二级界面对水泥基材料孔结构和性能的影响

将粉煤灰、硅灰和纳米纤维材料--活性NR粉应用于水泥基材料中，依据最大密实度理论和微粒级配数学模型设计出水泥基材料，研究了水泥基材料中二级界面对其性能的影响．结果表明，加入活性NR粉纳米纤维矿物可改善体系的颗粒级配和水泥基材料中二级界面的显微结构，提高均匀性，降低孔隙率，优化体系的孔结构．改善二级界面的显微结构可降低体系的总比孔容，提高球形孔隙体积率，降低体系的最可几孔径，优化硬化浆体的孔结构以及提高体系的内部拉应力，提高水泥基材料的抗弯强度．     

The chloride ponding test and its correlation to the accelerated chloride migration test for concrete

Abstract

In this study, the total chloride content and penetration depth of concretes were measured by the 90‐day salt ponding test, and the flux of chloride ions passing through the concrete was measured by the accelerated chloride migration test (ACMT; the electrochemical technique is applied to accelerate chloride ion migration). Fick's second law was fitted to the data from the ponding test to determine the diffusion coefficient. The steady‐state and the non‐steady‐state migration coefficients were determined from the modified Fick's first and second laws, respectively. The steady‐state migration coefficient, the non‐steady‐state migration coefficient, and the diffusion coefficient were compared. The non‐steady‐state migration coefficient, steady‐state migration coefficient, and diffusion coefficient were linearly correlated. The non‐steady‐state migration coefficient gave the highest value, being about 1.5 times higher than the steady‐state migration coefficient, and up to about 4 times higher than the diffusion coefficient. Since the 90‐day ponding test is time‐consuming, the ACMT provides a time saving method to obtain the transport property of concrete.     

Prediction of the diffusivity of cement-based materials using a three-dimensional spatial distribution model

A three-dimensional image of hardened cement paste was reconstructed using a backscattered electron image (BEI) and used to predict the diffusion properties of hardened cement paste. After the BEI observations, an autocorrelation function (ACF) was calculated for each phase of the hardened cement paste, including the unhydrated cement, portlandite, and large pores. A three-dimensional image was reconstructed on the basis of the ACF based on random distributions. The dynamic elastic modulus and diffusion coefficient were calculated using a finite-element or finite difference method with the reconstructed three-dimensional images. The elastic modulus of the C-S-H phase was determined by micro-indentation, and the diffusivity of C-S-H was calculated using this elastic modulus based on previous reports. The resulting predicted dynamic elastic moduli and diffusion coefficients were in good agreement with the experimental results. Although, it was observed that the predicted values of the diffusivity of the blended cement pastes is different from the measured values, a new relationship between diffusivity and porosity of C-S-H in blended cement pastes was developed in this study.     

Preparation of waste glass powder by different grinding methods and its utilization in cement-based materials

Waste glass, as a hard-to-grind material, was often grinded into powder by ball-mill in order to be used as a supplementary cementitious material in concrete. In this study, three different glass powders (GP) referred to as GPd, GPw and GPe were fabricated by different methods (i.e. dry condition, water condition and ethyl alcohol condition), and the effect of GP on the properties of cement-based materials was systematically evaluated. The results showed that the milling efficiency of GP was significantly affected by grinding condition. Ultrafine GP can be obtained as additional water or ethyl alcohol was added during the grinding process. GP showed low pozzolanic reactivity in the early age, even when the particle size was decreased to about 300 nm. GPd with large particle size and non-absorbent feature could increase effective water-to-cement ratio and thus improved the workability and early strength of specimens containing GPd, while the later strength was lower than that of reference ones due to low pozzolanic reactivity of GPd. In contrast, specimens containing GPw and GPe exhibited higher early mechanical strength than reference specimen due to the filling and acceleration effects of GP. An encouraging result indicated that GPe presented high pozzolanic reactivity at 28 d, which was seldom reported in the literature.     

Temporal and spatial development of drying shrinkage cracking in cement-based materials

In optical microscopy and acoustic emission (AE) experiments, the development in time and space of drying shrinkage cracks in hardened cement paste and a cement composite containing mono-sized glass particles has been studied. The results indicate two types of restraint, i.e. self-restraint of the specimen/structure, and aggregate restraint. In plain cement paste cracks initially develop perpendicular to the drying surface, but may subsequently grow parallel to the drying surfaces. In composites containing glass particles, aggregate restraint causes continuous growth of microcracks. AE monitoring has revealed that drying shrinkage cracks develop almost instantaneously at the onset of drying. Several AE parameters elucidate the details of the process. The two techniques are complementary: AE monitoring is suitable for temporal development assessment, whereas optical microscopy is very well suited for measuring crack geometry.     

