不同取代率下再生混凝土的抗冻融性能试验

采用快冻法对9种再生混凝土进行了冻融循环试验。分析了经受100次冻融循环后不同取代率下再生粗骨料和再生细骨料对混凝土立方体抗压强度的影响;研究了每25次冻融循环后再生混凝土的棱柱体质量损失率和相对动弹性模量的变化;比较了100次冻融循环作用对不同取代率下再生混凝土抗压承载力的影响。结果表明,再生混凝土抗冻融性能有所下降,且降低幅度随再生骨料取代率的增加而加剧;100次冻融循环后,再生粗骨料取代率为50%,细骨料为天然骨料的再生混凝土,其质量损失率、相对动弹性模量衰减幅度和抗压承载力损失率均与普通混凝土接近,建议再生粗骨料掺量不高于50%的再生混凝土可在寒冷地区推广应用。     

压剪作用下PVA纤维再生混凝土力学性能试验研究

为了研究压剪作用下外掺聚乙烯醇(PVA)纤维对再生混凝土力学性能的影响,以再生粗骨料取代率、压应力比和PVA纤维体积掺量为变化参数,设计并制作144个立方体试件进行压剪试验。观察了试件的破坏形态,得到了荷载-位移曲线及垂直变形-剪切位移曲线,分析了不同变化参数对抗剪强度、峰值位移的影响规律。结果表明：0.1%体积掺量的PVA纤维对再生混凝土的抗剪强度提高了10%;随着压应力比的增大,试件的抗剪强度呈增大趋势,平均增大了2.03倍;与普通混凝土相比,再生混凝土试件的抗剪强度平均降低了13%;当再生粗骨料取代率为100%时,PVA纤维最佳掺量为0.1%;提出了纤维掺量为0.1%时压剪作用下PVA纤维再生混凝土抗剪强度计算公式。     

玻化微珠在自保温墙体中的应用研究

建筑节能和墙体改革工作的深入开展,为自保温墙体发展提供了良好的机会。该文结合课题组多年研究成果,在理论计算、试验研究和工程实践基础上,阐述了高效节能、无机、耐高温的玻化微珠新型保温材料在涂抹式、砌块式、墙板式、砌模式和现浇整体式自保温墙体中的应用,形成了集结构功能与保温功能于一体,能满足国家现行节能标准的新型玻化微珠建筑节能自保温体系,为玻化微珠在节能建筑中的应用奠定了理论和实践基础。     

钢纤维再生粗骨料混凝土受压声发射特性与损伤演化

为了探究钢纤维掺量(体积率0、0.8%、1.5%)对C30再生粗骨料混凝土(质量分数取代率0、100%)基本力学性能的影响，结合声发射特征参数和应力-应变曲线来描述钢纤维再生粗骨料混凝土在轴心受压过程中的损伤演化规律。试验结果表明，通过对声发射损伤定位、撞击计数与能量计数分析，可实现钢纤维再生粗骨料混凝土轴心受压破坏从累计损伤到微裂缝演变，再到宏观裂缝扩展的全过程动态监测，不同钢纤维掺量再生粗骨料混凝土与普通混凝土试件在加载过程中损伤点的密集集中位置与试件最终破坏位置相符；基于声发射累计撞击计数建立的混凝土损伤模型可用于分析钢纤维再生粗骨料混凝土的损伤演化规律。     

物理化学强化对再生混凝土抗氯离子渗透性能的影响

废弃混凝土经简单破碎、一次颗粒整形和二次颗粒整形后分别制得Ⅱ类再生粗骨料、准类再生粗骨Ⅰ料和Ⅰ类再生粗骨料,将三类再生粗骨料在浓度6%的有机硅烷防水剂中进行24h化学浸渍处理,得到三类物理化学强化再生粗骨料。分别研究不同品质物理化学强化再生粗骨料和不同取代率(取代率:0%、25%、50%、75%、100%)取代天然骨料对再生混凝土的抗氯离子渗透性能的影响。结果显示:再生粗骨料混凝土抗氯离子性能为:化学强化二次颗粒整形再生粗骨料混凝土化学强化一次颗粒整形再生粗骨料混凝土化学强化简单破碎再生粗骨料混凝土,且均优于普通混凝土;三类化学强化再生粗骨料混凝土的氯离子迁移系数均随着取代率的增大而减小。     

