Expansion joint filler

The designer should make clear on his drawings that the expansion joint must extend all the way down to the membrane (through the bed) and may contain absolutely no hard or rigid material-only the specified expansion joint filler. 

Expansion joints improperly designed, in wrong places, or wrong size or wrong expansion-joint filler. (1) (See also II, 3, 4. 5.)... 

ASTM D 1752-84 Standard Specification for Preformed >onge Rubber and Cork Expansion Joint Filler for Concrete Paving and Structural Construction, 2 pp (DOD Adopted) (FSC 5610) (YD) (Comm D-4)... 

Numerous construction products are formulated from asphalt and coal tar for such applications as driveway sealers, cutback asphalts, flashing cements, conerete primers, concrete cold mixes, roof cements, expansion joint fillers, patch liquids, waterproofing liquid-applied membranes, and pipeline eoatings. All these produets are likely to contain... 

AASHTO M 33. 2012. Preformed expansion joint filler for concrete (bituminous type). Washington, DC American Association of State Highway and Transportation Officials. 

ASTM D 1752-04aR13. 2013. Standard specification for preformed sponge rubber cork and recycled PVC expansion joint fillers for concrete paving and structural construction. West Conshohocken, PA ASTM International. 

Construction Low thermal conductivity Energy absorption Compressibility High abrasion resistance Higher thermostability Sound absorption Thermal pipe wraps, thermal insulations, eave and expansion joint fillers, sealant backer, floor imderlay, roofing imderlay... 

Construction Low thermal conductivity Sealing against water, dust, air, etc. Sound reflection Vibration damping Tube insulation, parquet underlay, air duct insulation, sealing strips, gymnastic walls, floating floors, sealant backer, expansion joint filler, closure strips... 

Many years ago, expansion joints in concrete floors were frequently filled with hot asphalt, and it was sometimes used as a space filler in void areas to prevent fluid penetration. Neither of these applications is recommended. If extruded by the two sides of a closing joint, when the structure expands in hot weather, it stays extruded when the weather cools off, and the structure shrinks back to its old size, leaving a void to be filled with rainwater, etc. (which can freeze causing expansion damage) or with chemicals which can attack the concrete. 

There is a great difference between a compressible expansion joint material and a deformable joint material. A true compressible material is one that can be squeezed together without extruding from the joint. The majority of the useful compressible joint fillers are closed-cell sponges or foams of the type best suited for the environment in which they will be employed. (They are required in totally enclosed joints where materials may not be extruded without disrupting the masonry.) They are installed by compressing them about 25% of their volume and then sliding them into the joint. 

If there is no membrane under the joint, as in an expansion joint in a tile floor laid directly over a crack in the concrete slab, the deformable sealant will adhere to the bottom as well as the sides of the joint. If this happens, the deformable material will not function properly. The joint cannot open without pulling the filler off the sides of the joint at the bottom, or close without tearing it loose at the bottom and top of the joint. 

Figure 52-4 Note the unacceptable variation in the width of expansion joints and poor selection and placement of joint filler.

The REZKLAD epoxy-based system consists of a Concrete Primer and Flooring Compound, plus an Expansion Joint Compound and Surface Sealer available for use where necessary. The CLADKOTE Flooring Compound is a modified polyester, resin-based monolithic overlay for concrete. The composite of resins and siliceous reinforcing material cures to a tough, chemical resistant topping. CLADKOTE C utilizes a 100% carbon filler specifically designed for service in hydrofluoric acid and fluoride salts. 

Another large market which h6ld sway for approximately 6 years in the early 1960s was the use of the sealant for military runway expansion joints. These sealants were highly extended with filler and coal tar, and used specialty polymers to meet the required low cost. The bubble burst when the sealants hardened with time, lost adhesion, and had to be replaced. The new system was a hot melt of plasticized PVC, which has done an admirable job with a simpler system and was eventually covered by ASTM specifications. 

The majority of tribological applications f polymers involve the inclusion of relatively hard second phases certain civil engineering expansion joints and the well-known use of ultra high molecular weight polythene in prosthetic joints are notable exceptions. In many cases the filler is present for economic or cosmetic reasons, but there are many cases where the filler is chosen primarily because it conveys a substantial improvement in tribological performance. It is not uncommon to find that an appropriate filler may reduce the rate of wear by three orders of magnitude. 

There are several possible solutions to the expansion mismatch problem. One is to use a resilient adhesive that deforms with the substrate during temperature change. The penalty in this case is possible creep of the adhesives, and highly deformable adhesives usually have low cohesive strength. Another approach is to adjust the thermal expansion coefficient of the adhesive to a value that is nearer to that of the substrate. This is generally accomplished by selection of a different adhesive or by formulating the adhesive with specific fillers to tailor the thermal expansion. A third possible solution is to coat one or both substrates with a primer. This substance can provide either resiliency at the interface or an intermediate thermal expansion coefficient that will help reduce the overall stress in the joint. 

The improvements in adhesive strength of cured epoxy joints that are attributable to fillers are not as much related to the improved cohesive characteristics of the adhesive as to the reduction in internal stress due to modification of the coefficient of thermal expansion, shrinkage, etc. 

Metal fillers for high-temperature adhesives must be carefully selected because of their possible effect on oxidation, as indicated in the previous section. Carrier films, such as glass cloth, are generally used to facilitate the application of the adhesive, but they also provide a degree of reinforcement and lowering of the coefficient of thermal expansion. Thus, they reduce the degree of internal stress experienced at the joint s interface. 

Polytetrafluoroethylene has a somewhat higher coefficient of expansion than other plastics. This differential expansion can result in leaking of joints when PTFE is combined with other materials. Addition of fillers such as glass, fiber, graphite, bronze, and molybdenum disulfide alters the coefficient of expansion of polytetrafluoroethylene compounds (Table 3.36). A compound containing 25% filler has a coefficient of expansion about half that of the unmodified resin. 

In adhesive joints, for example with epoxy resin adhesives, internal stress in the adhesive layer may result from different coefficients of expansion in the glued materials, whereby their moduli of elasticity are important factors. The glass transition temperature, and thus the curing temperature, also play a role. The reaction shrinkage of the resin is another source of internal stress. Suitable formulations with added fillers, oligomers or copolymers are among the measures taken to reduce these influences. 

The exact cause of premature adhesive failure is very difficult to determine. If the adhesive does not wet the surface of the substrate completely, the bond strength is certain to be less than maximal. Internal stresses occur in adhesive joints because of a natural tendency of the adhesive to shrink during setting, and because of differences in physical properties of adhesive and substrate. The coefficient of thermal expansion of adhesive and adherend should be as close as possible to minimize the stresses that may develop during thermal cycling or after cooling from an elevated temperature cure. Fillers are often used to modify the thermal expansion characteristics of adhesives and limit internal stresses. Another way to accommodate these stresses is to use relatively elastic adhesives. 

Significant differences in thermal expansion coefficient between substrates and the adhesive can cause serious stress at the plastic s joint interface. These stresses are compounded by thermal cycling and low-temperature service requirements. Selection of a resilient adhesive or adjustments in the adhesive s thermal expansion coefficient via filler or additives can reduce such stress. 

Hot-applied polymeric sealants are formulated with a carefully balanced blend of polymer with certain compounds, like asphalt, plasticisers and inert reinforcing fillers to produce a hot-pour point sealant with excellent bonding properties, high resiliency, ductility and resistance to degradation from weathering, to provide a positive seal during expansion and contraction of the joint. 

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