Effect of nano-silica on rheology and fresh properties of cement pastes and mortars

Amorphous nano-silica (nS) particles (0–2.5 wt%) by cement were incorporated in cement pastes and mortars, and their effect on the fresh state behaviour was analysed. Rheological tests showed that after 75 min from the mixing start, the mortar having 2.5 wt% nS shows insufficient flowability to allow its continuous monitoring in a Viskomat PC viscometer. The influence of nS content was better observed on yield stress when compared with plastic viscosity values (the first increased about 66.5% while the latter just increased 3.6%). With nS addition, spread, setting time and the moment to reach the maximum temperature decreased 33%, 60% and 51.3%, respectively, when compared with samples without nS. X-ray diffraction showed presence of calcium hydroxide after 9 h in the sample with 2.5 wt% nS. The air content increased 79% and apparent density decreased 2.4% when nS was added.     

矿物掺合料对铁铝酸盐水泥力学性能影响研究

针对铁铝酸盐水泥早期水化热高的问题,提出采用掺加矿物掺合料的方法改善铁铝酸盐水泥性能。研究了单独掺加不同掺量粉煤灰、矿粉、石灰石粉、粉煤灰微珠、硅灰的铁铝酸盐水泥用水量、力学性能,以及复合掺加粉煤灰-矿粉、粉煤灰微珠-矿粉、粉煤灰微珠-硅灰及石灰石灰石粉-矿粉的铁铝酸盐水泥用水量、力学性能。结果表明,粉煤灰等掺合料均会降低铁铝酸盐水泥强度,但是对用水量的影响不同,粉煤灰及硅灰会显著增加铁铝酸盐水泥用水量,石灰石粉及粉煤灰微珠会降低用水量。当掺合料单独掺加或复合掺加等量取代30%水泥时,复合胶凝体系的抗压强度降至45.0MPa左右,掺合料的掺量宜控制在30%以内。     

不同粒径废玻璃粉对水泥胶砂力学性能的影响

采用3种粒径(20、200、2 000目)的废玻璃粉等体积取代水泥胶砂中的标准砂,体积取代率分别为5%、10%、15%、20%,研究玻璃粉粒径和掺量对水泥胶砂的抗压强度和抗折强度的影响,并对玻璃粉水泥胶砂强度随龄期的变化规律进行了分析讨论。结果表明:不同粒径玻璃粉水泥胶砂的强度随玻璃粉掺量的变化规律存在较大的差异;在玻璃粉掺量相同的情况下,掺入较大粒径玻璃粉的水泥胶砂强度明显降低,玻璃粉粒径越小,强度降低程度越小,当玻璃粉粒径达到微米级,水泥胶砂的抗压强度和抗折强度均显著提高;玻璃粉水泥胶砂的抗压强度随龄期增长,早期强度增加的较快,后期发育增速变缓,而抗折强度早期增长的幅度较大,后期发育比较平缓。     

甘蔗糖蜜对水泥缓凝和减水的性能研究

甘蔗废糖蜜对水泥同时具有缓凝和减水作用.采用酒精凝聚法分离废糖蜜得到胶体和非胶体组份:从水泥水化热、表面张力以及吸附性能阐述了其对水泥减水和缓凝的原因.结果表明,糖蜜中的胶体组份主要起分散作用,而非胶体组份主要起缓凝作用.     

