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From page 6...
... B-2 INTRODUCTION Researchers have distinguished between the different aspects that constitute aggregate particle geometry or morphology and have found that it can be fully expressed in terms of three independent properties: shape (or form) , angularity (or roundness)
From page 7...
... B-3 Shape (Form) Angularity Texture Figure B-1.
From page 8...
... B-4 The contents of this appendix focuses on presenting the findings of previous studies that are relevant to the influence of aggregate shape on performance of different types of pavements and on identifying aggregate characteristics affecting performance. THE INFLUENCE OF AGGREGATE CHARACTERISTICS ON PAVEMENT PERFORMANCE This section documents the collected and reviewed information relative to the effect of aggregate shape properties on performance of different types of pavements.
From page 9...
... B-5 of the aggregates. There was no correlation between geometric irregularities and resilient modulus or indirect tensile strength of the HMA mixtures.
From page 10...
... B-6 the four sections developed permanent rutting within two years of service. They found that HMA mixtures used in the binder course and the surface course of the rutted section had lower amounts of angular coarse aggregate compared to the other three sections.
From page 11...
... B-7 component of the HMA mixture. Its quantity and characteristics controlled, to a large extent, the Marshall stability.
From page 12...
... B-8 were statistically related to the rutting behavior of selected HMA mixtures. A comprehensive study by Kandhal et al.
From page 13...
... B-9 Figure B-2. Correlation between Coarse Aggregate Texture Measured Using Image Analysis and Rut Depth in the Creep Compliance of HMA (after (28)
From page 14...
... B-10 and properties is a key to enhancing pavement life; otherwise, poor selection can lead to premature failure in the pavement structure. Concrete is expected to perform well during construction and service life, so PCCP will have good performance and serviceability and will last longer.
From page 15...
... B-11 Coarse aggregate particle shape and angularity are related to critical performance parameters such as transverse cracking, faulting of joints and cracks, punchouts, and spalling at joints and cracks. Using a high percentage of flat and/or elongated particles might cause problems when placing the concrete, which will result in voids and incomplete consolidation of the mix and thus contribute to spalling.
From page 16...
... B-12 aggregate (of the same rock type) generally give the same strength for the same cement factor.
From page 17...
... B-13 Rao et al., (37) studied the effect of aggregate shape on strength and performance of pavement layers.
From page 18...
... B-14 50-50 Blend AI = 308 Crushed Stone AI = 423 Gravel AI = 176 400 500 600 700 800 900 1000 1100 42 44 46 48 0 100 200 300 400 500 Angularity Index σ3= 35 kPa σ3= 69 kPa σ3=104 kPa φ( de gr ee s)
From page 19...
... B-15 IDENTIFYING AGGREGATE CHARACTERISTICS AFFECTING PERFORMANCE Most of the available information on the influence of aggregate characteristics on performance emphasizes that shape, angularity, and texture play important roles in controlling performance of HMA mixtures, hydraulic cement concrete mixtures, and unbound layers. However, different shape properties influence the performance of these layers to different extents.
From page 20...
... B-16 elongated, and flat and elongated particles through measuring the three dimensions particles. Although most available tests could not separate texture from angularity, recent studies using image analysis techniques have emphasized the significant influence that texture has on performance (29, 40)
From page 21...
... B-17 planes in the direction of traffic on pavements. The stiffness anisotropy should be considered in the design of asphalt pavements (41)
From page 22...
... B-18 REFERENCES 1. Barrett, P
From page 23...
... B-19 7. Barksdale, R
From page 24...
... B-20 13. Campen W
From page 25...
... B-21 20. Kandhal P.S., and Wenger M.E.
From page 26...
... B-22 27. Kandhal, P
From page 27...
... B-23 33. Folliard, K
From page 28...
... B-24 40. Masad, E

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