Improved quality assurance & methods of grouting post-tensioned tendons

Exploitable results

This Project has been targeted to solve problems encountered in post-tensioned structures and identified as due to inadequate grouting.(1-9) A high performance grout, named BE (Brite Euram) Grout, was developed through studies of particle packing theory and exhaustive testing of various formulations. The end product is a method of formulation to enable a thixotropic stable grout to be produced from any source of cement. In the past, the source of cement has strongly influenced grout properties. Even though cement has to conform to a European Standard permissible variations in composition can lead to wide variations in grout performance. As part of the grout development work it was necessary to examine critically the standard performance tests.(10,11,14) It was found that many are inadequate. For example, the flow cone is unable to cope with a thixotropic grout. Likewise the bleed test is unable to identify unstable grouts.(12) The research has enabled a new suite of performance tests to be devised. Work in the laboratory and on a construction site using the BE Grout, traditional grouts and poor grouts, demonstrated the shortfalls in the standard tests and confirmed the practicality of the proposed tests. As an aid to improving grouting procedures various types of QA instrumentation were investigated, some were based on new ideas and developed to prototype stage, others were commercially available viz capacitance and resistance sensors to detect the presence and passage of grout, pressure sensors to provide stress-time records of the grouting, and a flow meter to provide records of flow rate and quantity of grout pumped into the ducts. These sensors were developed with the aid of laboratory tests on eight curved beams of 20m span, and a final demonstration on a bridge under construction in Denmark. The bridge was 40m long, of three-span continuous construction, and having 14 longitudinal tendons with vertical post-tensioning through the piers. It was constructed as part of a relief road round the town of Brande in Jutland. Work was carried out on different types of pump and mixing platforms. It was found that grout performance is strongly influenced by the type of mixer and it is necessary to match them together to get good results. The benefits of the project are the development of a high performance grout that meets all requirements, a suite of more discriminating grout performance tests that are recommended for inclusion in revised standards, prototype sensors recommended for commercial development, commercially available sensors recommended for immediate inclusion in future grouting operations and a QA plan.

Exploitable results

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