Comparative analysis of asphalt concrete mixtures employing pebbles and synthetic coarse aggregate of calcined clay in the Amazon region

ABSTRACT

Several parts of the Amazon region present high costs concerning to pavement services, mainly because of their geological condition where there is a lack of rocky material. In these areas, natural pebble deposits or stone quarries are very distant from the consumption locations. The frequently used coarse aggregate in the State of Amazonas, Brazil, is the pebble taken from the riverbeds, with an at least 500 km distance from the greatest consumption centre, resulting in a high transportation fee which approaches in about 50% of the final product cost. Searching for an alternative and non-conventional material which could replace the pebbles, the natural clay was studied due to its mineral abundance in the Amazon region. The production process adopted by the ceramic industry was reproduced in laboratory tests, in a handcrafted way, using a manual mill composed by four nozzles with dimensions of 12.7, 9.5, 4.8 and 2.0 mm. The wet aggregates were calcinated at temperatures of 780, 850, 950, 1050 and 1150 °C, and physically characterised. It was made a comparative analysis between the conventional hot mixed asphalt concrete (with pebbles) and using synthetic aggregates, studying several physical and mechanical parameters. Asphalt mixtures made with synthetic aggregates offered better bonding between their components when compared with those made with pebbles, favouring gain in mechanical resistance, since they represented a structural skeleton more resistant than pebbles. In addition, as the firing temperature of the synthetic aggregates increased, the consumption of asphalt cement decreased, due to the phase transformations of the crystal to the amorphous phase. The results of the resilient modulus to static indirect tensile strength ratios allowed to infer that asphalt mixtures made with synthetic aggregates point to a longer fatigue life when compared to the pebble mixture principally at values lower than 3500.

KEYWORDS:

• Synthetic aggregate
• calcined clay
• asphalt concrete
• burning temperature
• hot mixed asphalt concrete
• Marshall dosage
• resilient modulus
• Amazon region

Acknowledgement

The authors would like to thank Laboratory of Pavement of COPPE/UFRJ for some tests carried out in that place.

Additional information

Funding

This work was supported by the CNPq [grant number 620244/2008-9]; FAPEAM [grant number 864/2003], [grant number 1376/2004].