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Building and Environment 42 (2007) 1151–1157

www.elsevier.com/locate/buildenv

Performance of ‘‘Agave lecheguilla’’ natural fiber in portland cementcomposites exposed to severe environment conditions

Cesar Juarez�, Alejandro Duran, Pedro Valdez, Gerardo Fajardo

Academic Group of Concrete Technology, School of Civil Engineering, Universidad Autonoma de Nuevo Leon, Monterrey, Mexico

Received 11 October 2005; received in revised form 8 November 2005; accepted 2 December 2005

Abstract

The main objective of the present research was to provide the housing alternatives to istle zone rural areas in Mexico, which represent

about 10% of the national territory. The proposed solution involved a sustainable portland cement-based composite material, reinforced

with high tensile strength natural fibers of ‘‘Agave lecheguilla’’.

The results indicated that the ‘‘Agave lecheguilla’’ or simply lechuguilla fiber shows a high tensile capacity, but can be severely

deteriorated in the alkaline environment of the composite. However, if the fiber is protected with paraffin and the composite matrix is

modified with a pozzolan admixture such as fly ash, the composite performs acceptably well at exposure to aggressive environments and

variations in humidity and temperature.

r 2005 Elsevier Ltd. All rights reserved.

Keywords: Natural fiber; Reinforcement; Composite; Durability; Sustainability; Fly ash; Flexural strength; Deterioration

1. Introduction

Historically, natural vegetable fibers or simply naturalfibers (NF) were empirically used to reinforce severalconstruction materials, as the case for the production oftextile material. However, only recently scientists start tostudy the application of this type of fiber as concretereinforcement [1]. NF can be obtained at a low price usinglocally available manual labor and adequate techniques.These fibers are usually known as unprocessed NF.However, NF can be chemically or mechanically processedto enhance their properties; usually, these fibers are basedon wood derivate cellulose. Such chemical or mechanicalprocesses are commonly utilized in the developed coun-tries; whereas, because of relatively high costs of proces-sing, these technologies are rarely adopted in developingcountries [1].

Natural fibers are readily available in large quantities inmany countries and they represent a continuous renewablesource. At the end of the 1970s, a systematic evaluation ofengineering properties of NF was performed, including the

e front matter r 2005 Elsevier Ltd. All rights reserved.

ildenv.2005.12.005

ing author.

ess: cjuarez@fic.uanl.mx (C. Juarez).

performance of portland-cement-based composites con-taining these fibers. Even the results of flexural and impactstrength were encouraging, the deficiencies related to thelong-term performance of NF reinforcement were alsoreported [1]. These deficiencies are related to a degradationof the fiber by the alkaline cement paste environment andthe increase of fiber dimensions related to variations inhumidity [2].Durability is related to concrete ability to resist damage

caused by external factors (variations in environmenthumidity and temperature, sulfate or chloride attack,etc.) and internal factors (chemical reaction between theingredients, high water/cement ratio, and volumetricchanges due to paste hydration).Canovas et al. [3], studied possible ways to prevent the

damage of sisal fibers in alkaline environment. Accordingto their results, fiber strength is reduced due to theextraction process and the chemical reaction with thealkaline environment affects the inner structure of fiber.The chemical reactions are initiated at temperature changesand on the exposure to humidity and highly alkalineenvironment. One of the most important works related todurability of NF was performed by Gram [4,5], whostudied sisal fibers in the Concrete and Cement Research

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Table 1

Chemical composition of cementituos materials

Material Chemical composition (%)

SiO2 Al2O3 Fe2O3 CaO MgO Na2O

Fly ash 63.93 24.32 4.29 2.34 0.78 0.20

Portland cement 17.55 4.70 1.77 64.74 1.23 0.37

Table 2

Grading of the aggregates

Aggregate type Passing, % at a mesh (mm)

