超声回弹法对混凝土强度早期预测

本文根据合肥地区常用混凝土材料、外加剂、配合比、施工工艺及养护条件,分析不同强度等级混凝土强度随龄期变化特点以及7d龄期与28d龄期混凝土强度相关性。通过测量7d龄期混凝土超声波速和回弹值,根据建立的合肥地区超声回弹测强曲线预测7d早龄期混凝土强度并由此对28d龄期混凝土标准强度进行了推定,应用结果表明能较好符合实际。     

短龄期老混凝土与新混凝土粘结的劈拉强度研究

实际工程新老混凝土粘接时,老混凝土龄期可能从初凝至数十年。目前,对短龄期老混凝土与新混凝土粘接劈拉强度研究较少,本文在不同界面剂、不同浇筑结合方式下研究了老混凝土龄期从初凝至28d的新老混凝土的粘结劈拉强度,发现粘结劈拉强度随老混凝土龄期增大而减少,并逐渐趋于稳定;界面剂的使用提高了新老混凝土的粘结劈拉强度,水泥砂浆界面剂的效果略优于水泥净浆界面剂;水平结合的劈拉强度均远大于竖直结合的劈拉强度;在机理分析的基础上拟合出粘结劈拉强度随老混凝土龄期变化的公式。     

水灰比对普通混凝土抗二氧化硫腐蚀性能影响研究北大核心

长期处于工业环境条件下的混凝土结构或构件,在含二氧化硫环境条件下,会发生类似于碳化的中性化反应,影响混凝土结构或构件耐久性能,带来经济损失。通过加速硫化试验研究不同水灰比的混凝土在不同腐蚀龄期的质量、强度及后期元素变化历程,以硫化深度作为混凝土抗硫化性能的研究指标,试验结果表明:硫化反应过程中,混凝土质量及强度变化率呈现先增后减的趋势,硫化深度随腐蚀龄期的增大而增大;水灰比越大,混凝土质量变化率随腐蚀龄期增减变化越明显,混凝土抗压强度变化率随龄期增减变化幅度也越大,相同龄期内腐蚀深度也越大,抗硫化能力越差。     

水灰比对普通混凝土抗二氧化硫腐蚀性能影响研究

长期处于工业环境条件下的混凝土结构或构件,在含二氧化硫环境条件下,会发生类似于碳化的中性化反应,影响混凝土结构或构件耐久性能,带来经济损失。通过加速硫化试验研究不同水灰比的混凝土在不同腐蚀龄期的质量、强度及后期元素变化历程,以硫化深度作为混凝土抗硫化性能的研究指标,试验结果表明:硫化反应过程中,混凝土质量及强度变化率呈现先增后减的趋势,硫化深度随腐蚀龄期的增大而增大;水灰比越大,混凝土质量变化率随腐蚀龄期增减变化越明显,混凝土抗压强度变化率随龄期增减变化幅度也越大,相同龄期内腐蚀深度也越大,抗硫化能力越差。     

不同龄期混凝土高温后力学性能研究

为研究不同龄期混凝土高温后的力学性能变化,对不同养护龄期的混凝土设置不同的温度和继续养护时间,对其抗压强度和劈裂抗拉强度进行试验。结果表明：各龄期混凝土的抗压强度和劈裂抗拉强度随经历温度的升高基本呈下降趋势,但当温度不高于100 ℃,龄期不大于14 d 时,其强度反而略有上升。混凝土经历相同温度情况下,高温时龄期越早,强度越低。随着高温后继续养护时间的增加,混凝土的强度逐渐恢复,且高温龄期越早,恢复程度越高,但强度恢复增幅逐渐降低。     

考虑龄期与气象条件的混凝土强度验算方法

通过对工程中同条件不同月份混凝土试块的抗压强度数据统计,分析了在温度、湿度作用下,混凝土自然养护强度随龄期、水灰比与气象条件而变化的规律,并提出考虑龄期与气象条件下自然养护混凝土强度的验算方法,从而为上海地区现浇混凝土结构工程施工提供依据。     

