双掺活性混合材对高强混凝土性能的影响

本文对比研究了普通硅酸盐高强混凝土、粉煤灰高强混凝土以及双掺粉煤灰和沸石粉混合料的高强混凝土的力学性能,研究表明,双掺混合材的高强混凝土的早期和后期的力学性能均较好。本文同时观测了高强混凝土的内部微观结构,对活性混合材的作用机理进行了初步的探讨。     

玻璃粉对玻璃骨料混凝土力学性能和ASR影响的研究

ASR膨胀是限制废弃玻璃作为细骨料运用到混凝土中的主要因素之一,玻璃粉具有潜在的火山灰活性,当一定细度的玻璃粉替代部分水泥可以有效的抑制ASR同时还可以增强混凝土后期强度;在玻璃细骨料混凝土(细骨料替代率分别为10%、20%、30%)中采用玻璃粉取代20%作为辅助胶凝材料,通过混凝土抗压试验和砂浆棒试验,研究玻璃粉对玻璃细骨料混凝土力学性能及ASR影响;研究表明,玻璃粉掺入可以提升玻璃细骨料混凝土后期强度,特别是90 d后玻璃粉混凝土抗压强度超越普通混凝土;同时,玻璃粉可以有效抑制玻璃细骨料混凝土ASR,掺入20%玻璃粉的玻璃细骨料混凝土14 d砂浆棒膨胀率均小于规范限定值0.1%,而未掺入玻璃粉的试件恰恰相反。所以,玻璃粉可以有效的改良玻璃细骨料混凝土的后期强度和ASR膨胀不足。     

Paving blocks made with recycled concrete aggregate and crushed clay brick

Clay brick generated from construction sites is usually delivered to landfills for disposal. With the limited landfill space in Hong Kong, there is an immediate need to explore the possible use of crushed clay brick as a new civil engineering material. In Hong Kong, government specifications promote the use of paving blocks made with 70–100% recycled concrete aggregate in order to facilitate the recycling of construction and demolition (C&D) waste. This paper presents a recent study at the Hong Kong Polytechnic University on the investigation of blending recycled concrete aggregate and crushed clay brick as aggregates in the production of paving blocks.The results indicated that the incorporation of crushed clay brick reduced the density, compressive strength and tensile strength of the paving blocks. Due to the high water absorption of crushed clay brick particles, the water absorption of the resulting paving blocks were higher than that of the paving blocks that did not incorporate crushed clay brick. Although it was found that crushed clay brick impaired the quality of the resulting paving blocks to a certain extent, the paving blocks using 50% crushed clay brick met the minimum requirements specified by AS/NZS 4455 and ETWB of Hong Kong (Grade B) for pedestrian areas. Furthermore, it was feasible to produce paving blocks prepared with 25% crushed clay brick that satisfied the compressive strength requirement for paving blocks (Grade B) prescribed by ETWB of Hong Kong for trafficked area.     

Effect of glass cullet on the improvement of the dynamic behaviour of asphalt concrete

The stiffness modulus is one of the most important parameters for the prediction of pavement strength against dynamic loads. Previous research indicated that glass can reduce the construction costs of asphalt concrete pavements while providing better dynamic behaviour because of its unique properties. In this research, the behaviour of Hot Mix Asphalt (HMA) in different temperature conditions depending on the variation of the admixture contents and the gradation of the aggregates will be evaluated. Afterwards, for the first time, models for the prediction of the stiffness modulus of waste glass–asphalt in terms of three different parameters including temperature, percentage of additives and the aggregate gradation will be presented. The results of this research are indicative of an improvement in the dynamic behaviour of glass–asphalt mixture in comparison with conventional HMA mixtures.     