0.15 0.30 0.60 1.18 2.36 4.75 9.50

Sand 6.0 20.0 42.5 67.5 90.0 97.5 100.0

C. Juarez et al. / Building and Environment 42 (2007) 1151–11571152

Institute, Stockholm, Sweden. He stated that the decom-position of the main structural component of fiber–cellu-lose in an alkaline environment, and hemicelluloses as wellas separation of lignin, could progress according to twodifferent mechanisms. The first one was related to fiberremoval and separation, which occurred when linealglucose chains of cellulose were dissolved due to theirreaction with hydroxyl-ions; OH�, resulting in methanolradicals (–CH2OH), which could be easily liberated fromthe molecular chain, causing decomposition of the cellulosemolecular structure. Therefore, the separation of fiber wascontinuous process and it happened at exposure to alkalineenvironment and at temperatures lower than 75 1C. Thesecond mechanism of cellulose decomposing was related toalkaline hydrolysis. This process involved the division ofmolecular chain, and was combined with chain separation,since the division of chain provided further exposure toinner structure of the fiber. Usually, this process wasrealized at temperatures around 100 1C. Also, Gram [4,5]performed tensile tests on fibers subjected to a concen-trated solution of calcium hydroxide and water. In bothcases, the tensile strength was considerably reduced. In thefirst case, this reduction was due to an effect of alkalineenvironment and, in the second, due to the microbiologicalaction. It was detected that when the composite wassubjected to humidity variations, strength was substantiallyreduced. It was observed that in carbonated concrete with apH of less than 9, fibers preserved their flexibility andstrength, but in noncarbonated zones, the fibers werefragile.

As other developing countries, Mexico has a largeproduction of NF. Meanwhile, this country has aninadequate infrastructure and housing deficit demandedby growing population. Despite of this fact there were onlyfew scientific research related to the rational utilization ofsuch viable resource as NF. Belmares [6], used ‘‘Yucca

carnerosana’’, a vegetable fiber available in the State ofCoahuila, Mexico to reinforce the polyester matrices. Thestudy carried out by Castro and Naaman [7], concludedthat it was possible to reinforce portland cement mortarswith maguey fibers, since this fiber has an adequatephysical and mechanical properties. The northeast part ofMexico is represented by the States of Coahuila, Zacatecas,Nuevo Leon, San Luis Potosı, and Tamaulipas and isknown as the istle zone. This region is propitious for growof lechuguilla plant, on which thousands of familiesinhabiting these zones rely.

The wide availability of this plant in Mexico [8] and thepotential use of lechuguilla fiber in materials, were the mainreasons of the research conducted at UANL. This paperfocuses on the application of the lechuguilla fiber asreinforcement in portland cement composites.

2. Research significance

Thousands of families reside in arid and semiarid zonesof Mexico, living in a precarious economic situation. This

is mainly the result of the deficient agrarian investmentsthrough the years, which motivated farmers to abandontheir fields and immigrate to the big cities looking for newopportunities, in most cases without success. The remain-ing population suffers because of extreme drought and lackof financial support, both reducing their harvest produc-tion and lack of affordable housing. Therefore the researchof technical alternatives aiming to improve rural housingand use of local materials are required.

3. Experimental program

3.1. Materials

Natural fiber ‘‘Agave lecheguilla’’, portland cement CPC30R, fly ash (FA) and local limestone aggregates were usedin the experimental program. FA is a pozzolan, whichcame from burning charcoal, used by the Rio Escondidopower plant, located in Piedras Negras, Coahuila. Thechemical composition of FA is shown in Table 1. Fly ashwas used at dosage of 60% by cement weight for compositewith the W/C ratio of 0.65 and 15% by cement weight forcomposite with the W/C ratio of 0.35. The proportioningof fine aggregate was provided according ASTM C 33-97

[9] and the grading of the sand is given in Table 2. Naturalfibers with length of 20–30mm were used at dosage of 1%by volume. Commercially available sulfonated naphtha-lene-based superplasticizer admixture was used at a dosageof 1% of cement weight, for FA mix with W/C ratio of 0.35the dosage was 1.2% of cement weight. These contents ofsuperplasticizer were selected to maintain a 1271 cmslump of all mixtures.

