potential of structural pozzolanic matrixâ€“hemp fiber grid...

Construction and Building Materials xxx (2011) xxx–xxx

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Construction and Building Materials

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Potential of structural pozzolanic matrix–hemp fiber grid composites

Domenico Asprone a,⇑, Massimo Durante b, Andrea Prota a, Gaetano Manfredi a

a Department of Structural Engineering, University of Naples ‘‘Federico II’’, Naples, Italyb Department of Materials and Production Engineering, University of Naples ‘‘Federico II’’, Naples, Italy

a r t i c l e i n f o

Article history:Received 1 September 2010Received in revised form 13 December 2010Accepted 24 December 2010Available online xxxx

Keywords:Hemp fiberPozzolanic mortarSustainabilityInorganic compositeStructural retrofit

0950-0618/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2010.12.046

⇑ Corresponding author. Address: via Claudio, 21 8081 7683672; fax: +39 081 7683491.

E-mail address: [email protected] (D. Asprone).

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a b s t r a c t

Currently, sustainability represents a primary issue for construction industry. New material and techno-logical solutions are widely proposed and investigated to meet sustainability requirements and naturalfibers represent one of the most studied materials. The work presented here investigated the mechanicalbehavior of a sustainable composite system made by pozzolanic mortar reinforced with hemp fiber grids.To improve the durability of the system and in particular of the fibers in the pozzolanic mortar environ-ment a latex coating was used. The objective of the study was to investigate the mechanical behavior ofthe proposed composite system and assess the feasibility of using the system for structural retrofit appli-cations on existing structures. A mechanical characterization of the fibers was conducted and the effec-tiveness of the latex coating in improving the durability of the fibers was investigated. The mechanicalbehavior of the composite system was studied, through a three-point bending test program.

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1. Introduction

Low environmental impact of operations on built environmentis often a primary condition to be respected by constructiondesigners and operators. Thus, recently, new technological solu-tions are proposed and new materials are investigated and used[1,2]. For this reason, in recent years, natural fibers have beenwidely investigated, to be used as an alternative to carbon, glassor plastic fibers, in several composite applications for constructionindustry. In fact, given their low environmental impact both in pro-duction and in disposal phase, natural fibers represent a highly‘‘sustainable’’ material. Furthermore, natural fibers can be locallysupplied, ensuring a sustainable production chain.

The recent increasing scientific interest in natural fibers as acomponent of construction applications is also due to the goodmechanical properties exhibited by natural fibers. Available litera-ture provides the mechanical characterization of natural fibers, interms of elastic properties and tensile strength [3–5]; in particular,attention has been focused on different fibers, e.g. flax [6], jute[7,8], hemp [9,10], sisal [11]. The available reviews [3,5] reportsthe main mechanical properties of various natural fibers. It canbe observed that the tensile strength can reach more than1000 MPa, in case of flax fiber and vary from about 400 MPa to800 MPa in case of jute fiber, whereas hemp fiber exhibits a tensilestrength of 690 MPa. Furthermore, the ultimate tensile strain var-ies from 1.5% for the jute fiber to 3.2% for the flax fiber, whereas

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et al. Potential of structural po

hemp fiber presents an ultimate tensile strain of 1.6%. Young’smodulus is equal to 26.5 GPa and 27.6 GPa for jute and flax fiber,respectively, whereas, according to Dhakal et al. [10], Young’smodulus for hemp fiber varies from 30 GPa to 60 GPa. Thus, thevalues of the main mechanical properties of natural fibers are notso far from those exhibited by the most used synthetic fiber, i.e.glass or carbon.

