In-situ experimental tests on masonry panels strengthened with Textile Reinforced Mortar composites

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Procedia Structural Structural IntegrityIntegrity Procedia1100(2018) (2016)355–362 000–000

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XIV International Conference on Building Pathology and Constructions Repair – CINPAR 2018 XIV International Conference on Building Pathology and Constructions Repair – CINPAR 2018

In-situ experimental tests on masonry panels strengthened with Textile Reinforced Mortarpanels composites In-situ experimental tests on masonry strengthened with XV Portuguese Conference on Fracture, PCF 2016, 10-12 February 2016, Paço de Arcos, Portugal Textile Reinforced Mortar composites Francesca Giulia Carozzi1*, Tommaso D’Antino1, Carlo Poggi1 Thermo-mechanical ofConstruction a high pressure turbine 1 1 1blade of an Francesca Giuliamodeling Carozzi *, and Tommaso D’Antino , Carlo Poggi Department of Architecture, Built environment engineering ABC. Politecnico di Milano, airplane gas Piazza Leonardo da Vinci turbine 32, 20133, Milanengine (Italy) 1

Department of Architecture, Built environment and Construction engineering ABC. Politecnico di Milano,

1

Abstract a

a da Vinci 32, 20133, Leonardo (Italy) P.Piazza Brandão , V. Infanteb, Milan A.M. Deusc*

Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa,

Abstract Textile Reinforced Mortar (TRM) composites are a retrofitting Portugal techniques used for strengthening masonry structures. The system b IDMEC, Department of Mechanical Engineering, Instituto Superior Técnico, Universidade Lisboa, Av. Rovisco 1, 1049-001 Lisboa, is composed of dry fibers grids embedded in two layers of inorganic matrix. Thedepaper describes thePais, results of an in-situ Portugal Textile Reinforced Mortar (TRM) composites are areinforced retrofittingwith techniques used strengthening masonry structures.inThe system experimental masonry panels differentUniversidade TRMforsystems. The tests were performed a building c CeFEMA, campaign Departmenton of ancient Mechanical Engineering, Instituto Superior Técnico, de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, is composed of dry fibers grids embedded two layers ofofPortugal inorganic matrix.Four Thediagonal paper describes the tests results of performed an in-situ located in Finale Emilia (north of Italy) built atinthe beginning the last century. compressive were experimental campaign on ancient masonry panels reinforced with different TRM systems. The tests were performed in a building on unreinforced and reinforced walls. located in Finale Emilia (northwith of Italy) builtconfigurations: at the beginning of panels the lastwere century. Four diagonal compressive were performed The walls were strengthened different two reinforced with a TRM systemstests composed of a lime onAbstract unreinforced and reinforced walls. mortar and two different types of glass fiber grids and twist steel bars used as anchors; one panel was reinforced with a layer of The walls were strengthened with different configurations: twoonpanels wereone. reinforced with a TRM systems composed of a lime TRM on one side and a Near Surface Mounted (NSM) system the other mortar and two different types of glass fiber grids and twist steel bars used as one paneldemanding wassystems reinforced with layer of During their operation, modern aircraft engine components are subjected to the increasingly operating conditions, The results of the tests are described and a complete mechanical characterizationanchors; of reinforcement and of theamasonry especially pressure turbineMounted (HPT) blades. conditions cause thesemodels. parts to undergo different types of time-dependent TRM on one the side and a Near (NSM) system on the other one. was performed tohigh analyze theSurface experimental results andSuch validate simple analytical degradation, onetests of which is creep.and A model usingmechanical the finite element method (FEM) was developed,systems in orderand to of be the ablemasonry to predict The results of the are described a complete characterization of the reinforcement theperformed creep behaviour HPT blades. Flight a specific aircraft, provided by a commercial aviation was to analyzeofthe experimental resultsdata andrecords validate(FDR) simple for analytical models. company, used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model Copyright © were 2018 Elsevier B.V. All rights reserved. Copyright 2018 B.V. All rights reserved. needed ©for theElsevier FEM analysis, athe HPT blade 2018 scrap organizers was scanned, and its chemical composition and material properties were Peer-review under responsibility of CINPAR Peer-review under responsibility ofgathered the CINPAR 2018 organizers obtained. The data that was was fed into the FEM model and different simulations were run, first with a simplified 3D Copyright © 2018 Elsevier B.V. All rights reserved. rectangularunder blockresponsibility shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The Peer-review of the CINPAR 2018 organizers Keywords: TRM materials, in-situ diagonal tests, masonry overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data. Keywords: TRM materials, in-situ diagonal tests, masonry

© 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of PCF 2016. Keywords: High Pressure Turbine Blade; Creep; Finite Element Method; 3D Model; Simulation.

