Effect of high temperature and cooling regimes on the compressive strength and pore properties of high performance concrete

This paper describes the behavior of high performance concrete (HPC), compared with normal strength concrete (NSC), after subject to different high temperatures (800 and 1100°C) and cooling regimes (gradual and rapid cooling). Deterioration of compressive strength of the concrete was measured. The results obtained showed that the strength of both the HPC and NSC reduced sharply after their exposure to high temperatures. Thermal shock due to rapid cooling caused a bit more deterioration in strength than in the case of gradual cooling without thermal shock. However, thermal shock did not significantly increase the spalling of HPC. Mercury intrusion porosimetry (MIP) tests were carried out to measure changes in the pore size distribution in the concrete. Test results showed that the pore volume in the HPC increased much more than that in the NSC. A significant change in the cumulative pore volume was observed and the difference in cumulative pore volume between the two cooling regimes was less after subject to the peak temperature of 1100°C when compared with that of 800°C peak temperature.     

高温后不同冷却方式下自密实混凝土力学性能研究

对54个标准立方体和27个标准棱柱体C40自密实混凝土试件高温后,采用自然冷却和喷水冷却两种方式下的力学性能进行研究,并观察试块的表观特征及测量高温后损失率,结果表明:两种冷却方式下,500℃时混凝土试块的表观特征均发生显著变化;高温后质量损失率和峰值应变随温度升高而增大,弹性模量随温度升高而下降;试块的抗压强度、劈拉...     

若干主要因素对蒸压加气混凝土性能的影响

通过试验就铝粉膏掺量、拌合水温度、水料比和六偏磷酸钠掺量对蒸压加气混凝土(以下简称AAC)干密度和抗压强度的影响进行了研究.结果表明,随铝粉膏掺量的增加,AAC的干密度逐渐降低;随拌合水温度升高,AAC的干密度先降低后略微升高,抗压强度先降低后基本保持不变;随水料比增大,AAC的干密度先降低后升高,抗压强度不断降低;随六偏磷酸钠掺量的增加,AAC干密度先降低后有所增加,抗压强度先增加后有所降低.合适的铝粉膏掺量为0.30％.～.0.35％,拌合水温度为60～65℃,水料比为0.60～0.63,六偏磷酸钠掺量为0.7％～1.0％.     

砌筑砂浆对蒸压加气混凝土砌体力学性能的影响

研究普通砌筑砂浆、保水砌筑砂浆、薄层砌筑砂浆和保温砌筑砂浆等4种砌筑砂浆对B04、B06级蒸压加气混凝土砌体力学性能的影响。结果表明,使用较高保水率的砌筑砂浆能明显提高砌体的轴心抗压强度、通缝抗剪强度等力学性能。相比于普通砌筑砂浆,薄层砌筑砂浆使B04和B06级砌体的通缝抗剪强度分别提高116%和100%,砌体轴心抗压强度分别提高30%和61%。同时采用扫描电子显微镜观察经载荷破坏后的砌体与砌筑砂浆界面的微观形貌,进而分析了不同砌筑砂浆对蒸压加气混凝土砌体力学性能的作用机理。     

高温条件下混凝土施工中的裂缝分析与控制

结合阿联酋混凝土工程施工状况，对影响混凝土裂缝问题的因素作了简要分析，总结了一些相关认识和观点，并提出了具体的预防措施，以使混凝土裂缝的发展降低到最小程度。     

Influence of zeolite additive on properties of autoclaved aerated concrete

In this experimental study, the effect of zeolite on the properties of autoclaved aerated concrete (AAC) was investigated. Zeolite was used as a quartzite replacement in conventional AAC mixtures. The zeolite containing AAC (ZAAC) specimens were prepared at bulk densities of 270–500 kg/m³. The specimens were examined by X-ray diffraction, X-ray fluorescence, and thermal analysis. Bulk density, compressive strength and thermal conductivity parameters were investigated. According to the results of research, the commercial AAC is mainly composed of tobermorite, quartz and anhydrite, but the specimens of ZAAC, besides tobermorite and quartz, contain unreacted anhydrite and clinoptilolite phases. XRD patterns of ZAAC obtained after treatment at 700–1000 °C show that wollastonite, gehlenite and orthoclase are the new phases formed. It was observed that application of zeolite in AAC significantly lowered the thermal conductivity of autoclaved products (0.08–0.12 kcal/m h °C) providing the compressive strength at the level of 1.22−3.34 N/mm².     