掺合料混凝土早期强度的试验研究

通过不同掺合料种类及掺量的掺合料混凝土早期抗压强度试验,分析粉煤灰掺量、矿粉掺量、煤矸石掺量对混凝土强度的影响规律,并研究双掺、三掺掺合料对混凝土强度的交互作用。研究结果表明:随着粉煤灰掺量的增加,粉煤灰混凝土抗压强度减小,但后期抗压强度增长幅度增大;矿粉掺量对矿粉混凝土的抗压强度和强度增长规律的影响不明显;掺入小于20%的煤矸石混凝土强度早期强度明显降低而后期强度变化不明显,掺入超过30%的煤矸石各龄期混凝土抗压强度均有明显降低;在矿粉混凝土中掺入粉煤灰,混凝土抗压强度随粉煤灰掺量的增加而减少,但减小幅度随龄期的增长而减小;在粉煤灰混凝土中掺入矿粉,混凝土强度有不同程度的提高;在煤矸石混凝土中掺入粉煤灰,混凝土抗压强度随粉煤灰掺量的增加而减小,减小幅度随龄期的增长而变化不大;在粉煤灰混凝土中掺入煤矸石会导致混凝土早期强度降低但后期强度提高;在煤矸石混凝土中掺入小于40%矿粉时混凝土抗压强度略有提高,而掺入超过40%矿粉时抗压强度降低;若在矿粉混凝土中掺入煤矸石,对矿粉掺量小于40%的混凝土强度影响不大,矿粉掺量大于40%时混凝土强度降低。     

石灰岩骨料混凝土弹性模量与强度相关性研究

试验研究了不同强度等级的石灰岩骨料混凝土的抗压强度、弹性模量随龄期发展规律,并与砂岩骨料混凝土进行了比较.通过数值模拟,建立了石灰岩骨料混凝土的抗压强度、弹性模量与龄期之间的相互关系模型.结果表明：不同强度等级的石灰岩骨料混凝土弹性模量发展比抗压强度快,且比砂岩骨料混凝土高;不同强度等级、不同岩性骨料混凝土的弹性模量与抗压强度平方根均呈线性关系,随强度等级的增大,石灰岩骨料混凝土弹性模量增长减缓,砂岩骨料混凝土则与之相反.     

基于等效龄期的大体积粉煤灰混凝土强度检测与分析

以秋冬季自然养护大体积粉煤灰混凝土为研究对象,实施了龄期14、28、56、91 d的钻芯和回弹试验。对不同钻芯深度的芯样强度进行了比较,基于等效龄期对钻芯和回弹的强度测试结果进行了比较研究。结果表明:秋冬季自然养护条件下,至龄期91 d时混凝土抗压强度才接近其设计强度;龄期14 d钻芯试样内部强度高于外部强度,28 d后试样内外钻芯强度趋于一致;与推算标准养护强度相比,钻芯强度稳定在其0.84~0.88之间,而回弹强度均在其1.21倍以上,且随龄期增长变化较大。钻芯强度更能体现实际结构混凝土强度。     

硫酸盐腐蚀对透水混凝土抗压强度及透水性能的影响

采用体积法配制了3种不同透水混凝土,对其不同硫酸盐腐蚀龄期(30、60、90、120 d)的抗压性能及透水性能进行研究,分析了硫酸盐对透水混凝土的腐蚀机理。结果表明:随硫酸盐腐蚀龄期的延长,透水混凝土的抗压强度有不同程度的降低;腐蚀龄期一定时,骨料粒径越小,其抗压强度的降幅越大。透水系数随腐蚀龄期的延长有增大的趋势,腐蚀龄期一定时,骨料粒径越小,其透水系数的提升幅度越大。硫酸盐与混凝土内部集料反应,生成物体积发生膨胀而导致混凝土内部开裂,使混凝土整体强度降低;并导致混凝土的胶凝物质含量下降,由于生成物自身强度较低,使混凝土的粘结力随之下降,宏观强度降低。     

Influence of supplementary cementitious materials on engineering properties of high strength concrete

The influence of supplementary cementitious materials (SCMs), namely silica fume, metakaolin, fly ash and ground granulated blast-furnace slag, on the engineering properties of high strength concrete (HSC) has been investigated in this study. Workability, compressive strength, elastic modulus, porosity and pore size distribution were assessed in order to quantify the effects of the different materials. The results show that the inclusion of the different SCMs has considerable influence on the workability of HSC. Silica fume and metakaolin significantly enhanced the strength of HSC. Fly ash reduced the early-age strength; however, it enhanced the long-term strength of the HSC. Likewise, ground granulated blast-furnace slag impaired the early-age strength, but marginally improved the long-term strength at low replacement levels. The general effect of the different SCMs on the elastic modulus of HSC is rather small compared to their effect on strength. There are good correlations between both static and dynamic moduli and compressive strength. The EC 2 and ACI 209 provide a good estimate of static modulus of elasticity from compressive strength, while the BS8110 gives a good estimate of static modulus of elasticity from dynamic modulus of HSC containing the different SCMs. Porosity and pore size were reduced with the addition of the different SCMs. The volume of mesopores in the ranges of <15 nm and 15 – 30 nm was notably increased for HSC containing SCMs, whereas the percentage of macropores was significantly reduced.     

