International Concrete Abstracts Portal

In 1997, CANMET in association with the American Concrete Institute and several other organizations in Australia sponsored the Fourth International Conference on the subject. The conference was held in Sydney, Australia. More than 120 papers from 30 countries were received and peer reviewed in accordance with the policies of the American Concrete Institute; 81 were accepted for publication. The accepted papers deal with all aspects of durability of concrete, including chloride and sulphate attack, freezing and thawing cycling, alkali-aggregate reactions, cathodic protection, and the role of supplementary cementing materials to enhance durability of fiber-reinforced concrete and performance of repaired concrete structures. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP170

Concerns have been expressed to the Building Research Establishment (BRE) by a number of United Kingdom (UK) structural engineering consultants and local government bodies about the in-service performance of reinforced autoclaved aerated concrete (RAAC) planks. Many RAAC roof planks are reported to have developed appreciable in-service deflections and soffit cracking, which has raised concerns about the implications for the future structural performance and safety of the planks. Exploratory structural testing has been undertaken with the general aim of establishing the current strength and deformation characteristics of a small number of RAAC planks removed from a roof. The testing found that the load capacity of the RAAC planks tested was adequate for the circumstances in which the planks were being used, even where the planks were exhibiting signs of appreciable in-service deflection and extensive cracking on their soffits. The ability of the RAAC planks to meet the standard deflection serviceability criteria used for beam and slab structures is more doubtful. There are a number of mechanisms which may be contributing deflection and cracking problems observed in RAAC roofs. to the

Lightweight concrete was designed and used for the construction of structural elements by the pre-Columbian builders who lived in a very advanced civilisation in El Tajin near Mexico City, in Mexico. This investigations present data on the engineering and performance properties of this lightweight concrete obtained from the slab of a floor of one of the buildings discovered in El Tajin. Detailed drawings made during the exploration show that the unreinforced thick slabs were supported by columns placed four metre apart and that they probably behaved structurally as arches. Data obtained includes strength, porosity and permeability. A detailed study of the composition of the aggregate and binder show that the aggregate was pumice and the binder was a pozzolanic cement made with volcanic ash and lime. Microstructural features obtained by electron microscopy reveal interesting features of this lightweight concrete which as far as the authors know was the oldest lightweight concrete found in the world. The concrete has survived for more than 2000 years in a very good condition providing an outstanding example of a concrete of low strength and very long-term performance.

The aging of concrete dams is a major problem that is often the cause for partial or total repair of the structure. One of the most important parts of the dam to be repaired is the upstream face where.water infiltration through joints and cracks contributes significantly to the overall degradation. The usual repair technique consists in removing the damaged concrete then applying a new layer of either concrete with formwork and reinforcement or shotcrete. Whichever the case, however, the new concrete may be subjected to similar deterioration and also to adhesion problems. An alternative to this technique is to apply a durable watertight coating to the upstream face after removing the damaged concrete. The study described in this paper identifies various types of applicable coatings including metallic sheets, bitumen-based products and synthetic geomembranes (prefabricated or sprayed). The focus here is on the latter, which seem best suited to present needs. Eight geomembranes were subjected to tests designed to determine their characteristics and performance under different conditions : four prefabricated products (PVC-A, PVC-B, HDPE and SBS) and four sprayed (Polyurethane-A, Polyurethane-B, Methacrylate and Neoprene). The study was divided into two experimental phases. First, standard tensile, puncture and pull-off tests to verify the effects of freezing and thawing cycles, ultraviolet radiation and low temperatures on the mechanical properties of the products. Four products showing the best performance, namely PVC-B, Polyurethane-A, Polyurethane-B and Methacrylate, were selected for the second phase. Measurements of the shear strength to assess the adherence of ice to the geomembranes were conducted in a specially built test bench. In cold climates such as Canada’s, the ice that forms on the surface of the reservoir in winter applies complex forces (compression, shear and even tensile forces sometimes) on the upstream face of dams and can damage the protective geomembrane. The shear strength was therefore studied under various loads. The products tested yielded a similar performance, all substantially reducing the ice adherence on the dam face. It was concluded that the application of a geomembrane provides additional protection against the deleterious action of ice and therefore represents a valid technique for the repair of concrete dams in cold climates.

In the present work an acrylic polymer (based on 2-ethylhexyl acrylate) was mixed with cement and fine aggregate and was studied as rubber-like coating to protect reinforced concrete beam specimens. Two acrylic polymer-cement coatings (both with water-cement ratio of 0.50, polymer-cement ratio of 0.50 and fine aggregate-cement ratio of 2) were produced by changing the type of the cementitious component (Portland cement or high alumina cement). The two coatings were applied to a porous concrete substrate with a water-cement ratio of 0.80. Preliminary tests on the uncoated and coated concrete specimens were carried out to study the penetration of water, chloride, sulphate and carbon dioxide. The resistance to penetration of these aggressive agents was very poor in the uncoated specimens and became as good as that of a watertight and durable concrete in the coated specimens. Then coated beam specimens have been kept for 1 year in three different environments (laboratory at 20°C and 65% R.H.; outsides environment exposed to natural changes in temperature and relative humidity; under water) in order to examine the influence of the ageing on the bond strength as well as the flexibility and therefore the ability of the acrylic coatings to bridge the cracks of the concrete substrate. The bond strength of the two coatings was substantially unchanged by the exposure to the three different environments. The flexibility of the polymer-cement coating remained substantially unchanged when portland cement was used independently of the exposure environment. On the other hand, when high-alumina cement was used there was a flexibility loss of the coating in humid environment, particularly in the underwater exposure.