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Section III: Surface Gravel

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.

aggregates such as limestone, quartzite and granite; glacial deposits of stone, sand, silt and clay; and river run gravels that generally are a mix of stone and sand. One thing should be stressed: it pays to use the best quality material available. (31) Difference in Surface Gravel and Other Uses Too often surface gravel is taken from

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Transcription of 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.

2 (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.

3 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 ?

4 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.

5 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

6 Fromprocessing the material by means that a good percentage of the stone will be fractured in thecrushing process. 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.

7 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.

8 (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

9 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.

10 Is it not wise toinvest a few hundred dollars in testingthe material to insure that the rightaggregate is used? 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.


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