Micro-stress analysis and identification of lightweight aggregate’s failure strength by micromechanical modeling

This work is based on a dual approach of experiments and micromechanical modeling in order to characterize the failure behaviors of lightweight aggregate concretes (LWAC). Many classes of LWAC were tested, based on five families of lightweight aggregates (LWA) and three types of mortar matrices: normal, high performance (HP) and very high performance (VHP). Micromechanical modeling is based on an iterative homogenization approach and associated localization: local stress distributions during the uniaxial compression tests can be predicted in LWAC’s components and at their interface. Experimental compressive strengths were measured on manufactured 16 × 32 cm cylindrical specimens. The confrontations between micromechanical modeling and experiments were used to identify LWA’s failure strengths which are difficult to measure, and to quantify the inaccuracies related to conventional methods. These corrected values of LWA’s failure strength were introduced into a failure criterion modeling: associated predictions of LWAC’s compressive strength are in good agreement with the experimental measurements.     

Preliminary study on mitigating steel reinforcement corrosion with bioactive agent

Corrosion causes over $100 billion in damage annually. Cinnamaldehyde, a bioactive agent derived from cinnamon bark, can mitigate the corrosion of metals but has a negative effect on hydration when incorporated in cementitious systems. In order to avoid these negative consequences while harnessing anti-corrosive properties, cinnamaldehyde was incorporated in a cementitious mixture through the use of lightweight aggregate (LWA). The same method was used for penetrating corrosion inhibitors in an attempt to reduce the time required for the inhibitor to reach and protect reinforcing steel. The setting time, compressive strength, heat evolution (via semi-adiabatic calorimetry), and autogenous shrinkage of the experimental mixtures were measured and an accelerated corrosion test (ACT) was used to quantify performance in a corrosive environment. Experimental mortars showed prolonged setting times, reduced compressive strength, heat evolution, and autogenous expansion. However, the experimental mortars showed an increase in time to cracking when exposed to a corrosive environment.     

“灯芯效应”下珊瑚骨料混凝土氯离子传输行为

研究了“灯芯效应”下珊瑚骨料混凝土在Mg²⁺、SO₄^2-共同作用下Cl^-的传输规律，建立了“灯芯效应”下珊瑚骨料混凝土Cl^-传输模型.结果表明：Cl^-沿半浸泡混凝土高度方向由下而上传输的同时也由表层向中心传输，其在混凝土内部的含量呈类抛物面分布；SO₄^2-的存在会加快Cl^-在混凝土中的传输，而Mg²⁺的加入会抑制Cl^-的传输，导致混凝土在相同高度及深度处的Cl^-含量小于SO₄^2-与Cl^-共同作用下的Cl^-含量；本文建立的“灯芯效应”下珊瑚骨料混凝土氯离子传输模型计算结果与实测结果吻合良好.     

Use of pre-wetted lightweight fine expanded shale aggregates as internal nutrient reservoirs for microorganisms in bio-mineralized mortar

Interest in developing bio-based self-healing cement-based materials has gained broader attention in the concrete community. One of challenges in developing bio-based self-healing cement-based materials is that cell death or insufficient metabolic activity might occur when the cells are inoculated to the cement paste. This paper investigates the use of internal nutrient reservoirs via pre-wetted lightweight fine expanded shale aggregates to improve cell viability in mortar. Incorporation of internal nutrient reservoirs resulted in an increase in the vegetative cells remaining without any substantial loss in strength. These results pave the way to develop a self-healing and self-curing concrete with an extended service life.     

The performance of steel-making slag concretes in the hardened state

The use of oxidizing slag from electric-arc furnaces as an aggregate is a sustainable option in the manufacture of concrete, the performance of which is similar to an ordinary aggregate concrete. This study examines the reuse of two different types of oxidizing slag in concretes designed for use in structural components and compares their performance against relevant specifications contained in current working standards. Fundamental aspects are discussed, among which density and workability that are related to the proportioning of the concrete and its mechanical and physical properties. The results show that overall concrete quality is maintained and that its performance is acceptable for the proposed application.     

Bond strength prediction for deformed steel rebar embedded in recycled coarse aggregate concrete

This paper summarizes the results of an experimental investigation into the bond behavior between recycled aggregate concrete (RAC) and deformed steel rebars, with the main variables being the recycled coarse aggregate replacement ratio (RCAr) and water-to-cement ratio of the concrete mixture. The investigation into splitting cracking strength indicates that the degradation of the bond splitting tensile stress of the cover concrete was affected by not only the roundness of the coarse aggregate particles but also the weak interfacial transition zone (ITZ) between the cement paste and the RCA that has a more porous structure in the ITZ than normal concrete. In this study, a linear relationship between the bond strength and the density of the RCA was found, but the high compressive strength reduced the effects of the parameters. To predict the bond strength of RAC using the main parameters, a multivariable model was developed using nonlinear regression analysis. It can be inferred from this study that the degradation characteristic of the bond strength of RAC can be predicted well, whereas other empirical equations and code provisions are very conservative.     

高效的无证书广义指定验证者聚合签名方案

研究无证书广义指定验证者聚合签名的安全模型,基于双线性映射提出无证书广义指定验证者聚合签名方案。在随机预言模型和计算Diffie-Hellman困难问题假设下,证明方案不仅可以抵抗无证书广义指定验证者聚合签名的3类伪造攻击,而且满足指定验证性和不可传递性。方案的聚合签名长度和单用户签名长度相当,签名公共验证和指定验证需要的双线性对数固定。     

基于正交设计的复杂环境下土石混填体大型直剪试验研究

为了更加系统、全面的研究土石混填体处于复杂环境时的强度特性,综合考虑含水率、浸泡时间、干湿循环、含石量、岩性与土性等因素,采用美国Geotest公司生产的大型直剪仪,并基于正交设计方法开展了一系列土石混填体室内大型直剪试验研究,进而确定出了不同因素对土石混填体抗剪强度有何影响及影响程度,为此类受多因素、多水平影响的试验研究探讨出了一种新的思路。试验结果表明：土石混填体抗剪强度主要源于内部石料间的相互嵌入、咬合及摩擦等作用;含石量是影响土石混填体强度特性最主要的因素,随着试样中含石量的增加其内摩擦角近似呈线性增加;对于试验中所涉及的3种水作用环境,含水率对土石混填体抗剪强度的影响最为显著,且含水率对其剪应力-剪切位移关系曲线亦存在非常重要的影响,相比之下,浸泡时间与干湿循环对试样抗剪强度影响较弱,且试样在浸泡48 h或干湿循环4次后其抗剪强度基本不会再继续弱化;当试样中含石量≥55%时,其抗剪强度受岩性影响较为明显。     

自编EXCEL程序调整混凝土粗骨料级配

粗骨料级配对混凝土和易性影响较大,粗骨料级配不良易导致混凝土拌合物离析。本文采用EXCEL软件编制程序,以快速确定粗骨料混合比例,使其混合后能符合连续级配要求。