In the art of concrete construction, it is commonplace to form "cold joints" between two or more poured concrete slabs. Such cold joints frequently become uneven or buckled due to normal thermal expansion and contraction of the concrete and/or compaction of the underlying soil caused by inadequate substrate preparation prior to the pouring of the concrete. As a means of preventing buckling or angular displacement of such cold joints, it is common practice to insert smooth steel dowel rods generally known as "slip dowels" within the edge portions of adjoining concrete slabs in such a manner that the concrete slabs may slide freely along one or more of the slip dowels, thereby permitting linear expansion and contraction of the slabs while at the same time maintaining the slabs in a common plane and thus preventing undesirable buckling or unevenness of the cold joint.
In order to function effectively, slip dowels must be accurately positioned parallel within the adjoining concrete slabs. The positioning of the dowels in a nonparallel fashion will prevent the desired slippage and will thus defeat the purpose of the slip dowel application. Additionally, the individual dowels must be placed within one or both of the slabs in such a manner as to permit continual slippage or movement of the dowel within the cured concrete slab(s).
In the prior art, two methods of installing smooth slip dowels have become popular. According to the first method, a first concrete pour is made within a pre-existing form. After the first pour has cured, an edge of the form (usually a wooden stud) is stripped away. A series of holes are then drilled parallel into the first pour along the exposed edge from which the form has been removed. The depth and diameter of the individual holes varies depending on the application and the relative size of the concrete slabs to be supported. As a general rule, however, such holes are at least twelve inches deep and typically have a diameter of approximately five-eighths (5/8) of an inch.
After the parallel series of holes has been drilled into the first pour, smooth dowel rods are advanced into each hole such that one end of each dowel rod is positioned within the first pour and the remainder of each dowel rod extends into a neighboring area where a second slab of concrete is to be poured. Thereafter, concrete is poured into such neighboring area and is permitted to set with the parallel aligned dowels extending thereinto. After the second pour has set, the slip dowels will be held firmly within the second slab, but will be permitted to slide longitudinally within the drilled holes of the first slab thereby accommodating longitudinal expansion and contraction of the two slabs while at the same time preventing buckling or angular movement therebetween.
Although the above-described "drilling method" of placing slipped dowels has become popular, it will be appreciated that such method is extremely labor intensive. In fact, it takes approximately ten minutes to drill a five-eighths (5/8) inch diameter by twelve inch long hole into the first pour and the drilling equipment, bits, accessories, and associated set up time tends to be very expensive. Moreover, the laborers who drill the holes and place the slip dowels must be adequately trained to insure that the dowels are arranged perpendicular to the joint but parallel to one another so as to permit the desired slippage during subsequent use.
The second popular method of placing slip dowels involves the use of wax-treated cardboard sleeves positioned over one end of each individual dowel. According to such method, a series of holes are drilled through one edge of the concrete form and smooth dowels are advanced through each such hole. Thereafter, treated cardboard sleeves are placed over one end of each dowel, with a first pour subsequently being made within the form which covers the ends of the dowels including the cardboard sleeves thereon. After the first pour has set, the previously drilled form is stripped away, leaving the individual dowels extending into a neighboring open space where the second pour is to be made. Subsequently, the second pour is made and permitted to cure. Thereafter, the slip dowels will be firmly held by the concrete of the second pour, but will be permitted to longitudinally slide against the inner surfaces of the wax treated cardboard sleeves within the first pour. Thus, the waxed cardboard sleeves facilitate longitudinal slippage of the dowels, while at the same time holding the two concrete slabs in a common plane, and preventing undesirable buckling or angular movement thereof.
This second method, while presently popular, is nonetheless associated with numerous deficiencies. For example, after the first pour has been made, the free ends of the dowels are likely to project as much as eighteen inches through the form and into the open space allowed for the second pour. Because the drilled section of the form must be advanced over those exposed sections of dowel to accomplish stripping or removal of the form, it is not infrequent for the exposed portions of the dowels to become bent and, thus, non-parallel. Additionally, the drilled section of the form may become damaged or broken during the removal process, thereby precluding its reuse.
Each of the above-described methods of placing slip dowels between concrete slabs often results in the dowels being finally positioned at various angles rather than in the desired parallel array. When such occurs, the necessary slippage of the dowels is impeded or prevented. Additionally, each such method necessitates that a first pour be made and permitted to set, with a second pour being made subsequent to the setting of the first pour and the removal of the form from at least one edge of the slab created by the setting of the first pour. As such, these placement methods, and in particular the "drilling method", are not suited for use in relation to monolithic or continuous concrete pours wherein the second pour occurs immediately after the first pour, with an edge of the form (e.g., a wooden stud or metal imbed form) remaining between the pours and thus the resultant concrete slabs. In many applications, continuous pours are the preferred method of concrete construction due to the reduced labor and time/cost savings associated therewith. Such savings are the result of not having to wait for the first pour to set and not having to subsequently strip an edge of the form from the first poured concrete slab. Accordingly, there is a need in the art for devices and/or methods for facilitating the proper placement of slip dowels in monolithic or continuous concrete pour applications.
USPTO Backgrounds
USPTO Backgrounds