Cold in Place Rock Crushing and Stabilization of Northern Low ...

Berthelot, Gerbrandt, Safronetz, and Sparks. Page: 17emulsion stabilized test sections required minor shaping for a period of approximately two weeks after placement untilthe emulsion fully cured. Minor wheel path abrasion was also observed two months after placement with no wearingsurface coarse placed on the stabilized sand subgrade after construction. To minimize wheel path abrasion, it isrecommended that a thin layer of crushed rock or traffic gravel be embedded into the wearing surface immediately afterplacement and prior to the asphalt emulsion curing. In addition, a residual pen asphalt emulsion and/or faster settingemulsion may help reduce wheel path rutting and abrasion and eliminate the need for blading during curing. Double sealwearing coarse was also placed on select portions of the asphalt emulsion stabilized test sections, one-year afterconstruction the sealed test sections constructed on the asphalt emulsion stabilized subgrade was found to be performingwell with only minor edge breaks present.6 SUMMARY, CONCLUSIONS AND FUTURE RECOMMENDATIONSSDHT is responsible for maintaining approximately 6500 kilometers of northern gravel roads. Many of thesegravel roads are built on poorly graded sand subgrades and may contain protruding bedrock and/or large boulders.Furthermore, many of these roads exhibit washboarding, protruding rocks, rutting and potholes, which result in severeroad roughness and a potential driving hazard. Routine blading is often ineffective because unstable sand does notmaintain shape and compaction, protruding bedrock and boulders damage motor grader blades, boulders may becomedislodged leaving holes in the road, and dislodged boulders are a safety hazard when windrowed along road side-slopes.SDHT undertook an in-place rock crushing and subgrade stabilization pilot project on sections of Highway918-01. The objective of this project was to evaluate cold in-place rock crushing to reduce protruding boulders and toevaluate the feasibility of in-place modification/stabilization to stabilize sand subgrades. The construction of theHighway 918-01 test sections determined that in-place rock crushing with the CMI R/S 650 is technically feasible andprovides a workable surface free of large boulders. The addition of clay and calcium chloride and asphalt emulsion tothe uniform sand subgrade resulted in increased stability and reduce traffic dust. The construction costs for this pilotproject ranged from $13,684 for in-place rock crushing and a gravel wearing coarse to $52,017 for in-place rockcrushing, asphalt emulsion stabilization and a double seal wearing coarse.Based on the results of this study, further investigation of in-place rock crushing and sand stabilization shouldconsider:a) A roto mixer mandrel specifically designed for in-place rock crushing.