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The influence of concrete mixes and commonly used mineral additions and their effects on the near surface performance of vertically cast concrete against controlled permeable formwork (CPF) are the focus of this study. Three grades of concrete (C25, C30 and C45) and mineral additives including GGBS and PFA have been tested for surface performance in situ with CPF. The various loadings were chosen to represent the minimum and maximum levels seen in standard industry practice. The range of tests used to characterise the near surface performance include subjective assessment of surface quality, surface hardness and surface tensile strength. Permeability studies of the liners after casting indicate that no excessive embedding of fine particles occurred irrespective of constituents used. Surface quality was dramatically improved in each case and changes to surface colour through densification were quantified. Near surface performance studies indicated a significant improvement for all systems studied. 相似文献
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Helena Figueiras Sandra Nunes Joana Sousa Coutinho Joaquim Figueiras 《Construction and Building Materials》2009,23(7):2518-2526
The work presented in this paper aims at contributing to sustainable construction through enhancement of durability of concrete structures. Full size precast elements were cast with both self-compacting concrete (SCC) and conventional vibrated concrete (CC) using controlled permeability formwork (CPF). SCC is known to impart a more homogeneous and finer microstructure, compared to conventional concrete, therefore leading to more durable reinforced and pre-stressed concrete structures. CPF enables, in fresh concrete, drainage of excess water and air besides retaining binder particles at the concrete surface, leading to a blow-hole free surface and enhanced quality of the outer layers. The research program developed was designed to compare performance of two different CPF systems and also assess the combined effect of using CPF on SCC compared to CC. 相似文献
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有机硅烷与透水衬里模板对提高混凝土表层渗透性试验研究 总被引:3,自引:1,他引:2
有机硅烷与透水衬里模板(CPF)都是通过降低混凝土表层渗透性而提高混凝土耐久性的技术,通过空气渗透性试验与表层水吸附试验(ISAT)分别研究了有机硅烷、透水衬里模板单独使用时,以及有机硅烷与透水衬里模板共同使用时对混凝土表面渗透性的影响,试验表明有机硅烷能有效降低普通混凝土表层水吸附作用但对空气渗透性没有明显影响,透水衬里模板对普通混凝土表层的空气渗透性与水吸附作用都有明显降低作用,有机硅烷和透水衬里模板同时使用能进一步提高混凝土表层上的抗渗透性. 相似文献
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采用透水模板衬与真空脱水工艺相结合的方法浇注低水灰比混凝土,探讨以中高强度配比的真空成型混凝土达到高强混凝土抗冲磨性能的可行性.试验结果表明: 降低水泥的比表面积可提高低水胶比混凝土的真空脱水率,进而提高混凝土抗冲磨性能;采用透水模板衬和真空脱水工艺相结合的方法,可使配制强度为C50的真空成型混凝土抗冲磨性能达到或超出配制强度为C70的非真空高强混凝土,由此可减少单方混凝土胶凝材料用量,有利于减少混凝土的收缩.真空脱水工艺提高混凝土抗冲磨性能的机理在于其明显降低了混凝土孔隙率,靠近表层的混凝土最可几孔径、临界孔径和平均孔径均明显减小,孔结构得到明显优化. 相似文献
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透水衬里模板(CPF)通过其滤层排除新拌混凝土表层水分和因振捣而富集于混凝土表层的气体来提高混凝土表层强度和抗渗透性。通过混凝土表层水吸附试验(ISAT)评价了透水衬里模板对混凝土抗渗透性的提高作用,并利用文献提供的混凝土表层水吸附试验(ISAT)与压汞法(MIP)之间的关系式分析了采用透水衬里模板后混凝土表层孔结构参数的变化。在对比分析用压力试验机获得的混凝土整体抗压强度与回弹法得到的表层抗压强度后,可以发现透水衬里模板可以提高混凝土的表层抗压强度而不是混凝土的整体抗压强度。 相似文献
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现浇钢筋混凝土楼板裂缝的成因与防治 总被引:3,自引:1,他引:2
对现浇钢筋混凝土楼板裂缝的原因进行了分析 ,阐述了现浇钢筋混凝土楼板裂缝的施工防治措施 ,提出了其裂缝的处理方法和有效控制现浇钢筋混凝土楼板裂缝的重要手段 相似文献
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《Building and Environment》2001,36(5):637-655
In recent years, there has been a renewed interest in heated concrete slab floors to provide for space heating in both residential and commercial buildings. The existing design procedures for these heating systems are based on simplified thermal models with several assumptions. In particular, the simplified models assume that both the upper and the lower concrete slab surface are isothermal and that the heat transfer through the bottom of the slab surfaces is uniformly distributed over the entire surface. In this paper, a more realistic and flexible model for heated or cooled concrete slab floors is considered to determine the heat transfer between the concrete slab and the ground. In particular, steady-state and steady-periodic semi-analytical solutions are developed to determine the temperature field within the ground medium and within the concrete slab-on-grade floor where hot or chilled water pipes are embedded. The solution presented in this paper is applied to determine the ground heat loss/gain for a heated or cooled floor under various design conditions including the level of floor insulation, and the temperature of the water pipes. These solutions are obtained using the interzone temperature profile estimation (ITPE) procedure. Detailed analysis is presented to determine the effect of the slab insulation configuration on soil and slab temperature field and on the monthly variation of the total slab heat loss. 相似文献