Hence, given these properties, natural fibers can be feasiblyused as a component of composite materials, in different applica-tions. In fact, whereas in industrial applications natural fibers arealready used in fiber-reinforced plastic composites, structuralapplications in construction industry represent an interestingdevelopment for natural fiber use. In scientific literature, severalworks from structural and material engineering communities haveinvestigated these applications. In particular, fiber reinforced mor-tars composed of short natural fibers reinforcing inorganic matri-ces have been studied [12–14]. Also textile reinforced laminates,composed of inorganic matrices reinforced by long natural fibershave been investigated [15–17]. A number of works have been alsoconducted on the development of natural fiber reinforced concrete[18–21]. The objective of these works is to study and develop newmaterials and technological solutions for structural applications.On the contrary, the objective of the current paper is to developa composite material, made by a pozzolanic mortar reinforced bya hemp fiber grid, to be potentially used in retrofitting applicationof civil structures and in particular in seismic retrofitting opera-tions of existing masonry structures.

In fact, Italian guidelines from National Research Council [22]permit to use, for seismic retrofitting of masonry structures, exter-nally bonded fiber reinforced composite systems, using inorganic

zzolanic matrix–hemp fiber grid composites. Constr Build Mater (2011),

http://dx.doi.org/10.1016/j.conbuildmat.2010.12.046

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2 D. Asprone et al. / Construction and Building Materials xxx (2011) xxx–xxx

matrices. From the structural point of view, the use of natural fi-bers and in particular hemp fibers guarantees a good mechanicalcompatibility of the composite system with the masonry elements,given the low Young’s modulus of the fibers. Here, the results ofthe preliminary experimental characterization of the compositesystem are presented. In particular, the single hemp fibers havebeen characterized in terms of tensile strength; furthermore, thedurability of the fibers in the matrix environment was also ad-dressed and a latex coating was investigated. Finally, the flexuralbehavior of the composite was investigated using different config-urations of the fiber reinforcement. It is emphasized that the choiceof the specific components for the composite system is led by sus-tainability criteria. In fact, both hemp fibers and pozzolanic mortarare very common in Italy and the production of the composite sys-tem can be provided by a local supply chain. In particular, the usedmortar is a commercial product, PLANITOP HDM from MAPEI, com-posed by natural hydraulic lime, pozzolan and natural fine aggre-gate. It is a GP-CS IV masonry mortar, according to EN 998-1 [23].

2. Mechanical characterization and durability assessment of thehemp fibers

The hemp fibers employed in the investigated composite sys-tems were produced in Italy, from a local growing. Fig. 1 reportsa bundle of the investigated fibers. In order to characterize themechanical properties of the fibers 10 tensile failure tests werecarried out on fiber specimens, using a displacement control test-ing machine. The tests were conducted and elaborated accordingto ASTM C1557 [24]. The free length of the fiber specimens was15 mm and the tests were conducted at 0.1 mm/s of elongationvelocity. The specimens used for the tests came from five fibers;each of them were divided into two specimens. During the tests,the load and the specimen elongation were acquired and elabo-rated into stress–strain relationships. To do this, the cross area Aof the fibers was evaluated as

A ¼ PLc

ð1Þ

being P the weight of the fiber, L the length of the fiber and g thespecific weight of the fiber, which can be considered equal to

Fig. 1. Hemp fibers.

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1.4 � 104 N/m3 for cellulose based materials [25]. The specimensexhibited an elastic behavior up to failure. Table 1 reports the aver-age failure stress, ultimate strain and Young’s modulus from eachcouple of specimens. As it was expected, the values are highly var-iable; the obtained average tensile failure stress and averageYoung’s modulus were equal to 898 MPa and 21.3 GPa, respectively,whereas the average ultimate strain was equal to 6.1%.

