Abstract
Two-stage concrete (TSC) is a sustainable concrete which is produced by forcing a flowable cement grout mixture through the voids of a skeletal mass made of compacted preplaced aggregates. From the technical and economic aspects, TSC is particularly useful for construction and repair of concrete structures especially foundations, underwater construction, nuclear reactors, concrete dams, heritage structures and in constructions with closely spaced reinforcement. TSC differs from ordinary concrete in that it contains a higher proportion of stone aggregate and the aggregate stays in point-to-point contact as placed. Thus, the mechanical characteristics of the TSC in failure conditions are distinctly different from ordinary concrete. This paper presents the results of experimental investigations conducted to evaluate the compressive, tensile strength and modulus of elasticity of TSC using grouts with different water-to-cement ratios and admixture contents. It was found that the modulus of elasticity and splitting tensile strength of TSC are equivalent or higher than that of conventional concrete at the same compressive strength. In this method of construction, the splitting tensile strength can be conservatively estimated using the American concrete institute (ACI) equation for conventional concrete.
Highlights
The preplaced aggregate concrete (PAC) or two-stage concrete (TSC) gets its name from the method used for placement
Results from Equation (4) indicated that splitting tensile strength could be well estimated using the American concrete institute (ACI) equation presented in Equation (3)
The data from both studies show that the tensile strength of TSC is at least as high as that of conventional concrete, and it can be higher depending on the selection and properties of the coarse aggregate
Summary
The preplaced aggregate concrete (PAC) or two-stage concrete (TSC) gets its name from the method used for placement. Proper proportioning of the structural grout mix components is necessary to produce the required strength and durability requirements of the finished preplacedaggregate concrete [2] It may be used advantageously on repair jobs of heritage structures, and large concrete repair jobs: - Where placement by conventional methods is difficult (e.g., massive reinforcing steel and embedded items are present or access to the area is difficult, such as the underpinning of the toe of a dam or apron). In Poland large-scale two-stage concreting was tested in two applications, namely while laying foundations for an 18 story building in Gdansk (Poland) (about 350 m3) and the repair of damage to a water dam in Czchow near Cracow (Poland) (about 400m3) underwater concreting, on the River Dunajec In both cases good technological and economical results were obtained [3]. The displacement of aggregate was less noticeable as the w/c ratio was increased; at a w/c ratio of 0.55 there was no displacement
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