Dust Control Handbook for Industrial Minerals Mining and Processing

oad maintenance, reduce equipment maintenance cost, and will aid in effective dustcontrol and increased tire life. In particular, dust control will be augmented from areduction of fine material generated and through an increase in the longevity of dustsuppressants.When a vehicle travels over a haul road, the wheels exert forces on the road surface. Ofall the forces, the normal shear stresses created by the vehicle are the most critical. At thelocation of the wheel, the road is put into compression. Once the wheel passes thislocation, the road rebounds to its initial position through tension. On a properly designedroad, this compression and tension cycle will occur within the elastic limits of the roadstructure.Permanent deformation of the road can occur if it is not properly designed. Roadsconstructed of weak materials will readily degrade, which can produce fine material thatcan be entrained by mobile equipment traveling the road. Roads constructed of the propermaterials will degrade less rapidly, which in turn lessens the dust emission potential of theroad over the same period of use. Additionally, road failure will cause any dustsuppressant to exceed its bonding strength, thereby reducing the effectiveness of thesuppressant. Generally, dust suppressants work by forming a layer, or crust, over the topof the road. If the bonding strength of the dust suppressant is exceeded, the suppressantwill break up, deteriorate, and wear away.Materials selected for road construction must possess certain physical properties. Theyare: resistance to wear, soundness, maximum size, particle shape, and gradation [MidwestResearch Institute 1981].A high resistance to wear is desired for the road material. It should be hard andtough such that it will not be easily disintegrated under traffic load. The resistanceto wear can be measured by conducting abrasion tests such as the Los Angeles7Abrasion test. Generally, the most desirable materials include granite orlimestone. Soft and unsound materials such as shale, coal, mica, or vermiculiteshould be avoided as the use of such material will lower the road's strength anddurability.Soundness represents the ability of the material to withstand climatic conditions.A material is desirable if it can resist weathering. Materials that are weak,extremely absorptive, easily cleavable, swell when saturated, or are susceptible tobreakdown through natural weathering processes are not recommended for roadconstruction.7The Los Angeles Abrasion test provides information on aggregate resistance to crushing, degradation, anddisintegration from activities such as manufacturing, stockpiling, production, placing, and compaction.Testing is conducted by placing a coarse aggregate sample in a rotating drum with steel spheres. As thedrum rotates the material degrades by abrasion and impaction, with itself and with the spheres. Once the testis complete, the calculated mass of aggregates that has broken apart to smaller sizes is expressed as apercentage of the total mass of aggregate. Lower Los Angeles Abrasion values indicate that the aggregate istougher and more wear resistant to abrasion. Specifications for the test can be found in AASHTO T96 orASTM C 131 "Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in theLos Angeles Machine."Haul Roads, Stockpiles, and Open Areas 245