The durability of natural fibers represents a critical issue for theuse of such fiber in composite systems. Physical and mechanicalproperties of natural fibers can be affected by significant modifica-tions due to environmental factors [26–28]. In particular, inorganicmatrix environment can induce a significant degradation of fiberproperties [27,15]. In case of cementitious environment, durabilityof natural fibers is affected by different factors: alkali attacks,chemical reactions with products of cement hydration and fibersvolume variation due to water absorption [15,29–31]. In order toincrease natural fiber durability in inorganic matrices, different ap-proaches have been proposed in literature. Gram [26] proposed dif-ferent fiber treatments with blocking agents, such as sodiumsilicate, magnesium sulphate, iron or copper compounds and oth-ers, but fiber durability did not increase significantly. Toledo Filhoet al. [15] proposed to use silica fume products in order to reducethe degradation due to alkali attacks. Bilba and Arsene [32] studieda silane coating of natural fibers to reduce external agents attacksand then the degradation of the mechanical properties.

In order to assess the sensitivity of the used hemp fibers to suchdegradation phenomena and in particular to alkali attacks andwater adsorption, the tensile failure tests described above were re-peated for conditioned fibers. Fiber conditioning consists of15 days of immersion in water with a value of pH of 13. In partic-ular, as for tensile tests on unconditioned fibers, five couples ofspecimens were tested. Results are reported in Table 2, where astrong decrease of both tensile failure stress and Young’s moduluscan be observed. This confirmed that environmental alkalinity andwater adsorption represent critical issues for the mechanical prop-erties of the used hemp fibers.

Actually, in the present study, the use of a pozzolan-based mor-tar, characterized by a lower alkalinity than those presented bypurely cementitious mortars, can reduce the effects of the alkali at-tacks on the hemp fibers. However, in order to improve the dura-

Table 1Tensile properties of the hemp fibers.

Fiber crossarea(mm2)

Tensilefailurestress (MPa)

Ultimatestrain(%)

Young’smodulus(GPa)

0.0036 676 3.9 16.30.0025 738 5.7 19.40.0050 533 6.0 12.60.0020 1488 6.0 43.40.0040 1055 8.7 14.9

Average 0.0034 898 6.1 21.3Standard

deviation0.0012 381 1.7 12.6

Table 2Tensile properties of conditioned hemp fibers.

Fiber cross area(mm2)

Tensile failure stress(MPa)

Ultimatestrain (%)

Young’s modulus(GPa)

0.0036 80.0 3.0 3.10.0025 77.6 2.1 2.00.0050 288 9.0 13.80.0020 60 2.5 1.00.0040 124 10.7 3.8



D. Asprone et al. / Construction and Building Materials xxx (2011) xxx–xxx 3

bility of the hemp fibers in the proposed composite system, a latexcoating was investigated, as described in the following sections.

Table 3Tensile properties of conditioned fiber strings.

Specimen type Bundle crossarea (mm2)

Tensile average failurestress (MPa)

NL–NC 1.00 108.4L–NC 1.78 112.4

3. Latex coating of the hemp fibers

To overcome the degradation of both physical and mechanicalproperties that could occur to hemp fibers in the inorganic matrixenvironment, a latex coating was proposed and used. The objectiveis to provide an external protection, in order to insulate fibers fromalkali agents and moisture of the inorganic mortar. In order to as-sess the effectiveness of this solution, tensile failure tests wereconducted on hemp fiber strings, before and after moisture andalkaline conditioning, in presence of the latex coating and in theunprotected configuration. The employed hemp fiber strings aremade by discontinuous fibers twisted together to form a bundle.Due to its configuration, the string presents a lower ultimate stress,if compared with that exhibited by the single fiber.

In particular, tensile failure tests were conducted on stringspecimens, of 100 mm of free length, using a displacement controltesting machine, with a maximum load capacity of 50 kN. Fig. 2 de-picts a string specimen during the test. Different typologies ofspecimens were tested; in particular, for both the specimens withand without the latex coating, the tests were conducted (i) in caseof no conditioning, (ii) in case of immersion in basic water, to testthe contemporary effect of alkali and moisture induced degrada-tion, and (iii) in case of immersion in neutral water, to test the ef-fect of the water adsorption. In details, four tests were carried out,for each of the following typology (labels in parentheses are usedhereafter to indicate the corresponding specimen):

� strings without coating and without conditioning (NL–NC);� strings with latex coating and without conditioning (L–NC);� strings without coating, subjected to 25 days of immersion in

pH 13 water (NL–AC);� strings with latex coating, subjected to 25 days of immersion in

pH 13 water (L–AC);� strings without coating, subjected to 60 days of immersion in

neutral water (NL–MC);� strings with latex coating, subjected to 60 days of immersion in

neutral water (L–MC).

