International Concrete Abstracts Portal

This research project was undertaken to determine the effect on the chloride permeability of concretes of increasing amounts of fly ash in low water-cementitious material ratio concrete as compared with comparable high-quality concretes containing combinations of portland cement, silica fume, and ground-granulated blast furnace slag. The test method utilized was the Rapid Determination of the Chloride Permeability of Concrete (AASHTO T-277). Fifteen superplasticized concrete mixtures were evaluated for compressive strength at ages of 28 and 56 days, and for chloride permeability at 56 days. The inclusion of fly ash, silica fume, and ground-granulated blast furnace slag all significantly reduced the chloride permeability of concrete as compared with concrete containing only portland cement. Increasing amounts of fly ash generally showed decreased permeability in the tests conducted.

Long-term exposure test results of reinforced concrete beams are reported. One hundred forty-nine pairs of beams with open cracks were exposed to sea air for 2 to 20 years. The main variables were thickness of concrete cover, type of cement, cement content (water/cement), and crack width. The type of cement has a great influence on the depth of chloride ion penetration. The thickness of concrete cover is the most important factor in the prevention of corrosion of the reinforcing steel. With a thin cover, the crack width has no influence on corrosion of reinforcing steel. Epoxy coating is effective in improving corrosion protection. Measurements of electrical potential on the surface of concrete give valuable information on corrosion activity of reinforcing steel.

The biological effects and chloride penetration studies were carried out on a 10-year-old concrete structure of the arch bridge on the island Krk in the North Adriatic. Concrete cores of 100 mm diameter were drilled from three main locations of the structure and tested for chloride content at depths 0 to 10, 10 to 20, and 20 to 40 mm. The influence of aggressive organisms on the elements below sea level was determined. The biological life of the concrete below sea level was massive, the value being 1300 units per mý at a depth of about 18 m. The shell Recellaria Dubia can make depressions of 5 to 10 mm diameter.

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.

Durability of fibers in concrete is a concern for nonmetallic fibers. This paper presents the results of durability studies conducted for synthetic fibers made of Nylon 6, polypropylene, and polyester. Long-term durability was estimated using an accelerated aging process. In this process, the specimens were stored in lime-saturated water maintained at 50 C. The integrity and the effectiveness of the fibers were studied using flexural toughness of 100 x 100 x 360-mm prisms tested under four-point loading. The concrete was designed for a 28-day compressive strength of 20 MPa, which is commonly used for field applications. A higher-than-normal fiber content of 4.75 kg/m3 (approximately 0.5 volume percent) was used to obtain consistently measurable toughness index values. All the fibers were 19 mm long. Nylon 6 and polyester fibers were made of single filaments, whereas polypropylene fibers were fibrillated. The results indicate that, at a fiber loading of 4.75 kg/m3, all three fibers provide post-crack resistance. Nylon 6 and polypropylene fibers are durable in alkaline environment present in concrete. This is demonstrated by the effectiveness of fibers measured in terms of flexural toughness values and the general load-deflection response. Specimens with polyester fibers had some loss of ductility when subjected to accelerated aging.