Structural Analysis of Historic Construction – D’Ayala & Fodde (eds)© 2008 Taylor & Francis Group, London, ISBN 978-0-415-46872-5

Consolidation and reinforcement of stone walls using areinforced repointing grid

A. Borri, M. Corradi & E. SperanziniDepartment of Civil and Environmental Engineering, School of Engineering, University of Perugia,Perugia, Italy

A. GiannantoniServizi di Ingegneria srl, S. Eraclio di Foligno (PG), Italy

ABSTRACT: A new technique for reinforcing rubble stone masonry walls (double and triple-leaf walls), whenit is required to keep the fair-face masonry. The reinforcement technique consists of a continuous mesh madeof tiny steel cords embedded perfectly in the mortar joints after a first repointing, and anchored to the wall bymeans of galvanized steel eyebolts driven into the facing. A second repointing covers the cords and the heads ofthe eyebolts completely. This leads to genuine reinforced fair-face masonry in which, as already confirmed bythe first experiments, the compression, shear and flexural strength are increased, effective transverse connectionbetween the facings of the masonry due to the presence of the eyebolts and also the capacity to withstand tensilestresses. The reinforcement is non-invasive and reversible, and is aimed at integrating the masonry rather thantransforming it. It is compatible with preservation of the material of which the artefact is made and is long-lastingin view of the materials used, which are very resistant to aggression.The analysis of this reinforcement/upgradingwork has led to the formulation of practical criteria for sizing the reinforcement and to the assessment of thestrength of the reinforced panel.

1 INTRODUCTION

The consolidation and strengthening of verticalmasonry elements of masonry buildings that are sub-jected not only to their own weight but also to possibledynamic stresses (seismic events, wind), constituteone of the most important reinforcement works forachieving an adequate level of safety.

This is because poor quality referred to the mechan-ical features of the masonry (compressive strength,shear strength, etc.), in particular in ancient buildings,has often been the cause of collapsing or of seri-ous damage, for example (although not only) duringseismic events.

Another element that has a particular impacton the seismic behaviour of a masonry construc-tion is the connection between vertical walls andbetween these and the horizontal elements. If theseconnections are present and effective, they can allowthe construction to respond adequately, in the formof “box-like” behaviour, to dynamic stress, withoutlosing the balance of single portions.

In the absence of these connections, each single ele-ment (a wall, floor slab, etc.) will be more vulnerable,since it will be free to collapse separately from the restof the construction.

Various different techniques are used currently toreinforce masonry constructions.Among the works forstrengthening wall panels it is possible to recall herethe following:

A) works for restoring the internal continuity ofmasonry which has developed cracks, such as localrebuilding operations on the masonry or insertionsof metal bars.

B) works connecting the various masonry elements toone another, in addition to the “sewing” mentionedabove. It is possible to mention here circling withstrips of composite material (FRP: Fiber Rein-forced Polymers, based on carbon fibre, glass fibreor other materials), which is particularly effectiveand not very invasive. A negative aspect is the factthat the reinforcement remains visible, so that it isnot very suitable for fair-face walls.

C) works aimed at reinforcing the masonry. Here it ispossible to mention:C1) injection into the masonry of mixtures (typi-

cally cement or lime-based grouts), having thepurpose of filling the empty spaces inside thewall panels, and also of replacing the origi-nal mortar, which is often not very solid. Thistechnique, however, is not very effective in the

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case of walls with a low index of voids (whichis a fairly frequent occurrence). Also, it is noteasy to investigate the actual spreading of themortar injected into the panel.

C2) ferro-cement, consisting of making two thinreinforced concrete walls connected to oneanother by means of metal connectors. Thistechnique is often used to reinforce irregularor poor-quality masonrywork and is undoubt-edly very effective from the mechanical pointof view, however it is very invasive. The inter-nal masonry is “lost” from every point of view,not only because it is no longer visible butabove all since it is subject in time to rapiddeterioration. Another negative aspect is thatthe new wall panel is far stiffer than the orig-inal one (and this often has a negative impacton the structural behaviour of the building).

C3) Another technique used is that of deeprepointing of the mortar joints.This consists ofstripping the joints in the masonry by removingthe original poor-quality mortar for a depth ofseveral centimetres (typically 6 to 8 centime-tres) and then repointing the joints with a goodquality mortar. If this rienforcement is carriedout on both sides of the wall facing and thefacing is not very thick, it has a good degreeof effectiveness.

