Subject matter

Composite materials are widely used to strengthen and repair masonry structures (buildings, bridges, towers) and structural components (walls, arches and vaults, piers and columns). FRP (Fibre-Reinforced Polymer) has been adopted in the past to realize externally bonded reinforcement systems, but other types of composites are now available. In the case of masonry buildings the use of composites with inorganic matrix is recently receiving great attention since, despite a lower bonding strength, presents numerous advantages in terms of permeability, fire resistance, simplicity of application, cost, time of execution.

Numerous innovative products have been developed (bars, strips, laminates, sheets, grids) and various materials have been proposed such as high tensile steel wires (also known as SRP/G – Steel Reinforced Polymer/Grout), glass, basalt. Also, natural textiles such as flax and hemp are currently under study.

Even if the interest towards these topics is increasing, as it is demonstrated by the growth of the scientific production and the development of new technologies, exhaustive design instructions, assessment procedures to verify the effectiveness of the repair, monitoring programmes and inspection criteria still need to be fully defined. As a consequence, currently available standard codes (ACI 440 7R-10, CNR-DT 200 R1/2012) do not provide practising engineers for comprehensive instructions for the strengthening design, in particular for what concerns application procedures, quality assurance of the materials, durability verification, laboratory and field testing methodologies, check of the laying quality and the effectiveness of the installation, which is instead crucial for the success of the repair/strengthening work.

When the reinforcement of historic constructions is faced, the sustainability of the materials plays a fundamental role in the perspective of the preservation, valorisation and extension of the expected life of the architectural and cultural heritage, within reasonable economical and environmental efforts. Both the compatibility with masonry support and the durability need to be ensured. Accurate studies on this field, however, are still lacking and this topic appears one of the most attractive challenges to be undertaken by the scientific community in the next future.

The work of the present TC aims at getting into this complex scenario, following the research activities carried out within a previous RILEM research project (TC223 - Masonry Strengthening with Composite materials - MSC). Relevant steps forward will be done, mainly focussing on the sustainability and compatibility of the materials when applied on the architectural built heritage. To this purpose, the application with of inorganic matrices and the use of natural textiles in addition to carbon, steel, glass and basalt, will be investigated as they offer good performance in terms of durability, fire resistance, material compatibility, reversibility, transpirability, application simplicity.

The work will focus on the following topics:

1. Collection of existing data and widening of a systemized state-of-the-art on externally bonded mortar-based composites including the various strengthening materials and techniques and their application for the structural repair and retrofitting of masonry constructions, under both static and seismic loads.

2. Experimental and numerical activities on the use of composite materials with inorganic matrixes: investigation of mechanical properties and development of testing procedures. Sustainable composite materials will be investigated that ensure a compatibility with masonry. Natural textiles such as flax and hemp together with classical glass, basalt, carbon and steel fabric will be studied.

3. Development of techniques for the sustainable strengthening of the architectural heritage. Sustainability will be pursued in terms of environmental and economical impact of the materials adopted in the strengthening, durability, reversibility, interaction with decorative settings, upgrade of existing constructions by repair rather than substitution.

4. Proposal of guidelines for testing and designing externally bonded mortar-based systems for the strengthening of existing masonry constructions.

5. Dissemination of results and interaction between multidisciplinary competences from academia, institutions, producers, contractors and practising engineers.

In terms of work organization, the collaboration among institutions (Universities, Public Bodies, Research Agencies), service providers and users will contribute to promote and consolidate a more qualified and conscious approach towards existing masonry constructions, to be also diffused during the following dissemination and exploitation phase.

The FRP subject in the ambit of RILEM is already present for concrete structures. The large contexts of possible applications on masonry developed in the last decade at international level and the issues related to the compatibility and the sustainability of the use of composites on the architectural heritage, may well justify a group working in this field, following the activities undertaken by the previous research project (TC223- MSC).

The proposed TC will clarify the general problems on the basis of current experiences and will also point out possible developments and in-depth studies on specific problems (e.g., durability, sustainability, performance of particular components, bridges, field testing, use of NDT – Non Destructive Test, fire resistance, seismic retrofitting) which may promote activities of further TCs focussed on these topics.

Terms of reference

The TC is proposed to work for 4 years, planning regular meetings (two per year) and additional opportunities to exchange knowledge (seminars, symposia), possibly in conjunction with the activities of the RILEM Weeks.

