EN 1504-10-2003 pdf download.Products and systems for the protection and repair of concrete structures – Definitions – Requirements – Quality control and evaluation of conformity – Part 10: Site application of products and systems and quality control of the works.
If corrosion is present on the circumference of the reinforcing bar which is exposed after removal of damaged concrete, the depth of removal may need to be increased to expose the whole bar depending on the repair specification. The clearance around reinforcement and the minimum distance between the reinforcement bar and the remaining substrate should be at least 15 mm or the maximum aggregate size of the repair material plus 5 mm whichever is the greater to allow proper compaction. Chloride contaminate concrete should be removed on all sides of the reinforcement for a minimum of 20 mm.
If there is no corrosion on the reinforcement, carbonated and or chloride contaminated concrete may remain if electrochemical methods are used or the concrete is sufficiently dry.
In thermal and mechanical removal of concrete, micro-cracks may occur in the Concrete left in place. The layer containing micro-cracks should be removed using water blasting with or without abasive or should be treated to restore its integrity if the surface tensile strength is not sufficient for the poducts and systems to be applied. Cracking can be detected by wetting the surface and allowing it to dry. Cracks retain water and can be seen as dark lines. If thermal processes are used to remove concrete, the introduction of heat must be carefully controlled to prevent damage and if damage occurs further removal carried out by other means to remove any contaminated concrete.
Hydrodemohtion is a fast and effective way of removing concrete, keeping the removal of sound concrete to a minimum. No micro-cracks develop and unsound concrete is removed selectively leaving sound concrete intact. Selection is carried out around a mean removal depth. This procedure may be employed if it is carried out with equipment of known performance. The requirements to be met are to achieve the selection between sound and unsound Concrete, to remove concrete without leaving shadows and only a small amount of low ridges underneath the reinforcement and to do the work without creating pits. Removal to a generally predetermined minimum depth is possible, but where concrete is locally weak, the depth of removal will be deeper.
The equipment normally used for selective hydrodemolition operates with a pressure of 60-110 MPa. In selective hydrodemolition, it is necessary to specify equipment prequalified for the method. Surface roughness may vary considerably and is affected by the distance between the nozzle and the substrate, water pressure, water flow, feed rate, equipment and concrete quality.
A.7.3.2 Cleaning
For practical reasons, cleaning will normally be to the whole periphery of the bar. It will normally extend 50 mm or more beyond the extent of the corrosion along the length of the bar. Structural considerations may limit the amount of concrete which can be removed and the cleaning which can be carried out. Potential mapping may assist in detecting corrosion.
The standard of cleaning for method 11.1, using coatings with active pigment, is normally to Sa2. “thorough blast- cleaning”. For method 11.2. using barrier coatings to Sa2½. “very thorough blast-cleaning. is normally specified. Cleaning may be difficult to achieve under site conditions.
Where access for cleaning is prevented or difficult due to bar congestion, contact between bars, proximity to the concrete substrate, or other bars or other factors, the method and standard of cleaning should be specified. If corrosion products and contaminants cannot be removed or, if the coating cannot be applied to all areas intended to be treated, the performance of the coating may be changed. Sa standards for blast-cleaning are given in ISO 8501-1. Any method of cleaning, including grit blasting. may be used.
Removal of chlorides on the surface of the steel or in pits in the steel can only be achieved by water under pressure, normally at low pressure below 18 MPa but if low volumes of water are required pressures up to 60 MPa may be necessary.
A.8 Application of products and systems
A.8.1 General
The temperature of the substrate and repair mortar or concrete should not differ materially to avoid the risk of loss of bond and loss of hydration.
Surface working of concrete or mortar may cause the formation of shrinkage cracks as the treatment may give rise to a cement rich surface layer.
A.8.2.1 Bonding
A rough surface profile is beneficial for the bond between old and new concrete and repair products and systems, This can be achieved by hydrodemolition or mechanical means. The roughness produced by hydrodemolition is considerab’y greater than that produced by mechanical hammers which is in turn greater than that produced by grit blasting. It hydrodemolition is used there is normally a good bond between the concrete substrate and the repair material and mechanical connection is not necessary for the transfer of shear and tensile stress less than 0.4 MPa.
A textured surface can be given to the surface of repair mortar or concrete before it has set to assist in the mechanical key for a subsequent layer.EN 1504-10-2003 pdf download.