OTTA SEAL TRIALS IN KWAZULUNATAL SOUTH AFRICA by

OTTA SEAL TRIALS IN KWAZULU-NATAL, SOUTH AFRICA by S. Oloo, D. Thevadasan and H. Bennett

Outline l Introduction l Location of test site l Characteristics of trial section l Performance of trial section l Conclusions

Introduction l Where is Kwa. Zulu Natal?

Introduction l Road Network – Total 23 000 km, Gravel 17 000 km (74%) l Problem – Shortage of gravel – Accelerated gravel loss – Long haul distances (> 30 km) l Solutions – Blacktop even under low traffic – Seals too expensive – Consider Otta seal

Location of test site Bothas Hill Drummond Hillcrest Everton

Characteristics of trial sections l Pavement Otta seal 150 mm decomposed granite 150 mm Road Bond treated decomposed granite l Trial Sections: – 11 No. , 8 discussed – Combinations of aggregate, prime, anti- stripping agent

Characteristics of test site Section 1 2 3 4 5 6 7 8 Aggregate Anti-Stripping agent Prime Aggregate Crushed stone Natural gravel Wetting agent Prime None 0. 8% by weight MC 30

Characteristics of test site l Aggregates – Crushed quartzite & Decomposed granite l Binder – 150/200 pen. Bitumen, 1. 6 – 1. 9 l/m 2 spray rate, 8 – 11% paraffin cut back l Prime: MC 30 l Anti-stripping agent: duominic-T, 0. 8% by mass

Quartzite stone

Decomposed granite

Performance of trial sections l One week after – Large quantities of loose stone on surface – Binder barely visible – No difference between sections

Performance of trial sections l One month after – Binder visible following brooming – Curing advancing well – Higher binder content section showing signs of bleeding – Rutting & corrugations in some sections

Performance of trial sections l Two months after – Binder moved to surface – Higher spray rate sections bleeding – Potholes in crushed rock sections

Performance of trial sections l Six months after – Curing complete – Uniform dark premix-like surface – Bleeding serious on gravel sections – Severity of potholing increased

Conclusions l l l The performance of both aggregates unsatisfactory partly due to grading being outside recommended envelope. Binder application rates and amount of cutback appear to influence the performance of the Otta seal. Priming did not influence performance. Rutting and corrugations can occur as a result of Otta seals following the contour of the base. Proper finishing required. Generally Otta seal has potential.