* Corresponding author. Tel.: 0223995108 E-mail address: [email protected] * Corresponding author. Tel.: 0223995108 E-mail address: 2452-3216 [email protected] © 2018 Elsevier B.V. All rights reserved. Peer-review under responsibility of the CINPAR 2018 organizers. 2452-3216 Copyright © 2018 Elsevier B.V. All rights reserved. Peer-review under responsibility of the218419991. CINPAR 2018 organizers. * Corresponding author. Tel.: +351 E-mail address: [email protected] 2452-3216 © 2016 The Authors. Published by Elsevier B.V.

Peer-review under responsibility of the Scientific Committee of PCF 2016. 2452-3216 Copyright  2018 Elsevier B.V. All rights reserved. Peer-review under responsibility of the CINPAR 2018 organizers 10.1016/j.prostr.2018.11.046

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1. Introduction Historical masonry structures are composed of brittle materials and often present low mechanical properties and damages in the bricks or in the mortar joints. Moreover, these elements present low resistance to seismic events. Different reinforcement techniques were developed and applied on masonry and concrete structures to improve their performance and resistance to seismic events. Composite materials like Fiber Reinforced Polymers (FRP) represent an effective technique that presents many advantages like the high resistance, lightness, speed of execution. In the last decades, different composite systems were developed to retrofit these structures with more compatible and sometimes reversible materials. The more common systems are Textile Reinforced Mortar (TRM), Fabric Reinforced Cementitious Matrix (FRCM) and Steel Reinforced Grout (SRG); they are composed of different fiber textiles (glass, carbon, PBO, steel) applied with lime or cementitious matrices. In the literature a lot of research works are available on the investigation of mechanical and bond properties of this composite systems (Peled et al; 2008), (Contamine et al., 2011), (D’Antino et al., 2014), (Carozzi et al., 2015), (De Santis et al., 2015). These reinforcement systems are mainly used to improve the masonry walls resistance in case of out-of-plane bending (D’Ambrisi et al., 2014), inplane shear stresses (Prota et al., 2006), retrofitting of arches and vaults (Carozzi et al., 2018). The most common test set-up used to investigate the in-plane performance of masonry walls is the diagonal compression. The wall is located on two steel shoes and the load is applied with a jacket on a diagonal (Parisi et al., 2013), (Babaeidarabad et al., 2016), (Menna et al., 2015). The displacements and strains are usually measured on the tensile and compressive diagonals with LVDTs or strain gauges (Marcari et al., 2017). (Almeida et al, 2015) studied also the effect of a cycling loading application to assess the stiffness degradation during each cycle and the progressive failure of the strengthening systems. Few experimental campaigns were performed in-situ. The in-situ tests are obviously more complicated due to the variability of the masonry mechanical properties, the geometry and texture of the walls and to the maintenance status of the structure. In (Borri et al., 2011) a series of experimental diagonal compression tests performed on different masonry panels in Umbria and Abruzzo (central Italy) was described. In the same work the mechanical behavior of a particular masonry type and the effectiveness of reinforcing systems with either traditional or innovative techniques were investigated. In the present paper a series of diagonal compression tests were performed in-situ on panels cut from an ancient masonry structure. One panel was tested without any treatment in order to define the mechanical properties of the masonry, and three samples were reinforced with different TRM systems. The paper describes the mechanical characterization of the reinforcement systems, the in-situ experimental results and the analysis of the performance of these reinforcement systems. 2. Samples geometry and properties The in-situ experimentation was performed on elements cut from an ancient masonry structure (Fig. 1a) located in Finale Emilia (Modena), in the north of Italy. The four panels presented nominal dimensions equal to 1000x1000x300 mm3 and were characterized by the presence of two running bond masonry panels coupled by means of a 10 mm thick vertical layer of mortar. Some diatons were used to enhance the connection between the two masonry leafs. The original component materials were very poor, the mortar joints were irregular and the presence of holes was noted. Moreover, the masonry texture was quite irregular and the bricks presented no constant dimensions (Fig. 1a). Compressive tests were performed to characterize the mechanical properties of the bricks. Cube samples (dimensions 40x40x40 mm3) were extracted from a brick to perform compressive tests. In many cases the internal part of the bricks was characterized by the presence of holes and impurity elements. Despite this, the compressive strength of the undamaged samples was around 40 MPa. Four masonry panels were cut, one was tested without any treatment as “control” and three elements were reinforced with different TRM systems (Table 1). Both the sides of two samples were reinforced with TRM systems composed of two different glass fiber grids (named G-TRM and cG-TRM) and a lime mortar. The third sample was reinforced on one side with TRM system and on the other side with a Near Surface Mounted (NSM) system. The sample preparation is showed in Fig. 1b.



