Plastic and nonmetallic article shaping or treating: processes – Reactive gas or vapor treatment of work
Patent
1979-09-04
1982-12-07
Czaja, Donald E.
Plastic and nonmetallic article shaping or treating: processes
Reactive gas or vapor treatment of work
106102, 106117, 264 87, 264101, C04B 1514
Patent
active
043626793
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of casting and rapidly curing concrete without the need of using a special curing chamber or autoclave, based on such binders as Portland cement, slag, lime, magnesium oxide, waterglass and the like. However, the method can also be used when casting other types of concrete products such as sandwich elements.
Concrete normally hardens within 7 to 28 days, unless measures are taken to accelerate the hardening process, in which case the time for the concrete to harden normally can be reduced to 4 to 16 hours. A number of accelerated curing processes based on heating the concrete at production of concrete elements, either in moulds or after remoulding, are known.
Autoclaving, i.e. high pressure steam curing, is another method of accelerating the hardening process. This process, however, requires the provision of expensive equipment and also consumes high-levels of energy. A much older, since antiquity applied process of hardening of plaster, mortars, and concretes, based on slaked lime, is carbonation, a natural process, in which the binder calcium hydroxide is transformed into calcium carbonate by absorbing carbon-dioxide from the atmosphere. The process, however, is slow and the resultant mechanical strength of the product is generally low.
A more recent development is the concept to speed-up the carbonation process of lime or lime cement mortar by means of a treatment with artificially produced carbon-dioxide. The procedure is used for drying lime plaster in residential building by applying exhaust gas containing carbon-dioxide.
The same principle in which exhaust gas is combined with steam or with moist warm air is used for accelerated hardening of different concrete products in curing chambers. This method is used in particular for hardening concrete blocks, and is in reality a combination of carbonation and hydration hardening. It has been possible to achieve hardening times of from 8 to 16 hours by means of this method. In addition to accelerating the hardening process, the gaseous mixture applied also greatly reduces shrinkage of the product.
Artificial carbonation of a concrete mass in order to accelerate hardening has been described in many U.S. patent specifications since 1870. In the U.S. Pat. No. 109,669 of 1870 to Rowland there is described a method of hardening concrete elements by means of carbonic acid gas, while in the U.S. Pat. No. 128,980 of 1872 the same inventor is using a carbonation procedure in which gas is dissolved in the mixture water-concrete.
Since then a multiplicity of methods have been proposed for the carbonation of lime and cement concrete masses and asbestos cement products (U.S. Pat. Nos. 2,496,895; 3,149,986; 3,468,993; 3,492,385). These patent specifications have claims which are directed to the composition of concrete to the compaction methods and the conditions of carbonation performed generally in chambers or on conveyors without application of vacuum. The first-mentioned application of vacuum evacuation of concrete products before carbonation applied in chambers is found in U.S. Pat. No. 591,168 of 1897. According to this specification the concrete elements are placed in a hermetically sealed vessel, to which a gas, e.g. carbon-dioxide or steam, is fed subsequent to exhausting the vessel of air. After being hardened, the concrete elements may additionally be impregnated; this latter step is also carried out in vacuo.
In UK Pat. No. 1,460,284 of 1976, German lay-open print No. 1,915,563 of 1974, and German open-to-public print No. 2,008,247 of 1971 there are described different methods of carbonation hardening of concrete, and glass fibre reinforced concrete also using vacuum treatment. The elements are moulded, placed in a special chamber or autoclave and vacuum treated before the carbonation. High strength is obtained at a carbonation time not exceeding four hours. The procedure is similar to that one described in U.S. Pat. No. 591,168 mentioned above. A carbonation procedure also applying vacuum treatment for producing shape
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Czaja Donald E.
Thompson W.
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