Section III: Surface Gravel

1 The answer to this question will vary depending on the region,localsources of aggregate available andother regions of thecountry do not have good sources ofgravel (technically called aggregate).A few coastal regions use seashells for Surface material on their ,this Section of themanual will discuss the most commonsources of are quarryaggregates such as limestone,quartziteand granite;glacial deposits of stone,sand,silt and clay;and river run gravelsthat generally are a mix of stone thing should be stressed:it pays to use the best quality materialavailable.(31)Difference in Surface Graveland Other UsesToo often Surface Gravel is taken fromstockpiles that have actually beenproduced for other uses. For instance,the Gravel could have been producedfor use as base or cushion material for a paved are two majordifferences between Surface Gravel andbase (cushion) Gravel forSection III: Surface GravelSection III: Surface Gravel39base courses will generally have largertop-sized stone and a very small per-centage of clay or fine is necessary for the strength and gooddrainability needed in base gravels.

2 Thismaterial will not form a crust to keepthe material bound together on a will become very difficult Gravel could have beenproduced simply as fill material for useat building sites. This material often hasa high content of sand-sized particleswhich make it very drainable. This is adesirable characteristic in fill materialsince water can quickly flow through itand drain away from under buildingfoundations and parking the same material will remain loose and unstable on a Gravel a Gravel road needs is sufficient finematerial that has a plastic or binding the good blend of stone,sand andfine-sized particles tightly bound together on this road is Good Gravel ?Good GradationGravel is a mixture of three sizes ortypes of material:stone,sand and will be discussed further in the a good blend of thesethree sizes,the Gravel will ,poor performinggravel will often be blamed on themaintenance the operatorcannot make good Gravel out of or poorly graded Gravel can not be changed to good gravelwithout additional costs,but it is often well worth common practice of improvingsurface Gravel is to add new,clean,virgin fine Surface gravelneeds a percentage of stone whichgives strength to support loads particularly in wet alsoneeds a percentage of sand-sizedparticles to fill the voids between the stones and give apercentage of good,plastic fines arealso needed to bind the materialtogether which allows a Gravel road toform a crust and shed manyregions of the country.

3 This is a naturalclay which gives the Gravel a strongcohesive characteristic and keeps areasonably tight Surface especiallyduring periods of dry ofthe fine material in Surface Gravel willbe lost,under traffic action,in the formof dust that rises from the Surface andsimply blows away. This can becompensated for by specifying a higherpercentage of fines in the new ,no Gravel Surface will performlike pavement! There will be some looseaggregate or float on the Surface ofvirtually all Gravel striving toget as good a material as budgets andlocal sources allow will improve theperformance of a Gravel of CrushingIn a few cases the Gravel may simply beloaded onto trucks without is often referred to as bank run or pit run are fewnatural deposits of material that havean ideal gradation without some areas of the countryit is still common to process gravelsimply by screening to a maximum top great benefit is gained fromprocessing the material by means that a good percentage of the stone will be fractured in thecrushing process.

4 The broken stones will embed into the Surface of a Gravel road much better than rounded,natural-shaped also means thatthe material resists movement underloads better and gives better strengthor stability. This will vary throughout thecountry,but bank run gravels are nearlyalways improved through the gravels are consideredvery good material since they are com-posed of virtually all fractured Asphalt As more of our asphalt pavements wearout,many of them are isusually done by milling or the material is available foruse on a Gravel can be a goodsurface,but there are thismaterial,the bituminous portion of the old pavement becomes the placed on a road in hot weather,the recycled asphalt can take on thecharacteristic of it will bea weak will often developpotholes and will be hard to maintainwith simple blade maintenance. To helpovercome this problem,the materialshould be placed at a minimum threeinch compacted depth and only on a road that has a strong better option is to mix the recycledasphalt 50/50 with virgin generally provide a material thatstill has a good binding characteristic,but remains workable for maintenanceand asphalt hasalso been mixed with crushed,recycledconcrete and the performance has been of a good blend of material for Gravel surfacing.

5 (Courtesy of Road Research Ministry ofRoads/Transportation,Sweden)40 What is Good Gravel ?It is very important to understand that all gravels are not the can tell a little about them byvisual inspection or by running yourhands through the material but realquality can only be determined For TestingAll managers and decision makers in local government need a goodunderstanding of the benefit of testingaggregates in order to work towardsbetter quality in road and street everyone needs to understand how to do the requires special knowledge and equipment which is generally notavailable or affordable to most localgovernments. We simply need to recognize the benefits of knowing more about the aggregate that is used in construction and maintenanceoperations. This knowledge gives powerto decision makers to specify goodmaterials,to know when to accept orreject materials,and to communicatebetter with crushing contractors,consultants,DOT,and others involved in the business of building andmaintaining an objection is raised to samplingand testing because the cost is claim can be countered withthe argument that if several thousandtons of aggregate are going to bepurchased or crushed,is it not wise toinvest a few hundred dollars in testingthe material to insure that the rightaggregate is used?

