DUST

Abstract

Increasing investment on strengthening of structures and use of new materials raise questions of technical alternatives, performance and economy, as well as aspects of impact on the environment. Short durability of materials requires frequent repairs or replacement of structures, consumes energy and resources and creates a heavy environmental burden and source of waste. Required studies to extend the durability of structural materials are twinned with sustainability of construction and need further research. In particular, deteriorating concrete infrastructures affect productivity and impose severe impact on resources, environment and human safety. Strengthening reinforced concrete structures is a major source of activities in civil engineering and FRPs have become one of the solutions often selected. The degradation of concrete and the insufficient knowledge about lifetime of FRPs led to research pioneered by UNL. There remain, however, aspects requiring further durability studies. The ageing of concrete, RC and GFRP, as well as of the behavior of beams with outer reinforcement of GFRP are typically such cases and a major objective of this proposal. The study requires participation of several disciplines, from monitoring degradation to the study of micro-changes of materials along the ageing process, under various environmental conditions, including the use of modern experimental techniques to gain understanding of the process. Computational modeling validated against experimental data is also considered to allow generalization of conclusions and possible design recommendations. Issues selected to analyze derive from the need to complement previous research and from paucity of available information: i) Effects of salinity, temperature cycles and sulfates attack on the mechanical strength of structures. ii) Testing, individual behavior of GFRP laminates, concrete, and performance of RC beams with GFRP outer reinforcement, including the important and poorly known subject of bond degradation. iii) SEM and petrographic techniques to monitor the temporal evolution of the degradation of the materials, together with DSC for Tg alterations, and electrochemical techniques to study corrosion of steel bars. Thus, it is expected to correlate data to phenomenological observations and mechanical tests with microstructural changes. Linkage between accelerated tests and real life degradation is planned, using concepts associated with time-temperature superposition. iv) Computational modeling, considering the nonlinear constitutive properties of concrete and bond. Dissemination of the results that lead to better design procedures and extend the life of structures is planned. Educating young researchers is also a natural byproduct of the activities. On all issues the team has ISI publications and experience. Choice of environmental conditions deserves a few remarks. Chlorides are especially severe for steel, FRP outer structural strengthening and mortars. Temperature cycles, especially near the vitreous temperature of the adhesives, as well as salt fogging, may severely affect affect bonding. There is growing evidence that above ground components of highway structures are subject to sulfate induced deterioration and inspection works have revealed that sulphate attack is often mis-diagnosed as alkali-silica attack. UNIC has a SO2 chamber available, ICEMS has experience on these types of corrosion, and the above facts showed that the Project could contribute to a wider view of durability of structures working also on this subject. Computational modeling needs no justification and shall constitute the subject of a PhD thesis considered as a deliverable and to be authored by a former Master student on the topic. The degradation of the macroscopic properties required in structural design due to environmental aging has to be understood. The Project includes the use of techniques of petrography, infrared rays, SEM, DSC, electrochemical techniques that, associated with a vast program of mechanical tests and computational modeling led by structural engineers. A very unusual broad interdisciplinary approach characterizes the proposal. The research units, i.e. ICEMS-IST, CICEGe, members from CENIMAT and UNIC, are part of the National Scientific Network, have participated in many Research Projects and shall have access to the advice of a most prestigious consultant. In terms of equipment, only one more salt fog chamber is necessary due to the high number of specimens involved.