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1.
Investigations on the effects of W/C ratio and silica fume on the autogenous shrinkage and internal relativehumidity of high performance concrete (HPC), and analysis of the self-desiccation mechanisms of HPC showed that the autogenous shrinkage and internal relative humidity of HPC increases and decreases with the reduction of W/C respectively; and that these phenomena were amplified by the addition of silica fume. Theoretical analyses indicated that the reduction of RH in HPC was not due to shortage of water, but due to the fact that the evaporable water in HPC was not evaporated freely.The reduction of internal relative humidity or the so-called self-desiccation of HPC was chiefly caused by the increase in mole concentration of soluble ions in HPC and the reduction of pore size or the increase in the fraction of micro-pore water in the total evaporable water (Tr/Tte ratio). 相似文献
2.
INDRODUCTIONMeso-poroussilicafilmswithanexcellentheat-insulatingpropertyandtherelativelylowdielectricvalueplayparticularlyimportantroleinelectronicandmagneticdevices(Moonetal.,1997),etc.;thosewithporesizesof5nmto50nmarealsoofinterestforapplicationsinphotonics,optoelec-tronics,lightweightstructuralmaterialthermalin-sulation,opticalcoating(Moonetal.,1997;HusingandSchulert,1998;Davis,2002).Theirspecialnetworkstructureisusedinsounddetector(HusingandSchubert,1998);theirexcellentinsulatingpro… 相似文献
3.
Shrinkage and cracking behavior of high performance concretes containing chemical admixtures 总被引：1，自引：0，他引：1
Modern concretes often incorporate several chemical admixtures to alter the properties of fresh or hardened concrete. In this work, the influences of three types of chemical admixtures, calcium nitrite inhibitor (CNI), retarder (D-17) and superplasticizer (W-19) on free shrinkage and restrained shrinkage cracking of high performance concrete were experimentally investigated. The test results showed that, with the same water to binder ratio (0.4), mixtures containing D-17 of 0.25 percent or higher ratio of W-19 (2.76 percent) all exhibited a reduction in free shrinkage and shrinkage cracking width. However, the incorporations of various ratios of CNI into mixtures led to an increase in free shrinkage and shrinkage cracking width as compared to control mixture. In order to study the influence of CNI, the microstructure of concrete mixture containing CNI were investigated by Mercury Intrusion Porosimetry as well as Scanning Electronic Microscopy(SEM) technique. 相似文献
4.
A homogeneous crack-free nano- or meso-porous silica films on silicon was fabricated by colloidal silica sol derived by hydrolyzing tetraethyl orthosilicate (TEOS) catalyzing with (C4H9)4N OH- in water medium. The solution with ratio of H2O/TEOS≥15, R4N and glycerol as templates, combining with the hydrolyzed intermediate, controlled the silica aggregating; the templated silica film with heterostructure was developed into homogeneous nano-porous then meso-porous silica films after being annealed from 750 ℃ to 850 ℃; the formation mechanism of the porous silica films was discussed; morphologies of the silica films were characterized. The refractive indexes of the porous silica films were 1.256-1.458, the thermal conductivity < 0.7 W/m/K. The fabricating procedure and the sequence had not been reported before. 相似文献
5.
Super absorbent polymers (SAPs) are gradually being applied in concrete production as internal curing agents.SAP can effectively reduce early age autogenous shrinkage of concrete,alleviate the hazards caused by concrete cracking and improve its freeze–thaw resistance.However,the relationships between SAP dosage,SAP particle size and the water–cement ratio of concrete have certain influences on the evolution of the compressive strength of SAP-incorporated concrete.In this study,experiments were conducted to investigate the relationships between the water–cement ratio of concrete,the SAP dosage and SAP particle size.The significant factors influencing concrete strength are determined and equations are proposed for predicting the strength of SAP-incorporated concrete at 3,7 and 28 days.The findings from this study,such as the SAP dosage should not be larger than 0.2%,are expected to form a theoretical basis for the rational use of SAP as an additive to concrete. 相似文献
6.
姚志雄 《福建工程学院学报》2015,(1):10-14,53
结合福建当地材料,配置C50等级高性能混凝土,研究不同矿物质及掺量对拌合物工作性、劈裂强度及耐久性等影响。试验得到粉煤灰、矿粉在改善拌合物工作性、抗渗性及劈裂强度等指标的较优掺量及影响规律。双掺性能更优,体现了其在粒形级配改善,工作性提高及火山灰效应的复合优势。提出可综合考虑质量变化率、相对动弹性模量及强度等的混凝土损伤程度指标,对混凝土在快速冻融、盐水腐蚀等因素共同作用下的损伤情况进行半定量评估。结果表明,素混凝土损伤程度最大,而矿粉掺量20%和粉煤灰掺量15%的损伤指标明显降低,表明该掺量下混凝土的耐久性能明显提高。 相似文献
7.
