Control Joint Filler

Abstract

Sealing strip for joints in concrete structures which prevents water and debris from entering the joint consisting of continuous length of flexible polymer material with special cross section configuration for anchoring.

Description

This invention relates to sealing strips for joints in concrete structures, and particularly to so-called base sealing strips which are used to prevent the passage of water through the joint and debris into the joint space of concrete structures or slabs, and also to prevent debris from entering or packing into the joint space.

The purpose of the present invention is to provide base seals which will remain tight and prevent the passage of water through the joint and prevent the entrance of debris into the joint space despite hardening, shrinkage, or thermal movement of the concrete sections.

It has been found that if relatively massive side-anchoring members are formed adjacent the margins of the base sealing strip and if they extend upwards from the base a sufficient distance so that a substantial mass of concrete may envelope them, very little stress is transmitted to the anchoring members as the concrete sections move apart, and very little movement or change in dimension occurs in the anchor portions of the seal. Consequently, the stress is mainly confined to the flat base seal portion which may extend or contract without in any significant degree loosening the anchorage in the concrete. The invention which flows from this discovery appears in three forms.

The base sealing strips, according to this invention, are used to seal three forms of joints:

A. "Control joints" in which the strip is formed with a divider strip so as to induce the shrinkage crack which forms when the concrete hardens to follow a predetermined line;

B. "Construction joints." Such joints always must be formed when one pour of concrete stops, and a succeeding pour begins; and

C. "Expansion joints." Such joints are spaces left between adjacent slabs of concrete to allow for the dimensional changes in the concrete slab due to changing temperature which are filled with expansion joint fillers.

The three types of base seal strips are illustrated in the accompanying drawings.

The control joint base seal includes a control joint former which is a fin attached to and usually, although not necessarily, molded integrally with the base seal. The fin rises from a position which lies along the median line of the base strip. The height of the fin above the base may vary substantially according to the demands of the specifying authority, but specified heights usually will be found to lie between about one-fifth and one-third of the thickness of the concrete slab which is to overlie the base seal.

In the construction joint base seal (FIG. 3), the control joint former is omitted. The base seal then is composed of the base portion and the anchoring members.

In the base seal for expansion joints, an expansion element is formed along the median line of the base sealing strip. This is a keystone-shaped, tubular member, the upper and sidewalls of which have the same cross section as the thickness dimension of the base. However, the wall which forms the base of the tube is made thin so that it may stretch far more easily than any other section of the seal. Hence considerable expansion may take place in the thin section, while the side and upper wall sections merely swing about the hinge points at the corners as the gap between the slabs enlarges. Since most of the stress developed by contraction is exerted in the thin section, very little stress is transmitted to change the dimension of the anchors. Such expansion joint base seals are rarely loosened as the slabs pull apart from each other and give long, dependable life.

Whatever the type of joint control, construction, or expansion, the base seals have two common parts: (a) a flat base wide enough to span the joint space, and (b) continuous longitudinal anchors rising upwards from the base adjacent its margins which, in use, are securely embedded in the hardened concrete. As a result of anchoring one of the margins of a base seal in one concrete slab and anchoring the opposite margin in the concrete of the abutting slab, base seals provide an impervious diaphragm which spans the joint space. As a result, water, either from behind or below the concrete structure, cannot pass through the joint, and also as in the case of a slab, the joint is sealed against the entrance of any debris which might otherwise work up from the subgrade.

All base seals are formed from a continuous strip of a flexible and somewhat resilient substance, preferably an age- and oxidation-resistant polymer. The strip may be formed by a conventional rubber molding process, but usually is formed by the extrusion of an appropriate "rubber" or plastic compound through a heated die. Base seals extend uninterruptedly along the entire joint.

It should be understood that specifications for structures which require base seals vary considerably and that base seals which are wider, thicker, or even which possess considerably smaller dimensions than those given, are frequently required. However, the dimensions given below meet a considerable range of construction requirements.

In the accompanying drawings,

FIG. 1 is a transverse cross section of a base seal having a control joint former,

FIG. 2 is a transverse cross section of a control joint base seal installed in concrete,

FIG. 3 is a transverse cross section of a construction joint base seal, and

FIG. 4 is a vertical cross section of a base seal for use in expansion joints.

Referring to FIG. 1, the base seal, 10, comprises a base portion, 11, anchoring members, 12-12, and a control joint former, 13. The entire seal is usually extruded as a unitary structure and is formed from an elastic, distortable polymer having good age- and zone-resistant characteristics.

Typical among numerous substances known to the art and which experience has shown give satisfactory service are the so-called "rubber" polymers such as polybutadiene, butadiene-acrylonitrile, polyisoprene blends, polyurethanes, polybutene combined with isoprene or butadiene, ethylene-propylene co- and ter polymers, polyvinylchloride, and other thermoplastic compositions.

