Effect of Natural Sand on the Performance of Asphalt Concrete Mixes
Harith M. Al-Beiruty Amjad H. Albayati
Research student Assistant. Professor
College of Engineering-University of Baghdad
ABSTRACT
Frequently, load associated mode of failure (rutting, and fatigue) as well as, occasionally, moisture damage in some sections poorly drained are the main failure types found in some newly constructed roads within Baghdad and some suburban areas. The use of excessive amount of natural sand in asphalt concrete mixes which is attractive to local contractors because it is generally less expensive than crushed fines and readily available could be one of the possible causes to lack the strength properties of asphalt concrete mixtures and as a final result frustration in pavement performance
In this study, the performance properties of asphalt concrete mixes with two natural sand types (desert and river) and five replacement rates for each one (0, 25, 50, 75, and 100% by weight of the sand passing sieve no. 8 and retained on sieve no 200) were evaluated . The performance properties include moisture damage, resilient modulus, permanent deformation and fatigue characteristics. These properties have been evaluated using indirect tensile strength, uniaxial repeated loading and repeated flexural beam tests. Also, in this study VESYS5W software was implemented and the pavement performance is evaluated in term of the change in present serviceability index (∆ PSI) over the analysis period for two pavement traditional sections widely used in local practice.
. The replacement of all crusher sand in a mix with a desert sand shows, respectively for wearing, binder and base course, a decrement in Tensile Stress Ratio (T.S.R.) values by 21, 23.6, and 20.7 percent , a decrement in resilient modulus values by 38, 43, and 37%, an increment in the accumulation rate (slope) values of permanent deformation by 33.6, 41.5, and 32% and finally a decrement in the fatigue parameter (k2) by 20.5, 19.5, and 21%. The corresponding test results obtained from the use of 100 percent river sand shows further deterioration in the performance as compared to the above mentioned results for desert sand.
The general theme viewed from the results of this study has added to local knowledge the ability to produce more durable asphalt concrete mixtures with better serviceability by reducing the amount of natural sand (either desert or river) in the asphalt concrete mixes as first , and as a second the necessity to refine the limits of natural sand content in the current local specification which is 25 percent for asphalt concrete mixes of wearing and binder courses whereas for base course no limit exist yet.