Investigation of the Effect of Adding Silica Fume on Asphalt Concrete Properties

Practical experience of highway networks showed that high percentage of road pavements are suffering from cracking and rutting. This problem had often occurred due to the shortage in asphalt mix properties as well as the increase in traffic loading. Fatigue, creep and rutting of asphalt mix in long term may be occurred due to the shortage in the mechanistic properties of either of the binder and/or the asphalt mix. This study investigates the effect of using silica fume (SF) as an additive to the binder on the behavior of asphalt mixes. The scope of the study includes the investigation of the properties of the asphalt mixes using different percentages of SF (2, 4, 6 and 8% by bitumen weight). Marshall, Direct Compression (DC), Indirect Tensile Strength (ITS) tests are used to examine the mixes properties whereas the wheel tracking (WT) test is carried out to investigate the rutting properties of the modified mixes. Results indicate that, the optimum SF percentage is 6% by weight of bitumen which achieve the best results in Marshall, DC, ITS and WT tests. Marshall Stability and flow are increased by about 23.61% and 4.67%, respectively. The unit weight increases, while the air voids percentage (AV %) is kept within the accepted limits. Adding SF reduces rutting depth by about 35.82%. The DC value increases by about 25% while the ITS value increases by about 3.83%. Finally, adding SF to the asphalt cement success in enhancing the properties of hot mix asphalt.