温度和湿度对水泥凝结时间的影响

1问题的提出 在我省对水泥企业化验室组织的“2007年全省水泥性能检测大对比”中凝结时间对比合格企业达90％,但仍有10％的企业凝结时间对比超差,有几个企业初凝时间出现过大误差,超差近1h。我省公路交通系统的化验室也参加了大对比．凝结时间对比合格率为70％多,较低。     

Role of dispersant and humidity on the setting of millimetric films of aluminous cement prepared by tape casting

An aluminous cement (Secar 71 from Lafarge) has been used for preparing millimetre thick films by tape casting. Slurry preparation is described. The effect of several dispersants has been studied. The optimum dispersion, associated with the minimum viscosity, is obtained with minimal amounts of dispersant in the case of acetic and propionic acids. Indeed, the corresponding quantities of dispersant are less than 0.5% by weight relative to cement. In addition to its dispersive role, acetic acid plays a role in the setting. It has a retarding effect below 1% by weight relative to the mass of cement and from this amount, it plays an accelerating role on setting. Tapes prepared with cement, water, acetic acid, PEG 300 have been left to set in different environments at 20 °C (50% or 95% relative humidity, water). The formation of aluminous calcium hydrates is most important when setting is done in water. Lastly, the advantage of setting in water is also discussed with respect to the elimination of the different organic products that have been used for tape casting.     

Effect of humidity and temperature on the adhesive strength of pressure sensitive adhesives

This paper reports the effect of humidity and temperature on the adhesive strength of a pressure sensitive adhesive (Flexbond 150) used to bond Mylar films. It has been found that, ill general, the adhesive strength decreases significantly with an increase in temperature. The effect of humidity on the bonding strength, however, was found to be process dependent. The sample preparation conditions, e.g., press weight for the bonding and the press time, are important in determining the humidity effect. The water sorption isotherm A 24°C for the adhesive was also determined. The amount of water sorbed by the adhesive at 95 percent relative pressure was found to be less than one weight percent.     

关于负温下水泥强度发展的研究

水泥在常温下可以正常水化,但在负温下水化及强度的发展都受到了一定的抑制。实验研究了水泥在负温环境下的强度发展规律,结果表明:在恒负温环境下养护时间的延长对水泥后期强度的增加有一定影响但意义不大;自然变负温环境下养护时间对水泥后期强度发展的影响具有重要意义,后期强度基本可以达到标准水平。     

Ultrasonic measurements as an in situ tool for characterising the ageing of an aluminous cement at different temperatures

In situ ultrasonic measurements have been done to characterise the ageing of a calcium aluminate cement, namely Secar 71, between 24 to 3500 h (5 months) after mixing the constituents. The longitudinal velocity, V_L, has been measured on pastes prepared at 5, 20, 40 and 60 °C with a water over cement weight ratio, W/C, equal to 0.33. These in situ and real time data are compared with ex situ measurements such as DTA, XRD and porosimetric characterisations. DTA and XRD permit to follow the chemical and crystallographic changes occurring in the material during hydration. The variations of V_L as a function of porous volume fraction, P, show that the relation between these two parameters is linear if P<0.15 and V_L>4300 m/s. When P>0.15 and V_L<4300 m/s, the relationship between V_L and P is no longer linear; the variations of V_L as a function of P depend on many other parameters such as chemical nature of interfaces, nature of hydrates, morphology of crystals.     

Curing temperature effect on mechanical strength of smokeless fuel briquettes prepared with molasses

Environmental acceptable smokeless fuel briquettes have been prepared with a low-rank coal and olive stone as biomass. The binder chosen for this study was molasses which acts with different roles, as chemical and matrix type. The effect of the curing temperature on these briquettes has been studied by Fourier transform infrared spectroscopy, temperature programmed decomposition (TPD) followed on-line by mass spectrometry and optical microscopy. TPD experiments help to predict the final properties of the briquettes more clearly than infrared spectroscopy. The aliphatic structures and methoxy groups as well as the hydrogen bonds decrease during the curing. On the other hand, the carboxylic groups tend to be formed due to the oxidation produced by the effect of curing temperature. In addition, the briquettes cured at 200 °C, 2 h showed the highest mechanical strength. These curing conditions also produce waterproof briquettes due to the presence of carboxylic groups which contribute to the stabilisation of the briquettes because of the formation of hydrogen bonds.     

