海洋潮汐浪溅区混凝土表面氯离子浓度的改进计算模型

收集世界不同地区304组海洋潮汐浪溅区自然暴露混凝土的试验数据,据此分析水胶比、胶凝材料种类和暴露时间对混凝土表面氯离子浓度C_(s,ts)的影响规律,进而结合二阶段多元非线性回归分析,分别确定了硅酸盐水泥、粉煤灰、矿渣和硅灰等胶凝材料对C_(s,ts)的修正系数,建立了海洋潮汐浪溅区C_(s,ts)的改进模型,并利用现有模型和试验数据对比,验证了该模型的适用性。分析表明:C_(s,ts)与水胶比之间近似呈线性关系,且胶凝材料种类对C_(s,ts)的影响显著;C_(s,ts)在前5a内快速增长,随后逐渐趋于稳定,可以利用指数型函数来描述其时变规律。     

A simple damage model for concrete considering irreversible mode‐II microcracks

A simple damage model with the concept of mode‐II microcracks on crack wall contributing to the irreversible strains for concrete is developed. By applying the micromechanics method, a microcell‐based damage model is introduced to understand the damage behaviour. Further, by introducing the physical interpretation of the damage variable using thermodynamic method, a novel damage variable (irreversible‐damage variable) is proposed to describe the irrecoverable strains generated by both mode‐II microcracks and irreversible‐frictional sliding. With this methodology, a simple continuum damage mechanics model is developed in which both elastic and irreversible damages are considered. As demonstrated by the comparison with experimental results, the proposed model is characterized by accuracy of solutions, sufficiency of physical sense and convenience of implementation.     

Assessment of empirical formulas for prediction of the effects of projectile impact on concrete structures

The prediction of the response of structures subjected to projectiles impact may often be accomplished by means of empirical or semi‐empirical formulas available in the technical literature, which address mainly cases of relevance in engineering practice in terms of the observed failure modes. The paper presents an evaluation of the performance of the equations most widely used in predictions of penetration, scabbing and perforation of concrete and rock structures by comparing the predicted results with experimentally observed response and with the results of detailed numerical analyses employing the truss‐like Discrete Element Method (DEM). Numerical DEM predictions were shown to be close to the experimentally determined responses of concrete plates subjected to impact throughout the range of velocities examined and were also consistent with the empirical formulas. In all cases the authors attempted to quantify the uncertainty inherent both in the predictions of empirical formulas and of the numerical analysis.     

Size independent fracture energy evaluation for plain cement concrete

The present work deals with the investigation of a robust analytical scheme to assess the size‐independent fracture energy of concrete. The study involves the numerical modelling of three‐point bend (TPB) concrete beams that are geometrically similar, having constant length to depth ratio with varying range of notch to depth (a/W) ratios. The unique nonlinear behaviour of concrete 1material is incorporated through fracture energy‐based strain‐softening model in the finite‐element numerical simulation. The International Union of Laboratories and Experts in Construction Materials, Systems and Structures (RILEM) fracture energy values are evaluated through numerical simulation of several set of experimentally observed load‐load line displacement response. The RILEM fracture energy values associated with geometrically similar beams have been utilised to develop a methodology for assessment of the size‐independent fracture energy of concrete. The numerically predicted and experimentally evaluated size‐independent fracture energy using the RILEM fracture energy values are found to be in close agreement.     

基于热力学原理的混凝土热-力耦合本构模型

为了解决高温条件下混凝土材料力学性质描述的问题，基于热力学理论，将损伤理论与经典弹塑性理论结合，建立了一个考虑温度影响的混凝土热-力耦合本构模型，用于描述高温条件下混凝土材料的力学性质。基于热力学原理推导了考虑温度影响的弹性应变增量的表达式，并基于经典塑性理论，构造了一个考虑温度影响的硬化参数，推导出相应的塑性应变增量表达式，将上述2部分应变增量叠加得到混凝土热-力耦合本构模型的表达式。将模型预测结果与试验结果进行对比，符合良好，表明上述热-力耦合本构模型能够对高温条件下混凝土材料的力学性质进行较为准确的描述与预测。     

