Water-Swelling Sealants

Among the wide range of Sika s construction sealants, the water-swelling sealant, SikaSwell , shows some construction features and is described here. 

In the construction area, optimal sealing is often required between hardened and fresh concrete, between two pre-cast concrete elements, etc. The special formulated moisture-reactive sealant offers a watertight construction joint in such applications. In contact with water, the sealant swells within 7 days to more than 100% of its original volume and creates a counter pressure between the surfaces that stops water flow (Fig. 107). 

In Fig. 108 further examples for sealing with SikaSwell S-2 are illustrated. When SikaSwell S-2 is in a confined space, its expansion results in the filling of the gaps and cracks around the construction joint (Fig. 109). 

With SikaSwell S-2 water can pass at the beginning but in a very limited quantity. 

SikaSwell S-2 After expansion the pressure generated by SikaSwell S-2 assures a perfectly watertight joint 

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Water-Swelling Sealants 297 Swelling of Water-Swelling Rubbers 298 Water-Stopping Capability of Water-Swelling Rubbers 299... 

Table 3 lists the types of sealants, which can be divided into nonswelling and water-swelling sealants. As can be seen by a comparison of waterswelling and non-swelling rubbers in Table 4, water-swelling rubbers are superior in water-sealant ability to nonswelling rubbers but expense is a drawback. 

Let us consider the example of water swelling of sealant materials. If the polymer is able to swell and stop water leakage when in contact with fresh water but it does not swell when in contact with sea water, then it will not have achieved its function as a sealant. It is desirable for these materials to swell to the same degree regardless of the type of water encountered. Therefore, the required property for this application to be superabsorbent is to swell similarly, independent of ion concentration and type in the absorbate. Furthermore, it must absorb as much water as possible (see Fig. 4b/sulfonic acid-type salt resistant superabsorbent polymer, Aquaric CS-7L). 

Application of Water-Swelling Rubbers as Sealants Types of Sealants 296... 

Water-Stopping Experiment for Water-Swelling Rubbers 300 Basic Design of Sealants 301... 

Table 2 lists those applications for water-swelling rubbers in the construction market. Most of the sealants used for tunnel construction are made of water-swelling rubbers. Construction and civil engineers and sealing materials manufacturers have been working together to develop effective sealing materials. 

Urethane elastomers sealants Rubber blends sealants Water-swelling rubber - - nonswelling solid rubber sealants... 

Sealants from Blends of a Rubber and a Water-Swelling Urethane Elastomer... 

These are sealants made of water-swelling and nonswelling rubbers. The properties of each type of rubber combine to improve water-stopping ability and lower costs. 

The compression repulsive force of the nonswelling sponge rubber reduces over time. The compression repulsive force of the water-swelling rubber shows a temporary decrease at the beginning of measurement but an increase as time passes. This can be verified as shown in Fig. 1, in which compressive repulsive force is shown to increase as a result of the swelling pressure. Hence, water swelling is demonstrated to be usefiil for sealants. 

The properties of a sealant made of a water-swelling rubber were shown in the previous section. However, a higher performance sealant requires using the structure as described in section 6.1. 

Figure 7 illustrates the structure of a sealant groove in which a water-swelling rubber is placed and swollen. The gasket s effective contact area... 

If a ditch cannot be used on a concrete structure, composites made of water swelling and nonswelling rubbers will be effective. Figure 8 depicts an example of a composite sealant. The gasket s effective contact area pressure is confined within the nonswelling solid rubber and prevents diversion of the repulsive force, which improves the water-stopping function (there are many patents on this technology). 

Application and usefulness of water-swelling rubbers as construction sealants have been described. Unfortunately, the market share of this material is low, even though most sealant used in the sealed technique adopt this material. This is due to expense. Because superabsorbent polymers and water-swelling urethane elastomers are costly compared to ordinary rubbers, water-swelling rubbers will be expensive. In the future, sealants manufacturers should lower their costs by increasing use of... 

These solutions are not recommended for exposed structures since subsequent delamination will further contribute to water intake. The elastic modulus of the adhesive should match that of the timber to avoid it acting as a wedge should the timber swell and try to close the fissure. Another inconveifience of such interventions is that the sealant will hide the fissures, preventing periodical inspection to check its possible progress. 

The results are reported of a study of the disparate swell behaviour in hot water of polysulphide sealants produced with different curing agents (manganese dioxide and ammonium dichromate). Sealants tested were commercial aircraft sealants PR-1750, Pro-Seal 899 and PR-1422 and laboratory formulations prepared using Thiokol liquid... 

The resistance of the sealant to chemical and environmental attack is the principal property that determines the ultimate life of most sealant joints. During the life of a sealant joint, the sealant maybe subjected to hot and cold temperature extremes, thermal cycling, moisture, and UV and solar radiation. Many sealants are also exposed to chemicals such as petroleum-based fuel, alkali or acidic solutions or fumes, ozone, and salt water spray. Chemical and/or environmental exposure can cause sealants to soften, harden, contract, swell, embrittle, crack, craze, and dissolve or disintegrate. Such exposure can also inhibit sealant solidification or cause sealant to debond from the substrate. 

Solar radiation causes the most widespread damage of sealants used outdoors. The majority of this damage is in the form of breaking chemical bonds within the sealant polymer molecules. Water and water vapor can degrade sealants chemically by hydrolysis of the chemical bonds or physically by cyclical swelling and contracting of the sealant caused by moisture absorption and desorption (Wolf 2009). 

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