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Journal of Industrial Technology Volume 15, Number 1 November 1998 to Januray 1999

The Official Electronic Publication of the National Association of Industrial Technology

1998

A Study Conducted toInvestigate the Feasibility of RecyclingCommingled Plastics Fiber in Concrete

By Dr. Kenneth W. Stier & Dr. Gary D. Weede

Volume 15, Number 1 - November 1998 to January 1999

Reviewed Article

Materials & ProcessesPlastics/Polymers

Composite MaterialsEnvironmental Issues

KEYWORD SEARCH

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IntroductionManufacturing industries contribute

significantly to wealth creation in theUnited States, but they also generateapproximately 5.5 billion tons of non-hazardous waste and 0.7 billion tons ofhazardous waste per year. The directcost of handling and disposing of the

hazardous waste alone in the UnitedStates is estimated to be $50 billion peryear (NSF, 1995).

In the United States the paradigm ofmanufacturing is shifting from pollutiondisposal to themes of industrial ecologyand environmentally conscious manu-facturing. The National Science andTechnology Council (1994) outlined anenvironmental strategy to support this

manufacturers have been recycling theirown waste since commercial-scaleplastics processing began (Nir, Miltzand Ram, 1993). The post-consumerwaste represents the largest constituentgoing into the municipal waste stream(approximately 90-95%) (Rebeiz,1992). As a result, the post-consumer

waste has been the focus of governmentregulations and environmental concernsrelated to plastics in recent yearsbecause most of it ends up in themunicipal waste stream. Rebeiz (1992)cites the difficulty in collecting thesematerials and the fact that they areusually contaminated as the key reasonswhy they are so routinely discardedrather than recycled.

The post-consumer waste describedin this study consisted of commingledplastics which came from greeting card

racks that were produced by companyXYZ. The racks consisted of highimpact polystyrene (HIPS), acrylic, anda hot melt used to bond some of theparts. One of the HIPS parts used in thecard racks had a colorant added to it.

Previously received damaged cardracks were landfilled. Due to increasedlandfill costs the plastic was separatedand sent to a recycling firm. Thecompany was interested in otherrecycling alternatives.

PurposeThe purpose of this study was to

generate new knowledge about recy-cling commingled plastics and helpsupport the environmental strategyoutlined by the National Science andTechnology Council (1994). Thisresearch focused on using the com-mingled plastics in fiber form. Theobjectives of this project were to:

Ken Stier is a professor and Certified Manufactur-ing Engineer (CMfgE) in the Department of Indus-trial Technology at Illinois State University (ISU).He teaches materials technology, manufacturingprocesses, and industrial production. Ken has beenpresented the following awards while at ISU: theSociety of Manufacturing Engineers OutstandingFaculty Advisor Award, the Outstanding ResearchAward for the Department of Industrial Technol-ogy, the Outstanding Service Award for the De-partment of Industrial Technology, and the PeoriaSociety of Manufacturing Engineers PresidentsAward.

Gary Weede is a professor in the Department ofIndustrial Technology at Illinois State University(ISU). He teaches plastics technology, manufactur-ing processes, and industrial production. Gary hasbeen presented the following awards while at ISU:

the Chicago Section of the Society of Plastics En-gineers Outstanding Achievement Award, the Out-standing Research Award for the Department ofIndustrial Technology, the Outstanding TeachingAward for the Department of Industrial Technol-ogy, and the Epsilon Pi Tau Laureate Citation.

new paradigm and lay the groundworkfor long-term national economic growthbased on this transition.

One part of the environmentallyconscious manufacturing movement isthe use of waste to create other prod-ucts, thus offering significant potentialfor reducing costs to industry and

society. An example of this is usingplastics for reinforcement in concrete.Natural polymers have been used bybuilders since ancient times to improvethe properties of construction materialsas indicated by Chandra and Yoshihiko(1994). Today, synthetic polymers suchas polypropylene, polyethylene, andacrylic are used for fiber reinforcementin concrete as explained by the PortlandCement Association (1993).

Since synthetic polymer fibers arealready being used for reinforcement in

concrete, it would seem logical to assumethat recycled commingled plastics (amixture of different plastics which arenot easily separated or sorted) could offersimilar benefits if used in fiber form. Thisarticle describes a funded recyclingresearch project which investigated thefeasibility of utilizing mixed varieties ofplastics in extruded fiber form for use asreinforcement in concrete. The firminvolved will be referred to as companyXYZ for purposes of this article. Thespecific name of the company has beenwithheld to enable honest discussion ofthe project.

