International Concrete Abstracts Portal

Presents information on the development and use of carbon fiber reinforced plastic (CFRP) to strengthen reinforced concrete chimneys, bridge piers, and beams in Japan; bridge beams in Switzerland; and ongoing structural research and use of fiber reinforced plastic (FRP) composite materials to strengthen such structures in the U.S. The concept and equipment for strengthening existing reinforced concrete chimneys by wrapping them with carbon reinforced plastic materials began in Japan. The procedure permitted earthquake-damaged chimneys to be repaired without taking them out of service. Research in Switzerland has led to the use of adhesively bonded sheets of carbon reinforced plastic laminates to strengthen existing bridges. This concept is an extension of use of bonded steel plates to strengthen many types of structures throughout Europe. Research, development, and some use of these techniques has been done in the U.S.

Addresses shotcrete used primarily for rehabilitating concrete structures. Field experience has demonstrated that the use of detailed specifications and strict on-site surveillance can minimize workmanship problems that have been a concern with the shotcrete process. This paper discusses key points that make the specifications a useful tool. Types of shotcrete quality found in practice are illustrated. Preconstruction testing, ongoing quality control testing during construction, a core grading system, and tensile bond strength tests are discussed. Several brief case histories are presented where the use of the core grading system has proved successful. In the case histories, an independent laboratory conducted evaluations of in-place shotcrete, developed specifications for new work, and provided on-site surveillance during placement. The case histories include a drydock, cooling tower, parking garage, swimming pool, lighthouse, and two chimneys. The system adopted has resulted in structures that should provide durable, long-term service.

An analytical procedure is described for predicting the development of vertical cracks in thin-walled and thick-walled cylindrical structures subjected to membrane forces and thermal loads. Sustained, axisymmetrical (thermal) loads and thermal cyclic loading may jeopardize, due to cracking, the serviceability (in this case the tightness) of thin-walled cylinders. Mathematically obtained crack patterns have been compared with field observations: a good agreement between theory and practice could be established from this comparison. On the basis of a reliable prediction of crack patterns, cost-benefit analyses are feasible to weigh crack control measures against possible repair costs in case these measures were neglected. An example of such an analysis shows an initial increase of reinforcement in view of crack control to be preferable to repair (grouting) of cracks.

The paper discusses the results obtained by testing concrete quality and the degree of reinforcement protection in the piles of the submarine tunnel for the Coke Plant at Bakar, and in the walls of the water intake for the Rijeka Thermo-Power Plant, both placed by the tremie method. The shafts of the high chimney stacks of the Rijeka Thermo-Power Plant and the Bakar Coke Plant, erected by slip forms, were similarly investigated. The results obtained by tests and observations show that concrete for thin and highly-reinforced elements, to be placed by tremie, must be made with pure portland cement, or portland cement incorporating slag, having a low need of water for standard consistency, (measured according to Vicat), and with clean well-graded sand and coarse aggregate. Otherwise, mass concrete structures are preferred. Slipform erection of structures by the sea should be avoided, or, if used, the surface of the concrete should be protected additionally and completely (while slipform advancement is still under way) with cement mortar reinforced by the addition of polymer binders . This operation must be planned at the design stage and clearly specified.