Crushed cement concrete substitution for construction aggregates - PDF document

ARCH3,1849 .S.DEPARTMENTOFTHEINTERIOR Construction AggregatesÑA Materials Flow Analysis Any use of trade, product, or Þrm names in this publication is for descriptive purposes only anddoes not imply endorsement by the U.S. GovernmentThis report is only available on-line at:http://greenwood.cr.usgs.gov/pub/circulars/c1177/index.html U.S. DEPARTMENT OF THE INTERIORBRUCE BABBITT, SecretaryU.S. GEOLOGICAL SURVEYThomas J. Casadevall, Acting Director III CONTENTS ..........1.......1Importance of Construction Aggregates to the U.S. Economy ...........................................1The Future of Crushed Cement Concrete Substitution......................................................... 2The Materials Flow Cycle ...................................................................................................3Material Substitutions for More Than a Single Commodity ...............................................3The End Uses for Crushed Cement Concrete ......................................................................4The Materials Flow Diagram for Substitution...................................................................... 5Availability and Transportation Cost Factors in Use as Road Base ....................................7Effects of Physical Properties of Crushed Cement Concrete on Its Use .............................7Other Applications for the Materials Flow Diagram ...........................................................9Tracking Waste and Dissipative Losses ..............................................................................10A Static Representation of a Dynamic Process ...................................................................10Conclusions and Implications for the Future .......................................................................11References Cited ..................................................................................................................11Appendix of Supplemental Information ..............................................................................12 1.Graph of natural aggregate consumption in the United States (historical and projected).........................................22.Graph of projections of U.S. consumption of crushed stone and sand and gravel....................................................33.Flow chart of the materials ßow cycle.......................................................................................................................44.Flow chart showing generic materials ßow concept for minerals and materials.......................................................55.Pie chart of end uses of crushed cement concrete.....................................................................................................66.Flow chart showing ßow of construction materials (construction aggregates vs. crushed concrete), 1996..............77.Pie chart of end uses of crushed cement concrete (combining several categories)...................................................88Ð10.Flow charts showing:8.Flow into end uses (construction aggregates vs. crushed cement concrete).......................................................99.Flow of natural aggregates, 1996........................................................................................................................1010.Flow of construction materials (construction aggregates vs. crushed concrete), 1996 (annotated)....................12 1 Construction AggregatesÑA Materials Flow Analysis Thomas Kellymaterials flow analysis. The amounts of substitution in eachstruction, landscaping, and other construction uses. Theyconsumption occurred. The consumption of natural aggre-are visible. The dips in aggregate consumption reach a lowstruction industry in particular. Figure 1 projects the con-increase until the year 2020. These projections assume that CRUSHED CEMENT CONCRETE SUBSTITUTION FOR CONSTRUCTION AGGREGATES 2 1900191019201930194019501960197019801990200020102020 3 MATERIAL SUBSTITUTIONS FOR MORE THAN A SINGLE COMMODITYdone by the Portland Cement Association. Approximately95 million t (metric tons) of crushed cement concrete substi-tutes for construction aggregates, which are consumed atapproximately 2 billion t per year. But the use of crushedcement concrete is rapidly increasing. More than half of the81 companies contacted for the phone survey reported anincrease in amount of recycled concrete from 1996 to 1997.Natural aggregate producers, who represent only part ofcrushed