A Simple Cement Hydration Model Considering the Influences ofWater-to-Cement Ratio and Mineral Composition

A simple hydration model is used here by taking the composition of the cement and the initial water: cementratio (w/c) into account explicitly. Its conceptual basis is a combination of the Avrami equation and Bentz’s modelbased on simple spatial considerations. In this model, the Avrami equation determines the initial reaction, andBentz’s model describes the following hydration stage. The model favors engineers for it relies on one experimentalparameter and has a reliable approximation in the practice.

Effects of porosity,dry unit weight,cement content and void/cement ratio on unconfined compressive strength of roof tile waste-silty soil mixtures

One of the conventional ways to improve the mechanical behavior of soils is to mix them with cementing agents such as cement, lime and fly ash. Recently, introduction to alternative materials or sub-products that can be adopted to improve the soil strength is of paramount importance. Therefore, the present study aims to investigate the effects of porosity(h), dry unit weight(gd) of molding, cement content(C)and porosity/volumetric cement content ratio(h/Civ) or void/cement ratio on the unconfined compressive strength(quor UCS) of silty soileroof tile waste(RT) mixtures. Soil samples are molded into four different dry unit weights(i.e. 13 kN/m^3, 13.67 kN/m^3, 14.33 kN/m^3 and 15 kN/m^3) using 3%, 6% and 9%cement and 5%, 15% and 30% RT. The results show that with the addition of cement, the strength of the RT esoil mixtures increases in a linear manner. On the other hand, the addition of RT decreases quof the samples at a constant percentage of cement, and the decrease in porosity can increase qu. A dosage equation is derived from the experimental data using the porosity/volumetric cement content ratio(h/C_(iv)) where the control variables are the moisture content, crushed tile content, cement content and porosity.

Influence of MgO/MgCl_2 Molar Ratio on Phase Stability of Magnesium Oxychloride Cement

Formation, solution and phase change of hydration products in MgO-MgCl2-H2O system was studied with thermodynamics method, and resistance to water immersion and phase change of magnesium oxychloride cement with different MgO/MgCl2 molar ratio was experimented. The results show that pH value of immersion solution of cement paste has a remarkable influence on phase stability of hydration products. A higher pH value leads to a lower solubility and a better phase stability of hydration products. When the solution pH value is higher than 10.37, the precipitation of much Mg（OH）2 crystal induces a worse phase stability of hydration products. With the increasing MgO/MgCl2 molar ratio （lower than 6）, the more amount of MgO in the hydration products enhances the alkalinity of solution and the phase stability is improved. However, when the MgO/MgCl2 molar ratio is higher than 6 and the excessive MgO exsits in the hydration products, the cement paste may be damaged by the excessive crystallization stress of a great deal of Mg（OH）2 formation.

The Hydration of Blended Cement at Low W/B Ratio

The hydration process,hydration product and hydration heat of blended cement paste mixed with mineral admixture and expansive agent at low W/B ratio are studied by XRD,thermo analysis,and calorimetry instrument,and they were compared with those of pure cement paste.The results show that pure cement and blended cement at low W/B ratio have the same types of hydration products,but their respective amounts of hydration products of various blended cements at same ages and the variation law of the amount of same hydration products with ages are different;The joint effect of tumefaction of gel-ettringite due to water absorption and the expansive pressure on the pore and rift caused by the crystalloid ettringite is the impetus of the volume expansion of cement paste,and the former effect is much greater than the latter one.

Form and Mechanism of Sulfate Attack on Cement-based Material Made of Limestone Powder at Low Water-binder Ratio under Low Temperature Conditions

The development of strength and the form of attack of cement-based material made of limestone powder at low water-binder ratio under low-temperature sulfate environment were studied. The results indicate that when water-binder ratio is lower than 0.40, the cement-based material with limestone powder has insignificant change in appearance after being soaked in 10% magnesium sulfate solution at low temperature for 120 d, and has significant change in appearance after being soaked at the age of 200 d. Expansion damage and exfoliation occur on the surface of concrete test cube at different levels. When limestone powder accounts for about 28 percent of cementitious material, with the decrease of water-binder ratio, the compressive strength loss has gradually decreased after the material is soaked in the magnesium sulfate solution at low temperature at the age of 200 d. After the specimen with the water-binder ratio of less than 0.4 and the limestone powder volume of greater than 20% is soaked in 10% magnesium sulfate solution at low temperature at the age of 200 d, gypsum attack-led destruction is caused to the concrete test cube, without thaumasite sulfate attack.

