TECHNICAL FIELD

This invention relates to the preparation of concrete articles that must be waterproof or protected from corrosive liquids or gases, and it particularly relates to reinforced concrete sanitary sewer pipes and sanitary sewer structures, such as manholes, lift station wetwells and sewage plant structures.

BACKGROUND ART

The preparation of poured concrete structures is a well known art that has been developed over many years. Protecting the surface of these concrete structures, whether of poured in-place or of precast concrete, against corrosive compounds has been a never-ending problem. Various approaches have been taken in an effort to combat the problem, with little or no success. Among these methods are the use of various liquid coatings, such as bitumastic, asphaltic, and rubberized coatings. Another approach has involved the use of two-part epoxy coatings. The one real inadequacy with coatings, as described above, is that no matter how carefully one follows preparations and application instructions, there will be a pinhole in the film; and with the passing of time, corrosive elements find this minor flaw and start eating into the concrete. Eventually the film comes off in sheets, leaving the concrete subject to an ac¬ celerated deterioration rate.

Another approach has been to use an extruded PVC liner with T-shaped appendages which are buried in the concrete when poured. These T's create a physical interlock with the concrete. However, it has been found, that if the structure is subject to high hydrostatic heads, the T's are forced out of the concrete, with resultant failure.

In a more recent development fine silica sand is mixed with two-part epoxy compounds, to a trowelable con¬ sistency, applied at a thickness of about 0.125 to 0.25 inch. Some short term positive results have been achieved, but the economics of this procedure are not good and the long term results may not warrant the extreme expense.

It is an object of this invention to provide a novel poured concrete article with a corrosion resistant and waterproof laminate adhered to a surface thereof with a remarkably improved bond strength. It is another object of this invention to provide an improved process for pre¬ paring corrosion resistant and waterproof concrete articles. Still other objects will become apparent from the more detailed description which follows:

DISCLOSURE OF INVENTION

This invention relates to a process for casting a concrete article of manufacture comprising preparing a form for pouring a concrete article of manufacture and covering a surface of said form with a liquid impervious barrier sheet having a sticky or tackified surface facing the cavity into which concrete is to be poured, filling the cavity with a concrete mix containing a polymeric modifier, and recovering a concrete article with the surface covered with the barrier sheet having excellent adhesion to the cured concrete.

In specific preferred embodiments of this inven¬ tion the concrete article of manufacture is a reinforced concrete pipe or sanitary sewer structure with the inside surface covered with the barrier sheet. The bond between the sheet and the concrete is far stronger than any experienced in the concrete industry for waterproof and corrosion resistant materials.

BRIEF DESCRIPTION OF DRAWINGS

The novel features believed to be characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be under¬ stood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a top plan view of a concrete form for a sewer pipe made in accordance with this invention;

FIG. 2 is a cross section taken at 2-2 of FIG. 1;

FIG. 3 is a perspective view of the first step in attaching a liquid impervious barrier sheet to a core of a concrete form;

FIG. 4 is a perspective view of the core of FIG. 3 ready to be inserted into the form;

FIG. 5 is a perspective view of a jacket with a barrier sheet attached thereto prior to pouring concrete therein; and

FIG. 6 is a perspective view of a preferred asphaltic laminate used as the barrier sheet in this invention.

BEST MODE FOR THE INVENTION

The full understanding of this invention is best reached by reference to the attached drawings.

FIGS. 1 and 2 show a concrete form for use in pre¬ paring a reinforced concrete sewer pipe with an interior corrosion resistant and waterproof lining. Jacket 10 and core 11 define a cavity 25 into which polymer modified concrete is poured. After the concrete has set, clamps 25 are loosened, jacket 10 and core 11 are removed, and the final form of pipe remains.

