A WATERSTOP

Abstract: The waterstop (1) used to prevent the passage or leakage of water through a concrete construction joint is shaped in a continuous belt-like form and provided with a water-swellable rubbery layer (3) on at least a portion, or, for example along the peripheries thereof. The waterstop (1) comes into contact with the concrete bodies to serve as a water­ tight filling of the joint by being swollen with water. The water-swellable rubbery (3) layer is protected temporarily prior to use with a coating film of an alkali-soluble polymeric material (5) which can at least partially be disolved away by the alkalinity of the water in the concrete joint.

Description: The present invention relates to a waterstop which is placed in a concrete construction joint and serves to prevent or bar the passage or leakage of water through the joint. In the prior art, it is known that the passage or leakage of water through a concrete construction joint can be prevented by using a waterstop which is in a belt-like form of board provided on at least a part thereof with a layer of a water-swellable material. Such a conventional waterstop shaped in a continuous-length belt-like form is shipped from the manufacturer in a roll and transported to the construction site where the rolled board is unrolled and cut to a length suitable for putting into the concrete joint. A problem frequently encountered in construction works using such a waterstop is that the water-swellable layer becomes inadvertently swollen with rain water or underground water prior to use in the course of transportation to and storage at the site of construction. Once the water-swellable layer has been prematurely swollen prior to use, the waterstop can be mounted on the concrete joint only with great difficulty or, in some adverse cases, the waterstop can no longer prevent water leakage through the joint. We have now developed a waterstop which is free from the above described problems and disadvantages of premature swelling of the water-swellable layer by rain water and underground water prior to use which was unavoidable in the prior art products. Thus, the waterstop of the invention exhibits the water-leakage preventing effect by swelling of the water-swellable layer only after the waterstop is embedded in a concrete body. Thus, the waterstop of the present invention is an integral body in the form of a continuous-length belt-like form made from a water-swellable rubbery composition as a whole or, preferably, made from a non-swellable plastic resin or rubber provided on a least a portion of the surface thereof with a layer of a water-swellable rubbery composition, the surface of the layer of the water-swellable rubbery composition being coated with a temporary protecting film of a polymeric material which is at least partially soluble in alkaline water. A preferred cross-sectional configuration of the waterstop of the invention in the form of a continuous-length belt is one in which the peripheries of the plastic or rubber belt bulge length-wise and each of the these peripheries is provided with a bore running therethrough, optionally filled with a porous cushioning material to serve as a stress absorber when the water-swellable rubbery layer formed along the outer surface of the periphery is swollen with water. It will be understood that the most characteristic feature of the waterstop of the invention is that the layer of the water-swellable rubbery composition is temporarily protected with a water-shielding film made from an alkali-soluble polymeric material so that the waterstop is prevented from premature swelling on inadvertent contact with rain water or underground water. The water-shielding film is at least partially dissolved when it is contacted with alkaline water in a concrete body in which the waterstop is embedded and the water-­ swellable rubbery layer becomes fully swollen with water and exhibits the desired waterstopping effect. The waterstop of the invention is described in more detail with reference to the accompanying drawings, in which:- Figure 1 is a perspective view of a water stop of the invention showing a transverse cross-section; Figure 2 illustrates a cross-section of the waterstop of Figure 1 embedded at a join of concrete bodies; Figure 3 is a perspective view showing a transverse cross-section of a waterstop of another embodiment of the invention; Figure 4 illustrates a partial cross-section of a further different embodiment of a waterstop showing the peripheral portion; Figures 5A to 5J illustrate the transverse cross-­ sections of various modifications of the waterstop according to the present invention; Figure 6 is a graph showing the change in the dimension of a waterstop of the invention as a function of the length of time in water; and Figure 7 illustrates the testing assembly of the inventive waterstop by a cross-section. The waterstop 1 of the invention is shaped as a continuous length belt-like form comprising a board base 2 of a plastic or rubber