碳化水泥砂浆分形特征研究

利用压汞试验对不同碳化程度水泥砂浆孔结构的分形特征进行研究。结果表明:水泥砂浆具有多重分形的特征;碳化使水泥砂浆总孔隙率降低,孔径细化,凝胶孔的孔隙体积分形维数降低;而生成的碳酸钙在大孔、毛细孔中沉积,大孔、毛细孔的体积分形维数增大。因此,分形维数能表达碳化对混凝土材料孔结构的影响。     

硫酸盐侵蚀下硬化水泥浆体中硫元素分布规律的微观测试研究

利用SEM的BSE成像模式和EDS的Line(线扫描)模式测试了2.5%和5.0%硫酸钠溶液中侵蚀1年的水泥净浆试样中硫、钙、硅元素的分布趋势,定量描述与分析了试样中硫元素的分布规律及其产生的主要原因。结果表明:两种浓度硫酸钠溶液侵蚀下的试样,其表层浆体中硫元素含量较低,近表层区出现"高硫含量"带,"高硫含量"带以内,硫元素含量随试样深度的增加,开始下降明显,后缓慢下降,最终趋于稳定;但5.0%硫酸钠溶液中试样"高硫含量"带的宽度和硫元素含量峰值明显大于2.5%硫酸钠溶液中的试样。为进一步研究水泥基材料中硫酸根离子的传输规律及硫酸盐侵蚀下水泥基材料的损伤劣化机理提供了基础。     

Multiscale mechanical modeling of hydrated cement paste under tensile load using the combined DEM-MD method

In this paper, a combined DEM-MD method is proposed to simulate the crack failure process of Hydrated Cement Paste (HCP) under a tensile force. A three-dimensional (3D) multiscale mechanical model is established using the combined Discrete Element Method (DEM)-Molecular Dynamics (MD) method in LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator). In the 3D model, HCP consists of discrete particles and atoms. Simulation results show that the combined DEM-MD model is computationally efficient with good accuracy in predicting tensile failures of HCP.     

汞压法对水泥浆和掺合料水泥浆孔隙分析

硬化后混凝土材料具有细观、微观多孔隙特征,即使配制良好的高性能混凝土,也含有微孔隙和微裂纹。混凝土内部孔隙率及孔径分布对混凝土材料的性质有重要影响,如强度、变形、容重、导热性、吸水性、抗渗性及耐久性等;而矿物掺合料可改变混凝土内部孔隙的分布,从而影响混凝土的性能;因此,对混凝土材料内部孔隙的研究也是混凝土微观研究的一个重要方面。     

强紫外线辐照下水泥砂浆的强度与干缩及水化性能

为掌握紫外线辐照对水泥基材料力学强度、干缩变形及水化作用的影响规律,通过模拟试验,研究分析标准干缩环境、紫外线辐照环境等三种条件下不同组成水泥砂浆的强度、干缩变形、质量变化率及水化进程等参数变化。结果表明,强紫外线辐照对水泥砂浆的抗折、抗压强度存在不利影响,且随着紫外线辐照时间延长,不利影响越显著。同时,紫外线辐照作用显著增加砂浆试件的水分蒸发速率和干缩变形,而试件的水化程度呈下降趋势。     

稳定剂水泥浆流变机理研究

对聚合物稳定剂水泥浆和膨润土稳定剂水泥浆进行了流变性试验研究,按宾汉流变模型对其流变参数进行了理论计算;研究结果表明,聚合物稳定剂水泥浆动切应力较膨润土稳定剂水泥浆低,其浆液的可灌性和扩展半径要优于膨润土稳定剂水泥浆,可成为GIN灌浆法中优良的稳定水泥浆液,该项研究具有很强的工程实用价值。     

蒸养参数对水泥净浆水化性能的影响

研究了在蒸汽养护条件下蒸养参数(静养时间、恒温时间及恒温温度)对水泥净浆水化性能的影响,揭示上述各因素与水泥净浆化学结合水量之间的关系,并且提出各蒸养参数的参考指标值;试验结果表明,在其他条件相同的情况下,预养阶段是蒸养过程必不可少的环节,且预养时间不宜低于2h;为避免胶凝材料的后期水化性能遭到破坏,恒温阶段的恒温时间不宜超过8h,恒温温度不宜超过60℃。     

废瓷粉掺量对水泥净浆水化性能的影响

运用激光粒度分析仪、XRD、SEM等试验方法以确定试验所用废瓷粉的粒径分布、主要成分及微观形貌。通过研究废瓷粉掺量对水泥净浆化学结合水量及水化产物的影响,揭示废瓷粉-水泥净浆的水化机理。试验结果表明:废瓷粉能促进水泥的水化,对水泥水化产物的种类无明显影响,但对水化产物的数量却有一定的影响。     

水化硫铝酸盐水泥粉体对硫铝酸盐水泥自身水化进程的影响

制备并表征了水化硫铝酸盐水泥粉体材料(HCSAP),并结合水化热、化学收缩、XRD、TG、SEM等测试研究了HCSAP对硫铝酸盐水泥自身水化进程的影响.结果表明:在大水灰比条件下,硫铝酸盐水泥完全水化后主要生成钙矾石、水铝黄长石、单硫型水化硫铝酸钙及少量氢氧化铝.在硫铝酸盐水泥中混掺10％HCSAP,该改性浆体后期水化...     