镁硅比和养护温度对硅酸镁水泥电磁性能的影响

采用波导法测定硅酸镁水泥的电磁性能,分析镁硅比和养护温度的影响,并基于微观测试结果进行机理分析.结果表明:提高养护温度可以显著增强硅酸镁水泥的早期强度;硅酸镁水泥的复介电常数实部随着镁硅比和养护温度的提高逐渐增大;提高养护温度使硅酸镁水泥的复介电常数虚部和损耗角正切值增大;与镁硅比相比,养护温度对硅酸镁水泥的透射率、反射率和吸收率的影响更为明显.微观测试结果显示含水量和孔结构对硅酸镁水泥的电磁性能有重要影响.

煤矸石机制砂C20混凝土力学性能研究

为探究煤矸石机制砂对低强度等级C20混凝土力学性能的影响,调控煤矸石机制砂掺量和水灰比浇筑混凝土试块,开展抗压和抗折强度试验。结果表明:相同水灰比下,随煤矸石机制砂掺量增加,混凝土的抗压强度先增强后降低;相同取代率下,混凝土的抗压和抗折强度随水灰比增大而降低。相较于煤矸石机制砂取代率,水灰比对混凝土抗折强度的影响更大。取代率不超过30%时,对混凝土的抗压和抗折强度均有利,水灰比为0.55、取代率为25%时,混凝土抗压和抗折强度提高最多。

地聚合物注浆材料的制备工艺及病害公路加固中的应用研究

为提高病害路面修复效率和修复效果,利用矿渣、粉煤灰、偏高岭土、碱激发剂等材料制备一种早期强度高、收缩性小、工作性能优异的地聚合物,并将其应用到实际工程中。结果表明,当采用矿渣∶粉煤灰∶偏高岭土=3∶5∶2制备地聚合物粉料时,碱最佳掺量为8%,碱激发剂最佳模数为1.4,最佳水灰比为0.32;最佳注浆参数为:注浆压力0.6 MPa,注浆孔距为150 cm,注浆量为70~120 kg/m^(2);利用制备的地聚合物对某病害路段进行注浆加固处理,加固完成7 d后,可以将加固路段的平均弯沉值从39.1 mm降至21.8 mm,路面结构得到有效加强,加固效果良好,具有十分明显的社会和工程经济效益。

Stabilization of a Lateric Clay from Burkina Faso with Cement-Metakaolin for an Application in Road Construction

The objective of this work is to obtain a composite of clay-cement-metakaolin having good mechanical properties and geotechnical. To do this, a lateritic clay from Burkina Faso referenced ALK was characterized by various methods (X-ray diffraction, infrared spectrometry, thermal analysis and Inductively Coupled Plasma, Atomic Emission Spectrometry) in order to be used as a base course after adding cement and metakaolin. The results of the mineralogical characterization of this clay showed that it is composed of kaolinite (65.7 wt.%), quartz (19.3 wt.%) and goethite (10.8 wt.%). The geotechnical tests carried out showed that ALK is moderately plastic with a plasticity index Ip = 22%. The optimum moisture content and the maximum dry density are respectively 15.9% and 1.76 g∙cm-3. Simple compressive strength and splitting tensile strength are Rc = 1.59 MPa and ft = 0.149 MPa respectively. The California Bearing Ratio (CBR) index at 95% is 40% and above the minimum value of 30% shows that ALK can be used as a sub-base course in road construction. The addition of cement and metakaolin in various proportions improved the CBR index and the mechanical strength of the composites produced. This improvement is due to the formation of hydrated calcium silicate (CSH) resulting from the pozzolanic reaction between the portlandite of the cement and the amorphous silica of the metakaolin. Thus the 2 wt.% metakaolin and 6 wt.% cement formulation with a 95%CBR index of 81% is suitable for the development of a base course in road construction.

有机醇胺TEA-M-无机盐体系对固硫灰渣活性激发的影响

固硫灰渣的处理以及环保型激发剂材料的开发是防止环境二次污染的有效途径。本文开发了一种有机醇胺TEA-无机激发剂M-无机盐复合激发剂,通过SEM、FTIR、XRD等测试方法对所制备的复合激发剂进行表征,先后探索了M、TEA-M、TEA-M-无机盐三个系列的激发剂对水泥胶砂流动度比和抗压活性指数的影响。结果表明,TEA的助磨作用改善了颗粒的粒径,无机激发剂M能影响参与水化反应的Ca(OH)_(2)含量,无机盐CaSiO_(3)后期会产生C-S-H并提供碱性条件。复合激发剂中的不同材料间的协同作用使水泥胶砂7和28 d的抗压活性指数分别提高了29个和18个百分点(与空白样相比),并且胶砂净浆的流动度比仍然保持在较高水平。本文为固硫灰渣提供了一种环保型的复合激发剂材料,促进了固硫灰渣的绿色化应用。

