Joint Structure And Method

Abstract

A semi-rigid flat cover strip, having permanently bonded over one of its major surfaces a tacky, self-sealing, and shock-resistant adhesive composition, is applied with its adhesive covered surface over the adjoined edges of adjacent structural members to provide a permanent joint structure which is useful, for example, as a highway construction joint.

Parent Case Text

This application is a continuation-in-part of our prior copending application Ser. No. 852,256, filed Aug. 22, 1969.

Description

This invention relates to sealing of cracks between structural members and to novel joint structures formed thereby. In one particular aspect the invention relates to the sealing of highway contraction joints with semi-rigid flat strip coverings permanently held in place at the plane of the highway surface by a tacky, self-sealing and shock-resistant adhesive.

Sealing joints between adjacent structural members such as the concrete slabs that form a highway has heretofore been a difficult problem. The problems attendant with such joint sealing could easily be solved if they were not aggravated by environmental fluctuations in temperature. In cold weather the concrete slabs will contract, increasing the width of the opening between them. This will cause seals formed with many known adhesive compositions to pull apart. Other adhesive compositions are inadequate for other reasons, e.g., because they are subject to fracture especially during cold weather upon being subjected to continuous impact caused by traffic on the highway, or they are insufficiently tacky to provide a good seal to such structural materials as concrete.

It has now been found that a superior joint structure is formed by applying a strip coated with an adhesive composition provided by highly aromatic, high-boiling, viscous oils, modified by the incorporation of restricted amounts of certain block copolymers of non-elastic vinyl arene and elastic conjugated diene polymers, together with small amounts of other modifiers as desired. These adhesive compositions have physical properties which provide excellent adhesion to concrete, wood, metal, glass, plastics and other structural materials, and which are particularly useful in highway construction and maintenance. Unlike the adhesive compositions employed in pressure-sensitive adhesive tapes, these adhesives are more adhesive than cohesive.

The adhesive composition has a tacky, self-sealing, and shock-resistant nature and an adhesion value of at least 10 gm./sq.cm., tensile of at least 4 psi, elongation of at least 100 percent, brittle point of not above 20.degree. F., and slump of not more than 1/8 inch. This balance of physical properties has been found to provide a joint structure that is useful under environmental conditions including the extreme temperature variations as experienced in the northern states.

The adhesion value of at least about 10 gm./sq.cm. is required for effective use as a highway sealant. Adhesives having lower adhesion values could be used in some similar applications but they have a tendency to part from the surface to which they are applied when pulled away from such surface. The tensile strength must be at least 4 psi to prevent excessive flow of the adhesive under pressure such as would be encountered in highway joint sealing applications. An adhesive which exhibits excessive flow is forced out from between the strip and the surface to which it is applied to leave an insufficient amount of adhesive causing the joint to fail. Elongation of at least about 50 percent is required if brittleness is to be avoided; preferably elongation of at least 100 percent is desired. Brittleness is also determined by the brittle point which must be below about 20.degree. F. Brittle adhesives will not be sufficiently shock-resistant to provide an adequate seal for highway use. The adhesive should also have appreciable resistance to viscous flow (i.e., have no appreciable slump) up to a temperature of about 140.degree. F., preferably up to about 160.degree. F. Adhesives that have appreciable viscous flow at these temperatures are easily displaced from the joint structure causing it to fail. Furthermore, the adhesive of the invention preferably is more adhesive than cohesive and has a self-sealing nature, i.e., if it fails temporarily at isolated areas by internal splitting or separation, e.g., during cold weather when the opening of the joint widens, it will reseal, upon narrowing of the opening, to form a continuous adhesive mass. An adhesive composition having the above specified adhesion value, tensile strength, elongation, brittle point and slump will inherently have a tacky and shock-resistant nature.

In the preferred adhesive compositions, the aromatic oils found useful are high-boiling viscous materials having an initial boiling point of at least about 700.degree. F. and an SSU viscosity at 210.degree. F. of at least about 250. Analysis by the clay-gel method indicates an aromatic content of at least about 55 percent. Many of the "Dutrex" aromatic hydrocarbon process oils of Shell Chemical Company fall within such classification.