3.2. Test procedures

3.2.1. Tests to assess the performance of protective agents

for enhancing the durability of fibers

This procedure was used to obtain the most effectiveprotective agent to reduce the water absorption of fiber

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Table 3

Mix proportions of fiber-reinforced composites

Materials Composite mix proportion (kg/m3)

Series 1 Series 2 Series 3 Series 4 Series 5 Series 6

Cement 380.8 380.8 380.8 706.9 706.9 706.9

Fly ash 228.5 106.0

Sand 1540.0 1540.0 1287.5 1309.8 1309.8 1192.7

Water 247.4 247.4 247.4 240.3 240.3 238.9

Superplasticizer 7.1 7.1 8.5

Fibers untreated 6.9 6.9

Fibers treated 6.9 6.9 6.9 6.9

W/C ratio 0.65 0.65 0.65 0.35 0.35 0.35

C. Juarez et al. / Building and Environment 42 (2007) 1151–1157 1153

and, in a long-term preserves the mechanical properties offiber in the alkaline environment of the cement matrix. Inorder to reduce the water absorption and protect the fibersin the alkaline environment, a comparison study wascarried out by using several organic water repellentsubstances to figure out the most suitable one, whichshould be not harmful to composite, nontoxic, as well asinexpensive and easy for disposal. The following sub-stances were selected [11]: linseed oil (LO), paraffin wax(P), linseed oil/rosin (colophony) (C), and paraffin/rosin(PR). These substances used to saturate the fibers provid-ing the water resistance and durability against alkalineenvironment. Once the fibers were treated, water absorp-tion was determined and compared to that of untreatedfibers (UF).

In order to assess the performance of the protectiveagents in composite, an alkaline environment was simu-lated through a concentrated calcium hydroxide solution,with a pH of 12.5. The research program involved fourseries of treated fibers and one series untreated fibers ascontrol. Each series had 120 randomly selected fibers.Fibers were exposed to the calcium hydroxide solution at23 1C. For 6 months, 12 fibers of each series were tested intension monthly and, thereafter, every 3 months untilcompleting a year. As a reference, 12 fibers of each serieswere tested without exposure to the alkaline environment.Maximum and minimum failure load were rejected, gettingan average of 10 remaining loads. All fibers were dried inthe lab environment for 24 h prior to testing and the failuretensile stress was calculated based on the total area of thefiber transversal section.

3.2.2. Accelerated tests to assess the durability of fiber-

reinforced composites

The main objective of this group of experiments was toimprove the density of cement matrix and improve thedurability of fiber-reinforced composites (FRC). In orderto realize this objective an accelerated deterioration testswere designed to simulate natural environment [3,4,21].The experimental program included the cement matrixes ofdifferent density and permeability, obtained with differentW/C, 0.65 and 0.35, and addition of FA.

The mix proportions of composite are specified in Table3. Investigated composites were mixed in a high-perfor-mance countercurrent mixer. The composite mixing,placing and curing procedures were conducted accordingto ASTM C 192-98 [12]. In case when FA was used, it washomogenized with aggregates. All specimens were kept inthe molds for 24 h, protected from moisture loss and thenwere cured at standard conditions for 7 days.

Three specimens for each group of treated fibers and anadditional three with untreated fibers as control wereproduced. Besides, the FA effect on the cement matrix withdifferent fibers types was studied. The dimensions of thespecimens were 75� 75� 280mm. Mixtures of the sixseries as per as Table 3 were produced for each acceleratedtest, as well as six reference series which where not

subjected to any type of exposure. Following the curingperiod, the control specimens were kept in laboratoryconditions, and were tested at 28 days age.In order to evaluate the effect of the accelerated tests on

flexural strength of fiber composites, three specimens pereach series as per as Table 3 were tested. The following testswere carried out, after which flexural tests were performedaccording to ASTM C 78-94 [13]:

Test 1:

Exposure to 15 cycles of wetting and drying atconstant temperature. Each cycle consisted ofthe exposure to a humid environment in an ovenat 70 1C for 24 h, followed by the exposure to adry environment in an oven at 70 1C for 24 h.