BackgroundPlastic wastes are separated into

two categories based on their use, (1)post-consumer or public waste and (2)manufacturing waste. Manufacturingwaste constitutes a very small percent-age of the municipal waste stream. Thisis largely due to the fact that plastics

A Study Conducted toInvestigate the Feasibilityof Recycling CommingledPlastics Fiber in Concrete

By Mr. Kenneth W. Stier & Mr. Gary D. Weede

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1. Determine the feasibility ofextruding specific commingledplastic fibers.

2. Conduct testing on concretespecimens containing com-mingled plastics in fiber form toidentify a feasible recyclingalternative for these materials.

3. Disseminate the results.

MethodologyThis study consisted of three

phases. Phase I of the study consisted oftesting for the compression and flexurestrength properties of non-air-entrainedconcrete (concrete without an air-entrainment additive to resist the affectsof freezing and thawing) that containedplastic fibers in various quantities.

The plastic greeting card racks fromcompany XYZ were shredded with a

plastic granulator. The material wasground to approximately 3-7 millimetersin size.

A multistrand die was designed andprecision machined for the extruder inthe plastics laboratory in the departmentso the extrusion of the granulatedcommingled plastics could be studied todetermine the most efficient method ofcreating fiber. Figures 1 and 2 show themultistrand die which was used in thestudy. The plastic granules wereextruded to produce fibers approxi-mately 0.010" to 0.030" in diameter andcut to one inch lengths for use in theconcrete. The type and amount ofplastics fiber added to each batch mix inphase one is shown in table 1.

The concrete materials used in thisstudy included: torpedo FA1 sand, 0.75inch CA11 crushed stone, gray type Iportland cement, and air-entrainment(only used in phases 2 and 3). The batchmix specified by the Portland CementAssociation (Kosmatka & Panarese,1992) for one cubic foot of concrete wasused for this study. Four batch mixes

were used in phase one of this study forcomparison. Each batch mix consistedof four compression and two flexurespecimens. A 1.5 cubic foot capacitycement mixer was used to mix theconcrete. The specimens were preparedaccording to the C192 American Societyfor Testing of Materials (ASTM)Standard (Making and Curing ConcreteTest Specimens in the Laboratory). A

slump test was conducted for each batchmix using the ASTM 143 standard(Slump of Portland Cement Concrete).

A local commercial testing firmcured the compression and flexurespecimens and conducted the tests. Thecompression specimens were testedaccording to the ASTM C39 standard

(Compressive Strength of CylindricalConcrete Specimens) to determine theultimate strength of the specimens. The

tests were run on the following curedates: 7 days, 14 days, 28 days (twospecimens were broken on the 28thday). Standard procedure at the testingfirm used in this study is to test twospecimens at 28 days and take theaverage since this is the optimum curetime for concrete.

The flexure specimens wereprepared in the same manner as thecompression specimens and tested

Figure 2. Base for the multistrand extruder die.

Figure 1. Cap for the multistrand extruder die.

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according to the ASTM C78 standard(Flexure Strength of Concrete Speci-mens Using Simple Beam with ThirdPoint Loading) to determine the ultimateflexural strength. The tests were run onthe following cure dates: 14 days, 28days (one specimen was broken on eachtest date).

The second phase of this studyinvolved the investigation of the effectsof commingled plastics fibers in air-entrained concrete. Air-entrainmentcement additive is used to improvedurability to repeated freezing andthawing. This phase of the project calledfor conducting compression, flexure,and freeze-thaw tests to investigate thefeasibility of recycling the plastics wastein air-entrained concrete.

An air meter was used to take theair content readings. The desired aircontent for the project was 6% because

the American Concrete Institute recom-mends between 4.5% and 8% aircontent for the location of the research.

Concrete specimens were preparedfollowing the ASTM C192 standard. Aslump test was conducted for each batchmix using the ASTM C143 standard andthe air content was measured using theC231 standard (Standard Test Methodfor Air Content of Freshly MixedConcrete by The Pressure Method). Thesame quantities of commingled plasticsfibers were added as in phase one of the

study. However, two control groupswere used this time for comparisons,one with no plastic fiber and a secondcontaining commercial plastic fiber inthe normal amount (see table 2). Thecompression and flexure specimenswere tested by the same local commer-cial testing firm used in phase one of thestudy. The specimens were cured in acuring room until they were tested. Thecompression tests were conducted at the

following intervals: 7, 14, and 28 days.Two compression specimens werealways tested at the 28 day interval toobtain an average. The flexure testswere conducted at 14 and 28 days.

