On the relevance of volume increase for the length changes of mortar bars in sulfate solutions

The ingress of sulfate ions into cementitious materials leads to the formation of ettringite, gypsum and other phases. The increase in solid volume through the formation of these phases is often assumed to be the only reason for expansion. In this paper we systematically compare the volume increase predicted by thermodynamic modeling to macroscopic expansion for mortars made with CEM I in different sulfate solutions and for mortars made with a range of blended cements in sodium sulfate solution. It is shown that the length changes cannot be explained by simple volume increase alone.A more plausible explanation of expansion lies in the theory of crystallization pressure, in which crystals forming from a supersaturated solution may exert pressure on their surroundings. It is observed that expansion occurs in systems where thermodynamic modeling predicts the co-existence of ettringite with gypsum. In such a case, if monosulfate and gypsum are both present locally, the solution can be highly supersaturated with respect to ettringite, whose formation in confined conditions (such as within C–S–H) can then exert expansive forces.     

304 Stainless steel oxidation in sulfate and sulfate+ bicarbonate solutions

The electrochemical characterization of 304 stainless steel in 0.1–0.5m Na2SO4 and Na2SO4 + NaHCO3 aqueous solutions at pH8 was done in combination with SEM surface analysis. Passivation of the surface film without any pitting events is observed for the current–potential and current–time experiments, and no anodic current spikes, which are associated with depassivation events, are distinguishable above the background current level. However, SEM pictures of an electrode surface polarized at potentials above 0.4V show microscopic pit nucleation. Even when the metal may be regarded as passive from a current–time or current–potential characteristics, passivity is not stable and localized film breakdown can still occur. The events are ascribed to pit nucleation at the active inclusion sites. The pits do not grow even into the metastable state but die through repassivation by metal salt precipitation immediately after birth. The effect is ascribed to the solubility of metal salts with the electrolyte produced by dissolution in the nucleation sites. The results show that pit nucleation and pit growth are two distinct processes. The importance of solution composition and the protective effect of bicarbonate ions is also discussed.     

颗粒尺寸对砂岩集料压蒸膨胀行为的影响

为研究和改进中国压蒸法检测砂岩类集料碱活性的适应性,以混凝土棱柱体法为基准,采用中国压蒸法研究了9种国内外砂岩类集料的碱活性,同时研究了集料颗粒粒径对砂浆试体压蒸膨胀行为影响.结果表明:中国压蒸法不能准确评定某些砂岩集料的碱活性且砂浆试体膨胀结果与混凝土中的膨胀结果相关性较差;颗粒粒径0.16~0.63 mm不是最敏感粒级;采用粒级1.25~2.50 mm、试体尺寸20 mm×20 mm×80 mm,在150℃、1 mol/LNaOH溶液中压蒸30 h可以大大改善中国压蒸法对砂岩类集料的适应性.     

Electrodissolution of iron in sodium sulfate and sodium bicarbonate solutions at pH8

The effect of sulfate ions on the electrochemical behaviour of iron electrodes in the presence of bicarbonate ions has been investigated. In solutions containing sulfate ions only, iron electrodes experience uniform corrosion and sulfate ions are aggressive. In the presence of bicarbonate ions, the sulfate ions become less aggressive and a pitting–repassivation process is observed. The differences in electrochemical behaviour have been compared and explained by examining the formation of probable products and their physicochemical properties during electrochemical polarization.     

Electrodissolution of iron in sodium sulfate and sodium bicarbonate solutions at pH8

The effect of sulfate ions on the electrochemical behaviour of iron electrodes in the presence of bicarbonate ions has been investigated. In solutions containing sulfate ions only, iron electrodes experience uniform corrosion and sulfate ions are aggressive. In the presence of bicarbonate ions, the sulfate ions become less aggressive and a pitting–repassivation process is observed. The differences in electrochemical behaviour have been compared and explained by examining the formation of probable products and their physicochemical properties during electrochemical polarization.     

Influence of the migration of chloride ions on the electrochemical impedance spectroscopy of mortar paste

During the last decade, electrochemical impedance spectroscopy (EIS) started to be effectively exploited to investigate the electrical properties of hydrated cement pastes.This paper is devoted to the study of the high- and medium-frequency regions of the impedance spectrum and focused on determining the relationship between chloride migration and impedance spectroscopy in accelerated diffusion tests carried out on samples of mortar.After introducing an experimental protocol based on a four-electrode arrangement, we present the results of a parametric study which is related to the thickness and water-cement ratio (W/C) of the samples.Firstly, all our measurements show that the presence of chloride ions modifies the impedance response of mortar and reveals a small loop as of modification of the composition of the upstream solution. This loop is probably due to the development of interfacial phenomena between material and the solution.Secondly, as the migration of chloride process progresses, an increase followed by a decrease of the bulk electrical resistance is observed, whereas the second loop, due to the presence of chlorides, remains constant.An equivalent electrical circuit is then proposed to fit the different experimental data.     