6 It is a good practiceto test the aggregate before placing iton the ,if the tests fail,youcan work with the crushing contractorto try to blend and improve or reject becomes even morecritical in producing material forpavement or issue critical to testingaggregate is obtaining a good sampleof the material to be to get a good representativesample from a crushing operation,a stockpile,a windrow,or a pavingoperation is absolutely critical togetting good test results from a sampling techniques have led tomore controversy in aggregate testingthan any other effort mustbe made to make sure that the samplebrought to a lab is truly representativeof the material in the is wise to follow national standards such asThe Benefit of Testing Aggregates41 Figure 9:Stack of sieves used for testing the gradation of Benefit of Testing Aggregates42 The Benefit of Testing AggregatesASTM for aggregate goodvideo titled Sampling Aggregates,produced for the Michigan DOT,coversseveral interesting topics on the video should be available from any state s LTAP is alwaysadvisable to work with an experiencedsampler if you are not familiar then are the benefits of testingaggregate?

7 The primary concern hereshould be gradation of material.(18,31,34)Sieve AnalysisGravel is made up of three groups of aggregate:stone,sand,and on what the material is to be used for,the ideal blend of thesethree groups varies greatly. For example,good Surface material for a Gravel roadwould need more material passing a#200 sieve than a good base is also a difference in the need for plastic or cohesive needs some good natural claywhich gives a binding characteristic. The chart adjacent is an example of onestate s base and Gravel surfacing states have their ownspecifications and therefore it is highlyrecommended that state specificationsbe governments are not held to these specifications when doing theirown construction and maintenance work without state or federal fundingand ,it is wise to befamiliar with them and follow themwhenever if you chooseto modify the specifications to suit alocal material source or project,it isbest to begin with a state the major differences in theabove specification in the top-sizedmaterial and the smallest sized base course requires 100% of thematerial to pass a 1 inch sieve,butallows up to 20% of the stone to beretained on the 3/4 inch could make excellent base Gravel .

8 Itwould likely perform poorly if used asgravel would be toomuch large stone resulting in verydifficult blade ,the high percentage of coarsematerial would make a rough drivingsurface. Yet,a percentage of large stone is needed for strength in the base and Plasticity IndexNotice also the difference in the finematerial and the plasticity index (PI).While Gravel surfacing allows 4% and up to 15% of the material to pass a #200 sieve,base course can have as little as 3%,but not more than 12% passing the same ,the PI can fall to 0 in basecourse and rise to no more than index can rise as high as 12 or be no less than 4 in Surface is good reason for Gravel needs a percentage ofplastic material,usually natural clays,which will give the Gravel a binding characteristic and hence a smoothdriving Surface . This is critical during dry wet weather,thesurface may rut a bit,but will quicklydry and harden in sunny and ,any great quantity of plastic fines in base Gravel will cause moisture gets underthe paved Surface ,the base will lose its strength and stability and causerutting or even failure of the often the same Gravel is used forboth base work and Surface ,it will be good for onepurpose or the other,but will not work for both D contains a sample of acomplete Screen Analysis and PIWorksheet typical of those used bytesters across the again,it should be stressed that only bysampling and testing the aggregate canone really determine the quality of visual inspection canbe thing in particularthat is very hard to determine withouttesting is plasticity.

9 This is a laboratorytest which,in simplified terms,tells youwhether the fines are clays or are not familiar with this testing,the whole process may appear ,it really pays to increaseyour knowledge of these matters inorder to be a better local road/street departmentmanager has a big job and there isnever enough money to cover all of is imperative that moneyshould be spent Base CourseGravel SurfacingSievePercent PassingPercent Passing1"1003/4"80-1001001/2"68-91No. 446-7050-78No. 834-5437-67No. 4013-3513-35No. 2003-124-15 Plasticity Index0-64-12 Table of Gradation Requirements and Plasticity for Two Types of South Dakota Standard Specifications. (16)Process for Obtaining Good Gravel43 Reduced Blading andMaintenance CostsBy spending some money to testmaterial for quality,overall maintenancecosts will be Gravel thathas good gradation and plasticity willcompact will develop a tightlybound Surface that needs with excesswashboarding,rutting in wet weather,or loosening (floating) in dry weather,will be greatly is well worththe effort to better understand thebenefits of aggregate agency must strive to locate and use good Gravel even if it costs alittle long term benefits interms of less maintenance will oftenpay for the extra initial costshould not be the primary considerationwhen purchasing SpecificationsGravel for local roads is often boughtfrom a local supplier at a negotiatedprice for an estimated quantity.

10 Theremay be some assurance that the gravelwill perform well on the road based on past ,materialsources can change rapidly as thematerial is only realassurance of getting good qualitymaterial is to establish a specificationand then sample and test the productto make sure these specifications are local agency generally would not be held to state specifications whendoing maintenance ,this is what crushing contractors andaggregate suppliers are usually familiar one is confident in knowledge ofsurface Gravel and wishes to change the specifications,that is fine;but it iswise to use the state specification as abenchmark to work example,These two roads show remarkable contrast in Surface condition due to the quality of carry virtually the same volume and type of traffic in an agricultural topphoto shows a good Surface Gravel with a nice blend of material,particularly some plastic fineswhich keep the Surface tightly bottom photo shows a road Surface t