Masonry buildings are structures without a load-bearing frame system such as columns, beams, shear walls, instead, load-bearing walls formed by placing structural elements such as stone and brick on top of each other; thus, the loads that the building is exposed to are transferred to ground by transferring from top to bottom through the load-bearing walls.
When constructing masonry walls, lime-based mortars are generally used. Therefore, mortars having natural hydraulic lime as a binder are used in the repair and strengthening applications of masonry structures. Cementitious mortars are not suitable with the natural characteristics of the structure and cause damages due to their salt content.
Globally recognized method for strengthening masonry structures is the FRCM strengthening system. 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.
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.
In masonry structures, various cracks, abrasions, and damages may occur over time depending on the loads they are subjected to, soil settlements, design errors such as insufficient cross-sections, application errors, strength and characteristics of the mortar used with materials such as stone, brick, or mudbrick forming the masonry walls, and external effects such as efflorescence and fungal growth. Since gaps may be occurred in the load-bearing walls of masonry structures over time due to various effects, these gaps are filled with natural hydraulic lime-based injection mortars to increase the load bearing capacity. After injection, the structure is reinforced with the FRCM system making the structure safely bear the various loads on it, increasing the durability of the structure by using of mortars suitable with the characteristics of the building.
- 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.
For injection application:
- Large cracks, gaps, etc. on the masonry wall surface is repaired with TOH303 or TGH101.
- For the repair, the selected mortar is mixed with the specified amount of water for the mixing duration written on the kraft bag, then the repair is completed by applying it to the relevant places on the wall.
- For injection, holes are drilled on the wall surface and the injection pipes are installed.
- TEH911 is filled into the injection machine after mixing with the specified amount of water for the mixing duration written on the kraft bag.
- Using the injection machine, the mortar is injected through the holes on the wall with a pressure of about 2 bars.
For masonry wall strengthening:
- 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.
- TGH101 is mixed with the specified amount of water for the mixing duration written on the kraft bag, and then applied with a trowel or spray to the wall surface 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 wall with the selected mechanical anchor.
- TGH 101 is re-applied as the second layer with a minimum thickness of 10 mm fully covering anchors or mesh.
- As a finishing plaster, a mortar with CALCE is prepared or TOH303 is used.
DETAILS TO BE CONSIDERED
- The holes drilled on the wall for injection should be a minimum of 4 pieces per square meter.
- Injection application should be made from low elevation to high elevation.
- Strengthening should be done directly on the masonry wall surface, loose layer on the surface, plaster, ceramic, paint, etc. should be removed.
- The strengthening mesh should be placed 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.
- The strengthening mesh should not be finished in the wall plane, it should be finished in adjacent planes by turning inside the door-window spaces and extending 20 cm. Connections should not be made at the corner points.
- In double-sided applications, a double layer of strengthening mesh should be used at the slab level outside the building. The mesh to be used must be extended 20 cm from the slab level at the bottom and top.
- 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.