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Masonry Structure Strengthening Systems

Masonry (kargir) structures are buildings that do not have a load-bearing skeletal system consisting of columns, beams, or shear walls, but rather rely on load-bearing walls formed by stacking structural elements such as stone or brick to carry the loads. The loads to which the structure is subjected are transmitted from top to bottom through the load-bearing walls and transferred to the ground. Mortars with lime binders are generally used when building masonry walls. For this reason, mortars with natural hydraulic lime binders are utilized in the repair and strengthening applications of masonry structures. Cementitious mortars do not comply with the natural character of the structure and cause damage to the building due to the salts they contain.

The globally accepted system for strengthening masonry structures is the FRCM strengthening system. The FRCM strengthening system derives its initials from the phrase Fabric-Reinforced Cementitious Matrix, and it is a modern and up-to-date method in repair and strengthening. In its simplest form, the strengthening matrix consists of a textile reinforcement (also referred to as strengthening reinforcement or technical textile) and a cement- or lime-based mortar.

FRCM systems are increasingly preferred over traditional polymer-bonded, fabric or plate-reinforced (FRP) strengthening systems due to their ease of application, reversibility without damaging the structure, higher resistance to elevated temperatures, resistance to UV radiation, breathability (allowing vapor transmission), and applicability in damp areas.

PRINCIPLE APPLICATIONS

In principle, FRCM strengthening systems are based on the composite action of mortar and textile reinforcement, similar to the joint behavior of concrete and steel in reinforced concrete. In this context, the mortar withstands the compressive stresses, while the textile reinforcement withstands the tensile stresses.

In masonry structures, various cracks, deterioration, and damages can occur over time depending on the loads they are exposed to, ground settlements, design errors such as insufficient cross-sections, application errors, the strength and characteristics of the mortar and materials forming the masonry walls (such as stone, brick, adobe), and external influences like efflorescence and mold growth. Since the load-bearing walls of masonry structures can become hollowed over time due to various effects, the load-bearing capacity of the structure is increased by filling these voids with natural hydraulic lime-based injection mortars. The structure, strengthened with the FRCM system after injection, can safely withstand various loads acting upon it, and the use of mortars suitable for the structure's characteristics increases the durability of the building.

RELATED STANDARDS

CNR-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”

 

The FRCM strengthening system is a recognized system in the field of strengthening included in international standards, and the above-mentioned standards are taken as a basis for the relevant application principles and engineering calculations.

APPLICATION STEPS

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For injection application:

  • Large cracks, voids, etc. on the masonry wall surface are repaired with TOH303 or TGH101.

  • For this purpose, the selected mortar is mixed with water in the amount specified on the package and for the specified period, then applied to the relevant areas on the wall to complete the repair.

  • Holes are drilled into the wall surface for injection.

  • TEH911 is mixed with water in the amount specified on the package and for the specified period, then filled into the injection machine.

  • The application is completed by injecting into the holes in the wall with an injection machine at a pressure of approximately 2 bars.

For masonry wall strengthening:

  • The application surface is cleared of all foreign substances and dust, and then moistened.

  • The selected strengthening mesh is cut to the desired size using appropriate cutting tools.

  • TGH101 is mixed with water in the amount specified on the package and for the specified period, then applied to the wall surface with a thickness of approximately 5 mm using a trowel or spraying method.

  • The strengthening mesh is placed by hand onto the mortar surface, a load distribution plate is positioned, and it is anchored to the wall using the selected mechanical anchoring element.

  • TGH101 is reapplied so that the final layer thickness is a minimum of 10 mm, covering the surface completely so that neither the anchors nor the mesh are visible.

  • As a finishing plaster, a mortar containing Calce is prepared or TOH303 is used.

DETAILS TO CONSIDER

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  • The number of holes drilled in the wall for injection must be a minimum of 4 per square meter.

  • The injection application must be carried out from the lower elevation towards the higher elevation.

  • The strengthening must be applied directly to the masonry wall surface; loose layers, plaster, ceramic, paint, etc. on the surface must be removed.

  • The strengthening mesh must be placed without leaving any gaps and with an overlap of approximately 20 cm.

  • Anchors must be applied with a minimum of 4 pieces per square meter.

  • In order to prevent the mortar on the surfaces from cracking, the surface must be wetted 20 minutes after the initial curing is complete and the mortar has hardened.

  • The strengthening mesh must not be terminated on the wall plane; it must be turned into the door and window openings, extended by 20 cm, and terminated on these planes. Connections must not be made at the corner points.

  • In double-sided applications, a double layer of technical strengthening reinforcement must be used at the slab level on the exterior of the building. The material to be used must extend 20 cm above and below the slab level.

  • No other additives such as cement, etc., must be added to the mortars, and the water ratio must strictly be used in line with the instructions in the technical data sheet. The mixing equipment must have the mixing speed recommended in the technical data sheet.

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