引气剂对水泥基材料电磁波反射率和透波率的影响

为研究孔隙对水泥基材料电磁波反射与透射性能的影响,在砂浆中掺入引气剂,利用矢量网络分析仪和压汞仪对水泥基材料的反射率、透波率以及孔结构进行测试。结果表明,引气剂可以显著降低水泥基材料反射率,当引气剂掺量为0.01%时样品反射率最低;水泥基平板透波率在8.2~12.4、12.4~18和26.5~40 GHz范围内均随着频率增大呈减小的趋势,掺加引气剂对水泥基平板的透波性能有明显的改善;随着引气剂掺量由0增加到0.015%,水泥砂浆0.1μm以下的孔隙明显增多,且孔隙率也逐渐增大,掺量为0.015%时,孔隙率达到29.8%。孔隙率的增大降低了材料的介电常数,改善了材料表面对电磁波的反射和透射性能。     

Use of tomography to understand the influence of preconditioning on carbonation tests in cement-based materials

Recognition of the rising amount of atmospheric CO₂ has brought renewed interest in understanding the effects of carbonation on reinforced concrete performance. In laboratory testing, the specimens must be preconditioned to effectively study carbonation. This paper studied the influence of several preconditioning schemes on the carbonation profiles of cement paste specimens subjected to accelerated carbonation tests. The evolution of microstructure and moisture during carbonation were investigated accordingly. Bulk of the work was based on an extended X-ray attenuation method (XRAM), which relied on X-ray computed tomography (CT). A novel method was introduced to evaluate the extent of damage due to drying. Based on extent of damage, the paper recommends standard-cured specimens for carbonation tests as compared to water-cured specimens. Also, when comparing between oven drying and mass balancing, the latter was shown to be more suitable, as the inner moisture distribution becomes more uniform after this drying protocol, and less fluctuation of humidity will occur during carbonation.     

Determination of diffusion coefficient of chloride in concrete: an electrochemical impedance spectroscopic approach

For predicting the service life of concrete structures in marine environment, diffusion of chloride (D) is an important parameter. Electro-migration tests and ponding tests are two techniques conventionally adopted, however they are destructive in nature. EIS (Electrochemical impedance spectroscopy) being non-destructive appears a promising technique to arrive at ‘D_R’ (D from EIS) in situ in structures. The D_R of ordinary Portland cement concrete (OPC) was compared with that of Portland pozzolana cement concrete (PPC). The effect of curing on D_R was analyzed. The splash zone condition was created by subjecting the specimens to alternate wetting and drying cycles. At the end of 28 days of curing, the D_R of PPC concrete is only 66.7% of that obtained in OPC concrete. A linear correlation was established between D_R and the porosity of the concrete_. Due to pozzolanic reaction, the rate of pore refinement is faster in PPC concrete compared to OPC concrete. In M25-PPC concrete at the end of 28 days of curing, the pore size is decreased to 14.6% of that obtained at the end of 3 days of curing. The reduction of pore size by densification of pore structure due to pozzolanic reaction reduces the D_R value in PPC concrete. In 30 MPa concrete the D_R under wet cycle is 3 times higher than in dry cycle, which implied that corrosion is initiated 3 times faster in concrete exposed to the splash zone condition.     

球形孔通孔和闭孔泡沫铝合金的超声衰减性能

研究了球形孔通孔和闭孔泡沫铝合金在1 MHz～10 MHz的超声衰减性能.结果表明:泡沫铝合金的超声衰减性能决定于其孔结构;通孔泡沫铝合金的超声衰减系数α随着孔径d的减小、孔隙率Ps减小和比表面积Sv的增加而增大;闭孔泡沫铝合金的超声衰减系数α随孔径d的减小、孔隙率Ps的增加和比表面积Sv的增加而增大;当孔径d、孔隙率Ps相近时,闭孔泡沫铝合金的超声衰减性能优于通孔泡沫铝合金;在1 MHz～10 MHz二者是具有良好阻尼性能的轻质材料.其衰减机制为在弹性范围内超声应力波在具有大量孔隙界面的泡沫铝合金中的衰减.     

