Concrete surface preparation

Research carried out in the United Kingdom for the DoT led to development of a system that was durable in UK conditions. The North American manufacturers developed their materials further and improvements in concrete surface preparation have lead to more durable systems. A range of coatings is now available. 

In the case of concrete, the main reasons for preparing the surface before bonding are similar, namely (1) to produce a close fit between the adherends (2) to remove laitance and contaminants and to expose pieces of aggregate and (3) to produce a mechanically sound surface. Any typical sequence of steps in the process of concrete surface preparation should then include the removal of any damaged concrete and its replacement with new material, and the elimination of dust and other contaminants by brushing, air blast or vacuum. In some situations, additional steps like cleaning with a solvent to eradicate specific contaminants and application of a primer may be required. 

The application of a CFRP lining system to a pipeline is a bond critical application, so the surface of the pipeline must be prepared sufficiently to ensure proper adhesion. Concrete surfaces are profiled using abrasive or water blasting to a minimum International Concrete Repair Institute (ICRI) concrete surface preparation CSP 3, as shown in Figure 1.3, whereas a metallic surface will be prepared using abrasive blasting to a near white metal surface profile. Surface contaminants (laitance, carbonated and weak concrete, cracked and spalled concrete) are removed and the substrate is repaired as necessary. The work requires the pipe surface to be thoroughly cleaned, dried, and dehumidified. 

ICRI Guideline No. 310.2, Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, and Polymer Overlays. International Concrete Repair Institute (ICRI). 

Paring is the surface preparation in a processing faciUty which may be concrete, asphalt, gravel, cmshed shell, or brick. 

Berger, D. M., Preparing concrete surfaces. Concrete Construction, 481-494, September (1978). 

Two-pack epoxy Section 12.3.3. These are widely used to give the maximum protection to concrete surfaces, floors and walls. They can be applied as relatively thin coatings by spray or as thick epoxy surfaces applied by trowel. In all cases, the application must be preceded by adequate surface preparation (see Section 12.6.1). To allow maximum penetration into the concrete the first coat must have a low viscosity. Coal tar epoxies are used where protection is the main requirement. 

Surface preparation of concrete consists mainly of removing laitence, form oils and air pockets. Laitence is the fine cement powder that floats to the surface of concrete when it is placed. Coatings applied over such a powdery, weak layer will lose adhesion. Form oils are used for the easy stripping of forms or shuttering. Their presence will also cause loss of adhesion of subsequent coatings. Forms should be coated with non-migratory hard coatings and the use of oils or waxes prohibited. 

The following alternative methods of surface preparation can be used for new concrete. 

L.4.3 Approximately 10 to 25 mm (0.5 to 1 in.) of the top of the cementitious foundation material should be scarified with a chipping hammer before the grout is applied. This procedure is recommended to remove low-strength, high-porosity concrete in this area. The concrete foundation should be allowed to cure for at at least 7 days prior to this surface preparation. 

Test Method for Adhesion in Peel of Elastomeric Joint Sealants Recommended Practice for Surface Preparation of Concrete for Application of Chemical Resistance Resin Monolithic Surfaces Method of Testing Release Papers Used with Preformed Tape Sealants Test Method for T-Peel Strength of Hot Applied Sealants Test Method for Tensile Adhesive Strength of Preformed Tape Sealants by Disk Method... 

Surface preparation depends on coating formulation and intended usage. This could vary on steel substrates from a commercial to a white metal blast. Profile is also essential to obtain ultimate adhesion. The depth of profile required is proportional to the total dry film thickness of the coating system. On concrete surfaces, the general requirement is to remove latents and contaminants and this can be accomplished by chemical preparation, scarifying or abrasive blasting. 

In order to minimize surface preparation, concrete surfaces are usually water cured for 28 days however, the use of curing agents cannot be altogether avoided so special care must be taken to assure the selected agent is compatible with the coating used. 

If other types of membranes are used, and/or if surfaces other than concrete are to be membrane protected, read carefully the specifications and the manufacturer s literature on each and the section in this volume on that type, and verify surface preparation and thickness, uniformity and continuity of membrane. Make sure that not only the finished surface, but each intermediate one is free of dirt, blisters and voids. Where the substrate is metal, and the membrane is suitable for such testing, supervise spark testing to be sure that the voltage is adequate to provide liquid-tightness, but not so high as to burn holes in the membrane. 