Useful as modifiers of the aromatic oils are block copolymers having the type formula A-B-A, wherein each A is a non-elastomeric polymer block of a vinyl arene and having an average molecular weight of about 5,000 to about 125,000 or even higher, and B is a polymer block of a conjugated diene and having an average molecular weight of about 75,000 to about 250,000. The total A component is between about ten and about forty percent, with preferred examples being between about fifteen and about thirty percent of polystyrene A blocks and the balance being polyisoprene or polybutadiene B blocks. Certain of the Shell "Kraton" block copolymers are typical examples of such materials. The amount of such copolymer is between about 25 to 50, preferably 35 to 45 parts per 100 parts of the process oil.

The styrene-diene block copolymers are soluble in the aromatic process oils and may be dissolved therein by prolonged heating and mixing, but with degradation of the polymer. Some means of protecting the latter component is therefore required. The hindered phenol antioxidants are useful for this purpose, and they offer continued protection of the composition during subsequent exposure. Amounts of approximately 1 percent by weight on the weight of the polymer are ordinarily adequate, but greater or lesser amounts may be used. Furthr protection during mixing and compounding may be achieved by accomplishing these operations under an inert atmosphere of nitrogen or carbon dioxide.

The tendency of the aromatic process oils to crystallize at low temperatures and to cause embrittlement or loss of shock resistance in the adhesive mass may be reduced by selection of the lower viscosity oils or by addition of minor proportions of non-crystallizing parafinic oils or polymers. The amount of such additives must be small in order to avoid excessive softening and flow of the adhesive at high use temperatures, a tendency which results also when using the lower molecular weight or low styrene content block copolymers.

The addition of small amounts of compatible low molecular weight polyolefin polymers, e.g. polyethylene, serves also as a means of overcoming softening and plastic flow in these compositions, but has a tendency to reduce the adhesion and elongation values. The proportion of such polyolefin additive is therefore to be restricted to not greater than 30 parts, or preferably 25 parts, per 100 parts of the copolymer.

The aromatic process oils are ordinarily adequately tacky and provide good adhesion to most surfaces. Where additional tackiness is required it may be achieved by the incorporation of small amounts of compatible tackifier resins such for example as polyterpene resin or other non-crystallizing resinous tackifiers, of which a number are included in the list of tackifying resins given in U.S. Pat. No. 3,239, 478.

In the drawing,

FIG. 1 is a view in perspective of a cover-strip product useful for the highway joint structures of this invention,

FIG. 2 is a partial cross-sectional elevation of a highway contraction joint area of FIG. 1, and

FIG. 3 is a partial cross-sectional elevation of another embodiment of a highway joint.

The cover-strip 10 consists essentially of a semi-rigid thin plastic or metal strip 11 having chamfered longitudinal edges and coated over one surface with a coterminous uniform layer of adhesive 12. A removable liner or cover-strip 13 having a surface release coating 14 covers the adhesive surface during storage and shipping.

FIG. 2 illustrates abutting sections 15 of a concrete highway separated by a narrow crack-like opening which may or may not have been filled with an asphalt-based filler 16. The upper surface of the highway carries a thin water-resistant layer 17 which is ground away, together with a thin layer of the concrete, to form a shallow trench 18. The cover-strip 10, with liner 13 removed, is laid along this trench and is pressed into place. The adhesive layer is thereby brought into full adhesive contact with the surfaces defining the trench and with the edges of the coated strip.

In another aspect of the joint structure of the invention, illustrated by FIG. 3, cover-strip 10 is applied directly to a narrow crack between abutting concrete sections 15 which were previously one but have broken apart. Adhesive covered cover-strips are applied to all such cracks in a section of highway and layer of asphalt 19 is applied thereon to obscure the cover-strips and provide a smooth roadway surface.