静态破碎剂性能分析及致裂效果实验研究

为解决现有煤矿井工开采过程中预裂爆破安全性低、适用性差以及水压致裂条件苛刻,破岩效果弱的问题,提出静态致裂的方法,通过研究不同影响条件下静态破碎剂的反应状态和致裂效果,对不同拌合水温、水灰比条件下的静态破碎剂反应温度、反应时间、反应体积变化、岩样致裂效果、应力变化进行了研究。结果表明:水灰比一定,静态破碎剂完全反应时间随拌合水温升高而降低,但最终反应完全后温度不变;相同拌合水温条件下,水灰比越小,静态破碎剂反应时间越短,反应速率越快;水灰比越小,混凝土试件开裂时间越短,水灰比越大,开裂时间越长,开裂效果与裂缝位置有关,块体应变呈现先增后减的趋势。

机制砂全再生粗骨料混凝土的力学性能

为探究骨料类型、水灰比与石粉含量对机制砂全再生粗骨料混凝土力学性能的影响,制备了不同石粉质量分数(5%、10%和15%)和不同水灰比(0.50、0.37和0.32)的全再生骨料混凝土试件.以72个立方体试件用于抗压强度试验,72个圆柱体试件用于弹性模量试验.结果表明,合理的石粉含量能有效提高再生骨料混凝土的力学性能,但在不同的水灰比下,最佳石粉含量存在差异;当水灰比和石粉含量双因素交互作用时,水灰比为0.32、石粉质量分数为15%的再生混凝土力学性能达到最优.构建了机制砂再生粗骨料混凝土抗压强度、弹性模量与水灰比、石粉含量的关系模型,计算结果的标准差与离散系数均不超过5%,模型精度良好.研究成果可为提高再生骨料混凝土力学性能及其工程应用提供理论依据.

改性干粉型聚合物水泥砂浆试验研究

本文研究两种不同的可再分散乳胶粉(醋酸乙烯-乙烯共聚物和醋酸乙烯/叔碳酸乙烯酯共聚物)对干粉型聚合物水泥砂浆力学性能、粘结强度、吸水率、干燥收缩的性能影响。结果表明,可再分散乳胶粉的掺量、类型对聚合物水泥砂浆的性能影响较大,力学性能较普通水泥砂浆有明显的提升和改善。可再分散乳胶粉的加入虽然降低了砂浆的抗压强度,但显著提高了抗折强度和折压比,改善了砂浆的柔韧性和抗裂能力;砂浆的干燥收缩、粘结强度和吸水率等性能均有较为明显的改善。

稻壳灰-废旧砖再生透水混凝土的配合比研究

为探究稻壳灰-废旧砖再生透水混凝土的配合比,采用4因素3水平正交试验,探究水灰比、目标孔隙率、废旧砖骨料取代率、稻壳灰掺量对透水混凝土的强度、透水性、抗冻性的影响。结果表明:水灰比为0.3、目标孔隙率为10%、废旧砖骨料取代率为40%、稻壳灰掺量为6%时,稻壳灰-废旧砖再生透水混凝土的性能更优,其抗压强度为11.28 MPa、劈裂抗拉强度为1.99 MPa、透水系数为0.56 cm/s、孔隙率为37.5%、50次冻融循环后抗压强度为3.74 MPa。

石灰石粉-矿渣混凝土的碳化性能及可靠性分析

为探究石灰石粉及矿渣对混凝土碳化性能以及可靠性的影响,以掺合料比例、水胶比、石粉比表面积以及龄期为参数进行快速碳化试验,得出了试验环境和自然环境下的碳化预测模型,由此展开自然碳化下的可靠性预测分析,并以分析得到的可靠度指标为因变量,选取混凝土的水胶比、保护层厚度、石粉的掺量以及龄期4个自变量设计正交试验,对4个因素的重要性进行判定。结果表明:掺加石粉或矿渣后混凝土抗碳化能力均有所降低,其中以单掺20%石粉的混凝土抗碳化能力下降最为明显。石灰石粉-矿渣混凝土抗碳化能力随着水胶比的减小、石灰石粉比表面积的增大而变强。掺加不同比例的矿物掺合料对碳化结构可靠性均有一定减弱影响,对碳化结构可靠性的影响程度为水胶比>碳化龄期>混凝土保护层厚度>石灰石粉掺量,其中水胶比大小、石灰石粉掺量大小、碳化龄期长短与可靠度指标大小负相关,保护层厚度大小与可靠度指标大小呈正相关。

