Effect of Curing Regime on Degree of Al^(3+) Substituting for Si^(4+) in C-S-H Gels of Hardened Portland Cement Pastes

The effect of curing regime on degree ofAl3＋ substituting for Si^4＋ （Al/Si ratio） in C-S-H gels of hardened Portland cement pastes was investigated by 29Si magic angel spinning （MAS） nuclear magnetic resonance （NMR） with deconvolution technique. The curing regimes included the constant temperature （20, 40, 60 and 80 ℃） and variable temperature （simulated internal temperature of mass concrete with 60 ℃ peak）. The results indicate that constant temperature of 20 ℃ is beneficial to substitution ofAl3＋ for Si4＋, and AI/Si ratio changes to be steady after 180 d. The increase of Al/Si ratio at 40 ℃is less than that at 20℃ for 28 d. The other three regimes of high temperature increase Al/Si ratio only before 3 d, on the contrary to that from 3 to 28 d. However, the 20 ℃ curing stage from 28 to 180 d at variable temperature regime, is beneficial to the increase of AI/Si ratio which is still lower than that at constant temperature regime of 20 ℃ for the same age. A nonlinear relation exists between the Al/Si ratio and temperature variation or mean chain length （MCL） of C-S-H gels, furthermore, the amount ofAl3＋ which can occupy the bridging tetrahedra sites in C-S-H structure is insufficient in hardened Portland cement pastes.

Nondestructive Microstructure Analysis of the Carbonation Evolution Process in Hardened Binder Paste Containing Blast-furnace Slag by X-ray CT

We used micro-XCT（X-ray computed tomography） to in-situ investigate the microstructure evolution of hardened binder paste containing different contents （0%, 30%, 50% and 70%） of blast-furnace slag at different carbonation time （O, 3, 7 and 14 days）, respectively. The carbonation front shape, the degrees of carbonation and cracks spatial distribution were studied for hardened binder paste containing BFS. In addition, the porosity and pore volume distribution of macro-pore were measured at different carbonation ages. The results reveal that the degree of carbonation at different times can be measured by the volume fraction of the uncarbonated and carbonated parts.

Sulfate Ions Immobilization of Calcined Layered Double Hydroxides in Hardened Cement Paste and Concrete

The sulfate ions immobilization behavior of calcined layered double hydroxides(CLDHs) in the hardened cement paste was investigated. The experimental results show that the sulfate ions in cement paste are immobilized by CLDHs to reconstruct the layered structure and aggregate around CLDHs. The immobilization amount of sulfate ions by CLDHs reaches 4.74×10^-3 mol/g, while the increasing amount indicates non-linear relation with the addition of CLDHs. The incorporation of CLDHs decreases the amount of ettringite formed to limit the expansion of cement paste, which decays the sulfate reaction to enhance the sulfate resistance of concrete.

Effects of Carbonation on Micro Structures of Hardened Cement Paste

In order to investigate the effects of carbonation on the microstructure of cement concrete,the carbonation depth and microstructure of cement paste with 0.3,0.4 and 0.5 water/cement ratio after 7,14,21 and 28 d accelerated carbonation were studied respectively.The results showed that with the increase of waterto-cement ratio and carbonation age,the carbonation depth was deepened with faster early carbonation speed and slower later carbonation rate.Carbonation densified the structure of hardened cement stone with refinement of pore structure and reduced porosity.Then,during the carbonation process from the surface to the inside of carbonation area,it was prone to form micro-cracks extending to the interior specimen,resulting in cement paste carbonation depth uneven.It is further illustrated that the color reaction method using phenolphthalein solution combined with X-CT and X-ray diffraction analysis is much more reasonable to evaluate the cement concrete carbonation degree.Moreover,during carbonation process sulfur element in cement paste migrated to the area un-carbonated and the concentrated shape of sulfur element is consistent with the coloring region in carbonation interface.Finally it was identified that carbonation not only reduced the p H value in cement concrete but also made prone to crack in carbonation zone,which increased the probability of reinforcement corrosion.

Degradation of Pore Structure and Microstructures in Hardened Cement Paste Subjected to Flexural Loading and Wet-dry Cycles in Sea Water

Hardened cement paste was subjected to the flexural loading and wet-dry cycles in sea water. The degradation of microstructures was obtained using scanning electron microscope （SEM）, and the energy dispersive spectrum （EDS） analysis was carried to analyze the local composition. Mercury intrusion porosimetry （Poremaster GT-60） was used to analyze the degradation of pore structures. The experimental results show that the synergistic action of the flexural loading, wet-dry cycles and sea water leads to significant deterioration of hardened cement paste. The degradation of microstructures in the tensile region is more serious than that in the compressive region. The flexural loading and wet-dry cycles accelerate the chemical attack of sea water.

