废轮胎钢丝水泥基复合材料的电磁屏蔽性能

利用同轴法兰-频谱分析仪法研究了掺废轮胎钢丝水泥基材料在0.03～1500 MHz频率范围内的电磁屏蔽性能.结果表明:掺废轮胎钢丝可明显改善水泥浆体的电磁屏蔽效能;复掺钢丝-石墨或钢丝-导电炭黑均可在单掺试样基础上使得屏蔽效能获得更显著的改善,其中复掺钢丝-导电炭黑试样的屏蔽效能在测试频段内最大可达29 dB.     

石墨、不锈钢纤维、焦炭对水泥基材料电磁屏蔽效能的影响

介绍了高频电磁屏蔽原理,研究了石墨、不锈钢纤维和焦炭对水泥基材料的高频电磁波屏蔽效能和电阻率的影响.结果表明,石墨是一种较好的屏蔽材料,掺石墨10%、不锈钢纤维1.0%、焦碳5%,当频率为11GHz时,屏蔽效能为49.3dB,复合 材料的电阻率为85.23Ω·m.     

水泥基电磁屏蔽材料的研究现状

当今社会电磁辐射问题日益严重,这些电磁辐射不仅会危害人类的身体健康,还会对各类电子设备造成危害。针对存在问题阐述了电磁辐射的原理和表征方法,介绍了金属填充水泥基复合材料、碳系水泥基复合材料以及微波吸收型水泥基材料三种电磁屏蔽材料,最后对水泥基电磁屏蔽材料的发展趋势做了展望。     

垃圾焚烧灰熔融重构矿渣对水泥基材料性能的影响

研究了不同掺量下(10%、20%、30%、50%)的垃圾焚烧灰和重构矿渣对水泥基材料性能的影响,并通过扫描电镜(SEM)、X射线衍射(XRD)等测试技术分析了影响机理。研究结果表明:相比于纯水泥,垃圾焚烧灰掺量为50%的水泥基材料终凝时间缩短为75 min,标准稠度用水量增加至28.7%,重构矿渣掺量为50%的水泥基材料终凝时间延长至335 min,标准稠度用水量增加至29.8%。垃圾焚烧灰的活性较低,随着垃圾焚烧灰掺量的增加,水泥砂浆抗压强度先增大后减小,当其掺量为10%时,28 d抗压强度达到最大(51.5 MPa);重构矿渣的活性高于垃圾焚烧灰,在碱性环境的激发下,水化后期重构矿渣发生二次水化反应,生成较多的水化产物,掺重构矿渣的水泥砂浆强度先增大后减小,当重构矿渣掺量为20%时,28 d抗压强度达到最大值48.8 MPa。     

稻壳灰的理化性质对水泥基材料主要性能的影响综述

由农业副产物燃烧制备的稻壳灰（RHA）具备与硅灰媲美的火山灰活性,作为一种补充胶凝材料,能够显著提高水泥基材料的各项性能。综述RHA的生产工艺、材料性能及其对水泥基材料主要技术性能影响的相关研究,如水泥水化、强度、氯离子渗透、抗硫酸盐侵蚀、碳化和收缩等主要性能的影响。结果表明,RHA颗粒的多孔结构起到的保水功能对后期水泥水化有极好的辅助作用;基于对RHA-水泥基材料各方面性能的总结,认为RHA的优选含量范围为10%～20%。最后,由于稻壳回收存在困难、制备工艺的局限性以及缺乏分类标准等问题,导致RHA在混凝土中的应用研究还处于起步阶段,有待于进一步开拓和拓展。     

集料对水泥基材料热膨胀性能影响的研究

通过石英砂、石灰石和花岗岩3种集料分别对水泥基材料热膨胀性能的影响进行研究,对集料、水泥石及不同灰砂比(C/S)混凝土从室温至600℃范围内热膨胀率的测定与分析,得出集料掺加量对混凝土热膨胀率的影响规律:混凝土的热膨胀率为集料和水泥石的双重作用所致,在室温至集料与水泥石热膨胀率"交汇点"(石灰石、石英砂和花岗岩与水泥石热膨胀率"交汇点"温度分别为197、160和180℃)温度范围内,集料的膨胀对水泥石的膨胀起限制作用;在"交汇点"温度到600℃范围内,集料的膨胀对水泥石的收缩起限制作用;集料热膨胀率越大(如石英砂),在混凝土中掺加量越多,制得的混凝土的热膨胀率随温升而增大越明显.     