化学腐蚀作用下煤矸石混凝土力学特性试验

探究煤矸石混凝土在化学腐蚀条件下的力学特性，以不同pH值化学溶液浸泡过的试样为研究对象进行三轴压缩试验，通过浸泡过程中试样质量变化、溶液pH值变化及三轴压缩试验结果，分析不同pH值化学溶液对煤矸石混凝土力学特性的影响。结果表明：随着浸泡时间的增长，每种试样都有质量损失，而且溶液的pH值都稳定趋于碱性；围压大小与溶液pH值都是影响煤矸石混凝土力学特性的重要因素，在围压相同的情况下，随着溶液pH值的增大，试样三轴压缩试验的强度随之增加；在溶液pH值相同的情况下，随着围压的增大，试样三轴压缩试验的强度随之增加；并进一步分析了化学溶液对试样的腐蚀机理。     

固硫灰复合掺合料的制备及应用研究

以石屑、脱硫石膏、超细固硫灰和炉渣等工业固体废物为原料，制备了各项指标均满足GB/T 18736-2002《高强高性能混凝土用矿物外加剂》Ⅰ级磨细粉煤灰要求的固硫灰复合掺合料，并确定了性能优异、最经济的掺合料配比。将该掺合料用作矿物掺合料取代P·I 42.5水泥制备C40混凝土，结果表明其最大取代量可达25%。     

Effect of cooling methods on residual compressive strength and cracking behavior of fly ash concretes exposed at elevated temperatures

This paper presents the effects of cooling methods on residual compressive strength and cracking behavior of concretes containing four different class F fly ash contents of 10%, 20%, 30% and 40% as partial replacement of cement at various elevated temperatures. The residual compressive strength of the aforementioned fly ash concretes is measured after being exposed to 200, 400, 600 and 800 °C temperatures and two different cooling methods, for example, slow cooling and rapid water cooling. Results show that the residual compressive strengths of all fly ash concretes decrease with increase in temperatures irrespective of cooling regimes, which is similar to that of ordinary concrete. Generally, control ordinary concrete and all fly ash concretes exhibited between 10% and 35% more reduction in residual compressive strength because of rapid cooling than slow cooling except few cases. Cracks are observed over concrete specimens after being exposed to temperatures ranging from 400 to 800 °C. Samples that are slowly cooled developed smaller cracks than those rapidly cooled. At 800 °C, all fly ash concretes that are exposed to rapid cooling showed the most severe cracking. X‐ray diffraction analysis shows reduction of Ca(OH)₂ peak and formation of new calcium silicate peak in concretes containing 20% and 40% fly ash when subjected to 800 °C in both cooling methods. Thermo gravimetric analysis and differential thermal analysis results show increase in thermal stability of concrete with increase in fly ash contents. The existing Eurocode also predicted the compressive strength of fly ash concretes with reasonable accuracy when subjected to the aforementioned elevated temperatures and cooling methods. Copyright © 2014 John Wiley & Sons, Ltd.     

无机聚合物混凝土高温性能研究综述

分别从无机聚合物胶凝体高温性能，无机物聚合物混凝土高温劣化机理，高温静、动力学特征，耐火混凝土5个方面综述了目前国内外关于无机聚合物混凝土高温性能的研究进展，指出并探索无机聚合物混凝土高温性能需要进一步深入研究的问题和今后的发展方向。     

Mechanical Properties of Modified Concrete Based on Nano-Silicon Dioxide

Abstract

In order to solve the problem of insufficient durability and long-term performance of concrete, the compressive and splitting properties of nano-silicon dioxide modified concrete are analyzed in this study, which provides strong evidence for the synergistic interaction between nano-silicon dioxide modified concrete, fly ash and mineral powder and the improvement of durability. Firstly, ordinary concrete and high-performance concrete are modified and mixed. Then, they are separately mixed with nano-silicon dioxide. Nano-silicon dioxide is mixed with fly ash, and nano-silicon dioxide is mixed with mineral dust. Compressive strength and splitting tensile strength of modified concrete are tested and compared, and mechanical properties of modified concrete are analyzed. The results show that the synergistic effect of nano-silicon dioxide, fly ash and mineral powder on the strength of concrete is remarkable. The maximum increment of compressive strength of modified ordinary concrete is 10Mpa, and that of synergistic modified high-strength concrete is 20 MPa. In addition, a small amount of nano-silicon dioxide can improve the splitting tensile strength of ordinary concrete, but it has no obvious effect on the splitting tensile strength of high-strength concrete. Therefore, the problem of insufficient durability and long-term performance of concrete can be solved to some extent by adding nano-silicon dioxide in concrete according to reasonable proportion.