International Concrete Abstracts Portal

In September 2000, the American Concrete Institute sponsored the ACI Fourth International Conference in Seoul, Korea. Sixty-two papers are included in this publication. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP193

Durability limitations of steel reinforced concrete are well documented. Corrosive environments (e.g. the presence of chlorides), carbonation of concrete structures, poor workmanship and other factors can cause corrosion of the reinforcing steel. Normally, reinforcing steel embedded in concrete is protected because the concrete cover acts as a barrier and the high pH value of the pore fluid assures a passive state. Both the presence of chloride ions at concentrations above a given threshold level and carbonation can put reinforcing steel into an active state and result in corrosion rates that markedly decrease the expected service live of reinforced concrete structures. Aqueous surface-applied corrosion-inhibiting impregnations are featuring the ability to reduce the corrosion rate of corroded steel reinforcement embedded in hardened concrete due to their corrosion-inhibiting action and in the case of a carbonated concrete structures by realkalization. Additionally the corrosion rate is further reduced due to the water repellent action of organosilicone compounds. The careful selection of hydroxyalkylamino compounds as well as of inorganic-or organic acid compounds allows the formulation of corrosion-inhibiting impregnations with high buffer capacity. When applied on the surface of a concrete structure, said corrosion-inhibiting compositions are capable of penetrating into the concrete, and raising the pH value of the pore fluid in the vicinity of the reinforcing steel to a level, where the corrosion rate is markedly reduced. Laboratory tests and results from field applications are reported.

Roller-compacted concrete (RCC), because of its superior properties, Synopsis: low cost, rapid and relatively simple construction methods, and proved performance, has been used extensively in recent years in rehabilitation projects at existing concrete and earth and rockfill embankment dams and related hydraulic structures. These applications include increasing the existing spillway capacities, construction of new service and emergency spillways, overtopping protection, and seismic strengthening. This paper presents case histories of selected applications of RCC in rehabilitation of dams and related hydraulic structures. These case histories are presented to show the range of previous applications and to illustrate typical design and construction practices in repair and rehabilitation of dams with RCC. For each of the case histories presented in this paper, an attempt is made to discuss (a) the description of the project, (b) the cause and extent of the deficiency that necessitated rehabilitation, (c) design details, (d) RCC mixture proportions, (e) description of materials, equipment, and placement procedures, (f) cost, and (g) RCC performance to date.

This paper describes the repair of a high-strength silica fume concrete structure using a high-strength repair material that also contains silica fume. The repair represented the largest single application of this material and the largest single use of low-pressure spraying of the repair material. Information is provided on the repair procedures, proficiency of the nozzlemen, acceptance criteria applied to this type of operation. Because of the lack of actual in-situ bond and compressive strength data in the literature for high strength concrete repair materials, preliminary trials were conducted for material acceptance and to establish acceptance criteria for the actual repair. Approximately 1,300 m3 of the repair material was used to repair 24,000 m2 of concrete surface damaged during a slipform operation. The damaged concrete had compressive strengths in the range of 78 to 82 MPa. The repair material had a target compressive strength of 80 MPa and an in-situ bond strength requirement (minimum) of 1.5 MPa. Using low-pressure spraying techniques because of confined working areas, the repairs were successfully completed over a 24-week period. Compressive strengths of cores from sprayed production test panels averaged 85 MPa at 28-days. The in-situ bond strength of the repairs did not appear to increase with age and averaged 1.87 MPa for all ages evaluated.

The unacceptably high failure rate for concrete repairs is a major Synopsis: problem in the repair industry. To achieve durable repairs, it is necessary to consider the factors affecting the design and selection of repair systems as parts of a composite system. Compatibility between repair material and existing substrate is one of the most critical components in the repair system. This paper summarizes research initiated by the Corps of Engineers to develop performance criteria for cement-based repair materials. Results of laboratory and field performance tests were correlated to provide a basis for development of performance criteria for the selection and specification of dimensionally compatible cement-based repair materials. Proposed performance criteria include a minimum value for tensile strength and maximum values for modulus of elasticity, drying shrinkage, and coefficient of thermal expansion. Also, resistance to cracking in restrained shrinkage tests is a requirement. A data sheet protocol is proposed for cement-based repair materials that would provide reliable, standardized information on pertinent material characteristics. Also, current efforts to develop a comprehensive analytical model to predict cracking resistance of repair materials are briefly described.