The Influence of Carbon Nanotubes and Nano-Silica Fume on Enhancing the Damping and Mechanical Properties of Cement-Based Materials

This paper conducted experimental studies on the damping and mechanical properties of carbon nanotube-nanosilica-cement composite materials with different carbon nanotube contents. The damping and mechanical properties enhancement mechanisms were analyzed and compared through the porosity structure test, XRD analysis, and scanning electron microscope observation. The results show that the introduction of nanosilica significantly improves the dispersion of carbon nanotubes in the cement matrix. At the same time, the addition of nanosilica not only effectively reduces the critical pore size and average pore size of the cement composite material, but also exhibits good synergistic effects with carbon nanotubes, which can significantly optimize the pore structure. Finally, a rationalization suggestion for the co-doping of nanosilica and carbon nanotubes was given to achieve a significant increase in the flexural strength, compressive strength and loss factor of cement-based materials.

Effect of Nano Silica on Hydration and Microstructure Characteristics of Cement High Volume Fly Ash System Under Steam Curing

The influences of nano silica (NS) on the hydration and microstructure development of steam cured cement high volume fly ash (40 wt%, CHVFA) system were investigated. The compressive strength of mortars was tested with different NS dosage from 0 to 4%. Results show that the compressive strength is dramatically improved with the increase of NS content up to 3%, and decreases with further increase of NS content (e g, at 4%). Then X?ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSCTG), scanning electron microscope (SEM), energy disperse spectroscopy (EDS), mercury intrusion porosimeter (MIP) and nuclear magnetic resonance (NMR) were used to analyze the mechanism. The results reveal that the addition of NS accelerates the hydration of cement and fly ash, decreases the porosity and the content of calcium hydroxide (CH) and increases the polymerization degree of C-S-H thus enhancing the compressive strength of mortars. The interfacial transition zone (ITZ) of CHVFA mortars is also significantly improved by the addition ofNS, embodying in the decrease of Ca/Si ratio and CH enrichment of ITZ.

Replacement of alkali silicate solution with silica fume in metakaolin-based geopolymers

A metakaolin(Mk)-based geopolymer cement from Tunisian Mk mixed with different amounts of silica fume(SiO_2/Al_2O_3 molar ratio varying between 3.61 and 4.09) and sodium hydroxide(10M) and without any alkali silicate solution, is developed in this work. After the samples were cured at room temperature under air for 28 d, they were analyzed by X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, environmental scanning electron microscopy, mercury intrusion porosimetry, ^(27)Al and ^(29)Si nuclear magnetic resonance(NMR) spectroscopy, and compression testing to establish the relationship between microstructure and compressive strength. The XRD, FTIR, and ^(27)Al and ^(29)Si NMR analyses showed that the use of silica fume instead of alkali silicate solutions was feasible for manufacturing geopolymer cement. The Mk-based geopolymer with a silica fume content of 6 wt%(compared with those with 2% and 10%), corresponding to an SiO_2/Al_2O_3 molar ratio of 3.84, resulted in the highest compressive strength, which was explained on the basis of its high compactness with the smallest porosity. Silica fume improved the compressive strength by filling interstitial voids of the microstructure because of its fine particle size. In addition, an increase in the SiO_2/Al_2O_3 molar ratio, which is controlled by the addition of silica fume, to 4.09 led to a geopolymer with low compressive strength, accompanied by microstructures with high porosity. This high porosity, which is responsible for weaknesses in the specimen, is related to the amount of unreacted silica fume.

Analysis of the Damping Behavior and Microstructure of Cement Matrix with Silane-treated Silica Fume

The surface treatment of silca fume with silane coupling agent prior w incorporation in a cement mortar resulted in composites exhibiting increuses in loss tangent by 5%-200% and storage modulus by 10%-20% , relative to the value obtained by using as-received silica fume. The scanning electron microscopy （SEM） images iindicate that there is a morphological difference in the cement paste with treated and as-received silica fume, The, X-ray diffraction （XRD）, infrared （IR） spectrum analyses and mercury intrusion porosimetry （ MIP ） have provided evidence to understand the reaction mechanism between treated silica .fume and the hydrate product of cement. This has led to the establishment of an initial microscopic model describing the damping behavior of cement matrix.