不同水灰比条件下碳酸钙晶须对水泥净浆收缩性能的影响

为探究碳酸钙晶须对水泥净浆收缩性能的影响,分别测试了3种水灰比试样在不同龄期的干燥收缩、化学收缩和自收缩,并采用X射线衍射(XRD)和压汞法(MIP)分别分析了自收缩试样的物相和孔隙结构变化特性。结果表明:碳酸钙晶须在水泥基体中具有吸附和转移自由水的特性;在不同水灰比条件下,碳酸钙晶须对干燥收缩的影响不同,且影响程度与其掺量呈正相关关系;化学收缩随碳酸钙晶须掺量呈先升后降的变化趋势;碳酸钙晶须对自收缩具有明显的改善作用,尤其是早期自收缩,且水灰比的提高使碳酸钙晶须对早期自收缩的改善效果更加显著;碳酸钙晶须细化了孔隙结构,且未生成新的水化产物。

磷酸镁水泥研究进展

磷酸镁水泥(MPC)具有凝结速度快,早期强度高,耐磨性高以及黏结性高等优点,使其在机场跑道、高速公路和市政道路的快速修补方面以及有害物质的固化等领域很受欢迎。但磷酸镁水泥水化极快,凝结时间非常短,导致工程施工无法进行。综述了磷酸镁水泥凝结时间受原材料、缓凝剂、掺合料、配合比等因素影响的新成果。其高脆性的特点限制了它的工程应用,对各种MPC基纤维复合材料的研究进展进行了梳理,讨论了磷酸镁水泥的发展前景。

热活化锂渣复合水泥基凝胶材料配比优化

为提高热活化锂渣复合水泥基凝胶材料工程性能,实现锂渣高效资源化利用,基于室内单因素试验,采用响应面法分析了热活化锂渣掺量、水玻璃掺量、水固比、水玻璃模数和水玻璃波美度对流动度、凝胶时间、析水率及3 d、28 d抗压强度的影响,确定最优配比,并验证该配比下材料的工程效果。结果表明,在热活化锂渣掺量7.32%、水玻璃掺量8.81%、水固质量比0.6∶1、减水剂0.4%的条件下,制备的热活化锂渣复合水泥基凝胶材料流动度为235.69 mm,凝胶时间为73.54 s,析水率为1.123%,3 d、28 d抗压强度分别为11.54 MPa、22.9 MPa。与传统水泥基凝胶材料性能相比,其工程性能和抗硫酸盐侵蚀性均表现更优。

不同母土对水泥土微观结构及强度的影响

为探究多元变量组合差异下水泥土强度的变化规律,以江西省内常见的黏性土、砂性土和砂砾土为研究对象,在不同配合比方案下开展无侧限抗压强度试验,并通过SEM测试分析水泥土微观结构。试验结果表明,在母土为最优含水状态下的三种水泥土中,水泥掺入比为21%(质量分数,下同)、水灰比为0.5、土质含砂砾率为100%的水泥土抗压强度最高,其C-S-H凝胶含量较多,孔隙数量较少,砂砾基质的粒状骨架较多。

金属声屏障用陶粒吸声板制备及性能实验研究

陶粒吸声板耐候性好、对环境影响小,是一种极具潜力的吸声材料,应用于金属声屏障需要深入研究其吸声、隔声性能。基于多孔材料的声学机理,通过振动加压成型技术,制备了陶粒吸声板,研究不同因素对其吸声、隔声性能的影响。测试结果表明:不同工况陶粒吸声板吸声系数、隔声量曲线趋势基本一致,中低频区段吸声系数逐渐增加,1000 Hz左右达到峰值,1000~5000 Hz吸声系数曲线存在波动及第二峰值;隔声量曲线基本呈先降低后增加趋势,区间存在波动,5000 Hz达到峰值;陶粒吸声板采用的陶粒粒径越小,吸声系数、隔声量越高;骨胶比由3.5提升至5.0,吸声系数、隔声量降低;降低水胶比,高频区段吸声系数增加明显,中高频隔声量降低明显;板厚增加,中高频段吸声系数曲线有向低频平移趋势,隔声量整体变化不大;陶粒吸声板放入金属外壳形成单元板后,吸声系数、隔声量较单一陶粒板整体提升显著。经过设计配比陶粒吸声板可以达到Ⅱ级吸声要求,同时兼具一定的隔声效果,放置入金属外壳组成声屏障单元板后,满足TB/T 3122—2019《铁路声屏障声学构件》标准要求,将陶粒吸声板用于金属声屏障吸声材料是可行的。