共查询到19条相似文献,搜索用时 703 毫秒
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《低温建筑技术》2015,(12)
水泥混凝土抗冻性是影响其耐久性的关键指标。本次通过水泥混凝土快速冻融试验研究了水灰比、循环次数、含气量、气泡特征参数、掺合料种类等对抗冻性影响的主次因素规律及变化趋势。研究结果表明:含气量、循环次数、掺合料的掺量是影响混凝土抗冻性的主要因素。水泥混凝土抗冻性随着水灰比的升高而降低;随着冻融循环次数的增加而下降;随着气泡间距系数的降低而提高;随着含气量的增加而提高,但当含气量低于4.2%时,混凝土前期抗冻性下降迅速,引气混凝土含气量控制在5.6%~6.4%时具有良好的抗冻性。水泥混凝土中添加一定量的粉煤灰或矿渣粉,混凝土的抗冻性随着掺合比例的增加而降低。但在相同掺量下,改善混凝土抗冻性的效果矿渣粉好于粉煤灰。 相似文献
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评价混凝土冻融破坏的指标参数较多,为研究这些评价参数对抗冻性的敏感程度,测试了不同含气量和粉煤灰混凝土的抗冻性能,着重从含气量、气泡间距系数、相对动弹性模量、相对耐久性指数、抗折强度损失率、剥落量6个方面分析混凝土冻融破坏。结果表明,含气量、气泡间距系数均是评价混凝土抗冻性的敏感指标,水冻环境和盐冻环境下分别增加抗折强度损失率和剥落量作为评价混凝土抗冻性的敏感指标。 相似文献
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通过宏观、微观以及孔结构的研究,开发满足快冻300次和快冻600次混凝土即F300的高抗冻混凝土和F600的超抗冻混凝土。研究结果表明,运用525#普通硅酸盐水泥时,在混凝土处于≤0.50的水灰比、50.5%的含气量、气泡间距系数低于300μm或平均气泡间距系数≤150μm情况下,混凝土达到F300的满足高抗冻混凝土的抗冻要求;在混凝土处于≤0.40的水灰比、50.5%的含气量、气泡间距系数低于300μm或平均气泡间距系数≤150μm情况下,混凝土达到F600的满足超抗冻混凝土的抗冻要求。 相似文献
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《混凝土与水泥制品》2016,(7)
对高原环境桥用高性能混凝土的配制技术与性能进行了研究。结果表明,采用骨料级配设计技术、粉煤灰和高性能减水剂双掺技术和引气技术配制的C50高性能混凝土具有早强、高强和低收缩性能,同时具有良好的抗冻性能。分析表明,控制含气量为4.5%~6.0%,气孔的孔径范围为40~280μm,气泡间距系数为120~150μm,其抗冻性均大于300次冻融循环。含气量是提升混凝土抗冻性的重要参数,而所引入气孔的性质也同样重要。适当增加含气量、减小孔径和气泡间距系数,可明显提升混凝土的抗冻性能。 相似文献
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通过使用掺量为30kg/m3的100目精细橡胶粉,在水灰比为0.42、蒸养时间为26h的条件下,研究橡胶混凝土蒸养后的抗冻性能.试验结果表明:蒸养制度未影响橡胶混凝土的抗冻性,标准养护和蒸汽养护下橡胶混凝土的气泡间距系数分别为0.130mm和0.141mm,均小于气泡间距系数临界值(0.200~0.250mm),从而提高了混凝土的耐久性. 相似文献
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对比了自制引气剂PYQ与常用引气剂K12、AES、AOS的溶液性能、新拌混凝土性能及硬化混凝土性能。结果表明:起泡能力从优到差依次为K12PYQAESAOS,泡沫稳定性从优到差依次为PYQAOSAESK12;保持混凝土初始含气量相同,气泡间距系数从小到大依次为PYQAOSAESK12,直径20~200μm有效气泡个数从多到少依次为PYQAOSAESK12,1 h含气量-硬化含气量-气泡间距系数-孔径分布-稳泡能力间存在关联性规律,1 h含气量越大,硬化含气量越大,气泡间距系数越小,20~200μm有效气泡个数越多,稳泡性越优,气泡间距系数可准确反映出引气剂引入的气泡稳定性;PYQ的引气及稳泡性能佳,对混凝土强度影响低,能有效改善混凝土的抗冻性。 相似文献
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从粉煤灰的掺量与品质、含气量、配比、水灰比、龄期、气泡特性等方面对二级配干硬混凝土抗冻耐久性的研究表明:选用品质好的粉煤灰和合适的掺量,掺入外加剂并使混凝土达到足够的含气量,可以大大地提高其抗冻耐久性;另外,采用合适的水泥用量对提高抗冻性也有明显的效果。 相似文献
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Erdoğan Ozbay Ahmet Oztas Adil Baykasoglu Hakan Ozbebek 《Construction and Building Materials》2009,23(2):694-702
In this study, mix proportion parameters of high strength self compacting concrete (HSSCC) are analyzed by using the Taguchi’s experiment design methodology for optimal design. For that purpose, mixtures are designed in a L18 orthogonal array with six factors, namely, “water/cementitious material (W/C) ratio”, “water content (W)”, “fine aggregate to total aggregate (s/a) percent”, “fly ash content (FA)”, “air entraining agent (AE) content”, and “superplasticizer content (SP)”. The mixtures are extensively tested, both in fresh and hardened states and to meet all of the practical and technical requirements of HSSCC. The experimental results are analyzed by using the Taguchi experimental design methodology. The best possible levels for mix proportions are determined for maximization of ultrasonic pulse velocity (UPV), compressive strength, splitting tensile strength and for the minimization of air content, water permeability, and water absorption values. 相似文献
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针对高寒地区混凝土抗冻耐久性问题,在混凝土中加入不同掺量的粉煤灰研究其抗冻性能,通过非金属声波检测仪进行冻融循环过程中混凝土强度无损测试,研究了冻融循环作用下混凝土强度损伤和动弹性力学参数的演化特征,分析了冻融循环过程中混凝土声波波速与力学性能变化规律。研究结果表明:掺入引气剂能够提高混凝土的抗冻性,相同引气剂掺量下,粉煤灰掺量为10%的混凝土抗冻性较好;冻融循环过程中,超声波纵波波速、横波波速与动弹性模量、动剪切模量均随着冻融循环次数的增加呈相似性衰减,且存在较高相关性。 相似文献
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W. Micah Hale Seamus F. Freyne Bruce W. Russell 《Construction and Building Materials》2009,23(2):878-888
