International Concrete Abstracts Portal

The electrical chloride test was developed some years ago and is carried out by driving chlorides through concrete samples using electric fields with high voltages up to 60 V. In the test, the total current passing through the sample in a few hours is used as an estimate of the transport properties of the chlorides in the concrete. This test has major advantages that it is rapid, and can be used insitu; and, it has been accepted by the ASTM. It has been criticised in the literature and has, for example, been found to give misleading results when pozzolanic materials are present. It has been pointed out by the author that if silica fume is added to the concrete, the current falls during the test. However, in plain concretes it normally rises. This paper is based on the premise that the current test procedure only makes use of part of the available data . Therefore, it provides only part of the possible results for evaluation and analysis. By analys in the shape of the current-time curve, mu’c h more information about the constituents and properties of the concrete may be obtained. For the data presented in this paper, a large number of samples were tested and computer analysis of the shape of the current-time transients was used to identify the causes of the different attributes of the current-time transients. This analysis is of particular importance in Europe where new Eurocodes for cement permit addition of pozzolanic materials to almost all cements.

Cathodic protection is an highly reliable protection method mostly suitable for concrete structures exposed to salt-attacked conditions, such as the splash zone and above in marine environments. Nevertheless, there has been no effective method to prevent salt-induced damage for reinforced concrete structures situated in tidal zones. The applicability of cathodic protection for structures in tidal zones is evaluated both by ease of execution and protective efficiency under wave and tidal action. This paper describes the results of a study on the use of a new cathodic protection method for concrete structures located in the tidal zones. The new method was developed using anode panels together with an injection material applied to gaps between the panels and concrete surface. Using a tidal water pool, exposure tests were conducted on test specimens treated with this method. From a series of exposure tests, it is concluded that the new cathodic protection method was suitable for concrete structures in a tidal zone in marine environments.

air-entrained concretes were made using a silica fume blended cement and six lightweight aggregates having a wide range of absorption values. The properties of the fresh concrete, including the autogenous temperature rise were determined. Concrete specimens were subjected to the determination of the compressive, flexural and splitting-tensile strengths, Young’s modulus of elasticity and drying shrinkage; the resistance to the freezing and thawing cycling, chloride-ion penetration and carbonation were also determined. The tests for the freezing and thawing resistance were performed on concretes made using dry and saturated lightweight aggregates. Small reinforced concrete beams made using three of the lightweight aggregates, and some incorporating polypropylene fibres, were tested for hydrocarbon-fire resistance. The target compressive strength at 28 days (60 to 65 MPa) was generally reached with five of the lightweight aggregates used. As expected the mechanical properties of the concrete were somewhat related to the degree of absorption of the lightweight aggregates. All the concretes investigated demonstrated excellent resistance to chloride-ion penetration at 28 days, negligible depth of carbonation after 448 days of air drying, and excellent performance in the freezing and thawing cycling. Based on the visual evaluation, the use of the polypropylene fibres improved considerably the performance of the high-strength semi-lightweight concrete in hydrocarbon fire.

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.