thumb Picture3

Remedial Grouting of Voided Post Tensioned ducts

This bridge has a clear central span of 27m which is supported off 2 V-shaped end piers. The outer raking legs of the V-shaped piers each features 3 vertical Macalloy bars (varying in size from 32 to 35 mm) bars in 41 mm duct. The Macalloy bars act as tension ties to restrain the ends of the main span.

During an intrusive inspection of the post tensioning system some voids were found. The inspection concluded that the ducts had been grouted, although the grout flow had not extended along the full length of the ducts due to the small size  of the annulus around the Macalloy bars and the possible movement of the ducts during the casting of the concrete, resulting in a restriction to the free flow of grout along the duct.

Topbond were appointed to undertake remedial grouting of the voided ducts and undertook further intrusive inspections and pressure testing.

Because of the small size of the duct, a system to inject small measurable volumes of grout was developed using a pneumatic grout injection plant. Injection ports were fixed at 1m vertical centres, allowing the grout to be injected from the bottom upwards, forcing air out of the upper injection point. Follow up inspections proved the success of the injection technique.