稻壳灰对水泥基材料力学性能的影响研究

为了研究稻壳灰对水泥基材料力学性能和抗冻融性能的影响,在不同稻壳灰掺量、不同龄期以及不同冻融循环次数等因素影响下开展了基本力学性能试验和冻融循环试验的研究,运用SPSS软件建立了冻融循环试验后掺入稻壳灰的水泥基材料抗压强度的多元线性回归方程,并通过SEM试验揭示了稻壳灰对水泥基材料的抗冻融性能的影响机理。结果表明：稻壳灰掺量在一定范围内,水泥基材料的强度与稻壳灰掺量成正比例关系;养护龄期28 d、稻壳灰掺量7%水泥基材料的抗折和抗压强度与基准组相比分别提高了44.1%、74.4%;随着冻融循环试验次数的增加,稻壳灰水泥基材料的抗折和抗压强度降低速率与基准组相比较为缓慢;SEM试验结构表明水泥基材料在冻融循环作用下,稻壳灰可有效提高水泥基材料的抗冻融性能。     

基于非接触电阻率测量法的水泥基材料早期水化特性研究

采用非接触电阻率测量法,基于电阻率与温差曲线,研究了硅灰掺量（5%、10%）和粉煤灰掺量（20%、40%）对水泥基材料早期水化的影响。结果表明：掺粉煤灰组水泥浆体的电阻率在约580 min前高于C组（基准组）,在580 min后低于C组,而掺硅灰组水泥浆体正相反,在580 min后,掺硅灰组水泥浆体的电阻率高于C组;与C组相比,掺入粉煤灰后,水泥浆体的放热量减少,放热峰对应的时间延迟,而掺入硅灰后,水泥浆体的水化反应明显加快,放热峰对应的时间也随着硅灰掺量的增加而提前;相比于C组,掺粉煤灰组水泥浆体的凝结时间略微延长,掺硅灰组水泥浆体的凝结时间缩短;相较于掺入粉煤灰,掺入硅灰可以促进水泥水化,使水泥浆体微观结构更加致密。     

硅灰对水泥性能影响试验研究

为研究硅灰对水泥性能的影响,通过测定水化过程中C3S和β-C2S的变化,得岀如下结论:硅灰的加入加速了C3S的早期水化,尤其是3d前的水化;3d以后,硅灰的这种加速作用逐渐减缓直到28 d龄期;之后.C-SF体系中C3S的水化近乎停止;硅灰掺量越高、水灰比越低,则C3S和β-C2S在28-112 d期间的水化减速就越明显。由此可见,在水泥中掺入硅灰能够调节水化过程的快慢,进而在实际工程中可以结合丁程项目所需混凝土的特点,来配制早强水泥。     

粉煤灰细度和掺量对水泥基材料性能的影响

比较了不同细度和掺量的粉煤灰对水泥基材料工作性能、水化性能以及胶砂流动性、强度的影响。结果表明：粉煤灰的掺入对提高浆体的流动性有明显改善作用，不同细度的粉煤灰对浆体流动性的改善程度不同；粉煤灰掺入使浆体的凝结时间明显延长，并使早期化学结合水量和早期强度降低。粉煤灰的掺入提高了砂浆流动性，降低了早期强度，但后期强度可赶上甚至超过不掺粉煤灰的砂浆强度。     

Sulfate resistance of the cement materials based on the modified silica fume

The object of the study was the influence of chemically modified silica fume (MSF) on the sulfate resistance of cement-based materials. MSF is a liquid product prepared from a suspension of silica fume and a water solution of a reactant under the defined composition of suspension, defined ambient temperature and time of procedure. MSF is added into mortar or concrete mixtures instead of water in the quantities needed for the desired consistency. The results obtained at the application of MSF shows a significant increase of sulfate resistance of materials based on Portland cement slag blends and slag binder. This positive effect represents a further beneficial potential of MSF that has already been shown as an effective hardening accelerator together with its ability to increase the acidic resistance of materials based on Portland cement slag blends and slag binder.     

纳米硅粉对水泥硬化浆体的改性研究

与普通硅粉相比,纳米硅粉具有更加优异的火山灰活性,在水泥基材料改性研究中,掺加性能优异的纳米硅粉成为一种新的探索.分析了普通硅粉和纳米硅粉的颗粒细度、晶体结构及火山灰活性,通过掺加纳米硅粉的水泥硬化浆体强度性能试验研究,结合试验测试和理论分析,探讨了纳米硅粉在水泥硬化浆体中的作用机理,为纳米硅粉应用于高性能水泥基材料的研究奠定理论和试验基础.     

微硅粉对纤维增强水泥物理性能影响的试验研究

利用微硅粉作为矿物掺合料,研究了微硅粉对纤维增强水泥物理性能(抗折强度、抗冲击强度、吸水率、容重和干缩率)的影响。研究结果表明,微硅粉的掺入,明显提高了纤维增强水泥的抗折强度、抗冲击强度,降低了吸水率,体积质量、干缩率略有增大。在此基础上,着重分析了微硅粉对纤维增强水泥物理性能影响的作用机理。同时,探讨了微硅粉在生产应用中的最佳掺量及常见的几个应用问题。     

硅灰对铝酸盐水泥胶合剂性能影响的试验研究

通过引入硅灰来改善铝酸盐水泥后期强度倒缩的问题,采取内掺的方式,研究了硅灰掺量对铝酸盐水泥胶合剂性能的影响.结果表明:适宜掺量下,硅灰能大大改善铝酸盐水泥的工作性能、力学性能和收缩性能,当内掺8％硅灰时,其早期抗压强度虽低于空白组,但28 d抗压强度接近空白组,达到123.6 MPa,且56 d抗压强度持续提高至127...     

