In Situ Stabilization of Pavement Base Courses Roads Pavement Forum Thursday, May 17, 2001

Introduction u Clients –Gautrans –C&CI –SANRAL u Laboratory and Heavy Vehicle Simulator results from R243/1 u One building block in a long-term process u Focus on mechanical properties and structural bearing capacity

Layout of presentation u Purpose of the study u Materials u Experimental plan u Results for each laboratory test u Conclusions

Purpose u Assess the benefits of in situ stabilization in terms of improvements in the mechanical properties and structural bearing capacity of the treated material u Mechanical properties –Resilient modulus –Compressive and tensile strength –Flexibility –Shear strength u Bearing capacity –Effective fatigue –Permanent deformation

Materials u Basic material –Ferricrete milled from HVS test site, including existing surfacing and upper portion of subbase u Treatment processes –Cement (Laboratory) »2 % cement –Foam and cement (Laboratory and HVS) »2 % cement, 1.8 % residual binder –Emulsion and cement (Laboratory and HVS) »2 % cement, 1.8 % residual binder

Materials: Untreated u Nominal maximum aggregate size 37.5 mm

Materials: Untreated u Classification –GradingG4 –Atterberg limitsG5 –CBRG7

UCS, ITS, Flexural Beam Test u Treated materials only u Foam and emulsion tested at 2 binder contents –1.8% residual binder content + 2% cement –3.0% residual binder content + 2% cement

Flexural beam test u Strain at crack initiation u Indication of flexibility

Triaxial Tests u Untreated and treated materials –1.8% residual binder content, 2 % cement u Variables –Density –Saturation –Confining pressure –Stress ratio

Triaxial tests u Static triaxial tests –Shear strength parameters u Dynamic triaxial tests –Resilient modulus –Permanent deformation response

Compressive strength: UCS Results u Cement-treated ferricrete has highest UCS u Addition of binder reduces the UCS

Tensile strength: ITS Results u Cement-treated ferricrete has highest ITS u Addition of binder reduces the ITS

Tensile strength: ITS Results u Samples dried to equilibrium MC at ambient temp u 72 h in oven at 40º C

Flexibility: Flexural beam test u Flexibility only increases at higher binder content

Elastic stiffness (M r ): Dynamic triaxial tests u Estimation of stiffness values –Use regression model for untreated ferricrete –Use ranges for treated materials

Comparative results: Average strain-at-break

Comparative results: Effective fatigue life u SAMDM transfer functions u Working strain of 125  u  b –values from flexural beam test

Comparative results: Cohesion

Comparative results: Friction angle

Comparative results: Shear strength at  3 = 50 kPa

Comparative results: Bearing capacity (9 % PD)

HVS tests: Pavement structure u 30 mm Asphalt u 250 mm FTG / ETG -1,8 % residual bitumen -2 % cement u In situ material u In situ subgrade

HVS tests: Materials Foam-treated Emulsion-treated

HVS tests: Programme u 2 x 100 m long experimental sections –Foam-treated –Emulsion-treated u 1 st Phase of HVS testing –80/100 kN tests ( / repetitions) –Completed u 2 nd Phase of HVS testing –40 kN tests ( repetitions) –In process

HVS tests: Deflection result

Conclusions: UCS, ITS and Flexibility u Complex relationship between UCS, ITS and –Percentage binder –Cementation –Curing procedure u Flexibility –No increase in flexibility at low binder content –Increase in flexibility and effective fatigue life at higher binder content –Strain-at-break slightly higher for foam-treatment at higher binder content u Effective fatigue life models to be validated with HVS results

Conclusions: Resilient modulus u Increase in resilient modulus with treatment u Untreated ferricrete –Resilient modulus influenced by »Relative density and saturation »Stress state u Treated ferricrete –Resilient modulus dictated by the stabilizing agent and largely insensitive to the above parameters –No significant difference between stabilizing agents u Resilient modulus values to be validated by HVS back-calculation results

Conclusions: Shear strength and plastic strain u Shear strength increases with treatment u Vastly improved bearing capacity in terms of permanent deformation –Cement-treatment shows highest benefit –No significant difference between foam- and emulsion-treatment u Models need to be calibrated with HVS results

Conclusions: General u Only considered mechanical properties u Other properties to investigate –Permeability and erodibility –Workability –Shrinkage cracking –Time to opening the road – early strength u Improved understanding of mechanical properties and behaviour u Properties of stabilized material significantly different from untreated material even at low binder content u First structural design models for these types of materials