Effect of a carboxylic acid on the rheological behavior of an aluminous cement paste and consequences on the properties of the hardened material

Aluminous cement pastes (Secar 71 from Lafarge) containing increasing quantities of acetic acid, HOAc, are prepared ((w_HOAc/w_cement) × 100 ranges from 0 to 10%). Pastes containing HOAc present a Newtonian behavior. The best dispersion is obtained when the mass content of acid with respect to the cement is equal to 0.5%. Microstructural characterizations of samples aged for 4 days at 20 °C and 95% relative humidity reveal a significant increase in density, a reduction in porosity as well as a displacement of pore diameter towards low sizes. The open porous volume decreases with time from 25 to 9 vol.% when samples are 4 days and 6 months old, respectively. The addition of HOAc also has a beneficial effect on the flexural strength of set samples.     

Modeling the coupled effects of temperature and fineness of Portland cement on the hydration kinetics in cement paste

This paper revisits the coupled impacts of fineness and temperature on the kinetics of Portland cement hydration. The approach consists in i) modeling the impact of fineness on cement dissolution through the hypothesis that the surface dissolution rate of cement particles is independent of their size, in order to, in a second step, ii) model the impact of temperature on the kinetics of cement dissolution. The analysis of the experimental results shows that the effect of cement fineness on the hydration kinetics can be captured by a simple hypothesis: for any age, the reacted thickness of cement grains can be considered independent of the initial cement particle size. In addition, the analysis of the results at different temperatures shows that a constant activation energy can account for the effect of temperature on the hydration kinetics, with an Arrhenius equation applied to the kinetics of surface dissolution. The results from the model give a good agreement with the experimental results in a significant number of combinations (different Portland cements, water/cement ratio from 0.5 to 0.6, cement Blaine fineness from 3500 to 6600 cm²/g, temperature histories between 20 and 60 °C).     

Influence of phase composition of aluminous porcelain on its mechanical strength

Translated from Steklo i Keramika, No. 12, pp. 16–17, December, 1989.     

Influence of humidity on the flexural strength of alumina

The influence of humidity on the flexural strength of alumina was investigated. The strengths tested at relatively high relative humidities (>45%) were smaller than those tested at relatively low relative humidities (<45%) as much as ∼10%. It was demonstrated by a round robin test that the influence of the humidity could produce a problem in the reproducibility of the strength data. It was discussed, that the problem in the reproducibility can be avoided by testing and using the inert strength in the comparison of strength data. It was recommended that, to test the inert strength, the strength measurement be made after the specimens had been coated with oil to protect them from contact with environmental moisture.     

Modeling the effects of solution temperature and concentration during sulfate attack on cement mortars

Simple chemistry-based empirical models have been developed to assess the role of temperature and concentration of the sulfate solution in the process of expansion of cement mortars that are subjected to external sulfate attack. ASTM Type I PC mortars, prepared according to ASTM C-109, were immersed in sodium and magnesium sulfate solutions at five different concentrations and four different temperatures. For both solutions, the trends in the measured expansion suggested the use of a simple rate law to analyze the effect of concentration. For the effect of temperature, an Arrhenius relationship was developed to determine the activation energy required to initiate expansion in sodium sulfate solution. Regression-based statistical models were found to be sufficient to explain the effect of temperature of magnesium sulfate solution on the expansion. Implications of using these models for developing potential test methods, as well as to enable interpretation of data from nonstandard test methods, are discussed.     