cement concrete producers, increased their produc-tion of recycled concrete by 37 percent between 1995 and1996 (Bolen and Tepordei, 1996, tables 16 and 22). Severalfactors presented herein show why this substitution shouldcontinue to increase. A method of tracking this increase is toanalyze the flow of construction aggregates through thematerials flow cycle.THE MATERIALS FLOW CYCLEThe materials flow cycle is illustrated in figure 3. Mate-rials are extracted from the earth in a crude form, refined, andpurified, so that they can be manufactured into products. Atthe end of a productÕs lifetime, the materials are either dis-carded or recycled. At every step of a materialÕs lifecyclethere are potential material losses. These losses may occurthrough the discard of wastes or through dissipative losses ofmaterial into the environment. The mineral commodity spe-cialists of the former U.S. Bureau of Mines (now with theU.S. Geological Survey) tracked the lifecycle of 12commodities through the material cycle. A generic represen-tation of the materials flow concept, illustrated in figure 4,was used for the 12 studies (Kostick, 1996, p. 220).In tracking a commodityÕs lifecycle each study alsoconsidered the flow of that commodity through the U.S.economy. Waste and dissipative losses, recycling, exports,and imports were tracked to give a thorough picture of thecommodityÕs flow. The studies provided an understanding ofthe resource production, manufacturing processes, and con-sumption for these commodities, and also provided a frame-work for analyzing a material substitution.MATERIAL SUBSTITUTIONS FOR MORE THAN A SINGLE COMMODITYMaterial substitution occurs when an alternate materialis substituted for a traditional material in a product. Substitu-tion often involves more than one commodity, because mostproducts are a combination of several minerals, metals, orplastics. Thus the substitution process must be analyzed atthe product level to be understood. Examples of recent sub-stitutions include the material changes in motor oil cans andconstruction framing studs: plastics have replaced metal andpaper in oil cans; steel studs require an alternative form ofinsulationÑfoam panelsÑto produce an exterior residentialhouse wall, a product traditionally insulated with fiberglass.An analysis of material substitution should include flows of 196519701975198019851990199520002005201020152020 Sand and gravelÑActual Crushed stoneÑActual Crushed stoneÑLinear trend Sand and gravelÑLinear trendEXPLANATIONFigure 2. Projections of U.S. consumption of crushed stone and sand and gravel. CRUSHED CEMENT CONCRETE SUBSTITUTION FOR CONSTRUCTION AGGREGATES 4 RecycledflowWaste or lossesPost-consumerdiscardsRenewable andnonrenewableresourcesLandfills, impound-ments, deep wells, andocean disposalReleases to air,land, and water ResourcesupplyProduction andmanufacturingRecyclingConsumption material. For example, construction aggregates are used in aface of a road. At the point of substitution, in the product, thecurrent amount of substitution has on the U.S. economy. Forbuildings. Figure 5 illustrates these end uses and quantifies 5 THE MATERIALS FLOW DIAGRAM FOR SUBSTITUTION CHANGES Quaternaryrecycling Tertiaryrecycling Secondaryrecycling Primary recyclingOre-Finished Product ConcentratesSemi-Mgfr.Products AnimalVegetableMineralGases SOURCES POST CONSUMPTION Solid waste discharged Primary CoproductByproduct of materials through the material cycle. The figure repre-sents data or estimates for 1996. (See the appendix for adiscussion of this issue.) Figure 6 represents the flow of allstitution process. As previously mentioned, the substitutionroadsÓ and Òbuildings.Ó Therefore, those uses of construc-substitute are eliminated. For example, crushed limestonethe crushed stone commodity flow. Maintaining this CRUSHED CEMENT CONCRETE SUBSTITUTION FOR CONSTRUCTION AGGREGATES 6 the products. The substitution process is quantified so thatcrete for many years. To indicate the time dependency of thedata, ovals and rectangles are used. All of the data flowingspan more than a yearÕs time. By subtracting the knownlated. (Split flows occur downstream of a total commodityor recycled flow.) It is necessary that all flows except oneance on a process oval. This condition is met for the ovalsmanufacturing.Ó Material balances were performed on theand others.