If the masonry is made of bricks, it isalso possible to insert small metal bars intothe joints (reinforced repointing). These canincrease the strength of the panel considerably.It is clear, however, that even minor irregular-ities in the fabric of the wall will lead to theneed to cut the bricks, which is out of keep-ing with the principles of preservation of oldbuildings.

In the case of irregular masonry (stones ofdifferent shapes and sizes giving rise to irreg-ularly shaped joints) reinforced repointing isnot suitable, since even if the diameter of thereinforcement rods is small, the rods cannotfollow the irregular shapes of the joints.

C4) Another recently suggested technique con-sists basically of a system of tie-rods leadingout in the three orthogonal directions (CAMsystem – Dolce et al.). The tie-rods can alsobe tensioned. This technique is definitely veryeffective in mechanical terms and improvesthe monolithic quality and the mechanicalbehaviour of the body of the wall, howeverit cannot often be proposed for old buildings,since it has a strong impact on preservation ofthe old material.

The main aim of the technique suggested in thispaper is to eliminate or at least reduce the problemsreferred to above.

The system proposed can be used both at locallevel, that is to say for single walls of existing build-ings (and also for boundary walls such as, by way ofexample, town walls), and at global level, that is tosay as a system for reinforcing a masonry construc-tion in its overall behaviour, with particular but notsole reference to behaviour during seismic events.

The system can be used to treat masonry, whetherregular or irregular, without causing the impact andwithout the invasiveness of other techniques. It istherefore particularly suitable for fair-face walls ofbuildings listed due to their historical and architecturalfeatures.

The improvements that can be achieved do notconsist simply of improvement of the mechanical char-acteristics of the wall treated in this way. Indeed, inaddition to strengthening the wall panel, the “rein-forced skeleton” of the continuous mesh introducedinto the wall (and which has been given the nameof “Reticolatus”) also connects the contiguous wallelements to one another (adjacent orthogonal walls,horizontal elements, foundations, etc), thus forminga genuine system for reinforcing the whole masonrybuilding.

The small size of the reinforcing elements and theease with which they can be fitted into the mortar jointsalso enables widespread use, thus avoiding harmfuland dangerous concentrations of stress, such as thosethat occur, for example, when metal rods are used.

2 DESCRIPTION OF THE SYSTEM

To sum up, the system consists of a continuous meshmade of tiny cords made of high strength steel, insertedperfectly into the mortar joints and thus embeddedin the wall in a natural way (that is to say withoutintervening on the stone parts).

This reinforcing technique can be used equally onregularly shaped walls (made of bricks or workedstone blocks) or irregular (rubble and barely cut stone)walls (multi leaf walls). It is in any case in the lattercase that it is often more necessary to improve themechanical properties of the wall, making this tech-nique more interesting.This is because the possibilitiesprovided by other current techniques (repointing with-out reinforcements or grout injection into walls thatare unsuitable since they are very compact) may notbe very effective or may be invasive and thereforeunacceptable from the point of view of preservation(ferro-cement).

The system is based on the use of materials easy tofind on the market even if commonly used for otherpurposes, that is to say:

a) High strength steel cords, which can be made fromcoils to be found on the market. The coils are about30 cm wide (Fig. 1) and variable in length from15 m up to 1500 m, and consist of a series of cords

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Figure 1. Coil of high strength steel cords.

Figure 2. (a) 3X2 cord , (b) 3SX cord.

Figure 3. Close-up showing the hooking of steel eyebolts.

arranged parallel to one another (Fig. 2) and heldtogether by a polyester mesh.

It is easy to pull the steel cords out from thestrip so as to use them separately for the applicationsuggested here. It is also possible, in any case, touse other materials, such as composite materials(cables or cords), provided it is possible to use acement or lime-based mortar as a matrix.

b) galvanized steel “eyebolts” (Fig. 3), also availableon the market, normally used in mountaineering forproviding a grip in rock faces. Basically, these arepointed rods that can be driven into the facing, withhooks or rings on their ends through which cablescan be passed.

As an alternative, it is also possible to use smallgalvanized steel rods with threaded ends enabling the

Figure 4. Close-up of hooking system of threaded bars withwashers and nuts.

Figure 5. Reciprocal confinement of the “stone-mortar-cord system.

cord to be held in place by means of a metal washerand a locking nut (Fig. 4).

