International Concrete Abstracts Portal

The chlorides from the sea and the marine breeze are the main source of corrosion in marine environments. Their penetration into concrete occurs through capillary absorption, diffusion or a mix of both. A chloride threshold for producing reinforcement corrosion can be predicted through mathematical models but no reliable results may be obtained if the action of environmental agents as the RH, temperature, winds, rains, and drying periods are not well known. Although these limitations are recognized in several works, there are few field data in the literature to support, according to different exposure conditions, the form of the chloride penetration profiles. This work presents the form of chloride profiles from different exposure conditions. It discusses their behavior and justifies the results according to the presence of the environmental conditions. Some of the results indicate that the environments with chloride saturation produce profiles with a well defined concentration gradient, while those with strong periods of rains, drying, winds, as well as strong variations of RH and temperature show a two-zone profile. In the last case, one zone is close to the concrete nucleus where the supposed reinforcement is positioned and that stays dampened due to the high chloride concentration, and the other one is close to the concrete surface, in which continuous wetting and drying cycles take place. It was also found that, under this research trial, the chloride penetration mechanism did not change with the micro-climate but nucleus concentration changed with the distance from the sea and concrete quality.

Attempts to study the effect of vibration of fresh concrete have mainly been based on visual observation of, for example the radius of influence of the insertion vibrator, or the rate of flow of concrete down a tube when vibration is applied. The reason for this has been the difficulty of measuring the sinusoidal wave form created by mechanical vibrators. Advances in electronic equipment have made devices for measuring this wave form commercially available, and they have therefore been used in this research project to gain a better understanding of the consolidation process. The amplitude of the sinusoidal signal was calculated from the acceleration measured at distances up to 250mm from the surface of the insertion vibrator. Preliminary tests indicate that the amplitude of the vibratory wave decays exponentially with distance. The damping coefficient is greater for superplasticized high-strength concrete mixtures with low W/C than it is for normal-strength concretes. An attempt was made to relate the damping coefficients to the rheological properties, yield (g) and plastic viscosity (h) values determined from tests carried out with Tattersall's two point test apparatus. Both the yield (g) and plastic viscosity (h) values were found to increase by decreasing the W/C, despite the concrete having an equal slump of 150 mm. This shows that the slump values obtained by the use of high dosages of superplasticizers, as is the case with low W/C, are not directly comparable to those resulting from high water contents, with respect to the rheological behavior of concrete.

This paper presents the results of laboratory studies conducted to determine freezing and thawing and scaling resistance of high-performance concrete. High-performance concretes were made using a combination of different cementitious materials (Blast-furnace slag and silica fume). The water-to-cementitious materials ratio was .27, and the bulk volume of coarse aggregate and fine aggregate per unit volume of concrete were fixed at .50 and .60, respectively. All mixtures used a superplasticizer and were non-air-entrained. Test cylinders were cast for testing in compression at 1 and 28 days, and test prisms were cast for determining resistance to freezing and thawing cycles in accordance with ASTM C 666, Procedure A. and for resistance to scaling from deicing chemicals according to ASTM C 672. The curing methods were water curing and steam curing. The air-void parameters of the hardened concrete were determined on the sawn sections. The test results indicate that non-air-entrained, high-performance concrete with steam curing showed low durability factors. High-performance concrete with water curing performed satisfactorily when subjected to up to 1500 cycles of freezing and thawing. Water-cured, high-performance concrete showed no appreciable scaling after 100 freezing and thawing cycles, showing high resistance to scaling.

This paper deals with measurement of concrete durability by means of initial absorption test of the concrete surface. The criterion used for this analysis is the amount of water absorbed after one hour. The specimens were placed in a constant water level of 1cm, and the quantity of absorbed water was measured by mass. It was observed the influence of cement type, temperature, relative humidity and surface protection in the initial absorption. Two concrete mixtures were made with ordinary portland cement blended with calcareous filler (12% and 25% by mass). These concretes were cured at two temperatures (20 degrees C and 40 degrees C) and different relative humidities (30%, 60%, and 100%). In some specimens a curing compound was used to observe its influence on surface protection from initial water absorption. The concrete strengths ranged from 28 to 62 Mpa. The experimental results showed that by changing the relative humidity from 60% to 100% during 7 days, the initial absorption can diminish by a factor of 2. The curing temperature can increase the initial absorption by 64%. The curing compound have a real influence in the concrete initial absorption.

This paper is concerned with the structural behavior of reinforced high-strength concrete corbels. The flow of internal forces and the solution of the problem are discussed. A design approach based on strut-and tie models is proposed. The paper presents the results of experimental investigation conducted with reinforced high-strength concrete corbels and give explanation for them by means of the proposed model. At the end it is shown that, when proper main and web reinforcements are provided, the failure by yielding of the main reinforcement can be achiev3ed and that the models originally developed for normal-strength concrete corbels are suitable to those made with high-strength concrete.