纤维混凝土高温后力学性能的研究

阐述了混凝土高温力学性能研究现状及纤维混凝土的优良特性,揭示了纤维混凝土高温力学性能的研究意义。通过试验,揭示了纤维混凝土强度随温度变化规律,并分析了温度对纤维混凝土力学性能的影响机理。研究表明:低于200℃时,纤维混凝土抗压强度均有所增加;200℃后,抗压强度开始下降;高于400℃时,纤维混凝土抗压强度下降明显,但是下降的速度较素混凝土小得多。温度低于600℃时,钢纤维混凝土抗折强度下降十分缓慢;600℃时,钢纤维混凝土相对残余抗折强度值为81%,素混凝土已下降至59%。     

伊通加气混凝土砌块基本性能试验研究

对伊通双排孔和单排孔不同强度的加气混凝土砌块进行了轴压和通缝抗剪试验，并对试验数据做了分析，旨在了解加气砌块砌体的基本性能，了解砂浆强度和砌块强度对砌体强度的影响。     

基于温度荷载的加气混凝土填充墙裂缝研究

对温度荷载下加气混凝土填充墙的受力进行理论分析,采用数值模拟方法研究裂缝的可能开展部位,并针对裂缝防治提出了一些合理的建议,以有效解决填充墙裂缝问题,从而确保建筑产品质量。     

Effect of moisture and temperature on the mechanical properties of concrete

Concrete mechanical properties are determined under laboratory conditions of ideal air temperatures between 20 and 22 °C and relative humidity between 40% and 60%. This paper describes the development of concrete mechanical properties when cured under different environmental conditions. Tests to measure modulus of elasticity, compressive strength, and split tensile strength were conducted at varying temperatures and humidity conditions to examine their effects on normal concrete. An environmental chamber was constructed in the laboratory using available materials. The chamber works in conjunction with a freezer to provide chilled air and a heat gun to provide hot air. The heating and cooling functions were controlled via a microcontroller. The moisture content in the concrete specimens was controlled by massing the specimens. The results indicate that concrete strength and modulus of elasticity are inversely related to temperature as well as moisture content in the concrete. Concrete modulus of elasticity was directly related to concrete compressive strength in both temperature and moisture testing. Mathematical formulas were developed for modulus of elasticity, compressive strength, tensile strength, and Poisson’s ratio.     

高强混凝土高温条件下爆裂的原理及模型

本文从混凝土本身的物理,力学性能入手研究了高强混凝土在高温条件下的爆裂原理,并给出了相应的模型以便为今后改善它的性能而采取措施提供了一个理论参考。     

威维纤维混凝土的高温后力学性能研究

火灾的发生不仅会破坏建筑物,而且会对人们的生命财产安全产生危害。传统混凝土材料的抗拉强度低,易发生脆性变形等缺点在火灾中就可能成为致命的安全隐患。威维纤维作为一种特殊玻璃纤维,其加入对传统混凝土的抗拉强度及脆性均有良性改变。了解有关玻璃纤维混凝土的研究现状,并通过试验了解威维纤维在高温作用后对混凝土究竟有多少增强作用,对威维纤维混凝土高温后增强效果提供数据及理论依据。     

不同冷却条件混凝土显微痕迹研究

对相同温度下,喷水冷却与自然冷却混凝土试样进行扫描电子显微镜(SEM)对比,分析特征部位的变化特点。结果表明,和自然冷却相比,喷水冷却条件下,混凝土试样的C-S-H凝胶结构和骨料与水泥浆体界面处发生特征变化时的温度更低,并且混凝土的微观形貌随温度呈现一定的变化规律。对分析火场中混凝土的受热温度,更准确地确定起火部位和起火点具有参考意义。     

