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Self stressing, produced through the action of an expansive-cement component in concrete, was used to prestress high tensile strength steel in tension, thereby creating designed degrees of precompression in the concrete. The so-called expansive cement consists of a blend of portland cement of high tricalcium silicate and low tricalcium aiuminate content with an expansive component made by grinding a clinlter of calcium alumino sul-fate composition. The concrete elements manufactured and tested, all self stressed by chemical prestressing, include four pressure pipes, three beams, a two-way reinforced slab, a one-way reinforced slab, and a hyperbolic paraboloid thin shell. Only the four pressure pipes and the two slabs are described in detail. The behavior and the strength of pressure pipes and slabs determined by experiment are compared with analytical values based on conventional theory of elasticity and principles of prestressing. It is shown that experimental results obtained with chemical prestressing of pressure pipes and flat slabs agree closely with calculated theoretical values. [ABSTRACT FROM AUTHOR]

Expansion characteristics and compressive strengths were determined for concretes containing expansive cement to evaluate the factors relating to control of the expansive reaction. The expansive cement consists of a portland cement component and a calcium-sulfoalumlnate anhydrite com-ponent. The factors influencing the magnitude and rate of the expansive reaction include: chemical composition of the components, fineness of the sulfoaluminate component, proportions of the two components in the total cementing material, ratio of water to total cementing material, richness of mix, conditions of curing, and degree of restraint. In this investigation, the chemical composition of the components and the fineness of the sulfoaluminate component were kept essentially constant, and other factors influencing magnitude and rate of expansion were varied. For this study, restraint in all cases was provided by external steel mechanisms, in some cases restraint being uniaxial, and in other cases biaxial. In the absence of restraint, concretes exhibited free expansions up to 6 percent or more. The properties of the concretes reported herein indicate that certain of the expansive cements tested are suitable for structural work and can effectively be employed in the manufacture of chemically prestressed members under conditions of external restraint. It was established that with proper mix proportioning and curing, with compositions, proportions, and fineness of components fixed, it is possible to produce concretes having desired predetermined characteristics within a practical range. [ABSTRACT FROM AUTHOR]