The air-entrained concrete batchmixes were also tested for their abilityto withstand freezing and thawingconditions over time. The freeze-thawtests were conducted according to theASTM C666 standard (Resistance ofConcrete to Freezing and Thawing).These specimens went to a secondcommercial testing facility where theywere cured and subjected to 354 cyclesof freezing and thawing. Measurementswere taken at various intervals with aprecise dial-indicator instrument todetermine the amount of expansion in

the specimens as a result of theseconditions. Passing these tests is a goodindication that the concrete and plasticsmixture will perform well in a naturalfreeze-thaw environment.

The batch mixes for the third phaseof the study are shown in Table 3. Thisgroup of tests was conducted to focus

on specific quantities of commingledplastics in the batch mixes and to gathermore data with regard to the strengthand durability of these batch mixescompared to the two control groups.

The procedures for preparing thespecimens and testing them was thesame as in the previous phase with twoexceptions. The first exception was thatno 14 day flexure test was conducted.Another exception was that a secondflexure specimen and two additionalcompression specimens for each batch

mix were run through freeze-thawcycles for 28 days and then tested. Thiswas done to investigate the durability ofthe concrete.

ConclusionsFigure 3 shows the compression

strength values for the non-air-entrainedconcrete used in phase one of the study.The results of the compression testsshow good strength values for all of the

Table 1. Quantities of Plastic Fibers in the Non-air-entrained Concrete

Batch Mixes -- Phase I

Table 2. Quantities of Plastic Fibers in the Air-Entrained Concrete

Batch Mixes -- Phase II

Table 3. Quantities of Plastic Fibers in the Air-Entrained Concrete

Batch Mixes -- Phase III

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concrete specimens. A minimum of2500 psi is often required by code in acompression application. The strengthvalues far exceeded the minimum in allcases. Most interesting is that batch mixnumber four, which had the largestamount of plastic fiber, had betterstrength than the specimens in batch

mix numbers one and three with loweramounts of fiber. Batch mix numberfour also had comparable strengthvalues to batch mix number two whichdid not contain any plastics fibers.

Figure 4 shows the compressivestrength values for the air-entrainedconcrete used in phase two of the study.Once again, the batch mixes with thecommingled plastics fiber (1, 3, and 4)show comparable strength values to thetwo control groups (2 and 5). Batch mixnumber four, which contained one and

one-half times the normal amount ofplastic fibers, showed strength values asgood or better than the two controlgroups (2 and 5) in both early cure timetests and the 28 day tests.

Figure 5 shows the compressivestrength values for the air-entrainedconcrete used in phase three of thestudy. Batch mix number three, withtwice the normal amount of plastic fiberin it, showed better compressivestrength values than any of the otherbatch mixes at all cure times.

Figure 6 shows the flexure strengthvalues of the concrete without air-entrainment used in phase one of thestudy. The strength values were clus-tered in a similar range. Batch mixnumber three, with one-half the normalamount of plastic fiber, had the highestflexure strength (1190 psi) as comparedto 1090 psi in the control group (batchmix number 2).

Figure 7 shows the flexure strengthvalues for the air-entrained concreteused in phase two of the study. Thespecimen for batch mix number two was

mistakenly tested at 14 days instead ofthe 28 day cure time. All the specimenshad good flexure strength.

Figure 8 shows the flexure strengthvalues for the air-entrained concreteused in phase three of the study. In thisphase only one concrete beam wasprepared for each batch mix and theflexure testing was conducted at 28days. Figure 8 shows there is very little

Figure 5. Compressive strength values for concrete specimens

with air-entrainment - Phase III.

Figure 3. Compressive strength values for concrete specimens without

air-entrainment - Phase I.

Figure 4. Compressive strength values for concrete specimens

with air-entrainment - Phase II.

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variation in the strength values. It alsoshows that batch mix number three, withtwice the amount of plastic fiber, hadthe second highest strength value.

The results of the study also show adecrease in the strength values goingfrom phase one to three. Adding air-entrainment will generally cause a

reduction in the strength of the concrete.Figures 9 and 10 show the percent of aircontent in the specimens. Anywherefrom 4% to 8% was the suggestedamount. Figure 9 shows that thespecimens in phase two had low aircontent readings and figure 10 showsthat the percent of air content was high.Further indication of the affects of theair content can be seen by looking atbatch number three in the third phase.The air content was the lowest of allfour batches (5.5%) in that phase of

testing and the compressive strengthvalues were the highest at all cure times(see figures 5 and 10).

Another factor that can affect thestrength of the concrete is the amount ofwater in the batch mix. The slump test isused to determine the consistency of thebatch mix. Figures 11, 12 and 13 showthe slump values for the batch mixes inthe three phases of the study. Thedesired slump values for this study werebetween 3" and 5". The slump values inphase two most closely matched thedesired range (see figure 12). Thevariance in slump values for the flexurespecimens did not appear to substan-tially affect their strength. For examplebatch number one in phase two had arather low slump (2.75") and yet itsflexure strength was consistent with theother specimens in that phase (seefigures 7 and 12).

