橡胶粉改性水泥沥青砂浆的研究

采用橡胶粉改性水泥沥青(CA)砂浆,并对其力学性能进行了重点测试。结果表明,随着橡胶粉替加入量的增加,CA砂浆早期强度呈减小趋势,但28天强度则相反;抗压强度均随温度的升高而减小,且随加载速率的增大而增大;橡胶粉越多,CA砂浆对温度的敏感性降低,且加载速率对其抗压强度的影响减小。     

Behaviour of high volume fibre cement mortar in flexure

Tests are reported on the behaviour of high volume percentage steel fibre mortar specimens subjected to flexure. Flexural and cyclic load tests were conducted; in addition, comparison tests were made on conventional fibre mortar and ferrocement specimens. Both strength and deflection characteristics were studied. The results of the investigation indicate that with 8% high volume, steel fibre mortar specimens possess a flexural strength of about 40 MPa.     

Waste printed circuit boards nonmetallic powder as admixture in cement mortar

In this paper, the nonmetallic powder recycled from waste printed circuit boards (PCBs) is used in cement mortar as admixture. The mechanical properties, bulk density, air content, water-retention property, shrinkage rate and water capillary adsorption are tested. The results show that the waste PCBs nonmetallic powder causes an increase in air content and improves the water-retention property of fresh mortar, decreases the bulk density of hardened mortar. The compressive strength and flexural strength of mortar with PCBs nonmetallic powder change slightly with the m _p/m _c below 15%. The tensile bond strength goes down continuously with the increase of the m _p/m _c but the reducing trend in the m _p/m _c range from 0 to 10% is slow. The drying shrinkage rate of mortar has little change as the m _p/m _c varies from 0 to 15%. The water capillary adsorption of mortar with the m _p/m _c of 5, 10 and 15% are lower than that of control. Cement mortar made with recycled waste PCBs nonmetallic powder is a new type of green building materials, which is friendly to environment and has broad application prospects.     

含石灰石粉水泥砂浆在低温环境中的硫酸盐侵蚀

分析了掺30%石灰石粉砂浆与纯水泥砂浆在(5±1)℃的2%MgSO4溶液中浸泡不同时间后试件表面层的矿物成分变化与微观结构,研究了强度与外观的变化.结果表明:掺入石灰石粉使水泥水化产物中的单硫型水化硫铝酸钙转变为稳定的单碳水化铝酸钙,物理填充作用使水泥石结构更加致密,因而在短期的低温硫酸盐侵蚀环境下掺石灰石粉砂浆比纯水泥砂浆表现出更好的耐腐蚀性.在经受低温硫酸盐侵蚀后纯水泥砂浆生成大量的石膏和钙矾石,而掺石灰石粉砂浆在经受同条件210 d侵蚀后的腐蚀产物中除了石膏、钙矾石外,还有少量的硅灰石膏生成,表明水泥石中的CSH凝胶体也受到侵蚀.     

A novel method to evaluate the setting process of cement and asphalt emulsion in CA mortar

Cement and asphalt mortar (CA mortar) is the key component in the structure of Shinkansen slab track and serves as the elastic shock-absorber. A new method was put forward to evaluate the setting process of cement and asphalt emulsion (CAE) in CA mortar. It was noted that the setting process was governed by several factors such as cement types, cement/asphalt emulsion ratios (C/AE ratio). Results also indicated that the setting process of CAE was faster, the higher proportion of cement content was; the early age strength and the separation rate of CA mortar could be improved by using cement of high early age strength and rapid hydration rate, or a blended cement with ordinary Portland cement partially replaced by sulfoaluminate cement, or by increasing C/AE ratio. Nevertheless, the replacement ratio of ordinary Portland cement by sulfoaluminate cement should not exceed 15% and C/AE ratio should be not less than 0.8.     

