Long-Term Evolution Of Delayed Ettringite And Gypsum In Portland Cement Mortars Under Sulfate Erosion

The magnitude evolution of ettringite and gypsum in hydrated Portland cement mortars due to sulfate attack was detected by X-ray powder diffraction. The influences of sulfate concentration and water-to-cement ratio on the evolution of ettringite and gypsum were investigated. Experimental results show that the magnitude of ettringite formation in sodium sulfate solution follows a three-stage process, namely, the 'penetration period', 'enhance period of strength', and 'macro-crack period'. The cracking of concrete materials is mainly attributed to the effect of ettringite. The gypsum formations occurred in two stages, the 'latent period' and the 'accelerated period'. The gypsum formation including ettringite formation was relative to the linear expansion of mortars to some extend. Both water-to-cement ratio and sulfate concentration play important roles in the evolution of ettringite and gypsum. (C) 2008 Elsevier Ltd. All rights reserved.

Equivalent Model Of Expansion Of Cement Mortar Under Sulphate Erosion

The expansion property of cement mortar under the attack of sulfate ions is studied by experimental and theoretical methods. First, cement mortars are fabricated with the ratio of water to cement of 0.4, 0.6, and 0.8. Secondly, the expansion of specimen immerged in sulphate solution is measured at different times. Thirdly, a theoretical model of expansion of cement mortar under sulphate erosion is suggested by virtue of represent volume element method. In this model, the damage evolution due to the interaction between delayed ettringite and cement mortar is taken into account. Finally, the numerical calculation is performed. The numerical and experimental results indicate that the model perfectly describes the expansion of the cement mortar.

EQUIVALENT MODEL OF EXPANSION OF CEMENT MORTAR UNDER SULPHATE EROSION

The expansion property of cement mortar under the attack of sulfate ions is studied by experimental and theoretical methods. First, cement mortars are fabricated with the ratio of water to cement of 0.4, 0.6, and 0.8. Secondly, the expansion of specimen immerged in sulphate solution is measured at different times. Thirdly, a theoretical model of expansion of cement mortar under sulphate erosion is suggested by virtue of represent volume element method. In this model, the damage evolution due to the interaction between delayed ettringite and cement mortar is taken into account. Finally, the numerical calculation is performed. The numerical and experimental results indicate that the model perfectly describes the expansion of the cement mortar.

新型轮—腿—履带复合移动机构及稳定性分析

为提高反恐防暴机器人对非结构环境的适应能力,设计出了一种具有良好的机动性能和转向性能的新型轮—腿—履带复合移动机构.通过机器人机构分析与本体的稳定性分析,论证了其结构设计的可行性及好的稳定性.

反恐防暴机器人机构与控制的研究

西方国家早在20世纪60年代就开始采用防暴机器人处理爆炸物。自从9.11事件后，国际社会恐怖活动更是愈演愈烈，许多国家相继对此给予了高度重视。反恐防暴机器人可应用于核工业、军事、燃化、铁路、公安、武警等部门，代替人在危险、恶劣、有害环境中执行探查、排除或销毁爆炸物、消防、抢救人质以及与恐怖分子对抗等任务。本项目依托课题由最初的“危险作业机器人”到现在的“反恐防暴机器人的产业化研究”，由国家“863”计划资金滚动支持。就现有的反恐防暴机器人，存在速度较慢或机动灵活性不强或可靠性不高等不足，现研究出一种新型反恐防暴机器人，目的是在保证适应一定的非结构环境的前提下（适用所有的非结构环境的移动机构设计是不可取的，也是不现实的），提高机器人本体转向性能和移动速度，降低功耗，机构简单化，同时在硬件与软件设计时采取一些相应的措施，提高其在实际应用环境中的可靠性和抗干扰能力。首先，通过对以往反恐防暴机器人在非结构环境中采用的复合移动机构对比分析研究，提出了一种新型的轮-履带-腿复合移动机构，应用在”灵豹”机器人上。它的特色是移动机构继承了“灵蜥”系列反恐防暴机器人轮与履带移动方式自动切换功能，并且针对“灵蜥”系列机器人轮式移动时，四轮滑动转向灵活性不高、功耗大的问题，提出了三轮式移动机构，在狭小移动空间有着广泛的应用。并对该机器人本体做了运动学分析和稳定性分析，论证了该机构的可行性。其次，根据课题项目研究的需要，在控制方面，主要完成了“灵狐”小型反恐防暴机器人的系统构建与功能实现。通过从事“灵蜥”系列机器人项目开发，积累了一些移动机构设计与分析以及控制系统一些问题解决的实际经验，在“灵狐”控制系统设计过程中，由于采用单片机作为微控制单元，因此着重考虑了提高系统可靠性与抗干扰能力。在“灵狐”机器人样机试验中取得了好的效果，均达到预期目标。