In warm weather the adhesive is sufficiently firm to resist further flow under heavy traffic, and the vinyl strip protects the adhesive from excessive localized pressures and from pickup of loose pebbles or sand. The assembly is also fully waterproof and permits no entry of water through the crack-like opening. In cold weather the concrete slabs contract, increasing the width of the opening and pulling away from the filler 16. Plastic flow of the adhesive is sufficient to avoid breakage or loss of the protective vinyl strip. In extremely cold weather the adhesive may fail temporarily, but its self-sealing properties are such that subsequent traffic recoheres the surfaces and renews the bond. During the next period of warmer temperatures the slabs again expand. The protective cover is maintained throughout repeated cycles.

The adhesive may be spread directly on the surface of the vinyl strip or on any other desired substrate either at an elevated temperature or suspended or dissolved in a volatile vehicle. A preferred procedure involves coating the adhesive on a removable carried sheet, e.g. by hot spreading using a heated spreader bar and base plate, and then transferring the adhesive layer to any desired surface and removing the carrier.

The following specific Examples, in which all proportions are in parts by weight unless otherwise noted, will further illustrate the invention.

EXAMPLE 1

A preferred adhesive composition is prepared by first heating to 270.degree. C. 70 parts of aromatic hydrocarbon process oil boiling above 700.degree. F. and having an SSU viscosity at 210.degree. F. of 478 and analyzing 57.6 percent aromatics by the clay-gel method ("Dutrex No. 957" oil). Under an inert atmosphere and with continued agitation there is then added 0.3 part of liquid hindered phenol antioxidant ("Wingstay T") followed by 30 parts of an A-B-A type styrene-isoprene block copolymer containing 28% polystyrene ("Kraton 1108"). Solution of the copolymer in the hot oil is accomplished in about 3 hours of mixing at the elevated temperature. There is then added 6 parts of high melting polyterpene resin tackifier ("Piccolyte S-115"), followed by 5 parts of powdered polyethylene resin having a melt index of 22 ("Microthene MN 725-20") and 1 part of carbon black.

The adhesive composition is tested as hereinafter described for adhesion value, tensile strength, elongation, brittleness and resistance to viscous flow, with results as follows:

Adhesion 20 gm./sq.cm. Tensile 160 psi Elongation 1500% Brittle Point 5.degree. F. Slump none (10 min. at 160.degree. F.)

the well-mixed plastic adhesive composition is then smoothly spread over the surface of a silicone-treated paper liner using a knife coater and at a temperature of about 250.degree. F., which is sufficient to maintain a spreadable consistency. After cooling, the coating has a thickness of approximately 0.06 inch.

While the coating is still at a relatively high temperature, or after reheating the cooled material to about 150.degree. F., the coated web is pressed against flat strips of rigid pigmented unplasticized extruded vinyl chloride resin having cross-sectional dimensions of 0.096 .times. 3.0 inch and chamfered edges. The coating adheres firmly to the strips and after cooling the treated paper liner may be stripped away, leaving a smooth glossy tacky surface.

A highway contraction joint structure is prepared on a section of concrete highway containing a contraction joint area by first grinding away the surface to a width of 31/8 inch and depth of 0.15 inch along the joint area. The area is blown free of loose dust, leaving a clean flat freshly exposed concrete surface extending equally from both sides of the joint, which in this instance contains residual asphalt filler material. The strips of coated vinyl resin as laid end-to-end along the groove and are pressed in place by rolling with a 3 inch diameter, 3 inch width smooth-surfaced steel roller weighted to a total of 300 lbs. The adhesive composition adheres firmly to the concrete. It flows beyond the edges of the vinyl strip to fill the edge voids between the strip and the edges of the groove, leaving the upper surface of the strip in the plane of the highway surface. The highway is immediately opened to traffic. The seal is highly resistant to traffic and maintains a water-proof joint under prolonged service under both summer and winter conditions as experienced in the northern states.