高温净浆法快速检验水泥强度

从检测机理、试验条件、试验方法等方面介绍了快速检验水泥强度的高温净浆法,指出高温净浆法检验水泥强度时间短,费用低,检验结果可靠,可满足施工企业工程进度的要求。     

Compaction index of cement paste of normal consistency

Knowing the virtual packing densities of all the components in a mixture is necessary to calculate its granular packing density with the compressible packing model. The calculation of these virtual packing densities is based on real packing density measurements carried out according to specific operating modes, each one with a different compaction index K. For powders, the current method consists in adding water to powder in a mixer until obtaining a smooth paste (K = 6.7). But this method remains subjective since the degree of smoothness achieved is estimated by the operator. The objective of this work is to put forward a more rational alternative method based on tests of normal consistency used in cement plants. This paper presents experiments on binary mixtures (cement–mineral admixtures), with or without superplasticizer, which have resulted in a compaction index K = 4.8. Using these results, the amount of water (given in the technical data sheet) needed to obtain a normal consistency allows the calculation of virtual packing densities of standardized cements. However, if a superplasticizer is used it is necessary to carry out this test. Its saturation proportion can also be estimated with the test of normal consistency.     

如何提高水泥石的弹性模量

通过正交试验设计探讨了水泥石弹性模量与石英粉、石英砂掺量以及水灰比之间的关系.试验结果表明:随着石英砂掺量的增加,水泥石的弹性模量有了很大的提高,最高达到了56 GPa;同时,石英粉的掺量变化与水灰比的不同也会对试验结果产生一定的影响.这是由于石英砂的增加,促进了水泥的水化,形成了结晶核心,同时起到密实填充作用.此次试验对于提高陶粒混凝土弹性模量具有参考价值.     

Microstructure-based modeling of water diffusivity in cement paste

In view of the crucial influence of water diffusion in cement paste on durability, it is necessary to predict the water diffusivity of cement-based materials. The main purpose of this paper is to present a computational approach to predict the water diffusivity in cement paste. A computer-based cement hydration model HYMOSTRUC3D is used to generate the 3D microstructure of cement paste. The simulated pore structure is compared with the experiments. Based on the generated microstructure, finite element method (FEM) is applied to simulate the diffusion process of tritiated water through the saturated cement paste. In the FE simulation, cement paste is modeled as a three-phase composite material, consisting of capillary pores, un-hydrated cement and hydration products. Un-hydrated cement is considered non-diffusible. The contribution of capillary pore phase and hydrating products phase to the diffusivity of tritiated water in cement paste are taken into account. Finally, the diffusivity modeling is applied for series of hardened cement paste with variations on water-to-cement (w/c) ratio and curing age. The simulations are validated with experimental data obtained from literature. The comparison between simulation and experiments indicate that the simulated and experimental data are of the same order of magnitude. Furthermore, the tendency of simulated relationship (diffusivity vs. w/c ratio, diffusivity vs. curing age) shows a good fit to the experiments.     

Filtration behaviour of soil-nonwoven geotextile combinations subjected to various loads

Geotextiles are often subject to different load types in their filtration applications. The load action can cause changes in soil density, geotextile stretching and flow interaction at the soil-geotextile interface. All of these load-induced changes to a geotextile may affect the filtration behaviour of the soil-geotextile system. The impact of load type on the filtration behaviour of soil-nonwoven geotextile combinations has been studied through a series of tests using an experimental apparatus designed specially for the laboratory tests. In these tests, the soil-geotextile combination was fabricated by inserting a piece of nonwoven geotextile between a 50 mm thick soil layer and a layer of steel beads. Two chemical-bonded nonwoven geotextiles were employed in this study. One of the three load types, namely sustained, pulsatory and a combination of both was applied to the combination prior to each filtration test. The frequency of the pulsatory load was 0.1 Hz and a total of 5000 cycles of repeated load applied to the combination for each load type test. After applying this specific type of load on a soil-geotextile combination, water was allowed to flow down through the combination from the soil into a drainage layer set at various hydraulic gradients. The flow rates corresponding to elapsed times were measured and the average hydraulic conductivity value was extracted by using Darcy’s law to characterize the filtration performance of the entire soil-geotextile combination. Variations in the average hydraulic conductivity value with respect to the soil void ratio, magnitude and type of normal load were examined.The experimental results revealed that the void ratio of soil decreased with the increase of total load. Although two parent geotextiles under study, namely GT1 and GT2, have similar filtration characteristics, soil-geotextile combinations composed of these two geotextiles exhibited different filtration responses to the normal load. Soil-GT1 combinations exhibited a normal relationship between the average hydraulic conductivity and the normal load applied; the average hydraulic conductivity increased with an increase in the total load. Soil-GT2 combinations exhibited different load-dependent responses to a normal load with the average hydraulic conductivity depending on the magnitude and type of load. Such load-dependent hydraulic conductivity changes are attributed mainly to the geotextile in-plane strain and the pumping action in the combination.     