The most interesting property of the cords used inthe proposed system is the fact that the very smallsize of the cords (typical average diameter 1 mm) andtheir shape, formed by wrapping the single steel fil-ament around each other helically (typically 3 or 4filaments) give rise to high bonding and compatibilitybetween the cords and the mortar surrounding them.This ensures excellent mechanical behaviour of the“stone-mortar-cord” assembly. What is more, becausethe cords are so small, they can easily be bent intoshape as required in order to pass them through thejoints between the various pieces of stone forming thewall (Fig. 5). Cords made of composite material havesimilar characteristics.

The eyebolts or threaded rods have two purposes: onthe one hand they provide “fixed points” for anchoringthe cords in the wall facing, on the other they createconnections between the two sides of the wall, thushelping it to behave as a monolith.

The procedure for reinforcing a single wall panelusing the system suggested here is carried out in thefollowing stages:

• strip the mortar joints for a depth of 6–8 cm;• wash the stripped joints;• repoint with mortar (cement or lime-based mortar);

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• insert the eyebolts or the rods, typically 4 per squaremetre, arranged as regularly as possible accordingto a square mesh and driving them in far enough toinvolve the opposite facing, leaving the head belowthe surface on which the work is being carried out(at a depth of at least 3–4 cm);

• insert the cords into the stripped joints, passing themtrough the hooks of the eyebolts or behind the wash-ers of the rods, proceeding in a horizontal or verticaldirection all over the facing being treated. If thelength of the single cords is insufficient, they canbe joined together with resin or, simply, overlappedagainst each other for a length of about 20 cm;

• if considered necessary to further increase thestrength of the panel it is possible to apply addi-tional cords diagonally, both in one direction and inthe other;

• repoint the joints again with mortar, so as to coverup completely both the cords and the heads of theeyebolts or of the rods.

Upon completing the operations described above,a grid-like pattern (irregularly shaped) made of metalor of composite material will have been obtained. Itwill be perfectly incorporated into the wall facing butnot visible from outside, and capable of giving thepanel the mechanical characteristics (shear strength,tensile strength and compression strength) it needs towithstand both static and dynamic stresses.

To understand the effectiveness of this treatment, itis possible to compare it with the ferro-cement tech-nique. The end result of this technique is to confinethe masonry between two new thin reinforced concretewalls (the two layers of plaster consisting of cementmortar, reinforced with metal netting, on the two sidesof the masonry and connected to one another).With thetechnique suggested here, the result is absolutely com-parable in terms of effectiveness but the original facingremains visible and perfectly intact, and its ability totranspire remains unaffected. Indeed, here again thereare two new resisting walls (several centimetres thick)connected to one another that enclose the masonrybetween them (Fig. 6), but these are actually the origi-nal external facings which have become genuine layersof reinforced masonry (reinforced wall facings) thanksto the grid of metal cords inserted “discreetly” butintimately into the joints.

Moreover, in addition to considerably increasing thetensile (and shear) strength of the masonry, this gridalso has the beneficial effect of confining the piecesof stone, that are enclosed within the circuits of thecords.

To reinforce the whole masonry construction usingthe proposed system, it is possible to proceed asfollows.

At the ends of the wall panel, the cords can be foldedin so that they also take in the opposite surface side ofthe same panel. In the case of a corner panel, they can

Figure 6. The two reinforced masonry facings enclose theinner masonry work.

Figure 7. Close-up of a corner area.

also be folded over to take in the panel at right-angles(Figs 7–8), thus connecting the vertical elements atright-angles to one another in a particularly effectivemanner (since they create an extensive connection).

As far as concerns the bottom part of the panel (e.g.in the foundations), the cords can be anchored effec-tively by folding them around the pieces of stone atthe bottom of the panel (Figs 7–8) or connecting themto the foundations (if any) by means of connectors, asthe case may be.

At the top, the cords can be connected to the metalor RC tie (if any), or, for example, in boundary townwalls, folded over the coping so that they reach theother side of the wall.

As a result of these operations, each single wall wasreinforced locally, and all the different elements wereconnected to one another, giving rise to a construction

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Figure 8. Folded and anchored cords.

in which the resisting system now consisted of amasonry reinforced to a widespread extent.

To sum up, the system presented here calls for a net-ting structure with flexible sides consisting of the cordsmentioned above, which can be positioned accord-ing to paths corresponding to the joints between theelements of the wall and which can be anchored topre-established points of the latter by means of metaleyebolts or transverse rods. Since the sides of the net-ting are flexible and pass through the hooks or the ringsof the transverse elements without being an actual partof them, it is possible to arrange them precisely alongthe joints (previously stripped) of the elements formingthe masonry, however they are arranged.

