偏高岭土对混凝土抗碳化性能的影响

为了提高混凝土的抗碳化性能,在混凝土中掺入偏高岭土并进行碳化实验.实验结果表明:随着偏高岭土掺量的增加,混凝土的抗碳化能力也相应的提高了,且当矿物掺合料总掺量为35%,其中偏高岭土掺量为15%时,混凝土抗碳化能力最大的提高率达到38.02%.实验结果可为提高混凝土抗碳化性能提供一种新的思路.     

偏高岭土改善海工混凝土抗氯离子侵蚀性的效果及机理

以不同掺量偏高岭土单掺以及与粉煤灰、矿粉复掺制备混凝土,分别采用浸泡法和RCM法测试混凝土氯离子扩散系数,采用压汞法测试混凝土的孔结构;同时制备相应掺NaCl水泥净浆,采用自动电位滴定仪测试水泥浆中总氯离子和游离氯离子量,计算氯离子固化率,并通过XRD法分析其物相组成。结果表明,偏高岭土可显著降低混凝土氯离子扩散系数,其与粉煤灰或矿粉复掺时效果更优,且与粉煤灰复掺时对后期氯离子扩散系数的降低作用显著;偏高岭土提高了水泥浆对氯离子的固化率,提高掺量可改善固化效果;偏高岭土复掺粉煤灰或矿粉进一步增强了固化效果,且与粉煤灰复掺效果最优;偏高岭土细化了混凝土孔结构,降低了毛细孔含量,促进了含氯水泥浆中F盐的生成,从减少氯离子传输通道和提高氯离子固化作用两方面改善海工混凝土的抗氯离子侵蚀性能。     

偏高岭土改善混凝土体积稳定性的实验研究

对以偏高岭土为主要掺合料的砂浆体积稳定性进行了分析,并结合混凝土耐久性原理进行了水泥胶砂的干缩试验来评定混凝土的干缩性能,研究不同掺合料配比下对水泥砂浆试件的膨胀的影响,从而确定了以偏高岭土为主要掺合料改善砂浆体积性能的效用,为混凝土开裂研究提供了依据.     

矿物功能材料对混凝土氯离子渗透性的影响

在单因素影响方案的基础上 ,研究了多种磨细工业废渣及天然矿物材料的不同组合与叠加对混凝土氯离子渗透性的影响。通过试验研究和理论分析证实了硅灰与偏高岭土、粉煤灰、矿渣之间存在着“超复合叠加效应”,为合理选择矿物功能材料的种类及掺配方式 ,特别是偏高岭土的合理应用提供了技术思路 ,实现了矿物功能材料在提高混凝土抗氯离子渗透性方面的性能优化与降低成本的双重效用     

偏高岭土高性能混凝土的轴压应力-应变关系

采用美国产MTS试验机,研究了掺偏高岭土(Melakaolin,MK)的混凝土轴压应力-应变关系．试验结果表明,随着MK掺量的增加,混凝土的抗压强度随之提高,特别是早期强度提高更为显著．弹性模量略有提高,但幅度明显小于强度提高值．混凝土的韧性得到改善．此外,MK对混凝土的流动性影响较小,且能显著改善粘聚性和保水性．因此,偏高岭土是一种优异的高强高性能混凝土掺合料．     

钢纤维和聚丙烯粗纤维对活性粉末混凝土强度和延性的影响

众所周知,混凝土强度越高,脆性越显著,特别是超高强度混凝土。本文就钢纤维和聚丙烯粗纤维对掺偏高岭土活性粉末混凝土抗压强度和延性的影响进行了研究,结果表明:掺入一定量的钢纤维,可以改善混凝土内部孔隙结构,延迟和阻碍裂缝的形成和发展,从而提高混凝土的抗压强度,改善混凝土的脆性;掺入一定量的聚丙烯粗纤维,混凝土强度不会提高,但具有改善混凝土脆性的作用。     

LDHs-MK复合改性混凝土抗氯离子渗透性能的研究

以LDHs材料和偏高岭土为主要功能组分开展混凝土试验,针对混凝土的工作性能、力学性能和抗氯离子渗透性能进行研究。结果表明,偏高岭土在混凝土中的火山灰作用可促进水泥的水化进程,改善混凝土内部的显微结构,而LDHs材料可有效固化外界侵入的氯离子,从而在混凝土内部形成一个防御屏障。LDHs与MK的复合可实现固化氯离子和优化孔结构的叠加效应,从而大幅度增强混凝土的抗压强度和抗氯离子渗透性能。     

掺石灰石粉混凝土的性能及其改善途径

采用不同掺量的石灰石粉取代水泥配制混凝土,同时配制复掺6%偏高岭土和20%石灰石粉的混凝土,并采用相同的胶凝材料体系制备水泥净浆,开展Na_2SO_4溶液浸泡试验。测试了混凝土抗压强度,采用RCM法和硫酸盐干湿循环侵蚀试验分别测试混凝土的氯离子扩散系数和抗硫酸盐侵蚀性,采用MIP法测试混凝土孔结构,进一步采用SEM观察浸泡后净浆试件的微观形貌。结果表明,石灰石粉对混凝土抗压强度、抗氯离子渗透性和抗硫酸盐侵蚀性均有一定的不良影响。采用偏高岭土与石灰石粉复掺可以有效提高掺偏高岭土混凝土的强度、抗氯离子渗透性和抗硫酸盐侵蚀性。其机理主要在于优化了混凝土孔结构,降低了有害离子在混凝土中的传输速度,阻止了混凝土在硫酸盐环境中钙钒石、石膏等侵蚀产物的形成。     