废弃纤维再生混凝土框架中柱节点抗震性能试验研究

完成了再生骨料取代率为50%,废弃纤维长度分别为12 mm、19 mm、30 mm以及废弃纤维体积掺量分别为0.08%、0.12%、0.16%的5个废弃纤维再生混凝土框架中柱节点在低周反复荷载作用下的抗震性能试验研究。主要对不同废弃纤维长度、不同废弃纤维体积掺量下梁柱节点的破坏形态、滞回特性、延性性能、耗能特性等问题进行了对比分析。结果表明:废弃纤维再生混凝土框架节点的破坏均经历了初裂、通裂、极限、破坏四个特征阶段,当纤维长度为19mm,废弃纤维体积掺量为0.12%时,废弃纤维再生混凝土梁柱节点构件的滞回性能、延性性能及耗能性能较好;废弃纤维的体积掺量比废弃纤维长度对梁柱节点抗震性能的影响大。提出了废弃纺织纤维再生混凝土的抗剪承载力计算公式,计算结果与试验结果吻合较好。     

新型脱硫石膏基保温砂浆的配制及性能研究

以脱硫石膏及膨胀玻化微珠为研究对象,通过对比选取和交叉试验的方法,首先考察了脱硫石膏与膨胀玻化微珠的配比对保温砂浆的表观密度和抗压强度的影响,再利用柠檬酸、乳胶粉、纤维素醚和聚丙烯纤维等掺合物对保温砂浆进行改性试验,重点研究了各添加剂对保温砂浆的保水率、压折比、极限变形量、断裂能和线性收缩率的影响.结果表明,要配制性能优异的脱硫石膏基保温砂浆,应将玻化微珠和胶凝材料的体积质量比控制在4.5L∶1kg,必须掺入石膏质量0.1％左右的柠檬酸调节凝结时间,乳胶粉、纤维素醚和聚丙烯纤维的掺量分别控制为胶凝材料质量的2％、0.6％和0.6％.     

3D打印再生粗骨料混凝土抗冻性能试验研究

3D打印技术在建筑领域得到显著发展,为解决混凝土3D打印行业实现可持续发展。通过对再生粗骨料(RCA)取代率为0%、50%、100%的3D打印试件和铸模试件进行抗冻性能研究,结合3D打印再生粗骨料混凝土(3DPRAC)界面过渡区的电镜扫描分析其劣化成因。结果表明,在前200次冻融循环中RCA的掺入并没有明显降低3D打印混凝土的质量和动弹模量;在600次冻融循环后RCA为100%掺量的3D打印再生混凝土抗冻性能表现优于RCA掺量为50%。基于3D打印再生混凝土逐层堆叠的建造特点,提出了3DPRAC孔隙区域集中分布模型,揭示了3DPRAC冻融损伤劣化机理。建立的冻融损伤模型能够较好地反映3DPRAC抗冻性能变化规律。     

高强再生骨料混凝土的配制及性能研究

采用再生粗骨料配制强度在50MPa或更大的高强再生骨料混凝土,并对其变形能力和耐久性进行测定,为高强再生骨料混凝土在工程上的应用提供理论和实验基础。通过一系列的抗压实验确定再生粗骨料的强度极限,并通过对水灰比的调整,使配制的高强再生骨料混凝土在强度上达到设计值,并以再生粗骨料取代率为0、30%、50%、80%和100%的高强再生骨料混凝土为研究对象进行实验。当再生粗骨料取代率为30%时,对再生混凝土的强度影响不大;之后混凝土强度随再生骨料的增加而降低。高强再生骨料混凝土与天然混凝土在耐久性上具有相似的性能,可以将高强再生混凝土应用于工程中。     

再生粗骨料硅烷浸渍处理对混凝土介质传输性能的影响

由于残余砂浆的存在,再生粗骨料的物理力学指标远不及天然骨料,致使再生混凝土力学和耐久性能较差;此外,水分及有害离子侵入混凝土内部是引起混凝土材料性能劣化的主要原因。本试验用质量分数为8wt%的硅烷乳液浸渍强化再生粗骨料,通过抗压强度、毛细吸水和抗氯离子侵蚀试验对硅烷浸渍前后不同骨料质量取代率(0%、30%、50%)的再生混凝土介质传输性能进行了研究,最后利用SEM对再生混凝土内部的微观结构进行分析。试验结果表明,硅烷浸渍处理再生粗骨料的吸水率显著降低,由其制备的混凝土强度稍有所下降;再生混凝土毛细累积吸水量明显减少,且抗氯盐侵蚀性能显著提高,其中骨料质量取代率为50%的再生混凝土浸渍处理后氯离子扩散系数降低了37.5%。研究表明,硅烷浸渍处理再生粗骨料是提高再生混凝土耐久性的有效途径。      