provided with elongated water-swellable rubbery layers 3,3 provided along the peripheries 2a,2a of the board base 2. A typical water-swellable rubbery composition for the layers 3,3 is prepared by dispersing a crosslinked water-swellable polymeric material, such as a compolymer of maleic anhydride and isobutylene, in the matrix of a non-swellable rubber or plastic resin. As is illustrated in these Figures, the peripheral portions 2a,2a of the board base 2 are each shaped to have a cylindrical cross section. Each of the cylindrical peripheral portions 2a,2a is provided with a bore 4 running therethrough in the longitudinal direction to serve as a stress absorber. The outer surface of the cylindrical peripheral portion 2a is recessed length-wise to form an elongated groove 2d which is filled with the water-swellable rubbery composition to form the water-­ swellable layer 3. Another elongated bore 2c is provided along the centre line of the board base 2 and also serves as a stress absorber. Line protrusions 2e are formed somewhere between the centre line of the board base 2 and each of the cylindrical peripheral portions 2a,2a on both sides of the right and left wings 2b,2b so as to give a corrugated appearance to the waterstop 1. The cross-section of each of the stress-absorbing bores 4,4,2c need not be circular but may have a rectangular, elliptical or other cross-section. The bores 4,4,2c may optionally be filled with a porous cushioning material to enhance the stress-absorbing effect of the bores. In the waterstop of the invention, each of the water-swellable rubbery layers 3,3 is coated with an alkali-soluble water-shielding film 5 to provide the water-swellable layer 3 with temporary protection. The water-shielding film 5 should be insoluble in neutral water but as least partially soluble in water made alkaline by contact with uncured concrete. Although the water-shielding film may be formed from a material insoluble in neutral water but soluble in alkaline water alone, it is preferred with regard to the film-formability, controllability of the water-­ absorbing velocity from uncured concrete and durability of the water-stopping power tha the water-­ shielding film 5 is formed from a composition comprising a water-insoluble polymeric material such as a synthetic resin, natural rubber or synthetic rubber as the matrix and a material insoluble in neutral water but soluble in alkaline water dispersed in the matrix. The dispersed material insoluble in neutral water but soluble in alkaline water may be formed, for example, a weakly acidic synthetic polymer electrolyte such as a copolymer of a lower olefin or styrene with maleic anhydride, poly(acrylic acid), poly(methacrylic acid) or poly(glutamic acid) or a polymer of an acrylic or methacrylic acid ester, as well as several inorganic compounds such as aluminium phosphate or basic zinc carbonate. The polymeric electrolytes, such as the copolymers of maleic anhydride are particularly preferred. The water-insoluble polymeric material forming the matrix of the water-shielding film 5 should preferably have a good adhesion to the surface of the water-swellable layer 3 and may be the same as the rubber or synthetic resin for the water-inswellable board base 2 or water-swellable layer 3. For example, preferred material include chlorinated poly­ ethylenes, polychloroprenes and nitrile rubbers. The amount of the dispersed material in the water-insoluble matrix should be in the range of from 5 to 150 parts by weight or, preferably, from 10 to 100 parts by weight per 100 parts by weight of the matrix polymer. The thickness of the water-shielding film 5 should be in the range of from 5 to 500 um or, preferably, from 20 to 300 um although it should be selected having regard to the solubility behaviour and the amount of the dispersed material. When the thickness is too small, no sufficient temporary protection can be obtained. When the thickness is too large, on the other hand, too long a time would be taken before the water-swellable layer 3 is brought into contact with water thereby to be swollen and exhibit its water-stopping power. In the above description, the expression neutral water should not be construed to mean a pH value of exactly 7 and the alkali-soluble dispered material should not be affected by slightly alkaline water such as that sometimes encountered in neutral water in construction sites. The alkalinity of the above description means an alkalinity which the water content in uncured concrete may have. For example, an alkalinity of a pH value of 13.5 to 13.8 is exhibited by uncured concrete in which a Portland cement containing about 0.5 to 1.0% of total alkali is mixed with water in a 2:1 ratio. The water-shielding film 5 on the waterstop can be formed by various known methods. For example, the uncoated waterstop may be immersed in or spray- or brush- coated with a solution or aqueous emulsion containing the dispersed material insoluble in alkaline water, followed by drying. The thickness of the