掺钢纤维的活性粉末混凝土(RPC)力学性能影响的研究

分析钢纤维对RPC抗压强度以及抗折强度的影响,通过试验研究不同种类的钢纤维在不同的掺量下对RPC的抗压强度以及抗折强度的影响,研究结果表明在其它条件不变的情况下,钢纤维的直径对于RPC的强度的影响的区别;钢纤维对RPC强度的影响当掺量大于一定值后有放缓的趋势。     

测量不确定度在水泥胶砂抗折强度检测中的应用

不确定度是表征合理地赋予被测量值的分散性与测量结果相联系的系数.本文仅就水泥胶砂28天抗折强度测试为例,依据JJF1059-1999《测量不确定度评定与表示》进行不确定度的分析和评定,为实际检验工作中的测量不确定度评定提供参考.     

养护温度对核防护用地聚合物早期强度影响研究

分析了养护温度、养护时间及砂子种类对核防护用地聚合物强度性能的影响,并进行了一系列的温度响应实验,实验结果表明,养护温度对核防护用地聚合物的早期强度影响巨大,温度越高,早期强度越高,强度提升越快;发现养护温度对养护时间6.5小时以上地聚合物样品的影响不大,且不能改变地聚合物的最终强度;掺合湖北砂的地聚合物样品强度最高,性能最好。     

养护条件对碱-矿渣-偏高岭土复合胶凝材料强度的影响

研究了偏高岭土对碱矿渣水泥强度的影响规律和不同养护条件下碱-矿渣-偏高岭土复合胶凝材料(M-AAS)的强度发展情况.结果表明:80%湿度和40℃温度下,掺入适量偏高岭土能提高碱矿渣水泥的强度性能,最佳掺量为20%左右;对于掺20%偏高岭土的碱-矿渣-偏高岭土复合胶凝材料,在80%湿度下,养护温度的提高有利于抗压强度的发挥,但对抗折强度的发挥不利;在80%湿度和20℃温度下,复合材料的抗折强度出现倒缩,对80%湿度养护和水中养护两种养护条件进行适当的组合,强度倒缩现象没有发生.     

混凝土抗折强度尺寸效应的分形研究

本文对形状相似，尺寸不同２０根素混凝土梁试件进行了抗折试验，对试件侧面的破坏裂缝图形作了分维测定，发现了分维与试件尺寸之间的客观规律，借助于分形几何理论对试件断面特征的描述，对混凝土抗折强度的尺寸效应建立了新的公式，本文研究概念清新，所得结果能较好的地符合试验。     

亲水型功能化石墨烯的分散性及其对水泥基复合材料力学性能的影响

为了解决石墨烯纳米片在水泥基体中的分散问题,采用芳基重氮盐(F)对氧化石墨烯(GO)进行改性,制备了一种新型亲水型功能化石墨烯(FG).结果表明,FG在水溶剂中最大的分散浓度能够达到2.1mg/mL.FTIR、拉曼光谱和XPS结果表明F成功对石墨烯进行了表面改性.对比纯水泥基体材料,本文所制备的亲水型FG/水泥复合材料...     

引气轻集料混凝土工作性和力学性能的研究

为配制高性能轻集料混凝土,研究了优质引气剂对大流动性轻集料混凝土的工作性及力学性能的影响规律.研究表明:引气剂对大流动性轻集料混凝土的坍落度的影响不大,对黏度影响较大;引气可减少离析、泌水及坍落度损失,明显改善轻集料混凝土拌合物的工作性能;一定范围内,引气对轻集料混凝土的力学性能有益;含气量小于5.5%时,抗压强度未降低,而是有所提高,提高幅度约3%～4%;含气量小于5.5%时,抗折强度提高,提高幅度约8%～10%.     