Influence of Silica Fume on the Reflectivity and Transmission Efficiency of Cement-Based Materials

As a kind of mineral admixture, silica fume has low permittivity, which will affect the electromagnetic properties of cement-based materials. To study the effect of silica fume on the properties of cement-based materials, the reflectivity, transmission efficiency and pore structure were analyzed by using the vector network analyzer and mercury injection apparatus. Results show that silica fume can make the mortar more compact and the porosity of sample with 9% silica fume is only 17.8%, which is far lower than the control sample;With the increase of the silica fume content, the peak of reflectivity curve increases from -23.2 dB to -16.0 dB, and then decreases from -16.04 dB to -28.7 dB in the frequency range of 6 – 18 GHz. Reflectivity of sample with 3% content of silica fume is lower than other samples within 26.5 - 40 GHz;Transmission efficiency of samples shows the trend of increase with silica fume content increases from 0% to 6% within 8.2 - 12.4 GHz, 12 - 18 GHz and 26.5 - 40 GHz, but when the content increases from 6% to 9%, the transmission efficiency of samples reduces.

Reaction Degree of Silica Fume and Its Effect on Compressive Strength of Cement-silica Fume Blends

The compressive strength of the cement-silica fume blends with 5mass%, 10mass%, 20mass% and 30mass% of silica fume and water to binder ratio of 0.28, 0.32 and 0.36 from three days to ninety days were investigated. The reaction degree of silica fume was calculated from the Q4 silica tetrahedron, which was used as a probe obtained from 29 Si solid state nuclear magnetic resonance analysis. The fl at of compressive strength after 28 days disappeared for blended cement with inereasing reaction degree of silica fume. The compressive strength of the blended cement pastes approached that of P.I. cement pastes after 56 days and exceeded that after 90 days. The addition of silica fume and the w/b ratio of blends are both critical to the reaction degree of silica fume. The appropriate addition of silica fume, high silica fume reaction degree and low w/b ratio are benefi cial to the compressive strength of the cement-silica fume blends.

Hydration Mechanism of Silica Fume- sulphoaluminate Cement

Setting time and strength of sulphoaluminate rapid hardening cement （SAC） incorporated in the presence and absence of silica fume （SF） were determined. Combined with the techniques of＂ isothermal calorimeter, XRD and FSEM, the hydration kinetics of the two systems and the effect mechanism of SF on SAC were investigated. The experimental results showed that SF was proved to be beneficial for SAC system, in terms of setting time and late strength gain. Evidence of accelerator effect of silica fume was found during the first 8 hours of hydration. The formation of AFt was accelerated and the microstructure of the hydration products grew denser with incorporation of SF. SF was proved to play the role of dispersion and setting control at early age and had a greater contribution to later strength due to the increment of crystal nucleation point and the pozzolanic activity. Therefore, SF can be used to not only control the hydration kinetics of SAC, but also develop the late strength and improve the microstructure.

Influence of Fly Ash and Silica Fume on Water-resistant Property of Magnesium Oxychloride Cement

By incorporation of fly ash or silica fume into magnesium oxychloride （MOC） cement, a high water resistance material can be formed for successful industrial applications. The influences of fly ash and silica fume on water-resistant property were investigated by SEM and EDS. It is found that the incorporation of fly ash or silica fume can improve the water-resistance of the MOC. The improvement of the water resistance of the MOC incorporated with fly ash or silica fume may be attributed to the alumino-silicate 5·1·8 gel or silicate 5·1·8 gel.

