Experimental Research on Performances of Dry-grinding Fine Cement for Grouting

The performances of dry grinding fine cement (DFC) in grouting procedure were experimentally studied.The measurement of its fineness and simulated test for injectability showed that this DFC could be used to inject rock mass with micro fissure.In order to improve the grouting quality,the water cement ratio and discarding time of slurry should be controlled precisely.If the water cement ratio is over 2∶1 in slurry that is made from DFC,it is not suitable to grout.Finally,the influence of different mixing times on strength of hydrated cement made from the DFC is explained by microstructure analysis with SEM.

Preparation of Fine Cement Slurries by Wet-Ground Using a Pneumatic Colloid Mill

This study aims to investigate the preparation of fine cement slurries by wet-ground using a pneumatic colloid mill. A pneumatic colloid mill was designed and produced. Furthermore,ordinary Portland cement slurries were ground using the pneumatic colloid mill. Moreover,the fineness of ground cement slurries was studied. The particle sizes of ground cement slurries with various cumulated percent were all better than those of cement slurries before grinding. When water was used as the dispersant,the best average diameter of cement slurries was obtained by grinding for 10,and 15 min for cement slurries with water / cement ratio of 1∶ 1,and0. 9∶ 1,respectively. When ethanol was used as the dispersant,the particle sizes of all cumulated percent decreased gradually with the increasing grinding time,and the particle sizes of cumulated percent of D97 decreased rapidly with the increasing grinding time. The grinding effect of big particle sizes of cement slurries is better than that of small particle sizes.

Packing Density Improvement through Addition of Limestone Fines, Superfine Cement and Condensed Silica Fume

Adoption of a low water/powder (W/P) ratio is the key to improve the strength and durability of concrete, which relies on a high packing density because fresh concrete requires excess water to offer flowability. To obtain a high packing density, powders with different particle sizes, including limestone fines (LSF), superfine cement (SFC), condensed silica fume (CSF), were added to the cement paste and the resulting packing densities were measured directly by a newly-developed wet packing test. Results demonstrated that addition of powders with a finer size would more significantly improve the packing density but the powders should be at least as fine as 1/4 of the OPC to effectively improve the packing density. Packing density and voids ratio relationship showed that a small increase in packing density can significantly decrease the voids ratio, which could allow the W/P ratio to be reduced to improve the strength and durability of the concrete without compromising the flowability.

Research on rheological properties of micro-fine grouting cement

This article studies the influence of the fineness of cement, fly ash(FA), its composite admixture and the amount and way mixed with superplasticizer on the rheological properties of micro fine cement(MC). By means of modern instruments and technologies (such as XRD, SEM, laser granulometer and superficial potential apparatus etc.), the article studies the mineral compositions, the appearance character of grains, particle size distribution and superficial potential of FA and its composite materials. And through that, the reducing mechanism of FA is thoroughly analyzed. The study shows that FA and its composite admixture are excellent components which can effectively improve the rheological properties of micro fine cement, and that the superplasticizer has a saturation point and the mixing way of it has a great influence on the rheological properties.

The Rheological Properties of Ultra-fine High Performance Grouting Cement

The material properties of surface and powder, rheological property, and mineral composition were investigated by means of SEM, XRD, Malvern laser granulometer and rotary, viscometer. The influence of a admixture on ultra-fine cement rheological properties and its mechanism, were studied in material theories. The results show that the ultra-fine fly ash has a higher zeta potential, and improves flowability of ultra-fine cement paste, decreases flowability loss as time prolonging, improves compatibility between superplasticizers and cement because of the electrostatic repulsion, ball bearing effect, filling and dispersing effect of admixtures and delay-releasing effect of superplasticizers.

Hydraulicity of Wet-milling Ultra-fine Grouting Cement

The physical and mechanical properties of wet-milling ultra-fine grouting cement were studied,and its microstructure was observed through modern instrumentation analysis such as scanning electronic microscopy(SEM),X-ray diffraction and Hg-intrusion micromeritics.The experimental results indicate that wet-milling ultra-fine cement possesses high rheological properties and groutability.It can be filled densely in cracks of rock and hydrate fully,which may endow hydrated cement with high mechanical strength.Main hydration products of wet-milling ultra-fine cement are poorly crystalline C-S-H(Ⅰ),acicular AFt and plank-shape Ca(OH)_2.The dense crystal-network structure can be formed in the rock gaps filled with cement paste,but some weak regions exist owing to Ca(OH)_2.The features of micro-pore structure of hydrated wet-milling ultra-fine cement are few big harmful pores,abundant harmless micro pores and little most possible pore radius.

