Possibility of using uncrushed river gravel for bituminous pavements and surfacings

Abstract

Scope of Study: The standard specifications for highways in the Philippines require that aggregates for bituminous surfacings and pavements shall be crushed, just as any other specification of highway organizations in the United States. There is an abundant supply of natural river gravel and unless this is crushed same can not be used as an asphalt paving aggregate. Remote projects in the Philippines which are considerably small can not produce specification requirements economically due to insufficient crushers available. The use of a rented crusher or crushing by hand may prove prohibitive in some places. Reference to past laboratory test and actual construction procedures were compiled using uncrushed river gravel to advantage and satisfactory behavior was observed on the mixtures.

Findings and Conclusions: Laboratory tests have shown that the stability of pavement mixtures depends more on the roughness characteristics of the aggregate rather than angularity. For surface treatments, considerations only on quantity, type of binder, amount of moisture and presence of dust are the ones emphasized. For macadam gravel pavements, gradation was the most important and only materials passing the 2 inch sieve and retained on the 3/4 inch should be used. A great deal of labor and control are required for a successful result. On the plant-mix surface types, comparisons on strength we made .and that there was no difference in strength whether gravel or crushed gravel was used. The two important properties of an asphalt mix are the angle of internal friction and cohesion whose values can be increased by the use of strong mortars. 'This strong mortar is produced' by using angular sands as fine aggregate. It was determined that the strength of the mixtures responded to the shape of the fine aggregate rather than the shape of the coarse aggregate. There should be no standard for gradation but it should be one that utilizes the available aggregates to give as many of the desired properties. The Los Angeles percentage of wear for all bituminous aggregates shall not be more than 40.