International Concrete Abstracts Portal

A part of the Statpipe Development Project is a landfill for two gas pipelines on the exposed western coast of Norway. The pipelines are placed inside a submerged concrete tunnel that acts as an underwater protecting bridge over the rocky sea bed. The 590 m long tunnel was cast in five separate elements produced in two dry docks. The tunnel starts at a water depth of 30 m and ends up at water level. The tunnel elements were produced and placed during the summer of 1982. The splash zone element encompassed the following characteristics; 400 kg ordinary portland cement and 32.5 kg silica fume per m3 concrete. The water-cement-sand ratio was 0.36, the slump value was approximately 200 mm, and the 28-day cube strength was approximately 78 Mpa. After 7 years in service, cores were drilled from the splash zone element. The testing of the cores included compressive strength, capillary absorption, chloride profile, thin-section analyses, x-ray diffraction, scanning electron microscopy, and element analysis. The results indicate that in such a low-porous concrete, the reaction products between seawater and cement paste will fill up the original low porosity and tighten the concrete so that the ingress of chlorides will cease. For concrete exposed to seawater, ingress of clorides and risk of reinforcing bar corrosion represents the most severe problem. The tightening effect of seawater in such a high-performance concrete seems to reduce this problem to a minimum.

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.

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.

Durability of concrete is commonly associated with the effects of aggressive environments, such as freeze-thaw cycles, or the penetration of liquids with high chloride ion concentrations into the matrix of the concrete that can degrade the physical and mechanical properties of concrete. Cyclic loading that causes a progressive disruption of the matrix structure by crack initiation and propagation allows aggressive environments to accelerate the rate of deterioration of the concrete and/or the reinforcement. The growth of cracks and their propagation during cyclic loading can be retarded or arrested by fibers incorporated in the concrete and thereby delay the formation of pathways for the penetration of aggressive environments or the formation of corrosion products that disrupt the matrix structure of the concrete. This paper presents test data on the flexural fatigue strength and toughness index of concrete reinforced with three types of metallic and one type of synthetic fiber in volume percentages ranging from 0.1 to 2.0. The beams reinforced with metallic fibers exhibited greater fatigue strength than beams reinforced with synthetic fibers. The fatigue strength increased with fiber volume percentage for each type of fiber. The fatigue strength of the beams varied with the deformed shape of the metallic fibers. The toughness index of the fiber reinforced beams was computed from the area under the static load-deflection curve. The toughness indexes for two of the three types of metallic fiber reinforced beams were greater than for the synthetic fiber reinforced beams. The toughness index increased with fiber volume percentage.