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This Symposium Publication includes 30 papers selected from the Third Conference on High-Performance Concrete (HPC) and Performance and Quality of Concrete Structures, held in Brazil. Topics covered include chloride penetration models in reinforced concrete structures, high-strength concrete with crushed and natural sand, sewage sludge ash as an addition in concrete, and the mechanical properties of polymer-modified high-performance lighweight aggregate concrete. 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. SP207

Most of the carbonation studies are carried out by means of accelerated tests in conditioned chambers in order to obtain data in a shorter time, although the results are not always well correlated with field or laboratory data in natural tests. This work presents a comparative study between a reference portland cement concrete and pozzolanic mixtures with 10% to 50% fly ash, rice husk ash and silica fume in binary and ternary mixtures. Accelerated tests in a conditioned chamber with carbonation depth readings after 4, 8, 12 and 16 weeks, and natural tests with similar specimens exposed to the lab air environment with readings after 0.5, 1 and 2 years, were performed. The calculated rate between the carbonation coefficient of accelerated and natural tests was approximately 1 mm.week0.5 = 1 mm.year0.5 for concrete with w/cm < 0.45 and pozzolan contents up to 25%. For higher w/cm rates and w/cm < 0.45 and pozzolan contents up to 25%. For higher w/cm rates and pozzolan contents, the accelerated tests showed coefftcients 2 to 6 times higher than those observed in the natural test. This work presents preliminary data and it will be continued for 5 years more, in order to obtain readings after exposure to lab air for 4 and 8 years, after casting.

The characteristics of cement paste are very important for the workability, the mechanical properties and the durability of concrete, particularly in High Performance Concrete (HPC). Several problems of concrete such as slump loss, retardation in setting time or excessive heat of hydration, are directly related with some characteristics of the cement paste. This paper presents the results of a study made on cement pastes to select cementitious materials and chemical admixtures, and adjust mixture proportions before the concrete mixture design. Changes in the fluidity and the behavior of different super-plasticizers combined with cementitious materials including cements of different fineness, and different types or contents of mineral additions (calcareous fillers, natural pozzolans or silica fume) were comparatively studied by using the Marsh cone. It was found that the saturation point (defined as the dosage of superplasticizer over which the flow is not substantially modified) may change significantly with the type of superplasticizer, the fineness of the cementitious material and the incorporation of mineral additions (especially silica fume). Moreover, a quick and easy procedure was applied to analyze the behavior of different cement pastes regarding hydration process, setting time and heat development during the first ages.

This paper analyzes the mechanical behavior and its relation with the development of the hydration reaction in concretes with low water-to-cementitious material ratio made with binary and ternary cements containing limestone filler and blast furnace slag. It explores the maximum level of replacement of portland cement by both additions to obtain high early strength concrete. At 3 days, the compressive strength was 43 to 45 MPa and it was greater than 60 MPa at 28 days. All studied concretes present a very similar strength development. Results show that the combination of limestone filler and blast furnace slag is complementary: the limestone filler improves the early strength of concrete while the slag improves the later strength achieving to an optimal strength development. The concrete performance analyzed in terms of water penetration test also classified these concretes as very low permeability.

The results of an experimental investigation of the effects of short steel fibers on the shear behavior of reinforced concrete beams are presented. Two types of steel fiber with different shapes, lengths and cross sections were used. Two series of reinforced concrete beams were cast and tested in the laboratory. Each series had a different ratio of transverse reinforcement as well as the addition or not of steel fibers in the concrete mix. The test results indicate the better performance of the beams made with fibers. These beams exhibited smaller crack width and spacing and consequently more stiffness and load carrying capacity. The results also show that the steel fibers improve the shear resisting mechanisms of the concrete represented by the aggregate interlocking and dowel action and behave as an additional transverse ireinforcement, consequently reducing the stresses in the stirrups. This finding suggests a code revision of the concrete contribuition for the shear design of beams when steel fibers are used. Their use can reduce the labor costs in the fabrication of these beams.