Influence of grading on the strength of water-bound macadam

Abstract

The research work was undertaken to study the influence of. grading on the strength of water-bound macadam (WBM). The study includes the selection of a suitable aggregate grading for waterbound macadam construction from the considerations of strength and stability. Attempts are also made to study the properties of brick-aggregate used for WBM construction. The whole research work was carried out in three stages. In the first stage, compaction type was selected from degradation of brick aggregate due to different compactive efforts (i.e. 2.5 kg, 4.5 kg and vibrating hammer). Use of screenings was selected in the second stage from bearing capacity of the mix for two conditions -- one by mixing screenings with coarse aggregate and / another by providing screenings on the top surface of coarse aggregate. Finally. aggregate grading was selected from strength and stability of the aggregate mix. Four gradations were initially selected from the recommended specified gradations .. Modified Bearing Ratio (MBR) tests were then performed after compacting by a vibrating hammer at optimum moisture contents as CBR test is not applicable to most of the gradings used. The study reveals that "Picked Jhama" brick-aggregate-sandsoil mixes are good for use in WBM construction, from the" standpoint of strength and stability. WBM mixes with picked jhama brick aggregates give satisfactory results when they are constructed using dense grading compacting by vibrating hammer at optimum moisture content.