空心砌块高层建筑专用砂浆及注芯混凝土

专用砌筑砂浆及注芯混凝土是混凝土小型空心砌块砌筑高层建筑的配套材料。其研制成功为混凝土小型空心砌块非框架高层建筑结构体系的开发与推广提供了必要的条件，也为混凝土空心砌块的稳步发展奠定了基础。文中介绍了专用砌筑砂浆及注芯混凝土的开发研究过程、产品性能及应用情况。指出专用砌筑砂浆及注芯混凝土不仅质量可靠、施工方便，而且成本分别比普通砌筑砂浆及商品混凝土低。     

Properties of concrete made with recycled crushed glass at elevated temperatures

The effect of replacement of fine and coarse aggregates with recycled glass on the fresh and hardened properties of Portland cement concrete at ambient and elevated temperatures is studied. Percentages of replacement of 0–100% of aggregates with fine waste glass (FWG), coarse waste glass (CWG), and fine and coarse waste glass (FCWG) were considered. Soda-lime glass used for bottles was washed and crushed to fine and coarse aggregate sizes for use in the concrete mixes. Samples were cured under 95% RH at room temperatures (20–22 °C), heated in the oven to the desired temperatures, allowed to cool to ambient temperatures, and then tested for their residual compressive strength. The compressive strength of the concrete samples made with waste glass was measured at temperatures up to 700 °C. Moreover, the effect of the percentages of replacement with recycled glass on the slump values and initial and final setting time of concrete has also been measured.     

纳米混凝土的ASR试验研究

碱集料反应(AAR)是影响混凝土耐久性的重要因素。在普通混凝土中掺加适量纳米SiO_2或纳米Al_2O_3,研究纳米混凝土在抗AAR方面的性能。试验结果表明:不同掺量的纳米SiO_2或纳米Al_2O_3可以不同程度地抑制混凝土的AAR,纳米SiO_2或纳米Al_2O_3在混凝土中的最优掺量均为2. 0%,且2%掺量下的纳米SiO_2混凝土的抑制效果更佳。为纳米混凝土耐久性的进一步研究及其在实际工程中的应用提供了依据。     

玻璃及其与其他材料的构造连接方法探究

针对建筑施工中大量采用建筑材料玻璃的现状,阐述了建筑施工中净片玻璃、装饰玻璃、安全玻璃等具有不同功能的玻璃的特性,对玻璃与玻璃之间、玻璃与金属之间的构造连接方法进行了分析,并对不同的连接方法进行了评价,为今后玻璃与其他材料的连接提供了参考依据。     

废玻璃集料对混凝土强度的影响

利用废弃玻璃等质量取代混凝土粗、细集料.通过坍落度、抗压强度等试验,研究取代率及取代形式对混凝土性能的影响.随着玻璃取代率的增加,混凝土坍落度增大,取代石子大于取代砂的坍落度;抗压强度随着取代率的增加而降低,但掺量低时影响不显著;废弃玻璃集料的抗压强度随龄期增长幅度高于普通混凝土;废弃玻璃集料混凝土的抗压强度随粗骨料压碎指标增大而提高,满足鲍罗米线性关系式;掺加粉煤灰和矿渣粉等对玻璃混凝土抗压强度影响与普通混凝土的程度相当.     

自保温混凝土复合砌块热工性能检测方法研究

从目前自保温砌块热工性能检测方法存在的问题入手，通过对多个检测方法的综合运用和研究，提出一套能检测当量导热系数和当量蓄热系数的方法，其检测结果可直接用于建筑节能工程设计。     

废弃玻璃利用现状及其在混凝土材料领域的应用

废弃玻璃在当今城镇固体废弃物中占有很大比例,大量的堆积引起了一系列的环境和资源浪费问题。目前废弃玻璃的回收利用可以分为自身的循环利用与其他领域的应用两大类,而将其应用到混凝土领域里无疑是大量处理废弃玻璃的最佳途径。废弃玻璃既可用作混凝土骨料,又可用做混凝土的掺合料。发达国家对此已开展了多年研究,在各种类型的混凝土中都做了有益的尝试,取得了一些成果。研究表明:将废弃玻璃应用于混凝土中在生态、经济及工程方面都能取得较好的效益,前景十分广阔。     