Preparation of Rapid Hardening Mortars Using Ultrafine Portland Cement

During the hydration process, the Ultra-fine Cements present specific physical and chemical characteristics; they are, very short setting time and high heat release. For special applications, such as rapid hardening and early high strength mortars or concretes, these characteristics can be considered advantageous. Some commercial products used for concrete reinforcement and repairs are the Rapid Hardening Mortars, these mortars must develop a time of setting up to 3 h and an initial compressive strength of about 3.5 MPa once the hardening of the paste is reached. The objective of the present research work is to use Ultra-fine Cement for the preparation of a series of different Rapid Hardening Mortars （with different percentages of Ultra-fine Cement）, these mortars required the addition of a polycarboxylate-base specification F Superplasticizer. It was observed that the optimum water/cement （W/C） ratio for the hydration of the Ultra-fine Cements is W/C = 0.385. The Ultra-fine Cements were obtained by the High Energy Ball-milling technique at laboratory scale, 90% of the Particle Size Distribution is below 11 μm and the Blaine Specific Surface Area is over 9000 cm^2/g.

Recycling of End of Life Concrete Fines into Hardened Cement and Clean Sand

One of the massive by-products of concrete to concrete recycling is the crushed concrete fines, that is often 0 - 4mm. Although the construction sector is to some extent familiar with the utilization of the recycled coarse fraction (>4 mm), at present there is no high-quality application for fines due to its moisturized and contaminated nature. Here we present an effective recycling process on lab scale to separate the cementitious powder from the sandy part in the crushed concrete fines and deliver attractive products with the minimum amount of contaminants. For this study, a lab scale Heating-Air classification system was designed and constructed. A combination of heat and air classification, resulted in a proper separation of finer fraction (0 - 0.250 mm), from coarser fractions. Heating of the materials was followed by ball milling to enhance the liberation of the cementitious fraction. Experiments were carried out at different heating temperatures and milling durations. Experimental results show that by heating the materials to 500℃ for 30 seconds, the required time of ball milling is diminished by a factor of three and the quality of the recycling products satisfies well the market demand. In addition, the removal of contaminants is complete at 500℃. The amount of CaO in the recovered finer fraction from the recycling process is comparable with the amount of CaO in low-quality limestone. By using this fraction in the cement kiln as the replacement of limestone, the release of the chemically bound CO2 could be reduced by a factor of three.

Properties and microstructure of VC/Cr_3C_2-doped WC/Co cemented carbides

This paper deals with the effects of codoped VC/Cr3C2 and sintering temperature on the magnetic and mechanical properties of ultra-fine grained WC-12%Co alloys. Results show that the synergistic action of doped VC/Cr3C2 in optimal proportion enhances both the hardness and transverse rupture strength （TRS） of the alloys, with more homogeneous microstructtLre. When the alloy is sintered at 1430℃ and with 0.5% Cr3C2/0.2% VC, the TRS reaches 3786 MPa, the hardness is 91.7 HRA and the grain size smaller than 0.6 μm. The numerical analyses on grain growth during the sintering process show that both VC precipitating on the WC grain boundary and Cr3C2 dissolving in the Co phase decrease the solid/liquid interfacial energy γ, the process of dissolution and reprecipitation is greatly retarded and the coarsening of WC grains is inhibited.

Microscopic Pore and Filling Performance of Coal Gangue Cementitious Paste

To obtain the influence laws of the fine gangue rate on the properties of coal gangue cementitious paste, the slump, divergence, stratification, bleeding, setting time and mechanical strength with the change of fine gangue rate were studied on the basis of keeping the amount of cementing material and slurry concentration unchanged. The porosity and the distribution of pore diameter of the filling specimen for curing 28 d were tested by a mercury injection instrument under different fine gangue rate conditions. It was shown that the slump, divergence, setting time and compressive strength of the paste firstly increased and then decreased with increasing fine gangue rate. The stratification and bleeding rate decreased with increasing fine gangue rate. The smaller the critical pore size of the paste was, the smaller the porosity was, the smaller the average pore size was. When the fine gangue rate was 40%, the maximum critical pore diameter of the paste was 55.79 μm, and the corresponding porosity was 17.54%, and the properties of filling paste were the best. When the fine gangue rate further increased, the aggregate surface area increased, and the reaction product of cementitious materials could not effectively fill the pores. It weakened the agglomeration effect. The particles surface of coal gangue was fragmental and flake deposit with irregular shape and uneven fold morphology. It was easy to be bonded with the surface of other filling material. The hydration products of coal gangue cementitious material were a large number of C-S-H gel with fibrous shape and ettringite（AFt） with compact block structure. The theoretical reference was provided for the preparation of low cost gangue cemented filling materials in coal mines.

