FLY ASH IN ROAD BASE

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  • Lime-fly ash base course(LFA)

    • . LFA was originally patented in the 1950's as POZ-O-PAC and used in Illinois. An example was the 3.5 mile service road from state route 195 to the Coffeen Power Station in Coffeen, IL. Here 3% hydrated lime + 32.5% class F fly ash and 64.5% boiler slag was used. Nonplastic mixtures of lime, fly ash, and aggregate are mixed and sufficient water is added to achieve maximum dry density ( see AASHTO T-180)upon compaction. Construction is usually limited from April to October for areas of the country experiencing freeze-thaw cycles. Subgrade shouldnot be frozen or muddy. Minimum average compressive strengths of 600 psi(at 14 days at 72F) should be obtained on laboratory specimens with no individual test below 500 psi. Required unconfined compressive strengths must exceed 600 psi, depending on the time of year and freeze-thaw cycles. Outside temperature should exceed 40F.

    Typical mix design: (in % by weight of oven-dry aggregate)
     
        Ingredient
      Hydrated lime
    		 2-6%
      Fly ash
    		 9-20% (see ASTM C 593,AASHTO M 295)
      Aggegrate
    		 74-89% (100% passing 1.5 in.sieve, 90-100% passing 1 in. 

    and 60-100% passing 0.5 in.)

    LFA is constructed in layers not less than 4 compacted inches. Final thickness and actual proportions are set by Engineer. After LFA has been constructed, the surface must be kept continuously moist until the bituminous curing cover is applied. Surface course paving then may proceed after at least 14 hrs. after curing cover has been applied.

  • Cement-fly ash base course (CFA)

    • . CFA was first used in West Virginia in 1971-1972 in the construction of West Virginia Route 2. It had 54% boiler slag + 46% bottom ash and 5% portland cement. NonPlastic mixtures of cement, fly ash, and aggregate are mixed and sufficient water is added to achieve maximum dry density ( see AASHTO T-180)upon compaction. See above.

    Typical mix design: (in % by weight of oven-dry aggregate)
     
      Ingredient
      Cement
    		 2.5-5%
      Fly ash
    		 9-20%
      Aggregate
    		 75-88.5%

    See individual state DOT for specifications on materials, equipment, general construction conditions, composition of base course mixture, mixing, placing, compacting and finishing of base course mixture.

    Pozzolanic Contracting and Supply Co.-in Tennessee

    See Ash Development Association of Australia-Literature on Road Stabilisation

    Stabilizing process

    See a pictorial about roadbase. Western Ash