钢筋混凝土桥梁的维修与保护的材料及方法

1　前言钢筋混凝土桥梁是一个耐久性结构 ,但是经验告诉我们即使是混凝土材料、设计和施工的质量都很好 ,随着服役时间的延长 ,桥梁结构还是会出现各种各样的病害。钢筋混凝土桥梁的耐久性与如下因素有关 :1 混凝土的密实度 ;2 混凝土抗开裂能力 ;3 结构所处环境的潮湿度 ;4 结构所处环境的冻融循环情况 ;5 结构所处环境的二氧化碳浓度 ;6 结构所处环境的化冰盐使用情况等。如果混凝土材料或施工质量不好 ,或设计有缺陷等都会加速病害的发生和发展速度。另外 ,由于混凝土碳化反应或氯离子渗入会导致钢筋锈蚀 ,而钢筋锈蚀又会引起混凝土…     

玻璃混凝土及其织物增强薄板试验研究

玻璃混凝土的研制,不仅开辟了废玻璃回收利用的新途径,而且节约了有限的砂石资源.为探索废玻璃作为混凝土骨料的可行性,开发织物增强玻璃混凝土薄板.首先,通过比较砂骨料和玻璃骨料混凝土的强度、变形随时间变化的特征,研究在玻璃混凝土拌合料中掺入适量偏高岭土超细粉末对碱-硅反应(ASR)的抑制作用;然后,分别制作出预应力和非预应力的碳纤维织物增强砂骨料、玻璃骨料混凝土薄板,并对四种类型的薄板进行拉伸、弯曲、和织物与混凝土之间的界面黏结性能试验.研究表明,掺入适量的偏高岭土超细粉末,能抑制玻璃混凝土中的碱-硅反应,并能制作出变形稳定、后期强度较高的细骨料玻璃混凝土;预应力和非预应力玻璃骨料混凝土薄板与砂骨料混凝土薄板相比,具有较好的抗拉、抗弯和界面黏结性能.     

Strength and stiffness of compacted crushed concrete aggregate

A comprehensive series of drained triaxial compression tests were performed on crushed concrete aggregate (CCA) moist as compacted. When compared to ordinary natural well-graded gravelly soils, the peak strength and stiffness increase more significantly with dry density, while the effect of the degree of saturation during compaction is much less significant. In a range of confining pressure of 30–600 kPa, the strength and stiffness of well-compacted CCA is similar to, or, in some cases even higher than, typical selected high-class backfill materials (e.g., well-graded gravelly soil of crushed quarry hard rock). The strength and stiffness of CCA with a maximum particle size D_max=37.5 mm obtained from a typical concrete crushing plant are noticeably lower than CCA sieved to D_max=19 mm compacted using the same energy. However, when compacted to the same dry density, the original CCA exhibits the strength and stiffness higher than the sieved CCA. Effects of the strength of original concrete on the strength and stiffness of compacted CCA are insignificant, while the strength and stiffness of compacted CCA are, respectively, noticeably higher than, or similar to, the original concrete aggregate (i.e., natural gravelly soil) compacted using the same energy. All these results indicate that well-compacted CCA can be used as the backfill material for important civil engineering soil structures requiring a high stability while allowing a limited amount of deformation.     

Effects of contaminants on the properties of concrete paving blocks prepared with recycled concrete aggregates

The use of recycled aggregates for preparing concrete products has been successfully implemented and gaining wider acceptance. However, the allowable level of contaminating materials (e.g., crushed clay bricks, crushed ceramic tiles, waste glass cullet, wood chips, etc.) in the recycled concrete aggregate, in the some of the current specifications, is low (<1%) due to stringent quality control standards that are usually taken from specifications for raw granular virgin materials. This paper presents a recent study on the properties of concrete paving blocks prepared with recycled concrete aggregates that are contaminated by materials (tiles, clay bricks, glass, wood) commonly found in the construction and demolition waste. The density, compressive strength, tensile splitting strength, water absorption value, abrasion resistance, skid resistance and some durability parameters were measured for laboratory prepared samples. The results show that it is feasible to allow a higher level of contamination in the recycled concrete aggregates for making the concrete products. Recommendations are made on how the specifications could be revised to facilitate a wider application of recycled aggregates that is contaminated by foreign materials.     

