Copyright © 2018 Authors. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. International Journal of Engineering & Technology, 7 (4.20) (2018) 338-346 International Journal of Engineering & Technology Website: www.sciencepubco.com/index.php/IJET Research paper Evaluation of Optimum Content of Rice Husk Ash to Improve the Hot Asphalt Concrete Performance Gholamali Shafabakhsh 1* , Hassan Divandari 2 , Seyed Reza Sajadi 3 1 Professor, Faculty of Civil Engineering, Semnan University, Semnan, I.R.Iran. 2 Department of Civil Engineering, Nowshahr Branch, Islamic Azad University, Nowshahr, I.R.Iran, 3 Phd Student, Faculty of Civil Engineering, Semnan University, Semnan, I.R.Iran * Corresponding author E-mail: Ghshafabakhsh@semnan.ac.ir) Abstract Durability of asphalt pavements is related to choosing proper materials. Fillers as the smallest particles of stone materials, and one of the most important parts of asphalt mixtures, exert pivotal effects on the performance of asphalt mixtures, by filling empty spaces and because of their softness, surface features and chemical compounds. Rice husk ash is one of the waste products of burning rice husk in powerhouses that is accounted as biomass. Recently, a good many of investigations have shown that rice husk ash, as a high quality pozzolan, can be properly replaced of common aggregates. In this study rice husk ash was used as filler in hot mix asphalt, and the result mixtures’ mechan- ical properties was compared with ordinary mixtures whose filler was stone powder. Asphalt mixture samples with two different aggregate graded, and 0, 25, 50, 75 and 100 percent of rice husk ash which were the substitution of stone powder content, were made and the effects of using rice husk ash on the moisture sensitivity, resilience modulus, rutting and dynamic creep of asphalt mixtures were investigated. The results demonstrated that increase of using rice husk ash as the replacement of prevalent fillers in hot mix asphalts, noticeably improves their performance; however, because of excessive stiffness created by rice husk ash, it's better to use it in optimized percentage. Accordingly, statistical analysis of the tests’ results leads to presenting an optimized model for the content of Rice Husk Ash to be used in hot mix asphalt. Finally, Rice Husk Ash content were suggested 26% for graded number 4 and 48% for graded number 5 as replacements for stone powder filler. Keywords: Hot Mix Asphalt, Rice Husk Ash, Biomass, Moisture Sensitivity, Rutting, Dynamic Creep 1. Introduction Nowadays, various kinds of asphalt mixtures, are widely used in construction of pavements, because of good performance and ser- viceability, soft and comfortable driving and high endurance and durability. [1] In fact, researchers are aiming to provide more eco- nomic, durable, smooth and safe roads which have enough strength against predicted transportation loads. [2] Asphalt mixtures are formed out of three parts which are filler, asphalt binder and aggre- gates. In order to increase the bound between aggregates, the mastic resulted from mixing filler and asphalt binder, fills the spaces be- tween aggregates. [3] Filler, as the fine-grained part, exerts pivotal role on mechanical properties and chemical behaviors of asphalt mixtures and is effective in fastening the materials. Mineral fillers are added to asphalt mixtures for two purposes, a part of natural filler which is smaller than binder film thickness, is mixed with as- phalt binder and makes a primer which causes improving asphalt mixtures’ stiffness. Particles greater than binder film thickness op- erate like natural aggregates and help bound between stone parti- cles. [4] Moreover, fillers are different in graded, particles’ shapes, and amount of empty spaces, mineral material combinations and physical-chemical properties. Therefore, their effects on hot mix as- phalts characteristics are different. [5] filler‘s role in asphalt mix- tures is significant, for the reason that the interaction between filler and asphalt binder can influence asphalt mixtures’ properties. Ad- ditionally, fillers by having large surface areas, cause increase in asphalt binders’ absorptions which alters asphalt mixtures’ perfor- mance. It is reported that type and amount of filler can affect as- phalt mixture’s properties such as resistance against deformation, fatigue behavior and moisture sensitivity. [6] It is observed that in recent years, the development of mining in- dustry and heavy usage of raw materials put serious limitations on natural resources. Enormous volume of exploitations and the short- age of raw materials have resulted in production and recycling waste materials. In addition, one of the major concerns of numerous countries is how to manage the increasing amounts of waste mate- rials, since the locations of these huge volumes’ burials near many cities are super saturated. [7] Moreover, the construction and maintenance of roads require plenty amount of aggregates for base, subbase and pavement layers. [8] On the other hand, nowadays, be- cause of shortage and limitation of existing resources, there is a huge demand for waste materials in highway industry. Therefore, replacements of various ordinary aggregate parts used in asphalt mixtures with waste materials, is an efficient approach for cutting down the costs and also improving pavement properties. Besides, researches claim that burning biofuels does not provoke the in- crease of greenhouse effects which are results of releasing carbon dioxide in the atmosphere [9-11] Biomasses approximately provide 10 percent of the world’s energy for producing heat and electricity. [12] Rice husk ash is a biomass ash which comes from burning rice husk in powerhouses and furnaces. Currently, rice husk ash, be- cause of having proper characteristics, is widely used in concrete production industry, and has the potential of being used as filler in pavement industry, too.