International Concrete Abstracts Portal

The exhaust from the auxiliary power unit (APU) of the modern F/A-18 aircraft has caused spalls and erosion on portland cement concrete (PCC) pavements. The exhaust gas has a maximum temperature of 385 F (196 C) and a maximum velocity of 140. At this temperature, PCC seems to lose its integrity when subjected to repeated and prolonged exposure. Spills of hydraulic fluid and jet fuel on the pavement aggravate the spalling process. The main objective of this investigation was to determine effects of cyclic heating on the strength of portland cement concrete subjected to high temperature, and compare the effects of cyclic heating on concrete contaminated with hydraulic fluid and jet fuel with noncontaminated concrete. Five different concrete mixtures were investigated. Twenty-one prisms and 21 cylinders were made from each mixture and tested for compressive strength, flexural strength, pulse velocity, and dry unit weight. Within each group, specimens were tested after each of the following heating/cooling cycles: 0, 15, 30, 60, 120, 240, and 400. A heating and cooling cycle is defined as heating in an oven at 400 F (204.4 C) for 60 min and cooling at room temperature for 30 min. After every 15 heating/cooling cycles, the contaminated specimens were soaked in jet fuel or hydraulic fluid overnight before the next heating/cooling cycles. Test results indicate that jet fuel contamination is more detrimental than hydraulic fluid contamination. Compressive strength, flexural strength, and pulse velocity are adversely affected by the cyclic heating.

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.

Long-term durability of structural lightweight concrete used in bridges, ships, and buildings is reviewed. Particular attention is given to mature structures located throughout the world that have been subjected to severe weather conditions. Ongoing testing programs carried out on structures subjected to several decades of exposure are reported. The nature of both the vesicular lightweight aggregate itself as well as the interfacial contact zone between aggregate and cement paste matrix are analyzed, as the microstructure of lightweight concrete reveals factors that contribute to long-term durability. The information gained on the microlevel is used to explain observed performance, and provides a basis for predicting behavior. To facilitate the practical design of durable structures, long-term field exposure studies of normal weight and lightweight concretes are being conducted to assess their relative performance in a severe environment. The results obtained from ongoing testing programs conducted by the Canadian Concrete Technology Section of CANMET at the U.S. Corps of Engineers Treat Island Severe Weather Exposure Station are discussed in relation to the design process.