Fig. 2. Tensile test on string specimen.


Table 3 reports the results of the tests, in terms of average ten-sile failure stress. It can be observed that in case of the NL–NCspecimens, corresponding to the unprotected and unconditionedstring, the ultimate stress is much lower than that exhibited bythe single fibers, since, in case of the string, the failure is due tothe fraying of the specimens and not to the failure of the fibers.This can be observed in Fig. 3, which depicts a string specimenclose to failure.

Furthermore, it can be observed that, the contemporary effect ofalkali attacks and water adsorption produces a more significantdegradation than that induced only by the water adsorption, as itwas expected, since the ultimate stress for the specimens NL–MCis higher than that for the specimens NL–AC. However, in bothcases, latex coating is able to reduce such degradation, as it resultsfrom ultimate stress values from L–MC and L–AC, which are higherthan ultimate stress value of NL–MC and NL–AC, respectively. Inparticular, for the water adsorption and alkali attack conditioningthe ultimate stress, if compared with that of the reference speci-mens, presents a reduction of the 49% and of the 36%, in case ofthe unprotected and the protected specimens, respectively. Onthe contrary, in case of the water adsorption conditioning, the ulti-mate stress presents a reduction of the 40% and of the 26%, in caseof the unprotected and the protected specimen, respectively.Hence, it is observed that, even if the specimens present a latexcoating the conditioning phenomena induce a reduction of the ulti-mate stress. However, it should be mentioned that the adoptedconditioning procedures are much more severe than the actualdegrading processes, which the hemp fibers would be subjectedto, when submerged into the inorganic matrix environment.

In order to assess the mechanical behavior of the bond betweenthe hemp fibers and the pozzolanic mortar, a pull-out test programwas carried out. The tests were conducted on hemp strings par-tially embedded in pozzolanic mortar specimens.

Fig. 3. A string specimen close to failure.

NL–AC 2.00 55.5L–AC 1.60 69.0NL–MC 1.70 64.9L–MC 0.90 80.4




The tests were carried out also for specimens with an epoxy re-sin coating, in order to have a reference for the pull-out behavior ofcoated hemp fibers, since this type of resin presents good mechan-ical properties in terms of bond with the cementitious mortar.Hence, it could represent an optimal solution for the durability ofthe fibers, but the use of epoxy resin, if compared with latex, canbe more expensive and can lead to a higher environmental impact,according to Life Cycle criteria [33,34]. Furthermore, latex is lessdangerous than epoxy resin both for workers health and for dis-posal phase, as confirmed by USA National Institute for Occupa-tional Safety and Health (NIOSH) database [35].

The specimens were prepared by placing the hemp strings inprismatic mortar specimens, 10 mm � 30 mm � 50 mm in dimen-

Fig. 4. Pull-out

Table 4Results from pull-out tests on strings.

String type Embedmentlength (mm)

Diameter(mm)

Ultimatforce F

Without coating 10 1.30 402423

Without coating 20 3239

Without coating 40 5257

With latex coating 10 1.48 694554




With resin coating 30 1.60 219170919835

a String tensile failure occurred.


sions, at different embedment length, from 10 mm to 40 mm. Thetests were conducted after 28 days of curing of the mortar, using adisplacement control testing machine, with a maximum loadcapacity of 50 kN. During the tests, a pull out velocity of 2 mm/min was used. Fig. 4 depicts the pull-out test setup. Table 4 reportsthe main results of the tests in terms of ultimate pull-out force F,corresponding to the bond failure and the slip of the string fromthe mortar. The equivalent ultimate bond stress t is reported anddefined as the ratio of F over the string lateral area Al, which isequal to the string circumference multiplied by the embedmentlength; the corresponding average values for each type of speci-men are also presented. As it could be expected, it can be observedthat, as the embedment length increases, t decreases, since a stress

test setup.