water-shielding film 5 can be controlled by modifying the concentration of the film-forming material in the solution or emulsion. In this regard, solutions are preferred to emulsions. Alternatively, the technique of ternary coextrusion can be used. Namely, the water-inswellable rubber or plastic resin for the board base 2, the water-­ swellable polymeric material for the water-swellable layer 3 and the composition for the water-shielding layer 5 may be extruded simultaneously to form a finished waterstop 1 of the invention. In the following, a description is given of the manner of using such a waterstop in a concrete construction joint with reference to Figure 2. As illustrated in this Figure, the waterstop 1 is embedded in uncured concrete bodies A and B having a joint C in such a disposition as to bridge the concrete bodies A and B in a direction perpendicular to the joint gap C. When water intrudes into the gap C, the water penetrates along the surface of the right and left wings 2b,2b of the waterstop 1 to reach the cylindrical peripheral portions 2a,2a. Since the water has become alkaline in the course of penetration by contact with the strongly alkaline concrete body A or B, the water reaching the alkali-­ soluble water-shielding film 5 dissolves the film 5 entirely, or at least partially. Accordingly, the water-swellable rubbery layers 3,3 are brought into direct contact with water so as to be swollen therewith and they are firmly and water-tightly pressed against the concrete bodies A and B by the swelling pressure to prevent passage or leakage of water through the joint gap C. Even when the degree of swelling of the water-swellable layers 3,3 is excessively large, to give a contacting pressure to the concrete bodies dA and B larger than necessary to prevent water leakage, the swelling pressure of the water-swellable layer 3 is directed to the bore 4 and the stress caused thereby is readily absorbed by the deformation or collapse of the stress-absorbing bores 4,4 to effectively avoid the danger of stress-­ cracking in the concrete bodies A and B which may otherwise take place. When the waterstop of the invention is used in a joint between a pre-cured concrete body and an uncured concrete body freshly put thereon, it is advantageous that the alkali-soluble water-shielding film on the periphery of the wing to be fixed by adhesive bonding or nailing to the pre-cured concrete body should be at least partially dissolved before­ hand by applying alkaline water thereto. Figure 3 is a perspective view of a waterstop of the invention similar to that illustrated in Figure 1. The waterstop 11 illustrated in this embodiment has water-swellable rubbery layers 13,13 covering the cylindrical peripheral portions 12a,12a of the board base 12 over the outer surface having a span of 180° sector with an overcoating 15 of the alkali-­ insoluble water-shielding film. In other respects, the board 11 of this embodiment is similar to that shown in Figure 1 including the right and left wings 12b, 12b and the stress-absorbing bores 14,14 running through the cylindrical peripheral portions 12a,12a and a bore 12c running along the centre line. The surface surrounding the bore 14 is formed partly of the board base 12 and partly of the water-swellable rubbery layer 13. Figure 4 illustrates a further modified waterstop 21 of the invention showing a transverse cross-section only in the portion including one of the cylindrical peripheral portions 22a at a wing end of the board base 22. In this embodiment, the coverage of the water swellable rubbery layer 23 extends over the whole outer surface of the cylindrical peripheral portion 22a with a stree-absorbing bore 24 and further on to the surfaces of the flat portion of the board base 22. The alkali-soluble water-shielding film 25 naturally covers all of the outer surface of the water-­ swellable layer 23 without leaving any uncovered areas including the end surfaces of the layer 24 in contact with the flat portion of the board base 22. Figures 5A to 5J each illustrate in trasverse cross-section a different modification of the waterstop of the invention. The waterstop 31 illustrated in Figure 5A is formed from the water-swellable rubbery material as a whole in the form of a board 33, omitting the board base formed of a non-swellable plastic or rubber. Accordingly, the alkali-soluble water-shielding film 35 entirely envelops the board 33 made from the water-swellable rubbery composition. Figure 5B illustrates a modified version of the waterstop in Figure 5A, in which the board base 32 made of a non-swellable plastic or rubber as a core is covered allover the surface thereof with a layer of the water-swellable rubbery composition 33 and an alkali-soluble water-sheilding film 35. The other versions illustrated in Figures 5C to 5J need not be explained any further since the reference numerals correspond to those in Figures 1 to 4 including the board base 32, stress-absorbing bore 32c along the centre line, water-swellable rubbery layer 