EXAMPLE 2

Seventy parts of process oil having an SSU viscosity at 210.degree. F. of 516, an initial boiling point of 740.degree. F., and an aromatics content of 61.8 weight percent by the clay-gel method ("Dutrex 959") is heated to 240.degree. F. To the hot oil is added 0.25 part of antioxidant, 25 parts of styrene-isoprene block copolymer containing 14% styrene ("Kraton 1107"), 5 parts of rubbery polyisobutylene ("Vistanex"), and 3 parts of low mol. wt. polyethylene ("Microthene 702"), each polymer in turn being completely dissolved before the next addition. The composition exhibits the following properties:

Adhesion 10 gm./sq.cm. Tensile 5 psi Elongation 1900 % Brittle Point -30.degree. F. Slump none

It is applied to silicone-treated paper liner and transferred to strips of rigid vinyl resin which are then applied over a suitably prepared one inch width partially asphalt-filled contraction joint in a concrete highway, all as described under Example 1. The seal affords complete protection under all extremes of weather and traffic except for occasional slight water penetration between abutting strip ends.

EXAMPLE 3

The adhesive composition of Example 2 is similarly applied in 0.04-inch thickness to extruded strips of filled polypropylene containing 30% asbestos and having substantially the thermal expansion of concrete. The strips are 0.04 .times. 5 .times. 240 inches. The strips are laid over contraction joints and midpanel cracks in a concrete highway, being adhered to the wire-brushed cleaned surface. The highway is then resurfaced with bituminous concrete or "blacktop." The blacktop coating is protected from moisture normally rising through the cracks in the substrate and which loosens the blacktop layer at such areas. Highway maintenance requirements are greatly reduced.

EXAMPLE 4

A mixture of 52.5 parts of the process oil as used in Example 2 and 17.5 parts of a process oil having an SSU viscosity at 210.degree. F. of 294, an initial boiling point of 700.degree. F., and an aromatic content of 57.6 percent ("Dutrex 916") is heated to 270.degree. F. To the mixture is added 0.3 part of the antioxidant and 30 parts of the styrene-isoprene block copolymer of Example 1, and 3 parts of polyethylene. The following test values are obtained:

Adhesion 35 gm./sq.cm. Tensile 180 psi Elongation 1800 % Brittle Point -11.degree. F. Slump none

A 0.008 inch coating of the adhesive is transferred to a 0.002 inch polyvinyl fluoride film. The coated film in widths of 3 inches is laid over 3/4 inch junction line areas between concrete slabs forming a factory roof. No leakage of water during heavy rains is observed after prolonged exposure, whereas severe leakage occurs through comparable joints sealed with conventional neoprene-based sealing compositions after a single seasonal cycle.

EXAMPLE 5

A composition containing 67 parts of process oil as in Example 2, and 0.3 part of antioxidant, 30 parts of block copolymer, 3 parts of polyethylene and 6 parts of terpene resin all as defined in Example 1, is further modified by the addition of 3 parts of heavy mineral oil ("Nujol"). The compounding and coating procedures are as described in the previous Examples. The properties are as follows.

Adhesion 79 gm./sq.cm. Tensile 150 psi Elongation 1700 % Brittle Point 12.degree. F. Slump none (trace in 15 min. at 160.degree. F.)

An 0.008 inch coating is applied to 0.004 inch flexible vinyl resin film which is then employed as a repair covering over cracks and joints in a concrete swimming pool, the painted concrete surface being first wire-brushed and washed. The strip is applied so as to extend at least 1/2 inch beyond each side of the opening. In those areas where the surface cannot first be dried due to excessive ground water, a priming mixture consisting of one part of the adhesive composition in 3 parts of a 4:1 mixture of methylethyl ketone and ethyl alcohol and to which is added 5 percent of wetting agent is first painted over the surface. Hydroxylated soybean lecithin is a preferred example of a suitable wetting agent. The pool is effectively sealed and the seals remain intact under long continued operation.

The same priming composition is useful in forming an adherent water-proof seal between vinyl resin moldings and glass or metal, as in automotive window construction. The composition may alternatively but less desirably be applied from solution in aromatic or chlorinated aliphatic hydrocarbon solvents or from aqueous suspension. The solvent-free adhesive is also useful in extruded rod or flat strip form as a sealing or caulking strip for windows and other applications.