3 FIELDS OF APPLICATION ANDEXPECTED BENEFITS

As already mentioned, the proposed technique is suit-able for treating rubble stone walls when, for reasonsof preservation, the fair-face wall is required to beretained and at the same time non-invasive reversibleand effective reinforcement is required. Typically,therefore, some of the structural problems of old build-ings and archaeological assets can be solved in amanner capable of meeting the need for the high-est safety standards combined with the requirementsrelating to protection and preservation.

The proposed technique complies with the princi-ples underlying the protection f historical buildings,since it is:

– “compatible” with preservation of the material ofwhich the building is made, as it is able to adaptand integrate perfectly into the walls;

– “long-lasting”, since the materials used have a highresistance to chemical and physical aggression andto weathering;

– intended to integrate the structure without trans-forming it;

– non-invasive;– reversible (or at least removable);– compliant with the principle of the “least upgrading

work”.

It is easy to identify the possible advantages fromthe mechanical point of view. They concern:

1) improved mechanical characteristics, that is to saycompressive strength and shear strength, and alsoflexural strength in relation to stresses on the sameand at right-angles to the plane of the masonry;

2) the ability to connect extensively any damages, thevertical walls to one another and the vertical wallsto the horizontal elements;

3) giving the masonry the tensile strength that, in thecase of irregular masonry (where the vertical jointsare often aligned) cannot even benefit from the“chain effect” present in regular walls with properlystaggered orthostats and joints;

4) transverse connections between the facings of themasonry, since the eyebolts or the transverse rodsare arranged as artificial stones capable of mak-ing the wall panel act as a monolith. They do thisby contrasting detachment of the facings from oneanother and providing adequate tensile strength(also necessary in the presence of vertical loadsonly and shear strength (necessary in the event ofstresses that tend to make the wall panel tilt over,and therefore to make the facings slide in respectof one another).

4 EARLY EXPERIMENTS

In order to investigate the effectiveness of the rein-forcement technique described above, a series of testswere planned.

After a description of the materials used, the firstresults of the tests are reported on below.

4.1 Fibre characterization

The fibres used during the experiment were suppliedby Hardware LLC. One peculiarity of these materialsis their macroscopic structure. Indeed, all the fibresare made up of high-resistance steel filaments coveredwith a layer of brass to prevent oxidation of the metallicfibres. The specifications of the cords used are shownin Table 1.

4.2 Tests with flat jacks

In the tests with double jacks, portions of walls about50 cm high were subjected to compression on a singlevertical axis.

Masonry walls were tested while subjected to com-pression using two flat jacks (Fig. 9). During the test

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Table 1. 3X2 cord mechanical properties.

Fibre type 3X2 cordCord diameter (mm) 0.89Cross section area (mm2) 0.620Failure tensile load (N) 1539Young’s modulus (E) (MPa) 206842Failure stress (MPa) 2479Elongation at failure (%) 2.1

0

2

4

6

8

10

12

14

0,000 0,002 0,004 0,006 0,008 0,010

Normal strain ε

Ver

tical

str

ess

[kg/

cm2 ]

SRE 05

SRE 04

REP 03

URM 01

REP 02

Figure 9. σ−ε diagram resulting from the tests with doubleflat jacks.

Table 2. Results of the tests with flat jacks.

Max Young’scompression modulus

Reinforcement Index stress (MPa) E1/3(MPa)

Un-reinforced URM 01 0.595 480Deep repointing REP 02 0.807 393Deep repointing REP 03 0.857 512Reinforced repointing SRE 04 1.261 486Reinforced repointing SRE 05 1.312 2416

measurements were recorded the load history, maxi-mum compression stress σmax, and deflections of somepoints using centesimal transducers. An equivalentnormal stiffness E1/3 was then calculated:

where ε1/3is the normal strain corresponding to 33%of the maximum stress σmax reached.

Figure 9 shows the results for the first tests carriedout using double jacks.

On analysing the results, it is possible to statethat deep repointing of the joints, reinforced withmetal fibres, is capable of increasing significantlythe compressive strength σmax of the masonry. Oncomparing these results with those concerning the non-reinforced masonry and those for masonry reinforcedwith repointing alone, increases in the resistance werefound of 116% and 50% respectively (Tab. 2).