Variance in slump values for thecompression specimens appeared tohave mixed results. Figure 11 showsthat the compression specimens in batchnumber 2 in phase one had a 3" slump

while batch number three had an 8"slump. Figure 3 shows slightly highercompression strength values for batchnumber two versus batch number three.This trend appears to be reversed inphase three as can be seen by reviewingthe results of batches two and three infigures 5 and 13. In phase three thehighest slump value resulted in thehighest strength values.

Figure 6. Flexure strength values for concrete specimens without

air-entrainment Phase I.

Figure 7. Flexure strength values for concrete specimens with

air-entrainment - Phase II.

Figure 8. Flexure strength values for concrete specimens with

air-entrainment - Phase III.

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Of particular concern was how theplastic would affect the expansion of theconcrete during the freeze-thaw testingsince they have different coefficients ofthermal expansion. Any concretespecimen that expands over 0.06% isconsidered to have failed. Figure 14shows that batch mix numbers one and

two in phase two failed the freeze-thawtest with 0.114% and 0.065% expansionrespectively and batches three, four, andfive passed with 0.050%, 0.008%, and0.024% expansion respectively. While itwas encouraging to see that batches threeto five passed this test, there did notappear to be consistency in the results inthis phase because batches one and twofailed the test. Batch number one had thenormal amount of commingled plasticsfiber and batch number two did notcontain any plastic fiber. This inconsis-

tency was one of the reasons for doingthe third phase of tests.Figure 14 shows that all the

specimens in the third phase failed thefreeze-thaw test. Again the results wereinconsistent because batches two andfour should have passed since theycontained no plastic fiber and commer-cial plastic fiber respectively. At thesame time the freeze-thaw test speci-mens were cycling through freezing andthawing conditions, one compressionspecimen for each batch mix was takenthrough 143 freeze-thaw cycles and thentested at 28 days to further examine thedurability of the concrete. The speci-mens showed strengths similar to theircounterparts that were tested withoutbeing exposed to these conditions (batchnumbers one to four respectively - 4,510psi, 4,180 psi, 4,992 psi, and 4,427 psi).Normal compression breaks wereexhibited in the specimens.

RecommendationsThe concrete containing recycled

plastics fiber showed promising results in

compression, flexure, but inconsistentresults in freeze-thaw testing. Furthertesting would need to be conducted withmore precise control of variables such asair and moisture content before furtherconclusions could be made. Commercialbatch mixing would be needed to providemore precise control and determine thefeasibility of using these commingledplastics fibers in real world applications.

Figure 9. Percent air content for concrete specimens with

air-entrainment Phase II.

Figure 10. Percent air content for concrete specimens with

air-entrainment Phase III.

Figure 11. Slump values for concrete specimens without

air-entrainment Phase I.

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Two variables, the length of fiberand diameter of the fiber, should also beinvestigated for their affect on thestrength or characteristics of the concrete.

CommentsThis research project is one ex-

ample of how an industrial technology

department can service local industrysneeds and support the environmentallyconscious manufacturing movement.This type of work offers many researchopportunities for faculty and students. Itcan very easily be used as the basis forexperimentation and problem-solvingtype laboratory activities. One way tomotivate students is to challenge themwith project work like this which has thepotential to improve the environment,help manufacturing companies, andbenefit their community.

Additionally, this type of research isa means for faculty to stay current withtechnology and transfer their knowledgeinto the classroom. It is a means toexamine the problems which face oursociety and allow everyone to benefit.

ReferencesChandra, S. and Yoshihiko, O.

(1994). Polymers in concrete. AnnArbor, MI: CRC Press.

Kosmatka, S. H. & Panarese, W. C.(1992). Design and control of concretemixtures, (13th ed.). Skokie, IL:Portland Cement Association.

National Science Foundation.(1995). Environmentally consciousinitiative announcement. Arlington, VA.

National Science and TechnologyCouncil. (1994). Technology for asustainable future. Washington, D. C.

Nir, M. M., Miltz, J., and Ram, A.(1993, March). Update on plastics andthe environment: progress and trends.Plastics Engineering, 49, 75-93.

Portland Cement Association.(1993). Fiber reinforced concrete.

Skokie, IL.Rebeiz, K. S. (1992). Recycling

plastics in the construction industry.Waste Age, 23, 35-38.

Figure 12. Slump values for concrete specimens with

air-entrainment Phase II.

Figure 13. Slump values for concrete specimens with

air-entrainment Phase III.

Figure 14. Aggregate freeze-thaw average final expansion

percentages for concrete specimens with air-entrainment Phases II and III.

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