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Table 1 – Samples layout Sample name Reinforcement system DW_control DW_G-TRCM G-TRM + 4 Steel connectors DW_cG-TRM cG-TRM + 4 Steel connectors G-TRM (south side) + 4 Steel connectors + 3 NSM DW_G-TRM-NSM (north side)

a

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Dimensions [mm] 1040 (h) x 990 (w) x 300 (t) 1045 (h) x 1000 (w) x 300 (t) 1040 (h) x 990 (w) x 300 (t) 1010 (h) x 950 (w) x 300 (t)

Fig. 1. (a) Original masonry structure ; (b) Preparation of the reinforced masonry element.

b

3. Reinforcement materials The G-TRM system was composed of a glass fiber textile (Fig. 2a) and a lime mortar. The textile was a balanced grid with fiber yarns disposed in two orthogonal directions at a nominal distance of 20 mm. The cross section area of each yarn was equal to 0.8 mm2. The cG-TRM system was composed of a coating glass textile (Fig. 2b) and the same lime mortar. The unbalanced net presented a Styrene Butadiene Rubber (SBR) coating that provides a resistance to alkaline environments. The free space between yarns was 17x12 mm and the cross-section area of the yarns was 0.90 mm2 and 0.92 mm2 in the warp and weft directions respectively. Both the TRM systems were applied on the whole surface of masonry walls. The total thickness of the two layers of mortar was about 10 mm on each side. The textile was applied in the mid-thickness. Four connectors were located in each wall on the diagonals, at a distance of about 350 mm from the corner. The connectors were helical steel bars with a diameter equal to 9 mm applied without any matrix. The NSM system was constituted by helical steel bars with a diameter equal to 6 mm (Fig. 2c). The bars were located in three mortar joints and immersed in the reinforcement lime mortar.

a

b

Fig. 2. Reinforcement components: a) glass fiber grid; b) coating glass fiber grid; c) NSM bars

c

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Tensile tests were performed on samples composed of a single yarn extracted from the textile [Carozzi et al., 2018], [Carozzi et al, 2015]. The test were carried out using a testing machine with a maximum load capacity of 2 kN. Cardboard tabs were glued at the ends of the specimens to avoid local damage and guarantee a homogeneous stress distribution. In order to avoid a premature failure of the dry glass yarns, the samples were impregnated with a thin layer of epoxy resin. Five tests were performed for each material and the average values and the coefficient of variation are reported in Table 2. The mechanical properties of the lime mortar were investigated according to EN 1015-11 and EN 13412. The average flexural and compressive strength are equal to 3.16 MPa and 7.48 MPa respectively, and the elastic modulus was equal to 6.08 GPa. Table 2 – Reinforcement component mechanical properties Sample Tensile strength [MPa] Glass yarn 1443 (11.4%) Coated glass yarn 1233 (2.7%) (warp direction) Coated glass yarn 1120 (1.7%) (weft direction) Steel bars 1110*

Elastic modulus [GPa] 75.4 (6.2%) 55.6 (30.5%) 60.5 (28.2%) 195*

*From data sheet

4. Tests set-up and instrumentation Two steel shoes were placed on diagonally opposite corners of the wall and connected by two Dywidag bars creating a close-loop system. The walls were loaded diagonally by means of two parallel manual jacks positioned at the top corner on one steel shoe. Two load cells were used to measure the applied loads. Four LVDTs were located on the diagonals of the walls to measure the relative displacements; other two LVDTs were used to measure the displacement imposed by the jacks and control the homogeneous stresses distribution between the two sides of the specimen during the tests. In Fig. 3 and Fig. 4 the test set-up and the localization of the LVDTs are shown.

a

b

Fig. 3. Instrumentation: a)Test set-up ; b) Detail of the steel shoe and jacks



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Fig. 4. Localization of the LVDTs

5. Experimental results The experimental results are reported in Table 3. - 𝐹𝐹𝑚𝑚𝑚𝑚𝑚𝑚 is the maximum load applied on the diagonal, - 𝜏𝜏 represents the maximum shear stress. This value was computed according to ASTM E519-10: 𝜏𝜏 = 0.707

𝐹𝐹𝑚𝑚𝑚𝑚𝑚𝑚 𝐴𝐴𝑛𝑛

Where 𝐴𝐴𝑛𝑛 is the cross section transversal area computed as 𝐴𝐴𝑛𝑛 =

ℎ+𝑤𝑤

- ΔLVDT is the relative displacement recorded by the four LVDTs

2

𝑡𝑡𝑡𝑡 (𝑛𝑛=1).