Dimensions of the seal which meet a majority of specifications for pavement slabs are as follows:

Width of the base--3 to 9 inches

Thickness of base--0.115 to 0.130 inch

Base thickness of the control joint former (fin)--0.135 inch

Height of the former--11/2 inches, or 10 times thickness of base.

The anchor portions, 12, have a raillike cross section, are continuous, and lie adjacent to the margins of the base, 11. The top surface of the rail head lies one-half inch above the base. The thickness of the web is three-sixteenth inch. The width of the rail head is seven-sixteenths inch.

In FIG. 2, a control joint base seal as installed in a highway or runway apron is shown placed directly on the subgrade, 14, and covered by concrete, 15-15. The joint former fin, 13, projects upwardly into the mass of concrete--in this case approximately one-third of the thickness of the overlying concrete slab. As the concrete hardens, a crack, 16, forms, extending from the apex of the fin, 13, to the outer face of the concrete slab. In this manner the position of shrinkage cracks is closely determined, and unwanted cracks appearing in other portions of the slab are prevented.

Assuming that the slabs, now separated by the crack, draw apart, the stress across the joint is imposed on the base portion, 11, of the seal. Very little stress is imparted to the web section, 17, of the anchors, 12, and even less is transmitted to the head section, 18. There is, therefore, very little tendency for the pull to thin the anchoring members, 12-12. They remain rigidly bedded in the concrete matrix and give long, dependable life. The performance of base seal equipped with these relatively massive anchors contrasts markedly with performance when anchorage is secured by, e.g., serrations formed in the base, 11, itself. In this instance, elongation of the seal due to the contraction of the slab thins the entire base and loosens the anchorage between the seal and the concrete.

When the specifications so state, some control base seals are laid on a footing, and other control joints may be formed by the combined action of the former fin and a thin control joint former insert which is pushed down into the wet concrete from above after the concrete has been poured and leveled. The inserts are frequently made of waterproofed fibrous material such as impregnated fiber board and are quite thin. By thus separating the concrete both from above and below, a joint former insures that the concrete will crack solely along the common plane occupied by both the joint former and the fin.

A construction joint base seal is shown in FIG. 3. Since construction joints represent the end of one pour and usually terminate against a form, division between the slabs or other concrete sections is already established. Control joint former fins are unnecessary. Control joint base seals are, in consequence, a unitary extruded strip having a base, 11a, and two anchor members, 12a-12a, which rise from the upper surface of the base, 11a, and extend along the margin of the strip. Just as in the case of the control former base seal, construction joint base seals are embedded in the concrete slab, the difference in installation being that as a construction joint base seal is installed, one-half of the base seal is left protruding into the unpoured area beneath the concrete form. Alternatively, a separate thin joint former may be employed with the construction joint base seal.

Expansion joint base seals are illustrated in cross section in FIG. 4. Since the purpose of such a base seal is to seal the joint between adjacent slabs, and at the same time maintain the seal despite the expansion and contraction of the slabs due, e.g., to summer and winter conditions, as expansion member, 19, is formed along the median line of the base seal. Expansion member, 19, is a keystone-shaped tube, the side and upper walls of which have approximately the same thickness as the base portion, 11b. The lower wall, 21, of the expansion member, 19, is, however, quite thin, and when subjected to stress may stretch freely. Expansion joint base seals are almost always used in conjunction with an expansion joint filler strip which, after the concrete has been poured over the base seal and has been floated, is inserted from above, either by a machine or by hand. As can be seen from the cross section, as the slabs draw apart, the lower wall portion, 21, can expand easily, and the side and upper walls of the expansion member, 19, may merely move about their hinge points. Very little stress is imposed on the anchor members, 12b-12b, and, as stated, such seals remain tight through long service life.

Since the base seals are flexible and can be formed as continuous rolls, all of the foregoing types of seals are furnished to the contractor in the form of large rolls from which appropriate lengths may be cut and installed at the job site.

Claims

What I claim is:

1. A unitary base seal for joints in concrete structures comprising a continuous length of a flexible, extensible, resilient polymeric substance, the said seal having a flat base including thick marginal portions and a thin median portion, continuous anchoring portions extending upwardly from a position adjacent each of the longitudinal margins of said base, the anchoring portions having a rail-shaped cross section including a web and a head, the said web and head portions having a substantially greater thickness than that of the marginal portions of said base, and the said anchors having a vertical dimension equaling at least three times the base thickness, an upstanding hollow expansion element of keystone cross section formed above the median of said base, having side and top walls at least equal in thickness to the said marginal portions, the said thin median portion of said base constituting an extensible diaphragm.