THE PROPERTIES OF SILICA FUME-MAGNESIUM OXYCHLORIDE CEMENT MATERIALS

The properties of a new magnesium Oxychloride cement (MOC) material formed by silica fume uniformly mix in MOC paste was presents. The influence of silica fume on the water resistance and compressive strength of MOC paste was invesigated in this study. It is shown that when 30 weight percent of silica fume is added to the MOC paste, a high strength and water resisting new material with 112MPa compressive strength and 1 00 water resisting coefficient could by obtained.

Hydration Products of Cement-silica Fume-quartz Powder Mixture under Different Curing Regimes

Composition, morphology, and structure of hydration products in hardened pastes of three kinds of blended cement（cement-silica fume, cement-quartz powder and cement-silica fume-quartz powder） hydrated under different curing regimes（standard curing, 90 ℃ steam curing, 200 ℃ and 250 ℃ autoclave curing） were investigated by X-ray diffraction and field emission scanning electron microscope equipped with EDAX system. Results showed that the main hydration products in three kinds of hardened pastes under standard curing condition are all C-S-H gels, CH, and AFt. Under 90 ℃ steam curing condition, the main hydration products of cement-silica fume and cement-silica fume-quartz powder are C-S-H gels, whereas those of cement-quartz powder are C-S-H and CH. Under 200 or 250 ℃ autoclave curing condition, no obvious crystallized CH phase is found in hardened pastes of three kinds of blended cement, and C-S-H gels are transformed into one or more crystalline phases such as tobermorite, jennite, and xonotlite. The chemical composition and morphology of these crystalline phases depend on the composition of mixture and autoclave temperature.

Hydrothermal Characteristics of Blended Cement Pastes Containing Silica Sand Using Cement Kiln Dust as an Activator

The hydrothermal reactivity of silica sand was studied using cement kiln dust (CKD) as an activator in addition to the Portland cement fraction of El-Karnak cement (a blend of ordinary Portland cement and ground sand). Autoclaved EI-Karnak cement pastes were studied at pressures of 0.507, 1.013 and 1.520 MPa of saturated steam with respect to their compressive strength, kinetics of hydrothermal reaction and the phase composition of the formed hydrates. The role of CKD in affecting the physicochemical and mechanical properties of EI-Karnak cement pastes was studied by autoclaving of several pastes containing 5, 7.5, 10 and 20% CKD at a pressure of 1.013 MPa of saturated steam. CKD was added either as a raw CKD (unwashed) or after washing with water (washed CKD). The results of these physicochemical studies obtained could be related as much as possible to the role of CKD (raw or washed) in affecting the hydrothermal reactivity of silica sand in EI-Karnak cement pastes.

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.

The Impact of Aluminum- and Iron-Bearing Admixtures on the Resistance of Portland Cement Mortars to Alkali-Silica Reaction and Sulfate Attack

Study of sulfate resistance of mortars with aluminum- and iron-bearing admixtures (Al(OH)3, Al2(SO4)3, FeSO4, Fe2(SO4)3) in conditions close to those established in ASTM C 1012, and the study of the mitigation effect of these admixtures on alkali-silica reaction in accordance with accelerated “mortar bar” test ( GOST 8269.0, ASTM C 1260) were performed. Iron (II) and (III) sulfates show ability for mitigation alkali-silica reaction, while also, in contrast with Al-bearing substances, do not induce the drastic reducing of the initial setting time and do not promote the progress of sulfate corrosion. Compared with FeSO4, iron (III) sulfate has moderate deleterious impact on the early strength of cement paste and can be of interest alone as an inhibitor of ASR. Iron (II) sulfate may be used together with aluminum sulfate to offset the accelerating effect of the latter on the setting of cement paste and to reduce a risk of sulfate corrosion. During prolonged water storage, the mortar elongation and secondary ettringite formation do not occur, even when Al2(SO4)3 is available. Therefore, the investigated admixtures cannot act as agents of internal sulfate attack, however, Al2(SO4)3 can enhance the outer sulfate attack.

