International Concrete Abstracts Portal

This study numerically investigates the long-term effectiveness of using externally bonded fiber-reinforced polymer (FRP) plates as a strengthening technique for reinforced concrete (RC) beams. A two-dimensional finite element model (FEM) that can accurately predict the flexural behavior of FRP strengthened RC beams, is developed. Weathering exposure time of 0.0, 15.5, 35, and 75 years were considered. In total, 28 different concrete beams were modelled using the developed FEM. The results show that prolonged exposure to natural weathering can cause premature FRP debonding, even before reaching the yielding load. The ultimate load capacity, midspan deflection, and ductility of strengthened RC beams can be reduced by up to 38%, 62%, and 100%, respectively. In addition, the findings raised concerns about the applicability of the ACI 440.2R-17 provisions for calculating the design flexural strength of FRP strengthened RC beams with prolonged exposure to natural weathering. To ensure a safe design for strengthened beams with FRP debonding or concrete crushing failure modes, this paper recommends an additional reduction factor ranging from 0.8 to 0.9. Furthermore, periodic inspection using non-destructive testing and FRP anchorage system are highly recommended for both existing and new applications of FRP in structures.

Deterioration of concrete bridges has resulted in reduction of their service lives and increase in required maintenance which is associated with cost and inconvenience to the public. A prevalent cause of concrete bridge deterioration is corrosion which initiates by chloride ions penetration past the protecting layers and by corroding the steel reinforcement. Because corrosion in prestressed concrete members has more serious consequences than in non-prestressed reinforced concrete, it is important that bridge designers and inspectors be aware of the potential problems and environments that may cause the issue and address them as soon as they are detected. This paper discusses a case study of a highway bridge (Hyndman Bridge, Ontario) including its deterioration, causes, mitigation measures, structural evaluation and the selected repair method. The rehabilitation design is based on guidelines of the latest editions of the CHDBC and ACI 440.2R. CFRP strengthening techniques have been proposed to address the flexure and shear deficient capacity of deteriorated girders. It is concluded that by using a suitable repair methodology employing CFRP, it is possible to upgrade the bridge to comply with the latest requirements of the code and increase the service life of the structure which otherwise would have needed imminent replacement.

A special concrete was used to erect the MAXXI building in Rome designed by Zaha Hadid and her team with long, inclined, curvilinear walls. Due to the very congested reinforcements, the original concrete issued by Zaha Hadid and her team was self-compacting concrete (SCC). However, irregular cracks -caused by the restrained drying shrinkage- appeared on the surface of this concrete a few days after removing the formworks. On the other hand, due to aesthetic reasons, neither saw cuts in the hardened concrete to produce regular contraction joints -carried out to avoid the irregular cracks caused by a restrained drying shrinkage- were accepted by the Architects. Therefore, a special 3-SC mixture was developed and used; it is characterized to be: - a self-compacting concrete based on the use of an acrylic superplasticizer, a viscosity modifier to avoid the bleeding risk, and a special particle size distribution of the aggregates; - a self-compressive concrete due to the use of a CaO-based expansive agent; - a self-curing concrete based on the use of a shrinkage-reducing admixture (SRA). This concrete called 3-SC, because it is 3 times “self”, was very successful in producing a crack-free concrete surface even in the very long, curvilinear, and inclined walls: after 18 years of building the long, inclined, curvilinear walls of the MAXXI museum have been carefully examined and during the last inspection their surface resulted to be still sound and crack-free. However, just before the building’s inauguration in 2009, in very few areas some micro-cracks were observed on the concrete surface and considered to be dangerous for the future of the building. Therefore, the concrete surface was treated with a transparent varnish in order to avoid the ingress of the aggressive humid air to protect the steel reinforcements from the corrosion promoted by the carbonation process.

The conservation state of foundation piles of highway viaducts close to a train line was investigated with a visual inspection, laboratory tests on the cementitious material and electrochemical monitoring, as well as galvanostatic pulse measurements for the steel parts. Each viaduct pile had 10 to 15 foundation piles inserted into the ground to a depth down to 15 meters. Two main types of piles were observed. Reinforced concrete piles and steel piles were embedded internally and externally in the cementitious material. The results indicated the absence of significant corrosion of the metals in the upper part of the piles. This was also due to poor carbonation in the ground. Along a viaduct, the presence of chloride in the groundwater increased the risk of corrosion, although it did not reach the steel parts yet. The monitoring of the stray currents did not exhibit a relevant shift in the anodic direction of the steel corrosion potential, thus indicating a reduced corrosion risk. The galvanostatic pulse measurements showed some possible local corrosion issues that may arise, especially with depth. This also depended on the formation of macroelements along the piles. Nevertheless, this latter problem may be reduced due to the higher presence of humidity and the oxygen depletion with depth.

To guarantee concrete infrastructure functionality over time inspection and maintenance interventions are required. These inspections are typically scheduled on a periodic basis but may not be sufficient to prevent the onset of deterioration. When these problems occur, extraordinary maintenance operations shall be carried out, causing inconvenience to users and additional costs. The continuous monitoring of the infrastructures allows the transition from programmatic maintenance to predictive maintenance strategies, with a consequent increase in the safety of the structures as well as a reduction in management costs. This work aims to provide a brief overview of continuous monitoring systems for concrete structures developed by Università Politecnica delle Marche, focusing in particular on methods based on free corrosion potential measurement and electrical impedance spectroscopy in the so-called “self-sensing” concrete. The “self-sensing” characteristic of concretes can be improved through conductive additions such as fillers and fibers. The study conducted within the H2020 EU project EnDurCrete has demonstrated how expensive and sometimes toxic commercial conductive carbon-based additions, can be replaced by low-cost, non-toxic industrial by-products, enabling to perform relatively cheap and sustainable continuous monitoring of structures.