The volume change at the superconducting transition of lead and aluminum

The volume change at the magnetic field-induced transition from the super-conducting to the normal state has been measured on single crystals of lead and aluminum between 0.3 K andT _c. From these data we have deduced the pressure dependence of the critical fieldH _c, of the critical temperatureT _c, and of the electronic specific heat coefficient . In lead, the results are in good agreement with theoretical calculations by Carbotte, where strong coupling effects are taken into account. We find ln / lnV=3.1±0.8, whereV is the volume. The measurements on aluminum giving ln / lnV=3±4 are consistent with results derived from thermal expansion experiments.This work was in part financially supported by the Schweizerischer Nationalfonds.     

Interaction mechanism of cement and asphalt emulsion in asphalt emulsion mixtures

The interaction characteristics of cement asphalt composite mastic (CAM) and performance properties of cement asphalt emulsion mixtures (CAEM) were evaluated in this work using chemical and mechanical test methods to investigate the effect of the presence of cement on asphalt emulsion mixtures (AEM). The chemical composition of the CAM was obtained through use of X-ray diffraction, Fourier-transform infrared spectroscopy, and environmental scanning electron microscopy (ESEM) as a means to describe the interactions between the cement and asphalt in the composite materials. Test results demonstrated that cement can hydrate with the water phase of the asphalt emulsion. Asphalt droplets can simultaneously enclose cement particles and delay the hydration reaction process of cement. The interaction mechanism of cement particles or hydration products and residual asphalt is a physical compound process. The influence of these findings on asphalt emulsion mixture design and performance properties was assessed using varying mix design components and conducting laboratory-based mechanical test methods for rutting resistance and moisture susceptibility. Mix design components varied including added water content, emulsion content, and cement dosage levels. The optimum fluids content was determined based on the dry indirect tensile strength. It was found that the cement content significantly impacts the optimum fluids content for both added water and emulsion. Furthermore, the presence of cement improves the dry tensile strength, rutting resistance, and moisture susceptibility. Based on microstructural analysis of CAM and CAEM, the mechanism by which cement improves the performance of AEM is attributed to the ability of hydration products to increase both the stiffness of the asphalt binder and the adhesion at the mastic–aggregate interface. In practical applications, this study recommends a mix design method for cement-modified asphalt emulsion mixes (CAEM) based on selection of optimum cement and emulsion contents using indirect tensile strength and verification of the design through evaluation of the moisture susceptibility and rutting resistance of the CAEM mix. Threshold values of CAEM mix mechanical properties to determine the quality of the design are proposed.     

Early age and hardened performance of cement pastes combining mineral additions

To asses the influence of mineral additions (MA) at early age and on hardened performance of fluid cement based pastes, an experimental program was carried out. The design of the mixtures correspond to paste compositions used in self compacting concretes of moderated strength, as those employed for architectural applications. Two types of fillers (limestone and quartzite) have been used to substitute 50 % of cement in a reference paste, with and without a high range water reducing admixture. Then, three active MA (microsilica, nanosilica and metakaolin) were combined. A physical and mechanical characterization in the hardened state showed that the inclusion of MA to a cement-filler mixture can moderately improve the hardened performance of the pastes. Air and water cured samples were tested in order to evaluate the influence of curing conditions. At early ages (24 h), in situ temperature and ultrasonic pulse velocity were monitored on samples with limestone filler, combined with the three active MA, to study the reaction process and microstructure development, respectively. The reaction degree of the samples under study during the first 24 h was related to the microstructure development. Evaporation, drying shrinkage and cracking at early age were also monitored, considering an air flow of 3 m/s on the exposed sample surface. Some relations were described linking cracking risks at early ages with the chemical and physical phenomena involved at early age microstructure evolution.     

Chloride corrosion of steel fibre reinforcement in cement mortar

This paper presents an experimental study on the corrosion resistance of steel fibres and steel bar reinforcement in cement mortar. The mortar matrix incorporated various amounts of calcium chloride from 2 to 10%, and the rate of corrosion was monitored by the electrode potential method. The structure of the mortar and the steel surfaces were examined by scanning electron microscopy. The results showed that the addition of calcium chloride modified the microstructure of the mortar matrix, both its water absorption capacity and its porosity increased with increasing amounts of calcium chloride. The electric potential measurements showed that while the bar reinforcement displayed corrosion at 2% calcium chloride, the fibres did not indicate any harmful corrosion until the chloride content was 6%. Chloride admixtures added to concrete may thus be less harmful to steel in steel fibre concrete than in reinforced concrete.     

