Abstract
The thesis presents details of a laboratory study of the behaviour of cemented roadbases under load, the work relating to the use of relatively lean concrete mixes having sufficient workability to allow placing by slip-form paver. Large-scale comprehensively instrumented static loading tests were undertaken on 3 m diameter discs, continuously supported by a simulated subgrade of rubber, in order to investigate the material behaviour under conditions approaching those in a pavement structure. Test variables included mix type, slab thickness and subgrade support for which, in each instance, two cases were considered. Laboratory tests on associated control specimens provided material properties for use in subsequent analyses, and considerable emphasis was placed on determining the tensile stress-strain response under flexural and under uniaxial tension loading. The control tests were later extended to give the characterising properties at ages other than 7 days so that, in particular, the longer term performance under trafficking could be estimated. Test slab performance was evaluated primarily by an elastic multilayer analysis and it was found that good initial agreement was obtained between observed and predicted performance in terms of strain. The load at which a well-defined fracture of the test slabs occurred was very much higher than the value predicted from theoretical considerations and this is difficult to explain satisfactorily. It would seem, however, that the primary cracks induced were relatively stable under the test conditions imposed since pronounced discontinuity in both the load-strain measurements and the load-deflection measurements was identified at much lower loads, indicating the initiation of a failure mechanism. Comparison of tensile strains at discontinuity in the large-scale tests with those at discontinuity in the laboratory flexure tests showed good agreement. These strains are therefore thought to define an upper limit for predicting satisfactory long-term behaviour under trafficking whereby higher induced tensile strains would lead to reduced life-expectancy. A method for estimating these strains based on the use of tensile strength and electrodynamic elastic modulus is proposed. In conclusion, the investigation highlights the difficulty of obtaining meaningful data relating to the structural design of pavements incorporating a new material, and recommendations are made for further work in this area.