A new multi-scale approach to characterize concrete creep and its implications in long-term durability

最近对71座混凝土桥梁进行了为期约20年的监测调查，结果表明徐变挠度不断增加，并且高估了几个国家规范的预测。随后发出了警钟，指出目前的国家设计建议和规范“不仅在理论上过时，而且站不住脚”。建议的研究计划旨在更好地理解和表征混凝土的长期徐变，并最终提高目前的设计方法预测的长期行为。* 估计混凝土的长期徐变（例如，30-50年）使用短期蠕变测试（例如，3-12几个月）一直是土木工程中不可回避的难题。在这种情况下，新的微压痕技术已经提供了一个突破性的解决方案，因为它们允许在几分钟内表征长期蠕变的对数性质。从设计的角度来看，现代模型代码fib 2010最近采用了对数函数来预测长期蠕变。这是非常有吸引力的拟议的研究计划，打算发展微压痕技术，以快速估计这种对数函数的参数，用于预测混凝土的长期徐变。* 本研究计划的具体目标是：*（1）在微观结构水平上，通过微压痕试验充分表征和更好地了解温度和可能的损伤对水泥浆体蠕变行为的影响; *（2）将在水泥浆体水平上测量的性能提高到混凝土水平;* （3）为了实现用于预测结构在不同环境条件下的长期变形的数值模型（例如，* （4）改进目前预测长期蠕变的设计方法; *（5）发展一个国际卓越网络，培养学生高度专业化的能力。这一创新的研究方向将为土木工程提供杰出的贡献，例如：*（i）促进目前对混凝土长期徐变的理解，重点是其对温度和损伤的依赖性; *（ii）开发用于表征水泥浆体长期徐变的超快速微压痕技术;* ㈢开发工程工具，以便更好地预测桥梁等混凝土结构的长期徐变;* ㈣为更好地预测混凝土结构的长期徐变和确保未来所需的耐久性而增强的设计建议做出贡献加拿大基础设施*****

A recent survey on 71 concrete bridges monitored over a period of about 20 years showed that the creep deflection increases incessantly and it overestimates by far the predictions of several national codes. A wake-up call was then launched stating that the current national design recommendations and codes “are not only theoretically obsolete, but also indefensible”. The proposed research program aims at better understanding and characterizing the long term creep of concrete, and finally, to enhance the current design methods for predicting the long term behavior. ***Estimating the long-term creep of concrete (e.g., 30-50 years) using short term creep tests (e.g., 3-12 months) has been an unavoidable crux in civil engineering. In this context, novel microindentation techniques have been provided a breakthrough solution as they allow characterizing the logarithmic nature of the long term creep in few minutes. From a design point of view, the modern model code fib 2010 has recently adopted a logarithmic function for predicting the long term creep. This is extremely appealing for the proposed research program which intends to develop micro-indentation techniques to rapidly estimate the parameters of such logarithmic function for predicting the long term creep of concrete. ***The specific objectives of this research program are: ***(1) At the microstructure level, to fully characterize and better understand the effect of the temperature and possible damage on the creep behaviour of a cement paste by means of microindentation tests; ***(2) Upscale the properties measured at the level of a cement paste to the concrete level; ***(3) To implement a numerical model for predicting the long term deformation of a structure at different environmental conditions (e.g., temperature) and with possible damage due to durability issues;***(4) To improve the current design methods on the prediction of the long term creep; ***(5) To develop an international network of excellence and train students in highly specialized competences.***This innovative research direction will provide outstanding contributions to civil engineering, such as: ***(i) Fostering the current understanding on the long term creep of concrete with emphasis on its dependence on temperature and damage; ***(ii) Developing of ultra-rapid microindentation techniques for characterizing the long term creep of cement paste; ***(iii) Developing engineering tools for better predicting the long term creep of a concrete structures, such as bridges; ***(iv) Contribution to enhanced design recommendations for better predicting the long term creep of concrete structures and assuring the desired durability of the future Canadian infrastructure. *****