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采用移动刚体(GMO)方法,将新拌自密实混凝土(SCC)视为粗骨料与砂浆相混合的两相固液介质,对粗骨料运动及静态离析现象进行计算流体力学(CFD)数值模拟.分析了砂浆的屈服应力和塑性黏度对粗骨料运动过程的影响,研究了3种级配的SCC中粗骨料在砂浆中的运动行为.结果表明:砂浆的屈服应力对SCC静态离析具有显著影响,而砂浆的塑性黏度对其影响不大;虽然不同的骨料级配在相同条件下的离析行为不尽相同,但仍体现出一定的规律性,其中大粒径骨料含量较少、小粒径骨料含量较多的级配相对稳定. 相似文献
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研究了骨料(石英砂、玻化微珠)、保塑剂(HMC)、塑化剂(KHC)、乳胶粉(FX)对3D打印轻骨料混凝土(3DPLAC)的流变性能、挤出性、堆积性能以及容重的影响.结果 表明:在相同水胶比下,随着玻化微珠取代量的增加,3D打印轻骨料混凝土的表观黏度、触变性和屈服应力明显下降,挤出性、堆积性能降低,容重显著下降;随着HMC和KHC掺量的增大,3D打印轻骨料混凝土的表观黏度、触变性、屈服应力均明显增大;随着FX掺量的增加,3D打印轻骨料混凝土的表观黏度、触变性以及屈服应力呈先减小后增大的变化趋势.通过优化各组分配比,3D打印轻骨料混凝土可获得适宜的流变性能,可打印性得到显著改善,容重明显降低. 相似文献
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The rheology of a fresh concrete is largely determined by the rheology of its mortar portion and hence proper design of the mortar portion should be the first step in the mix design of concrete, especially high-performance concrete. In recent studies, it has been demonstrated that the factors affecting the rheology of cement paste include the water content, packing density and solid surface area and that the combined effects of these factors may be evaluated in terms of the water film thickness (WFT). The present study aims to extend this concept of WFT to cement–sand mortar for the purpose of developing a mix design method based on the WFT. In the study, mortar samples with various water, cement and aggregate contents were produced for packing density, flowability, rheology, cohesiveness and adhesiveness measurements. It was found that both the WFT and cement/aggregate ratio have major effects on the rheological performance of mortar, but the WFT is still the single most important factor. Lastly, based on the test results, a design chart for the mix design of mortar was developed. 相似文献
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通过对新拌次轻混凝土的流变特性研究,分析了集料组成对新拌次轻混凝土屈服剪切应力和粘性系数的影响、新拌次轻混凝土的结构形成特点及其粒子的运动特点.结果表明:利用普通集料部分替代轻集料可显著改善混凝土的流变性能,提高水泥浆体的粘度、减小轻集料粒径可提高混凝土的匀质性,从而改善次轻混凝土的力学性能和耐久性. 相似文献
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通过再生骨料混凝土配合比试验,研究再生粗骨料材料性质对再生骨料混凝土配合比设计中水灰比、单方用水量和砂率等参数的影响;通过对试验结果的统计分析,建立了考虑再生骨料取代率影响的水胶比计算公式,考虑再生骨料吸水率和取代率影响的再生混凝土单方用水量计算公式,以及考虑再生骨料空隙率、取代率和表观密度影响的再生混凝土砂率计算公式。结果表明:再生骨料取代率、空隙率和吸水率对再生骨料混凝土配合比设计参数的影响较大;所得公式形式简单,反映了再生粗骨料的特点,提高了再生骨料混凝土配合比设计的精度,为再生混凝土配合比设计提供依据和参考。 相似文献
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基于BP网络的自密实混凝土配合比设计 总被引:3,自引:0,他引:3
原材料性能的波动对自密实混凝土性能影响很大,把水泥强度、砂石含泥量、砂石细度模数、石子的最大粒径、石子针片状含量、粉煤灰细度和粉煤灰烧失量这些原材料性能参数作为BP网络的输入,以对应的优化配合比作为网络的输出,用网络结构描述它们之间的非线性关系。利用正交试验数据样本完成了网络的训练并进行检验,计算结果表明,利用正交试验数据样本训练的BP网络可以预测不同情况下的配合比,预测精度高,完全可以代替繁重的实验室配合比设计。应用该技术可实现自密实混凝土配合比的实时优化,对控制自密混凝土的生产质量具有重要意义。 相似文献
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本文阐述了一种泵送混凝土的配合比设计方法。根据混凝土粗骨料与砂浆体积、细骨料与浆体体积的比例关系对混凝土流变性能的影响,提出以粗骨料拨开系数、细骨料拨开系数为基础,按照体积法计算混凝土配合比。该方法从实践中总结而来,能保证混凝土的工作性能满足要求,计算简便,混凝土体积准确,容易掌握。 相似文献
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《Construction and Building Materials》2010,24(5):640-649
