International Concrete Abstracts Portal

The purpose of this research is to examine the resistance to repeated freezing and thawing cycles of non-air-entrained and air-entrained concretes containing high dosages of condensed silica fume. Testing was carried out on a total of 76 air-entrained and non air-entrained cylindrical specimens. The compressive strength and the complete stress-strain curves of the specimens under uniaxial compression were determined from different freezing and thawing cycles. The influence of the treatment on the shape of the stress-strain curves was investigated. In addition, the dynamic modulus under the same cyclic conditions was determined. To investigate both the spacing factor and the specific surface, the air void and pore structure characteristics of hardened specimens were studied.

To determine the characteristics of deterioration of concrete under freezing and thawing, acoustic emissions of mortar were measured and analyzed. Acoustic emissions of the ice formation were examined to establish test conditions. In addition, propagation properties of acoustic emissions, such as wave velocity and amplitude, were examined with an acoustic emission (AE) pulser. The test results for water showed that acoustic emissions due to ice formation took place during both thawing and freezing. The test results with mortar showed that most acoustic emissions occur during the freezing and that the number of acoustic emissions does not increase with the number of freezing and thawing cycles. The test also showed that the propagation of acoustic emissions is effected by air content and curing period. Therefore, the propagation properties must be considered to evaluate the frost damage of mortar with acoustic emission events. Further, wave velocity and amplitude measured with an AE pulser decrease as the number of freezing and thawing cycles increase. It is concluded that the wave velocity and amplitude of AE pulse propagation can be used as indicators to evaluate the degree of frost damage of mortar.

Erosion by abrasion, cavitation and/or chemical attack in concrete hydraulic structures deteriorates spillways, stilling basins, chutes, slabs and transverse joints, concrete blocks under water gates, and any irregular surface subjected to high water flow rate. Countless overlays are commercially available for repairing deteriorated surfaces. However, the essential data provided by manufacturers is very limited and, even if it is available, it is normally limited to room temperature values. This persuaded the Canadian Electrical Association to support a comprehensive study on commercial overlays, especially from the viewpoint of resistance against erosion and the severe climatic conditions observed in northern parts of Canada. This paper presents laboratory test data on the erosion resistance and durability properties of various types of commercial overlays such as cementitious grouts, polymer-modified cement-based mortars, and epoxy mortars.

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.

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.