Estimation of the permeability of silica fume cement concrete

Deterioration and durability of concrete structures mainly depend on permeability of concrete. Silica fume (SF) as a mineral admixture for high performance concrete produces more discontinues and impermeable pore structure in concrete. The higher permeability reductions with silica fume are due to pore size refinement and matrix densification, reduction in content of Ca(OH)₂ and cement paste-aggregate interfacial refinement. During the hydration process the transition interfacial zone is gradually densified due to pozzolanic reaction between silica fume and calcium hydroxide. Based on a microstructure model, a procedure for predicting the permeability of high strength silica fume cement concrete is developed by considering water-to-binder ratio, silica fume replacement ratio and degree of hydration as major influencing factors. Results of the permeability calculated using the procedure is verified with the available literature. Subsequently, effects of silica fume on the permeability of concrete are evaluated. Finally, optimum silica fume replacement ratios that reduce the permeability of concrete reasonably are proposed for durable concrete.     

Acidic resistance of materials based on the novel use of silica fume in concrete

The objectives of this paper are the results of a study on the acidic resistance of cement-based materials prepared with chemically modified silica fume (MSF). MSF seems to be a highly effective hardening accelerator of materials based on combinations of Portland cement and basic blast furnace slag and on this slag alone. Besides the mechanical properties chemical resistance is a very important engineering property of concretes. This is very interesting even with cement-based materials with a MSF application. It was a reason for the study on the acidic resistance of the cement-based materials when MSF was applied. Based on the observation of changes of chemical composition, pore structure and mechanical properties of the test specimens, a high acidic resistance was found on the cement-based materials when MSF was applied. This allowed a solution to the problem of insufficient acidic resistance of current cement-based materials which represents a crucial world-wide problem.     

粉煤灰和硅灰对白云石基碱式硫酸镁水泥影响的研究

在白云石基碱式硫酸镁水泥(DBMSC)中掺加不同掺量的粉煤灰、硅灰,并通过研究其凝结时间、力学性能、流动度、水泥放热速率、孔径分布等,结合XRD观察其水化产物组成,分析粉煤灰、硅灰对DBMSC的影响。试验结果表明,在DBMSC中掺加适量粉煤灰有助于提高其后期强度,改善胶砂流动度;适量硅灰有助于提高其早期强度,但对改善其胶砂流动度的效果不明显;粉煤灰和硅灰均对DBMSC具有缓凝作用,降低水泥水化热。     

硅灰对PB-g-PS胶乳改性水泥砂浆的性能影响

质量比为50/50的聚丁二烯接枝聚苯乙烯(PB-g-PS)胶乳用于改性水泥砂浆。考察了硅灰含量和聚灰比对改性水泥砂浆的流动度、抗压和抗折强度以及吸水量的影响。研究表明:改性砂浆的流动度随硅灰含量的增加而降低,随聚灰比增加而增加;适量的硅灰能降低改性砂浆的毛细孔吸水量,而随聚灰比的增加,改性砂浆的毛细孔吸水量降低;胶乳的加入使抗压强度降低,部分改性砂浆的抗折强度有所提高,硅灰的加入极大地改善了砂浆的力学性能,改性砂浆的抗压、抗折强度最大值分别为34.97、6.86 MPa。利用SEM观察了改性砂浆的结构,改性砂浆结构更加致密,界面结构得到改善,并观察到了带状的聚合物膜结构和六角形的片状的氢氧化钙晶体结构。综上所述,硅灰和胶乳二者可以复合改性水泥砂浆。     

硅灰改良混凝土性能的研究现状

介绍了硅灰的含义与研究现状,结合硅灰改良混凝土的物理与化学机理,分析了硅灰对混凝土力学性能及耐久性能的影响,指出硅灰作为掺料制作混凝土时,可在一定程度上提高混凝土的强度与耐久性。     

Effect of superplasticizer on plastic shrinkage of plain and silica fume cement concretes

Four types of superplasticizers were used in conjunction with three types of silica fume to prepare cement concrete slab specimens that were utilized to measure plastic shrinkage strain and time to attain maximum strain. The concrete slab specimens were cast and placed in an exposure chamber in which the relative humidity, temperature, and wind velocity were kept at 35 ± 5%, 45 ± 2 °C, and 15 ± 2 km/h, respectively. Results of this investigation indicate that the plastic shrinkage strain varied with the type of superplasticizer and the type of silica fume. Maximum plastic shrinkage strain was measured in the undensified silica fume cement concrete with all superplasticizers. Incompatibility was noted between polycarboxylic ether superplasticizer and plain and two types of silica fume cement concretes.