Test 2:

Exposure to 15 cycles with humidity andtemperature variations. Each cycle consisted ofexposure to a dry environment in an oven at70 1C for 24 h, followed by water immersion at21 1C for 24 h.

Test 3:

Exposure to an environment with 95% relativehumidity and 23 1C for 150 days.

Test 4:

Exposure to a sodium chloride solution 3%NaCl at 23 1C for 150 days, to simulate a marineenvironment.

Test 5:

Exposure to a sulfate solution with 10,000 ppmconcentration of sodium sulfate (Na2SO4) at23 1C for 150 days. This condition is consideredas severe according to ACI 318-02 [14].

4. Test results and discussion

4.1. Performance of the protective agent for enhancing the

durability of fibers

According to Canovas [3], the effect caused by humidityis related to the increase of the fiber diameter, producing anintermolecular disorder and increase the permeability.Coutts [15,16] mentioned that humidity had a very stronginfluence mainly on the hemicelluloses and lignin, whichform the cellulose matrix. Coutts stated that with theincrease in the humidity, fiber strength dropped down to a

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50%. This is crucial when the fiber is used in compositeexposed to high humidity environments, since strength ofthe composite can be seriously reduced. Water absorptionof treated fibers is presented in Fig. 1. The research resultsindicate that paraffin is the most effective protective agent,providing significantly reduced water absorption, only37% of that for untreated fiber. This effect can be causedby partial sealing of the fiber pores with paraffin. Besides,paraffin film formed over the fiber acts as water repellent,preventing complete saturation. Canovas [3], reduced thewater absorption of sisal fibers by 53%, using colophony-turpentine, mix in a proportion of 1:6 as a sealer. However,colophony had little effect on lechuguilla fibers, possiblydue to the lack of complete penetration of the protectiveagent into the fiber pores, sealing only the larger pores ormacro-pores. Control of water absorption is important forfiber durability; however, it cannot ensure the volumetricstability of the fiber within the cement matrix.

The tensile strength results of treated fibers immersed inan alkaline environment are shown in Fig. 2. According toGram, chemical decomposition of lignin and hemicellu-loses with Ca(OH)2, is the main cause of brittle damage offibers in concrete [4,5]. Alkalinity of cement matrix poresolution dissolves lignin, breaking the integrity of themicro-cells. This explains the results, where the ultimate

98

64 6761 64

0

20

40

60

80

100

Saturation period = 24 h

Abs

orpt

ion

% r

elat

ed to

fibe

rdry

wei

ght

UF LO C P PR

Fig. 1. Water absorption of treated fibers.

0

50

100

150

200

250

300

350

400

0 12

Exposure period (months)

Ten

sile

str

engt

h (M

Pa)

UF LO C P PR

6

Fig. 2. Tensile strength related to expo

tensile strength tends to drop due to an effect of thealkaline solution (Fig. 2). However, the fibers treated withparaffin maintained a 53% of the tension strength, whereasthe other treatment options were capable to keep only31%.The treated and control fibers excluding fibers with

paraffin, became brittle after 6 month of exposure (Fig. 3),possibly because the protection was lost in the alkalineenvironment. Fibers treated with paraffin maintained a47% of their ductility, whereas the other fibers demon-strated only 17–27% of initial value. For fiber treated withparaffin, it is considered a positive solution to maintainabout 50% of the tensile strength and ductility in analkaline environment. This is an important finding since itwas reported [17–19], that NF completely deteriorates inless than a year of exposure to an alkaline environment,losing entirely its ductility and reinforcement capability.

