Résistance d'un milieu poreux à phase solide hétérogène

The strength of a porous medium, the solid phase of which is made up of composite spheres is determined in the framework of a micromechanical self-consistent reasoning. The strength of the spherical cores is infinite while the surrounding layers are made up of a von Mises material. Application of the modified secant method yields an analytical expression of the macroscopic strength. Such results can be used in order to predict the setting and strength criterion of a cement paste during hydration. To cite this article: J. Sanahuja, L. Dormieux, C. R. Mecanique 333 (2005).     

Heat of hydration of high reactive pozzolans in blended cements: Isothermal conduction calorimetry

A study was carried out comparing silica fume (SF) and dealuminated kaolin (DK) as pozzolanic materials in blended cements. Ten, 20 or 30 wt% of SF or DK were substituted for Portland cement. The kinetics of hydration up to 45 h were studied using isothermal conduction calorimetry. Blends containing pozzolanic materials usually have decreased heats of hydration compared to pure cement during the period of C₃S hydration, i.e. during the main hydration peak. Depending on the chemical composition and the activity of the pozzolan, the reaction taking place with the lime typically contributes to the heat output after the main hydration peak.The pozzolanic activity of DK is the principal factor and heat evolution increases with respect to pure PC mortar, during the first 15 h. The presence of hydrated silica (silanol groups) in DK increases the pozzolanic activity especially before and during induction period. The acidic silanol sites are capable of a fast acid-base reaction with the alkalis and with any Ca(OH)₂ present in cement during the induction period.     

Phase transformation on heating of an aged cement paste

The standard cement paste (C-43-St) was studied previously by static heating, SH, immediately after 1 month hydration at w/c = 0.4 [J. Therm. Anal. Calorim. 69 (2002) 187]. This paste after 5-year ageing (unprotected from contact with air) was subject to thermal analysis in air and in argon (DTA, DTG and TG), to XRD at various temperatures, T, in a high temperature chamber, to mass spectroscopy (MS) and to IR spectroscopy. The aim of this study was to compare the results of SH (fresh paste) and of TG (the aged one), to verify the assumptions made on SH interpretation and to check the change in hydration products with ageing as measured by phase transformation on heating (ΔM versus the final mass). The sorbed water (EV), escaping at 110 °C from the fresh paste, was bound on ageing with a higher energy and escaped at higher temperatures. The joint water content of hydrates and of C-S-H gel increased on ageing by 1–2% in the dense paste C-43-St and did not change in the less compact one C-43-I. C-S-H gel transformed on heating above 600 °C into C₂S and C₃S. Portlandite content did not change on ageing. In the air atmosphere it became partly carbonated, which was accompanied by an increase in mass between 500 and 600 °C. Carbon dioxide and/or carbonate ions to form carbonates, were sorbed during ageing and were present in the aged paste in some form undetectable by XRD (amorphous or crypto-crystalline). Sensitivity to carbonation ΔM(700–800 °C) increased highly with ageing.     

Utilization of waste phosphate aluminum slag for cement manufacture

The objective of this study was to investigate the feasibility of application of waste phosphate aluminum slag (PAS) for cement manufacture. To recycle waste PAS and minimize adverse effects on cement hydration induced by phosphate, NH₄OH was used to purify PAS. X-ray diffraction (XRD) analysis was used to determine to confirm the removal of harmful phosphate. The effect of PAS on the hydration product composition, heat release and compressive strength was also investigated. The results demonstrated that NH₄OH was effective in removing harmful AlPO₄ in PAS and 10% NH₄OH was considered as the optimal treatment concentration. In addition, the purification of NH₄OH alleviated the delay in cement hydration caused by AlPO₄ and the heat release curve of purified PAS (PPAS) cement tends to that of OPC. Moreover, the compressive strength of PPAS mortar at 28 days was 49.4 ​MPa, which is 18% higher than the compressive strength of PAS mortar. PAS purified by NH₄OH can be applied to cement manufacturing.     