双掺重钙粉和粉煤灰对自密实混凝土的影响

为了研究双掺重钙粉和粉煤灰对自密实混凝土的影响,在胶凝材料质量一定条件下,对不同掺量的重钙与粉煤灰之比的自密实混凝土进行坍落度、扩展度、立方体抗压强度、抗折强度的实验,得到相应的数据,不对其拟合。通过试验为双掺重钙和粉煤灰在自密实混凝土中台理的应用提供了相关理论依据。     

工艺因素对ZrO2( f ) / PMMA PMA复合材料抗折强度的影响

以聚甲基丙烯酸甲酯聚丙烯酸甲酯( PMMA-PMA) 为基体, 钇稳定氧化锆纤维为增强相, 采用悬浮聚合的方法, 制备了氧化锆短纤维增强PMMA-PMA 义齿基托复合材料。分别研究了单体配比、引发剂用量和氧化锆纤维质量分数对复合材料性能的影响。采用万能材料试验机、扫描电子显微镜和X 射线衍射分别对材料的抗折强度和断面的微观形貌等进行了测试和表征。结果表明: 当MMA/ MA = 9∶1 (体积比) 时复合材料抗折强度达到极大值; 随着引发剂过氧化苯甲酰(BPO) 用量的增加, 复合材料的抗折强度呈现先增大后减小的趋势; 随ZrO₂纤维含量增加, 复合材料的断裂面由平整向多层断裂变化, 材料的韧性有所提高。      

超细粉体对水泥基材料力学性能的影响

为了研究超细粉体在水泥基材料中的应用,对掺加不同活性超细粉体的水泥基试件进行了抗压强度和抗折强度的测试,讨论了矿粉A掺量、硅粉掺量、复掺矿粉A和硅粉对水泥基材料力学性能的影响。结论表明:活性超细粉体对水泥基试件的抗折和抗压强度有较大影响,尤其是硅粉能够很好地提高试件的抗折强度和抗压强度。通过SEM形貌分析,说明掺加的超细粉体能够与水泥基材料内部的不利成分Ca(OH)2发生二次水化反应,生成有利的C-S-H凝胶,有效改善水泥基材料的微观结构。     

橡胶粉对嵌锁密实水泥混凝土强度特性的影响分析

以嵌锁密实水泥混凝土为基础,掺加废旧橡胶粉,使其不仅具有橡胶粉混凝土的优点,同时能够解决橡胶粉水泥混凝土强度不足问题,并通过橡胶粉表面处理使嵌锁密实水泥混凝土与橡胶粉水泥混凝土能够有效结合。采用橡胶粉等体积置换部分砂(10%、20%、30%),分析橡胶粉掺量以及橡胶粉种类(表面改性和未改性)对水泥混凝土的抗压强度和抗弯拉强度的作用。分别应用线性模型、对数抛物线性模型、对数S-logistic模型分析混凝土强度在不同橡胶粉掺量下的变化。试验结果表明:橡胶粉掺量和种类对混凝土的强度有显著的影响,总体是随着橡胶粉掺量的增加强度降低;线性模型能够较好地反映强度随着未改性橡胶粉掺量的变化趋势;对数S-logistic非线性模型可以更加准确地模拟改性橡胶粉掺量对强度变化的影响。     

Ⅲ级粉煤灰掺量、细度对水泥强度发展的影响

为了开发和应用数量大、成分复杂、均匀性差且活性低的Ⅲ级粉煤灰,本文中通过对Ⅲ级粉煤灰的粉磨处理,研究了Ⅲ级粉煤灰的掺量、细度对硅酸盐水泥、普通水泥强度发展的影响。结果表明,为了更好地发挥粉煤灰的活性,Ⅲ级粉煤灰在配制硅酸盐水泥、普通水泥时存在一个合理的粉磨细度和适宜的掺量,当粉煤灰的掺量小于5%时,细度应控制在500m2/kg左右;当掺量为10%￣15%时,细应为600m2/kg左右。     