No-αnally, a steel rei-nforce-i-ent structure 12 of rods or welded wire mesh is placed in the form, to be embedded in the concrete. In order to make end joints for assembling one pipe section to another,

tongue forming ring 23 and groove forming pallet 24 are employed in opposite ends of the form. The above descrip¬ tion constitutes the component parts of a concrete pipe form which are well known in the art prior to this invention. The inside of the pipe becomes a conduit for sewage after the assembly of many pipe sections and sewer structures to form a complete, sewage system. Septic sewage is formed when sewage has been retained in the system for sufficient time for bacterial action to cause the substances in sewage to react with oxygen to produce corrosive materials, such as sulphurous acid and sulphuric acid. Septic sewage is very corrosive to concrete, particularly that portion of the con¬ crete which is above the liquid level of the sewage and therefore is accessible to the oxygen in the atmosphere. For this reason, it is important to have a corrosion-resistant, waterproof barrier covering the inside surface of the concrete pipe carrying the sewage. In accordance with this invention this is accomplished by wrapping around core 11 a corrosion- resistant, waterproof barrier sheet 13, which will become tightly bonded to the wet polymer-modified concrete poured into cavity 25 and cured to a solid pipe.

Previous systems of coating precast concrete pipe with liquid tar or an asphaltic material has not been suc¬ cessful because small pinholes are inevitably present and permit corrosive substances to have access to the concrete adjacent the pinhole. The corrosive action spreads out lat¬ erally and destroys the bond between the covering and the concrete. Eventually large sections of the covering peel away from the concrete and corrosion continues on a major scale.

The present invention employs any one of several commercially available barrier sheets that are physically strong, are free of pinholes, and are resistant to all known corrosive activity in the sewage. A preferred barrier sheet is the laminate shown in FIG. 6, having five layers including, in sequence, release film 17, rubberized asphaltic film 18, woven fiber glass reinforcement layer 19, rubberized asphalt

film 20, and woven sheet of polypropylene tape 21. This particular laminate is sold by Royston Laboratories, Inc. of Pittsburgh, PA as Membrane 104 ARHT. Similar laminates by Polyguard Products, Inc. of Ennis, TX, as Polyguard 665 Membrane; by W.R. Grace Co. of Cambridge, MA, as GRM and as Bituthene 3000; and by W.R. Meadows, Inc. of Elgin, IL, as Melnar. All of these products appear to be substantially identically usable in this invention. After the laminate is appropriately attached to the concrete form, release film 22 is removed to leave exposed a tacky surface 22 of rubberized asphaltic film 18. When the wet concrete is poured into cavity 25 it contacts surface 22 and upon curing of the con¬ crete an extremely tight bond is formed between the laminate and the concrete. It is not necessary that the laminate have five layers, since other numbers of layers are operable. It is necessary, however, that the outside layer which contacts the wet concrete be sticky, i.e., chemically tackified.

The concrete used in this invention must be a "polymer- modified" concrete. Several commercially available polymeric modifiers are known, although the exact composition of each is not known. It is believed, however, that these modifiers are the same as or substantially similar to Airflex 715 BP sold by Air Products and Chemicals, Inc. of Allentown, PA. The product is advertised to be a terpolymer of vinylacetate, ethylene, and vinyl alcohol. It is sold as an aqueous emul¬ sion of about 50% solids content having a viscosity of about 2500 cps. The polymeric modifier, usually in the form of an aqueous emulsion, is added to a concrete mix at a concentra¬ tion of about 5-20% based on a dry solids content of both the modifier and the concrete mix. The emulsion is used gener¬ ally to increase the strength of the concrete (compressive strength flexural strength and abrasion resistance) . Another such polymeric modifier is a styrene-butadiene emulsion sold by Dow Chemical Co. of Midland, MI. Still another polymeric modifier is PSI III sold by Gifford-Hill Chemical of Dallas, TX. In ASTMc494-80 these additives are known as water- reducing admixtures, retarding admixtures, or accelerating

admixtures; and sometimes are called "plasticizers". It is not known why polymer-modified concrete bonds so well to the sticky barrier sheet, but the resulting bond is very strong, in the order of about 50-100 pounds per square inch, and will not rupture under the ordinary stresses and hydrostatic pres¬ sures found in a sewer pipe. The barrier sheet must not have pinholes and it must be resistant to the corrosive agents in sewage, generally sulfurous or sulfuric acid or acid com¬ ponents.