玻化微珠保温混凝土高温后性能劣化及微观结构

配制普通混凝土（NC）和玻化微珠保温混凝土（GHB/NC）,研究从常温升温至1 000℃高温后表观现象变化、质量、抗压强度损失等性能的劣化过程,同时讨论超声波无损检测法评判混凝土高温后性能的普适性,对比分析相对波速、损伤度与受热温度、抗压强度损失率的关系,利用SEM观察不同高温后试件微观结构变化。结果表明:采用相对波速、损伤度评价混凝土高温后性能具有良好相关性,回归公式拟合度较高;随温度升高,NC和GHB/NC混凝土内部损伤逐步加剧,水泥胶凝受热分解、水分散失等在试件表面和内部产生空隙、裂纹并相互贯通,玻化微珠、粗骨料与水泥石界面黏结力逐步减弱甚至丧失,造成宏观力学性能劣化,抗压强度损失率增大。升温至800℃后NC强度损失72.3%,GHB/NC强度损失74.6%,1 000℃时基本丧失承载能力。      

空心玻璃微珠含量比对涂料隔热性能的影响

主要研究了自主研制的空心玻璃微珠涂料的隔热性能。通过隔热模型试验，考察了空心玻璃微珠涂料的隔热性能，对比了空心玻璃微珠含量比对涂料隔热性能的影响，并对其隔热机理和含量比的影响原因进行了探讨。指出空心玻璃微珠涂料是一种具有良好隔热性能的涂料，能产生明显的隔热效果，但过高的空心玻璃微珠含量比将对隔热性能产生劣化影响。     

Quantification of the residual mortar content in recycled concrete aggregates by image analysis

As the supply of suitable fresh aggregates in some locations is rapidly dwindling and such aggregates need to be transported from distant locations, there will be more and more economic and environmental reasons to use recycled concrete aggregates in making new concrete. The nature and properties of recycled concrete aggregates have a definite impact on the performance of recycled aggregate concrete and the effects can vary considerably. Existing literature and studies conducted by the authors have shown that the amount and properties of the residual mortar in the recycled concrete aggregates significantly affect the mechanical and durability properties of the new concrete. Consequently, a quick laboratory method was developed to determine the residual mortar content of recycled concrete aggregates, to serve as a quality control tool for such aggregates. In order to validate the results obtained by that laboratory test procedure, image analysis was used to quantify the residual mortar content in the different size fractions of the recycled concrete aggregates tested. The results confirmed that the quick laboratory test provides an accurate measurement of the residual mortar content in recycled concrete aggregates.     

纤维增强发泡保温复合材料的制备与性能

为了增强玻化微珠/水泥发泡保温复合材料的力学性能和保温性能,通过掺加改性物理泡沫降低发泡保温复合材料的密度和导热系数,采用改性纤维对发泡保温复合材料进行增强。研究了纤维增强发泡保温复合材料的力学性能和耐水性能,并利用扫描电镜对试样内部微观形貌进行观察,探讨了改性泡沫和改性纤维对发泡保温复合材料的增强机制。结果表明,掺加泡沫明显降低了发泡保温复合材料的密度和导热系数,当泡沫掺量为1.05 mL/g时,试样密度和导热系数分别为186 kg/m³和0.056 W/（m·K）。泡沫改性可有效改善发泡保温复合材料的强度和软化系数,掺加改性泡沫试样的抗折强度、抗压强度和软化系数较掺加乳胶粉试样的分别提高了21.05%、21.43%和13.56%。改性纤维可显著提高发泡保温复合材料的强度和软化系数,掺加改性纤维试样的抗折强度、抗压强度和软化系数较掺加未改性纤维试样的分别提高了25.93%、13.51%和8.33%。     

Influence of field recycled coarse aggregate on properties of concrete

This paper investigates the influence of different amounts of recycled coarse aggregates obtained from a demolished RCC culvert 15 years old on the properties of recycled aggregate concrete (RAC). A new term called “coarse aggregate replacement ratio (CRR)” is introduced and is defined as the ratio of weight of recycled coarse aggregate to the total weight of coarse aggregate in a concrete mix. To analyze the behaviour of concrete in both the fresh and hardened state, a coarse aggregate replacement ratio of 0, 0.25, 0.50 and 1.0 are adopted in the concrete mixes. The properties namely compressive and indirect tensile strengths, modulus of elasticity, water absorption, volume of voids, density of hardened concrete and depth of chloride penetration are studied. From the experimental results it is observed that the concrete cured in air after 7 days of wet curing shows better strength than concrete cured completely under water for 28 days for all coarse aggregate replacement ratios. The volume of voids and water absorption of recycled aggregate concrete are 2.61 and 1.82% higher than those of normal concrete due to the high absorption capacity of old mortar adhered to recycled aggregates. The relationships among compressive strength, tensile strengths and modulus of elasticity are developed and verified with the models reported in the literature for both normal and recycled aggregate concrete. In addition, the non-destructive testing parameters such as rebound number and UPV (Ultrasonic pulse velocity) are reported. The study demonstrates the potential use of field recycled coarse aggregates (RCA) in concrete.     