矿物掺合料对外墙保温材料泡沫混凝土的改性研究

为了改善泡沫混凝土作为外墙保温材料时的抗压性能、保温性能、收缩性能及防水性能,采用掺合料等质量替换水泥的方式研究粉煤灰、硅灰、矿粉及偏高岭土对250 kg·m~(-3)泡沫混凝土性能的影响。结果表明:适量粉煤灰可以使泡沫混凝土的收缩率和体积吸水率降低,抗压强度增加。适量硅灰可以使泡沫混凝土的收缩率和体积吸水率降低,抗压强度增强。适量矿粉可以使泡沫混凝土抗压强度增加、体积吸水率降低。适量偏高岭土可以使泡沫混凝土的导热系数、体积吸水率和体积沉降率降低,抗压强度增加。矿物掺合料掺入泡沫混凝土后,提高了泡沫混凝土抗压性能和保温性能,改善了泡沫混凝土的收缩性能及防水性能。     

偏高岭土改善灰土强度的试验研究

灰土被广泛用作建筑物和构筑物的基础,本文通过添加偏高岭土来进一步改善其力学性能,以期为改性灰土的应用提供试验依据.灰土强度受其组成原料如石灰含量、含水率和粘土性质的影响较大,通过控制石灰和偏高岭土含量以及水固比等因素,研究偏高岭土的加入对常规灰土材料抗压强度和软化系数的影响,并通过对含水率变化分析和扫描电镜揭示其内在机理.根据试验结果的对比分析,发现偏高岭土不仅能改善灰土材料的强度,明显缩短其强度形成时间,而且明显的提高灰土试样的软化系数.无论添加偏高岭土与否,试样抗压强度随水固比、石灰含量和偏高岭土含量均存在一个最佳配比.偏高岭土与Ca(OH)_2和水发生化学反应,反应产物致使灰土试样的结构更加致密,从而改善了试样的力学性能.     

Properties of High Volume Fly Ash Concrete Compensated by Metakaolin or Silica Fume

The compressive strength and dynamic modulus of high volume fly ash concrete with incorporation of either metakaolin or silica fume were investigated. The water to cementitious materials ratio was kept at 0.4 for all mixtures. The use of high volume fly ash in concrete greatly reduces the strength and dynamic modulus during the first 28 days. The decreased properties during the short term of high volume fly ash concrete is effectively compensated by the incorporation of metakaolin or silica fume. The DTA results confirmed that metakaolin or silica fume increase the amount of the hydration products. An empirical relationship between dynamic modulus and compressive strength of concrete has been obtained. This relation provides a nondestructive evaluation for estimating the strength of concrete by use of the dynamic modulus.     

Pore Size Distribution of High Performance Metakaolin Concrete

The Compressive strength, porosity and pore size distribution of high performance metakaolin (MK) concrete were investigated. Concretes containing 0,5%,10% and 20% metakaolin were prepared at a water/cementitious material ratio (W/C) of 0.30.In parallel, concrete mixtures with the replacement of cement by 20% fly ash or 5 and 10% silica fume were prepared for comparison.The specimens were cured in water at 27℃ for 3 to 90 days .The results show that at the early age of curing(3 days and 7 days),metakaolin re-placements increase the compressine strength ,but silica fume replacement slightly reduces the compressine strength.At the age of and after 28 days ,the compressive strength of the concrete with metakaolin and silica fume replace-ment increases.A strong reduction in the total porosity and average pore diameter were observed in the conctete with MK 20% and 10% in the first 7 days.     

The early hydration and strength development of high-strength precast concrete with cement/metakaolin systems

To study the relationship between material composition, curing conditions and strength development, the study simulated high-strength precast concrete pile production, and a high-strength mortar up to 90 MPa was designed and a hot-water pool was built for concrete curing. The major point of the study was to achieve a high early strength by using cement/metakaolin systems without autoclave curing with high-pressure steam. By means of XRD and thermal analysis, the progress of the hydration of the cement pastes blended with metakaolin was characterized. The main results indicate that high strength can be obtained at early age by the use of metakaolin and thermal treatment (hot-water curing). The improvement in strength of mortars with metakaolin can be explained by an increase in the amount of C-S-H and C-S-A-H hydrated phases and a decrease in the amount of calcium hydration(CH). Further more, a decrease in Ca/Si ratio of the matrix was observed from the results of EDX analysis, which also leaded to an improvement of the compressive strength. These results are of great importance for the high-strength precast concrete manufacturing industry.     

