Please read the abstract in the section 00front of this document / Thesis (PhD (Engineering))--University of Pretoria, 2006. / Civil Engineering / unrestricted

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.

Drivers for sustainability have made it necessary for the construction industry to adapt its traditional processes to become both more efficient and produce less waste. Performance based design and specification in the UK for motorways and trunk roads permits a very flexible approach to pavement design, material selection and performance related testing aimed at utilising materials to their maximum potential. However, it is clear that within the emerging philosophy of using materials that are 'fit for purpose' there are many technical challenges for design and specification. There is a need to develop suitable methods of evaluating materials prior to their being used on site. This project was born out of this requirement, with a particular emphasis on coarse granular materials due to their common role in capping construction and also their unique difficulty for measurement under laboratory conditions due to their large range of particle size. A novel assessment test for coarse capping materials for roads that can be used to indicate their likely short-term in situ performance, under controlled laboratory conditions before construction on site, has been developed during this research programme. Key findings relating to the behaviour of coarse capping materials, the use of stiffness measuring devices and variables that influence the measurement of composite stiffness are discussed in detail. The research highlights the necessity for adequate drainage and protection of foundation materials against increase in water content. When adopting a performance specification the timing of the pavement assessment is critical, both on site and in the laboratory. The performance measured on site should perhaps only be considered as a 'snapshot' relating to the stress state in the material at the time of testing.