Performance of autoclaved aerated-concrete masonry walls in Kuwait

The masonry walls used in building construction in Kuwait are non-load bearing. Traditionally, normalweight concrete blocks have been used throughout the region. However, with the enforcement of the Kuwaiti energy conservation code, autoclaved aerated-concrete blocks were introduced in 1985 as an efficient masonry material that can provide the necessary thermal insulation properties without the use of specific thermal insulation materials. This paper discusses the influence of material properties and specific construction practices on the performance of aerated-concrete-block walls. The provision of a partial movement joint through the use of sand-cement mortar, in place of higher strength epoxy glue mortar in the construction of wall and column intersections, reduced cracking in the immediate vicinity of the intersections. Studies are ongoing to recommend more effective measures for allowing greater movement at the wall and column intersections, thereby eliminating wall cracking due to restraint of movement.     

新型保温隔热外墙涂料的研制

以碳酸钙、金红石型二氧化钛、空心玻璃微珠、氧化锌为颜填料,以苯丙乳液为主成膜物,制备出的建筑外墙保温隔热涂料,其常规性能符合外墙涂料的相关标准要求。研究了添加碳酸钙、金红石型二氧化钛和氧化锌三种填料及复合添加四种填料对涂层隔热性能的影响。结果表明：添加碳酸钙、金红石型二氧化钛和氧化锌可提高涂层隔热性能;复合掺入碳酸钙、金红石型二氧化钛、氧化锌和空心玻璃微珠可进一步提高涂层隔热性能。掺加15％碳酸钙、7％金红石型二氧化钛、5％氧化锌和8％空心玻璃微珠时,隔热温差为7．9℃,导热系数为0．0767W／（m·K）,具有明显的保温隔热效果。     

钢纤维橡胶再生混凝土的抗冻性试验

为使废弃混凝土和再生橡胶在北方地区混凝土工程中得以应用,采用正交试验法研究再生粗骨料掺量、再生粗骨料强化方式、钢纤维掺量与橡胶掺量对钢纤维橡胶再生混凝土(C45)立方体抗压强度和抗冻性的影响规律。利用扫描电镜和螺旋CT扫描技术研究了钢纤维橡胶再生混凝土的宏观和细观结构及其对抗冻性能的影响机理。结果表明:橡胶颗粒掺量是影响再生混凝土含气量、抗压强度和相对动弹模量的重要因素,再生粗骨料掺量是影响相对动弹模量和强度损失率的次要因素,钢纤维掺量对混凝土抗压强度增强作用较小,粗骨料强化方式对混凝土性能影响不大;橡胶颗粒与砂浆界面的裂缝宽度在5~55μm之间,二者之间的相容性较差;当橡胶颗粒掺量(与砂的体积比)大于20%后,随橡胶颗粒掺量增大,混凝土内部孔洞数目增多,钢纤维橡胶再生混凝土抗压强度降低、抗冻性减弱。     

Mechanics of hollow concrete block masonry prisms under compression: Review and prospects

The aim of this work is to critically assess the mechanical properties of hollow concrete masonry using experimental results from prisms constructed with blocks of two different strengths and four types of mortar. A key conclusion is that mortar is mostly responsible for the non-linear behavior of masonry. Moreover, a strongly non-linear relationship between masonry elasticity modulus and compressive strength is found, which contradicts the simple linear relation proposed by Eurocode 6 [CEN. Eurocode 6: Design of masonry structures – Part 1 – Common rules for reinforced and unreinforced masonry structures. EN-1996-1-1; 2005.]. The porosity of mortar and the state of stress that mortar undergoes in the process of compressive loading can be responsible for changes in the mechanical properties, such as elasticity modulus and Poisson’s ratio. Finally, different types of mortars induce different failure modes in the masonry prisms and there is clear evidence that the failure of hollow concrete masonry starts after onset of mortar crushing. In order to better reproduce the observed experimental behavior, a tentative model for the mortar Poisson’s ratio variation upon loading is also presented.     

碱矿渣陶粒混凝土砌块砌体受压本构关系

为考察碱矿渣陶粒混凝土砌块砌体的受压本构关系及基本力学性能,完成了126个用碱矿渣陶砂砂浆和碱矿渣陶粒混凝土砌块砌筑的砌体试件的轴心抗压试验。研究结果表明:当砌块抗压强度和砌筑砂浆抗压强度相同时,由于碱矿渣陶砂砂浆收缩大,该类砌体的峰值压应变、极限压应变均低于普通混凝土砌块砌体。建立了以砌体抗压强度、砌块抗压强度和砌筑砂浆抗压强度为自变量的这类新型砌体峰值压应变、极限压应变以及弹性模量计算公式。