Effects of geometrically cubical shaped aggregate on the engineering properties of porous asphalt

Porous asphalt (PA) is predominantly made up of coarse aggregates. The coarse aggregate is instrumental in providing the strength and stability of the mix. The aggregate properties including shape is expected to greatly influence the performance of PA. In this study, five different proportions of geometrically cubical shaped (GCS) aggregate and normal shape aggregate combinations were introduced and designated as mix M0, M25, M50, M75 and M100. Further laboratory tests were carried out to determine the properties of PA including air voids, coefficient of permeability, abrasion loss, indirect tensile strength, resilient modulus and resistance to permanent deformation. The results obtained showed that mix M100 which consists of 100% GCS aggregate performed the best in all tests. Statistical analyses of one-way ANOVA and Duncan’s Post Hoc test results showed that the introduction of GCS aggregate has a significant effect on air voids, coefficient of permeability, abrasion loss and resistance to permanent deformation of the mixes. However, the results showed that GCS aggregate do not gave significant effect on indirect tensile strength and resilient modulus of the PA mixes tested

BINDER DRAINAGE TEST FOR POROUS MIXTURES MADE BY VARYING THE MAXIMUM AGGREGATE SIZES

Binder drainage occurs with mixes of small aggregate surface area particularly porous asphalt. The binder drainage test, developed by the Transport Research Laboratory, UK, is commonly used to set an upper limit on the acceptable binder content for a porous mix. This paper presents the results of a laboratory investigation to determine the effects of different binder types on the binder drainage characteristics of porous mix made of various maximum aggregate sizes 20, 14 and 10 mm. Two types of binder were used, conventional 60/70 pen bitumen, and styrene butadiene styrene (SBS) modified bitumen. The amount of binder lost through drainage after three hours at the maximum mixing temperature were measured in duplicate for mixes of different maximum sizes and binder contents. The maximum mixing temperature adopted depends on the types of binder used. The retained binder is plotted against the initial mixed binder content, together with the line of equality where the retained binder equals the mixed binder content. The results indicate the significant contribution of using SBS modified bitumen to increase the target bitumen binder content. Their significance is discussed in terms of target binder content, the critical binder content, the maximum mixed binder content and the maximum retained binder content values obtained from the binder drainage test. It was concluded that increasing maximum aggregate sizes decrease the maximum retained binder content, critical binder content, target binder content, maximum mixed binder content, and mixed content for both binders, but however for all mixtures, SBS is the highest