- The “pseudo-ductility” factor is computed as the ratio between the displacement reached at the peak load and the one reached at the end of the elastic phase. For the control sample and the reinforced with G-TRM and cG-TRM systems the values were computed with the average values recorded by the LVDTs, one parameter for the tension and one for the compression were analyzed. On the contrary it was not possible to evaluate the average value for the GTRM-NSM sample due to the different behavior of the two sides that present different reinforcement systems. For this reason two values are reported for tension and two for compression. Table 3 – Experimental results Sample DW_control DW_G-TRM DW_cG-TRM DW_G-TRM-NSM

𝑭𝑭𝒎𝒎𝒎𝒎𝒎𝒎 [kN]

32.07 113.57 130.59 54.91

𝝉𝝉 [MPa] 0.07 0.26 0.30 0.13

ΔLVDT1 [mm]

ΔLVDT2* [mm]

ΔLVDT3* [mm]

ΔLVDT4 [mm]

4.56 2,43 2.38 0.55

-0.15 -1.13 -1.44 -0.11

-0.37 -1.84 -0.97 -1.29

4.58 2,43 1.77 2.81

Pseudo-ductility factor [-] tension 16.36 31.86 11.05 11.90 / 32.14

compression 2.63 7.27 3.87 4.60 / 1.22

*negative values indicate compression The DW_control wall failed due to diagonal tensile cracking located in the vertical and horizontal mortar joints. 5a shows the load-displacement curves for the four LVDTs up to the maximum load. Two load cycles were applied, the first one in the elastic phase, at a load equal to 15 kN, the second one after the appearance of the tensile diagonal and to 0.2 mm in the compressive one. After the re-load cycle, there is an important cracking phase that reached a displacement in the tensile diagonal equal to 4.5 mm in correspondence of the maximum load. The cracks opening at the peak load generated a vertical drop in the load, with a residual displacement of about 4.3 mm. The load increased

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again up to 32 kN and a maximum displacement of 7.5 mm was reached before the complete collapse. Fig. 5b shows the load-displacement curves for the reinforced samples up to the peak load, to compare the behavior in the first phases, the end of the elastic phase and the non-linear increment of the load up to the maximum one. In Fig. 5c the comparison between all the results is reported. The applications of G-TRM and cG-TRM systems provide a higher peak load, equal to 3.5 and 4 times the one of the control specimen respectively. The G-TRM sample presented a limit of the elastic phase at a load equal to 90.7 kN and a non-linear phase characterized by the appearance of the first cracks up to the maximum load. The decreasing phase is caused by the opening of the main diagonal cracks, with the slippage and rupture of the filaments in the glass yarns. The cG-TRM sample showed a similar behavior, even if the non-linear increasing phase presented a higher stiffness. During the cracking phases the displacement reached values of about 5 mm, after that the sample collapsed due to the opening of a main crack and the tensile failure of the fiber grid. The GTRM-NSM wall reached a maximum load equal to 1.7 times the un-reinforced one. The load-displacement curves showed the different behavior with respect to the two faces that present two different reinforcement systems. The side reinforced with the G-TRM material presented an elastic phase with higher stiffness and reached a lower displacement at the peak load both in the tensile and compressive diagonals. The side reinforced with the Near Surface Mounted system failed to the diagonal crack of the vertical and horizontal mortar joints. In Fig. 6 the failure modes are represented.

a

b

c

Fig. 5. Load-Displacement curves: a) DW_control sample; b) DW_cG-TRM, DW_G-TRM, DW_G-TRM-NSM (up to peak load); c) comparison between the four samples



Francesca Giulia Carozzi et al. / Procedia Structural Integrity 11 (2018) 355–362 F.G. Carozzi et al./ Structural Integrity Procedia 00 (2018) 000–000

DW_control

DW_cG-TRM

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DW_G-TRM

Fig. 6. Failure modes

DW_G-TRM-NSM

6. Conclusions The paper presented the analysis of the performance of masonry panels cut from an ancient masonry structure. One panel was tested without treatments to investigate the masonry mechanical properties; the other three samples were strengthened with TRM systems with different glass fiber grids and a Near Surface Mounted (NSM) system. The mechanical properties of the reinforcement components were investigated. The results of this characterization are useful to calibrate the mechanical properties involved in analytical and numerical simulations that cannot be described in this paper.

