Composite materials are more and more applicated in the structural-reinforcement-field techniques. However, whether employed in reinforced concrete structures or in masonry buildings adaptation, in the choice of the materials we are never facing with a single solution.
But what do we really know about composite materials and about fields in where are applied? Furthermore, how to properly choose the right cycle and materials to use for?
The above questions are answered by Eng. Stefano Agnetti, Kimia S.p.A Tecnchical Support Dpt.
What composite materials are?
When I talk about composites materials I think about a famous popular proverb wich well explain the underlying principle: "Unity is strength". In fact, composite materials are constituted by a matrix, the resins for instance, and by a reinforcing material, the fibers. These materials have basic different characteristics but their union in a single final product enhances and compensates the respective properties by ensuring higher performance and by well extending the main application. Kimia, for example, uses composite since the early '80s and their usage has exploded over the past decade, riding on the recent trend of the market to favor the recovery of the existing heritage.
What are their main advantages of the traditional techniques in the building industry?
Precisely in the structural strengthening field emerge many advantages of the composites with respect to more traditional techniques. Firstly, the high tensile strength due to thickness and specific weight. This, allows to make bandages with very low thicknesses able to ensure minimal variations with regard to the original size of the products. Furthermore, when increasing the modified resistances, those composites are so much lighter than the traditional interventions, without significantly increasing the design loads. Moreover, in case of historical heritage interventions, perhaps restricted, those composites provide excellent reversibility features. This means that you can let the articfact return to the same antecedent existing conditions, with relative ease. Designers appreciate a lot the versatility and adaptability offered by composite materials in the strenghtening project.
The marks that characterize composites systems in building are many and is not easy to well understand them for a layman. Let's start with FRP systems: at what are we referring to?
The fiber-reinforced composite materials in polymer matrix are precisely those FRP (Fiber Reinforced Polymers). They consist of glass, carbon or aramid fibers with tape or mesh or pultruded rigid elements geometries, which are glued to the structure to be reinforced and impregnated with an organic matrix, usually an epoxy resin. Today, are widely used in the recovery field of the existing for strenghtening of masonry, reinforced concrete and wood structural and non-structural elements. They are particularly suitable, for instance, to plate inflexed elements, to shear-reinforce beams and partition wall, confine pillars and, in general, make reinforcement circle buildings.
SRG systems instead, on what they differ?
In SRG (Steel Reinforced Grout) system as our Kimisteel, what change, compared to FRP, are both elements: the fibers in anti corrosion stainless steel and the bonding matrix, no longer resinous but inorganic. A mortar, put simply. The use of steel, resistant to cutting, opens new design development enabling possible anchoring and pretensioning so as to realize structural reinforcements that play an active role (not only passive), since the application. The mortar also provides increased resistance to high temperatures than the resins and generally allows the support to breathe better.
Finally, we hear more and more talk about FRCM ... what is it?
Structural reinforcement systems FRCM (Fiber Reinforced Cementitious Matrix) derived from the coupling of a carbon fiber or glass mesh with an inorganic cement matrix. The FRCM fibers are meshes of different steps and weights with fabric rather wide to allow the perfect encapsulation of the mortar. FRCM has been the technology that has recently supplanted the traditional plasters reinforced with metallic mesh. Indeed FRCM systems have been shown to have numerous technical and applicative advantages in their favor such as the handling and the on-site workability on yard or the ray permeability with regards to the mesh as well as the possibility of application of reinforcing mesh with matrices based on natural hydraulic lime, which has good compatibility with existing masonries. In this sense, their spread, especially in the restoration field after-earthquake, has been remarkable. They are used for reinforced plasters, restoration of shrinkage cracks through (by applying them on two sides) and non-through (applying on only one side), or for the perimeter connection of claddings and internal partitions to pillars and beams emerging and not.
Could you give us some intervention examples with composite materials?
I have different interventions in mind. If I think about Assisi, for example, I think about Sala Norsa in where, between 1990 and 1991 has been runned a strenghtening intervention using resins and fiberglass fabrics. Well, the Sala, unlike many adjacent buildings, has stood up well to the devastating effects of the dated 1997 Umbria-Marche earthquake. The excellent behavior of both reinforced concrete and masonry structures as a result of the reinforcement is undeniable.
