1) Cement based coating
Metallic waterproofing nd latex coatings provide the required adhesive bond to resist hydrostatic pressure. Metallic waterproofing consists of finely divided metallic aggregate and oxidizing agents, mixed with sand and Portland cement. The mixture is mixed with water to form a plaster coat which may be applied by brush or towel depending on the consistency of the mix. After the coating is applied to the concrete surface, the metallic particles oxidize and expand to at least three times their original size, wedging themselves into pores and interstices thus creating a relatively dense waterproof barrier. However, any subsequent cracking of the concrete wall will open cracks in the coating which would render it ineffective in preventing moisture entry.
2) Bentonite - based products
a) Trowel or spray grades -
Finely divided bentonite clay, formulated with fibers, is often used in thickness of about 5mm in below-grade locations. In contact with sufficient water, it swells 10 to 20 times its original volume forming a gel that prevents further penetration by water. The material has some ability to reseal itself over cracks that from subsequently in concrete.
b) corrugated bentonite cardboard panels - Bentonite clay contained in biodegradable, corrugated, cardboard panels are suitable for application to exterior surfaces below grade. The panels are attached with tempered nails or roofing cement. Eater borne bacterial decomposes the cardboard and water swells the bentonite to form the gel.
3) Mastic asphalts
The products contain asphalt fillers, fibers, polymers, and solvents, and are usually reinforced with fiberglass mesh. These are usually laid by hand using wooden floats or squeegees. They are placed in two layers each of 10mm thickness, as blow holes frequently form in the first layer and the second layer covers these holes. The main advantage of mastic asphalt is that a protective layer is unnecessary, it is however , prone to the problem of blowing and is labour intensive.
4) Polymer rasin-based coatings
These are generally of two types :
(a) Resins blended with organic solvents and
(b) Solvent free coatings
Solvent based coatings are subdivided into single and two component coatings. The coatings on drying produce a smooth dense continous film that provides a barrier to moisture and mild chemical attack of the concrete. Because of the resistance to moisture penetration, staining, and ease of cleaning , they are preferred for locations of high humidity and those in which a lot of soiling occurs.
Most products are low solid content material which require multiple coats to produce a continuous film over concrete, since the materials are thermoplastic, and have a significant degree of extensibility they are capable of bridging minor cracks which may develop in the concrete surface they are applied in sufficient thickness. The number of coats required depends on the surface texture, porosity, and the targeted dry film thickness. Although some of the newer products have some moisture tolerance, enabling them to be applied over damp, in normal usage they should be applied over dry surfaces. Due to their relative in permeability to water vapour, they could blister when applied to concrete surfaces with high moisture content or where the opposite surface of the concrete is in constant contact with moisture. Careful control of wet film thickness is therefore necessary during application.
Two component polymer coatings consists of a solution of a compounded polymer with or without solvent and a reactive chemical component called the curing agent hardener bor catalyst. The materials are usually mixed just prior to use in accordance with manufacturers instructions. When using two components polymer based coatings the following items are of importance to the application of the materials.
a) Most produces are supplied as a kit containing the two components in the required proportions. Therefore, in order to realise the full potential of the product the correct mix ratio of the two components must be used.
b) To ensure a complete reaction of the two components they must be mixed thoroughly.
c) Some two component materials require an induction period of 15 to 40 min after mixing. Therefore , such products cannot be used immediately after mixing.
d) Viscosity reduction by the use of thinners should be resorted to only after the manufacturers are consulted.
e) The storage temperature of solvent based coatings is essential is not critical. They should be stored at a temperature 16 to 32°C just prior to use.
Some of the generic resin types used includes thin adhesive coatings based on epoxy, polyurethane, clorinated rubber, polyvinyl chloride, neoprene, and clorosulfonated poly ethylene. To overcome some of the drawbacks of solvent-based coatings a significant number of solvent-free coatings are on the market. These coatings are often specified for their high build, reduced risk of toxicity and fire hazard during applications where adequate violation of solvent-based meterials would be uneconomic. Their major disadvantages is that they are relatively high viscosity materials that are difficult to apply in comparison to their solvent-based counterparts. Suitable methods of application are rollers but in some cases it may be preferable to use squeegees. Their favoured application is to large areas such as floors.
5) Membranes
Membrane waterproofing is applied to prevent water intrusion through openings resulting grom construction defects, shrinkage cracking, and structural movement. Vertical surfaces are waterproofed from the potentially wet side the earth side of a foundation wall or the liquid side of a tank wall. Slab construction is treated similarly, except the membrane is often encased between two courses of concrete to protect it from mechanical damage. More recently, traffic bearing membrane system which combine an abrasion resistant top coat with an electrometric under layer have been used to protect bridge and packing decks, Membrane waterproofing system can be grouped according to fabrication and application methods as follows:
(a) Built up sheet membrane
(b) Prefabricated sheet and
(c) Liquid applied materials
Built up membranes:
Hot-applied membranes , built up from multiple plies of saturated felt fabric or coated sheets, set an interplay applications of hot coal tar pitch pr asphalt are the oldest type of membrane waterproofing.