Ó The ability to calculate unknown flows is onethat lead to end uses in the products. Smaller downstreamthey substitute. The details of the calculations performed and 7 EFFECTS OF PHYSICAL PROPERTIES OF CRUSHED CEMENT CONCRETE ON ITS USEAVAILABILITY AND TRANSPORTATION COST FACTORS IN USE AS ROAD BASEEighty-five percent of concrete recyclers have the abil-ity to go to the job site in order to crush concrete (Deal, 1997,p. 10). Only 24 percent are actually going to the job site tocrush concrete, but the ability to locate a yard near a job sitecan also be a consideration in the costs of recycling, becausetransportation cost is a major competitive factor amongsources of aggregate. Portability of the crushing operationcan provide the cost advantage to crushed cement concreteover other aggregate sources at a particular job site. This isespecially true for road base, because the material can becrushed on site or nearby and set in place. Crushed cementconcrete for use in bituminous and cement concretes, how-ever, may require transportation from the site of demolitionto a crushing operation, then to a mixing plant, and finallyback to a construction site. The advantage in transportationcosts for road base materials can be viewed as an advantagein availability as well as an advantage in transportation cost.It is as if the mine site were located on the construction site. Cement concrete pavements in highways, roads, park-ing lots, airport runways, and sidewalks contain less steelthan the concrete demolished from buildings. Steel is gener-ally not placed in pavement layers, because it can causecracking during freeze-thaw cycles. This also increases therecyclability of the crushed cement concrete from pave-ments, because it is easier to produce a product without thecomplication of having to remove and recycle or dispose ofthe steel byproduct of the crushing operation. EFFECTS OF PHYSICAL PROPERTIES OF CRUSHED CEMENT CONCRETE ON ITS USEThe difference in physical properties between naturalaggregates and crushed cement concrete is strongly influ-enced by the inclusion of the cement paste surrounding theaggregate in crushed cement concrete. (This fact was notedby Stephen W. Forster of the Federal Highway Administra-tion (FHWA) on October 5, 1997, in a talk given at a Con-struction Materials Recycling Seminar in Minneapolis, and roads 88.01110855 73395 29.223.7217121411323 91 2603785.4983.281094.824.148.90.88.6 5.618?? ? production gravelproduction production production mix asphaltmix manufact-uring pavement concrete roofing production 80.65.7 8.5 slag production 16.1 3.181.7311.1 ?? ?5.66 .Flow of construction materials (construction aggregates vs. crushed concrete), 1996. Flows in million metric tons. CRUSHED CEMENT CONCRETE SUBSTITUTION FOR CONSTRUCTION AGGREGATES 8 concrete9%Cement concrete 6%Road baseand others85%Minn.) Physical properties of this paste are markedly differ-ent from the properties of natural aggregates. The specificgravity of crushed cement concrete is commonly lower thanthat of the natural aggregate used to make the concrete, andthe absorption of water is always higher. The cement pastecomponent of crushed cement concrete produces more finesthan when stone is crushed. These fines have an absorptionas much as eight times greater than fines produced by crush-ing stone. As a result, the use of crushed cement concrete inhot asphalt mix requires the use of more asphalt binder thandoes the use of crushed stone, which then increases the costof bituminous concrete because asphalt is the most expensivecomponent of bituminous concrete pavement. If crushed cement concrete is being used for aggregatein cement concrete mix, specific gravity, absorption, fine-ness, and angularity are all important physical properties.Crushed cement concreteÕs absorption, when substituted incement concrete, requires that more water be used in thecement mixing ratio than when natural aggregate is used.Furthermore, the irregular surface of crushed cement con-crete has more nooks and crannies than does natural aggre-gate, and this causes more cement to be used to fill thesesmall holes (Wilson, 1993, p. 4). Cement is the most expen-sive component of cement concrete, so this adds to the costof using crushed cement concrete. The angularity of crushedcement concrete, especially in the fine sizes, affects concretefinishability and workability. Experience indicates that up to75 percent natural aggregate fines may be necessary to obtaina workable cement concrete mix that is capable of being fin-ished. (This fact was noted by Stephen W. Forster of the Fed-eral Highway Administration (FHWA) on October 5, 1997,in a talk given at a Construction Materials Recycling Seminarin Minneapolis, Minn.) This is a problem with the use ofcrushed stone sand