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Residential Concrete Mix and Recycled Concrete Life Cycle Assessment

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ResidentialConcrete Mix and Recycled Concrete Life Cycle Assessment

Affiliation:

Abstract

Cementis an invaluable material in building and residential constructionand in the infrastructure industry in general. Nevertheless, due toits extensive use, it is projected that there would come a time thatthe resources for its raw materials will be depleted. Hence,scientists and engineers are continuously findings ways to optimizeits use and to conserve whatever it was left in the resources.Recycling concrete is one of the ways to achieve such aims. Thisresearch studied the economic efficiency and environmentalfriendliness of concrete recycling using the Life Cycle Assessmentmethod. Results indicate that using recycled concrete is moreenvironmentally friendly than using raw concrete materials. Resultsalso showed that the economic soundness of using recycled concretedepends greatly in the method used for recycling and the planningstage of the construction or building effort.

1.Introduction

Thereare only limited resources in this planet to sustain the basic needsof each individual. One of these basic needs is shelter. Hundreds ofyears ago, people are using wood and cut stones to construct housesfor their residence – such method is tedious and expensive. Theinvention of cement and concrete has forever changed residentialconstructions. Not only does the use of residential concrete mixallowed the construction of mega structures but of also of cheaper,stronger residential buildings. Nevertheless, even though the lifespan of concrete is significantly long, it still has its end andtherefore needs to demolish and replaced. The changes in the needs ofpeople with regards to buildings and building designs alsonecessitate that previously constructed concrete structures bedemolished and replaced by newer once. As aforementioned, there isonly a limited source for the raw materials for making concrete hencescientists and engineers are continuously finding ways to maximizethe use of concrete. One of these ways is recycling. In order to dothis, certain parameters must be measured. Two of these parametersare the economic feasibility of concrete recycling and environmentalimpact – that is, is it more economically sound and moreenvironmentally friendly to recycle concrete or to simply replace itwith newly created one? This research therefore aims to study theeconomic and environmental benefits of recycling concrete

2.Literature Review

2.1What is a concrete and how is it made?

Concreteis basically a mixture of aggregates, rocks, and paste. The paste isusually composed of cement and water. In the creation of theconcrete, the paste coats the surfaces of the coarse and fine largerparticles called the aggregates. After the paste coats the aggregatesit begins to harden though a process called hydration gaining itsstrength forcing all aggregates to form into one piece of rock-likemass which is called the concrete.

Theprevalence of the use of concrete is due to its characteristicsduring the pre-hydration and post hydration phases. Accordingly,concrete is malleable and elastic when it is just newly mixed, thenit becomes durable and string when it hardens. Such properties allowsit to be used in numerous applications such as the creation of skyscrapers which would not been possible with the use of wood andstones considering only a small base for the building is available.Its long life cycle also makes it ideal for making buildings, evenresidential houses which are used through ages.

Theuse of residential concrete mix in this generation is thereforeindispensible in humanity’s strive to make a better civilization.Such is the reason why numerous scientists and engineers arecontinuously finding ways to improve the quality of concrete andmaximize its use. To achieve the latter goal, recycling or usedconcrete is one of the soundest ways.

2.2A brief history of concrete

Notethat the use of concrete is not new at all. The early use of concretecan be traced to as far back as 7, 000 BC in Israel wherearcheologists found ruins which makes use of concrete as flooring in1985. The second group people known to have used concrete is theEgyptians in the 3, 000 BC for the construction of the pyramids.Accordingly, they have used mud and straw – on modern concrete, themud is the cement and the straw is the aggregate. Then, in about thesame year the Chinese extensively used the same technology forbuilding the great wall of China. The great Roman Empire only startedusing concrete in 300BC. Their concrete was a mixture of groundedstones and cement which is made from grinding lime with volcanic ash.They have also found out that they can vary the composition of thecement in order to give it different properties. Some of theadditives which they put to vary its composition include animal fat,blood, and milk. After this great discovery about the variation ofconcrete properties by varying its composition, the use of concretewas suddenly stopped in the middle ages, due to the fall of the RomanEmpire. It was only in 1759 when John Smeaton made a waterproofconcrete. Accordingly, he discovered that by calcifying limestonewhich contains clay, the resulting mixture could undergo hardeningeven under water. This invention made the creation of the lighthousepossible, as the concrete could withstand sea attacks. Since thattime onwards, up to the present, different concrete were and arebeing made.