In situ micro-Raman spectroscopy to investigate pitting corrosion product of 1024 mild steel in phosphate and bicarbonate solutions containing chloride and sulfate ions

The nature of the corrosion products generated by localized attack on 1024 mild steel have been investigated in the presence of chloride and/or sulfate ions in bicarbonate and phosphate aqueous solutions. A spectroelectrochemical cell was used for in situ measurements of the Raman spectra of the corrosion products generated during pitting. These products were identified as the so-called green rust compounds. The assignment of the hydroxyl groups in green rust is confirmed by isotopic substitution. The composition of the green rust generated in bicarbonate or phosphate solution containing chloride and/or sulfate ions has been determined. A correlation between the green rust composition and the electrochemical behaviour after the initiation of pitting has been noted and discussed.     

Corrosion properties of electrodeposited cobalt in sulfate solutions containing chloride ions

The corrosion properties of electrodeposited pure cobalt were investigated in deaerated 0.5 M Na₂SO₄ solutions at pH 5, 7, 10 and 13 by using polarization techniques. The effect of chloride concentration (0.01 and 0.1 M NaCl) was also studied. The results showed that increasing pH shifted the anodic polarization curves to more negative potentials. At pH 5 and 7, cobalt exhibited active dissolution without any distinctive transition to passivation. However, at pH 10, the metal surface was partially passivated and anodic current increased sharply at approximately −0.2 V_SCE and the corroded surface revealed several well-defined pits. On the other hand, at pH 13, a clear passivation region was observed within the potential range of −0.5 to 0.6 V_SCE. With increasing chloride concentrations of 0, 0.01, and 0.1 M at pH 10, both the anodic current and the number of pits on the cobalt surface were gradually increased. X-ray photoelectron spectroscopic investigations showed that the cobalt surface was covered mostly with cobalt hydroxide after anodic polarization at pH 10 in 0.1 M NaCl.     

Effect of sulfate and chloride ions on the electrochemical behavior of iron in aqueous phosphate solutions

The electrochemical behavior of iron in aqueous phosphate solutions (0.005–0.1M) of pH8 at room temperature was investigated with an emphasis on the effect of chloride and /or sulfate ions on the initiation of the localized attack. Electrochemical techniques were complemented by SEM microscopy, FTIR, X-ray fluorescence analysis and ICP measurements. It has been shown that phosphate ions are very effective inhibitors against localized attack, and in the presence of sulfate ions still show an effect very similar to that of phosphate ions in the active–passive dissolution peak region.     

Effect of limestone filler on the deterioration of mortars and pastes exposed to sulfate solutions at ambient temperature

This paper presents data on engineering properties such as compressive strength, visual change and expansion of mortar specimens incorporating limestone filler subjected to severe sulfate attack at ambient temperature. Specimens with four replacement levels of limestone filler (0, 10, 20 and 30% of cement by mass) were immersed in sodium and magnesium sulfate solutions with 33,800 ppm of SO₄²⁻ concentration. In order to identify the products formed by sulfate attack, microstructural analyses such as XRD and SEM were also performed on the paste samples with similar replacement levels of limestone filler.The test results demonstrated that mortar and paste samples incorporating higher replacement levels of limestone filler were more susceptible to sulfate attack irrespective of types of attacking sources. However, the deterioration modes were significantly dependent on the types of sulfate solutions. Additionally, although the samples were exposed to sulfate solutions at 20 ± 1 °C, the deterioration was strongly associated with thaumasite formation in both sulfate solutions.The deterioration mechanism and resistance to sulfate attack of cement matrix incorporating limestone filler at ambient temperature is discussed in the light of the test results obtained.     

Comparative study of copper behaviour in bicarbonate and phosphate aqueous solutions and effect of chloride ions

Copper oxidation in aqueous solutions of pH 8 showed some differences in the presence of bicarbonate and phosphate ions. The bicarbonate ions did not interfere with Cu₂O film formation but the Cu²⁺ ions were stabilized by the complexing action of CO _2– ³ anions. In phosphate solutions, copper dissolved in the range of potentials associated with the Cu(I) oxidation state and the Cu(II) compound on the surface resulted in an extensive passivation region. In both solutions, a higher ion concentration caused an increase in the anodic current, suggesting that the copper ions were stabilized by the complexing action of the electrolyte. The copper oxidation current in a bicarbonate solution was higher than that observed in a phosphate solution of the same concentration. The thickness of the Cu(II) film rather than the Cu(I) layer appears to be the important factor related to the stability of the passive layer on the copper surface. The shift in the breakdown potential toward more positive values indicates that both bicarbonate and phosphate ions inhibit localized corrosion due to the presence of chloride ions. Their protective effect depends on the concentration of each anion, although the concentration of chloride ions necessary for pitting is larger in phosphate solutions than in bicarbonate solutions. In both solutions, long-term immersion of copper under anodic polarization results in the precipitation of a protective coating.     