Effects of formwork surface materials on concrete lateral pressure

In this study, the effect of formwork surface materials on the concrete lateral pressure was investigated. Seven wall formworks were constructed. Populus nigra timber, pinus silvestris timber, plywood and steel sheet were used as surface materials for these formworks. One of two formwork, which had the same surface material, was watered except for the steel formwork before placing the concrete. Concrete was placed into the formworks and the lateral pressures of concrete on formworks surface were measured by a strain measurement system. As comparison the limiting value of concrete lateral pressure was calculated by ACI-347 equation.It was concluded that, watering the surface of wood formworks increased lateral pressure of concrete on the formworks. Lateral pressure of steel formwork was equal to limiting value of ACI-347 and larger than lateral pressure of populus nigra, pinus silvestris, and plywood formworks. The lateral pressure of pinus silvestris formwork was some less than 3.3%, 7.2%, 21%, respectively, lateral pressure of populus nigra, plywood, and steel formwork”.     

Strength and durability of concrete incorporating crushed limestone sand

In recent years, there is a growing interest in the use of crushed sand obtained from limestone quarries in some countries where river sand is not widely available. The fines content is usually high in crushed sand which can adversely affect concrete properties. The influence of fines in crushed sand on physical and mechanical properties of concrete has been widely investigated. The results proved that up to 15% of fines content in crushed sand could be used without adversely affecting concrete strength. However, little work has been done so far on the effect of fines in crushed sand on the durability of concrete. This paper examines the influence of limestone fines in crushed sand on concrete properties. Properties include strength, water, gas and chloride-ion permeability and capillary water absorption. Four different cement types were used while maintaining a constant water/cement ratio. The results show that concrete containing 15% of limestone fines as replacement of crushed sand reduces the water permeability and increases the gas and chloride-ion permeability.     

Effects of compaction method and rubber content on the properties of concrete paving blocks

A wide variety of recycled waste has been successfully used in the production of concrete paving blocks. It is known that the mechanical properties of these concrete products tend to be inconsistent, which is understandable in view of the range of mix designs as well as the variety of materials and compaction methods that were adopted in the production. In this study, recycled waste tyre (crumb rubber) was used to replace sand by volume at the level of 0%, 10%, 20% and 30% in order to investigate how the soft rubber particles behave under plant-machine compaction method during the production of rubberized concrete paving blocks (RCPB). In the hardened stage, the physical properties as well as mechanical properties of RCPB including density, compressive strength, bending strength and skid resistance were studied. The results showed that as a small proportion (∼10%) of soft rubber particles was included in the mixture, the particles easily distorted and filled the voids between the solid particles. This filling mechanism reduced the porosity of concrete mixtures and effectively developed an adequate adhesion between the particles, resulting in higher gain in strengths. On the contrary, as the rubber ratio increased more than 10%, which the deformability is more predominant than the filling mechanism, this results in higher total stress concentrations and rebound stress of rubber particles, thus, increasing the porosity and micro-cracks, resulting in loss in strengths. Nevertheless, the presence of rubber in concrete did not demonstrate brittle failure, but rather a ductile which had an ability to withstand post-failure loads. In comparison, the mechanical properties of plant-made RCPB performed better than that of corresponding manually-made RCPB. Therefore, plant-compaction method is recommended for future RCPB production and crumb rubber content used to replace sand by volume should be kept at or less than 10%.     

Glazed tiles produced using paper sludge,glass cullet and a natural red clay: an experimental study

The paper describes the production, in single fast firing, of tiles containing 30 wt% of a natural red clay and a mixture of 42 wt% of paper mill sludge and 28 wt% of glass cullet which were coated with a commercial ‘matt white’ glaze. Fired materials have been characterized as a function of the top temperature (1090 or 1140 °C) reached at the top of the fast sintering process made by an industrial roller kiln. It has been observed that tiles fired at 1090 °C display the best overall performances because the matt glaze well covers the substrate, thus ensuring that the mechanical and physical properties of the tiles conform to the official standard.