2.3The optimization of concrete use through recycling

Despitethe fact that there was a continuous effort to improve concretequality starting from 1759, the concept of optimizing its use onlybecame popular in the 20thcentury due to the fact that humanity has become more aware of thegrowing scarcity of resources for making concrete. One of thediscovered ways of maximizing the use of concrete is recycling.

Ina study conducted by the European Concrete (2009) it was noted that ahuge amount of Construction and Demolition Waste (C&ampDW) isgenerated all over the world. In Europe alone, approximately 200million tons of C&ampDW is generated in a yearly basis. The UnitedStates also generates about the same amount of C&ampDW. The majorityof this material is concrete which has reached the end of its longlifecycle. Hence, it is needed that C&ampDW must be disposed of withminimal environmental impact. Fortunately, scientists and engineershave found a way to recycle old concrete. At first the recycledconcrete were only used for building roads or pavements, until onlyrecently in the 21stcentury that it was discovered that by crushing and mixing with somematerials the mix can also be sued for making residential buildings.

Accordingto the study conducted by World Business Council for SustainableDevelopment, WCSD (2009), recycling concrete is one of the essentialaspects of sustainable development in concrete use. This is becauseit benefits humanity environmentally and economically. The researchexplained that using raw concrete materials for every type ofconstruction is proven to be less sustainable than when usingrecycled concrete. In order to fully understand such findings it isfirst necessary to understand impact of a concrete structure over itslife cycle.

2.4Overview of the concrete life cycle

Asaforementioned, concrete essentially, has two major components: thecement, which acts as the paste and the aggregates which aresupported by the paste and provides volume to the concrete. Theentire concrete life cycle can therefore be divided into two parts:the production of the cement and the production of the aggregate.Accordingly, it is the cement preparation which actually requirestedious work. It starts with the purchase of raw materials, solidfuels, and gypsum &amp cementuous materials. These three aretransported to become part of the raw material preparation, pyroprocessing, and grinding, respectively. Note that the raw materialsare usually mixed with materials from quarry in the raw materialspreparation step. After mixing the products of these three processesthe cement is made and is transported to another area to be mixedwith aggregates, which are usually quarried stones. The mix is thenloaded, molded and used. The recycling part takes place when the usedconcrete is demolished, crushed, and grinded to be used as aggregatesin the mixing step. In figure 1, which is the entire life cycle ofconcrete, the recycling part is enclosed in the red box.

Figure1: The entire life cycle of concrete (Nisbet,Marceau &amp. VanGeem, 2002)

3.Methodology

Theconcrete life cycle can be an important tool in the assessment of theeconomic and environmental assessment of concrete. One of the methodsused which makes use of such life cycle is the Life Cycle Assessment(LCA) method. Accordingly, this method focuses on the accounting ofthe pro and cons of the steps in the entire life cycle of a productto the environment. The pros and cons are then used to makeimprovements to the product’s life cycle, for strategic planning,for public policy making, for marketing, and other applications. Asummary of the LCA is shown in figure 2.

Figure2: The Life Cycle Assessment (LCA) method and the applications ofits results( Rebitera, Ekyallb, Frischknechtc, Hunkelerd, Norrise, Rydbergf,Schmidtg, Suhh, Weidemai &amp Penningtonf, 2004)

TheLCA method was used in this study to weigh the environmental and theeconomic effects of recycling concrete for the creation ofresidential constructions. It also used this method to makeproposals for possible improvements of the concrete life cycle. Notethat the heart of the LCA is the Life Cycle Inventory Analysis, whichis the center box of the LCA framework in figure 2. Hence, this studydelved much deeper into this step of the LCA method (Guevarra, 2011).

Secondarydata were used in this study. The secondary data were derived frompast studies which focus on the pros and cons of concrete recyclingand reuse. Such data sources included those of the studies conductedby government organizations, individual and group studies, which havebeen peer-reviewed and were published in the 21stcentury. This criterion was used in the selection of data sources inable to increase the reliability and validity of the findings of thisresearch. These data were then used to determine the advantages anddisadvantages of using recycled concrete materials over using rawconcrete materials on residential construction.