The committee will start as a relatively small group of experts, well representing most of the main international centres working on the subject, with collaborative and fruitful purposes. Members will be recruited from international academic and research institutions, other RILEM TCs members working on masonry, standardization groups, Cultural Heritage administration and management, service providers and individual connections.

Detailed working programme

The work of the present TC is organized in five Work Packages (WP):

WP 1. State-of-the-Art:

Starting from the work carried out by the previous TC (TC223- MSC), the knowledge of the state-of-the-art on the use of mortar-based composite materials for the strengthening of masonry constructions will be extended. Recently developedmaterials and techniques such as natural fibres will be included. Experimental results and analytical/numerical design methods will be collected together with examples of application in the field and case studies. The global behaviour of the whole construction under static and seismic loads, as well as the structural response of structural components (walls, arches and vaults, piers and columns) will be treated. Local phenomena will also be deepened such as the bonding performance. The main feasibility problems of the execution on different masonry types (regular or irregular arrangement of blocks, uneven superficial finishing, level of porosity of the masonry units) will also be faced.

A particular attention will be paid on historical constructions to underline the specific aspects related to their preservation. A work on current standard codes will be also included and a significant contribution to their evolution and innovation is expected. Their reliability will be verified and any discordances indentified, to define shared and unified terminology, parameter definition, basic design, inspection and monitoring criteria, standardized methodologies for laboratory and filed testing.

WP 2. Experimental activity:

2a. Experimental investigation:

An experimental series of Round-Robin Tests (RRT) will be undertaken to investigate the bonding performance of composite materials with organic matrixes on masonry support. Steel, carbon, basalt and glass fibres will be used together with natural materials such as linen and hemp. Debonding tests will be carried out on different supports (brick, brick masonry, tuff masonry) to develop a deeper knowledge on material properties, local phenomena at the interface, effective anchorage lengths. The performance of the bond between reinforcement and support as well as that within the reinforcement itself, will be tested and assessed carefully. The latter, in particular, is expected to be crucial when dealing with inorganic matrixes, since sliding between fibres and mortar may occur within the strengthening pack.

The preparation of the support preliminary to the application of the strengthening layer will be deepened as it is crucial when working on irregular surfaces like masonry. To this purpose, the possibility of  applying a layer of another flexible material between the support and the reinforcement will be investigated, which is expected to provide a smoother transmission of shear stresses and, hence, a longer effective bonding length. Finally, the repair of masonry will be faced. Specimens already tested in the laboratory unstrengthened, will be repaired and strengthened and then tested again to investigate the improvement provided.

Field testing will also be carried out to start developing techniques for the quality assurance of the materials and the assessment of the strengthening effectiveness. Debonding and detachment test methods will be optimized. The problems of durability and reversibility will also be studied within specifically planned test series (DUR) as they are expected to play a crucial role in the application on the cultural built heritage and when mortar-based matrix are used especially if the fibres are made of steel.

WP 3. Sustainable design methods:

The parameters necessary to calibrate reliable models, that are suitable to represent the structural behaviour at both local and global level, will be identified. Adequate design tools, quantitative and qualitative evaluation measures, limitation parameters of efficiency and simplified analysis methods will be defined. Particular care will be dedicated to sustainability and compatibility issues to develop efficient methods to strengthen historic masonry constructions in the perspective of their preservation and valorisation, as well as to their repair and seismic retrofitting. Life-cycle analysis will be carried out as well, in order to assess the environmental impact of alternative strengthening techniques.

WP 4. Proposal of recommendations:

The reliability of currently available standards (such as CNR-DT 200 R1/2012 and ACI 440 7R-10) will be verified and updated instructions for a sustainable strengthening design will be proposed. The previous TC223 – MSC, as a consequence of the variability of strengthening systems and masonry supports, delegate the present follow-up TC to succeed in formulating a comprehensive proposal of international recommendations. Therefore, the present TC aims at prosecuting the work already undertaken in the recent past and developing updated guidelines for testing and designing externally bonded mortar-based systems for the strengthening of existing masonry constructions. Criteria of preservation of the historical structures (compatibility with the substrate, sustainability, reversibility) and sustainability of the strengthening techniques will be pursued.

WP 5. Dissemination of knowledge:

Dissemination of results will be performed by seminars to be organized in educational and professional institutions. Discussion workshops will be planned to be open to users, industrial and professional people and service providers. Training courses will be also provided to practising engineers, PhD students and young researchers.