研究了粉煤灰掺量对高性能混凝土自生收缩的影响,试验结果表明:随着粉煤灰掺量的增加,高性能混凝土的自生收缩随之减少.根据试验结果回归出的自生收缩应变函数的计算值与试验值较为吻合. 相似文献
8.
粉煤灰在混凝土中的强度贡献与W/C的大小密切相关。在中高W/C下，粉煤灰28天内对强度的贡献是有限的，W/C愈大，贡献程度愈小；到90天以后，随着龄期的增长和粉煤灰活性的发挥，其对强度的贡献逐渐增大，粉煤灰混凝土强度将会逐渐赶上或超过基准混凝土。在低W/C下，粉煤灰掺量在一定范围内增加不会明显引起混凝土早期强度下降，W/C愈小，粉煤灰对混凝土强度贡献愈大，建议粉煤灰应作为混凝土中一个独立组分参与配合比设计，才能最充分利用粉煤灰在混凝土中的作用。 相似文献
9.
探讨将具有良好弹性和柔韧性的废旧轮胎橡胶作为粗、细骨料,掺入混凝土进行材料改性、以及利用硅灰进行材料性能提升的可行性。试验研究结果表明:轮胎橡胶颗粒替代砂石骨料掺入混凝土后,其抗压强度、抗折强度以及弹性模量均随着轮胎橡胶骨料含量的增加而降低。粗橡胶颗粒对于强度的削弱要明显大于细橡胶粉。但是,当粗橡胶颗粒掺量不超过10%,细橡胶粉掺量不超过25%时,改性后混凝土力学性能没有太大的降低。而且在此掺量下,掺入少量的硅灰,就可以大大提升橡胶集料混凝土的力学性能,使其强度接近或超过普通混凝土。与普通混凝土相比,橡胶混凝土破坏过程柔和缓慢,特别是细橡胶集料混凝土具有更好的韧性。 相似文献
10.
A new type of green reactive powder concrete (GRPC) with compressive strength of 200 MPa is prepared by utilizing composite mineral admixtures, natural fine aggregates, and short and fine steel fibers. The quasi-static mechanical properties (mechanical strength, toughness, fracture energy and interfacial bonding strength) of GRPC specimens, cured in three different types of regimes, are investigated. The experimental results show that the mechanical properties of the C200 GRPC made with the powder binders that is composed of 40% of Portland cement, 25% of ultra fine slag, 25% of ultra fine fly ash and 10% of silica fume are better than the others'. The corresponding compressive strength, flexural strength and fracture energy are more than 200 MPa, and 30 000 J/ m2 respectively. The dynamic tensile behavior of the C200 GRPC is also investigated through the split Hopkinson pressure bar (SHPB) according to the spalling phenomenon. The dynamic testing results demonstrate that strain rate has an important effect on the dynamic tensile behavior of GRPC. With the increase of strain rate, its peak stress and relevant strain increase. The GRPC exhibits an excellent strain ratio stiffening effect under the dynamic tensile load with high strain ratio, resulting in a significant change of the fracture pattern. 相似文献
11.
Le Bourg E 《Learning & behavior》2005,33(3):265-276
The learned suppression of photopositive tendencies was studied at the individual level in young flies of both sexes. In a
T-maze, flies had to choose between an arm leading to a lighted vial associated with an aversive stimulus (i.e., a solution
of quinine chlorhydrate deposited on a filter paper in the vial) and another arm leading to a darkened vial free of quinine.
The present experiments were carried out to determine the roles of quinine and relative humidity in the maze. The flies avoided
the lighted vial containing quinine even if they had no tarsal contact with quinine, and this result was not due to any odor
of quinine. Subsequent experiments showed that relative humidity in the lighted vial, and probably in the arm leading to it,
was an aversive stimulus, which partly explains why the flies avoided the lighted vial. However, in conditions in which the
flies had tarsal contact with water or quinine it was confirmed that flies trained with quinine have higher avoidance scores
than those trained with water only. Moreover, individual aversion to humidity was not correlated with the individual avoidance
score: At similar levels of motivation (i.e., similar levels of aversion to humidity), some flies learn to avoid the lighted
vial containing quinine whereas others do not. All these results show that, in addition to quinine, humidity is an unconditioned
aversive stimulus in our paradigm and thus needs to be tightly controlled in experiments of conditioned avoidance. 相似文献
12.