also, and it is resolved by the use of nat-ural sand (McCarl, 1983, p. 72). The availability and trans-portation costs of natural sand may affect the amount ofcrushed cement concrete used in a cement mix. For the category Òroad base and others,Ó crushedcement concrete must have the appropriate physical proper-ties that permit servicing that particular end use. For bothroad base and fill material, fines may be a problem wheredrainability is required. Washing the crushed cement con-crete to remove fines may be required, but this adds to thecost of using crushed cement concrete. Dissolution of thecrushed cement concrete can occur over time in a fill or roadbase application, so the soundness of the concrete may be animportant factor for these end uses. Soundness is a test thatmeasures the aggregateÕs general resistance to environmentalexposure, including heating and cooling, wetting and drying,and freezing and thawing. If dissolution occurs, a possibleconsequence is an elevation of ground-water pH by theleaching of calcium hydroxide from the cement paste. If thisground water contacts air, calcium carbonate will precipitateout of the solution, possibly clogging drainage systems. Con-tact between vegetation and the high-pH ground water maycause vegetation damage (Snyder, 1995, p. 3). Dense roadbases will be less susceptible to leaching, and, in fact, mayeven become more tightly cemented together by the chemicalactivity occurring when water passes through the material.(This fact was noted by Stephen W. Forster of the FederalHighway Administration (FHWA) on October 5, 1997, in atalk given at a Construction Materials Recycling Seminar inMinneapolis, Minn.) Whether the use is for road base or fill,crushed cement concrete must be able to support the loadapplied to it over time, so the ability to retain compressivestrength, as measured by soundness, is a property that mustbe considered.For other uses in the Òroad base and othersÓ category(riprap or jetty stone or any use in which weathering mayhave an effect on the useful life of the product), soundnessmay be an important consideration. Aesthetic properties area consideration for use as landscaping rock. There have beenattempts to paint crushed cement concrete to increase its aes-thetic appeal. This extra treatment adds to the cost of usingcrushed cement concrete. In summary, crushed cement concrete must first meetthe physical specifications required by the end use and thenbe competitively priced in order to substitute for constructionaggregates from natural sources. It is able to meet these spec-ifications for all three categories of end uses, Òroad base andothers,Ó Òbituminous concrete,Ó and Òcement concrete.Ó Foruse as road base, transportation cost is an important factor inthe preference exhibited in the material flow of crushedcement concrete to this end use. The higher costs of usingcrushed cement concrete in bituminous concrete or cementconcrete are due to its increased absorption, requiring more Figure 7. End uses of crushed cement concrete (combining sever-al categories). 9 sumption, and disposal or recycling. Laying out this flow aggregates Road baseand othersCementconcreteBituminousconcrete1,9651,130494338Crushedcementconcrete 94.880.68.5(85%)(6%)(9%)(58%)(25%)(17%)5.7 Figure 8. Flow into end uses (construction aggregates vs. crushed cement concrete). Flows in million metric tons. CRUSHED CEMENT CONCRETE SUBSTITUTION FOR CONSTRUCTION AGGREGATES 8 also show this preference in flow. Crushed cement con-gravel mix. It flows preferentially to Òbituminous concreteÓin comparison to flow towards Òcement concrete.Ó Crushed production gravel production mix mix 83.2217411121 Figure 9. Flow of natural aggregates, 1996. Flows in millionmetric tons. 11 lifetimes. The materials flow diagram, figure 6, providesand the quantity of these flows. This information can bejust a few material flows. An example of an overview iscrushed cement concrete for construction aggregates. Thisstraints on the data included. Once the diagram was pro-became evident. An example of this is the preferentialfigure 9, an isolated portion of the total flow diagram. Theconstruction industry. For example: How much substitu-tion will occur in the future? The large difference betweenable; will it meet the specifications for the end uses? Theimportance when they can be compared through time; willcrushed stone? The relationships between material use andral materials and waste reduction in the future; should thisculate unknown flows, and data gaps are revealed. In thistrends:Illinois Department