http://worldcat.org/entity/work/id/137212598

Shock-absorbing materials. report 3. selection of a suitable low-density concrete for backpacking for a proposed field test

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 time 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 time density variations occurring in both the unhardened and hardened condition of the concrete. In situ density variations were studied by time 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 time estimation of form-removal times. Methods of reducing plastic shrinkage and bleeding are discussed, along with other features such as handling and storage requirements of mixture components and suggested prototype batching and placing equipment and techniques. An appendix describes a field placement trial of a cellular concrete arch section to determine time ease of placing and forming, required strength for arch to stand unsupported, and settlement of arch crown.

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