33, stress-absorbing bore 34 running through the cylindrical peripheral portion of the board base 32 and the alkali-soluble water-shielding film 35 covering the surface of the water-swellable layer 33. These follow several examples of the combination of the materials forming (a) the non-swellable board base, (b) the water-swellable rubbery layer and (c) the alkali-soluble water-shielding film, in which "parts" refers to "parts by weight". The combinations I and II are each a formulation for the preparation of a waterstop by coextrusion and the combination III is a formulation for providing the water-shielding film by coating with the solution. I. (a) 100 parts of a chlorinated polyethylene admixed with 1.5 parts of a stabilizer (b) a blend of 85 parts of a chlornated polyethylene, 15 parts of a polyisobutylene and 20 parts of a highly water-absorbing crosslinked copolymer of maleic anhydride and isobutylene admixed with 1.5 parts of a stabilizer. (c) a blend of 65 parts of a chlorinated poly­ ethylene, 35 parts of a polyisobutylene, 30 parts of dioctyl sebacate and 100 parts of an alkali-soluble copolymer of maleic anhydride and isobutylene admixed with 1.5 parts of a stabilizer ; II. (a) a blend of 50 parts of a chlorinated polyethylene and a plasticized polyvinyl chloride resin composed of 100 parts of a polyvinyl chloride resin and 54 parts of dioctyl phthalate admixed with 1.5 parts of a stabilizer (b) the same blend as I(b) (c) the same blend as I(c); III. (a) a plasticized polyvinyl chloride resin composed of 100 parts of a polyvinyl chloride resin and 54 parts of dioctyl phthalate admixed with 1.5 parts of a stabilizer (b) a blend of 100 parts of a thermoplastic nitrile-­ based elastomer and 60 parts of the same highly water-­ absorbing resin as in II(b) (c) the same copolymer of maleic anhydride and isobutylene as in II(c) dissolved in N,N-dimethyl form­ amide in a concentration of 20% In connection with the selection of the materials (a), (b) and (c) above exemplified, it is essential that good adhesion can be obtained between the board base (a) and the water-swellable rubbery layer (b) and that the water-swellable rubbery layer (b) should have good swellability in water even at a relatively low temperature. Since the material of the board base is limited to those above mentioned or, in particular, to plasticized poly­ vinyl chloride resins due to economic reasons, extensive investigations have been undertaken to develop a water-­ swellable rubbery composition which satisfies the above mentioned requirements. The investigations have led to a conclusion that the requirements for the water-swellable rubbery layer can best be satisfied when the layer is formed of a composition which comprises: (A) 100 parts by weight of a polymer blend composed of (A-1) from 10 to 35% by weight of a copolymeric rubber of acrylonitrile and butadiene, (A-2) from 40 to 75% by weight of a polyvinyl chloride resin, and (A-3) from 15 to 50% by weight of a chlorinated polyethylene; and (B) from 10 to 100 parts by weight of a water-swellable crosslinked polymer, with optional admixture of a plas­ ticizer in an amount not exceeding 150% by weight based on the polyvinyl chloride resin. The principle of the above described formulation of the water-swellable rubbery composition is the admixture of a water-swellable basic composition composed of a polyvinyl chloride resin and a water-swellable crosslinked polymer with a chlorinated polyethylene as a swelling aid and an acrylonitrile-butadiene rubber as a swelling moderator at elevated temperatures with optional admixture of a plasticizer. As described above, the polymeric matrix of the water-­ swellable rubbery composition is formed from a ternary polymer blend composed of the above mentioned polymeric components (A-1), (A-2) and (A-3). The acrylonitrile-­ butadiene copolymeric rubber serves to promote swelling of the composition at low temperatures and suppress excessive swelling of the composition at elevated tempera­ tures so as to impart stability at high temperatures to the composition with an adequately small ratio of the percentages of swelling at low and high temperatures. The amount of this rubber component in the polymeric matrix should be in the range from 10 to 35% by weight. When the amount thereof is too small, no good high tem­ perature stability of the composition can be obtained. When the amount thereof is too large, on the other hand, the water-swellable rubbery composition may lose the high swelling ratio, flexibility and adhesiveness to the board base more or less. The polyvinyl chloride resin as component (A-2) in the rubbery composition is used in an amount in the range from 40 to 75% by weight. When the amount thereof is too small, disadvantages are caused in the water-­ swellable layer in relation to a decrease in expansion and mechanical strength as well as in the ad­ hesiveness to the board base. When the amount thereof is too large, on the other hand, the water-swellable rubbery layer may become