Si cross-polarization magic-angle spinning NMR spectroscopy––an efficient tool for quantification of thaumasite in cement-based materials

²⁹Si{¹H} cross-polarization (CP) magic-angle spinning (MAS) NMR spectroscopy is a powerful and reliable tool for the quantification of thaumasite in cement-based materials. The most efficient method for quantifying thaumasite from ²⁹Si{¹H} CP/MAS NMR spectra is described and it is shown that the method allows detection of thaumasite contents below approximately 10 wt.% with a relative precision of 15% and contents above 10 wt.% with a relative precision of 10%. The applicability of ²⁹Si{¹H} CP/MAS NMR for quantification of thaumasite is demonstrated for different Portland cement pastes and shows that thaumasite contents as low as 0.2–0.5 wt.% can be detected in cementitious systems with low concentrations of paramagnetic impurities. For a Portland cement containing various amounts of limestone dust and stored at 5 °C in a MgSO₄ solution, large quantities of thaumasite have been detected. Furthermore, the quantity of thaumasite is found to be less sensitive to the amount of added limestone dust. For samples of a Portland cement with a fixed content of limestone dust but different quantities of added gypsum, the increased contents of gypsum are observed to result in larger quantities of thaumasite after prolonged hydration.     

气体分离复合膜制备中材料匹配和孔渗现象的研究

介绍了气体分离复合膜的基本构型、制备方法及近期的发展，阐述了制备气体分离复合膜时遇到的两个问题；材料匹配和孔渗现象。模拟计算了孔渗对复合膜分离性能的影响，并对如何防止孔渗现象的发生进行了讨论。     

Role of porosity in controlling the mechanical and impact behaviours of cement-based materials

This work deals with the influence of porosity on the tensile, the compressive and the impact behaviours of two fine cementitious mortars—one with silica fume and one without. The addition of silica fume is shown to change the pore size distribution. The mix without silica fume is characterized by porosity at the scale of the grains of fine sand (approximately 100 μm), while silica fume addition results in a more porous matrix with pore sizes of millimetre-length size. The mortar with silica fume shows a higher quasi-static compressive and flexural strength whereas the mix without silica fume is observed to be less compressible (by irreversible reduction of volume) under heavy confinement pressure (quasi-oedometric tests) and shows better ballistic performance. A numerical simulation of the impact tests employing the Krieg, Swenson and Taylor model, which accounts for both deviatoric and volumetric inelastic behaviour of the material, was undertaken using the data from quasi-oedometric tests. These calculations follow the experimental results and confirm the influence of the macroscopic porosity on the impact performance of cement-based materials.     

孔隙形状及孔隙率对多孔材料弹性性能的影响

利用通用单胞法(GMC)计算了不同孔隙形状及孔隙率对多孔材料等效弹性参数的影响,计算中分别采用二维方形、圆形孔隙模型和三维立方体、球形孔隙模型模拟多孔材料。不同孔隙率下等效弹性参数的计算结果表明: 不同孔隙形状下,多孔材料等效弹性参数随孔隙率增大的退化程度不同;通过对比二维简化模型与三维模型的差异,发现二维简化模型对多孔材料等效弹性参数的估算值偏低。进一步将GMC计算结果和已有文献实验结果进行比较,发现两者具有较高的吻合度。最后将GMC模型与有限元、经验模型进行对比,得出GMC模型的局限性。综合计算结果,GMC具有一定的计算精度,可应用于工程实际分析中。     

On the relation of setting and early-age strength development to porosity and hydration in cement-based materials

Previous research has demonstrated a linear relationship between compressive strength (mortar cubes and concrete cylinders) and cumulative heat release normalized per unit volume of (mixing) water for a wide variety of cement-based mixtures at ages of 1 d and beyond. This paper utilizes concurrent ultrasonic reflection and calorimetry measurements to further explore this relationship from the time of specimen casting to 3 d. The ultrasonic measurements permit a continuous evaluation of thickening, setting, and strength development during this time period for comparison with the ongoing chemical reactions, as characterized by isothermal calorimetry measurements. Initially, the ultrasonic strength-heat release relation depends strongly on water-to-cement ratio, as well as admixture additions, with no universal behavior. Still, each individual strength-heat release curve is consistent with a percolation-based view of the cement setting process. However, beyond about 8 h for the systems investigated in the present study, the various strength-heat release curves merge towards a single relationship that broadly characterizes the development of strength as a function of heat released (fractional space filled), demonstrating that mortar and/or concrete strength at early ages can be effectively monitored using either ultrasonic or calorimetry measurements on small paste or mortar specimens.     