EXAMPLE 6

A blend of 65 parts of process oil, 0.25 part of anti-oxidant, and 10 parts of mineral oil all as identified in Example 5, together with 25 parts of styrene-butadiene block copolymer containing 28% styrene ("Kraton 1101"), is prepared by mixing at 260.degree. F. and in accordance with previously described procedures. The properties of the composition are as follows:

Adhesion 22 gm./sq.cm. Tensile 4 psi Elongation 100% Brittle Point -4.degree. F. Slump 1/8 inch

Used as a coating on rigid polyvinyl chloride strips to seal concrete highway contraction joints, this composition flows slightly under traffic pressure in hot weather but is otherwise satisfactory. Reduction or elimination of the mineral oil content increases the adhesion and resistance to flow but results in brittleness at low temperature. Either composition is fully effective when not subjected to extremes of temperature.

EXAMPLE 7

Seventy two parts of process oil having an SSU viscosity at 210.degree. F. of 478 and analyzing 57.6 percent aromatics by the clay-gel method ("Dutrex No. 957") is heated to 240.degree. F. To the hot oil is added 0.25 parts of antioxidant, 75 parts of styrene-isoprene block copolymer containing 28% polystyrene ("Kraton 1108"), 3 parts white mineral oil, 6 parts of polyester gum ("Vinsol"), and 3 parts of low molecular weight polyethylene ("Microthene 725-20"), each polymer in turn being completely dissolved before the next addition, producing an adhesive composition having the following properties:

Adhesion 40 gm./sq.cm. Tensile 160 psi Elongation 1500% Brittle point -20.degree. F. Slump None

A flat ribbon, 4 inches wide and 0.040 inch thick, of completely amorphous, fully cross-linked, carbon-black-filled, polyether polyurethane having a softening point of 200.degree. F., melt temperature of 390.degree. F., ultimate tensile strength of 5,500 psi, ultimate elongation of 250-300%, and flexibility of -100.degree. F., ("Estane" 58300) is extruded at 325.degree. F. The hot ribbon is formed on matched chill rolls to provide a pleated structure having three centrally located longitudinally aligned pleats measuring 1/4 inch on a side, leaving a 11/4 inch flat area on each edge of the ribbon.

A 1 inch wide, 0.040 inch thick layer of the above-described adhesive was coated on a silicone-treated paper liner and transferred to the flat edge areas on the same side of the ribbon. The adhesive bearing pleated strip was applied in a 72-foot length to concrete roadway expansion joint that normally underwent unusual expansion daily due to its thin nature. The opening between the adjacent concrete structural members have a daily change from 1/2 inch in width to 11/2 inch in width. The sharp edges of the ribbon are sloped by application thereon of a viscous moisture curing polyurethane ("Deck Coating" Nos. 4833 and 5875). A waterproof joint structure was maintained for a period of 30 days under low speed traffic conditions. The joint structure, because of the nature of the adhesive, was capable of accommodating lateral movement of the ribbon caused by differential expansion of the ribbon and of the cement to which it was applied, as well as the dynamic movement of the concrete segments.

ADHESIVE TESTING

The adhesion value is obtained at room temperature by carefully placing the smooth flat end of a steel rod against the surface of the adhesive coating under defined conditions and measuring the force required to lift the rod from the adhesive mass, a portion of which is found to remain adhered to the rod. The rod is 1/16 inch in diameter, is applied at a weight of two grams, and is removed slowly after a dwell time of one second. An adhesive coating thickness of 0.02 inch is employed in critical determinations.

Tensile and elongation at room temperature (about 72.degree. F.) are determined at break, using a narrow flat strip of the adhesive produced by spreading on a release liner to a thickness of approximately 1/8 inch, removing the coating by careful hand manipulation after first cooling if necessary, powdering the surface to permit cutting, and cutting to a dumb-bell shape having a central section of 1/8 inch width, for testing on an Instron tensile test machine using an initial marked length of 1/2 inch and a machine speed of 12 in./minute. Results are calculated to the initial effective dimensions of the strip. Tensile strength must be at least about 4 psi if excessive flow under pressure is to be avoided.