This paper deals with the effect of fine aggregate particles on the rheological properties of high performance cement-based materials. The effect of narrow fractions of fine aggregate particles on the rheology of silica fume-modified low water cement systems was analysed by means of a mortar rheometer. Yield stress and plastic viscosity were derived for time intervals between 10 and up to 150 min after water addition, and comparison with the slump value taken by the flow table test was done. It is concluded that the fine aggregate particles act as water fixation points in the diameter range of 75–1000 μm, via surface area, whereas for higher particle diameters the governing factor in terms of the resistance to flow may be related to other physical phenomena, such as the particle dimension and the resultant friction forces. Moreover, the water requirement in order to give each system the same workability is performed by adjusting the water content on each system. Furthermore, a quantitative model is proposed to describe the characteristic initial torque peak and resistance to flow behaviour of high performance concrete, as function of the particle size of aggregate. The combined effect of silica fume and fine aggregate particles on the rheology parameters is discussed. 相似文献
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M.P. Seabra H. Paiva J.A. Labrincha V.M. Ferreira 《Construction and Building Materials》2009,23(2):1147-1153
Especially in rehabilitation works, the use of lime based mortars have been increasing due to the need of compatibility between the old and the new materials. The mortars fresh state properties are extremely important since determines the material workability and also have a great influence on its hardened state characteristics.In this work, the fresh state properties of aerial lime pastes and aerial lime based mortars were investigated. The torque variation with time and the mortar rheological parameters (relative yield stress and plastic viscosity) were obtained using a rheometer suitable for mortars. The correlation of rheological data with slump and relative density measurements was studied.The mortars workability is affected by several parameters, namely, the binder/aggregate and water/binder ratios, the kneading water content, the admixtures type and amount. The admixtures influence (type and amount) on the fresh state properties of aerial lime based mortars are discussed. The used admixtures were the most common ones for several mortars, such as a water-retaining agent, a plasticizer and an air-entraining agent. 相似文献
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超高性能混凝土抗高温爆裂性能试验研究 总被引:1,自引:0,他引:1
测定了含粗骨料超高性能混凝土与活性粉末混凝土的不同含湿量(质量分数,下同)试件在从常温加热至800℃过程中的抗高温爆裂性能.结果表明:含粗骨料超高性能混凝土的抗高温爆裂性能优于活性粉末混凝土.粗骨料的存在不仅降低了超高性能混凝土的内部应力,而且增大了钢纤维在砂浆基体中的分布密度,因此起到减轻混凝土爆裂的作用.试验中大量粗骨料从砂浆基体中剥离,这证实蒸汽压力是导致超高性能混凝土发生高温爆裂的重要因素.2种超高性能混凝土的0%含湿量试件均未发生爆裂,而含湿量在25%及以上的试件均发生了爆裂,且含湿量越大,试件爆裂越严重.可以用爆裂发生的温度范围和爆裂声响次数来判断超高性能混凝土高温爆裂的严重程度. 相似文献
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Geraldine Buchenau Dr.-Ing. Bernd Hillemeier Prof. Dr.-Ing. 《Beton- und Stahlbetonbau》2005,100(2):139-147
