Thesis (MEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: Two common methods of road pavement, granular material stabilisation used in road construction
throughout South Africa today include Cold in Place Recycling (CIPR) and stabilisation with cement
or bitumen and an active filler to create Bitumen Stabilised Materials (BSM).
As part of the updating of the South African Pavement Design Method (SAPDM) an experimental
section, investigating the structural capacity of cement and lime stabilised and BSM pavement layers,
was constructed and will be monitored over a two year period. As part of this study Falling Weight
Deflectometer (FWD) measurements were taken on the various experimental stabilised pavement
layers constructed. The FWD deflection data, measured at various time intervals over a 360 day
period, forms the basis of the study presented here.
The objective of this thesis was to identify typical back-calculated layer stiffnesses and their
variability over time for the various in-situ recycled and stabilised base layers constructed within the
experimental section. Stabiliser type, content and layer thicknesses were varied across experimental
sub-sections.
Trends in back-calculated stiffness of cement stabilised base layers consistently showed significant
reductions in layer stiffness subsequent to construction traffic loading. Subsequent to the initial
reduction in stiffness little change in stiffness was noted under normal traffic loads.
Observations on the trends in back-calculated stabilised layer stiffness per material type over time
indicated that seasonal moisture and temperature fluctuations have an effect on the stiffness of the
pavement structure as a whole. BSM materials showed significant variability over time in-line with
seasonal variability in the supporting subgrade stiffness in the southbound lane. BSM materials with
1% cement added in the northbound lane show initial stiffness reductions due to direct rainfall
application however a significant increase in layer stiffness occurs up to 360 days after construction.
BSMs with 2% cement in the northbound lane show significant increases in layer stiffness over the
360 day observation period. No significant difference in stiffness trend was observed between BSM
emulsion a BSM foam materials. The BSM emulsion with 0.9% residual bitumen and 1% cement was
observed to show rapid reduction in stiffness upon opening to traffic and reverting to stiffness values
similar to an unbound material of approximately 350 MPa.
Cement and lime stabilised materials showed typical post 28 –day average stiffnesses per sub-section
ranging between 600 MPa and 1800 MPa. BSM foam with 1% cement added were observed to have
average stiffnesses per sub-section in the range of 400MPa to 2200 MPa and BSM emulsion with 1%
cement with stiffnesses between 400 MPa to 1700 MPa over the 360 day period. BSMs with 2% cement added showed stiffness ranges between 900 MPa to 4300 MPa for BSM foam and 900 MPa to
3900 MPa for BSM emulsions over the 360 day period.
The spatial variability of back-calculated stiffness per sub-section of a particular stabilisation design
was significant and was observed, through the Co-efficient of Variation (COV), to increase over time.
The effect of the observed variability when incorporated into a pavement design scenario, requiring a
design reliability of 90%, showed 50% of the pavement structure would be overdesigned by a factor
of 4.
With respect to the current philosophies on the development of stiffness over time of cement and lime
stabilised and BSM pavement layers some useful observations were made. Cement stabilised
materials correlate well with stiffness development theories predicted by previous studies. Theories
relating to the stiffness development of BSMs however did not predict the levels of variability in base
layer stiffness observed on the experimental section.
The continued observation of the experimental section for another year will give greater insight to the
stiffness trends of the stabilised materials discussed above.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/85857 |
| Date | 12 1900 |
| Creators | Lynch, Alan Gerald |
| Contributors | Jenkins, K. J., Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xiii, 135 p. : ill. |
| Rights | Stellenbosch University |
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