高温天气条件下大体积混凝土裂缝的控制设计

结合工程实例，针对大体积混凝土产生裂缝的自身原因，提出在高温天气条件下预防大体积混凝土裂缝的施工技术措施，防止有害裂缝的产生，经过工程实际应用，未发现贯通性裂缝或其他有害裂缝。     

玻化微珠对高强混凝土高温性能影响研究

阐述膨胀玻化微珠的保温特性;研究了玻化微珠对高强混凝土材料在不同温度环境下力学性能的影响.研究结果表明:随着玻化微珠掺加比例的增加,高强混凝土在高温下的抗爆裂性能得到有效的改善.     

组成对铁尾矿加气混凝土性能的影响研究

以铁尾矿为主要原料,以铝粉为发气剂,在固定蒸压条件下,从加气剂的角度研究对加气混凝土抗压强度、表观密度和导热系数的影响。通过对制备的加气混凝土性能的分析评价,确定原材料组成和加气剂的最佳掺量。研究结果表明:当铁尾矿掺量在59%~63%范围内变化时,随着铁尾矿掺量的增加,加气混凝土的抗压强度逐渐升高而后逐渐降低,表观密度逐渐降低,而后趋于稳定,导热系数逐渐减小而后呈现略微增加趋势;当石灰掺量在23%~27%范围内变化时,随着石灰掺量的增加,加气混凝土的抗压强度逐渐增加,表观密度和导热系数均有降低趋势;当水泥掺量在8%~12%范围内变化时,随着水泥掺量的增加,加气混凝土的抗压强度逐渐降低而后逐渐增加,表观密度逐渐降低,导热系数先增加而后逐渐降低。通过正交试验确定的最优配合比为:铁尾矿61%、石灰27%、水泥8%、石膏4%、铝粉0.14%。对应此配合比,加气混凝土的抗压强度为2.91 MPa,表观密度为520 kg/m3,导热系数为0.078 W/(m·K)。     

混凝土冻结特征温度预测方法研究

根据已有文献的试验数据建立了混凝土孔隙结构分析的数学模型。基于孔隙结构的研究结果,提出了在冻融循环下混凝土中形成冰晶核的温度和混凝土冻结特征温度的预测方法。预测值与现有的试验观察数据有很好的一致特性。该预测方法可以可靠地用于评估混凝土的状态,判别其处于安全状态还是亚安全状态。     

外加剂与活性矿物掺合料对粉煤灰加气混凝土性能影响

研究了外加剂和活性矿物掺合料对免蒸压加气混凝土性能的影响,试验结果表明,原材料组合方案中通过复掺早强剂和磨细矿渣粉,加气混凝土的件能得到了显著改善.在85℃热养护工艺下制备的B08级加气混凝上性能指标达到了CB11968-2006<蒸压加气混凝土砌块>标准要求.     

尾矿微粉加气混凝土砌块的自保温性能研究

通过对专用砂浆加气混凝土墙体、普通砂浆加气混凝土墙体及加气混凝土清水墙进行稳态热传递试验,测定出三种墙体的传热系数。结果表明在清水墙上采用专用砂浆界面抹3~5 mm厚,再铺设纤维网格布,最后用10 mm厚专用砂浆抹面的专用砂浆加气混凝土墙的传热系数值小于1.0 W/(m~2·K),满足相关规范要求。     

不同预处理方式的半干法脱硫灰对蒸压加气混凝土性能的影响

研究了不同预处理方式的半干法脱硫灰对制备的加气混凝土性能和微观结构的影响。结果表明,半干法脱硫灰在低温潮湿环境下生成了碳硫硅钙石,该物质会在制备加气混凝土时降低其抗压强度;采用加水消化后的半干法脱硫灰提高了加气混凝土的抗压强度,降低其绝干密度;采用球磨磨细后的半干法脱硫灰提高了加气混凝土的抗压强度,降低其绝干密度,并减少了化学组分中CaSO4的含量,使托贝莫来石的结晶度提高,空间分布更加紧密。