Browsing by Author "Chilukwa, Nathan Ntanda"

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    Vibratory hammer compaction of granular materials
    (Stellenbosch : Stellenbosch University, 2013-03) Chilukwa, Nathan Ntanda; Jenkins, K. J.; Rudman, Chantal; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: Compaction is one of the key processes in the construction of road pavement layers. Not only is it significant in ensuring the structural integrity of the material in the road layers, but it also has an influence on the engineering properties and performance of the soil material. A poorly compacted material is characterised by low density, high porosity and below standard shear strength. This, as a result causes rutting, moisture susceptibility, potholing, corrugations and passability problems on the road. Therefore, it is vitally important that field compaction is done correctly. For this reason, laboratory compaction methods have been developed to simulate the field compaction process in the laboratory. The Mod AASHTO test has long been used as the laboratory compaction method of choice by virtue of its simplicity and the lack of bulky equipment required. However, previous studies have established that the Modified AASHTO method does not adequately simulate field compaction criteria especially for cohesionless materials. Two reasons have been advanced; The Mod AASHTO compaction method does not adequately simulate the compaction done in the field when the granular mix is laid; The compaction method may cause disintegration of the material. Alternative tests have been considered and much research has focused upon the use of a modified demolition hammer (vibratory hammer) for laboratory compaction of granular materials. This study undertook to evaluate the influence of test factors pertinent to the vibratory hammer compaction method. The influence of these test factors on compaction time and obtainable material density was assessed with the objective of developing a compaction method for granular materials. Vibratory hammer compaction tests were conducted on G3 hornfels, G4 hornfels and G7 sandstone material types and to a lesser extent, reclaimed asphalt (RA). Densities obtained were referenced to Mod AASHTO compaction density. Findings of the study showed that, the mass of the tamping foot has a significant influence on the obtainable compaction density. Other factors such as, moisture content, frequency and frame rigidity were also found to affect compaction with the vibratory hammer. In addition, it is shown that the surcharge load does not significantly influence the obtainable compaction density but does contribute to the confinement of the material and restricts the upward bounce of the hammer. On the basis of the results and findings, a compaction method was proposed, incorporating test parameters and factors that would provide ideal results for a set compaction time. Repeatability tests showed that, the developed vibratory hammer compaction method was effective in compacting graded crushed stone material types (i.e. G3 and G4) and probably RA. The test was not as effective on the G7 material. Further studies on this material (G7) are required. In addition to the previous testing regime, a comparative assessment of the developed vibratory hammer compaction method in relation to the vibratory table method was done. The results show that the vibratory hammer is capable of producing specimens of densities comparable to those of the vibratory table. A sieve analysis undertaken before and after compaction showed that compaction with the developed vibratory hammer compaction method does not result in any significant material disintegration. Based on the results of this study, a specification for the determination of maximum dry density and optimum moisture content of granular material using the vibratory hammer is recommended.