Toru Yamaji

CHLORIDE DIFFUSION, MICROSTRUCTURE, AND MINERALOGY OF CONCRETE AFTER 15 YEARS OF EXPOSURE IN TIDAL ENVIRONMENT

This research describes a detailed study conducted into the chloride diffusion, microstructure, and mineralogy of 15-year-old concrete specimens of dimensions 150 mm in diameter and 300 mm in height. These specimens were exposed to a tidal environment. The cement types were ordinary portland cement, slag cements of Types A, B, and C, and Type B fly ash cement. Water-cement ratio was 0.45. Compressive strength, carbonation depths, pulse velocity, water- and acid-soluble chloride profiles, microstructure, and mineralogy of concrete were evaluated. Results are provided.

MICROSTRUCTURES AND INTERFACES IN CONCRETE AFTER 15 YEARS OF EXPOSURE IN TIDAL ENVIRONMENT

Detailed investigations on the properties of concrete specimens after long-term exposure to a marine environment are very scarce in the technical literature. In this paper, a detailed study of microstructure and aggregate-matrix and steel-matrix interfaces in concrete specimens after 15 years of exposure to a tidal environment was conducted. Cement types were ordinary portland, slag cements, and fly ash cement. The results of this research will be useful in understanding the changes in microstructure and interfacial conditions after a long-term exposure, and comparing them with the short-term laboratory test results.

Corrosion of Steel Bars in Cracked Concrete Made with Ordinary Portland, Slag and Fly Ash Cements

Corrosion of steel bars in pre-cracked prism specimens exposed in marine environment for 15-years is presented here. The size of the specimens was 100x100x600 mm. The specimens were made with ordinary portland, slag (Type A, B and C) and fly ash (Type B) cements. A round steel bar of diameter 9 mm was embedded in each specimen. Water cement ratios were 0.45 and 0.55. Crack widths were varied from 0.1 to 5 mm. Chloride-ion concentrations in concrete and corrosion of steel bars were evaluated. Narrower cracks (< or = 0.5 mm) heal irrespective of the cement types. Chloride ingress and corrosion of steel bars in concrete are highest for the specimens made with ordinary portland cement and lowest for the specimens made with slag cement of Type C. Locations of the maximum corroded area as well as the deepest corrosion pit are not necessarily at or near the cracked region. Wider cracks are not healed and maximum corroded area and deepest corrosion pit are observed at the cracked region. The presence of voids at the steel-concrete interface results in corrosion pits even for chloride-ion concentration less than 0.4% of cement by weight.

Unexpected Expansion of Concrete Made with Laumontite Containing Aggregates Under Seawater Condition

Deterioration of steam-cured concrete specimens made with laumontite containing aggregates, under marine submerged, tidal, and atmospheric exposures for 30 years, was investigated. The expansion of the specimens exposed to the marine submerged and tidal exposures ranged from complete disintegration to the moderate deterioration. The deteriorated regions contains little calcium hydroxide as well as calcium silicate hydrates, but rich with ettringite, brucite, and calcite. At the deteriorated region, white rim of ettringite crystal is found around the aggregates. Ettringite, brucite, and calcite are also found at the voids as well as along the cracked path. No visible crack was found on the surface of the atmospheric specimens. It is clearly understood that exposure condition is a governing factor related to the expansion caused by the laumontite mineral. No expansion of 30 years old atmospheric and tidal specimens is found after further wetting and drying exposure utilizing natural seawater of temperature 60 o C.