4.2. Durability of fiber-reinforced composites

As any other material, natural fiber-reinforced compo-site is also vulnerable to the environment. When it has alow W/C ratio and it is properly compacted and cured,fibers are usually well protected by the cement paste.Natural fibers and also synthetic polymers suffer the loss ofperformance in the alkaline environment of the cementmatrix [1]. According to RILEM Technical Committee 19[20], the required durability of concrete with fibers dependson the application area. In case of structural componentsof a building it may require a durability of up to 100 ormore years. However, when such concrete is used for non-structural elements, the service life could be less. Gram[4,5], suggests some alternatives to produce a water-proofmatrix, by means of the reduction of the W/C ratio and theuse of high content of silica fume. Silica fume is highlyreactive and reduces alkalinity of the cement paste down toa pH of 9–10. However, it is expensive, and the reducedalkalinity can posses a corrosion problem for the steelreinforcement. This research was focused on obtaining adenser matrix by reducing the water/cementitiuos ratio,and adding FA, which is cheaper and less reactive,

30 31 31

53

31

0

10

20

30

40

50

60

Exposure period = 12 months

Fin

al/in

itial

str

engt

h %

UF LO C P PR

sure period in an alkaline solution.

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0

3

6

9

12

15

18

0 12

Exposure period (months)

Ten

sile

elo

gant

ion

(mm

) UF LO C P PR

2317

26

47

27

0

10

20

30

40

50

60

Exposure period = 12 months

Fin

al/in

itial

elo

ngat

ion

%

UF LO C P PR

6

Fig. 3. Elongation at fracture related to exposure period in an alkaline solution.

C. Juarez et al. / Building and Environment 42 (2007) 1151–1157 1155

compared with silica fume. The Addition of FA tocomposite results in a denser cement matrix, but maintainsits alkalinity. The combined use of FA with a naphthalenesuperplasticizer allows the reduction of W/C ratios of 0.65and 0.35 to water/cementitious ratios of 0.40 and 0.30,respectively.

The proposed accelerated tests were designed to simulatecommon environments in Mexico, for example, humidclimates of the central and southern parts of the country,high temperatures with dry climates in the North West andtropical coastal environments with humidity and tempera-ture variations and high chloride concentrations, and thechemical attack produced by the exposure to sulfates.Humidity changes and temperature variations causecracking due to concrete shrinkage [21]. This crackingallows the penetration of ambient moisture into concretereacting with the Ca(OH)2, and damaging the fibers;besides the fibers suffer volumetric changes affecting theiradherence to the cement matrix.

In relation to Tests 1 and 2, FA paraffin-treated fiber-reinforced composites, developed the highest flexuralstrength compared with other composites. When FA wasadded, the matrix became denser and the humidity ingresswas reduced. With the use of a superplasticizer, the initialW/C ratios 0.65 and 0.35 were reduced to 0.40 and 0.30,respectively, which produced a composite with an addi-tional density and a higher strength. Test 2 turned to be themost critical, demonstrating high values of strength loss inall composites. Dense matrix of composite with FA preventthe fiber deterioration caused by the humidity variations,therefore the fibers preserved their ductility and reinforcingcapability (Fig. 4).

Humid environments are favorable for common compo-site, provided that humidity conditions remain unchanged.According to Gram [4,5], transportation of the hydroxylions OH� or Ca2+ ions within the composite pores is veryslow when the outside environment remains constant,which diminishes the deterioration of fiber. In the sameway, volumetric changes due to fiber contraction andexpansion are not occurring in a stable environment. Theresults of Test 3 are shown in Fig. 4. It can be seen that

there is no significant difference in strength of controlspecimens tested at 28 days and those specimens, whichremained 150 days in a humid environment. These findingsconfirm the results of previous test, stating that stableenvironments without humidity or temperature variationsallow fiber in composite to remain durable. As a result thedegradation of NF in alkaline matrix of cement was veryslow in constantly dry or humid environments. This isimportant observation, since in the wet and dry cycles,flexural strength of FA composite decreased by 14–20%,and with exposure to constant humid environment suchreduction was only of 2%.Neville [22] explains that the most frequent forms of