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Release of copper from a naturally aged copper roof on a shopping centre building in a suburban site of Stockholm has been measured during different rain events after its interaction with the internal drainage system and storm drains made of cast iron and concrete. Concentrations of copper removed by means of urban storm water from a nearby parking space have been determined for comparison. Predictions and measurements of the chemical speciation of released copper are discussed compared to the total concentration, and to threshold values for freshwater and drinking water.The results clearly illustrate that the major part of the released copper from the roof is readily retained already during transport through the internal drainage system of the building, a pathway that also changes the chemical speciation of released copper and its bioavailable fraction. Most copper, not retained by cast iron and concrete surfaces, was strongly complexed to organic matter. The median concentration of free cupric ions and weak copper complexes was less than, or within the range of reported no effect concentrations, NOECs, of copper in surface waters. The parking space contributed with significantly higher and time-dependent concentrations of total copper compared to measured concentrations of copper from the roof after the interaction with the drainage system. Most copper in the surface runoff water was strongly complexed with organic matter, hence reducing the bioavailable fraction significantly to concentrations within the NOEC range. Dilution with other sources of urban storm water will reduce the released concentration of copper even further.The results illustrate that already the internal drainage system and the storm drains made of cast iron and concrete act as efficient sinks for released copper which means that any installation of additional infiltration devices is redundant. 相似文献
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混凝土现浇楼盖裂缝的成因和控制 总被引:11,自引:0,他引:11
从混凝土材料本身、施工、设计三个方面分析了混凝土现浇楼盖产生裂缝的原因,并提出了相应的预防控制措施。指出当前混凝土现浇楼盖裂缝日趋增多的主要因素是混凝土材料的收缩和温度变形。 相似文献
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现浇空心板的质量控制 总被引:1,自引:0,他引:1
介绍了现浇混凝土空心板,分析了现浇混凝土空心板的优点,简述了现浇空心板的施工准备,并详细地阐述了现浇混凝土空心楼盖板的施工质量控制措施,以促进该技术的发展应用。 相似文献
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《Construction and Building Materials》2001,15(4):149-156
In this study, the effects of formwork, with drainage holes that are attached with different liners, on the physical properties of concrete surfaces are investigated. Nine formworks, three of them normal (reference) and six of them with drainage holes, were prepared. The three formworks, which had drainage holes, were attached with type I geotextile+hessian and the remaining three were attached with type II geotextile. Blow hole ratio, surface hardness by using the rebound hammer test, pull-off strength, carbonation, chloride penetration, sorptivity and abrasion resistance tests were measured on concrete blocks which were cast with the three types of formwork. It was observed that the concrete that was made with formwork attached with type II geotextile had better surface properties than that made with the reference formwork and formwork attached with type I geotextile+hessian. 相似文献
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不同粘结介质中CFRP筋锚固性能的试验研究 总被引:10,自引:1,他引:10
为寻求一种更好的粘结介质以改善CFRP筋粘结式锚具的锚固性能,通过静载试验研究了不同表面形状和锚固长度的CFRP筋在超高性能混凝土RPC、环氧铁砂、环氧石英砂和普通混凝土等四种不同粘结介质中的受力锚固特征。结果表明:CFRP筋的表面形状显著影响其锚固性能;CFRP筋在环氧铁砂和环氧石英砂中的锚固性能基本一致;在其他条件相同时,RPC对CFRP筋的锚固性能最好,环氧砂次之,普通混凝土较差;对于抗拉强度保证值2550MPa、直径10mm的表面压纹CFRP筋,其在抗压强度为130MPa的RPC中的锚固长度达到25d(d为CFRP筋的直径)时即可保证CFRP筋的强度予以充分发挥,而同样的CFRP筋在环氧砂和普通混凝土中的锚固长度为35d时亦不能保证CFRP筋被拉断。因此,在目前可供选择的粘结介质中,RPC作为综合性能优良的粘结介质可在粘结式锚具中对具有表面压纹的高强CFRP筋提供最有效的锚固。 相似文献
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总结了整体现浇电缆工作井的工作特点和不足,分析采用预制装配式电缆工作井的优势,指出后者亟须解决的关键技术问题和可能的解决办法。针对现有预制电缆工作井专利技术的不足,建议采用混凝土空心板技术,并综述了现浇混凝土空心楼盖的研究与应用现状。通过SAP2000分析了实际电缆工作井的受力状况,用现有混凝土理论按空心井壁进行配筋设计,将其与现浇混凝土实心井壁进行技术经济对比分析后可知:在预制装配式电缆工作井中采用混凝土空心板技术是可行的,可取得节省材料、减轻自重和减少拼装接缝的效益,但空心板在压弯受力状态下的承载力计算理论尚需作进一步的研究。 相似文献
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大跨度预应力现浇空心板设计工程实践 总被引:1,自引:0,他引:1
Tong Weimin 《建筑结构》2008,(5)
大跨度预应力空心板的设计有不同于普通混凝土空心板和预应力实心板之处,需要在设计中加以注意。基于近年来在北京地区做的大量的预应力现浇空心板的设计与施工工作,就预应力现浇空心板的工程设计中的一些要点及经验进行了简单的论述。 相似文献