Apparatus for the manufacture of a precast building element of c

Details Apparatus for the manufacture of a precast building element of c Apparatus for the manufacture of a precast building element of c

1983-11-30

1985-09-10

Flint, Jr., J. Howard

Plastic article or earthenware shaping or treating: apparatus

Building forms or construction engineering type mold with...

425 59, 425 64, 425 89, 425447, B28B 2106

Patent

active

045403589

DESCRIPTION:

BRIEF SUMMARY
The present invention concerns an apparatus for the manufacture of a precast building element of concrete.
Precast building elements of concrete frequently consist of the following functional parts: a straight, plane top or bottom face, or simultaneously both of them, and of a supporting material connecting these faces, which material may be continuous or, as is frequently the case, made of longitudinal beams and of reinforcements that carry tensile strains.
In practice, such a precast element serves as a floor, ceiling, wall, or equivalent, the highest strains applied to such components being, besides their own weight, other strains directed downwards, mostly caused by the force of gravity.
In such a situation, the upper face of this precast concrete element must withstand compression forces, and the bottom face tensile strains. Out of these reasons, a portion of relatively low strength is required to bind the top face and the bottom face; in construction technology, an I-beam is known. When such I-beams are connected to each other, in the building technology, on the other hand, the notion of hollow slab has been adopted.
The problem in the manufacture of such a hollow slab or corresponding element is the formation of a cavity of desired shape continuously and without restriction in respect of the properties of the concrete mix used. The shape of the cavities is in each case determined by many individual factors.
In the prior art for the manufacture of hollow slabs that are used today, many compromises must be made between these factors and the properties of the concrete mix.
In such prior art in which the hollow slab is shaped continuously while taking advantage of the vaulting properties of fresh, substantially viscous concrete mix, at the stage of formation of the slab, a strong, rapidly varying force is required, which is, in concrete technology, called vibration.
In such a manufacture, when attempts are made to form hollow cavities of desired width in thick slabs, the intensive vibration causes difficult noise problems at the working sites as well as problems of strength of the machine elements to be used.
In order to avoid these drawbacks, attempts have been made to manufacture such hollow slabs or corresponding structural elements so that the cavity is shaped out of some inexpensive material while the concrete mix of substantially low viscosity is being cast around this material forming the hollow cavity.
Typically, such a material forming the cavity is sand or gravel or any other rock material, which can be removed on hardening of the building element of concrete in accordance with prior art technique (Finnish Pat. No. 47,295), e.g., by pouring, and which material can be used again as filler material for subsequent hollow slab elements to the extent that it did not adhere to the preceding element.
In such an operation a drawback consists of complicated machinery and equipment, recirculation of a large quantity of rock material with resulting losses of energy, and further the uneven faces of the cavities formed, which are harmful in the cases of certain application of use.
In an attempt to minimize the capital cost of such hollow slab factories, heating of the hollow slab elements has been introduced so as to make the necessary setting time of the concrete mix shorter.
This heating is mostly carried out so that the casting base of the concrete element cast is heated, the heat being conducted from the base further into the structural element itself.
Such a method always results in highly uneven heating of the cast object, with detrimental strains resulting therefrom, the strains being derived from different local temperatures and from resulting different degrees of setting of the concrete.
Now, after having studied how to form such a hollow slab most advantageously, it has surprisingly been discovered that there is a method in which all the desired aspects can be accomplished at the same time.
In this method, the desired cavities are produced by means of a liquid filler agent, said agent being isola

REFERENCES:
patent: 857586 (1907-06-01), Boyle
patent: 3193901 (1965-07-01), Lee et al.
patent: 3773874 (1973-11-01), Long
patent: 3957977 (1976-06-01), Godbersen
patent: 4017226 (1977-04-01), Long
patent: 4181696 (1980-01-01), Mayrl

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