The new reinforcement frontier:

FRCM composite materials

Ruregold strengthening systems utilize two different types of fibers, carbon and PBO (poly-paraphenyleneben- zobisoxazole), both synthetic materials with high mechanical performance properties able to absorb the stresses generated by overloads and exceptional events, such as earthquakes. The PBO fibers, compared to carbon fibers, have tensile strength greater than 40% and elastic modulus greater than 15%.

FRCM (Fabric Reinforced Cementitious Matrix) structural strengthening systems consist of the coupling of a high performance long fiber and a stabilized inorganic matrix used as an adhesive, replacing the epoxy resins of traditional FRP systems.

Ruregold has introduced a global innovation in the field of structural reinforcements by patenting several FRCM strengthening systems, each of which has been specifically developed to meet the needs related to reinforcement and seismic retrofit of various structures, such as reinforced concrete structures, masonry structures, and infill elements.

The adhesives are formulated to match each type of mesh reinforcement system, thus ensuring effective bond to both structural fibers of the mesh and to the materials constituting the substrate, guaranteeing the high reliability of the
structural reinforcement.

Ruregold composite reinforcements use woven structural fibers with a specific geometry to guarantee greater versatility of use, that is, a greater ability to manage stresses even in the most complex load situations, such as column buckling, shear strength of panels, bending and shear of beams, and actions in the plane and outside the plane.

FRCM strengthening systems have significant benefits:

Application on damp substrates

Fire resistance

Vapor permeability

Non-toxic matrix

Resistance to high temperatures

Resistance to freeze and thaw cycles

Ease of installation

Ecological

Compatible with masonry

Ductility

Passive protection

Reversible

FRCM: proven anti-seismic efficacy

Properties of Ruregold’s FRCM strengthening systems

Strengthening systems in a seismic zone are aimed at retrofitting the structure to the intensity of the expected seismic action. Composite materials are particularly suitable for this purpose since they increase the ductility of the structural elements they reinforce. In addition they are easy to apply, which allow applications in critical areas that may
be difficult to reach, especially in case of historic masonry.

The strategy of seismic retrofit interventions is aimed at eliminating the brittle fracture mechanism of load-bearing structural elements and the collapse mechanisms in correspondence of the joints, as well as at improving the overall deformation capacity of the structure.

In reinforced concrete structures this requirement
is mainly obtained by increasing the ductility of the plastic hinges. In masonry structures, the key procedure is box action of load-bearing masonry elements so as to make them more resistant to horizontal actions, eliminate the orthogonal thrusts to the wall panels and connect the perpendicular load-bearing elements to each other.
The deformation capacity of the reinforcing element
and the adhesion of the reinforcement to the structure are of fundamental importance for the effectiveness and reliability of FRCM seismic retrofit. Ruregold’s FRCM systems assure these characteristics even in extreme conditions, when cracks are forming in the support.

Application of Ruregold Strengthening System with inorganic matrix

Preparation of the substrate

The substrate must be structurally sound, clean, free of dust, loose parts and without any contaminants, such as paints, release agents, etc. Concrete substrate must be fully cured (28 days) with exposed aggregate.In the presence of macroscopic surface defects >1/4 in. (6,3 mm) deep, use a repair mortar suitable for the nature of the substrate in order to fill irregularities and repair damages. Round any edges to a bending radius of 1 in. (2.6 cm) radius.

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Preparation of the inorganic matrix adhesive

The adhesive is prepared as an ordinary cement-based mortar by pouring potable water into the mixer and then adding water. Mixing procedure requires using 90% of the water and mixing for a minimum of 2 minutes. Then the remaining 10% of water must be added to the mix. Mix for another 2 minutes. Let the adhesive rest for 2-3 minutes. Then mix again for 2-3 minutes. Use a hand-held slowspeed drill and paddle. Alternatively use a mortar mixer with a rotating drum. Do not mix by hand.

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Application of the Ruregold system

The substrate must be wet to saturation with no residual surface water. Apply the first layer of adhesive at a thin thickness of 1/8 inch (3 mm) to 3/16 inch (5 mm) using a smooth metal trowel. Lay a ply of the mesh over the adhesive and lightly press the mesh into the adhesive. Each ply of mesh must be totally encapsulated into the adhesive. Complete the installation adding a final layer adhesive at 1/8 in. (3 mm) thickness so as to completely encapsulate the mesh. Each layer of adhesive must be applied when the previous layer is still wet and has not hardened. The mesh must be lapped 6 in. (15 cm) minimum in the primary direction of fiber orientation. No lapping of the mesh is usually required in the secondary direction.

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INSTALLATION PHASES
Apply a multiple layers of the system as necessary

If the design requires more than one ply of the reinforcing mesh, proceed by laying a second layer of mesh and of the last layer of inorganic matrix by proceding always wet-on-wet. It is possible to offset the orientation of the mesh in successive layers by 45°, placing it diagonally versus the previous layer.

Possible application of a fiber connector
In some configurations it might be necessary to insert joints, made of PBO or carbon fibers, linking the system to the structure. Once a hole has been made in the supporting structure, fill it with the adhesive that has been used and insert the joint. The free end of the joint should be opened, spread out in a fan shape and then covered by a surface layer of the adhesive.