As far as concerned the normal modulus of elastic-ity E1/3, the results of the tests with flat jacks showedthat deep repointing of the joints on its own is not capa-ble of causing significant increases of the modulus ofelasticity. This was probably because the mortar usedfor repointing the joints was based on hydraulic lime.

As far as concerns the manner in which the masonryelements between the two flat jacks failed, it was seenthat a series of vertical cracks formed between thetwo flat jacks. Furthermore, there was no substiantialdifferentiation of the type of failure between the un-reinforced masonry (URM), the repointed masonry(REP) and the masonry reinforced with metal fibres(SRE). While in the cases of the unreinforced masonryand of the repointed joints the breakage occurred witha small number of fairly large vertical cracks, in thecase of the masonry repointed with metal fibres alarger number of smaller vertical cracks occurred.Thisindicates an improvement in the mechanical behaviourof the masonry.

The next experiments will investigate the increasesin shear strength and flexural strength. It is plannedto carry out on-site diagonal compression tests on un-reinforced and reinforced panels, and also loading testson panels that will first be reinforced, cut and thentilted over, positioning them horizontally. They willthen be tested up to breaking point by applying verticalloads.

4.3 Shear tests

The diagonal test was performed on site on panels of1200 × 1200 mm dimension with sections of differ-ent thickness and morphology. The load is given byhydraulic jacks.The test is defined byASTM E 519-81Standard. It is possible to calculate the characteristicstrength of the masonry τk through:

where P is the diagonal compressive load generated bythe hydraulic jack and A is the area of the horizontalcross-section of the panel and τu is the ultimate shearstrength.

Furthermore it is possible to calculate the shear stiff-ness G1/2 (secant value of the modulus at 1/2 of thepeak load) defined as:

where γ1/2 is the angular strain at 1/2 maximumload, τ]rmi and γi are respectively the initial shearstress (τi = 0.002 N/mm2) and strain values due to anapplication of a pre-load.

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Table 3. Results of diagonal compression tests.

Shear Shearstrength modulus

Reinforcement Index τk (MPa) G1/2 (MPa)

Un-reinforced DC 01 0.029 541Deep repointing DC 02 0.039 1403Reinforced repointing DC 03 0.063 653

The average thickness of the masonry turned out tobe about 53 cm. The material used was a roughly cutcalcareous stone (double leaf masonry wall). Of thethree panels obtained for the diagonal-compressiontest, the first (DC01) was tested without strengthen-ing, to determine its mechanical characteristics. Theremaining two were consolidated respectively withdeep repointing of mortar joints (DC02), and “Retico-latus” technique (DC03). The panel strengthened withmetal fibers shows an increase in strength τk comparedto the un-strengthened panel, of approximately 117%.The panel reinforced with only deep repoiting of mor-tar joints did not cause an appreciable increase in termsof shear strength τk compared to an un-strengthenedsimilar panel (+34%). This shows the inefficiency ofthis strengthening method for the particular masonrytexture to which it had been applied, especially due tothe high thickness of walls (Tab. 3).

The obtained value of the shear elastic modulus G1/2was equal to 541 MPa for un-strengthened panel, whileit reached 1403 MPa in the case of strengthened panelwith deep repointing.

5 MODELLING AND TESTS

In order to “design” a reinforcement work of a wallpanel with the proposed system, it is thought thatfollowing vertical and horizontal loads the collapsemechanisms may be summarised, basically, as follows:shear, sliding-shear and flexion for actions in the planeand out of the plane of the panel (Fig. 10).

The steel cords were arranged over an extensivearea on both outside surfaces of the panel, contributingtowards reinforcing the masonry in order to withstandthe formation of these collapsing mechanisms. Thiscreates a genuine reinforced wall in which the com-pressive stress is absorbed by the stone wall and thetensile stress by the cords.

To size /check the reinforcement elements, it is pos-sible to use a study of the generic cross-section, apply-ing the hypothesis of a flat cross-section guaranteed bythe monolithic character that the panel acquires follow-ing insertion of the transverse elements, eyebolts andthreaded bars.

Figure 10. Typical failure modes of unreinforced masonrywalls: sliding shear failure (a), shear failure (b), flexural fail-ure following subjecting to in-plane loading and out-of-planeloading (c).

dd-x x

bar

ftd0.85

tt1 t2

M

P

Figure 11. Wall subjected to out-of-plane loading.