Influence of Zn2+ ions on copper electrowinning from sulfate electrolytes

During electrowinning of copper from wastes, it was observed that Zn2+ impurities had some effects on the aspect of the deposits although the codeposition of these two metals is impossible under normal conditions. Cyclic voltammetry, impedance analysis and rotating disc electrode techniques were used to characterize the effect of the presence of small amounts of Zn2+ on the copper electrodeposition kinetics from acidic sulphate electrolytes. SEM and X-ray diffraction analysis were used to determine the morphology and the structure of the copper deposits. Their composition was determined using X-ray dispersive analysis. The addition of small amounts of Zn2+ had no effect, either on the crystal growth orientation of the copper deposits, or on their composition, but it modified slightly their morphology by increasing their microscopic roughness. An increase in the cathodic peak of the cyclic voltammograms observed in the presence of Zn2+ can be attributed to the higher roughness of the copper deposits. From impedance analysis, it can be deduced that Zn2+ ions are electrosorbed at the interface and have an effect on the copper electrodeposition kinetics. The adsorption capacitance, Ca, was calculated and correlated with the Zn2+ concentration. It was found that the nucleation time constant, parameter influenced by the growing mode of the deposit, decreased in the presence of Zn2+, especially at low concentrations.     

Influence of fly ash fineness on strength, drying shrinkage and sulfate resistance of blended cement mortar

In this paper, the influence of fineness of fly ash on water demand and some of the properties of hardened mortar are examined. In addition to the original fly ash (OFA), five different fineness values of fly ash were obtained by sieving and by using an air separator. Two sieves, Nos. 200 and 325, were used to obtain two lots of graded fine fly ash. For the classification using air separator, the OFA was separated into fine, medium and coarse portions. The fly ash dosage of 40% by weight of binder was used throughout the experiment. From the tests, it was found that the compressive strength of mortar depended on the fineness of fly ash. The strength of mortar containing fine fly ash was better than that of OFA mortar at all ages with the very fine fly ash giving the highest strength. The use of all fly ashes resulted in significant improvement in drying shrinkage with the coarse fly ash showing the least improvement owing primarily to the high water to binder ratio (W/B) of the mix. Significant improvement of resistance to sulfate expansion was obtained for all fineness values except for the coarse fly ash where greater expansion was observed. The resistance to sulfuric acid attack was also improved with the incorporation of all fly ashes. In this case the coarse fly ash gave the best performance with the lowest rate of the weight loss owing probably to the better bonding of the coarse fly ash particles to the cement matrix and less hydration products. It is suggested that the fine fly ash is more reactive and its use resulted in a denser cement matrix and better mechanical properties of mortar.     

Influence of sulfide ions on the formation and properties of gold nanoparticles in aqueous solutions

The influence of sulfide ions on the formation of gold nanoparticles during reduction of HAuCl₄ in an aqueous solution is studied using plasmon resonance spectroscopy and scanning tunneling microscopy. Upon the simultaneous addition of sodium citrate and sodium sulfide and for the molar ratios S/Au < 1, the nanoparticles have smaller sizes than those formed during the reduction only with sodium citrate under the same conditions; however, an increase in the sulfur content leads to an increase in the particle size. The gold nanoparticles are also obtained under microwave heating with a single-stage reaction of an AuCl ₄ ^? aqueous solution with sodium sulfide. The particle size decreases with an increase in the S/Au ratio.     