Determination of the Pozzolanic Properties of Olotu Marine Clay and Its Potentials for Cement Production

The physical and chemical properties of marine clay at Olotu in Ilaje local government of Ondo State, Nigeria were investigated. Some of the physical properties investigated include plasticity index, linear shrinkage and firing characteristics (firing colour, shrinkage percentage, and water absorption capacity). The physical properties were determined using X-ray diffractometry method. The chemical composition was determined using Atomic Absorption Spectroscopy (AAS) method. All tests were carried out according to procedures specified by relevant British and American Standards. It was established that the physical and chemical properties were adequate to qualify it as pozzolanic material for cement production when compared with other pozzolanic materials and measured against relevant standards. The cement produced was tested for compressive strength and setting times and the results confirmed the appropriateness of the use of the clay as a pozzolana.

钢纤维对细再生混凝土力学性能的影响研究

为研究细再生集料(FRAP)替代天然细集料(NFA)的可能性。配置1%钢纤维掺量下不同FRAP含量(0%、25%、50%、75%、100%)的水泥混凝土,并测定成型后试件的抗压强度、拉伸特性、应力-应变特性和耐久性能。研究结果表明:以FRAP替代NFA会导致细再生集料水泥混凝的土力学强度降低;加入1%钢纤维,可以显著提高细再生集料水泥混凝土劈裂抗拉强度和抗弯强度,峰值应力增加约15%,峰值应变增加50%,韧性及延展性提高约5倍;以FRAP替代NFA的最佳含量为50%左右。

复合水泥固化剂固化泥炭土渗透性研究

针对泥炭土工程性质差、改良难度高的问题,本文提出了一种由超细水泥(UFC)和普通硅酸盐水泥(OPC)组成的复合水泥固化剂(CCS)用于固化模拟泥炭土,并通过渗压试验和X射线衍射(XRD)测试研究UFC对水泥土试样渗透性的影响规律。渗压试验结果表明:CCS掺入量相同时,试样渗透系数k随UFC质量分数的增加而减小,UFC质量分数大于12%时k值下降趋势显著减缓;CCS中UFC质量分数为12%时,k随CCS掺入量的增加而减小,CCS掺入量大于25%时下降趋势明显减缓。XRD测试结果显示,试样中水化硅酸钙(C-S-H)的衍射峰强度随UFC质量分数及养护龄期的增加而增强。相较于OPC,CCS以更少的水泥用量便能达到优异的固化效果,从而实现减碳目标。

Properties of Rapid Hardening Controlled Low Strength Material Made of Recycled Fine Aggregate from Urban Red Brick Construction Waste

In some cases of emergency backfill engineering projects, traditional backfill materials cannot meet the requirements of fast construction due to their long curing time. This study presents a new kind of rapid hardening controlled low strength material, which utilizes both rapid hardening sulphoaluminate cement and recycled fine aggregate from urban red brick construction waste. Totally, sixteen mixtures were prepared for the experiment with different cement-to-sand ratios and water-to-solid ratios. The flowability and bleeding rate of fresh mixture were measured to evaluate its workability, and the compressive strength of hardened mixture was tested to evaluate its rapid hardening and mechanical properties. Test results indicate that rapid hardening controlled low strength material containing recycled fine aggregate from urban red brick construction waste can achieve the desirable flowability, but the bleeding rate increases with the increase of flowability. In addition, 2-hour compressive strength can reach 0.08 - 0.12 MPa, and 4-hour compressive strength is 0.32 - 1.54 MPa, which can meet the requirements of emergency backfill construction. At last, based on the derived compressive strength, a fitting model for predicting compressive strength evolution of this new rapid hardening backfill material is developed, which fits accurately with these experimental data.

火山灰硅酸盐水泥粒径对水化反应的影响

通过不同细度的筛网和调整磨粉时间获得不同细度的火山灰硅酸盐水泥,试验结合X射线衍射(XRD)、扫描电子显微镜(SEM)技术从微观的角度研究了火山灰硅酸盐水泥的细度对火山灰硅酸盐水泥宏观性能、钙矾石晶体与C-H-S凝胶的影响.结果表明,随着火山灰硅酸盐水泥的细度从224.45 m^(2)·kg^(-1)增加至576.88 m^(2)·kg^(-1),抗压强度与抗折强度提高,火山灰硅酸盐的水泥凝结时间下降,标准稠度用水量提高.结合XRD、SEM进行微观分析,利用SEM技术观察出水化产物为钙矾石晶体与C-H-S凝胶,通过XRD技术物相分析发现随着细度的增加钙矾石晶体峰值与Ca(OH)_(2)峰值逐步提升,得出不同细度的火山灰硅酸盐水泥水化产物随着水泥细度的增大而增多.

