Construction sealant, silicone

X2 Construction sealants. Silicone sealants have proven to be very useful in a number of applications related to concrete construction (Figure 6.5). Systems based on neutral or alcoholic cure are suitable. Acetoxy-cured sealants are not suitable because of the evolution of acetic acid by-product, which reacts with calcium-bearing surfaces such as concrete and mortar, resulting in uncertain adhesion (Spells and Klosowki, 1981). 

Polyurethane sealants have taken a good share in today s sealant market. Polysulphide sealants are in greater use for water-retaining structures, and silicone sealants for structural glazing purposes but polyurethanes have a greater market share as construction sealants. These sealants were first introduced to the construction industry in the early 1970s as two-component materials. 

Contractors 1000 2000 . [GE Silicones] Silicone construction sealants for glazing and general purpose sealing qq>lics. 

Chapter 1 Construction Sealants, by Philippe Cognard, including technical characteristics, different chemical types, applications in building, standards and regulations. This chapter will complement the chapters Silicone Adhesives and Sealants, MS Polymer Adhesives and Sealants, Polyurethane Adhesives and Sealants, Civil Engineering Sealants, which will be discussed in Volume 3 and also in later volumes. 

Cyanoacrylate Adhesives Anaerobic Compounds Epoxies Industrial Sealants and Adhesives Construction Silicones Construction Polyurethanes Latex Sealants Firestop Products Pool Spa Sealants Silicone Greases and Compounds Aerosols Cleaners... 

MalikP l used dynamic mechanical analysis to study the effect of accelerated weathering on the storage and loss moduli of commercially available polyurethane (PU) and silicone construction sealants. Three multicomponent PU and one-component silicone sealants were used in the study. The sealants were exposed to 8 hours of UV exposure at 65°C alternating with 4 hours of condensation at 50°C for 600 and 1000 hours. The moduli G, G tan 5, and the dynamic viscosity (77) were measured in the temperature range of 25° to 125°C. The temperature was increased to 125°C, held for 2 hours and cooled to 25°C. 

The study showed that silicone sealants exhibit very high dynamic moduli (10 dyn/cm ) compared to PU (lO dyn/cm ). Moreover, silicone is stiffer than PU sealants below -30°C (Fig. 5a-b). Malik reported that silicone and PU sealants behave similarly only above this temperature and that the modulus of the silicone sealant falls in the acceptable window. According to the author, the storage modulus for a good construction sealant should not exceed 10 dyn/cm at -40°C. Therefore, he indicated that silicone sealants may not be suitable for temperatures below -30°C because they are too rigid. 

Weathering (9). Free films of commercially available silicone and polyurethane construction sealants were placed back-to-back in a frame where the films were separated with an aluminum divider. All of the free films were loaded into a xenon-arc Weather-o-meter (Atlas Electric Devices Company) for weathering. One series of films was thus exposed to light and water while the other was exposed to water only. The total time of exposure was 8000 hours. 

Chapter 4 Construction sealants, by Philippe Cognard Chapter 5 Silicone sealants, by Andreas Wolf, Dow Corning Europe Chapter 6 Thermosetting formaldehyde based adhesives, by Dr A. Pizzi Volume 4 Adhesives for large volume applications and industries (Packaging, Graphic Arts, Hot melts, etc.)... 

Although the primary function of sealants is to seal, adhesion promoters are often added, which allows them to adhere to the adjoining base materials. It is therefore sometimes difficult to distinguish between an adhesive and a sealant. For example, structural silicone adhesives are used in the building construction industry owing to their sealing, adhesive, elastomeric properties, and their resistance to harsh environmental conditions [67,70,77]. 

The weather conditions also added headaches. In winter the temperature sometimes gets below -50°F (-45°C) and may remain at -30°F (-35°C) for sustained periods. It is so cold that certain buildings need air locks to prevent excessive heat losses when people enter or leave. Many ordinary construction materials cannot withstand the temperature. The usual mastic sealing compound has to be replaced by an expensive silicone sealant. In addition to this the region has high winds and is earthquake-prone. 2... 

Since the introduction of the first polysulfide sealants in the 1950s, the sealant market had grown by 1992 into a 1.4 billion industry. Sealant use is generally divided into four categories transportation, construction, consumer, and industrial. Table 9 lists the market segment value of each use as of 1992 and Table 10 the market share of the various material types. Continued growth is expected, especially for silicones, urethanes, and acrylics. Table 11 lists suppliers of sealants. 

As shown in Table 23, silicone sealants are used to seal various constructions and devices that operates in a wide temperature range (from -60 to 250-300 °C). Seals made from them are resistant to vibration, alternate and shock loads and atmosphere. 

In this book I have confined discussion to those polymeric materials which are cured by chemical reaction and which have found widespread application in the construction industry. As such, the book covers materials based on epoxies, polyurethanes, silicones, polysulphides, alkyds and polyesters. In addition, there is a chapter on hybrid polymer systems and one on acrylics. It is true that acrylic emulsions are not strictly thermosetting polymer systems, but their widespread use and importance made their exclusion difficult. These materials find use as coatings, sealants, adhesives, grouts, flooring compounds, repair compounds and waterproofing agents. 

Whereas epoxy crack injecting systems are applied in static cracks, polyurethane systems are suitable for cracks where some movement is anticipated. There are other applications where polymeric materials are considered as competitors to each other. For example, neutral cure silicone sealants and polyurethane sealants are both suitable for use in construction joints. The former type offers greater durability and ageing resistance. However, polyurethane sealants are widely used because of their cost-effectiveness. Furthermore, some products are preferred over their counterparts for environmental reasons. 

THERMOSETTING POLYMERS IN CONSTRUCTION APPLICATIONS Table 6.4 Properties of one-component and two-component silicone sealants... 

The main areas of application for one-component silicone sealants are glazing, structural glazing, construction, sanitary areas and as insulated-glass sealants. All these topics will be covered in the section on specific areas of application (section 6.3.8). 

Spells, S. and Klosowki, J.M. (1981) Silicone sealants for use in concrete construction, in Joint Sealing and Bearing Systems for Concrete Structures, publication SP-70, American Concrete Institute, Detroit, MI, pp. 217-35. 

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