水泥中金属元素的激光诱导击穿光谱实验条件研究

激光诱导击穿光谱技术(LIBS)是一种被广泛使用的物质元素检测技术。由于它的探测结果受多种因素的影响,因此,分析比较不同实验条件对LIBS光谱测量的影响对LIBS检测有着重要的意义。通过采用四川省北川县中联水泥有限公司生产的42.5普通硅酸盐水泥制成的水泥压片,利用八通道光纤光谱仪AvaSpec-2048-USB2-RM、延时触发器DG645进行了LIBS检测。针对影响水泥几种重要技术指标的金属元素Mg,Al,Na,K进行了分析。主要对比了激光频率、同一点测量次数对不同金属元素光谱信号强度的影响,得出在本实验条件下的最佳实验参数：10 Hz为最佳激光频率,激光频率为10 Hz时元素Mg,Al,Na,K所得到的光谱强度比8 Hz时分别提高了67.66%,47.88%,84.59%,43.36%。由于压片样品在放置过程中,表面会有少量的氧化、潮解, 在以测量10次求一次平均所得结果进行记录的条件下,以第三、四次记录结果为最佳。     

应用碱性水泥外掺剂固化天津海积软土的试验研究

天津海积软土具有高含水量、低强度、高压缩性、低pH值等特征,不能直接满足工程建设需要,必须进行人工处理。在水泥土搅拌法中使用适量碱性外掺剂NaOH或Na2CO3,可以提高桩身水泥土强度和复合地基承载力,同时能节省大量水泥,降低工程费用。现场试验中将海积软土与分别掺入0.5%NaOH和0.5%Na2CO3的10%水泥就地搅拌,形成两种新型水泥土,在与原状土及20%纯水泥土进行比较后,发现碱性外掺剂可以促使生成大量针状、棒状或纤维状水化硅酸钙晶体,抑制了能产生膨胀作用的钙矾石的生成,同时,有Ca(OH)2晶体析出,它们共同构成土颗粒间和土颗粒表面的充填物和包裹物,使水泥固化土的孔隙明显减小,密度和强度得到极大提高。检测结果显示水泥土强度提高了20%以上,复合地基承载力不小于120kPa。     

套管井超声导波成像系统开发与工程应用研究*

针对现有套管井检测与评价技术存在的缺陷,开展了进一步的导波成像方法与技术开发研究。对套管壁A0导波模式频散与泄漏衰减特性,以及泄漏衰减特性与管外粘结材料特性阻抗的关系进行了分析。在此基础上进行了不同粘结载荷钢板模型A0模泄漏衰减等特性以及脉冲回波厚度共振波特性的实验测试。结果显示,结合A0模式的衰减与管外粘结材料特性阻抗的测试结果,可有效定征管外粘结材料特性,进一步确定和成像管外环形空间水力联通特性。以此为基础,开发了耐温和耐压宽带超声换能器,以及检测与成像系统。通过模型井和实际井的测试,获得良好效果。     

基于GM(1,1)水泥产量预测模型

运用灰色系统理论中的GM(1,1)灰色预测模型,以全国近7年来的水泥产量为例,对其未来几年的生产状况进行科学预测,为今后的生产提供科学依据.     

Crystallization,pore relaxation and micro-cryosuction in cohesive porous materials

A poro-elastic analysis is undertaken to account for the pressure time history of water-infiltrated pores within a material subjected to freezing. The thermodynamic-mechanical equilibrium of undercooled water and ice crystal, and Poiseuille-like flow through the connection channels, combine to reveal three successive mechanisms: in-pore crystallization, in-pore partial melting and a micro-cryosuction process, driving liquid water from the yet unfrozen pores to the frozen sites. The model turns out to be apt to predict the macroscopic relaxation process observed at the onset of crystallization as reported in the literature for cement-based materials. To cite this article: O. Coussy, T. Fen-Chong, C. R. Mecanique 333 (2005).     

Evolution of properties in hydration of cements—A numerical study

The present work develops a numerical method for analysis of the microstructure and property evolution in the hydration of the cement. A time-dependent micro-mechanical model is established to investigate the microstructure development and the effective property evolution of the cement paste, while the input parameters of the model are based on experimental data. It is assumed that the cement paste composite consists of the anhydrous cement particles, cement gel and pores. The cement particles have a periodically spatial array and are wrapped by the cement gel. The Young’s modulus and Poisson’s ratio of the cement paste are calculated by direct average method and two-scale expansion method. The comparisons between the numerical results and experimental data show that this model can simulate the evolution of the microstructure and properties during the hydration of the cements quite satisfactorily.