of Natural Resources TechnicalDeal, T.A., 1997, What it costs to recycle concrete: C&D Debris Lefond, S.J. , edition: American Carr, D.D., and oth-and report: Department of Transportation, Federal High- CRUSHED CEMENT CONCRETE SUBSTITUTION FOR CONSTRUCTION AGGREGATES 12 and roads 88.01110855 73395 29.223.7217121411323 91 2603785.4983.281094.824.148.90.88.6 5.618? production gravelproduction production production mix asphaltmix manufact-uring pavement concrete roofing production 80.65.7 8.5 slag production 16.1 3.181.7311.1 ? amounts as reported in the year 1996. This is true for mostthe most accurate year currently reported. Other data in theseveral years. This inconsistency between data sets israte is assumed to apply in 1996 also. Improvements to thesescripts in the following version of figure 6, figure 10. Thelows. Details concerning a particular number in figure 10 13 Cement Production = 88.0 million t. This is a directCrushed Stone Production = 1,110 million t. This is agranules from table 13 of MYB1996. At first, this use wasthe material balance equations. The same mention of use bySand and Gravel Production = 855 million t. This is a1.Sand and gravel flowing to concrete = 914*.452.Sand and gravel flowing to road base and3.Sand and gravel flowing to hot asphalt mix =4.Sand and gravel flowing to construction fill =Table 1: LETTERDATA SOURCEAUSGS, Minerals Yearbook 1996BAnnual Energy Review 1996CAmerican Iron and Steel Institute phone call March 10, 1998DNational Asphalt Pavement Association FAX of data table and a calculationECALCULATION by authorFRecycling and Use of Waste Materials and By-Products in Highway ConstructionGCALCULATION by authorHCALCULATION by authorIPortland Cement Association and a calculation by authorJUSDOT, A Study of the Use of Recycled Paving Material KUSDOT, A Study of the Use of Recycled Paving Material LUSDOT, Pavement Recycling Executive Summary and Report March 1996MUSDOT, A Study of the Use of Recycled Paving Material and a calculationNC&D Debris Recycling Sep/Oct 97?Unknown Flows CRUSHED CEMENT CONCRETE SUBSTITUTION FOR CONSTRUCTION AGGREGATES 1.Iron and steel slag flowing to asphaltic concrete =2.Iron and steel slag flowing to cement concrete=3.Iron and steel slag flowing to road base, construc-4.Iron and steel slag flowing to roofing granulescontains 10 years of data. This estimate of steel in concretepavingÓ for the years 1970-1990. Unfortunately the asphaltfor paving can be estimated. This percentage can then belion t flowing to pavement. Assuming a by-weight ratio of 688.0/1 = (411 + 1.73 + 5.7+ x)/5.7 x = amount ofcrete. This is an underestimate if you compare to table 13 of 15 percent to buildings and 40.7 percent to highways. A typicalwater. Combining this information with total cement con-Associates. These two flows from ÒbuildingsÓ and Òhigh-ways and roadsÓ will help to fill in all the remaining questionplicates the recycling process. The waste contains approxi-asphalt. At least 11 States are allowing inclusion of oldBoard, 1997). As this process becomes more accepted, the 15 percent to buildings and 40.7 percent to highways. A typicalwater. Combining this information with total cement con-Associates. These two flows from ÒbuildingsÓ and Òhigh-ways and roadsÓ will help to fill in all the remaining questionplicates the recycling process. The waste contains approxi-asphalt. At least 11 States are allowing inclusion of oldBoard, 1997). As this process becomes more accepted, the CRUSHED CEMENT CONCRETE SUBSTITUTION FOR CONSTRUCTION AGGREGATES 1.Iron and steel slag flowing to asphaltic concrete =2.Iron and steel slag flowing to cement concrete=3.Iron and steel slag flowing to road base, construc-4.Iron and steel slag flowing to roofing granulescontains 10 years of data. This estimate of steel in concretepavingÓ for the years 1970-1990. Unfortunately the asphaltfor paving can be estimated. This percentage can then belion t flowing to pavement. Assuming a by-weight ratio of 688.0/1 = (411 + 1.73 + 5.7+ x)/5.7 x = amount ofcrete. This is an underestimate if you compare to table 13 of 13 Cement Production = 88.0 million t. This is a directCrushed Stone Production = 1,110 million t. This is agranules from table 13 of MYB1996. At first, this use wasthe material balance equations. The same mention of use bySand and Gravel Production = 855 million t. This is a1.Sand and gravel flowing to concrete = 914*.452.Sand and gravel flowing to road base and3.Sand and gravel flowing to hot asphalt mix =4.Sand and gravel flowing to construction fill =Table 1: LETTERDATA SOURCE