concrete chemical attack are sulfate attack, seawater, andslightly acid water. It is possible to use different types ofcement to neutralize the chemical attack. However, in somecases, concrete density and permeability affect its durabilityto such extent that it surpasses the influence of the cementtype used. Chemical attack results in harmful physicaleffects such as an increase of concrete porosity andpermeability, a decrease of its mechanical strength andloss of covering. The results of Tests 4 and 5 aresummarized in Fig. 4. For Test 4 (exposure to chlorides),FA paraffin- treated fiber-reinforced composites showed adecrease of approximately 12%, while plain compositeswith untreated fibers lost 30% of their original strength.This reduction of strength is due to salt penetration intocapillary pores. When specimens dried, the solutionevaporated resulting in salt crystallization and fracturesdue to crystal growth expansion inside the cement matrix.Sulfate attack (Test 5) resulted in a reduction of flexuralstrength of investigated composites (Fig. 4).Composites made only with paraffin treated fibers lost

18% of their original strength, while composites made withuntreated fibers suffered a 30% loss. However, FAcomposites made with paraffin-treated fibers lost less than20% of their original strength after 5 months of exposureto sulfates. It can be concluded that humidity andtemperature variations and chemical attack are the maindeterioration factors for NF reinforced composites. Ingeneral, FA composites reinforced with paraffin treated

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5.8

4.3 4.5

5.8

4.6 4.9

0.0

2.0

4.0

6.0

8.0

0.0

2.0

4.0

6.0

8.0

0.0

2.0

4.0

6.0

8.0

0.0

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6.0

8.0

0.0

2.0

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8.0

0.0

2.0

4.0

6.0

8.0

FRC with untreated fibers

Control Test 1 Test 2 Test 3 Test 4 Test 5 Control Test 1 Test 2 Test 3 Test 4 Test 5

6.0

5.0 4.9

5.85.2 5.3

FRC with treated fibersUlt

imat

e fl

exu

ral s

tren

gth

(M

Pa)

5.95.3 5.1

5.85.3

4.9

FRC with treated fibers+ FA

W/C = 0.65

7.4

5.9

4.6

7.4

4.8 5.1

FRC with untreated fibers

7.2

6.25.6

7.2

5.7 5.9

FRC with treated fibers

7.1 7.0

5.7

6.96.2

5.6

FRC with treated fibers+ FA

W/C = 0.35

Fig. 4. Effect of accelerated deterioration on flexural strength of FRC.

C. Juarez et al. / Building and Environment 42 (2007) 1151–11571156

fiber, turned to have the best flexural strength in wettingand drying cycles, as well as when exposed to chloride andsulfate chemical attack. This result can be explained by thereduction water/cementitiuos ratio, and application of FAresulting in denser and waterproof composite.

5. Conclusions

Based on the results of this research, the followingconclusions were made:

1.

Lechuguilla fibers possess high physical–mechanicalproperties, such as higher tensile strength, attractivefor their application as reinforcement for composite.

2.

Application of lechuguilla fiber as a reinforcementresults in a ductile post-crack behavior of compositeunder bending.

3.

The paraffin protective treatment allows reducing thewater absorption of fibers as well as maintainingsufficient tensile strength even after one year of exposureto humid and alkaline environments.

4.

The initial strength of natural fiber-reinforced compo-sites is reduced with exposure to wet and dry cycles, aswell as to aggressive chloride and sulfate environments.

5.

Fly ash added to the mixture provides a denser matrix,which protects the natural fiber-reinforced compositesfrom deterioration.

6.

The combined effect of paraffin protection and applica-tion of fly ash, results in durable composites that mayhave an economical application in construction. Thedeveloped composites can be applied in the internal non-structural separation walls, boards and masonry with anadequate service life. However, the application of suchmaterials in structural elements reinforced with steel

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bars, as well as in roofing materials will need anadditional investigation involving performance assess-ment and life-cycle-cost analysis.

7.

The correlation of accelerated deterioration test resultswith those obtained from the specimens exposed tonatural climate variations, will allow predicting theservice life of natural fiber-reinforced composites. Thecorresponding field experiments will be the subject ofour future work.

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