In this paper, an experimental study on the sulphate attack resistance of high-performance concrete (HPC) with two different water-to-binder ratios (w/b) under compressive loading is presented. The sulphate concentration, compressive strength, and the mass change in the HPC specimens were determined for immersion in a Na2SO4 solution over different durations under external compressive loading by self-regulating loading equipment. The effects of the compressive stress, the w/b ratio, and the Na2SO4 solution concentration on the HPC sulphate attack resistance under compressive loading were analysed. The results showed that the HPC sulphate attack resistance under compressive loading was closely related to the stress level, the w/b ratio, and the Na2SO4 solution concentration. Applying a 0.3 stress ratio for the compressive loading or reducing the w/b ratio clearly improved the HPC sulphate attack resistance, whereas applying a 0.6 stress ratio for the compressive loading or exposing the HPC to a more concentrated Na2SO4 solution accelerated the sulphate attack and HPC deterioration. 相似文献
13.
The efficiency of chlorine and chloramines disinfection on biofilm development in a simulated drinking water distribution system was investigated by using heterotrophic bacterial spread plate technique. The experiments were carried out with four annular reactors （ARs） with stainless steel （SS） or copper （Cu） material slides. The results showed that there were fewer bacteria attached to Cu slides without a disinfectant compared with those attached to SS slides. When the water was disinfected with chloramines, the heterotrophic plate counts （HPCs） on the biofilm attached to the Cu slides were significantly lower （by 3.46 log CFU/cm^2） than those attached to the SS slides. Likewise, the biofilm HPC numbers on the Cu slides were slightly lower （by 1.19 log CFU/cm^2） than those on the SS slides disinfected with chlorine. In a quasi-steady state, the HPC levels on Cu slides can be reduced to 3.0 log CFU/cm^2 with chlorine and to about 0.9 log CFU/cm^2 with chloramines. The addition of chloramines resulted in a more efficient reduction of biofilm heterotrophic bacteria than did chlorine. We concluded that the chlorine and chloramines levels usually employed in water distribution system were not sufficient to prevent the growth and development of microbial biofilm. The combination of copper pipe slides and chloramines as the disinfectant was the most efficient combination to bring about diminished bacterial levels. 相似文献
14.
通过对空气源热泵热水器的性能进行实验研究,考察了空气的相对湿度对其性能的影响。实验结果表明：空气的相对湿度对蒸发压力、COP和吸气温度等性能有一定的影响;相对湿度的增大会导致蒸发器表面冷凝水增多,有效润湿面积增大,空气侧与制冷剂侧换热系数增加,最终导致蒸发器潜热换热量增加,从而强化了传热。 相似文献
15.
通过设计在不同配合比的人工砂和天然砂试验,定性的找到了不同配比与人工砂混凝土抗压强度及干缩性的关系曲线。实验研究结果表明,随着人工砂掺量的增加,人工砂混凝土抗压性能有明显的提高,但是其干缩性能越差。因此,人工砂与天然砂的配合比为3:2时,C40人工砂混凝土有较好的抗压性能和干缩性能,能够达到相应规范的硬性指标。 相似文献
16.
卢静 《泰州职业技术学院学报》2012,12(2):25-27
当传统的3P词汇教学模式受到抨击后,新的词汇教学理念纷纷涌现,但高职学生并未因此而从如何记忆词汇的困惑中解放出来。笔者在多年的词汇教学中,通过研究学生课堂学习和自主学习词汇的过程和结果,总结出了一些适合高职学生的词汇教学方法。 相似文献
17.
常青 《泰州职业技术学院学报》2012,12(1):63-64
随着氯碱企业氯气干燥工艺的改进,设备和下游涉氯产品对水份要求的提高,,大部分氯碱厂液氯含水量都能达到400mg／L以下,有些厂能达到50mg／L以下。无水高氯酸镁是吸水性较强又不和氯气反应的干燥剂,气体通过高氯酸镁的剩余湿度低至O．0002mg／L,吸水后成为三水过氯酸镁,可用于液氯中微量水分的测定。 相似文献
18.
为了使表面形貌减阻效果的水洞试验结果可以模拟和预测自由边界的结果、使水洞试验中验证过的有效减阻措施可以成功运用到无限场的情况，该文采用当今最流行的数值模拟方法，基于FLUENT软件对有水洞壁的模型试验和自由边界的无限场模型进行模拟。结果表明，水洞试验的阻塞比不得超过25％，否则在水洞试验中验证的有效减阻措施将无法应用到自由边界的无限场。在水洞试验阻塞比的有效范围内，随着阻塞比的增大或来流速度的增大，表面摩擦系数随之增大。 相似文献
19.