less adaptabile to the changes possibly taking place in the concrete body after setting to affect the performance of water-leakage prevention. The polyvinyl chloride resin suitable as com­ ponent (A-2) is not limited to homopolymeric polyvinyl chloride resins,but may be any of vinyl chloride-based resins including, for example, copolymers mainly composed of vinyl chloride and graft polymers obtained by the graft-polymerization of vinyl chloride on to a base poly­ mer such as a polyurethane, chlorinated polyethylene, or copolymer of ethylene and vinyl acetate. Particularly preferred is a graft polymer of vinyl chloride on a polyurethane in respect of the adhesion of the rubbery composition to the board base, as well as the mechanical strength and flexibility of the water-swollen rubbery layer. The third component in the polymer blend for the matrix of the rubbery composition, is a chlorinated poly­ ethylene which serves as a swelling aid to moderate the swelling behavior of the composition, as well as to improve the adhesion between the water-swollen rubbery layer and the concrete body and to effectively prevent cracking of the concrete body consequently contributing to the improvement in the performance of the inventive waterstop for water-leakage prevention. The amount thereof in the polymer blend should be in the range from 15 to 50% by weight. When the amount is too small, the above mentioned advantageous cannot be obtained effectively. When the amount is too large, on the other hand, the rubbery composition may suffer a decrease in respect of the expansion and mechanical strength of the layer after swelling. The water-swellable rubbery composition is composed of the above described polymer blend as the matrix and a dispersed phase therein formed of a water-swellable cross-­ linked or gelled polymer. Various types of known water-­ swellable crosslinked polymers can be used for the purpose including, for example, crosslinked copolymers of maleic anhydride and isobutylene which can be prepared according to the procedure described in Japanese Patent Kokai 57-73007. Further, crosslinked (co)polymers based on an unsaturated carboxylic acid are suitable for the purpose such as crosslinked salts of poly(acrylic acid) ,and cross-­ linked salts of a copolymer of vinyl alcohol and acrylic acid. The amount of the water-swellable crosslinked polymer in the rubbery composition should be in the range from 10 to 100 parts by weight per 100 parts by weight of the ternary polymer blend as the matrix. When the amount thereof is too small, the water-swellable rubbery composition cannot be imparted with a sufficiently high water-swellability while, when the amount thereof is too large, the rubbery composition may suffer a decrase in mechanical strength and moldability. The water-swellable rubbery composition described above may optionally be admixed with a plasticizer in an amount not exceeding 150% by weight based on the content of the polyvinyl chloride resin in the ternary polymer blend. The water-swellable rubbery composition described above may optionally be admixed with a plasticizer in an amount not exceeding 150% by weight based on the content of the polyvinyl chloride resin in the ternary polymer blend. Suitable plasticizers are exemplified by dioctyl phthalate, diisodecyl phthalate, butyl lauryl phthalate, dioctyl adipate, diisodecyl adipate, dioctyl azelate, and dioctyl sebacate. These plasticizers can be used either singly or as a combination of two or more according to need. The formulation of a plasticizer in the water-swellable rubbery composition has an effect in improving the expansion and flexibility of the water-­ swellable rubbery layer, although an excessively large amount may adversely affect the mechanical strength of the water-swellable rubbery layer with consequent decrease in the water-leakage preventing effect. When adequately formulated within the above described ranges of the amounts of the respective components, the water-swellable rubbery layer formed of the composition may exhibit 1000% or less of volume expansion by swelling in water at 35 °C with at least one third of the ratio of the volume expansion in water at 5 °C to the volume expansion in water at 35 °C. The water-swellable rubbery composition for the inventive waterstop may optionally be admixed, in addition to the above described components, with small amounts of various kinds of additives including rubbery polymers such as polyisobutylene and stabilizers, lubricants, pigments and other additives conventionally used in polyvinyl chloride-based materials according to need. The following examples are given to illustrate the inventive waterstop in detail including the description of the above described newly developed water-­ swellable rubbery compositions. Example 1. Five water-swellable rubbery compositions No. 1 to No. 5 were prepared each according to the formulation indicated in Table 1 below in parts by weight, each of the components appearing in the table being characterized