• Ferreira, Rui Miguel
• Salparanta, Liisa
• Niemelä, Mari
• Leivo, Markku
• Fülöp, Ludovic A.
• Bohner, Edgar

Abstract

In the summer of 2016, a nearly-complete railway bridge under construction was demolished because of insufficient concrete strength. Concerns also arose regarding poor concrete quality at a hospital building site in Turku. As a result, the Finnish Transport Agency (Liikennevirasto) examined the concrete strength and air content of 18 bridges built between 2012 and 2016. The results of that examination led to the further study of an additional 95 bridges. The investigation included measurements of concrete strength and air content, as well as review of the quality inspection documents.<br/><br/>Experienced bridge inspection consultants collected samples and carried out measurements on the bridges. Approximately 1 500 samples were submitted to testing laboratories for analysis. VTT Technical Research Centre of Finland Ltd prepared the bridge inspection plans, analysed the test results and reviewed the quality inspection documents.<br/><br/>The quantity of data obtained to date in this research project is massive, yielding substantial potential for the extraction of additional information of interest. Further data analysis will likely generate a number of additional interesting results, and there is potential to re-examine or further analyse samples currently stored at VTT to obtain additional information. Some results obtained thus far are presented herein.<br/><br/>The review of the quality inspection documents revealed that only 6% of the bridges had a quality report that fulfilled Transport Agency´s regulatory requirements and 34% of the bridges had no quality report. Most of the documents were unclear and contained contradictory information. In most cases the quality inspection documents did not reveal whether the technical requirements were fulfilled. The Finnish Transport Agency created a grading scale (1 worst ... 10 best) to account for both the relative quality of the quality inspection documents, and the fulfilment of technical requirements. Analysis of this grade or rating as a function of concrete casting date revealed that the quality of quality inspection documents did not improve between the years 2003 and 2016.<br/><br/>Estimation of the compressive strength at an age of 28 days as determined from the samples taken during this project showed that the measured strength was not dependent upon the design strength. Rather, the average measured strength diminished with increasing design strength. Overall, no significant concrete strength problems were noted for Finnish bridges.<br/>Measurements of the air content of concrete determined in this study vs a function of casting date revealed a general increasing trend in concrete air content from 2003 to 2016. In several cases, the 7.5% upper limit of acceptable air content in this research was exceeded, which has negative effects on concrete strength and durability.<br/><br/>To avoid poor concrete quality in the future and address any concerns at an early stage the Finnish Transport Agency will carry out random inspections of bridges completed within the previous 12-month period, among other actions to mitigate risks. The guarantee period is also extended from 2 to 5 years. New training programmes and training materials will be probably be implemented, and human resources increased to contribute to quality assurance. Guidelines will be revised and clarified and new monitoring techniques will be applied. The ongoing DigiConcrete project developed innovative digital solutions for assuring good quality of concrete construction throughout the construction value chain are developed. Aalto University, VTT and conventional construction companies together with instrumentation and software companies participate DigiConcrete project.<br/>The Finnish Transport Agency, together with VTT and Aalto University, has initiated new research into the effect of high air content on the structural behaviour and durability of concrete. These results will be available in 2022 and will further inform quality guidelines for concrete materials for major infrastructure.

Topics

• impedance spectroscopy
• extraction
• strength
• casting
• random
• durability