In FIGS. 3-5 there are shown methods of incorporating the laminate into the concrete form. If the cast concrete article is to be a pipe with the interior surface covered with the waterproof, corrosion-resistant layer, core 11 (which normally is steel or wood) is covered with laminate 13 (such as that of FIG. 6) by wrapping laminate 13 around core 11 with layer 17 (see FIG. 6) being the outside surface of core 11. Since layer 21 is a polyolefin sheet there is no adhesiveness between core 11 and laminate 13. Laminate 13 is, therefore, made to overlap itself 14 and bands or strapping 15 are used to hold the wrapped, overlapped laminate in place. The overlapped area 14 is stuck to itself by peeling back an appropriate portion of layer 21 so that the tacky surface of layer 18 is stuck to itself, forming an excellent bond. In order to enhance that bond, the overlapped area 14 may be heated with a heat gun or a torch to make the bond even stronger. If the height of the structure is greater than the available width of the laminate, other horizontal wraps may be necessary. When this is the case, the first wrap should always be at the bottom and the next wrap should overlap the bottom wrap a minimum of about 4 inches, such that the poly¬ olefin layer 21 of the upper wrap contacts tacky layer 18 of the next lower wrap. Again, as described above, it is good practice to use heat to assure an excellent bond between the wraps. For the sake of appearance, vertical overlap seams 14 should be aligned. Release film 17 is then fully removed to leave tacky surface 22 available for contact by the wet polymer-modified concrete.

If the final article, e.g., a solid cylinder, is to be covered on the outside by a waterproof, corrosion proof layer, the mold 27 is lined on the inside with laminate 13, in the same general manner as described above, to provide an over¬ lapped area 16, which is tightly bonded to itself. Care should be taken before lapped area 16 is made, that accurate dimensions are taken to assure that adequate laminate is pro¬ vided for covering the entire inside periphery of the mold 27, without causing excessive stress at lap 16 when the concrete is poured. The laminate may be held in place in the mold with clamps or other appropriate means. When the polymer modified concrete is poured, the hydrostatic pressure of the concrete will push the laminate outward to the inside periphery of mold 27. The inside surface of the laminate form will be surface 22, which will bond, as described above, to the wet polymer modified concrete, to produce a cast article with an outside covering of the laminate.

Other forms can also be employed to produce whatever shape required and the laminate applied to the form following the above principles. In the case of a wall the laminate can be attached to the wall or hung on the wall by any convenient means. If the cast article results in holes in the laminate covering layer, those holes can be patched by applying pieces of laminate with a pressure and heat before putting the final article into use.

In a series of working examples test specimens were made of polymer-modified concrete bonded to a laminate of the type shown in FIG. 6 of the drawings and sold by Royston Laboratories under the tradename of Membrane 104 ARHT. The laminate was about 0.060 to 0.080 inch thick. Polymer- modified concrete was prepared with a variety of different polymeric modifiers using the amounts specified by the manu¬ facturer of the polymeric-modifier which in all instances was 5-20% by weight polymeric modifier (dry basis) . The re¬ sulting specimens were tested to determine bond strength in tension between the laminate and the concrete. The test was

conducted by cementing with epoxy cement a steel plate to the laminate and pulling the steel plate until the bond between the laminate and the concrete failed. The results are shown in the following tabulation:

POLYMERIC MODIFIER

Excell

Akset

Daracem

Airflex

Cormix

Acrylic 101

The bonds were analyzed by scanning electron micrography and showed well defined bonds with the concrete being interlaced into microvoids in the laminate at the interface between the laminate and the concrete. The polymeric-modifiers were analyzed by gel permeation chromatography infrared spectro- scopy. Each additive was found to have as a basic component a water-soluble polymer, copolymer, or terpolymer of vinyl alcohol. The copolymeric or terpolymeric component may be vinyl acetate or an olefin.

The mechanism of the bonding of cement to the laminate appears to involve the following:

1. When the mixture of water-soluble polymeric- modifier and pourable concrete is poured onto the softened and tackified laminate surface, the mixture penetrates and partially dissolves the tackified laminate at the interface.

