Susana Cabral-Fonseca

Durability of carbon fi bre reinforced polymer laminates used to reinforced concrete structures

Abstract Due to their excellent mechanical properties and easy application carbon fibre reinforced polymers (CFRP) are being successfully used to repair and renew old and damaged civil engineering infrastructures. In particular, the method of strengthening concrete members with externally bonding of CFRP laminates has become increasingly popular. In fact, extensive research has shown that this technique can lead to a substantial improvement in the flexural and shear strength capacities of the member repaired. In such applications, materials involved will be exposed to outdoor environmental conditions, including humidity, water from rain, saline-water, ground water and high alkalinity solutions due to chemical composition of the concrete itself, as well as solar ultraviolet (UV) radiation. Thus, it is of great relevancy to study the durability of the materials involved, namely epoxy adhesives and CFRP laminates, as well as, the integrity of the entire system, when subjected to those environmental factors. This work is part of a much larger research study to predict the long-term behaviour of several commercial CFRP laminate/adhesive systems used in the rehabilitation of concrete structures. In the whole project it is recognised that the durability of these solutions depends not only on the durability of the composite materials but also on the performance of the systems used to bond them to the concrete. This present document provides details about the durability of CFRP laminates and the study carried out to investigate the environmental and accelerated ageing effects on three types of commercially available CFRP laminates. The changes in CFRP laminates properties after exposure up to 18 months under different environmental conditions – immersion in demineralised water, saline and alkaline solutions at room temperature, 40°C and 60°C, as well as under constant humidity condensation atmosphere at 40°C – are reported and discussed. The results of tests performed in accelerated weathering chambers – with UV radiation – are also included. Results obtained offer valuable information about the progression of material degradation under different ageing conditions (some of them accelerated), which can be used, not only to characterise the behaviour of CFRP laminates, but also for a better understanding of the degradation mechanisms involved, which is a base for the design of service life-prediction models.

Creep of Sandwich Panels with Longitudinal Reinforcement Ribs for Civil Engineering Applications: Experiments and Composite Creep Modeling

AbstractComposite sandwich panels with reinforcement ribs or webs are being increasingly considered for structural applications in civil engineering. Such panels are prone to creep when subjected to significant permanent loads and therefore the effects of this phenomenon must be duly accounted for in their design. Data regarding the viscoelasticity of sandwich panels and their constituent materials is still scarce and often cannot be directly used for creep predictions in design practice. To address this issue, this paper presents the experimental assessment and the analytical modeling of the viscoelastic response of two types of sandwich panels, with and without reinforcement ribs. Panels comprising glass fiber–reinforced polymer (GFRP) faces, cores of polyurethane (PU) foam, and longitudinal GFRP ribs are considered. The ribs increased the flexural strength and stiffness of the panels by a factor of two, while providing a threefold reduction in their creep compliance. A composite creep modeling (CCM) ap...

Effects of hygrothermal ageing on the mechanical properties of glass-fibre-reinforced polymer pultruded profiles

This paper presents the results of an experimental study on the physical and mechanical changes suffered by glass-fibre-reinforced polymer (GFRP) pultruded profiles, made of either unsaturated polyester or vinylester resins, after accelerated hygrothermal ageing. Specimens from both types of profiles, comprising identical fibre contents and architectures, were subjected to: (a) immersion in demineralized water; (b) immersion in saltwater at temperatures of 20, 40 and 60°C for 12 months and; (c) continuous condensation at 40°C for 9 months. Batches of test specimens from both profiles, conditioned in those accelerated exposure environments, were periodically monitored with respect to: (a) mass changes; (b) variation in glass transition temperature evaluated through dynamic mechanical analysis (DMA) and; (c) degradation of mechanical properties, assessed by means of tensile, flexural and interlaminar shear tests.