Brittleness is also determined on a narrow unsupported strip of the composition, by determining the temperature at which a sudden change occurs in the ability of the strip to overcome twisting. As defined for the Gehman test, similar to ASTM test procedure D 1053, the specimen is 0.1 .times. 0.125 .times. 1.5 inches in dimensions. It is clamped between jaws spaced 1 inch apart and is brought to constant temperature. The upper jaw is supported on a torsion wire from a rotatable support which is rotated 180.degree. to rotate a pointer attached to the jaw through an arc of between 120.degree. and 170.degree.. The pointer slowly returns toward its former position and its position at 10 seconds is determined as the Gehman value. The test is repeated over an appropriate range of temperatures, and a graph of temperature vs. Gehman value is drawn. The point of intersection of the two straight portions of the graph is taken as the brittle point.

For the slump test, a narrow strip of the adhesive composition is pressed against a flat wooden surface and supported at an angle of 60.degree. to the horizontal in an oven under specified time and temperature conditions, and the extent of flow along the panel between the initial and final positions of the lower edge is determined to the nearest 1/64 inch. The strip is 1/8 inch thick and 1/2 inch wide and heating is continued for 10 minutes at 140.degree. F. unless otherwise indicated.

Claims

What is claimed is:

1. In a joint structure comprising adjacent structural members having coplanar surfaces and separated to define a narrow opening and a cover strip coextensive with the length of said opening and overlapping its edges, the improvement comprising a weakly cohesive self-sealing polymeric adhesive composition covering said opening and adherently bonding together said strip and members, said adhesive composition having adhesion greater than cohesion and the following properties when tested as described in the specification:

whereby said structure is capable of precluding moisture from entering said narrow opening under damp conditions, permitting temporary failure caused by separation of said structural members, and thereafter resealing when said members return to sufficiently close proximity.

2. The structure of claim 1 wherein said cover strip is a strip of organic plastic.

3. The structure of claim 2 wherein said organic plastic cover strip has a plurality of longitudinally aligned pleats spaced interior from its edges.

4. The structure of claim 1 wherein said structural members are sections of a concrete highway and said structure forms a highway expansion joint.

5. The structure of claim 1 wherein said structural members are sections of a concrete highway and said structure forms a highway expansion joint.

6. The structure of claim 5 wherein said narrow opening is channeled to provide a shallow groove having dimensions substantially the same as those of said strip and being capable of receiving said adhesive coated strip to bring the outer surface of said strip into coplanar relationship with said highway strip.

7. The structure of claim 1 including an asphalt covering layer over said cover strip.

8. The structure of claim 1 wherein said adhesive composition is a self-healing tacky composition comprising: a major proportion of an aromatic hydrocarbon process oil having a viscosity of at least about 250 (SSU/210.degree. F.), an initial boiling point of at least about 700.degree. F., and an aromatic content (clay-gel method) of at least about 50%; and a minor proportion of a block copolymer having an average molecular weight of at least about 85,000 and having the type formula A-B-A wherein the A components acoount for about 10-40 percent of the total, each A represents a non-elastomeric vinyl arene polymer block having an average molecular weight of about 5,000 to about 125,000, and B represents an elastomeric conjugated diene polymer block having an average molecular weight of about 75,000 to about 250,000; the amount of said copolymer being between about 25 and about 50 parts per 100 parts of said oil.

9. The structure of claim 8 wherein said adhesive comprises between about 35 to about 45 parts of said copolymer per 100 parts of said oil.

10. The structure of claim 8 wherein said adhesive composition includes a polyolefin polymer in an amount up to about 30 parts per 100 parts of said copolymer.

11. The structure of claim 8 wherein said adhesive composition includes a tackifier resin.

12. The structure of claim 8 wherein said adhesive composition includes a paraffinic mineral oil.

13. In a method of sealing a concrete highway contraction joint comprising the steps of abrading a shallow channel in the surface of said highway along both sides of the joint area, placing adhesive in said channel and pressing a cover strip into said channel to bring the outer surface of said cover strip into coplanar relationship with said highway surface, the improvement comprising using as an adhesive a weakly cohesive self-sealing polymeric adhesive composition covering said opening and adherently bonding together said strip and members, said adhesive composition having adhesion greater than cohesion and the following properties when tested as described in the specification:

14. The method of claim 13 including the additional step of covering said cover strip with a layer of asphalt in a thickness sufficient to obscure said strip and provide a smooth roadway surface.