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At the University of Salford, UK., a research team led by the author has developed a form of composite concrete construction in which fiber reinforced cement (FRC) units are employed as surface reinforcement. As part of an extensive program of investigation, full-sized rectangular and T-section beams, with and without FRC units as surface reinforcement, have been tested under fatigue in up to three million repetitions of loading. Companion beams having surface reinforcement have also been tested under short-term static loading. After a brief review of the concept of FRC composite concrete construction, the paper describes and details the test program. The behavior of the beams is examined regarding ultimate load, deflection, and cracking--the criteria of safety and serviceability. The performance under fatigue loading of beams with surface reinforcement is compared with that of companion beams without surface reinforcement but subjected to similar fatigue loading, and with surface reinforcement but tested under short-term static loading. It is concluded that the use of FRC as surface reinforcement is effective in controlling deflection and cracking well within the permissible limits without affecting ultimate load-carrying capacity for the beams subjected to fatigue loading.

Corrosion of steel reinforcement within concrete structural elements is a major problem in both research and practice. Laboratory studies have been conducted on fundamental mechanisms of corrosion within concrete in the presence of high chloride and others under conditions of reduced alkalinity. However, little has been published on the interactive effects of these two conditions and the ways in which corrosion rates of steel in concrete are thereby influenced. These two conditions occur concurrently under many practical environmental exposures. This paper presents data on methodology used to determine corrosion rates of steel in concrete. Information on corrosion activities in both carbonated and high-chloride environments is presented with reference to mechanisms involved in breakdown of steel passivation. Interactive effects of the two conditions are examined for a range of concrete types and grades. The data suggest that for normal reinforced concrete structural elements, the interactive effects of carbonation and chloride ion ingress lead to much more rapid corrosion than where the two phenomena occur independently. The interactive effects of carbonation and chloride ions as they influence concretes under service conditions are discussed. In particular, the reduction of carbonation rate in the presence of high-chloride ion concentrations is noted.

The concrete bridge structural members, called "skew members" (SM), which are positioned from 1.5 m above the sea level to about 20 m down in the sea, and are among the most important elements in bridge construction, were investigated for maintenance purposes after 11 years of service. The underwater arch foundation concrete was also tested. The compressive strength, determined as the average value of 10 concrete cores drilled out from each of two skew members--SM-St. Marko and SM-Mainland--was 62.3 Mpa and 57.4 MPa, respectively. Chlorides had penetrated through the high-alkaline composite by over 20 mm in the splash zone concrete and by over 45 mm in the fully submerged concrete, where {Cl-}-penetration was probably enhanced by hydrostatic pressure. The lack of corrosion of the steel in the concrete, even in the presence of high chloride concentration, could be explained by the absence of oxygen. The gas permeability coefficients Kg determined on the concrete core slices varied in the inner concrete layers of SM-St. Marko from 5.58 to 20.10 x 10-13 cmý and from 0.55 to 2.84 x 10-13 cmý in the concrete at SM-Mainland.

The results of investigation into the erosion-abrasion resistance according to CRD-C 63-80 test method and abrasion resistance according to Bohme test method of steel fiber reinforced concrete specimens are discussed in the paper. Nine mix proportions were used. The water-cement ratios (w/c) were varied from 0.30 to 0.65. The volumetric percentage of hooked steel fibers were varied from 0.25 to 2.0 volume percent at the w/c of 0.30 and at the others the quantity of fibers was constant. In addition, mixes without fibers were made at each w/c. The results show that adding steel fibers to the concrete improves the resistances as measured by both test methods. The erosion-abrasion resistance is improved by an increase of compressive strength and an increase in fiber content. It can be correlated to improvements of abrasion resistance from the Bohme test method but only at constant w/c and different content of fibers.

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.