SHOCK-ABSORBING MATERIALS. REPORT 3. SELECTION OF A SUITABLE LOW- DENSITY CONCRETE FOR BACKPACKING FOR A PROPOSED FIELD TEST
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS
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The objective of this study was to investigate three insulating concretes being considered for use as a backpacking material to determine their handling, mixing, and placing characteristics, as well as the density variation, plastic shrinkage, aggregate segregation, and rate of hardening occurring in large sections made with each concrete, and to determine the problems that may be associated with the use of these concretes in a prototype situation. Metal, half-scale model sections of a typical rock opening and tunnel liner were used in the study. The annular space of each section was pumped full or partially full of cellular, vermiculite, or polystyrene concrete. Each concrete was evaluated on the basis of ease of handling, batching, and placing and on the density variations occurring in both the unhardened and hardened condition of the concrete. In situ density variations were studied by the use of three techniques ULTRASONIC PULSE VELOCITY, HEAT DEVELOPMENT, AND HARDENED CONCRETE SAMPLES. Fresh concrete unit weights were used for the unhardened concrete quality control. Rate-of-hardening tests were conducted to aid in the estimation of form-removal times. Methods of reducing plastic shrinkage and bleeding are discussed.
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