves the maximum detergency performance interval to higher calcium concentrations.     

Dependence of oil stability index of fatty compounds on their structure and concentration and presence of metals

During storage and use, vegetable oil-derived industrial products such as biodiesel and biodegradable lubricants can be subjected to conditions that promote oxidation of their unsaturated components. The materials arising during oxidation and subsequent degradation can seriously impair the quality and performance of such products. Therefore, oxidative stability is a significant issue facing these vegetable oil-derived products, and enhanced understanding of the influence of various components of vegetable oils and storage parameters is necessary. In this work, the oil stability index (OSI) was used for assessing oxidation of monoalkyl esters of FA by varying several parameters. Neat fatty compounds and prepared mixtures thereof were studied for assessing the influence of compound structure and concentration. Small amounts of more highly unsaturated compounds had a disproportionately strong effect on oxidative stability. The recently developed concept of bis-allylic equivalents correlated more closely than the iodine value with the OSI times of mixtures of fatty esters. The OSI times of free acids were shorter than those of the corresponding alkyl esters. The presence of copper, iron, and nickel also reduced oxidative stability, but their effect was less than the presence of more highly unsaturated fatty compounds. Of these metals, copper had the strongest catalytic effect on OSI time. OSI may be an alternative to long-term storage tests for determining the influence of extraneous materials such as metals on oxidative stability.     

Influence of shrinkage-reducing admixtures on the reduction of plastic shrinkage cracking in concrete

Fresh concrete exposed to high evaporation rates is prone to plastic shrinkage cracking, especially in structures with large surface area/volume ratios. The present work shows that the reduction of the surface tension of the mixing water is an effective way for decreasing such cracking. In this study, conventional and high strength concretes with superplasticizers and shrinkage reducing admixtures (SRAs) were exposed to drying in the plastic state. Continuous monitoring of the surface displacement facilitated the identification of the different stages of plastic shrinkage cracking. Measurements of capillary pressure, settlement, internal temperature and evaporation rate were also made. The results show the effectiveness of SRAs in reducing plastic shrinkage cracking, even in high strength concrete. This is attributed to the reduction in the evaporation rate, delay of the peak capillary pressure due to the development of menisci in the pores and lower settlement.     

不同品种及掺量混凝材对GB—ISO强度的影响

０前言水泥新标准GB１７５—１９９９已于２００１年４月１日正式实施。该标准中强度检验方法采用了GB／T１７６７１—１９９９《水泥胶砂强度检验方法（ISO法）》（以下简称ISO法）。实验证明,采用ISO法检测的抗压强度值比用GB１７７—８５（以下简称GB法）检测的抗压强度值平均低一个标号。为了提高ISO法水泥强度,探索适应新标准的水泥生产用混合材品种及掺量,促进水泥产品结构调整和产品质量的提高,我公司进行了不同混合材品种在不同掺量下的GB—ISO强度对比试验,本文就有关试验情况作一介绍。１试验用混合材及其性能（…     

Influence of soil phosphorus and manure on phosphorus leaching in Swedish topsoils

In Sweden, subsurface transport of phosphorus (P) from agricultural soils represents the primary pathway of concern for surface water quality. However, there are mixed findings linking P in leachate with soil P and limited understanding of the interactive effects of applied P sources and soil test P on P leaching potential. Identifying soils that are susceptible to P leaching when manure is applied is critical to management strategies that reduce P loadings to water bodies. Intact soil columns (20 cm deep) from five long-term fertilization trials across Sweden were used in leaching experiments with simulated rainfall to explore the interactive effects of dairy cow (Bos taurus L.) manure application, soil test P and cropping system. Strong relationships were observed between ammonium lactate-extractable P in soil and dissolved reactive P (DRP) concentrations in leachate, although regression slopes varied across soils. For three soils, application of manure (equal to 21–30 kg P ha^?1) to the soil columns significantly increased DRP leaching losses. The increase in DRP concentration was correlated to soil test P, but with wide variations between the three soils. For two soils leachate P concentrations after manure addition were independent of soil P status. Despite variable trends in P leaching across the different soils, P concentrations in leachate were always moderate from soils at fertilization rates equivalent to P removal with harvest. Results clearly stress the importance of long-term P balance to limit P leaching losses from Swedish agricultural soils.     

Influence of photoirradation on reduction of hexavalent chromium by zero-valent iron in the presence of organic acids

Reduction of hexavalent chromium (Cr(VI)) by zero-valent iron (Fe⁰) was investigated systematically in the present study. No change in Cr(VI) concentration occurs using untreated Fe⁰ powders even after a long contact time. The Fe⁰ powders treated with acid washing shows a weak activity and a poor long-term performance to reduction of Cr(VI). The activity and long-term performance of treated Fe⁰ powders is not effectively improved in the presence of citric acid. In contrast, introduction of photoirradiation not only dramatically increases the reduction rate of Cr(VI) in the presence of citric acid but also effectively stabilizes the activity of Fe⁰ powders and films. Such enhancement should be attributed to photoreductive dissolution of the oxide layer on Fe⁰ surface. For this newly developed system, effective reduction of Cr(VI) is favored at low pH values and oxalic and tartaric acid are also effective as complex reagents.     