粉煤灰对水泥水化浆体微结构的影响

为探讨粉煤灰对水泥水化浆体微结构的影响,通过原子力显微镜以及能谱分析,对纳米尺度下基准及掺有粉煤灰水泥浆体中水化产物的形状、大小以及堆聚结构的形成机制进行了研究.试验结果显示,在基准水泥浆体中的水化产物大部分是粒级大约40～80 nm的圆球形颗粒,而且试验还观察到在它们中还镶嵌着一些尺寸大于1μm的板状和薄片状水化产物...     

微生物水泥净浆的自修复性能研究

研究了微生物矿化对水泥基材料的自修复作用,试验测定了微生物水泥净浆的裂缝自愈合、抗压强度、吸水率、孔结构等性能,并采用X射线衍射对矿化产物进行成分分析。结果表明微生物的掺入使普通硅酸盐水泥净浆和硫铝酸盐水泥净浆的抗压强度增加,吸水率下降;试件裂缝处自愈合形成了一条连续、饱满的灰白色矿物填充带。矿化生成的方解石型碳酸钙和菱镁矿型碳酸镁沉淀填充于试件内部缺陷、裂缝,使水泥净浆的总孔隙率及其增长率下降微细孔隙比例增加促进了材料的自修复,改善了其孔结构。     

Characterisation of the behaviour of high performance mortar subjected to high temperatures

An experimental investigation was conducted to evaluate the performance of mortar mixed with silica fume (SF) when exposed to high temperatures. A three-point bending test apparatus was developed to test concrete-like materials at high temperatures. Notched specimens were first heated at a rate of 3.3 °C/min to various target temperatures from room temperature to 900 °C and then maintained under constant temperature during 2 h. They were then subjected to a three-point bending test while the temperature was held constant. The maximum peak load occurred at 300 °C and decreased sharply at higher temperatures. The experimental results demonstrated a noticeable influence of the temperature on the fracture resistance of the high-performance mortar. The toughness parameters, such as intensity factor or fracture energy, evolved nonlinearly with the target temperature, and reached their maximum value at 300 °C; at higher temperature, their values decreased considerably. SEM micrographs of the heated specimens after the mechanical tests and cooling and TGA/DTA analysis of the dried material matrix facilitated the understanding of the material’s macroscopic behaviour.     

镁盐对微生物水泥净浆微观结构性能的影响

采用X射线衍射、扫描电镜、能谱分析、压汞测孔法等亚微观测试手段,研究了镁盐对微生物水泥净浆微观结构性能的影响。结果表明,当营养液中仅含钙盐时,微生物矿化产物以方解石为主,并含少量球霰石,矿物呈颗粒状、团簇状。适量镁盐的掺入促进了微生物的矿化作用,形成了针棒状菱镁矿型碳酸镁和方解石型碳酸钙,降低了孔隙率,增加了微细孔隙比率,改善了材料的孔结构。     

SJP注浆浆液水化进程与流变特性研究

针对陡倾宽缝、松散架空等复杂地层灌浆,普通水泥浆存在"灌不住"、"顺缝跑"等问题,研制开发的SJP水泥基灌浆材料具有初始流动度大、可灌性好,接近可泵期时表现为黏度突增、流动度突降的流变特性。SJP浆材是水泥基浆材掺加改性纤维、硅钙早强剂与稳定剂配制而成,助剂加量为2%~2.5%。掺入水泥浆中的助剂首先在水泥颗粒表面形成溶剂膜,起到调节水泥水化离子与助剂硅钙阳离子浓度变化的作用,实现水化加速期控制成核的速度,最后掺入的稳定剂可以调整水泥水化衰减期的成核和扩散,调节水泥浆的流动时间。SJP浆材由于水化速度快,流动时间可控,水化产物凝结胶连紧密,结石体后期强度较普通水泥浆平均提高15%~25%,解决了水泥基速凝浆材早期强度高后期强度低的问题,得到了较大范围的推广应用。     

自密实混凝土的胶结料流动性试验研究

为了配制高性能自密实混凝土,通过试验研究了硅灰、粉煤灰及超细粉等掺合料与减水剂对水泥浆体流动性的影响,试验结果表明,随着粉煤灰掺量的增加水泥浆体流动性先增大后减小;超细粉掺量越大,浆体流动性越大;硅灰掺量越大,浆体流动性越差。