Nanoindentation characteristics of calcium hydroxide-metakaolin blended with sodium hydroxide solutions

In order to determine the active mechanism of metakaolin (MK) as partial replacement of cement in concrete from the nanoscale structure perspective, nanoindentation characteristics of calcium hydroxide (CH)-MK blended with 5 M sodium hydroxide (NaOH) solutions simulating the condition of MK in concrete has been studied. The results indicate that three distinct phases are found by the nanoindentation and BSE tests, such as HD C-S-H gel, LD C-S-H gel and the reaction products with the network structure, the residual unreacted MK and CH, respectively. The volume fraction of HD C-S-H gel is about 96% of all reaction product phases. This means that the use of MK in concrete can increase the volume fraction of HD C-S-H gel and thus will improve the properties of concrete.     

Self-healing of cracks in concrete with various crystalline mineral additives in underground environment

Cracks can deteriorate mechanical properties and/or durability of concrete. A few studies have shown that, cracks can autogenously heal under a certain conditions besides the traditional passive repair with a deliberate external intervention. For underground concrete structures, the presence of water, as a necessity for chemical reactions of the healing additives, is beneficial to healing concrete. In this paper, a natural healing method by mineral additives was developed according to the chemical and physical characteristics of underground environment. The healing capacity of three different crystalline mineral materials classified namely, carbonate, calcium sulphoaluminate expansive agent and natural metakaolin due to permeation- crystallization, expansion and pozzolanic reaction, has been assessed from the mechanical properties, referring to the relative elastic modulus, the strength restoration, and the water permeability of the healed specimens. In addition, the morphology of the healing products in the vicinity of the crack was observed. The results indicate that the specimens incorporated with the three mineral additives show different healing capacity according to the improved mechanical properties and permeability. The permeability of the host matrix decreased a lot after crack healing by natural metakaolin followed by carbonate whereas no noticeable improvement of water permeability has been observed for the specimens mixed with expansive agent. The specimens incorporated with carbonate show the best mechanical restoration in terms of relative elastic modulus and compressive strength. Although the dominate element is CaCO3 by reaction of CO32-, either from the dissolved CO2 or from the additives, and Ca2＋ in the cementitious system to fill the cracks, the healing capacity depends greatly on the morphology and the properties of the newly formed products.     

偏高岭土对水泥净浆火山灰效应强度贡献率的影响

根据蒲心诚教授提出的偏高岭土火山灰效应定量分析方法,进行了偏高岭土对水泥净浆(以下简称净浆)火山灰效应强度贡献率(以下简称强度贡献率)的影响研究.结果表明:随着偏高岭土掺量的增加,其净浆强度贡献率增加;随着养护龄期的增加,其净浆强度贡献率呈现先减少后增加的趋势,且7,d时出现最低值;3、28,d时小粒径偏高岭土(2.5和3.75,μm)的净浆强度贡献率明显高于7,d时的值,这说明偏高岭土火山灰效应主要是发生在早期(3,d)和后期(28,d);而大粒径偏高岭土和补充激发剂则有利于提高其中期(7,d)净浆强度.     

偏高岭土活性评价方法的研究

采用多种方法对不同煅烧制度制备的偏高岭土进行活性评价。研究结果表明：只采用X衍射光谱的分析方法是不能说明煅烧出来的偏高岭土是否具有良好的活性；采用碱吸收法可区分偏高岭土是否具有活性，但其吸收量的规律与3d抗压强度的规律不一致；钙吸收法不适用于评价该系统中偏高岭土的活性；采用压缩测强法可以较好评价偏高岭土的活性大小。而最有效评价偏高岭土活性的方法是直接用偏高岭土制备土壤聚合物并养护到一定龄期下的强度采评价．其它方法应与其规律相一致．但此方法耗时过长，不适用于生产．     

Magnetic susceptibility measurements on metakaolin admixtured cement hydrated with ground water and sea water

The role of metakaolin in the properties of Portland cement hydrated with ground water and sea water was described by magnetic susceptibility study. Cement pastes containing 0wt%, 10wt%, 20wt% and 30wt% replacement of metakaolin and in a wa-ter/cement (W/C) ratio of 0.4 were prepared. The susceptibility at different hydration periods was determined by Faraday Curie bal-ance and it was related to the changes in setting time and compressive strength of admixtured cement. Compared with sea wa-ter-treated cement paste, the magnetic susceptibility of ground water-treated cement paste is higher in value. The observed result shows that, irrespective of water, the magnetic susceptibility increases with increasing metakaolin percentage replacement level in cement.     

STUDY ON HIGH ACID LEACHING REACTIVE CALCINED KAOLIN

Leaching experiments on metakaolin show that the final Al extraction ratio reached in a batch reaction is strikingly influenced by the inferior pore structure geometry of the metakaolin pellets. By calcining kaolin particles adhered in low humidity state, a variety of metakaolin pellet, inside which a large openings structure developed, has been prepared. The structure remarkably benefits leachant ion transference, so, the variety has high acid leaching reactivity, even coarse as the pellets are, its aluminum extracted ratio still has a linear relationship with leaching time, and the leaching kinetics is maintained zero order up to a significant conversion degree. A revised Pellet-Particle Model has been developed to interpret the structure influence on Al extraction ratio.