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 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.

The moisture condition of field concretes exhibiting evidence of alkali-silica reactivity was investigated utilizing relative humidity (RH) measurements. Prior determinations were made on laboratory mortar specimens to determine the threshold level required to sustain expansive reactivity. By comparing measurements of field concretes with the threshold level, environmental field conditions under which expansive reactivity is liable to occur were identified. Results indicated that RH values greater than 80 percent, referenced to 21 to 24 C, are required to support expansive alkali-silica reactivity. Field measurements revealed that most of the concrete in highways and dams in desert areas is sufficiently damp to sustain expansive ASR. Bridge decks and columns in dry climates are sufficiently damp on a seasonal basis to sustain expansive reactions. Massive concrete members indoors in controlled environments may remain sufficiently damp for more than 50 years to permit continued expansive reactivity. Both residual mixing water and external sources of moisture contribute to the moisture condition required for expansion to occur.

Mortars using heat-resistant glass as aggregate were made using water-binder ratio of 50 percent, replacement ratio of fly ash from 0 to 30 percent by weight, and an alkali content of 1.2 percent weight of cement. Eight fly ashes were used as supplementary cementing materials. These mortars were cured at a temperature of 40 C and a relative humidity more than 95 percent, and the expansion of these mortars was measured. The concentration of soluble alkali ion in fly ash immersed in the solution containing sodium hydroxide and calcium hydroxide was also determined. Expansion of mortar depended on the type and the replacement ratio of fly ash. The concentration of soluble alkali ion in fly ash depended on the type of fly ash. Although expansion of mortar was independent of equivalent sodium oxide content in fly ash, it correlated with the concentration of soluble alkali ion in fly ash. By studying effects of physical/chemical properties and the amorphous silicon dioxide in fly ash, a method to evaluate the expansion of mortars containing fly ash was proposed based on amorphous silicon dioxide, the replacement ratio, and particle diameter of fly ash.

Microstructure and mechanical properties of concrete with expansive additives are reported compared with ordinary concrete. Samples of long-term concrete (22 years) were collected from an actual building constructed in 1967 with calcium sulfoaluminate (CSA) used as expansive additive. Hydration products were separated from these samples by using heavy media and analyzed by means of DSC, XRD, and FT-IR. The morphology of the mortar portion was observed by SEM. No differences were detected on the carbonation depth and the compressive strength between CSA concrete and ordinary concrete. Qualitative analysis shows that following carbonation of concretes, C-S-H was changed to silica gel or to C-S-H with low Ca/Si ratio and CaCO3, AL(OH)3 gel, and gypsum. Quantitatively, hydration products in carbonated CSA concrete are larger than in carbonated ordinary concrete. Therefore, decomposition rate of AFt by carbonation is slower than that of C-S-H.