as follows. Polyvinyl chloride resin A: a homopolymeric poly­ vinyl chloride having an average degree of polymerization of about 1050, Geon 103EP, a product by Nippon Zeon Co. Polyvinyl chloride resin B: a graft polymer of vinyl chloride on a polyurethane, GC #4130, a product by Denki Kagaku Kogyo Co. Acrylonitrile-butadiene rubber: a copolymeric rubber of acrylonitrile and butadiene, Nipol HF21, a product by Nippon Zeon Co. Chlorinated polyethylene: Daisolac RA 135, a product by Osaka Soda Co. Polyisobutylene: Vistanex MML-80, a product by Exxon Chemical Co. DOP: dioctyl phthalate DIDP: diisodecyl phthalate DOS: dioctyl sebacate Water-swellable gel A: a crosslinked copolymer of maleic anhydride and isobutylene, KI Gel 201, a product by Kuraray Isoprene Chemical Co. Water-swellable gel B: a salt of vinyl alcohol-­ acrylic acid copolymer, Sumika Gel SP-520, a product by Sumitomo Kagaku Kogyo Co. Each of the compositions was shaped by extrusion molding into a sheet having a thickness of 2 mm, from which test pieces of 20 mm wide and 100 mm long were prepared by cutting. The test pieces were dipped for 7 days in baths of city water at 5 °C, 20 °C and 35 °C to determine the volume expansion in % by swelling to give the results shown in Table 1 which also shows the hardness of the test pieces prior to swelling and the hardness of the same when it was swollen by 200%. The values of hardness are in the JIS A scale. As is shown by the results in Table 1, the volume expansion of the compositions No. 1 to No. 3 compounded with the acrylonitrile-butadiene rubber was within an adequate range of 400 to 500% at 5 °C and about 700% at 35 °C while the composition No. 4 exhibited only smaller than 200% of volume expansion by swelling even at 35 °C and the volume expansion of the composition No. 5 was 3000% or even larger at 35 °C indicating that the com­ position was not suitable for shaping the water-swellable rubbery layer of the inventive waterstop. Example 2. Two types of waterstops I and II were prepared each having a cross section illustrated in FIGURES 1 and 2 by the technique of coextrusion. The polymeric compositions for the board bases and the alkali-soluble water-shielding films of these waterstops were in common to these two types while the water-swellable rubbery layers were pre­ pared using different rubbery compositions I and II, respectively. Table 2 below shows the formulations of the polymeric compositions in parts by weight for the board bases, water-swellable rubbery layers in types I and II and alkali-soluble water-shielding films. Isoban 04 used in the formulation of the alkali-soluble water-­ shielding film is a product by Kuraray Isoprene Chemical Co., which is a copolymer of maleic anhydride and isobutylene. Other ingredients, excepting the calcium carbonate filler, were the same ones as appearing in Table 1. The adhesive bonding between the board base and the water-swellable rubbery layer was quite satisfactory in each of the waterstops. When the waterstops, from which the alkali-soluble water-shielding film had been removed, were dipped in water at 35 °C, however, the water-swellable rubbery layer of the waterstop II was separated from the board base after 5 days of dipping. On the other hand, the adhesive bonding was complete between the board base and the water-swellable rubbery layer of the waterstop II. Example 3. A waterstop having a cross section as illustrated in FIGURES 1 and 2 was prepared using a chlorinated poly­ ethylene for the board base, a polymer blend of a chlo­ rinated polyethylene, polyisobutylene and highly water-­ absorbing crosslinked copolymer of maleic anhydride and isobutylene for the water-swellable rubbery layer and a polymer blend of a chlorinated polyethylene, polyiso­ butylene, plasticizer and alkali-soluble copolymer of maleic anhydride and isobutylene for the alkali-sluble water-shielding film. The cross section of the waterstop had following dimensions: 100 mm of the overall width; 8 mm of the thickness of the board base 2 in the flat portion 2b; 8 mm of the diameter of the central bore 2c; 6 mm of the diameter of the peripheral bore 4; 3 mm of the thickness of the water-swellable rubbery layer 3; 15 mm of the outer width of the water-swellable rubbery layer 3; and 0.2 mm of the thickness of the water-shielding film 5. Three test pieces I, II and III were prepared by cutting the thus prepared waterstop of continuous length and they were dipped for days in water at 20 °C after embedding in concrete bodies for 96 hours and 72 hours and without embedding in a concrete body. The overall widths of the waterstop were measured periodically to determine the increment by the swelling of the layer 5 with water. The results are shown in FIGURE 6 by the curves I, II and III for the test pieces after 96 hours and 72 hours embedding in concrete bodies and without embedding in a concrete body, respectively. As is understood from the results shown in FIGURE 6, the water-swellability of the water-swellable rubbery layers