Author(s):
B.M. Gallaway, W.J. Harper
Publication Date
August 1967
Abstract
This final report, the fourth in a series on the subject, sumarizes the findings of a study on the use of lightweight aggregate in flexible pavements. The study began in 1963 and was directed initially toward verifying expected performance and safety aspects of pavement lightweight aggregate when compared to precoated limestone used primarily as coverstone for seal coats.|Both laboratory and field studies were carried out to prove that lightweight aggregate is quite suitable as a coverstone for seal coats and surface treatments. Lightweight aggregate was found to cause no "flying" stone problem and thus damage to windshields and headlamps was eliminated where this material was used. Although not a part of the study, it was found that lightweight synthetic aggregate used as cover-stone for seal coats produced a surface of high and prolonged skid resistance.|Exploratory research in the laboratory and field with lightweight aggregate in hot-mix asphalt paving mixtures shows great promise for this new source of aggregate. Mixes designed to include as much as fifty percent (by volume) of lightweight aggregate appear entirely suitable for high quality asphalt surface courses.| The mixtures are highly stable, are not water susceptible, and above all, produce a non-skid surface. When proper use is made of local materials for the intermediate and fine sized fraction of the mix, designs containing lightweight aggregate compare favorably in cost with designs made from regular aggregates.|Based on two field trials involving "manufactured" aggregate from three sources, the coefficient of friction as measured wet at 40 mph on a locked wheel trailer is above 0.5. One of the sections with over four million vehicle passages is one year old and the other is over four years old and has in excess of three million vehicle passages over it.|In plant mixes, this new aggregate presents no construction difficulties for which easy adjustment cannot be made. And although asphalt content may at first appear high, it is quite normal when compared on a volume basis with that required by regular aggregates. Asphalt absorption is higher than that for most regular aggregates, but it is non-selective which gives it a definite advantage over absorptive limestones and sandstones, which may absorb the lighter fraction (smaller molecules) of asphalt thus leaving a harder residual binder subject, possibly, to earlier brittle failure.
Report Number:
51-4F
Link(s):
Document/Product
http://tti.tamu.edu/documents/51-4F.pdf
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