International Concrete Abstracts Portal

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.

In hot climate countries drying shrinkage of concrete is one of the major characteristics influencing its durability. In Australia, the majority of project specifications for concrete with requirements on durability set up criteria for drying shrinkage. Incorrect specification of this characteristic affects concrete durability and/or increases costs of construction. The paper analyses different sources of drying shrinkage variability, namely, metrological, within-sample, batch-to-batch, day-to-day, etc. The variabiiity of drying shrinkage resuits is compared with that of compressive strength data. Project specification requirements in terms of frequency of testing and acceptance criteria of drying shrinkage are discussed. The authors provide recommendations on drying shrinkage for project specification requirements which (a) decrease the consumer’s risk from the stand point of guarantee of getting the specified drying shrinkage and (b) decrease the concrete producer’s risk in the case of non-compliance of concrete in terms of drying shrinkage.

By now the theoretical foundations of the rational use of the SO called protective properties of concrete as a physico-chemical system have been laid. They are: the capacity to maintain stability and a non-equilibrium state in a changing environment. It should be kept in mind that concrete is practically the only material with such sensitivity to the environment components as clinkers, slags, ashes, and other relicts which can be considered reserve sources of creative processes in the building of structure by hydration and pozzolanic reaction. The technical state of knowledge of hydraulic cement concrete includes a wide range of characteristics defining its functioning and reaction to various factors of environment. During the service life of constructions it is possible to rely on the natural process of partial rehabilitation or of maintaining the reacted state of the concrete at a certain level of physico-chemical adaptation resulting from continuing hydration of reaction of clinker, slag, ashes, and other relicts. Moisture, electrolites, and elevated temperatures especially contribute to it. Here it should be ne marked as important for providing stable polymorphism in the form of stable hydrate phases, the appearance in their structure of ion-modifiers, specific for environment. to ensure correctness of the practical result it is necessary to observe the multitude of parameters of hydraulic cement concretes because real exploitation of the environment determines rather complicated responses of the object. It is especially important during comparative tests of durability of concretes intended for use in media with many kinds of impact. The modern theory of such tests is characterized by mathematical models elaborated by it that do not basically take into account the evolution of internal state in the cement paste caused by creative (hydration) and destructive (corrosion) processes. The determination of concrete adaptability by means of imitation modelling, while taking into consideration genetic and technological factors, should be perspective. All mentioned above is to provide optimal regimes for exploitation of concrete and reinforced concrete constructions.