What is the FRG System?
FRG System is a complete range of composites which, unlike traditional FRP, uses an inorganic, pozzolanic mortar rather than a polymer matrix to guarantee excellent chemical-physical and elasto-mechanical compatibility with masonry substrates (stone, bricks and tuff). They are used for the repair or static and seismic upgrading of all types of concrete and masonry structures.
The term FRG stands for “Fibre Reinforced Grout”. FRG’s are made from strengthening fibres set in an inorganic matrix. These types of material offer a series of advantages, including when used on buildings of historical or artistic interest, such as:
– high mechanical strength;
– low architectonic impact;
– high durability;
– ease of application;
The application of this type of material overcomes the problem of the inherently low tensile and shear strength of masonry and increases the overall ductility of structures. This innovative, technologically advanced consolidating system is used in this sector through a series of inorganic matrix composites consisting of glass or basalt fibre mesh with a square weave applied to structures using highly ductile, two-component, ready-mixed cementitious mortar. For listed buildings strengthening materials must have specific characteristics, so the choice of strengthening materials and techniques that may be employed is limited. We have to consider, for example, how strengthening work using cementitious-based products would be both historically and chemically incompatible with the lime-based materials originally used. This is why recent technology implemented by employing composite materials consisting of the combination of a structure of high strength fibres with a matrix of lime and Eco-pozzolan based mortar.
Advantages of FRG
There are numerous advantages deriving from the use of products from the FRG System compared with traditional repair techniques, and the most significant are as follows:
- simple, quick application: thanks to their low weight, they do not require special equipment or lifting gear to install them, only a small workforce is required to install the materials in a very short space of time and, in many cases, it is not even necessary to interrupt the normal activities of the structure itself;
- highly durable;
- unlike repair work by cladding with steel plates (the beton-plaqué technique), there is no problem of corrosion of the strengthening materials applied;
- no increase of the mass involved: installation using FRG System does not increase the overall mass of the structural members that have been strengthened. This is extremely important, particularly in the field of seismic upgrading, where the stresses are proportional to the mass involved;
- installations are completely reversible: installations using the FRG System are completely reversible, in that the strengthening materials and layers of adhesive may be completely removed and the structure returned to the same condition as before the installation. This characteristic is particularly important when carrying out work to make buildings temporarily safe, especially those of historical interest.
Types of intervention using FRG
Inorganic matrix composites may be used for the following:
- structural strengthening of facing walls, applied on the internal and/or external face;
- strengthened reinforcement for both concrete and masonry members to distribute stresses induced by seismic activity more uniformly;
- strengthened reinforcement and attachment points to hold load-bearing walls together correctly and more solidly to structures with a reinforced concrete framework.
Reference norms and standards
Design work incorporating the use of FRP’s is not covered by specific standards according to NTC 08 (the Italian Construction Standards Guide), although Chapter 8.6 of the guide does imply the use of “non-conventional materials with the premise that they comply with the standards and currently valid documents listed in Chapter 12” for interventions on existing constructions.
NTC 08 chapter 12: “With regard to those conditions not expressly specified in this guide, the indications contained within the following documents are to be considered valid in satisfying the principles on which this guide is based:
- Structural Eurocodes issued by CEN, the European Committee for Standardisation, with the clarifications and indications in the relative National Annexes or, in their absence, in the applicable international EN;
- Harmonised UNI EN Standards published in the Official Journal of the European Union;
- Testing, materials and product standards issued by UNI (the Italian Organisation for Standardisation).
Where specific indications do not exist, the following documents may be considered valid and used to integrate current norms and standards as long as they are not contradictory to such norms and standards:
- Instructions issued by the Board of Public Works;
- Guidelines issued by the Central Technical Services Department of the Board of Public Works;
- Guidelines for the evaluation and reduction of risk to the cultural heritage due to seismic activity and successive modifications and addendums issued by the Ministry of Cultural Heritage and Affairs, as granted by the Board of Public Works;
- Technical instructions and documents issued by the CNR (the Italian National Research Centre).”
The current reference norms actually applied in Italy for the design of strengthening installations with composites are contained in the document approved by the CNR DT 200/2004: “Instructions for the Design, Execution and Control of Static Consolidation Installations using Fibre Reinforced Composites” and “Guidelines for the Design, Execution and Testing of Structural Strengthening Interventions on Reinforced Concrete, Pre-stressed Reinforced Concrete and Masonry using FRP”, a document approved on the 24th of July 2009 by the General Assembly of the Board of Public Works.
The instructions contained in CNR-DT 200/2004 and the Guidelines approved on the 24th of July 2009, written by combining the knowledge and experience of manufacturers, users (designers and construction companies) and experts from universities and professional bodies, meet the country’s need to understand and standardise this topic, and provide an organic reference standard for the design of reinforced concrete and masonry members and structures strengthened with FRP, with an approach to overall safety in line with Eurocode standards.