Utilization of Cement Kiln Dust (CKD) with Silica Fume (SF) as a Partial Replacement of Cement in Concrete Production

This research aimed to clarify the role of by-product materials, such as CKD with SF as partial replacement by weight of cement in concrete manufacturing and inclusion on different characteristics of concrete. Concrete test specimens were mixed with 0%, 5%, 10%, 15%, 20% and 25% (CKD) with 15% (SF) as partial replacement by weight of Cement (CEM I-52.5N). Fresh concrete properties have been evaluated by workability measurement slump test. While hardened concrete properties have been evaluated by compressive, split tensile and flexural strengths tests at ages 7, 28 and 56 days, but evaluated for bond strength, modulus of elasticity and chemical composition measurement with X-Ray Fluorescence at age of 28 days. The test results have revealed that the increase of CKD amount with fixed amount of SF in concrete mixtures as partial replacement by weight of cement leads to gradual decrease of fresh concrete workability. In concrete mixtures, 20% CKD in the presence of 15% SF as partial replacement by the weight of cement are the optimum ratios which can be used without any negative effect on mechanical properties compressive, indirect tensile, flexural and bond strength at all the ages of concrete. Also modulus of elasticity and bond strength increased by 8.81% and 0.69% respectively at the age 28 days compared with control mixture.

硅灰对硫铝酸盐水泥力学和电磁传输性能的影响

研究了硅灰掺量对硫铝酸盐水泥力学性能和电磁传输性能的影响.结果表明:随着硅灰掺量的增加,硫铝酸盐水泥的抗压强度和抗折强度均先增大后降低,硅灰的最优掺量为10%;硫铝酸盐水泥的电磁传输性能随着硅灰掺量的增加而增大,与未掺硅灰的样品相比,硅灰-硫铝酸盐水泥在3.94~5.99 GHz频段范围内电磁传输性能均有所提升,电磁透射率峰值最高提升了23.9%.

硅灰对水泥胶砂耐硫酸侵蚀性能影响的试验研究

为更好地研究硅灰对水泥胶砂耐硫酸侵蚀性能的影响,本文将硅灰按不同配合比进行试验,将水泥胶砂置于pH=1的硫酸侵蚀环境中。通过探究试样的外观、质量损失率、抗压强度损失率、硫酸侵蚀下的生成物、微观结构,并结合相关理论分析了硅灰对水泥胶砂抗硫酸侵蚀作用的影响。实验研究表明:随着硅灰掺量的增加,水泥胶砂的抗硫酸侵蚀能力增强,XRD(x-ray diffraction)衍射表明,在硫酸侵蚀下表面生成物为二水石膏(CaSO_(4)·2H_(2)O),反应时会消耗Ca(OH)_(2),同时也会产生一定的体积膨胀;SEM(scanning electron microscope)检测表明,掺入硅灰可以提高试样的密实度,从而提高水泥胶砂的抗硫酸侵蚀性能。从宏观和微观角度综合来看,硅灰掺量为15%时的抗硫酸侵蚀性能最好。

改性硫铝酸盐水泥砂浆力学性能及耐久性能研究

过快的流动度损失和后期不稳定的强度发展限制了硫铝酸盐水泥工程中的进一步应用。因此以葡萄糖酸钠作为缓凝剂,掺入硅灰制备成改性硫铝酸盐水泥砂浆,并对其工作性能、力学性能和抗氯离子渗透性能开展了系统研究。研究结果表明:葡萄糖酸钠掺量0.4%可有效延长硫铝酸盐水泥砂浆凝结时间,提高砂浆流动性和抗氯离子渗透性能;硫铝酸盐砂浆工作性能、力学性能和抗氯离子渗透性能均随硅灰掺量的增加先提高后降低,硅灰最优掺量为20%。

