Effect of Mixing Process on Polypropylene Modified Concrete Mix Properties

This paper presents a part of research conducted to investigate the effect of addition of polymer polypropylene (PP) as modifier to bitumen. Two mode of mixing, namely dry and wet with different concentration of polymer polypropylene was used with 80 pen bitumen, to evaluate the bituminous concrete mix properties. Three percentages of polymer varying from 1-3% by the weight of bitumen was used in this study. Three mixes namely control mix, wet mix and dry mix were prepared at the same mixing condition. Optimum binder content was calculated considering Marshall Stability, flow, air voids and Marshall Quotient at different bitumen content varying from 4 - 6.5% for control, dry and wet mix. Engineering properties thus obtained at the calculated optimum bitumen content revealed that wet mixing process is advantageous in comparison to dry mixing as it increases the stiffness of the mixture with the increase in polymer content in bitumen. The decrease in density with the increase in polymer content for both dry and wet mix indicates that the mixture was lean and tender to allow further densification which was considered as positive sign reducing the chances of rutting in pavement if the air void content doesn’t fall below 4%.Stiffness value for wet mix increases with the increase in polymer content which is beneficial in terms of rutting when tested at the later stage of this study. 1% PP dry mix also shows enhanced stiffness, with the air void content limited to 4%.The flow behaviour of dry mix doesn’t indicate any major difference with the increase in polymer content revealing that polymer acting as an aggregate only without affecting the viscosity of the binder in the mix. Polypropylene (PP) when interacted with 80 pen base bitumen enhances its performance characteristics which are brought about by altered rheological properties of the modified bitumen.. The decrease in flow with the increase in binder content reflects the increase in viscosity of binder which induces the plastic flow in the mix which would be beneficial in terms of fatigue when tested at the later part of this study. Workability index indicates that wet mix were easy to compact up to desired void ratio in comparison to dry mix samples.