High strength concrete containing natural pozzolan and silica fume

Various combinations of a local natural pozzolan and silica fume were used to produce workable high to very high strength mortars and concretes with a compressive strength in the range of 69–110 MPa. The mixtures were tested for workability, density, compressive strength, splitting tensile strength, and modulus of elasticity. The results of this study suggest that certain natural pozzolan–silica fume combinations can improve the compressive and splitting tensile strengths, workability, and elastic modulus of concretes, more than natural pozzolan and silica fume alone. Furthermore, the use of silica fume at 15% of the weight of cement was able to produce relatively the highest strength increase in the presence of about 15% pozzolan than without pozzolan. This study recommends the use of natural pozzolan in combination with silica fume in the production of high strength concrete, and for providing technical and economical advantages in specific local uses in the concrete industry.     

A New Nomogram Proposal to Determine Concrete Compressive Strength by Combined Nondestructive Testing Methods

Concrete is the most widely used construction material in contemporary construction technology. In particular, it holds an important place in the building industry in the world. Since concrete is a nonhomogeneous material, determining the strength of concrete accurately is quite difficult. In this respect, to check the mechanical properties of concrete in-situ, nondestructive test (NDT) methods can be used. They are useful as they do not damage concrete; however, these test results are sometimes deceptive. To reduce these deceptive results, destructive test methods were proposed to increase the accuracy of nondestructive methods.

The objective of this study is to determine the strength of concrete with different characteristic strengths using destructive and NDT methods, and to establish new relationships between the compressive strength of concrete and Schmidt rebound values, and ultrasonic wave velocities. For this purpose, 101 concrete cube samples were prepared. After 7 and 28 days of curing, Schmidt rebound and ultrasonic wave velocity tests were applied as NDT methods. New formulations and graphs were established by carrying out a multiple regression analysis between the ultrasonic wave velocities, Schmidt rebound values, and compressive strengths. Thus, a new combined NDT method was developed with a nomogram. Furthermore, the applicability and accuracy of the formula and graph obtained were investigated by comparing the results of core samples from existing structures.

The most important findings obtained from the study are summarized below. The concrete strength can be determined with nondestructive formulas obtained with an accuracy of 85%. High strength concrete cube samples are obtained in-house with 1.6% deviation, and core samples in-situ can be obtained with 7.3% deviation with the newly developed NDT nomogram. These test results show that the newly developed NDT formulas in this study are a very good alternative for determining concrete strength in-situ.     

Effects of Fe2O3 Nanoparticles on Water Permeability and Strength Assessments of High Strength Self-Compacting Concrete

In this work,compressive,flexural and split tensile strength together with coefficient of water absorption of high performance self-compacting concrete containing different amount of Fe2O3 nanoparticles have been investigated.The strength and the water permeability of the specimens have been improved by adding Fe2O3 nanoparticles in the cement paste up to 4.0 wt%.Fe2O3 nanoparticle as a foreign nucleation site could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)2 amount especially at the early age of hydration and hence increase the strength of the specimens.In addition,Fe2O3 nanoparticles are able to act as nanofillers and recover the pore structure of the specimens by decreasing harmful pores to improve the water permeability.Several empirical relations have been presented to predict the flexural and the split tensile strength of the specimens by means of the corresponding compressive strength at a certain age of curing.Accelerated peak appearance in conduction calorimetry tests,more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results indicate that Fe2O3 nanoparticles up to 4 wt% could improve the mechanical and the physical properties of the specimens.     

Influence of limestone content,fineness, and composition on the properties and microstructure of alkali-activated slag cement

The influence of the fineness, concentration, and chemico-mineralogical composition of limestone on the workability, reaction kinetics, compressive strength, microstructure, and binder gel characteristics of sodium carbonate–based waste-activated waste slag cement pastes was investigated in this work. Alkali-activated slag cements incorporated with limestone, containing 33–100% of calcite, at a content of up to 60% with a 28-day compressive strength of 26.2–48.8 MPa were proposed. The main reaction products of hardened alkali-activated cement pastes and those incorporated with limestone are CSH, CaCO₃, Na₂Ca(CO₃)₂·5H₂O, and Na₂CaSiO₄. “Physically active” limestone does not chemically react with the binder gel but it can improve the physical structure. The higher packing density of mixed cement, without an increase in the water demand, the satisfactory binding strength of limestone with the binder gel lead to the improvement in the physical structure and compressive strength of alkali-activated slag paste.     