4.Analysis and Results

Asaforementioned, the concrete life cycle is composed of two majorsteps – the cement production and the aggregate production. Notethat the cement production is the same in using recycled and rawaggregate materials hence, the real assessment or point ofcomparison is the production and use of aggregates. This means thatthe efficiency of using raw materials, which are obtained throughquarrying, must be compared to the efficiency of using recycledconcrete. It is interesting to note that major expenses that shouldbe incurred for raw materials to be sued as aggregates would be spenton the quarrying and in the transportation steps. For recycledconcrete however, the steps are more tedious. Accordingly, after thedemolition, the demolished concrete would have to be segregated. Thesegregation is due to the fact the demolished materials may containother materials which may interfere with the grinding step which willdiscussed later on. Such materials include the steel which are usedin molding and reinforcing the concrete. Other materials may includeinsulation which could have been added to the concrete. Take forinstance the common practice during the 1800s and the early 1900s ofmixing asbestos with cement and aggregates to insulate the concrete.Note that asbestos is a very dangerous group of minerals which couldput in jeopardized the health of workers if such concrete is recycled(Wright, 2006).

Afterthe components of demolished materials have been segregated theconcrete is ready for grinding. This is necessary in order tobreakdown the concrete into smaller particles. While it may not benecessary to grinded concrete into relatively smaller particles inpavement and highway constructions, it is necessary for residentialconstructions as the objects to be constructed are relatively smallerand hence they would more uniform and smaller aggregate materials.Transportation could be necessary between the segregation step andthe grinding step, which will add up to the cost (Battles, 2000).After grinding, the grinded concrete can be mixed with othermaterials such as recycled plastics or other rock to change itsproperties according to what is desired. Note further, that there canbe transportation stage between grinding and mixing, and thesefurther ads up to the total cost of using recycled concrete.Nevertheless, it should be noted that there are indirect costsassociated with using raw materials over recycled concrete. Exampleof such indirect cost would be the cost associated with maintainingor monitoring the landfills where the demolished materials are kept.Such monitoring can last for years and hence years of spending(Elzafrane, Soroushian &amp Deru, 2005).

Thereare other forms concrete recycling methods aside from crushing it tosmaller particles. Some studies have shown that as long as theconcrete has not yet reached its life span – the time it takes forthe concrete to lose its ability to withstand normal adverseconditions – the blocks of concrete can be used in their entirety.These blocks can be used as walls to houses and flooring, even forceiling. The only cost associated with this type of recycling is thetransportation cost and the labor it needs to lift the huge blocks ofconcrete and put them into desired spots (Wright, 2006). EuropeanConcrete (2009) explained that such strategy in recycling concretecan reduce the total cost of construction to 30% – 50%.

Interms of environmental impact, recycling concrete significantlyreduces the need for landfill. It also limits the use of rawmaterials which are essentially mined on quarries which destroys theenvironment. Note also that possible cases of leaching of hazardouschemicals are minimized in recycling concrete (Garette, 2012). Basedfrom the study by Rebitera et al (2004) crushed concrete have higheraffinity to the different chemicals adhered to them. This means lessleaching. Nevertheless, the research explained that in using recycledconcrete, it will still be necessary that a check be conducted inorder to assess whether there are toxic chemicals previously mixed tothe recycled concrete increasing environmental and health risks(Obla, 2007).

Fromthe above results and LCA analysis, it can be inferred that the costof recycling concrete depends on many factors. These factors includethe previous design of the demolished structure. Accordingly, thestructure may have used other materials other than the usualmaterials used. Such materials include asbestos, which may render therecycling procedure highly expensive and even impossible. Somestructures allow the detachment of the building’s component parts,such as the ceiling, wall, etc. Such structures are easily demolishedand the parts easily reused without incurring significant costs. Such design is also more environmental friendly as leaching is lesslikely due to the fact that the concrete will never have to undergogrinding. Another factor that determines the cost of the recyclingconcrete is transportation, it more advisable that the recycledconcrete be used not far from or exactly within the area where theywere demolished. Such removes the necessity to transport them toother areas reducing or removing transportation costs. A summary ofthe factors which determine the cost of concrete recycling vs. usingraw concrete materials, as well as their respective environmentalimpacts are shown in table 1.