几种外加剂对硫铝酸盐水泥性能的影响

研究了高浓高效减水剂FDN、缓凝剂H3803和四种早强促凝组分(Li2CO3，NaNO2，Al2SO4和Na2SO4)对硫铝酸盐水泥标准稠度、凝结时间以及抗压强度的影响。结果表明，高效减水剂FDN与硫铝酸盐水泥相容性很好，减水效果明显；硼酸对硫铝酸盐水泥的缓凝效果不稳定，但通过复掺早强促凝组分能改善其缓凝效果和早期强度，且适量的硼酸能提高水泥浆的后期强度。碳酸锂对硫铝酸盐水泥有显著的促凝作用，但对后期强度不利。     

常用杀菌剂与有机磷的相容性研究

对杀菌剂优氯净、1427、有机溴、活性溴和ClO2与有机磷PBTCA,ATMP,HEDP,EDTMPS和HPA的相容性在实验室进行了研究。实验结果表明,氧化型杀菌剂对有机磷有分解作用,其影响顺序为优氯净>有机溴>ClO2>活性溴,亚甲基型有机磷药剂几乎不抗优氯净的分解,分解率达80%左右;非氧化型杀菌剂1427对PBTCA和HPA有一定的分解率,对其他有机磷影响不大。氧化型杀菌剂能使有机磷的缓蚀性能增加,但降低有机磷除PBTCA外的阻垢效果;非氧化型杀菌剂1427对有机磷的缓蚀和阻垢效果几乎无影响。     

The chemistry of hydration of high alumina cement in the presence of accelerating and retarding admixtures

The effect of accelerators, and in particular lithium salts and citric acid solutions, on the setting time of high alumina cement has been studied using calorimetry, solution analysis and X-ray diffraction techniques. Results are discussed with respect to the ternary CaOAl₂O₃H₂O solubility diagram. It appears that there is a nucleation barrier to the precipitation of the main products of hydration, CAH₁₀ and C₂AH₈ and that lithium salts function as accelerators by precipitation of a lithium aluminate hydrate which acts as a heterogenous nucleation substrate. It is suggested that retardation by citric acid is due to the precipitation of protective gel coatings around the cement grains which impede hydrolysis or inhibit growth of the hydration products.     

Microstructure and compatibility of PVDF/PS blends in the presence of PVA

This research refers to a compatibility study of binary and ternary PVDF blends with PS and PVA by means of the determination of the polymer polymer interaction parameter χ₁₂ calculated from melting point depression analysis of the blends. In addition, a PVDF spherulite growth rate study was conducted in the binary and ternary blends with PS and/or PVA. The nucleation factor is determined by applying the Lauritzen–Hoffman theory. The results obtained show PVA to be capable of compatibilizing PVDF/PS systems when present in concentrations of 30 vol%.     

Influence of inorganic and organic additives on the composition of the precipitate of synthetic hydroxylapatite and calcium oxalate monohydrate

Synthetic hydroxylapatites are prepared with additives, such as Mg²⁺, CO ₃ ^2? , and C₂O ₄ ^2? . An increase in the concentration of magnesium leads to the formation of struvite. In the Ca(NO₃)₂-(NH₄)HPO₄-Na₂CO₃-NH₄OH-H₂O system, an excess of carbonate ions leads to the formation of calcite. When the synthesis is performed using oxalate ions as additives, calcium oxalate does not form the inherent phase. Calcium oxalate monohydrate is synthesized with additives, such as CO ₃ ^2? , HPO ₄ ^2? , and SO ₄ ^2? ions and urea, glycine, and glutamic acid. X-ray powder diffraction analysis has revealed that the composition of the CaC₂O₄ · H₂O precipitate remains unchanged under these conditions and in the presence of the aforementioned additives.     

Hydration of calcium sulphate hemihydrate in the presence of calcium hydroxide

A study has been made of the effects of calcium hydroxide on the hydration of calcium sulphate hemihydrate in accelerated, inhibited and unmodified systems, using techniques developed in this laboratory. The results were interpreted in terms of an equation developed earlier, and the parameters k (which is related to the transport of matter in the system) and α₀ (which is a measure of heterogeneous nucleation) determined. A small addition of calcium hydroxide leads in all cases to a sharp increase in k. Further additions lead only to effects caused by dilution of the system. Calcium hydroxide has complex effects on α₀. These are large in inhibited systems. The basic effects of calcium hydroxide are to increase the concentration of hydroxyl ions which have specific effects, increase the concentration of Ca²⁺ ions, adsorb inhibitors and extend the system as an inert diluent.     

A review of the mechanisms of set-retardation in portland cement pastes containing organic admixtures

Various mechanisms have been proposed to explain how organic admixtures affect the hydration of cement clinker compounds. These are reviewed and discussed critically. Complex formation between the organic compounds and aluminate or silicate ions may enhance the initial reactivity of the anhydrous compounds. Set-retardation may be primarily due to retarding of the hydration of tricalcium silicate through the adsorption of organic admixtures onto calcium hydroxide nuclei. Adsorption onto the initial hydration products of tricalcium aluminate can also retard further hydration.