水泥细度和外加剂对水泥浆流动性能的影响

为了探究原材料的性能特点及外加剂对混凝土流动性能的影响,以水泥浆为研究对象,通过硅酸盐水泥细度、减水剂和增稠剂等对水泥浆中的填充水、吸附水和自由水的影响,分析了它们对水泥浆体流动性能的影响。试验结果表明:随着水泥颗粒粒径减小,填充水和吸附水呈现增大的趋势,但自由水量与流动度之间的线性关系表明,超细硅酸盐水泥浆体流动对随自由水量的增加幅度是大于普通硅酸盐水泥的,这说明水泥的细度对浆体流动性能的影响主要在用水量较小时,即水灰比较小时。无论是萘系减水剂还是聚羧酸减水剂,随着减水剂掺量的增加,填充水和吸附水均呈减小的趋势,流动度随自由水量增加增大的幅度逐渐增大。羧甲基纤维素(CMC)和羟丙基甲基纤维素(HPMC)均使填充水增大,在一定掺量范围内对吸附水基本上没有影响,但超过某一掺量时,均使吸附水大幅增加;CMC对流动度与自由水之间的线性关系影响不大,HPMC使流动度随自由水的增加幅度呈减小的趋势。这对探究原材料的性能特点和外加剂等对混凝土流动性的影响,具有较好的参考价值。

机制砂与特细砂抗氯盐侵蚀混凝土的制备及性能研究

利用机制砂、特细砂等制备抗氯盐侵蚀混凝土对降低生产成本、提升桥梁服役寿命具有重要意义。本研究通过优化骨料设计与水泥浆体组成提升混凝土的抗氯离子侵蚀性能,研究了骨料级配、特细砂用量、砂率、水胶比、胶凝材料种类对混凝土性能的影响。结果表明:8~16 mm碎石质量分数由50%增加至80%时,氯离子扩散系数由4.0×10^(-12)m^(2)/s降低至2.9×10^(-12)m^(2)/s;特细砂替代50%(质量分数)机制砂时,氯离子扩散系数为3.6×10^(-12)m^(2)/s,仍可以满足设计要求;砂率增大,氯离子扩散系数先减小后增大。水胶比在0.36~0.38时,氯离子扩散系数低于3.5×10^(-12)m^(2)/s;矿渣组分水化改善了混凝土的孔结构,并形成了更多的AFm、C-S-H产物,提升了混凝土对氯离子的固化能力,矿渣水泥混凝土氯离子扩散系数较普通硅酸盐水泥混凝土降低了40%。

水泥助磨剂助磨性能的表征方法研究

比表面积是水泥细度常用的表征方法之一,但其是否适合评价助磨剂的助磨性能有待商榷。选用了四种助磨剂进行了粉磨实验,分别测量了被粉磨水泥的负压筛余量、颗粒分布和比表面积。对比发现:各助磨剂都对水泥的负压筛余量和颗粒分布有规律性的影响,表现为负压筛余量变小,颗粒分布变窄,但比表面积没有表现出规律性的变化。根据透气法比表面积测量原理,分析了助磨剂对比表面积没有规律性影响的原因是:添加助磨剂后,空气流过速度增大和颗粒分布变窄。不建议采用比表面积作为助磨剂性能的表征方法。

抗高温低密度水泥浆体系研究与应用

为解决低密度水泥浆高温强度低、减轻材料承压能力不高、低密度水泥浆配浆困难等难题,研制了低密度增强材料DRA-2S、优选了耐压105 MPa的高性能空心玻璃微珠、聚羧酸分散剂DRS-2S及其他配套抗高温水泥外加剂,开发了抗高温低密度固井水泥浆体系。研究结果表明,该水泥浆能够满足循环温度150℃、井底静止温度180℃、耐压105 MPa的固井要求,顶部127℃静胶凝13.3 h起强度,24 h抗压强度12.4 MPa。开发的抗高温低密度水泥浆在西南油气田高温探井ZJ2井Ф127 mm尾管固井成功应用,固井质量合格率96.7%,为西南油气田高温易漏失复杂深井勘探开发提供了固井技术支撑。

超细低碳胶凝材料的制备及应用研究

为了在减碳的同时实现建材企业的降本增效,以矿渣粉和粉煤灰(质量比5∶5)为主要原材料,制备了一种超细低碳胶凝材料,研究了其对混凝土和水泥性能的影响。结果表明:在混凝土制备过程中,用适量超细低碳胶凝材料等质量部分替代水泥,可以有效提高混凝土的力学性能;在水泥生产过程中,用超细低碳胶凝材料等质量替代0~15%的水泥原料,对水泥的标准稠度用水量和凝结时间影响不大,但能有效提高水泥的抗折、抗压强度。研究结果可为建筑行业减碳增效途径的选择提供参考。