漂珠-微硅复合低密度水泥浆体系在苏丹1-2-4区块应用中的抗压强度与密度和温度之间的相关性研究

固井水泥浆抗压强度是固井质量的重要参数,而地层温度和水泥浆密度是影响抗压强度的重要参数指标。本文结合近年来苏丹1-2-4区块漂珠+微硅复合低密度高强度水泥浆体系的广泛应用与国内学者对该水泥浆体系进行的室内理论研究,利用多元回归分析方法对实验所得该水泥浆体系的抗压强度等重要参数数据进行线性回归分析,得到线性回归模型。结果表明:漂珠+微硅复合低密度高强度水泥浆体系抗压强度与实验温度(模拟地层温度)、水泥浆密度之间确实存在着线性相关关系,应用回归模型可以利用温度和密度数据来计算抗压强度,从而对固井现场施工工作起到指导作用。     

Reducing the sintering temperature of aluminous porcelain in the presence of mineralizers

Translated from Steklo i Keramika, No. 11, pp. 20–22, November, 1989.     

Effect of composition and the amount of spherical-particle aluminous fillers on the density and strength of corundum refractories

Conclusions Using a simplex-grid method of planning the experiment, we have calculated using an M-4030 computer the dependences of density and compressive strength on the composites consisting of -Al₂O₃--Al₂O₃-spherical fillers. It is shown that the strength of the composites, other things being equal, is greater the smaller the size of the particles of filler.Translated from Ogneupory, No. 2, pp. 20–24, February, 1987.     

Effect of humidity and porosity on fracture of hardened portland cement

The dependence of fracture mechanics terms (γ_T, K_c, G_c and J_c) on relative humidity and porosity is determined for hardened portland cement paste (HCP). The cardinal features of the fracture term/humidity curves and fracture term/porosity curves are discussed. Large hysteresis in fracture term/relative humidity curves is observed, the magnitude depending on the drying history of HCP. Meniscus effects, aging and moisture-assisted stress corrosion processes are thought to contribute to fracture of HCP. Unhydrated portland cement, Ca(OH)₂ particles, and pores with specific size distributions in the HCP system possibly act as crack arrestors.     

Effect of geometry and hybrid adhesive on strength of finger joints of Pinus elliottii subject to humidity and temperature

The optimized bonding of glued finger joints is required for structural and nonstructural applications. The use of nonspecific adhesives, combined with the joint geometry and exposure of joints to humidity and temperature, are factors that can compromise the durability of glued joints. The main objective of this study is the development of cross-linking poly(vinyl acetate) (PVAc) hybrid adhesive to produce nonstructural finger joints of Pinus elliottii with finger lengths of 6.5 and 4.5 mm. The adhesives were produced by emulsion copolymerization of vinyl acetate with n-butyl acrylate with different amounts of N-methylol acrylamide and blended with resorcinol-formaldehyde resin (RF) and aluminum chloride (AlCl₃). The rheological behavior of adhesives was investigated. We found that the joint configuration and the exposition time employed influenced joint strength. The PVAc/RF adhesive showed a thicker bond line and consequent deeper penetration into the pores of the wood as verified by microscopy analysis. Statistically differences in bond strength of the adhesive joints were found with respect to different conditioning times and finger length. The highest values were exhibited by the joints produced with a finger length of 6.5 mm and glued with the hybrid adhesive (AD-4) than that joints produced with a finger length of 4.5 mm.     

直接光度法测定印染废水中铈(IV)

在硫酸溶液中,铈(IV)的强氧化性对间甲酚紫有褪色作用,其褪色程度与铈的浓度有关,据此建立了直接光度法测定痕量铈的新方法。考察了各种实验条件对灵敏度的影响。结果表明,最佳实验条件为:硫酸1.3 m L,间甲酚紫1.4 m L,反应温度80℃,加热反应时间10 min。线性范围为0⁶μg/m L,检出限为0.046μg/m L。可用于印染废水中铈的测定。