International Concrete Abstracts Portal

The aim of this project is the production of a 28 m high CFRP-prestressed spun concrete pylon as a support for electric lines at the 110 kV voltage level (Duralight concept). It is intended to use this pylon as a support mast in a section of the 110 kV line of the Nordostschweizerische Kraftewerke (NOK, Power Company of North East Switzerland) Beznau-Baden. The fundamental advantage of this new design is the low weight in combination with an optimum corrosion resistance. The high corrosion resistance of the CFRP prestressing and shear reinforcement allows minimization of the concrete cover so that a cross-sectional wall thickness in the region of only 4 cm (1.6 inches) can be obtained. This is at present about 10 cm (4 inches) if steel reinforcement is used. The low weight of the CFRP reinforcement (the density of CFRP is only 1.6 g/cm3, which is a fifth of the density of steel) and its high tensile strength (CFRP pretensioning rods have a tensile strength of 3000 MPa, which is twice that of a prestressing steel) are also noteworthy. These two factors permit a weight reduction on the reinforcement side of 90% compared with conventional pre-stressed concrete construction. On the matrix side, high-strength spun concrete of strength class B110 is used. Owing to its high strength, it helps to achieve the stated minimization of the cross-sectional dimensions. The envisaged pylon weight of 4730 kg means a 45% weight reduction compared with the traditional steel reinforced spun concrete pylon. The transport and installation costs are thus lower and the expected life without maintenance is 50 years. This paper describes the technical fundamentals studied in a four year research program at the Swiss Federal Laboratories for Materials Testing and Research EMPA for designing and manufacturing this prototype pylon. The presented pilot project results from a close co-operation of the spun concrete element production plant SACAC with EMPA and the power company NOK.

The New York State Department of Transportation is evaluating the use of innovative materials for bridge repair. One application being investigated is the strengthening of cracked reinforced concrete cap beams using fiber reinforced polymer (FRP) composites. In-house maintenance crews repaired two piers with FRP as part of a demonstration project with industrial partners to evaluate the benefits. One of two repair systems used is described in detail and is evaluated in terms of additional strength gained, cost-effectiveness, ease and speed of installation, impact on traffic flow during the repair, and long term durability. For comparison, data from a past project that employed conventional repair techniques are provided. This paper describes the project scope, subsequent repairs using FRP, and long term plans for monitoring.

With their strength and their specific stiffness, composite materials present a significant interest in the conception of bearing structures. The influence of combined effects "time-temperature-loading" on composite reinforcement adhesive layer was studied to identify the long-term mechanical behavior of RC beam reinforced with FRP. A set of tests were conducted on reinforced concrete structures with carbon epoxy composites. The tests consist of applying a tensile shear stress during six months to obtain the long-term creep data and to carry out thermo-stimulated test to assess short-term creep data. The master curves set up with this method predicts with reasonable accuracy the long-term creep test data. The time-temperature superposition method is used to determine several master curves with several levels of shear stress. This method permits an evaluation of the long-term shear stress to apply in the adhesive layer to minimize the creep. The durability of repaired or reinforced structure depends on the adhesive behavior. We have assessed that the identification of the long-term creep can be done with a thermo-stimulated test. This test allows setting up the safety factor for any polymer to guaranty the structure durability.

Many pretensioning prestressed concrete (PC) beams using the grid glass fiber reinforced polymer (GFRP) reinforcements as prestressing tendons were manufactured. The initial prestressing forces were selected at various levels, namely from 0 to 52.5 % of the tensile capacity of the grid GFRP reinforcement. Then, the PC beams were left outdoors for a long time, namely from seven to eight years. Thereafter, they were demolished to take the grid GFRP reinforcements out. First, the tests on tensile properties of the grid GFRP reinforcements were carried out. Their residual tensile capacities decreased only a little, and moreover, their residual tensile rigidities did not change. Then, the cross sections of the glass fibers of the grid GFRP reinforcements were observed with a scanning electron microscope (SEM). The cross sections remained real circular and the glass fibers were not attacked by alkali of concrete.

This paper clarifies, experimentally, the degradation of aramid fiber, glass fiber and carbon fiber, used as reinforcement for concrete, in various solutions (alkaline solution, hydrochloric acid aqueous solution and pure water) at different temperatures. A calculation model is proposed to estimate the progress of the degradation by the solution. The accelerated degradation test, immersing fibers in several solutions, was carried out at the temperatures of 20, 40 and 60 degrees Celsius and the strength of the fiber after the immersion test was examined. Observation of the fibers was carried out by scanning electron microscope (SEM) in order to clarify the degradation of the fibers. As a result of this study, the strength changes of Kevlar 49 and Technora were quantitatively estimated using the weakest link theory of Weibull.