Table1: comparison of costs between using raw concrete materials vs.recycled concrete materials

Economic Aspect

Raw Materials Associated Cost

Recycled Concrete Associated Cost

Quarrying cost*

Segregation cost*

Transportation cost*

Grinding Cost**

Mixing and construction cost*

Transportation cost**

Chemical monitoring cost/ landfill monitoring (continuous)*

Hazardous chemical analysis cost (ones)*

Mixing and construction cost*

Environmental Aspect

Raw Materials

Recycled Concrete

Possible leaching in landfills

Possible contamination with hazardous chemicals

Contributes to depletion of natural resources

Contributes to conservation of natural resources

*Compulsory,**Optional

5.Conclusion

Fromthe results of the LCA analysis, it can be concluded that theeconomic and environmental efficiency of using recycled concrete overraw concrete materials in residential concrete mix is highlydependent in the planning of the building construction and the methodused for recycling. It is concluded in this study that building planswhich allows the dismantling of its parts are the best plans thatwill result to efficient concrete recycling. It should be pointed outhowever, that the method of recycling concrete which involvesgrinding and crushing it to smaller particles can also be costefficient if both the crushing and use of the crushed concrete aredone in the same area which minimizes transportation expenses.Recycling concrete is also more economically sound due to the factthat it reduces landfill which necessitates continuous environmentalmonitoring.

References

Battles,S. (2000). Changes in energy usage in residential housing units.Retrieved from: &lthttp://www.eia.doe.gov/emeu/recs/recs97/decade&gt.

Elzafrane,M. Soroushian, P. and Deru, M. (2005). Development ofEnergy-Efficient Concrete Buildings Using Recycled PlasticAggregates, JournalOf Architectural Engineering,11(4): 122 – 130.

EuropeanConcrete (2009). SustainableBenefits of Concrete Structures.Belgium: European Concrete Platform ASBL.

Garette,ECI (2012). Recycled Aggregates/Crushed Concrete. Retrieved from:&lthttp://garretteci.com/crushedconcrete.html&gt.

Guevarra,L. (2011). MIT Weighs the Lifecycle Impacts of Concrete. Retrievedfrom:&lthttp://www.greenbiz.com/news/2011/08/15/mit-weighs-lifecycle-impact-concrete&gt.

Nisbet,M.A. Marceau, M.L and VanGeem, M.G. (2002). EnvironmentalLife Cycle Inventory of Portland Cement Concrete.Portland: Portland Cement Association.

Obla,K. (2007). Crushed Returned Concrete as Aggregates for New Concrete,Final Report to the RMC Research and Education Foundation Project.Retrieved from:&lthttp://drum.lib.umd.edu/bitstream/1903/10029/1/Kim_umd_0117E_11016.pdf&gt.

Rebitzera,G. Ekvallb, T. Frischknechtc, R. Hunkelerd, D. Norrise, G.Rydbergf, T. Schmidtg, W.P. Suhh, S. Weidemai, B.P. andPenningtonf, D.W. (2004). Life cycle assessment Part 1: Framework,goal and scope definition, inventory analysis, and applications,EnvironmentInternational30(5): 701-720.

WorldBusiness Council for Sustainable Development (2009). The CementSustainability Initiative. Retrieved from: &lthttp://www.wbcsdcement.org/pdf/CSI-RecyclingConcrete-FullReport.pdf&gt.

Wright,F.G. Jr. (2006). FHWARecycled Materials Policy. Retrieved from: &lthttp://www.fhwa.org&gt.

Summary

Theamount of resources for making concrete is slowly depleting and theenvironment is adversely affected by its creation. Scientists andengineers are therefore continuously finding ways to maximize oroptimize the use cement and reduce its adverse effects to theenvironment. In line with such efforts, this research studied theeconomic and environmental impact of recycling concrete for makingresidential concrete mix. The assessment was done using the LifeCycle Assessment (LCA) method. The life cycle of the concrete wasfirst mapped out and the economic efficiency and environmentalfriendliness of using recycled concrete over using raw concretematerials were compared. Based from the results the economicefficiency of using recycled concrete lies on two factors, which are:the type of recycling method used, and the planning of the buildingconstruction. Accordingly, the recycling method which does notnecessitate the grinding of recycled concrete is more economicallysound in that it minimizes the expenses in transportation andprocessing, such as the grinding of concrete to smaller pieces andthe toxicity analysis prior to using it to new residential buildings.Buildings or structures which allows the dismantling of its partswithout the need of breaking them into smaller pieces also favorsrecycling at a minimum cost. This is because the huge parts can beused directly into constructing new residential buildings without theneed to crush them to be added into the residential concrete mix. ENevertheless, it was noted in this research that even if the methodwhich involved grinding the concrete to smaller pieces was used, itcan still be more economically sound compared to using raw concretematerials if transportation cost is minimized, by using the recycledconcrete right at the demolition site. Moreover, results from thisresearch revealed that recycling of concrete is more environmentallyfriendly than using new raw concrete materials due to the fact thatit allows the conservation of natural resources and minimizeslandfill.