A study of the effect of compaction on particle breakage of sub-base and base material used for pavement construction in Ghana

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The acquisition of naturally occurring soils for construction purposes involves first taking soil samples from trial pits in proposed borrow pits and testing them in the laboratory. In actual field practice, contrary to specification the results obtained from the said laboratory test are then compared with as placed and compacted material requirements of the MRH specifications for road and bridge works after which the suitability of the soil material is decided. Some selected soil samples from the three agro-ecological zones of Ghana were used for laboratory, model site and field compaction studies. The laboratory compaction method used was the modified ASSHTO T 190. The model site compaction studies involved three loose lift beds of 120 mm, 170 mm and 220 mm and three types of compaction plants; an 825kg duplex vibratory roller, 8,559kg static roller, and 15,380kg vibratory roller. The field compaction studies used a number of field compaction plants. The analysis used the decrease in gravel content as an index of particle breakage. It was generally observed that particle breakdown occurred for all the soil samples studied under both laboratory and field compaction. The extent of particle breakdown, however, was different for different soils and varied from a minimum of 1% to a maximum of 19% decrease in gravel content. In the laboratory, particle breakdown was observed to take place only during the initial stages of compaction. The breakdown of particles did not significantly affect the Atterberg limits and tended to lead to increase in strength of the compacted soils.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the award of Master of Philosophy degree in Civil Engineering, 2002