Soil Stabilization Field Trial

A five-year study was initiated seeking materials/additives and procedures that help to mitigate crack susceptibility in cement-treated material (CTM). A field test program of six 305-m (1000-ft) test sections was implemented in August 2000. The following additives/procedures were included for investigation: (1) 5.5% cement additive (control section), design based on a reduced strength criteria; (2) 5.5% cement precracked 24 to 48 hours after finishing; (3) 5.5% cement precut (grooved) every 3 m (10 ft); (4) 3.5% cement with 8% fly ash (CFA); (5) 6% ground granulated blast furnace slag (GGBFS) with 2% lime admixture (LGBFS); and (6) 3% lime and 12% fly ash, stabilization technique used by Mississippi Department of Transportation (MDOT) (LFA). First interim report covering the first phase of investigation/monitoring during the 28-day period was submitted on April 21, 2001. Two layers of hot mix asphalt (HMA) – 110 mm (4.5 in.) base, 60 mm (2.25 in.) polymer modified binder – were placed over the stabilized layer beginning September 21, 2000, followed by the second field monitoring on November 13, 2001. Field tests included deflection tests employing Falling Weight Deflectometer (FWD), retrieval of 100-mm (4-in.) cores for compression tests, and a manual crack survey. The results were presented in Interim Report II. On June 16, 2003, (nominally 3 years) the test sections were monitored; this time again deflection test employing FWD, and a manual crack survey. Prior to the June 2003 survey, a 50-mm (2-inch) polymer modified surface course was placed, with the road opening to traffic on July 8, 2002. Nominally five years after construction, again deflection tests deploying FWD (December 1, 2004), compression tests on 102-mm (4-in.) cores and a manual crack survey (March 8, 2005) were conducted. Presented in this final report are, (i) the results of deflection analysis and moduli of layers (ii) the compressive strength results of 102-mm (4-in.) diameter cores, and (iii) the crack survey results. Backcalculation of moduli from deflection data was accomplished by deploying MODULUS v.6, with pavement modeled as a four-layer system and in few cases, as a three-year system as well. The backcalculated results show that the moduli of all of the sections, except that of the cement-fly ash (CFA), increased steadily from 28 days to 1654 days. In CFA, however, the modulus was not only relatively low but it also leveled off after 440 days. In the LFA section, modulus remained significantly low in the beginning and continued at a low level over the five-year period. Unconfined compressive strength (UCS) determined from 102-mm (4-in.) diameter cores consistently increased with time in all of the six mixes. The strength gain of the 5.5% cement control mix leveled off after 440 days, thus not attaining the target strength of 2070 kPa (300 psi). Lime-fly ash mix strength was indeed low compared to those of the other mixes. With 220 mm (8.75 in.) of HMA overlay, no reflection cracks were observed throughout the five-year monitoring period. For a comparative evaluation of the six sections, their short- and long-term performance had been examined; short-term performance in terms of 28-day shrinkage cracks in the base layer and long-term performance in terms of stiffness modulus and UCS. Though considered satisfactory in regard to shrinkage cracks, the long-term performance of LFA mix is suspect as evidenced by its low stiffness, and in turn, large deflection. Though structurally adequate, based on the questionable short term performance of both CFA and LGBFS mixtures, their use in flexible pavement beneath HMA, especially thin layers, [102 mm (4 in.) or less] is deferred. Mixing two additives in small proportions is another construction-related problem in the CFA and LGBFS mixtures. The control CTM with 5.5% cement not only suffered excessive shrinkage cracking, but also its long term strength fell short of expectation. The precut CTM though structurally sound, two problems dissuade its application: the excessive shrinkage cracking, and logistics of cutting grooves while the layer is being compacted. From the point of view of overall performance, precracked CTM indeed excelled all of the other treatments/admixtures and, therefore, is recommended for stabilization of base layers.

Language

  • English

Media Info

  • Media Type: Print
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 68p

Subject/Index Terms

Filing Info

  • Accession Number: 01045511
  • Record Type: Publication
  • Report/Paper Numbers: FHWA/MS-DOT-RD-05-133, MS-DOT-RD-05-133
  • Contract Numbers: State Study 133
  • Files: NTL, TRIS, USDOT, STATEDOT
  • Created Date: Mar 21 2007 10:03PM