Scaling analysis of nanofiltration systems fed with saturated calcium sulfate solutions in the presence of carbonate ions

Nanofiltration of saturated calcium sulfate solution of 0.02 mol/L calcium content, with molar ratio ranging from 0.0500 to 2.8 × 10⁻³ was carried out in 6.5 × 10⁻⁴ m² active membrane area laboratory module at 1.2 × 10⁶ Pa transmembrane pressure using the total retentate recycle mode. Permeate mass flow and retentate calcium concentration vs. time and concentration factor (CF) curves allowed identification of calcium sulfate crystallization mechanisms. Though both bulk and surface crystallization mechanisms were identified, they were, however, strongly affected by water quality. A non-fouling CF range up to 2, which is probably due to the existence of metastable supersaturated CaSO₄ solution, was also observed in the case of molar ratio equal to 2.8 × 10^−3. Inorganic scales at the end of each experiment were removed from a NF module, dried at room temperature during 24 h and then examined using the X-ray diffraction method. Gypsum and aragonite were identified as the most common calcium sulfate and calcium carbonate precipitates, respectively. A mixed salt Ca₂(CO₃)(SO₄)·4H₂O (so-called rapidcreekite) was also identified as a result of carbonate and sulfate co-precipitation under low carbonate content conditions.     

Influence of sodium dodecyl sulfate on the characteristics of bovine serum albumin solutions and foams

Results from surface tension measurements on mixed solutions of the protein bovine serum alburnin (BSA) and an anionic surfactant (SDS: sodium dodecyl sulfate) suggested that at an air-liquid interface, adsorption was affected by the protein-surfactant interaction and by the relative concentration of each component in solution. Two plateaus corresponding to the critical aggregation concentration (CAC) and the critical micelle concentration (CMC) of SDS, respectively, were observed in the surface tension isotherms of SDS in the presence of BSA. The CAC and CMC depended on the concentration of BSA. Effects of SDS concentration on the conformational changes of BSA were investigated by Fourier transform-Raman spectroscopy. The results showed that the contents of α-helix decreased while the contents of random coil increased. The presence of the anionic surfactant SDS had a negative influence on the way that proteins adsorb at an air-liquid interface, leading to the change of behavior of protein-stabilized film.     

矿渣颗粒对砂浆性能的影响

研究了矿渣颗粒以不同比例替代河砂时对砂浆流动度和强度的影响规律。结果表明:(1)采用补水法制备含矿渣颗粒的砂浆,可以克服因矿渣颗粒吸水造成的流动度降低;(2)随着矿渣颗粒掺入量的增加,砂浆3d,7d的抗折、抗压强度下降,而28d抗折强度随矿渣颗粒替代河砂比例的增加变化不大,28d砂浆抗压强度随着矿渣颗粒替代量的增加是先减小后增加;(3)矿渣颗粒在建筑砂浆中具有陶粒的某些性能,通过吸水返水作用可以提高建筑砂浆的强度增进率。     

Nanofiltration study of the interaction between bicarbonate and nitrate ions

In contrast to other anions, there are not many studies focusing on the effect of bicarbonate ion on the rejection of other anions in nanofiltration. However, bicarbonate is one of the major anions in many inland waters and its concentration remains significant even after acidification. In order to obtain specific information about the interaction of bicarbonate and nitrate ions, nanofiltration experiments with the membrane SU-610 (Toray) were performed using solutions containing sodium, nitrate and bicarbonate ions. The influence of the bicarbonate ion concentration was studied in the range from 4 to 32 mol·m^− 3 of bicarbonate ion and from 1 to 4 mol·m^− 3 of nitrate ion. The experimental data were analysed by means of multiple linear regression. The results showed that nitrate rejection was decreased by bicarbonate ion concentration. This effect was compared with that obtained using sulphate or chloride as co-ions. The regression models obtained for nitrate and bicarbonate ion rejection showed good fitting to the experimental results (r-squared equal to 99.3% and 97.6% respectively). The models were able to predict the evolution of nitrate in a concentration process at constant pH.     

Diffusion of chloride ions in polymer‐mortar composites

In recent years, the rapid deterioration of various reinforced concrete structures has been a widely recognized problem in the world. Penetration of chloride ions into the concrete structures was found to be the major cause of premature corrosion of reinforcing steel and to promote their deterioration. The present articles deals with the resistance to chloride penetration of polymer‐mortar, which are often used as low‐cost promising materials for preventing or repairing various reinforced concrete structures. To gain more knowledge on the efficiency of polymer‐mortar, four mortar mixtures: one specimen with Portland cement (control sample) and three mixtures with 2.5, 5, and 7.5 wt % of the replacement of cement by polyethylene terephthalate (PET) were tested for chloride ion permeability under immersion in 5% sodium chloride solution. Their chloride ion penetration behavior is discussed by applying Fick's second law. In conclusion, the chloride ion penetration depth and apparent chloride ion diffusion coefficient of the polymer‐mortar composites are smaller than those of unmodified mortar. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

复合外加剂对水泥净浆水化热及砂浆强度的影响

系统地考察了矿物—化学复合外加剂对水泥净浆的水化热影响，外加剂对水泥砂浆各龄期强度发展的影响。分析了不同外加剂之间的交互作用及制约规律。