5.1 Flexural strength

The proof with combined compressive and bendingstress, for loads both on the plane and out of theplane of the panel, can be conducted as for anyheterogeneous cross-section.

Take a diagram of the compressive stresses of 0.85fmd and extended to the portion of cross-section fora depth of 60 to 80% of the distance of the neutralaxis of the compressed edge up to a maximum limitthat depends on the thickness of the compressed thinwall and on the depth of stripping. On the average, ifthe depth of stripping is 6 to 8 mm, the limit may beestimated at 10–12 mm.

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t1

t2

t

dd-x x

P

M

barycentre of the tensite bars

bar

0.85fmdftd

Figure 12. Wall subjected to in-plane loading.

With regard to flexion due to action out of the planeof the panel, all the bars arranged on the stressed wallcontribute in the same manner to the traction effort(Fig. 11).

In flexion on the plane, the cords in the tensile areareact differently depending on their position (Fig. 12).Their contributions can be calculated concentrating thearea of the re-acting rods in the centre of mass of thetensile bars.

5.2 Shear strength

For the shear check, since the formation of the resist-ing lattice is guaranteed by the presence of the verticalrods, the design resistance is supplied by the sumof the shear strength of the masonry VRd,m plus theshear strength consequent to the tensile strength of thereinforcements VRd,t (CNR-DT 200/2004):

where:

d is the distance between the compressed edge andthe centre of mass of the tensile bars,t is the thickness of the wall reacting to shear,Atw is the area of the cords arranged parallel to theshear action,pt is the main value of the pitch of the bars,fvd and ftd are the design shear resistance of themasonry and the design tensile resistance of thecords respectively,γRd is a coefficient for the resistant model.

The sliding-shear mechanism becomes significantin isolated walls where limited friction resistance isgenerated due to the small axial load. In this mech-anism, the vertical cords have an essential role inthat they prevent sliding along the horizontal mor-tar courses of one part of the masonry in respect ofthe other, when the horizontal thrust has exceeded thefriction resistance along the mortar joint.

The sliding shear strength of the reinforced paneloriginates from the combination of two resisting mech-anisms: the shear transmitted by friction from themasonry VRd,m and the shear consequent to the tensilestrength of the reinforcements VRd,ts.

As an alternative, to carry out a cautious check, thesliding shear strength can be assessed conservativelyusing the following relationship (Tassios 1988):

where:Atw is the area of the cords arranged perpendicular

to the shear action, and fmd is the design compressionresistance of the masory.

6 CONCLUSIONS

The technique suggested for reinforcing masonry isintended mainly for constructions with an irregular(stone double or triple leaf walls) masonry texture,such as stone walls, in order to eliminate or at leastreduce the problems of the techniques adopted forregular walls.

The reinforcement technique consists of inserting acontinuous grid of small high strength steel cords intothe mortar joints. The nodes of the cords are securedby means of metal rods transverse to the wall facing.

The result is that of a reinforced masonry, for whichthere is an increase in compressive, shear and flex-ural strength, and an effective transverse connectionbetween the leaves of the masonry.

The improvement does not concern solely themechanical characteristics of the masonry thus treated,but affects the whole masonry construction, since inaddition to reinforcing the wall panel, the “skeleton”of the continuous grid inside the masonry connectsthe various contiguous masonry walls to one another,thus forming a genuine complete reinforcement sys-tem. Furthermore, the small size of the reinforcementcords and the fact that they are easy to insert into themortar joints makes it possible to apply this treatmenton a widespread basis, that avoids dangerous concen-trations of stress such as those that occur, for example,when using metal rods.

The suggested system can be used both at locallevel, that is to say for single wall panels of exist-ing buildings or also for boundary town walls, and atglobal level, that is to say as a system for reinforcing amasonry construction, improving its overall behaviour.

The upgrading work is not very invasive, isreversible and integrates the masonry rather thanreplacing it. It is compatible with preservation ofthe original material of the building and long-lastingthanks to use of very durable materials and is therefore

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particularly suitable for fair-face walls of buildingslisted due to their historical or architectural value.

The effectiveness of the proposed technique wasinvestigated by means of a series of tests with doubleflat jacks, subjecting the masonry to vertical com-pression and diagonal compression tests (shear tests).Based on the results obtained, it was possible to notean improvement of the mechanical behaviour of themasonry and it was noted that deep repointing of jointswith metal fibres is capable of increasing compressivestrength significantly, even doubling it as comparedwith the non-reinforced masonry.

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