Download PDF version (40.9k) The full article is available as a free PDF document.
In the December 1969 (page 457) issue, the magazine reported briefly on a new concept called dry-cast concrete, which differs from conventional concrete mainly in that the introduction of water takes place after the mixture of portland cement and aggregates has been placed in the form and compacted and finished. The questions and answers that follow were taken from a day long question and answer session with the developers. What can be achieved with dry-cast concrete that is not equally achievable with wet-mix concrete? Because the developers have brought about a predetermined, ordered structure to gain better control over the properties of concrete, specifies can come much closer to getting precisely what they want with dry-cast concrete than with wet-mix concrete. The infusion of water is the key to more precise control. Our material has other advantages: water infusion is self-metering; due to the rapid cure of dry-cast concrete, it is often possible to use forms twice in a single work day; dry mixes, unlike wet mixes, cannot entrap air because they are completely porous; insulation materials, light weight conduits and void formers can be placed in dry-cast concrete quite readily with no danger of floating to the surface, as such materials do in wet-mix concrete; the largest hydrostatic force that would be developed by dry-mix concrete in a wall or column form would be the 62.4 pounds per cubic foot of the water as distinct from the 150 pounds per cubic foot produced by a wet mix; and in supported slabs and slab on grade work, concrete can be finished by rolling at enough cost savings finishing to offset the increased costs of drying the sand and providing for water infusion. What disadvantages will your material represent for the existing ready mixed concrete industry? The only disadvantage, if that is the proper term, is that there will have to be facilities for dying aggregates. If the concrete producer is operating a hot-mix asphalt plant, the plant will already have a drying setup. What about batching and mixing? Are these operation changed or made more critical with your material? No. In all of the work with dry-cast concrete, the developers have deliberately looked for solutions that would conform most closely to prevailing practices and standards.