Performance Evaluation of Quarry By-Products in Otta Seal Surfacing of Local Roads

Otta seal, a surface treatment method that typically employs locally sourced low-quality aggregates, has been recognized as a cost-effective and sustainable option for bituminous surfacing of low-volume roads. Because quarry by-products (QBs), sand-sized residues from quarrying operations, remain largely underutilized despite being readily available and exhibiting well-graded behavior, offering potential for use in Otta seal applications, a feasibility study on incorporating QBs into Otta seal design was conducted using adaptations of existing chip seal design methods: (1) modified McLeod; (2) modified Kearby; and (3) Austroads methods. The laboratory study on Otta-seal specimens incorporating QBs revealed that optimal lab-scale specimen preparation was achieved with a double-layer configuration where aggregates were separated using a No.8 sieve (2.36 mm). Using an optimized lab specimen configuration, three design methods were evaluated with two QBs and one typical Otta-seal aggregate as a control. Performance tests using sweep testing and a modified Hamburg Wheel Tracker (HWT) showed that specimens prepared with QBs demonstrated comparable or superior aggregate retention compared with those with typical Otta-seal aggregate, highlighting the feasibility of incorporating QBs in Otta seals. Among the design methods, the modified Kearby method consistently delivered the best performance, with an adequate binder/aggregate ratio resulting in the lowest aggregate loss in the sweep and modified HWT testing. Texture properties computed using close-range photogrammetry effectively captured the macro-surface texture of the Otta-seal specimens, accounting for the physical characteristics of QBs and typical Otta-seal aggregates and demonstrated an inverse relationship between surface roughness and aggregate retention.