Application of built up membranes involves the following:
(a) Priming the concrete surface
(b) Reinforcing the corners with two or more plies of felt and adhesive
(c) Sealing the openings
(d) Applying a coating of hot waterproofing bitumen
(e) Brushing or rolling the sheet into hot bitumen
(f) applying additional courses and
(g) Applying protection board over the membrane.
The advantages generally associated with hot applied built up waterproofing system are:
(a) Workmen are familiar with materials and methods
(b) Membrane is continuously bonded to concrete
(c) Allows the correction of filed errors
(d) Bridges existing joints and cracks in concrete
The disadvantages of the system are:
(a) Hot kettles of bitumen must be kept at correct temperature
(b) The method is labour intensive
(c) Organic felt and fabric deteriorate
(d) Organic felt and fabric deteriorate
(e) Conforming membrane to substrate contours and projections through concrete is difficult
Prefabricated sheet membranes:
Sheet meterials are typically 1.25 to 2.4 mm thick, and are applied by three methods: loosely laid, mechanically fastened and fully bonded. Loosely laid systems are usually used in the waterproofing of roof and require an overlay of smooth stones or earth for ballast. Mechanically fastening is usually required at perimeters and openings. Fully bonded systems use contact adhesives. Sheet membrane system includes:
(a) Vulcanized rubbers
(b) Thermoplastics
(c) Ethylene interalloy, and
(d) Impergnated asphalt composites
An advantage normally associated with prefabricated sheet waterproofing include the following:
(a) Workmen are familiar with application techniques
(b) The membrane is more elastic than built-up membrane
(c) Meterials bridge existing joints and cracks in concrete
(d) The membrane has uniform thickness controlled at the factory and note on site.
The disadvantages are:
(a) The seal at sheet laps and joints in some systems can be the weak link in membrane
(b) Confirming the membrane to irregular surfaces and projections through concrete is difficult.
Liquid applied membrane:
A number of liquid applied membranes are available:
(a) Hot-applied rubberized asphalts
(b) Liquid applied neoprene, and
(c) Cold applied polyurethane
Many of these meterials can be used en vertical surfaces as well as horizontal slabs. Most must be covered with protection board or traffic bearing slab or coating. A few formulations with sand sprinkled on the laid coating can accept pedestrian traffic. The performance of liquid applied waterproofing systems is related to membrane thickness, which should be checked during application using a wet film thickness gauge.
Advantages provided by the system are:
(a) Application is easy by several methods-spray, roller, squeegee etc.
(b) The continous bond formed prevents lateral movement of water between membrane and concrete.
(c) No hot meterial is used
(d) The membrane is more elastic than built-up membranes
The disadvantages associated with the system include the following:
(a) The thickness depends on the skill of the applicator and may therefore vary
(b) The meterial may require accurate mixing at job site
(c) Compatible sheet meterial or fiberglass reinforcement meterial must be added to bridge larger existing joints and cracks in concrete.
Multilayer membrane system:
Multilayer membrane systems are effective in reducing the ingress of moisture. They provide a watertight barrier that has elasticity to maintain integrity under the influence of temperature-induced structural movement. Membranes have proven to be especially effective at preventing the onset of corrosion in new structure by preventing contamination of reinforced concrete by salt. These are low basic types of membrane systems:
(a) Liquid applied, traffic bearing elastomeric membrane system and
(b) Asphalted systems.
Traffic bearing elastomeric membrane system should have the following basic properties:
(a) Impermeability
(b) Adhesion
(c) Crack bridging characteristics
(d) Durability
(e) Ease of applications
The asphaltic system are much thicker than liquid applied elastomeric membranes and use asphalt cement based waterproofing membrane, which is either hot or cold applied. An asphalt paving wearing course 32mm thick or more, is applied on top of the membrane. The asphalt paving may be latex modified for added flexibility, or may be applied as a mastic system which does not require compaction. Due to the softness of the bituminous membranes, the thicker the membrane layer the thicker the asphalt paving wearing course required to obtain a stable surface.
Final selection of a membrane system is based on meterial properties or field experience and should involve the following items for consideration:
(a) anticipated degree of structural movement
(b) anticipated traffic loading, exterior or interior application
(c) consideration of live load capacity and height limitations.
(d) Nature and extent of deterioration of the concrete deck
(e) Installation procedure recommended by the manufacture.
(f) Compatibility with expansion and contraction joint seals
(g) Cost
(h) Long standing example of successful application available for inspection
(i) Good standing of the manufacturer and the length and conditions of the guarantee
(j) The case of repair of the system and the effectiveness of the bond between old and new membranes.
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