Short and long-term behavior of structural concrete with recycled concrete aggregate

Recycling concrete construction waste is a promising way towards sustainable construction. Coarse recycled concrete aggregates have been widely studied in recent years, however only few data have been reported on the use of fine recycled aggregates. Moreover, a lack of reliable data on long-term properties of recycled aggregate concrete has to be pointed out.In this paper the effects of both fine and coarse recycled concrete aggregates on short and long-term mechanical and physical properties of new structural concrete are investigated. The studied concrete mixes have been designed by adjusting and selecting the content and grain size distribution of concrete waste with the goal to obtain medium–high compressive strength with high content of recycled aggregates (ranging from 27% to 63.5% of total amount of aggregates).Time-dependent properties, such as shrinkage and creep, combined with porosity measurements and mechanical investigations are reported as fundamental features to assess structural concrete behavior.     

我国主要城市经济发展水平研究

运用主成分分析法对国内9个主要城市的经济发展水平进行了评价,得出了各城市的综合排名结果,并结合聚类分析对各城市经济发展水平进行分类及探讨,依据分析结果,提出了相应的城市建设建议。     

振荡时间、离子强度、温度和pH值对GMZ膨润土中Cr（Ⅲ解）吸特性的影响

对吸附在高庙子（GMZ）膨润土上的Cr（III）进行解吸实验，研究振荡时间、解吸溶液离子强度、温度和pH值等因素对解吸特性的影响规律。结果表明：高庙子膨润土上Cr（III）的解吸过程较易发生；Cr（III）的解吸动力学过程较吸附过程慢，实验条件下解吸过程在3 h后达到平衡；当使用0.1 mol/L HCl、1 mol/L NaCl和1 mol/L CaCl 2作为解吸液时，Cr（III）的最终解吸率分别达89.4%,56.5%和77.2%；增大解吸溶液的离子浓度能够促进解吸过程的发生；pH值对Cr（III）解吸过程有重要影响；吸附/解吸过程较符合Freundlich等温模型。GMZ膨润土在处理Cr（III）废水时具有较好的再生能力，可以多次重复利用。     

Impact performances of steel tube-confined recycled aggregate concrete (STCRAC) after exposure to elevated temperatures

The impact behaviours of steel tube-confined recycled aggregate concrete (STCRAC) following exposure to elevated temperatures of 20 °C, 200 °C, 500 °C and 700 °C were experimentally investigated using a 100 mm-diameter split Hopkinson pressure bar (SHPB). The recycled coarse aggregate (RCA) replacement ratios were set as 0, 50% and 100%. The effect of RCA replacement ratio and exposure temperature on the impact properties of STCRAC were analysed in terms of failure modes, stress-strain time history curve and dynamic increase factor (DIF). The results show that the fire-damaged STCRAC can maintain its integrity during impact load. However, there were evident degradations in the dynamic behaviour of STCRAC after exposure to high temperatures of 500 °C and 700 °C. The ultimate impact strength, impact secant modulus and residual impact strength of STCRAC obviously decreased because of the damage due to high temperature exposure. But the degradations of both the ultimate impact strength and impact secant modulus of STCRAC under impact loading were less severe than those under quasi-static loading. The remaining strength factor and the DIF tended to increase with the raise of the elevated temperatures. Overall, during the impact loading, the fire-deteriorated STCRAC exhibited excellent impact behaviour.     

Structural behaviour of ferrocement–brick composite floor slab panel

This study introduces a semi-fabricated system for the construction of floor slab. The slab panel consists of two layers joined together using truss type shear connectors. The first layer is a precast ferrocement layer which acts initially as a formwork, while the second layer consists of bricks and mortar. Continuous truss shear connectors are used to connect the two layers. The paper experimentally investigates the structural response of ferrocement–brick composite panel under flexural load. Four full scale specimens were cast and tested under two-line loads. The study highlights the effect of shear connectors and brick layout on the overall structural response of the slab. The results in terms of load–deflection, crack pattern, strain distribution and failure loads indicate that the response of the composite slab to the flexural loading is satisfactory and can be used as a floor slab in construction sector.     

套筒与轴热套装过程的接触有限元分析

运用MSC.Marc对套筒与轴的热套装过程进行有限元模拟,涉及热机耦合分析和接触分析。在建立合理的有限元模型、正确定义和选择边界条件的基础上,分析套筒受热自由膨胀状态以及套筒与轴过盈配合的应力应变,最后通过对比分析模拟结果与试验结果验证有限元分析的合理性,为结构的进一步改进提供理论依据。     

In-line rheological measurements of cement grouts: Effects of water/cement ratio and hydration

The rheological properties of cement based grouts change with water/cement ratio and time, during the course of hydration. For this reason, it is desirable to be able to measure this change continuously, in-line, with a robust instrument during the entire grouting operation in the field.The rheological properties of commonly used cement grouts were determined using the Ultrasound Velocity Profiling combined with the Pressure Difference (UVP + PD) method. A non-model approach was used that directly provides the properties, and the results were compared with the properties obtained using the Bingham and Herschel–Bulkley rheological models. The results show that it is possible to determine the rheological properties, as well as variations with concentration and time, with this method.The UVP + PD method has been found to be an effective measuring device for velocity profile visualization, volumetric flow determination and the characteristics of the grout pump used.     

Large diameter shafts for underground infrastructure

The technique of large diameter shafts for deep excavations was analysed in terms of its basic construction elements, reported literature cases and design methods. The effects of the construction sequence and the geological deposition on the behaviour of the shaft was analysed using 3D finite element models. Induced stresses and displacements on the soil mass were investigated. Three methods to assess the stability of the shaft lining were presented and employed as a post-processing stage of analysis of the models. The results indicated a major influence of the height of the vertical excavation stages on the shaft behaviour, markedly on the induced settlements. The lining analysis also demonstrated the effects of the vertical excavation stages and how different safety assessment methods can produce significantly different results.     

Effects of twin tunnels construction beneath existing shield-driven twin tunnels

This paper presents a case of closely spaced twin tunnels excavated beneath other closely spaced existing twin tunnels in Beijing, China. The existing twin tunnels were previously built by the shield method while the new twin tunnels were excavated by the shallow tunnelling method. The settlements of the existing tunnels and the ground surfaces associated with the new tunnels construction were systematically monitored. A superposition method is adopted to describe the settlement profiles of both the existing tunnels and the ground surfaces under the influence of the new twin tunnels construction below. A satisfactory match between the proposed fitting curves and the measured settlement data of both the existing tunnels and the ground surfaces is obtained. As shown in a particular monitoring cross-section, the settlement profile shapes for the existing tunnel and the ground surface are different. The settlement profile of the existing structure displays a “W” shape while the ground surface settlement profile displays a “U” shape. It is also found that due to the flexibility of the segmental lining, the ground losses obtained from the existing tunnel level and the ground surface level in the same monitoring cross-section are nearly the same.