GROUTING POST TENSIONED TENDONS

The article describes the results of some full scale trials carried out on a bridge deck on the M10 motorway. The bridge, a two span structure with three webs, contains eight 150 mm diameter ducts in each web carrying 37 strands of no 15.6 diameter. The trial included the grouting of a 100 M long tendon, with a nominal 50 ton load, and subsequent dissection of the duct. Experience in Europe and with North Sea oil work led to the adoption of a single strand electrically operated pushing machine using a water-soluble oil lubricant to insert the tendons into the duct. The quantity of grout required needed two independent grout stations at either end of the duct. Allowances were made for the asymmetry of the duct profile and checked through venting ducts at 10 M spacings; the proposed grout mixture gave a 7 hr retardation. Grout strengths were found to be well in excess of the 28 day requirement of 30 n/mm2. Results from the grouting trial showed that the strand had pulled to profile under the nominal load and that the grout take was completely successful throughout, including the bunched strand area. Breaking out individual strands showed that although traces of oil could be observed in the interstices of the strand wires the bond was adequate. (TRRL)