Function of styrene-acrylic ester copolymer latex in cement mortar

This paper focuses on the effect of the styrene-acrylic ester copolymer (SAE) latex on the performance of cement mortar, through studying on the water-reduction and water-retention effects of the SAE latex in the mortar, and the influence of the SAE latex on the air-content and the bulk density of the fresh mortar and the bulk density, compressive and flexural strengths, shrinkage rate, water capillary adsorption and anti-penetration capacity of the hardened mortar. The experimental results show that the SAE latex has good water-reduction and water-retention effects in mortar. The SAE latex has also air entrainment effect, increasing the air content and reducing the bulk density of the fresh mortar. The apparent bulk density and dry bulk density of the hardened mortars decrease with the increase of the SAE latex/cement-ratio (m_p/m_c) and the change is in accordance with that for the bulk density of the fresh mortar. The SAE latex influences the development of the compressive strength but slightly on the flexural strength, and improves the toughness, shrinkage property, waterproofing quality and anti-penetration capacity of the mortar significantly.     

老化沥青砂浆损伤愈合性能研究

为研究老化作用对基质沥青砂浆和SBS改性沥青砂浆损伤自愈性能的影响,从内部条件和外部环境两方面,选取不同的影响因素,进行四因素三水平的正交试验设计,采用UTM-100万能试验机对两种沥青砂浆进行损伤—愈合—再损伤试验,选取破坏应变和断裂韧性作为自愈合评价指标对其进行分析。试验结果表明:以破坏应变作为愈合指标评价基质沥青砂浆的愈合性能不够准确全面,而断裂韧性能更合理的呈现两种沥青砂浆在不同条件下的愈合规律和差异;在4个影响因素中,老化程度对两种沥青砂浆损伤愈合影响最大;在相同的试验条件下,SBS改性沥青砂浆有较好的抗疲劳和抗开裂的能力,而与基质沥青砂浆相比愈合效果不明显,愈合温度、愈合时间、老化程度、损伤程度四个影响因素下基质沥青砂浆拥有更好的愈合能力。     

Effect of fly ash on the microstructure of cement mortar

A microstructural study of mortars prepared with a low-alkali, low-C₃A cement and a Class F fly ash, both of Swedish origin, was carried out using the scanning electron microscopy-energy-dispersive X-ray analytical technique. Supplementary phase analyses were made by X-ray diffraction and thermogravimetry-differential thermal analysis. Normally, CH crystals in the transition zone grow with their c axis parallel (or the (0 0 1) cleavage plane perpendicular) to the aggregate surface. The encapsulation of the fly ash particles by the growing CH reduces the amount of orientated CH at the aggregate-paste interface. The growth mechanism of these crystals is discussed. The reduction of CH, most significant after 28 days of hydration, is mainly due to the reaction of CH with the fly ash glass phase. Initially, the replacement of cement by fly ash weakens the paste-aggregate interfacial zone due to reduction of contact points, and increases the local water-to-cement ratio. This, however, improves significantly when the fly ash has reacted. In order to enhance the reaction of fly ash, extra gypsum was added. The results show that gypsum can accelerate the fly ash reaction, but the products formed, and the beneficial effects of gypsum, are mainly determined by the total amount of gypsum in the paste.     