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The reinforcement materials were very efficient since the maximum load reached on the unreinforced panel was increased by 3.5 and 4 times by the contribution of G-TRM and cG-TRM systems respectively. After the end of the elastic phase the reinforced structures were able to further increase the load and, in the case of cG-TRM, to carry a high load constant for larger displacement values. The panel reinforced with G-TRM-NSM reached a maximum load equal to 1.7 times the un-reinforced one. The panel presents a different behavior in the two sides due to the different reinforcement systems applied. The side strengthened with the NSM presents a lower stiffness and failed due to the diagonal cracking. In this paper only the experimental results are described, in future works these results will be compared with analytical and numerical models in order to validate these data and elaborate an analytical procedure that could be useful to define design guide lines for the strengthening with TRM systems. Acknowledgements T.C.S. s.r.l. is gratefully acknowledged by the authors for providing support for the experimental in-situ investigation and for the strengthening material. These tests were performed with the contribution of the Testing Laboratory for Materials, Structures and Constructions of Politecnico di Milano, the support of the technicians Antonio Cocco and Paolo Broglia is gratefully acknowledged References Almeida J.A.P.P, Pereira E.B., Barros J.A.O. 2015. Assessment of overlay masonry strengthening system under in-plane monotonic and cyclic loading using the diagonal tensile test. Construction and Building Materials 94, 841-865 ASTM E 519-10 Standard Test Method for Diagonal Tension (Shear) in Masonry Assemblages Babaeidarabad S., Arboleda D., Loreto G., Nanni A., 2014. Shear strengthening of un-reinforced concrete masonry walls with fabric-renforcedcementitious-matrix. Construction and Building Materials 65, 243-253 Borri A., Castori G., Corradi M., Speranzini E. 2011. Shear behavior of unreinforced and reinforced masonry panels subjected to in situ diagonal compression tests. Construction and Building Materials 25, 4403-4414 Carozzi F.G., Poggi C., 2015. Mechanical properties and debonding strength of Fabric Reinfoced Cementitious Matrix (FRCM) systems for masonry strengthening. Composites Part B 70, 215-230 Carozzi F.G.., Poggi C., Bertolesi E., Milani G., 2018. Ancient masonry arches and vaults strengthened with TRM, SRG and FRP composites: Experimental evaluation. Composites Structures 187, 466-480 Contamine R., Si Larbi, A., Hamelin P., 2011. Contribution to direct tensile testing of textile reinforced concrete (TRC) composites. Materials Science and Engineering 528, 8589-8598 D’Ambrisi A., Mezzi M. Feo L., Berardi V.P. 2014. Analysis of masonry structures strengthened with polymeric net reinforced cementitious matrix materials. Composite Structures 113, 264-271 D’Antino T., Carloni C., Sneed L.H., Pellegrino C. 2014. Matrix–fiber bond behavior in PBO FRCM composites: A fracture mechanics approach. Engineering Fracture Mechanics 114, 94-111 De Santis S., de Felice G. 2015. Steel reinforced grout systems for the strengthening of masonry structures. Composite Structures 134, 533-548 EN 1015-11. Methods of test for mortar for masonry – determination of flexural and compressive strenght of hardened mortar; 1999. EN 13412 Products and systems for the protection and repair of concrete structures - Test methods - Determination of modulus of elasticity in compression Marcari G., Basisi M., Vestroni F. 2017. Experimental investigation of tuff masonry panels reinforced with surface bonded basalt textile-reinforced mortar. Compoiste Part B 108, 131-142 Menna C., Asprone D., Durante M., Zinno A., Balsamo A., Prota A. 2015. Structural behavior of masonry panels strengthened with an innovative hemp fibre composite grid. Construction and Building materials 100, 111-121 Parisi F. Iovinella I., Balasamo A., Augenti N., Prota A. 2013. In-plane behavior of tuff masonry strengthened with inorganic matrix-grid composites. Composites Part B 45, 1657-1665 Peled, A., Zaguri E., Marom G., 2008. Bonding characteristics of multifilament polymer yarns and cement matrices. Composites Part A 39, 930939 Prota A., Marcacri G., FAbbrocino G., Manfredi G. Aldea C. 2006. Experimental In-Plane Behavior of Tuff Masonry Strengthened with Cementitious Matrix–Grid Composites. Journal of Composite for Construction 10, 223-233