The experimental program investigated the need for air entrainment in high performance concrete (HPC). Concrete mixtures with varying water to cementitious material ratios (w/cm) were subjected to ASTM C 666 (Procedure A). The variables for the mixtures were total air content and w/cm. The targeted total air contents for the mixtures were 2% (non-air entraining agent), 4%, and 6%. The w/cm ranged from 0.26 to 0.50. The 56 day compressive strengths varied from 41 to 96 MPa (6000–13,900 psi). The freeze-thaw tests continued until the specimen deteriorated, or until the specimen achieved 300 freeze-thaw cycles. For the materials used in the study, the research results show non-air entrained mixtures with w/cm less than 0.36 can be developed that have adequate frost resistance. The results also show for the mixtures developed in the study that a total air content of 4% is adequate to provide frost resistance for mixtures with a w/cm between 0.36 and 0.50. 相似文献
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为揭示短时冻融周期内土坡浅层的水热状况特征,选取典型短时冻土区域,采用现场气象监测与数值模拟相结合的技术手段对短时气温冻融周期内土坡浅层水热状况进行分析。结果表明:在3个月冻期总持续时间内,共有18次气温冻融周期,其中16次为1 d气温冻融周期,1次为2 d气温冻融周期,1次为6 d气温冻融周期。气温冻融周期内最低气温为-4.4℃,最高气温为10.8℃;日辐射峰值范围为41~827 W/m~2;平均风速为3.5~3.7 m/s;大气中水汽接近饱和状态。6 d与1 d气温冻融周期内土壤最大冻结时间分别为32 h与5 h,最大冻深分别为10 cm与5 cm,土壤含冰率分别为0.16与0.14,短时冻区应重点关注边坡浅层10 cm以内土壤强度的冻融损伤。1 d气温冻融周期内,土壤冻结时段一般为3∶00—8∶00之间。土壤冻结的开始时刻取决于最低气温,而土壤冻结持续时间取决于太阳辐射高低,若土壤冻结时间与太阳辐射时间相重叠或者气温处于土壤冻结温度以下的持续时间小于1.5 h,边坡土壤不易冻结。因此,同一边坡的阳面与阴面在土壤冻结开始时刻与冻结持续时间存在较大差异。 相似文献
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分别研究了不同浆骨比、含气量和水胶比情况下,掺入粉煤灰后高耐久性混凝土的抗碳化性能和抗氯离子渗透性能。研究结果表明:碳化深度随粉煤灰掺量的增加而增大;氯离子扩散系数随粉煤灰掺量的增加而减小,当粉煤灰掺量超过一定掺量时氯离子扩散系数又随粉煤灰掺量的增加而增加。碳化深度、氯离子扩散系数随含气量增加而减小,而当含气量大于4%时,碳化深度、氯离子扩散系数又随含气量的增加而增大;碳化深度、氯离子扩散系数随浆骨比(32.5/67.5至37.5/62.5)的增大而增大;水胶比越小的抗碳化性能越好、氯离子扩散系数越小。 相似文献
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Simulation and experimental analysis of a fresh air-handling unit with liquid desiccant sensible and latent heat recovery 总被引:1,自引:0,他引:1
This article introduces a liquid desiccant fresh air processor. Its driving force is low-grade heat (heat obtained from 65 – 75°C hot water). Inside the processor, the air is dehumidified by the evaporative cooling energy of the indoor exhaust air. A four-stage structure is used to increase the efficiency of the combined sensible and latent heat recovery from the exhaust air. A mathematical model of the fresh air processor was set up using Simulink®. A liquid desiccant fresh air processor was constructed and tested for outside air conditions of 29.1 – 33.6°C, 13.7 – 16.7g/kg humidity ratio, and supply air conditions of 23.6 – 24.2°C, 7.4 – 8.6g/kg humidity ratio. The average measured COP f was 1.6 (cold production divided by latent heat removed) for the range of conditions tested. The corresponding average COP sys of the system including the regenerator was 1.3 (cold production divided by heat input). The detailed operating parameters of each part of the test unit were also measured. The test data was compared with the simulated performance. The characteristic coefficients (such as the volumetric mass transfer coefficient of the air-water evaporative cooling module, etc.) in the mathematical model were modified to calibrate the model output to the measured data. The calibrated simulation model was used to investigate the control strategy of the fresh air processor. The flow rate of the strong solution into the unit and the number of operation stages may be controlled separately or together to meet different indoor air requirements at different outdoor conditions. The hot water driven liquid desiccant air conditioning system was compared with a typical vapor compression system with an average COP of 4.5; the pump and fan power of the proposed system was 40% of the combined chiller, pump, and fan consumption. We achieved savings of over 30% of the power consumption compared with the traditional system under the designed outdoor air conditions. 相似文献