纳米TiO_2对水泥基材料的增韧效果及作用机制

通过力学强度、SEM、XRD和MIP测试手段,研究了NT对水泥砂浆机械性能与微观结构的影响。结果表明,3%NT可显著提高水泥砂浆的抗拉和抗折强度,28 d时相比空白样分别提高了68.2%和63.2%;促进AFt的结晶析出,其含量较空白样提高了62.6%,并与水泥砂浆的抗拉和抗折强度呈现明显的正向关系;使28 d时硬化浆体内部孔隙率降低了37.0%,无害孔增加了41.0%,有害孔降低了37.9%,即孔结构明显细化并向无害孔转移。研究结果说明了3%NT可明显改善水泥砂浆韧性与密实度,并提出了NT对水泥水化晶体的形成具有模板成核作用和调控晶体生长效应。     

Contribution of limestone to the hydration of calcium sulfoaluminate cement

Calcium sulfoaluminate (CSA) cements can be blended with mineral additions such as limestone for properties and cost optimization. This study investigates the contribution of limestone to the hydration of a commercial CSA clinker regarding the hydration kinetics, hydrate assemblage and compressive strength. Nine formulations were defined at M-values of 0, 1.1 and 2.1 (M = molar ratio of anhydrite to ye’elimite) without and with medium and high limestone contents.Calorimetric results indicate that limestone accelerates the hydration reaction especially at M = 1.1, probably due to the filler effect. The phase assemblages were calculated by thermodynamic modeling using Gibbs Energy Minimization Software (GEMS). With increasing limestone content the formation of ettringite and calcium monocarboaluminate is predicted at the expense of calcium monosulfoaluminate. With increasing M-value more ettringite is predicted at the expense of the monocarbonate and less calcite takes part in the hydration reactions.The modeled results compare well with the experimental data after 90 d of hydration, except that calcium hemicarboaluminate was found instead of monocarbonate, which is assumed to be due to kinetics considerations.The lowest compressive strength occurs in ternary formulations, whereas in the absence of calcium sulfate, strength is significantly higher.The results presented here indicate that in CSA cements, limestone accelerates early hydration kinetics, takes part in the hydration reactions at M < 2, and has a positive effect on strength development in systems without anhydrite.     

我国利用高岭土、膨润土制备矿物纳米材料的研发现状与展望

文章介绍了多孔纳米粘土矿物、纳米高岭土、多孔状纳米煅烧高岭土、纳米级莫来石二氧化硅复合粉体、纳米级高纯莫来石、纳米蒙脱石、聚合物／纳米蒙脱石复合材料等矿物纳米材料方面的研发现状与进展、并分析非金属矿物高岭土、膨润土在纳米材料领域发展过程中的重要性、经济性与可操作性。指出了国家在相关政策上的鼓励与支持，是加速发展我国矿物纳米材料之重要前题。     

Fracture of Plain and Fiber-Reinforced High Strength Mortar Slabs with EA and ESPI Monitoring

The failure of cement-based materials is associated with the development of a damaged zone in the form of a more or less large region of microcracking. The development and the evolution of the damaged zone is of fundamental importance in defining the mechanical response in terms of both structural behavior and peak strength. For geometrically similar beams of different sizes, this paper presents and discusses experimental evidence from interferometric measurements (ESPI) and locations of acoustic emission (AE) of the damaged zone development, at the peak load, in terms of shape and size. The cement-based materials had an aggregate/binder ratio of 1.5, a microsilica/binder ratio of 0.1 and a water binder ratio of 0.22. Beams made with (2% by volume) and without steel reinforcing microfibres were considered. It is shown that the size effects appear to be reduced in the fibre- reinforced materials.