REINFORCED CONCRETE SLAB STRENGHTENING SYSTEM 

Reinforced concrete (RC) slabs are building elements that cover the openings in the buildings and transfer the vertical and horizontal loads they are exposed to the columns or shear walls in proportion to their rigidity with the help of the beams beneath them.

In addition to the traditional FRP method for strengthening RC slabs, FRCM system is globally recognized and widely used. FRCM strengthening system’s name comes from the initials of Fabric-Reinforced Cementitious Matrix, which is a modern and up-to-date method of repair and strengthening. In its simplest form, the strengthening matrix consists of textile reinforcement (also called strengthening textile or technical textile) and a cement or lime-based mortar.

FRCM systems become widespread and preferred over traditional polymer binder, fabric or plate strengthening (FRP) systems due to its ease of application, removability without damaging the structure, resistance to high temperatures, resistance to UV radiation, ability to allow vapor diffusion, and suitability for application in humid areas.
 

APPLICATION PRINCIPLES

FRCM strengthening system work principal is based on the matrix of mortar and textile reinforcement, similar to the way concrete and steel work together in reinforced concrete. In this context, mortar bears the compressive stresses and textile reinforcement bears the tensile stresses.

Owing to the loads they are exposed to, permanent cracks, punching cracks, shear cracks due to shear wall movement and excessive deflections can be occurred on RC slabs. In addition, the slab may have been designed thinner than what is necessary, without sufficient reinforcement or removed from the mold early due to application errors. Although slab damages are not seen as a primary damage to the structural system, it may pose a danger to the usability of the structure. The rigidity and bearing capacity of the slab increases when reinforced with the FRCM system; hence, it can transfer various loads to the relevant structural elements without any problem.

RELATED STANDARDS

• DT 2000 R1 / 2013 “Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Existing Structure”
• ACI 549. 4R-13 “Guide to Design and Construction of Externally Bonded Fabric-Reinforced Cementitious Matrix (FRCM) Systems for Repair and Strengthening Concrete and Masonry Structures”
• ICC-ES AC434 10-2018 “Acceptance Criteria for Concrete and Masonry Strengthening Using Fabric-Reinforced Cementitious Matrix (FRCM) and Steel Reinforced Grout (SRG) Composites”

FRCM strengthening system is an internationally accepted method in strengthening applications and the relevant application principles as well as the engineering calculations are based on the above standards.

PRODUCTS

APPLICATION STEPS
For slab strengthening from top:

• The application surface is cleansed of all foreign substances and dust, and moistened.
• The selected strengthening mesh is cut to the desired size with appropriate cutting tools.
• HPM100 or HPM120 is mixed with the specified amount of water for the mixing duration written on the kraft bag, and poured onto the surface of the reinforced concrete slab and spread with a thickness of about 5 mm.
• The strengthening mesh is placed on the mortar surface by hand, and the load distribution plate is placed and anchored to the reinforced concrete slab with the selected mechanical anchor.
• HPM100 or HPM120 is re-applied with a minimum thickness of 10 mm as the second layer with a minimum thickness of 10 mm fully covering anchors or mesh.

For slab strengthening from bottom:

• The application surface is cleansed of all foreign substances and dust, and moistened.
• The selected strengthening mesh is cut to the desired size with appropriate cutting tools.
• RPM40 or RPM60 is mixed with the specified amount of water for the mixing duration written on the kraft bag, and then applied to the bottom of the reinforced concrete slab with a trowel or spray in approximately 5 mm thickness.
• The strengthening mesh is placed on the mortar surface by hand, and the load distribution plate is placed and anchored to the reinforced concrete slab with the selected mechanical anchor.
• RPM40 or RPM60 is re-applied with a minimum thickness of 10 mm as the second layer with a minimum thickness of 10 mm fully covering anchors or mesh.

DETAILS TO BE CONSIDERED

• Strengthening should be done directly on the reinforced concrete slab surface, loose layer on the surface, plaster, ceramic, paint, etc. should be removed. If loose concrete cover or reinforcement corrosion is observed, the loose cover should be removed and the rust on the reinforcement should be mechanically cleaned. During moistening, free water should not be present on the surface.
• The strengthening mesh should be placed on top and bottom of the slab without any gaps and with an overlap of about 20 cm.
• Anchors should be applied in such a way that there are minimum 4 pieces per square meter.In order to prevent cracking of the mortar on the surface, the surface should be wetted after 20 minutes once the first curing is completed and the mortar has hardened.
• Where possible, the strengthening mesh should not be finished in the slab plane, it should be finished in adjacent planes by turning and extending 20 cm.
• No extra cement etc. other additives should be added to the mortars, the water ratio should be in accordance with the instructions in the technical data sheet and the mixing equipment must have the mixing speed recommended in the technical data sheet.