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FRCM Features

Post-cracking ductility

While FRP systems can show brittle fracture behavior under maximum load, Ruregold's FRCM strengthening systems enhance the ductility of the structural elements that they reinforce, in favor of a greater deformation capacity of the single bearing element and an overall increase in the effectiveness of the reinforcement on the entire structure. Structural strengthening is all the more effective and reliable the more it demonstrates ductile behavior after reaching the maximum load. This property can be quantified by the area under the load-displacement curve measured during a bending test. The largest is the area, the greater is the capacity of the FRCM system to dissipate energy. FRCM systems provide exceptional ductility since the deformation of the matrix under load is close to that of the support, ensuring adhesion and structural collaboration of the reinforcement even after the peak of the load.

STRESS (F/A_f)

STRAIN

Uniaxial traction type stress-strain curve of an FRCM specimen (A_f dry fabric area)
Resistance to high temperatures

Compared to unreinforced concrete, Ruregold's FRCM strengthening systems maintain their effectiveness up to a temperature of 550°C (288°F). Flexural strength was chosen as a significant parameter for this behavior since flexural strength is more sensitive than other parameters, such as compressive strength, to evaluate concrete deterioration caused by heat. The deterioration process begins at 130°C (54°F) and causes a noticeable decline in the mechanical performance of concrete, as reported in the graph. The graph noticeably shows that Ruregold's strengthening system maintains higher flexural strength than unreinforced concrete as the testing temperature increases. This is due to the fact that at high temperatures FRCM strengthening systems are able to counter the phenomenon of de-cohesion between aggregates and cement binder, which is the cause of loss of strength of unreinforced concrete.

MAXIMUM LOAD (KN)

CONCRETE BEFORE STRENGTHENING

FLEXURAL STRENGTH VARIATION ACCORDING TO TEMPERATURE

CONCRETE STRENGTHENED WITH PBO-MESH GOLD
Glass transition temperature

Since Ruregold’s FRCM strengthening systems do not depend on epoxy resins to externally bond a high-performance mesh reinforcement to the substrate, they are not affected by the risk of de-bonding that occurs when epoxies reach their Tg (glass - transition temperature). When epoxy resins reach their Tg, they change from a glassy to a visco-elastic state thus ceasing to secure the designed bond. Tg of epoxy resins used in commercially available FRP systems typically ranges from 140 to 180 °F (60 to 82°C). In a dry environment ACI 440.2R recommends that FRP service temperature not exceed Tg – 27 °F (Tg - 15°C). The same recommendations comes from European DT 200 R1 2013 (CNR). At a temperature of 113 °F (45°C) it is therefore likely that an FRP system no longer provides the designed reinforcement.
Fire Resistance

RureGold's FRCM system, subjected to fire reaction tests according to the European standards in force EN 13501-1, was certified in class A2 or as non-combustible material, which does not cause toxic fumes and does not form incandescent drops potentially very dangerous for people during a fire. All FRP systems, on the other hand, have been classified in class "E", because they use an organic adhesive that contributes to the generation and/or propagation of the fire and therefore require adequate protection.
Durability and humidity

Ruregold’s FRCM (Fabric Reinforced Cementitious Matrix) strengthening systems maintain the specified performance properties independently of the Relative Humidity (RH) and the environment temperature. The results of a durability test carried out at the ITC-CNR Laboratory of S. Giuliano Milanese show how deeply environmental conditions influence the mechanical performances of FRP structural strengthenings. Results are summarized in the graphs on the right. In FRP systems, the presence of moisture on the surface of the structure changes the type of break that from "cohesive", at the interface between support and reinforcement, from "adhesive". It is also noted that the prolonged exposure to moisture causes a progressive worsening of the mechanical shear and flexural strength, which in the interval 73-104°F (23-40°C) becomes increasingly rapid as the temperature increases. Results similar to the ones obtained at the ITC-CNR Laboratory were also obtained as MIT of Boston and the University of Edinburgh.

AVERAGE BREAKING LOAD (N)

FRCM FLEXURAL STRENGTH AS A FUNCTION OF TEMPERATURE, RH, AND DAYS OF EXPOSURE
Proven anti-seismic efficacy

Strengthening systems in a seismic zone are aimed at retrofitting the structure to the intensity of the expected seismic action. Composite materials are particularly suitable for this purpose since they increase the ductility of the structural elements they reinforce. In addition they are easy to apply, which allow applications in critical areas that may be difficult to reach, especially in case of historic masonry. The strategy of seismic retrofit interventions is aimed at eliminating the brittle fracture mechanism of load-bearing structural elements and the collapse mechanisms in correspondence of the joints, as well as at improving the overall deformation capacity of the structure. In reinforced concrete structures this requirement is mainly obtained by increasing the ductility of the plastic hinges. In masonry structures, the key procedure is box action of load-bearing masonry elements so as to make them more resistant to horizontal actions eliminate the orthogonal thrusts to the wall panels and connect the perpendicular load-bearing elements to each other. The deformation capacity of the reinforcing element and the adhesion of the reinforcement to the structure are of fundamental importance for the effectiveness and reliability of FRCM seismic retrofit. Ruregold’s FRCM systems assure these characteristics even in extreme conditions, when cracks are forming in the support.

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