Quality Inspection of Shore Approach High-Strength Concrete

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Title: Quality Inspection of Shore Approach High-Strength Concrete

Author(s): Magne and Steinar Helland

Publication: Special Publication

Volume: 126

Issue:

Appears on pages(s): 609-626

Keywords: capillarity; chemical analysis; chloride ingress; compressive strength; durability; high-strength concretes; microscopy; seawater; silica fume; Materials Research

Date: 8/1/1991

Abstract:
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.