Falling-Ball Rheometer to prove Self-Compacting Concrete Self-compacting concrete (SCC) is a high-performance concrete whose performance is predicated by the flow characteristics of the fresh concrete mix. In a fresh state, SCC may be viewed as a two-phase suspension containing coarse disperse aggregates as well as a viscous mortar that, when compared to conventional concrete, achieves its specific flow characteristics through a relatively high mortar content. The selection of appropriate raw materials – particularly for manufacture of plastic mortars – are essential factors in determining the rheological properties and thus performance of the concrete. By adding organic or inorganic admixtures, or a combination thereof, one may influence the flow characteristics of the mortar. Mix design for SCC is largely dictated by the rheological properties of the fresh concrete, such that the volumetric design approach, as used for conventional concrete with a given design compressive strength, is no longer applicable. This paper reviews the possibility to optimize the viscosity of mortar by replacing cement by rock powders with the objective to design SCC with normal strength. A research investigation has been conducted, investigating the effect of rock powders on flow characteristics of mortar matrices. Self-compacting concrete requires a careful control of its flow behaviour. Fresh concrete acts as a non-Newtonian fluid. It is insufficient to describe the rheological behaviour of non-Newtonian fluids with a conventional one-point workability test. Rheological measurements are essential, to determine the flow behaviour dependent on the shear rate and to modify the mixture with the aim to achieve self-compacting properties. In order to measure the flow behaviour of SCC, the authors developed a rheometer which can be used simply. 相似文献
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研究了矿物掺合料与化学外加剂对3D打印砂浆流变性能、凝结时间及打印性能的影响.结果表明:复掺矿粉与硅灰可显著改善打印砂浆的流变性能,延长打印砂浆的可操作时间,提高打印砂浆的打印性能;随着减水剂掺量的增加,打印砂浆的黏度、屈服应力及触变性均逐渐降低,凝结时间延长,减水剂掺量过低或过高均会对打印砂浆的打印性能产生不利影响;掺加适量缓凝剂可降低打印砂浆的黏度和屈服应力,改善其挤出性;随着石膏掺量的增加,打印砂浆的表观黏度、屈服应力、触变性及有效打印高度均呈现先降后增趋势,而挤出性变化规律与之相反. 相似文献
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Eva Vejmelková Martin Keppert Stefania Grzeszczyk Bartłomiej Skaliński Robert Černý 《Construction and Building Materials》2011,25(3):1325-1331
Rheological, mechanical and durability properties of self-compacting concrete (SCC) mixes produced using blended binders containing metakaolin and blast furnace slag are studied. The rheological properties of SCC mix with metakaolin are characterized by significant yield stress and relatively low viscosity, while the mix with blast furnace slag shows zero yield stress and higher viscosity. The compressive strength of SCC with metakaolin grows very fast during the initial hardening period and remains significantly higher, as compared with the mix with blast furnace slag, up to 90 days. Durability properties of the mix containing metakaolin are excellent. Water absorption coefficient and water penetration depths are very low. The freeze resistance tests show zero mass loss after 56 cycles in deicing salt solution. 相似文献
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3D打印建筑砂浆的打印性能受其流变性能的影响,基于自制的3D打印设备和提出的3D打印建筑砂浆挤出性能与打印性能的测试评价方法,对3D打印建筑砂浆的流变性能、打印性能以及凝结时间的试验结果进行汇总分析,结果表明:具有良好打印性能的3D打印建筑砂浆须具有适宜的流变性能以及合适的凝结时间;可挤出性是实现3D打印堆积过程的前提,随着打印砂浆挤出性能的增加,打印高度有降低的趋势;可打印砂浆的流变性能处在一定的参数范围内,其范围为:表观黏度在4.0~7.0 Pa·s之间、屈服应力在50~80 Pa之间,触变性在900~2000 Pa/s之间。 相似文献