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Instances of poor grouting practice of reinforcing bars in Drossbach tubes

Posted: 28 September 2017

The New Zealand Institute of Building Surveyors recently informed MBIE of instances of poor construction practice associated with the grouting of reinforcing steel bars inside Drossbach tubes set within reinforced concrete elements. These instances were investigated and confirmed by professional engineers.

This detail is typically used as a connection between a floor substructure and precast reinforced concrete wall panels. It is also used in precast concrete frame construction, where the projecting starter bars from the previous construction stage are grouted into Drossbach tubes set within precast concrete beam or column segments for the next stage of construction.

The instances reported were with concrete wall panel construction where there was either incomplete penetration of the grout or, in some cases, no grout at all around the reinforcing bars.

If undetected, the resulting loss of the reinforcing bar bond under service loads may at best cause poor performance of the structural element and at worst cause premature collapse of the structural component.

Site personnel, engineers reviewing construction, and building consent authority inspectors should be vigilant to ensure the tubes are effectively end sealed to prevent loss of the wet grout and that grout is injected to avoid air entrapment. Site quality practices such as non-destructive testing (NDT) should be undertaken to verify that the grout fully penetrates around the reinforcing bars.

This information is published by the Ministry of Business, Innovation and Employment’s Chief Executive. It is a general guide only and, if used, does not relieve any person of the obligation to consider any matter to which the information relates according to the circumstances of the particular case. Expert advice may be required in specific circumstances. Where this information relates to assisting people: