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INTRODUCTION

Concrete in normal conditions is a versatile, strong and durable construction material. However under several physical and chemical processes as well as certain environmental conditions it may deteriorate in a short period of time. This fact has led researchers in the last 30 years to develop the high performance concrete. High-performance concrete (HPC) is a concrete which possess high workability, high strength and low permeability.

The production of a high-performance concrete can be achieved basically with a better selection of component materials, adequate mixture proportion, careful placement and proper curing. The required workability is normally attained with the use of superplasticizers. Since the manufacture of high-performance concrete does not involve the use of exotic materials and complicated procedures, its production is within the reach of most concrete producers.

In most structures, concrete is often subjected to biaxial states of stress, and the behavior of the material under these types of actions must be well understood. It is, therefore, not surprising that numerous investigations into the behavior and strength of conventional concrete under biaxial stress states have been conducted in the past 40 years (1,2,3). On the other hand, HPC differs from normal strength concrete (NSC) in several aspects and these differences are not yet totally understood. Thus more studies are necessary to better understand the behavior of this material and to facilitate the design and construction of more structures with HPC.

The aim of this paper is to gain further understanding on the behavior and failure mechanism of HPC when subjected to biaxial stresses. Short-term static tests were performed on 125 mm square by 12.5 mm thick plates subjected to biaxial tension-compression stresses at selected stress ratios (4). The strain controlled tests were executed in a biaxial testing machine constructed at the University of Texas. The primary variables studied were the discontinuity and the ultimate stress levels at each stress ratio. A comparative study with normal strength concrete is also presented.