超细循环流化床粉煤灰对碱式硫酸镁水泥力学性能的影响

针对传统碱式硫酸镁(BMS)水泥制备工艺中硫酸镁需加热溶解及粉煤灰添加后相容性差的问题,采用硫酸、超细循环流化床粉煤灰(UCFA)、氧化镁为原料制备BMS水泥,主要研究了UCFA及其掺量对BMS水泥力学性能的影响。结果表明,BMS水泥的抗压强度随养护时间的延长而提高,随UCFA掺量的增加而降低。掺10%UCFA的BMS水泥抗压强度与不掺UCFA的相近,28 d抗压强度分别达到了79.1、79.5 MPa,且具有优异的早强性能。将UCFA与硫酸反应后加入氧化镁制备BMS水泥,优先酸浸可以对UCFA进行刻蚀,通过增加UCFA表面粗糙度来促进其反应,从而改善水泥性能,并且降低生产成本,而且掺入一定量的UCFA可以增加水泥的密实度,从而提高抗压强度。     

酸雨侵蚀对水泥砂浆力学性能的影响

研究了不同水胶比、不同胶凝材料的水泥砂浆受酸雨侵蚀后的力学性能变化。结果表明:在酸雨侵蚀条件下,砂浆抗压强度和抗折强度呈现先快速增长,而后迅速降低的趋势,且水灰比越小,强度增长和下降速度越快;粉煤灰掺量越高,56 d以前强度增长越快,56 d以后强度下降速度越缓慢;28 d前掺矿粉砂浆在酸雨中的抗压强度增长幅度高于未掺加矿粉的基准砂浆,且矿渣掺量越高砂浆抗压强度越高,矿粉对砂浆抗折强度的作用相对较小。     

Effect of temperature on porosity and on chloride diffusion in cement pastes

This paper is related to the effect of temperature upon the diffusive properties and the microstructural features of cementitious materials. Our experimental studies aim at linking the transport properties to the porosity and the cracks network of the microstructure.

The studied materials were three cement pastes having different water to cement (W/C) ratios (W/C = 0.35, 0.45 and 0.60). Rise of temperature in concrete structures was simulated by heating at different temperatures (45 °C, 80 °C and 105 °C). Evolution of microstructure was essentially characterized by mercury intrusion porosimetry (MIP). Diffusion tests in non-steady-state regime were carried out in order to characterize the diffusive properties. Apparent diffusion coefficients were determined from colorimetric method to follow the ingress of chloride and an analytical solution of Fick’s second law.

Our results showed that rise of temperature induced macroscopic cracking network and modification of pore size distribution. As a consequence, the transport properties were modified by thermal treatment. These modifications were mostly explained by the increase of capillary porosity.     

PTB乳液对水泥砂浆力学性能和抗侵蚀性能的影响

研究了PTB乳液改性水泥砂浆的力学性能、抗氯盐和抗硫酸盐侵蚀等性能.结果表明,掺入PTB乳液对水泥净浆有缓凝作用,大幅延长了水泥净浆的终凝时间;掺入PTB乳液降低了水泥砂浆的抗压强度,但是降低抗压/抗折强度比改善了水泥砂浆的延性,提高了水泥砂浆的综合力学性能.PTB乳液/水泥为0.22时的PTB乳液水泥砂浆在氯化钠、硫...     

加载速率对不同温度状态石灰岩力学性能影响的试验研究

借助美国MTS810电液伺服材料试验机和高温炉,对常温和600℃两种温度状态下石灰岩试件进行不同加载速率下的单轴压缩试验,得到石灰岩力学性能随加载速率的变化规律。结果表明:常温时,石灰岩岩样在3×10-4³×10-3 mm/s的低应变率范围内,加载速率对峰值应力和弹性模量影响不大,在加载速率为3×10-33×10-3 mm/s的低应变率范围内,加载速率对峰值应力和弹性模量影响不大,在加载速率为3×10-3³×10-1 mm/s的区段内,峰值应力和弹性模量均呈明显上升趋势;600℃时,峰值应力和弹性模量随加载速率增加变化不大。常温时,不同加载速率下石灰岩岩样均为竖向劈裂破坏,且在3×10-33×10-1 mm/s的区段内,峰值应力和弹性模量均呈明显上升趋势;600℃时,峰值应力和弹性模量随加载速率增加变化不大。常温时,不同加载速率下石灰岩岩样均为竖向劈裂破坏,且在3×10-3³×10-1 mm/s的加载速率区段中,随加载速率的增加,劈裂面逐渐增多;600℃时,石灰岩岩样在不同加载速率下均为剪切破坏。     