Statistical Characteristics of Microhardness of Hardened Cement Paste

Due to the intrinsic nature of a heterogeneous and anisotropic microstructure of cement based materials and the small indentation size, the measured microhardness values are subject to considerable variability. This work presents an in-depth assessment of microhardness of hardened cement pastes（HCPs） from a statistical perspective. Hundreds of microhardness measurements were conducted on an HCP sample using a Vickers Microhardness Tester. The results showed that the microhardness measured from the HCP sample significantly scattered with a large standard deviation, varying from tens to hundreds. The data-set of microhardness values was not normally distributed but fit best with a three-parameter lognormal model. By using a statistical software, the probability density function of the microhardness distribution can be readily obtained. The arithmetic mean and its 95% confidence intervals of the measured microhardness values can be used to best represent the microhardness characteristics of HCPs.

DURABILITY OF HARDENED FLY ASH PASTE

The mechanical properties and durability (mainly frost - resistance and carbonation resistance) of fly ash - CaO - CaSO//4 center dot 2H//2O hardened paste are studied. The relationship among durability of hardened fly ash paste, the quantity and distribution of hydrates and the initial paste texture of hardened fly ash paste is presented. (Author abstract) 3 Refs.

Mass Balance and Viscosity of the Pore Solution during the Hardening of Cement Paste

In the presented work,the results are provided of examining the properties of a pore solution during the process of cement paste hardening.Based on the experimental data of W.P.Halperin et al,the evolution of the mass balance of structured physical water is analyzed as a combination of interactions of capillary,gel,and other components.The formation and development have been studied of the pore solution viscosity.The comparison of the reported dependences of the water viscosity on the size of the pores with the experimentally determined values of the pores’radius has allowed estimating the rise of avid the pore solution viscosity in the process of hardening of cement paste.The separation of the structured pore solution’s viscosity into capillary and gel components allows for a quantitative and qualitative consideration of the cement paste hardening as the process of forming a macrocapillary matrix,inside which a microporous structure is formed of the cement gel.

碱激发胶凝材料硬化体内Na^(+)分布规律模拟

本工作通过试验探究了标准养护条件下的碱激发胶凝材料硬化体内Na^(+)在一维方向上的分布规律。同时,基于Fick扩散方程,采用COMSOL Multiphysics有限元模拟软件,通过有限元条件下硬化体内的Na^(+)扩散系数、湿度水头和孔隙率等边界条件的设定,建立了碱激发胶凝材料硬化体有限元模型,模拟了碱激发胶凝材料硬化体一维方向上Na^(+)的分布规律。试验结果表明,在标准养护条件下,0~3 d碱激发胶凝材料硬化体内Na^(+)的迁移量呈“∨”型分布,Na^(+)以两端析出为主,3~28 d碱激发胶凝材料硬化体内的Na^(+)迁移量呈“∧”型分布,Na^(+)以内部迁移为主。基于Fick扩散定律的COMSOL Multiphysics仿真模拟,在扩散系数D F,C=1×10^(-8)m^(2)/s、湿度水头∅=0.85、孔隙率p=20%的条件下建立溶质传递方程与溶剂运输方程,拟合得到的碱激发胶凝材料硬化体内Na^(+)一维分布规律与试验结果相近。本工作实现了基于试验的碱激发胶凝材料硬化体内Na^(+)一维分布的数学模拟。

Relationship between chloride diffusivity and pore structure of hardened cement paste

Based on effective media theory, a predictive model, relating chloride diffusivity to the capillary pores, gel pores, tortuosity factor, and pore size distribution of hardened cement, is proposed. To verify the proposed model, the diffusion coefficient of chloride ions, the degree of hydration, and peak radius of capillary pores of cement paste specimens were measured. The predicted results for chloride diffusivity were compared with published data. The results showed that the predicted chloride diffusivity of hardened cement paste was in good agreement with the experimental results. The effect of the evolution of pore structures in cement paste on chloride diffusivity could be deduced simultaneously using the proposed model.

膏体充填材料力学性能的初步实验

介绍了一种适合于煤矿膏体充填的专用膏体胶结料,它可以在50kg/m3左右的极少用量条件下,保证膏体快速凝结固化,达到膏体充填不迁村采煤工程需要的强度性能.该膏体充填材料具有典型的塑性特征,弹性模量大,在低围压下就转变为应变强化特征,是一种比较理想的充填胶结材料.

含裂缝水泥基材料的渗透溶蚀及其自愈

研究了含裂缝硬化水泥净浆、砂浆和混凝土试件中的渗透溶蚀过程及其对水泥基材料细观结构的影响。结果表明:在裂缝宽度和水力梯度相近情况下,硬化水泥净浆裂缝试件渗透性最高,而混凝土裂缝试件渗透性最低;在渗透的初始阶段,水泥基材料存在裂缝自愈过程,其中砂浆裂缝试件的自愈作用最大,而硬化水泥净浆裂缝试件的自愈作用最小;水泥基材料的渗透过程会导致硬化水泥浆体中Ca2+的溶出,破坏水泥石细观结构;当渗透速率较小,水泥基材料裂缝表面粗糙容易附着CaCO3晶体时,硬化水泥浆体中溶出的Ca2+可能与溶于水中的CO32–结合形成CaCO3结晶而成为混凝土裂缝自愈的原因之一。