炭材料的性质与炭-炭粘接性能关系的研究

为实现高温条件下炭材料的有效连接，利用陶瓷组元改性酚醛树脂制备了树脂基高温粘接剂，用该粘接剂粘接了4种不同孔隙结构的炭材料，并进行400～1200℃的高温热处理，利用万能材料试验机考察了上述粘接剂的高温粘接性能，通过压汞仪分析了4种炭材料的孔隙结构及其与粘接性能间的相互关系，结果表明：粘接样品在高温热处理后仍具有较为理想的连接强度；炭材料表面的孔隙率和孔径分布对粘接强度有一定的影响；合适的孔隙率和孔径分布是实现高性能连接的必要条件。     

超滤膜结构参数的测定方法及透水通量与膜结构关系的模型

用扫描电镜、场发射扫描电镜以及渗透率法测定了超滤膜表面孔径分布、孔隙率以及膜孔密度等结构参数．结果表明,用扫描电镜法和渗透率法测定膜平均孔径及膜孔密度等结构参数是可行的．基于获得的结构参数,建立透水通量和平均孔径、膜孔密度间的数学模型,并探讨了模型中平均孔径减小系数a1和膜孔密度减小系数a2的确定方法及不同原水性状下的a1和a2的值．     

Correlation between the capacitor performance and pore structure of ordered mesoporous carbons

Mesoporous carbons were synthesized by organic–organic self-assembly of triblock copolymer F127 and phenolic resin oligomers composed of resorcinol–formaldehyde or resorcinol–furfural. The mesostructure control was performed by using different polymerization catalysts, ammonia and acetic acid. The effects of the aldehyde and polymerization catalyst on pore architecture of mesoporous carbons were investigated. Disordered mesostructure with poorly disconnected mesopores was formed using furfural. In contrast, when formaldehyde was used, ordered structure with mesochannels was formed. In addition, changes in mesochannel length and the degree of long-range order are found to depend on polymerization catalyst. The porous carbons with different structure were used as a model material to investigate the ion storage/transfer behavior in electrical double-layer capacitor. Electrochemical cyclic voltammetry measurements were conducted in 1 M sulfuric acid electrolyte solution. The ordered mesoporous carbons show superior capacitances and rate performance over the disordered carbons. Electrochemical impedance spectroscopy was used to assess the transport properties. The impedance data clearly demonstrated that the degree of long-range order and channel length can influence the ion transport, resulting in superior capacitive performances.     

Thermal diffusivity and conductivity in low-conducting materials: A new technique

A comparative method is presented, suitable to measure both thermal diffusivity and conductivity of low-conducting solids. The repeatibility of the measurements of thermal conductivity is 3%, whereas for diffusivity is 6%. Data for some low-conducting materials are given, consistent with those reported in the literature.     

气孔结构参数与漂珠隔热耐火材料热导率的相关性研究

以漂珠隔热耐火材料为研究对象,通过调整漂珠的添加量(25%、35%、65%和85%)来改变试样的气孔结构参数,并研究了漂珠的添加量对试样气孔结构参数的影响,分别借助于回归分析理论和灰色关联理论探讨了试样的气孔率、以及气孔孔径区间等气孔结构参数与热导率之间的相关性。结果表明,随着漂珠添加量的增加,试样的闭口气孔率显著增加,但开口气孔率变化不明显;各组试样气孔孔径分布范围为1～300#m,其中以50～100#m孔径区间的气孔为主。在一定温度范围内,试样的热导率随着总气孔率的增大而呈指数关系减小;不同孔径区间与热导率的灰色关联分析表明,<150#m范围内的气孔与热导率的关联度最大。     

The relationship between charge passed and the chloride concentrations in anode and cathode cells using the accelerated chloride migration test

In this study the electrochemical technique is applied to accelerate chloride ion migration in cement-based material to estimate its permeability. Specimens with six fine aggregate volume fractions were cast and tested. For all test series, the chloride concentrations both in anode and cathode cells as well as the electrical current were simultaneously monitored in the accelerated chloride migration test. The chloride migration rates of anode and chloride cells were used to assess the permeability of cement-based materials. A good correlation was observed between the chloride migration rate of anode cell and cathode cell. And, a good correlation was also observed between the chloride concentration in anode cell, the chloride concentration in cathode cell and charge passed obtained from the accelerated chloride migration test.

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Résumé La technique electrochimique est appliquée pour accélérer la migration des ions chlorure dans des matériaux à base de ciment pour estimer leur perméabilité. Des échantillons avec six granulats fins ont été préparés et testés. Dans tous ces tests, les concentrations dans les cellules anode et cathode ainsi que les courants, électriques ont été simultanément suivis. Le taux de migration dans les cellules anode et cathode a été utilisé pour évaleur la perméabilité des matériaux testés. Une bonne corrélation a été observée entre le taux de migration de chlorure dans la cellule anode et dans la cellule cathode. Une bonne corrélation a aussi été observée entre ces concentrations et la charge passée obtenue de ces tests de migration de chlorure accélérés.