Effect of superplasticizers on workability retention and initial setting time of cement pastes

This paper presents an experimental study on the effect of a newly developed modified lignosulphonate (PLS) superplasticizer on the loss of workability and initial setting time of cement pastes in comparison to those of polycarboxylate (PCE) and polynaphthalene (PNS) superplasticizers. The workability loss was monitored by yield stress and effective viscosity of the pastes. The initial setting was monitored by heat development, change of rheological parameters with time, and penetration depth in cement pastes. The relations among these methods were discussed. Different dosages of the superplasticizers were used to obtain cement pastes with yield stress <6 Pa at 30 min at given water-to-cement ratios. The results showed that the pastes with PLS lost workability more slowly and had longer initial setting time compared with those with PCE and PNS admixtures. Although the longer workable time is beneficial for hot weather concreting, the longer initial setting time of such material has to be taken into consideration where early strength development is essential.     

Effect of copper slag and cement by-pass dust addition on mechanical properties of concrete

This research was undertaken to study the effect of copper slag (CS) and cement by-pass dust (CBPD) addition on concrete properties. In addition to the control mixture, two different trial mixtures were prepared using different proportions of CS and CBPD. CBPD was primarily used as an activator. One mixture consisted of 5% copper slag substitution for portland cement. The other mixture consisted of 13.5% CS, 1.5% CBPD and 85% portland cement. Three water-to-binder (w/b) ratios were studied: 0.5, 0.6 and 0.7. Concrete cubes, cylinders and prisms were prepared and tested for strength after 7 and 28 days of curing. The modulus of elasticity of these mixtures was also evaluated. Results showed that 5% copper slag substitution for portland cement gave a similar strength performance as the control mixture, especially at low w/b ratios (0.5 and 0.6). Higher copper slag (13.5%) replacement yielded lower strength values. Results also demonstrated that the use of CS and CBPD as partial replacements of portland cement has no significant effect on the modulus of elasticity of concrete, especially at small quantities substitution.     

An investigation into the properties of ternary and binary cement pastes containing glass powder

The properties of binary and ternary cement pastes containing glass powder (GP) were examined. Hydration at early age was evaluated using semi-adiabatic calorimetry and at late ages using non-evaporable water content and thermogravimetric analysis. The transport characteristic was assessed by measuring electrical resistivity. The binary paste with slag showed the highest hydration activity compared to the binary pastes with GP and fly ash (FA). The results indicated that the pozzolanic behavior of the binary paste with GP was less than that of the binary pastes with slag or FA at late ages. An increase in the electrical resistivity and compressive strength of the binary paste with GP compared to other modified pastes at late ages was observed. It was shown that GP tends to increase the drying shrinkage of the pastes. Ternary pastes containing GP did not exhibit synergistic enhancements compared to the respective binary pastes.     

电解锰渣改性炭质页岩对水泥力学性能的影响

通过将电解锰渣、炭质页岩和石灰石结合起来,压制成型后进行高温煅烧,研究了煅烧产物对水泥力学性能的影响,结果表明:当电解锰渣、炭质页岩与石灰石的质量比为20∶60∶20,煅烧温度为800℃,掺量为30%,取水胶比为0.5时,其作为掺合料效果最好。     

粉煤灰对外掺轻烧MgO水泥浆体膨胀的影响

研究了粉煤灰对MgO膨胀剂(MEA)水泥浆体膨胀变形的影响,MEA的活性指数为50、100、190 s,MEA的掺量为6％和8％,养护温度为20、80℃.结果表明:当MEA掺量由6％增加到8％时,粉煤灰对MEA水泥浆体膨胀的抑制作用减弱.粉煤灰对掺高活性MEA水泥浆体膨胀的影响比对掺低活性MEA水泥浆体小.20℃水中养...     