e pull-out(N)

Equivalent ultimatebond stress t (N/mm2)

t, average values(N/mm2)

3.02 2.201.811.771.19 1.321.450.98 1.021.074.01 3.262.623.141.77 2.062.242.172.17 2.131.722.50>1.45a 1.681.601.831.85>3.63a >2.03>2.82a

>1.51a

>1.63a

>0.58a



Table 5Results from pull-out tests on bundles.

Coatingtype

Diameter(mm)

Embedmentlength (mm)

Ultimatepull-outforce F (N)

Equivalent ultimatebond stress t(N/mm2)

Latex 0.3 5 14 >39.63a

5 24 >67.94a

20 51 >36.09a

20 59 >41.76a

30 12 >5.66a

30 30 >14.15a

40 29 >10.26a


concentration occurs at the top of the embedded portion of thestring. It is also observed that both the latex and the epoxy resincoating improve the mechanical bond of the string to the mortar;indeed, given the embedment length, higher values of t have beenobtained for the specimens with latex and resin coating, comparedwith those without latex protection. In particular, resin coatingdetermines the highest values of bonding stress, causing even thetensile failure of the string. Finally, the conducted test program jus-tified the use of the latex coating, since a significant protectionfrom fiber degradation is provided and even an improvement inbond between fibers and mortar is obtained.

1.0 10 192 24.4610 173 22.0420 416 26.5020 161 >10.25a

30 387 >16.43a

Resin 0.3 5 76 >215.15a

5 65 >184.01a

10 51 >72.19a

20 75 >53.08a

20 52 >36.80a

30 105 >49.54a

40 99 >35.03a

1.0 5 83 21.155 210 53.50

a String tensile failure occurred.

Fig. 6. Bond failure for a latex coated bundle.

Fig. 7. A composite specimen during preparation.

4. Mechanical characterization of the composite system

The investigated composite system consists of a thin pozzolanicmortar slab reinforced with different layers of hemp fiber grids. Toset-up the grids, long fiber bundles were preferred to the fiberstrings used in pull-out test, since in tensile failure tests the latterexhibited a worse behavior in terms of ultimate stress, due to thefraying of the strings, occurring at failure. To clarify the differencebetween strings and bundles a sketch is presented in Fig. 5.

To assess the bond between the fiber bundles and the mortar, apull-out test program was also conducted on coated bundles,embedded into mortar specimens. Again, as for pull-out tests onstrings, both latex and resin coating were tested. The dimensionsof the specimens and the set-up characteristics were the same asthose used for pull-out tests conducted on fiber strings. Two valuesof the bundle diameter were tested, 0.3 mm and 1.0 mm, whereasthe embedment length varied from 5 mm to 40 mm. The main re-sults are reported in Table 5. In case of 0.3 mm diameter bundle, foreach embedment length and for both coating types, fiber tensilefailure occurred outside the mortar specimens. Hence, for 0.3 mmdiameter bundle, the critical embedment length, representing thethreshold between tensile failure and bond failure, is even shorterthan 5 mm, for both latex and resin coatings. On the contrary, for1.0 mm diameter bundle, in case of resin coating, bond failure oc-curred only for 5 mm embedment length whereas, for latex coat-ing, bond failure occurred for 10 mm and 20 mm embedmentlength. Hence, resin coating exhibits a better bond behavior thanlatex coating, as it was already observed in pull-out tests on fiberstrings. Fig. 6 depicts a latex coated bundle after bond failure. Itcan be observed that failure occurred between fibers and latexcoating. This revealed that the bond between the latex and themortar is even stronger than the bond between the latex and thehemp fibers.