The spalling strength of ultra-fiber reinforced cement mortar

This is a research report about the effects of polypropylene fiber and wood fiber on mechanical properties of cement mortar. First, using advanced Hopkinson pressure bar (HPB) tests, it investigates the wave propagation in cement mortar comprised polypropylene fiber and wood fiber. Second, according to the experiment, the spallation position is recorded by high-speed camera. Thirdly, it analyzes the test data of ultra-fiber reinforced and common cement mortar by numerical method. Finally, it deduces the spalling strength of all kinds of cement mortar by integrating all experimental data above. The results indicate that, compared with the strength of common cement mortar, the dynamic spalling strength of ultra-fiber especially that of the polypropylene fiber reinforced cement mortar increases evidently. However, adding too much fibers will deteriorate the dynamic spalling strength of cement mortar specimen. So the results will provide a test basis for further optimizing performance of cement mortar.     

Pore structure of hardened cement paste and mortar

The paper describes an experimental investigation into the pore structure of hardened cement paste and mortar. The pore structure was studied using mercury porosimeter. Ordinary portland cement and natural river sand were used. Pore structure determination was carried out for both the cement paste and mortar mixes over four hydration periods and five water-cement ratios. The threshold radius which was found to be prominent in the hardened cement paste, flattens out as the fine aggregate content increased.     

减缩剂的作用及其机理

通过对减缩剂作用和机理的研究表明,减缩剂能较大幅度的降低干燥收缩和相对较小的提高塑性收缩抗裂能力,但在一定程度上降低了砂浆的力学性能.从塑性抗拉强度、表面水份蒸发率和孔结构三个角度对减缩剂的作用机理进行了试验分析,结果表明:减缩剂的加入能较显著的降低水溶液的表面张力,同时也降低了砂浆表面的塑性抗拉强度,增大了表面水份蒸发率,它对塑性收缩抗裂的效果取决于对塑性抗拉强度和毛细管收缩应力影响的权重;表面张力试验表明,减缩剂减小干缩的机理主要在于降低了孔溶液的表面张力;从对孔结构的分析表明,减缩剂掺入后增大了孔隙率,并增加了孔径＞0.1μm的孔的含量,从而降低了掺减缩剂的砂浆力学性能.     

Natural remanent magnetization of Portland cement paste and mortar

The presence of magnetic constituents in Porland cement-based materials permits acquisition of a weak magnetization of such materials under the influence of earth's magnetic field. This magnetization is caused by the alignment of individual magnetic grains during the casting process and can be measured readily using paleomagnetic techniques.

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Résumé La présence de composants magnétiques dans la pate de ciment Portland et le mortier occasionne une faible magnétisation de ces matériaux sous l'influence du champ magnétique terrestre. Cette magnétisation est provoquée par l'alignement statistique de grains magnétiques individuels pendant le processus du moulage, et peut se mesurer aisémrnt à l'aide des techniques relevant du domaine spécialisé de la géologie connues sous le nom de paléomagnétisme. L'intensité de la magnétisation dépend de le teneur en grain magnétique (fer et oxyde de fer) du liant, de la quantité de liant, de la fluidité initiale du mélange (viscosité) et de la vibration qui en découle. La direction de la magnétisation est généralement parallèle à celle du champ magnétique terrestre au lieu du moulage. Le degré auquel on enregistre le champ magnétique semble en rapport avec la rhéologie du mélange, le type et la teneur en matériau magnétique au sein du milieu. Cet article résume la recherche menée jusqu'à ce jour sur la magnétisation naturelle rémanente de la pate de ciment Portland et du mortier et indique les applications possibles de ce phénomène.

     

Relaxation characteristics of cement mortar subjected to tensile strain

Tensile relaxation characteristics are important for the crack resistance of concrete members subjected to restrained contraction, for example bonded overlays and patch repairs. In the experimental research discussed in this paper, relaxation characteristics were measured for mortar specimens subjected to constant strain which corresponded to stresses close to the tensile strength of the mortar. Relaxation was found to relieve a considerable portion of tensile stresses. Ultimate relaxation values ranged from 20 to 45%, depending on w/c ratio and specimen age. As expected, a decrease in specimen age and an increase in w/c ratio resulted in increasing relaxation values. The rate of stress decay was found to be rapid, with approximately 80% of the ultimate relaxation occurring in the first 12?h after loading. A basic equation for the prediction of time development of relaxation is proposed and future research needs are discussed.