纳米硅溶胶−EVA−粉煤灰水泥基复合浆材配比正交优化及对其物性的影响

针对传统水泥基浆材不能满足煤矿大变形巷道注浆加固实际需求的难题,通过添加纳米硅溶胶、乙烯−醋酸乙烯共聚物(EVA)和粉煤灰对普通硅酸盐水泥进行改性获得高性能复合浆材。采用正交试验和极差分析法系统研究复合浆材物理力学性能的变化规律,确定最优配比,并进一步分析最优配比复合浆材与纯水泥的物性差异,构建复合浆材的水化反应机理模型,阐明其加固破碎岩石的力学特性。研究结果表明,复合浆材最优配比为:水灰比0.7,粉煤灰掺量15%,硅溶胶掺量2%,EVA掺量7.5%;相较于纯水泥,复合浆材流变性略有下降,但浆液稳定性、力学性能等均有显著提升,初凝时间缩短了38.9%,终凝时间缩短了53.8%,析水率降低了60%,结石率提高了3.3%,单轴抗压强度提高了39.1%,抗拉强度提高了97.2%,拉压比提高了41.7%;硅溶胶和粉煤灰在不同时期与Ca(OH)2发生火山灰反应生成更多水化硅酸钙(C-S-H)和水化铝酸钙(CA-H),促进复合浆材的水化反应,并加速EVA成膜,使结石体更加致密;复合浆材注入量和胶结体单轴抗压强度均随注浆压力的增大而增加,随Talbot指数的增加,抗压强度先增大后减小,破坏形式多呈鼓状,剪胀变形明显;当注浆压力大于2 MPa,Talbot指数为0.5时,胶结体强度较大,破坏较小。本研究为水泥基复合浆材早期强度、增韧改性提供了可行途径。

纳米SiO_(2)对水泥浆体孔隙和微观力学性能的影响

为了研究不同纳米SiO_(2)掺量对硬化水泥浆体孔隙率与微观力学性能的影响,采用压汞实验,纳米压痕测试与GMM法获得了水泥浆体的孔隙率,压痕模量,硬度与各水化产物相的分布,并使用XRD与SEM表征了各性能最优样品的表面形貌与内部产物。试验结果表明,养护龄期为28天时,与空白对照组相比,当纳米SiO_(2)的掺量质量分数为1%、2%和3%、4%时,水泥样品总孔隙率分别降低了14.07%,16.67%,26.83%和7.43%,LD C-S-H与HD C-S-H的含量之和分别为对照组的99.34%,101.34%,117.48%和113.33%。但当纳米SiO_(2)的掺量质量分数为4%时,水泥样品的孔隙率比其他掺纳米SiO_(2)的样品更高,且与纳米SiO_(2)掺量质量分数为3%时相比,未水化的产物相也较多。纳米SiO_(2)可以充分发挥成核效应和火山灰效应,生成更多的C-S-H并改变硬化水泥浆体的微观形貌,从而有效降低水泥浆体的孔隙率并提高其微观力学性能。

超疏水改性水泥基材料设计及性能研究

【目的】研究纳米二氧化硅和硅氧烷对水泥基材料的超疏水改性效果及其性能影响。【方法】以水泥材料为主体,通过正交试验方法优选改性材料十二烷基三甲氧基硅烷(dodecyltrimethoxysilane,DTES)、纳米二氧化硅(nano-silica,NS)和聚羧酸高效减水剂(polycarboxylate superplasticizer,PCE)的最佳配比,并采用强度试验、水化热测试、水接触角测量和毛细吸水试验评估改性材料对水泥力学性能和疏水性能的作用。【结果】DTES、NS和PCE的最佳质量分数分别为3.00%、1.80%和0.25%;改性水泥试样表面的水接触角高达152.50°,毛细吸水系数降低91%以上,3 d抗折强度、28 d抗压强度分别下降19%、12%。【结论】改性材料的协同作用使水泥基材料表面达到超疏水状态,同时具备良好的抗水渗透性能,其中DTES影响水泥强度,NS对抗压强度和后期抗折强度起增强作用。