Authors: Aapo Räsänen and Jukka Lahdensivu, Tampere University 

Introduction to the reports: Procedure for quality management of reclaimed concrete elements, Properties and quality of precast concrete elements deconstructed in ReCreate’s pilots and Quality management best practices in reuse of precast concrete elements of the ReCreate project. The full reports are available on the website.  

The ReCreate report Procedure for quality management of reclaimed concrete elements presents the six stages process for safe reuse of reclaimed concrete elements as a part of bearing structures in new buildings. The key process stages are: 

• Pre-deconstruction audit, where the main actions are finding out the type and number of elements, assessing their reuse potential, and gathering information for the next stages. 

• Structural investigation, where the main actions are ensuring material properties of elements primarily with non-destructive (ND) or semi-destructive (SD) methods, determining the condition of the elements, and finding out the existence of possible hazardous substances. 

• Deconstruction design and execution, where the determination of safe deconstruction and lifting methods is the main action, together with transportation and storage of deconstructed elements. 

• Full-scale testing is carried out if the structural capacity of reclaimed elements cannot be uncovered through other means or if there is doubt about safety factors. Also newly developed retrofit connections need testing if original connections cannot be reused. 

• Redesign and reassembly, where the main actions are designing the reclaimed elements according to Eurocodes and standards in force. Also, the refurbishment of the reclaimed elements must be designed and carried out before delivering elements to new construction site. 

• Product approval and authorisation is the final stage, where documents from the previous stages, together with technical drawings and calculations, will be presented to authorities to obtain official permits for reuse. 

Visual investigation and thorough documentation are an essential part of each stage. Information must be carried through from stage to stage. 

Properties and quality of reclaimed elements 

Properties and quality of reclaimed elements were determined in four piloting countries: Finland, Germany, the Netherlands and Sweden. The report provides description of used test methods number of samples and measurements, and all test results carried out in laboratories of each donor buildings. In short, concrete grade used in reclaimed elements was higher than original design value, the elements were in good condition in general, and all found harmful substances could be removed before detaching of elements. 

Knowledge Level 

The ReCreate report Quality management best practices in reuse of precast concrete elements focuses on test methods and sufficient number of tests/samples needed for determining the material properties of concrete and the bearing capacity of elements. The actual condition, material properties, remaining service life, and probable repair needs of elements intended for reuse can be assessed through a systematic investigation. The need of testing depends strongly on the extent of available information. Therefore, four Knowledge Levels (KLs) are introduced: 

1. Knowledge Level 1 (KL1): No information is available regarding the concrete quality, reinforcement properties, or the manufacturer of the elements.  

1. Knowledge Level 2 (KL2): No information regarding the material qualities is available, but the manufacturer is known. 

1. Knowledge Level 3 (KL3): Some specifications describing the concrete and reinforcement properties of the elements exist, but no further information about the manufacturer or quality control applied during production is available.  

1. Knowledge Level 4 (KL4): Detailed archives of specifications describing the used concrete quality and reinforcement steel design are available, and both the manufacturer and its quality control system are well-documented. 

The first two knowledge levels (KL1 and KL2) describe situations where no design specifications are available on the donor building. In these cases, extensive non-destructive testing (NDT) and destructive testing (DT) is required. For KL3 and KL4, partial or complete archives of original documents are accessible, and the specified properties only need to be verified through selective testing, reducing the workload. 

Parallel test methods 

Many different test methods are available for determining properties of concrete elements. Some methods are simple, while others are more complex, potentially causing more damage and costs. Additionally, the reliability of the tests varies depending on the method used. The testing methods used should always selected to suit each specific situation, based on the project’s criteria. The criteria may include, e.g. the type of element, required level of reliability, requirements of the new building, or the test methods available. 

Ideally, the test methods should be selected to maximise the amount of knowledge gained while minimising costs and time. By using parallel test methods, reliability can often be improved by complementing each method’s shortcomings to create a more reliable aggregated method. In the report different test methods are presented for: 

• compressive strength evaluation of concrete 

• cover depth and diameter measurements of reinforcement 

• carbonation measurements of concrete 

• chloride content of concrete 

• corrosion of reinforcement 

• freeze-thaw resistance of concrete 

• deteriorated concrete. 

The methods are presented in tables containing information on suitable standards, representativity, reliability, workload and number of needed tests of each presented test methods when the information is available. 

Number of samples 

Number of samples needed for each test are mentioned in standards in the first place. Several tests presented in report have no standard, e.g., cover depth measurements reinforcement. Sufficient number of test specimen or full-scale tests for high reliable results is based on scientific research on the results from the pilot projects. High deviation of test results gives a recommendation of higher number of samples/tests than the minimum number in standards. The recommended number of samples are presented in the report. 

Conclusion 

Quality assurance measures carried out in the ReCreate project varied somewhat across different pilots. The best practices presented in the report are based on the necessary actions taken at each pilot. In particular, damage and deficiencies in structural elements required significant interventions. These defects were discovered at different stages of the pilots, leading to immediate responses each time, which resulted in multiple actions being taken. 

Overall, the quality assurance measures are especially useful in validating the reusability of elements. These measures will also benefit the structural designers by helping anticipate potential deficiencies and necessary modifications during refurbishment. Well-documented processes will provide evidence of reusability to authorities and other stakeholders involved in the reuse process. In Finnish pilots the developed quality management process was used successfully. The building inspection authorities in Tampere and Helsinki accepted the developed quality management process for reused concrete elements as a part of the site-specific authorisation.