What are the typical requests of both designers and applicators using composite materials?
Designers and companies, obviously in a different way, ask for a support by the company in the proper use of materials during design and application steps. For designers, support is not often connected to design itself, but also to earlier stages (diagnostic) and successive ones as procedures of acceptance and testing of materials on site. Obviously it begins strategic and fundamental for a company to be able to provide not only materials and technologies of certified quality and effectiveness, but also that additional service that can make the difference in getting the end result. In this sense, the over 30 years of experience in the development and use of composites in construction field surely put us in an advantageous situation compared to many other companies.
What do you expect in the future of composite materials in building industry?
As said, to this day composite materials have had a significant impact on the recovery of the existing building heritage and with regards to coming years, I believe the trend will not change. Strenghtening systems with carbon, stainless and other composites take advantage of factors that still make the difference such as speed and cost-effectiveness in the implementation since are not specifically required shorings up nor tilings. But future prospects are many. Recently, our company has introduced the anchoring system on carbon Kimitech FRP-LOCK, which allows to overcome some limitations in FRP traditional use. In this sense, has been emblematic the intervention performed for Michelangelo's Pietà Rondanini: a monolithic block made of composite carbon performed by Kimia, glued with resin to the statue basement in order to ensure the anchoring to the anti-seismic basement.
Thanking Eng. Stefano Agnetti for collaborating, we conclude with a summarizing table showing the main composite materials and their main characteristics. For more questions and supports, we invite you to use our Facebook and Linkedin pages or write to: info@kimia.it.
| FRP | SRG / SRP | FRCM | |
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| Fibers | Carbon / Glass / Aramid | Steel | Carbon/ Glass |
| Matrix | Organic: Epoxy resins of different characteristics and viscosity. | Inorganic (SRG): Cement mortars or other. Organic (SRP): Epoxy resins of different characteristics and viscosity. |
Inorganic: Cement mortars and mortars based on natural hydraulic lime. |
| Applications | Strenghtening of structural elements in reinforced concrete, masonry and wood. | Structural reinforcement of masonry elements, reinforced concrete and prestressed reinforced concrete. |
No structural reinforcement for the solidification of claddings and partitions to reinforced concrete structure Realization of reinforced plasters. |
| Examples |
Reinforcement of inflexed elements Shear strengthening of beams and partition walls Confinement of pillars and reinforcement circle buildings Strenghtening of vaults, beams and joists. |
Construction of reinforced edge beams Strenghtening of vaults, beams and joists. Strenghtening of concret precast elements with weak reinforcement and armed bricks. |
Double reinforced plasters or on single-sided. Restoration of cracks saved and not-saved on masonry piers. Perimeter binding of claddings and interior partitions to columns and beams emerging and not. |
| Benefits |
High mechanical strengthness with reduced weight and thickness. Speed of placing even on emergency works. Reduced invasiveness and good reversibility. Great adaptability and versatility in design stage. |
Resistant to cutting, opens up new design and applicative possibilities. Possibility of pretensioning so as to constitute an active reinforcement and not just reactive. Good permeability to vapour and fire resistance when used with mortar. Speed and ease of placing. |
Better handling and lightness in construction yard compared to traditional welded wire mesh.. Compatibility with supports in concrete and masonry.. Radiotransparency. |
| Kimia cycles |
Matrices: Kimitech EP-TX / Kimitech EP-IN / Kimitech EP-IN/50 / Kimitech CMP / Kimitech TX311. Fibers: Kimitech CB / Kimitech VR / Kimitech PLATE / Kimitech TONDO CB / Kimitech TONDO VR. Anti-delamination solution: Kimitech FRP-LOCK. |
Matrices (SRG): Kimisteel LM. Matrices (SRP): Kimitech EP-TX / Kimitech TX311. Fibers: Kimisteel INOX. |
Matrices: Tectoria M10-M15 / Betonfix AQM GG / Kimisteel LM. Fibers: Kimitech WALLMESH / Kimitech ST160R / Kimitech 550 / Kimitech 500. |