高强混凝土三轴强度规律与破坏准则

主要研究在三轴应力状态下高强混凝土的强度性能。进行了高强混凝土在三轴受压、三轴拉压和三轴受拉应力状态下共 1 0 1个试件的试验。为了对比 ,还开展了普通混凝土在相应应力状态下共 85个试件的试验。通过对不同强度等级混凝土三轴强度试验结果的分析和对比 ,总结了高强混凝土的三轴强度规律 ,建立了高强混凝土参数形式的破坏准则模型 ,并给出破坏准则模型中参数标定点的选取     

Performance of high strength concrete made with copper slag as a fine aggregate

This research study was conducted to investigate the performance of high strength concrete (HSC) made with copper slag as a fine aggregate at constant workability and to study the effect of superplasticizer addition on the properties of HSC made with copper slag. Two series of concrete mixtures were prepared with different proportions of copper slag. The first series consisted of six concrete mixtures prepared with different proportions of copper slag at constant workability. The water content was adjusted in each mixture in order to achieve the same workability as that for the control mixture. Twelve concrete mixtures were prepared in the second series. Only the first mixture was prepared using superplasticizer whereas the other eleven mixtures were prepared without using superplasticizer and with different proportions of copper slag used as sand replacement. The results indicated that the water demand reduced by almost 22% at 100% copper slag replacement compared to the control mixture. The strength and durability of HSC were generally improved with the increase of copper slag content in the concrete mixture. However, the strength and durability characteristics of HSC were adversely affected by the absence of the superplasticizer from the concrete paste despite the improvement in the concrete strength with the increase of copper content. All concrete mixtures did not meet the strength and durability design requirements due to the segregation and dryness of the concrete paste. Therefore it can be concluded that the use of copper slag as sand substitution improves HSC strength and durability characteristics at same workability while superplasticizer is very important ingredient in HSC made with copper slag in order to provide good workability and better consistency for the concrete matrix.     

高强度混凝土试验研究

高强度混凝土C80在建筑工程中的应用问题极为重要.为了使设计及施工单位正常设计及使用较高强度等级混凝土,扩大高强度等级混凝土C80在建筑工程中的应用,通过不同强度等级水泥、不同粉煤灰掺量、不同品种外加剂的混凝土进行试配试验,测定混凝土强度的变化过程,对水泥强度等级、粉煤灰掺量、外加剂掺量三者之间的相互关系进行了对比分析,得出了高强度等级混凝土C80在混凝土工程中应用的参考配合比.     

Slender reinforced concrete shear walls with high-strength concrete boundary elements

Reinforced concrete structural walls are commonly used for resisting lateral forces in buildings. Owing to the advancements in the field of concrete materials over the past few decades, concrete mixes of high compressive strength, commonly referred to as high-strength concrete (HSC), have been developed. In this study, the effects of strategic placement of HSC on the performance of slender walls were examined. The finite-element model of a conventional normal-strength concrete (NSC) prototype wall was validated using test data available in extant studies. HSC was incorporated in the boundary elements of the wall to compare its performance with that of the conventional wall at different axial loads. Potential reductions in the reinforcement area and size of the boundary elements were investigated. The HSC wall exhibited improved strength and stiffness, and thereby, allowed reduction in the longitudinal reinforcement area and size of the boundary elements for the same strength of the conventional wall. Cold joints resulting from dissimilar concrete pours in the web and boundary elements of the HSC wall were modeled and their impact on behavior of the wall was examined.     

高温下及高温后混凝土的力学性能研究

对混凝土的高温性能进行了分析和总结,包括高温下不同强度等级混凝土的强度和变形性能恶化的规律;不同降温方式、升温-加载途径对混凝土强度的影响;潮湿环境有利于高温损伤混凝土强度的恢复。此外还阐述了高强混凝土在高温作用下的爆裂现象和爆裂机理,并提出改进高强混凝土抗火性能的建议。     

钢纤维对高强混凝土高温作用后力学性能影响的研究

通过对钢纤维高强混凝土高温后力学性能的试验研究,探讨了钢纤维高强混凝土的抗压强度、抗拉强度和抗折强度在不同温度下的变化规律。与高强混凝土火灾后性能变化规律进行比较,分析了钢纤维对高强混凝土受高温作用后力学性能的影响机理。     

Critical factors governing the fire performance of high strength concrete systems

High strength concrete (HSC), is being increasingly used in a number of building applications, where structural fire safety is one of the major design considerations. Many research studies clearly indicate that the fire performance of HSC is different from that of normal strength concrete (NSC) and that HSC may not exhibit same level of performance (as NSC) in fire. This paper discusses the material, structural and fire characteristics that influence the performance of HSC under fire conditions. Data from earlier experimental and numerical studies is used to illustrate the impact the concrete (material) mix design and structural detailing (design) has on fire performance of HSC systems. An understanding of various factors influencing fire performance will aid in developing appropriate solutions for mitigating spalling and enhancing fire resistance of HSC members.     

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.