水泥浆液结石体强度试验研究

为了分析不同浆液配合比对水泥浆液结石体强度的影响,采用正交试验法研究了不同的水泥、速凝早强剂、膨胀剂与水结石体无侧限抗压强度和塑性强度的关系,试验结果表明,水泥浆液最佳配比为1.5∶1,速凝早强剂用量占水泥重的1.2%,膨胀剂用量占水泥重的0.02%。     

水性环氧乳液改性水泥复合材料的力学性能研究

采用研制的非离子型水性环氧乳液与水泥共混,制备高强度水性环氧乳液改性水泥复合材料。分别测试不同养护条件下水性环氧乳液对复合材料力学性能的影响。结果表明,水性环氧乳液能提高复合材料的抗压、冲击、弯曲强度及其韧性,同时可以降低复合材料的吸水率、提高耐腐蚀性。对水性环氧与水泥共混的机理进行了分析和模拟。     

双掺聚合物水泥混凝土声学特性试验研究

对同时掺入两种不同聚合物乳液的5组15个混凝土试件进行单轴压力条件下的超声波测试,研究了双掺聚合物水泥混凝土声速和加权谱面积等声学参数与应力的相关关系.研究发现,低应力状态,双掺聚合物水泥混凝士的声-应力敏感性较普通水泥混凝土有所增强,而随着应力水平的增大,其声-应力敏感性都不同程度的减弱.具体表现为:双掺纯丙乳液和聚...     

外加剂对硫氧镁水泥力学性能的影响及水化机理分析

对比了柠檬酸、磷酸二氢钠、乙二胺四乙酸3种外加剂掺量分别为0、0.5%、1.0%、1.5%(以氧化镁的质量计)时对硫氧镁水泥强度的影响,并通过XRD、XPS、FTIR、SEM对加入外加剂后硫氧镁水泥的水化机理进行了分析。结果表明:3种外加剂中,柠檬酸对硫氧镁水泥的改性效果最好;掺加1.5%柠檬酸的硫氧镁水泥28 d抗压强度达到73.33 MPa,较未掺加外加剂的试块提高了56.5%;加入外加剂后水化产物中出现了针状的5Mg(OH)2·MgSO4·7H2O相(517相)晶体,可以很好的改善硫氧镁水泥的力学性能;外加剂的加入阻碍了活性MgO表面Mg(OH)2的生成,促进了碱式硫酸镁复盐的形成。     

Physical and mechanical properties of mortars without cement

In this study, production of mortars with disposable polyethylene bottles, but without cement, was investigated. The disposable polyethylene bottles were crushed and converted into fiber formation. Then fibers were molten with different types of sands at the temperature range of 180-200 °C. Some physical (e.g. water absorption and abrasion resistance) and some mechanical (e.g. bending strength, compressive strength, toughness) properties of mortars were tested. The results indicated that bending strength and toughness of mortars were improved. Besides, water absorption of mortar was negligible and abrasion was nearly equal to zero.     

Effect of free water removal from early-age hydrated cement pastes on thermal analysis

In order to follow the progress of cement hydration by analytical techniques, the ongoing hydration reactions must be stopped by complete removal of free water. A comparison between solvent exchange, oven drying and vacuum drying, using thermal analysis, is presented for early-age hydrated cement pastes. Results show that oven drying at 105 °C accelerates hydration, causes dehydration of some hydrated cement phases and favours carbonation. Solvent exchange with ethanol, ether and methanol results in a strong absorption and an incomplete removal of solvents. FT-IR and XRD gave evidence of the formation of carbonate-like phases due to an interaction upon heating, i.e. during thermal analysis, between the strongly absorbed solvents and the cement compounds or hydrates. Vacuum drying reveals reliable results as no interaction products can be formed and the Ca(OH)₂ content, determined by thermal analysis, gives a good approximation of the real amount of Ca(OH)₂.