氧化石墨烯对水泥石微观结构及性能的影响

采用改进Hummers法和超声波分散方法制备纳米氧化石墨烯分散液(NGO),通过傅立叶红外光谱(FTIR)、X-射线衍射(XRD)对其进行了结构表征。将NGO掺入到含有聚羧酸系减水剂(PC)的水泥浆体中,研究了NGO对水泥浆流动度及黏度、水泥石微观结构及力学性能的影响,结果表明NGO片层对水泥石中水泥水化产物晶体的形成有模板效应和调控作用,能够促进水泥水化产物形成整齐、规整的纳米级微晶体,对水泥石有显著的增强增韧作用。

弯曲荷载对硬化水泥浆体和砂浆碳化过程的影响

研究了弯曲荷载对硬化水泥净浆和砂浆试体碳化过程的影响。结果表明:弯曲荷载会加速水泥浆体和砂浆的碳化过程,在弯曲荷载作用下水泥浆体和砂浆的碳化动力学过程可用式x=C_0e^(aη)t^b描述,其中b值均接近1/2;碳化时间对砂浆碳化深度的影响略小于对水泥浆体的影响,而应力水平对水泥浆体和砂浆碳化的影响大致相同。

碳化对水泥石中硫元素分布的影响

为合理评价混凝土中发生硫铝酸盐膨胀反应的硫酸根离子浓度,应用电子探针显微分析技术,研究了碳化对水泥石中硫元素分布的影响,阐明了碳化作用下混凝土中硫元素的迁移规律.结果表明:碳化前水泥石截面的硫元素分布比较均匀,碳化后水泥石中的硫元素由碳化区向非碳化区迁移和积聚,硫元素在碳化区浓度较低,非碳化区浓度较高,钙矾石含量也随之增大,这种因碳化作用造成的硫元素分布不均匀可能导致混凝土局部发生硫铝酸盐膨胀开裂.

低水胶比时水泥-粉煤灰复合胶结材的水化性能

研究了水泥粉煤灰复合胶凝材料在低水胶比条件下的水化产物与硬化浆体显微结构，探讨了高效减水剂对复合胶凝材料的水化产物、水化程度、硬化浆体显微结构的影响．水泥粉煤灰复合胶凝材料的水化产物与普通硅酸盐水泥相同．球形的粉煤灰微粒在浆体中起到微集料的作用，在低水胶比条件下，有助于改善新拌浆体的流动性与硬化浆体的断裂性能，提高其强度．掺有ＦＤＮ的复合胶凝材料其初期水化程度并不因表观水胶比低而降低．水泥粉煤灰复合胶凝材料与高效减水剂协同作用，在低水胶比条件下能获得较好的力学性能．

碳化对水泥石和砂浆的结构及砂浆渗透性的影响

用压汞法、扫描电子显微镜、X射线衍射及渗透高度法研究了碳化对水泥石和水泥砂浆的孔结构和显微结构及砂浆渗透性的影响.结果表明,碳化生成的碳酸钙在毛细孔中沉积后会堵塞毛细孔或将大的毛细孔分割成小孔,使水泥石和水泥砂浆总孔隙率降低、孔径细化,从而可提高砂浆抗渗性.

破碎岩体注浆加固体强度估计

在注浆压力和时间满足规范要求时,注浆前岩体强度、注浆后加固体强度、浆液结石体强度是影响注浆加固效果的主要因素。在分析了已有纯水泥浆结石体强度试验的基础上,利用非线性拟合分析,提出了P.O.42.5水泥结石体28 d强度与水灰比之间关系的经验公式。对已有岩体注浆前后强度试验值进行了无量纲分析,建立了量纲为1的参量——强度增长率和原岩体与浆液结石强度比,进而通过非线性拟合分析,提出了破碎岩体注浆加固体强度增长率的经验公式。根据莫尔库仑强度理论,推导出岩体注浆前后剪切强度参数增长率的计算公式。在现场进行了破碎岩体注浆试验,结果表明,强度增长率试验值与经验公式计算值基本吻合,满足岩体工程注浆设计的需要。

不同水灰比水泥硬化浆体受软水溶蚀作用后的微结构变化差异

利用MIP、TGA等试验方法对不同水灰比的水泥硬化浆体在软水溶蚀作用下进行研究。结果表明:水泥硬化浆体遭受软水溶蚀后,表现出一定程度的质量损失和微观结构劣化。而低较水灰比的水泥硬化浆体抗软水溶蚀的能力明显强于高水灰比的水泥硬化浆体。高水灰比的水泥硬化浆体在软水溶蚀作用下的质量损失大、Ca(OH)2含量降低快、孔结构劣化明显。

杂散电流干扰下掺矿物掺合料水泥石固化氯离子的特点

采用加载杂散电流、内掺氯化钠和化学滴定等试验方法,通过比较有杂散电流和无杂散电流两种情况下掺粉煤灰和矿渣微粉水泥石中固化态氯离子含量变化的差异,研究了杂散电流干扰下掺矿物掺合料水泥石固化氯离子的特点.结果表明:在上述两种条件下,矿物掺合料均对水泥石固化氯离子的能力有促进作用,杂散电流会对水泥石内部固化态氯离子的稳定性产生不良影响,矿物掺合料具有抑制这种不良影响的作用.