To assess the mechanical properties of the hemp fiber rein-forced composite system a bending test program was conductedon different composite specimens, with different grid reinforce-ment configurations. Fig. 7 depicts a composite specimen duringpreparation, where a hemp fiber grid has just been placed on thefresh mortar. In particular, three-point bending tests were carriedout. The samples were almost 300 mm long, 15 mm thick and100 mm wide. The span length L used for the test was equal to240 mm. Up to six reinforcement layers were placed in the com-posite samples. The position through the thickness of each layeris such as indicated in Fig. 8; in particular, two different configura-tions were tested, using four and six layers, adding the inner layersin the latter case.

single fiber fiber bundle fiber string

Fig. 5. Fiber configurations.

Please cite this article in press as: Asprone D et al. Potential of structural pozzolanic matrix–hemp fiber grid composites. Constr Build Mater (2011),doi:10.1016/j.conbuildmat.2010.12.046


reinforcement layer 2






top

bottom

Fig. 8. Reinforcement layers position.

0

5

10

15

20

25

0 5 10 15 20 25 30 35 40Flexural strain [‰]

Flex

ural

str

ess

[MPa

]

P

A

B

Fig. 9. Flexural stress–flexural strain curves (latex coating – four reinforcinglayers).


Two different values of grid spacing through the width of thesample, Sw, were used, equal to 10 mm and 20 mm, whereas thegrid spacing through the length of the sample, Sl, was equal to40 mm in each specimen. Two different values for the diameterof the single fiber bundle, Db, were used, equal to 1 mm and0.3 mm, corresponding to a weight per length of the bundles of1.1 g/m and 0.1 g/m, respectively. Both latex and resin coatingswere used. Table 6 reports the main characteristics of the testedsamples. For each type, three tests were conducted. The tests wereconducted after 28 days of curing the mortar, using a displacementcontrol testing machine, with a maximum load capacity of 50 kN.During the tests, the applied load P, and the midspan deflectionD, were acquired. According to ASTM C1018 approach [36], theload and deflection data were elaborated to obtain flexuralstress–strain curves, through the following relationships:

r ¼ 3PL

2bd2 ð2Þ

e ¼ 6Dd

L2 ð3Þ

where s is the flexural stress, e is flexural strain, P is applied load, Dis midspan deflection, L is span length, b is width of the specimen,and d is the thickness of the specimen.

Table 6Three-point bending tests.

Sample Coatingtype

Number ofreinforcing layers(#)

Bundlediameter, Db

(mm)

P – 0 –B Latex 4 0.3A 1.0D 6 0.3H 0.3L 1.0C Resin 4 0.3F 1.0E 6 0.3G 1.0I 1.0


The average flexural stress–flexural strain curves are reportedfrom Figs. 9–12. The average maximum flexural stress is also re-ported in Table 6. It can be observed that in the unreinforced spec-

Bundle spacingthroughthe width, Sw, (mm)

Reinforcementweight ratio(%)

Average maximumflexural stress(MPa)

– – 7.0320 1.2 10.2020 4.0 9.3520 1.8 9.2710 3.0 13.7010 12.0 13.2020 1.2 9.9020 4.0 10.2720 1.8 11.1020 7.0 15.0210 12.0 21.64



0

5

10

15

20

25

0 5 10 15 20 25 30 35 40

Flexural strain [‰]

Flex

ural

str

ess

[MPa

]

P

C F

Fig. 11. Flexural stress–flexural strain curves (resin coating – four reinforcinglayers).

0

5

10

15

20

25

0 5 10 15 20 25 30 35 40


Flex

ural

str

ess

[MPa

]

P

E G

I

Fig. 12. Flexural stress–flexural strain curves (resin coating – six reinforcing layers).

Fig. 13. Specimen reinforced with resin coated fibers after failure.

Fig. 14. Specimen reinforced with latex coated fibers after failure.