could be exhibited only when the waterstop had been embedded in a concrete body prior to dipping in water. Namely, the water-­ swellable rubbery layer of the test piece III exhibited little swelling even after 20 days of dipping in water indicating the effectiveness of the alkali-soluble water-­ shielding film against water-swelling of the water-swell­ able layer. Example 4. A model test was undertaken for the water-leakage preventing effect of the waterstop prepared in the preceding example. The testing assembly is shown in FIGURE 7 by a cross section. Thus, two test pieces 1,1 of the waterstop were each embedded at the lower half thereof in a concrete block A before curing and then another concrete block B was molded above the block A keeping a 10 mm space therebetween under restriction with several sets of bolts 6 and nuts 7 as a simulated construction joint and embedding the upper half of each waterstop board 1. After 7 days of curing of the concrete blocks A and B, water W was pressurized into the space surrounded by the concrete blocks A and B and two water­ stops 1,1 through the steel nozzle 8 in such a manner that the width of the joint gap space shown by t in the figure was first increased to 15 mm and 20 mm by untight­ ening the bolts 6 and nuts 7 and then decreased to 10 mm by again tightening the bolts 6 and nuts 7 under a hydraulic pressure varied in the range from 1 to 5 kgf/cm² to visually examine leakage of water out of the joint. The results obtained using the waterstop prepared in the preceding example were that absolutely no water leakage was found irrespective of the increase and decrease of the gap space t and the hydraulic pressure. When another waterstop prepared in the same manner as in the preceding example without providing the alkali-soluble water-­ shielding film was used instead for comparative purpose, on the other hand, leakage of water took place by increas­ ing the gap space t to 15 mm under a hydraulic pressure of 4 kgf/cm² or larger and by subsequently decreasing the gap space t to 10 mm under a hydraulic pressure of 3 kgf/cm² or larger to give an evidence for the advantageous effect obtained by the alkali-soluble water-shielding film provided according to the invention. The results of this comparative test were presumably due to the fact that the uncured concrete coming into direct contact with the water-swellable rubbery layer of the waterstop was deprived of water or dehydrated to cause poor curing of the concrete due to the deficiency in water.

Claims: 1. A waterstop in an elongated integral form which comprises: (a) a board base made from a non-swellable polymeric material in an elongated belt-like form; (b) an elongated swellable layer of a water-swellable rubbery composition integrally formed on at least a part of the outer surface of the board base extending in the longitudinal direction thereof; and (c) a water-shielding film made from a polymeric material which is at least partially soluble in water at an alkaline pH and which surround the surface of the layer of the water-swellable rubbery composition. 2. A waterstop in an elongated integral form which comprises: (a) an elongated belt-like board made from a water-swellable rubbery composition; and (b) a water-shielding film made from a polymeric material which is at least partially soluble in water at an alkaline pH and which surrounds the surface of the belt-like board made from the water-swellable rubbery composition. 3. A waterstop as claimed in claim 1 wherein the board base is provided with an elongated bore running therethrough along each of the longitudinal peripheries thereof. 4. A waterstop as claimed in claim 3 wherein the elongated swellable layer of the water-swellable rubbery composition is formed on the surface of the board base along the outer surface of at least one periphery. 5. A waterstop as claimed in any one of the preceding claims wherein the water-swellable rubbery composition comprises: (A) 100 parts by weight of a polymer blend composed of (A-1) from 10 to 35% by weight of a copolymeric rubber of acrylonitrile and butadiene; (A-2) from 40 to 75% by weight of a polyvinyl chloride resin, and (A-3) from 15 to 50% by weight of a chlorinated polyethylene; and (B) from 10 to 100 parts by weight of a water-swellable crosslinked polymer. 6. A waterstop as claimed in any one of claims 1 or 3 to 5 wherein the board base is made from a plasticized polyvinyl chloride resin composition. 7. A waterstop as claimed in claim 5 or claim 6 wherein the water-swellable rubbery composition further comprises a plasticizer in an amount not exceeding 150% by weight based on the polyvinyl chloride resin. 8. A waterstop as claimed in claim 5 wherein the water-swellable crosslinked polymer is a crosslinked copolymer of maleic anhydride and isobutylene.

Inventors: ISHIHARA, YUJI, KUSHIDA, TAKASHI, OTSUGU, SHOZO, SASAYAMA, HIROHARU, TERAUCHI, MICHIYOSHI
Applicants: C.I. KASEI CO., LTD
Application year: 1986
Main classification: E04B1
IPC codes: E01C11, E04B1