2. As the water in the concrete is absorbed and evap¬ orated the concrete is solidified within interstices in the laminate formed by the dissolving action. Any plasticizers in the laminate that may have been dissolved leave the lam¬ inate in a tough semi-rigid condition intertwined with the concrete.

3. The resulting intertwined mixture of concrete and laminate at the interface is considerably stronger than any cemented interface that does not include i-ntert-ined portions.

The concept of this invention is also applicable to repair corroded or deteriorated concrete structures. The deteriorated surface is thoroughly cleaned with high pressure water. The cleaned surface is then treated with any commer¬ cially available bonding agent to insure bonding of the old surface to newly poured concrete. A core or form, of approx¬ imately 6 inches smaller internal dimension than the original structure, and covered with the laminate of FIG. 6, having the tacky surface facing the cavity into which the concrete is to be poured. The polymer wet modified wet concrete is poured into the cavity and allowed to cure. Upon removing the form, the concrete article is repaired to its near orig¬ inal dimensions and has a corrosion resistant, waterproof, bonded laminate to prevent future deterioration. If the structure is so deep as to make it impractical to make the repair in one pour, successive pours may be made. First, the top of the concrete is treated with a concrete bonding agent for the first pouring of concrete. The procedure is then repeated until the structure is repaired to the final dimension. To prevent corrosive substances from getting into joints between adjacent layers of laminate 13 a tape, about 6 inches wide, of the same laminate should be applied under heat and pressure to secure tightly bonded seams. This same procedure should be followed if the structure is multisec- tional as in a vertical sanitary lift station wetwell or man¬ hole, or in a reinforced concrete pipeline. Also if the exterior joints are subject to high hydrostatic heads, they, too, should be taped in a like manner. If the exterior of the structure is plain unlaminated concrete, it is recom¬ mended that the area where the joint tape is to be applied, should first be treated with a primer that is compatible with the particular laminate used; and it should be applied in an adequate width to receive the tape. The laminate tape should then be applied to secure the best bond to the con¬ crete substrate.

The finished cast concrete article of this invention is particularly distinguished by the strength of the bond between the barrier sheet 13 and the concrete to which it is attached. In the prior art such barrier sheets 13 were attached by treating the cast concrete surface with an ad¬ hesive composition and then pressing barrier sheet 13 onto the adhesive-treated surface. Such a bond has a tensile strength of about 10-15 pounds per square inch. The test is conducted by fastening a steel plate (preferably 6 inches by 6 inches to the outside of the barrier sheet by epoxy cement and then pulling the steel plate away from the con¬ crete article until the bond between the barrier sheet 13 and the concrete ruptures.

In the present invention strengths of 20-90 pounds per square inch may be achieved while strengths of 40-80 pounds per square inch are normal. The variations in strength depend on the type of barrier sheet and its sticky surface. Among the types of barrier sheets that have been used are:

(1) aluminum foil (appx. 0.05 inch thick);

(2) polyvinylchloride duct tape;

(3) commercial cloth duct tape;

(4) commercial waterproof adhesive tape for human use on cuts and injuries to the body;

(5) commercial fiberglass reinforced plastic tape for packaging;

(6) plasticized and tackified polyvinylchloride sheeting; and

(7) several commercially available rubberized, asphaltic sheets specifically prepared to function as waterproof covers for concrete structures.

If the barrier material is commercially available with a sticky surface, the sheet may be used without further preparation as the barrier sheet 13 of this invention. If the barrier material does not have a suitable sticky surface, e.g., the aluminum foil mentioned above, a sticky surface

must be produced before use of the barrier material in this invention. In the case of aluminum foil, it must be coated with an adhesive having good bond strength to aluminum, e.g. epoxy cement. In the case of polyvinylchloride, rubber, or other synthetic materials, a treatment with an appropriate solvent will produce an adequately sticky surface.

The principal industrial use for this invention is in the sanitary sewer industry to provide reinforced concrete sanitary sewer pipe, and appurtenant structures, such as sanitary manholes, sanitary lift station wetwells and sewage treatment plant structures such as clarifier tanks, digestors, and the like.

While the invention has been described with respect to certain specific embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention. It is intended, therefore, by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.