He checks the surface of the substrate carefully for proper surface preparation, and verifies the compressive strength with a Schmidt (Swiss) Hammer, and the surface bond strength with an Elcometer, using the monolithic material itself as the bonding agent for the coupons. If a primer is used, then use it in bonding the coupons. The Elcometer test run in this manner also verifies the compatibility of the concrete surface and the monolithic. To be considered... 

Decisions regarding the method of preparation of concrete surfaces are complex and the application of surface coatings to a concrete floor should be made after carefully analyzing the geography of the site, the chemicals to be stored, the type of cement used, the potential exposure conditions and the life expectancy. 

The high relative standard deviation has contributions from surface PCB distribution (sampling error), PCB recovery during sampling and precision in quantitation. Because the analytical method had few steps, sample concentrations were similar, and the EC detector was operated in a linear region, analytical error was probably a minor contributing factor. A fine layer of dust and soil was present on the concrete, but no surface preparation was undertaken prior to the test. 

The preparation of surfaces to receive epoxy compounds is as important as the selection of the proper system for bonding. Concrete surfaces must be freshly exposed, free of loose and unsound material and should be at proper surface temperatures at the time of epoxy application. Among the methods for preparation of concrete surfaces are sandblasting, mechanical scarification and acid etching. The same procedures may be followed for preparation of steel surfaces. Temperature conditions for epoxy application should be in the range of 50°F. to 90 f. Temperature conditions v ill also affect pot life of mixed compounds, as well as curing time. 

A primer adhesive is first applied to a properly prepared concrete surface. A thin coat of epoxy mortar is then applied with a trowel. While this thin coat is still wet, a fiberglass membrane is rolled into the mortar. The edges of the membrane should be overlapped 2 inches. The mortar will squeeze up through the voids in the fiberglass mesh, resulting in adhesive base to which the final epoxy mortar will adhere. While this first application of mortar is still tacky, the second layer of epoxy mortar is applied over the glass cloth. This second layer may then be screeded and leveled. ... 

The effectiveness of a coating is related to the absence of pores or flaws and it increases in proportion to its thickness. The application requires thorough surface preparation, because a durable bond to the substrate is essential for coating effectiveness. The same applies to filling blowholes in the concrete surface. 

Bond to the substrate and dimensional stability. The repair materials should have a good bond to the concrete substrate. This bond depends on the surface preparation and the use of a bonding agent (Section 19.2.3) but is also influenced by the properties of the repair material and the compaction during its appfication. 

The surface of the structure to be investigated needs to be smooth in order to get sufficient energy into the concrete. Whereas gel couple methods such as the pundit require a smooth surface the dry couple transducers can accommodate a certain amount of roughness and therefore less surface preparation is necessary. 

ICRI (2004). Guideline for the Preparation of Concrete Surfaces for Repair Using Hydrodemolition Methods Technical Guide G03737 International Concrete Repair Institute Des Plaines, Illinois, USA. 

Installation is by airless spray to accessible areas and by roller or brush to inaccessible locations such as between the pairs of shear walls. Surface is prepared by a light grit blast or similar, to achieve an adherent surface. Requirements for a dry concrete surface 3°C or higher means that winter application can be difficult as even with enclosures and space heating, the cold concrete surface can create condensation. 

Although not strictly used as prime structural adhesives, polymer latices or dispersions have been included here because of their increasing use as aids to bonding in the patch repair of spalled concrete. They usually take the form of a polymer-cement slurry which is applied to the moistened and prepared concrete surface. In general, the repair mortar must then be applied before a film... 

Surface preparation should include (a) removal of all loose and unsound material until coarse aggregate is exposed (b) cleaning and (c) drying (although there exist some special polymeric systems which are claimed to bond to damp or wet concrete, and cementitious... 

In the practice of adhesive bonding for applications in construction, surface pretreatment is likely to be the most difficult process to control. The choice of treatments must be tempered by the scale of operations, the nature of the adherends, the required durability, the adhesive to be used, and the cost. The performance of joints constructed with cold-cure epoxies is likely to be critically dependent upon surface preparation, as exemplified by the experience of the Scottish Irvine Development Corporation. In 1978 they elected to use vertical externally-bonded steel plate reinforcement to strengthen the abutment walls of three pedestrian underpasses. A year later, the plates were reported to be falling off, accompanied by extensive interfacial corrosion the steel surfaces had been abraded by hand, and the concrete surfaces chemically etched. 

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