0

5

10

15

20

25

0 5 10 15 20 25 30 35 40


Flex

ural

str

ess

[MPa

]

P D

H

L

Fig. 10. Flexural stress–flexural strain curves (latex coating – six reinforcing layers).


imen a maximum stress of 7.03 MPa is reached; then a rapid failureoccurs with a drop of the flexural stress. On the contrary, for thereinforced specimen, after a peak stress occurring almost at thesame flexural strain value, the stress increases again and higher


values of strain are obtained. In particular, higher strain valuesare reached for the specimens with latex coated reinforcing fibers,whereas higher values of stress are obtained in case of the speci-mens with resin coated reinforcing fibers. This behavior revealsthat at the first peak stress, tensile failure of the mortar occursand cracks open at the bottom of the specimen; in the unreinforcedconfiguration, this cause the complete failure of the specimen,whereas in the reinforced configuration a further tensile capacityis provided by the fibers. Hence, in case of latex coating, specimensexhibited a more ductile behavior, whereas, in case of resin coat-ing, higher stress values were obtained, but a more brittle behaviorwas experienced. This behavior is probably due to different failuremechanisms of the fibers, occurring in case of latex and resin coat-ing. In fact, in case of resin coating, a tensile failure was experi-enced, as it can be observed in Fig. 13, reporting a resin coatingsample after failure, where the fibers present a sharp cut. On thecontrary, fibers slipped from the mortar in case of latex coating,as it can be observed in Fig. 14, where a failed latex coating sampleis depicted. In particular, the maximum flexural stress increased upto the 1.95 and 3.08 times the value obtained in the unreinforcedconfiguration, for the latex and the resin coating, respectively.With regard to the diameter of the fiber bundles, it can be observedthat, in case of the latex coating, unlike the resin coating, the in-crease of the diameter does not correspond to an increase of themaximum flexural stress. This reveals that latex coating is lesseffective than resin coating in transferring bond stress inside thebundles. Finally, it can be observed that, both for latex and resin




coating, an increase of the reinforcement ratio produces a growthof the maximum flexural stress, both in case of reduction of thebundle spacing and in case of increase of the reinforcing layers.However, such variation is much less significant in the latter case,as it could be expected, since the added reinforcing layers are lesseffective than the others, since they are closer to the neutral axis inthe bended cross section of the specimen.

5. Conclusions

The activities here presented addressed a preliminary mechan-ical characterization of an inorganic composite system that couldbecome a potential solution for the retrofit of existing structures.The system is made by pozzolanic mortar reinforced with hemp fi-ber grids, with a latex coating. Based on the results of the con-ducted experimental activities it can be concluded that:

� latex coating can improve the durability of the hemp fiber in thepozzolanic mortar environment;� the bond behavior between the hemp fibers and the pozzolanic

mortar is even improved by the latex coating;� hemp fiber grid reinforcement can provide a significant

improvement of the flexural behavior of the pozzolanic mortar,increasing the flexural strength and providing a considerabledurability enhancement.

At this step, further tests will be conducted to assess the dura-bility of the composite system within different environmental con-ditions and to investigate the feasibility of applications of thereinforced mortar on structural elements. However, the prelimin-ary outcomes here illustrated reveal that the composite systempresents considerable mechanical properties and can be furtherdeveloped to be used as an effective solution for structural retrofitof existing structures. Furthermore, once the mechanical behaviorof the composite per se has been optimized, it will be necessary toassess issues related to its bond to existing structural members.

As a final word, it is underlined that, as it was expected for nat-ural fibers, results from both fiber and composite tests presented ahigh dispersion. This represents a critical issue for structural appli-cations, where a design value for each mechanical property of theused materials is needed.

Acknowledgement

Authors gratefully acknowledge italian association Assocanapaand Mr. Michele Castaldo for the support and the assistance tothe conducted activities.

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potential of structural pozzolanic matrixâ€“hemp fiber grid...

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