Mechanistic evaluation of granular base stabilization systems in Saskatchewan
Date
2008
Authors
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Degree Level
Masters
Abstract
Saskatchewan Ministry of Highways and Infrastructure (MHI) is responsible for maintaining approximately 26,100 km of two lane equivalent highways network. Most highways in Saskatchewan are constructed primarily of granular materials. Granular materials serve various purposes in a pavement structure. In particular, granular materials distribute stress within the road structure and reduce the stress applied to the subgrade. Granular materials also mitigate pumping of subgrade fines into surfacing materials, as well as provide drainage for the pavement structure.As a result of the rapid deterioration of roadways and the increasing highway traffic, a significant portion of the Saskatchewan highway system is in need of rehabilitation in the next couple of decades. However, increasing costs associated with road construction as well as budget constraints render many conventional rehabilitation solutions untenable in many applications. In addition, the depletion of quality aggregate also exists in many areas of Saskatchewan. Given that much of Saskatchewan granular pavement system will be in need of strengthening in the next few decades, there is a need to apply new cost-effective and aggregate-preserving pavement rehabilitation technologies such as cold in-place recycling and base strengthening.The goal of this research is to improve the engineering design and performance of recycled and stabilized granular base systems under Saskatchewan field state conditions. The specific objectives of this research are to characterize the conventional laboratory behaviour, moisture sensitivity, and mechanistic behaviour of various granular base strengthening systems in the laboratory, to characterize the structural responses of various granular base strengthening systems in the field, and to evaluate the pavement thickness design and responses of various granular base pavement structures.This research is based on a cold in-place recycling and base stabilization project undertaken by Saskatchewan MHI in fall 2006. Control Section (C.S.) 15-11 between km 5.0 and km 8.0 was selected as a typical thin granular pavement under primary weight loadings that required strengthening. Unstabilized granular base, cement stabilized granular base, and cement with asphalt emulsion stabilized granular base were constructed and evaluated in this research. Materials employed on C.S. 15-11 were sampled and prepared for the various laboratory tests performed in this research. Conventional tests performed included sieve analysis, Atterberg limits, sand equivalent, standard proctor compaction, and California bearing ratio strength and swell test. Advanced mechanistic and moisture sensitivity testing included indirect tensile strength, moisture capillary rise and surface conductivity, unconfined compressive strength, and rapid triaxial frequency sweep testing.The cement and cement with emulsion asphalt stabilization of the granular base were found to improve the conventional, mechanical and moisture susceptibility properties of in situ C.S. 15-11 granular base materials. The cement stabilization applied on C.S. 15-11 provided a high degree of improvement relative to the cement with emulsion stabilization. The cement stabilization was found to be relatively easy to apply in construction, whereas the cement with emulsion stabilization was more difficult, particularly due to the problems associated with cold temperatures during late season construction.The rapid triaxial tester (RaTT) was found to be a practical and useful apparatus to characterize the mechanistic constitutive behaviours of granular materials. The C.S. 15- 11 in situ unstabilized base was found to have the poorest mechanistic behaviour among all three granular bases on C.S. 15-11, as expected. Cement stabilization improved the mechanistic behaviour of the in situ material significantly by providing the highest mean dynamic modulus, lowest mean Poisson’s ratio, lowest mean radial microstrain, and the lowest mean phase angle. The cement with emulsion asphalt stabilization also provided a considerable improvement on mechanistic behaviour of C.S. 15-11 granular base materials. However, the degree of improvement was less than the cement stabilization system.Non-destructive falling weight deflection measurements taken across the field test sections showed that the stabilization systems yielded a significant improvement of primary structural response profiles across the C.S. 15-11 test sections after stabilization. The cement stabilization system was found to yield the most significant structural improvements among all the test sections constructed on the C.S. 15-11. The deflection measurements taken in 2007 after hot mix asphalt paving further identified that the unstabilized system is more sensitive to the freeze-thaw effects relative to cement stabilization and cement with emulsion stabilization systems. This research also showed that the Saskatchewan MHI structural design system is not applicable to the design of stabilized granular base systems. Evaluation of the thickness design for C.S. 15-11 showed the unstabilized and the cement with asphalt emulsion stabilized test section met the criterion of fatigue cracking, but failed to meet the criterion of structural rutting in MHI design system. However, the cement stabilized section met both fatigue cracking and rutting criteria. The structural evaluation revealed that mechanistic pavement response analysis and validation are necessary in the thickness design of stabilized granular systems such as C.S. 15-11, where traditional MHI design system is not applicable. This research employed finite element modeling and linear elastic pavement modeling software to determine the maximum shear stresses within granular base under typical Saskatchewan stress state conditions. The maximum shear stress values were found to locate on top of granular base courses under the applied circular loading edges ranging from 177 kPa to 254 kPa. These maximum shear stresses within the C.S. 15-11 test section granular base courses under field stress states were compared to maximum shear stresses occurring within samples measured by rapid triaxial testing performed in this research. The comparison showed that the ranges of shear stresses applied in the laboratory RaTT testing were close to shear stresses of granular bases in the field computed from modeling. Therefore, this research showed a good correlation of lab RaTT testing and field results for granular pavements.In summary, this research met the objectives of mechanistically evaluating various granular base stabilization systems in Saskatchewan by means of various laboratory testing, non-destructive field testing, as well as mechanistic modeling and analysis. This research provided valuable data and showed considerable potential for improving design, construction, and QA/QC of conventional and stabilized granular base systems in Saskatchewan.
Description
Keywords
Falling Weight Deflectomer, Triaxial Frequency Sweep Testing, Cement, Asphalt Emulsion, Base Stabilization
Citation
Degree
Master of Science (M.Sc.)
Department
Civil Engineering
Program
Civil Engineering