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Task 06

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Technical documenttation of bio ash concrete

DTI will be responsible for carrying out this task.

In terms of traditional concrete technology a few concerns have been raised in connection with the use of bio ash concrete. For this reason, in Denmark, bio ash is only allowed to be used in concrete for passive environment. To use bio ash concrete in other more aggressive environmental classes more documentation is required primarily on long-term durability and strength development, in particular the role played by the high content of P2O5 in the bio ash. Consequently, the task will attempt to clarify the above issues and by performing a suite of tests that will provide better knowledge of the long-term durability and strength development of bio ash concrete. Whenever possible, testing will be based on ready-mixed concrete from UNICON.

Long-term durability
The long-term durability of bio ash concrete will be documented through accelerated performance testing, and through microscopic analysis of the bio ash concrete. Two bio ash concretes (AWS ash, LYNIS ash) and a reference concrete will be tested for each of the three environmental classes passive, moderate and aggressive. The following test methods will be performed:

•     Freeze-thaw resistance (SS 13724 and EN 480-11)
•     Cl-ion penetration (NT BUILD 492)
•     Alkali silica reaction, mitigating effect on (TI-B51)
•     Shrinkage (DS 434.6)
•     Microstructure characterization (TI-B5)

Only the last two tests apply to concrete in passive environment whereas all five tests will be carried out on concrete in moderate and aggressive environments.

Strength development
The influence on strength development (including setting time) will be investigated for a suite of six selected bio ashes (three from each of LYNIS WWTP and AWS WWTP). The ashes investigated will be selected based on their total P2O5 content as well as their soluble P2O5 content (soluble phosphate is strongly retarding the setting of concrete). The P2O5 parameters are available from Task 3. Two bio ash concretes will be tested in the passive and aggressive environmental class, respectively. The following tests will be performed:

·         Setting time EN 196-3 (Task 3)
·         Heat development and setting time of concrete through semi-adiabatic Hay-box calorimetry (NT BUILD 388:1992)
·         Compressive strength development of bio ash concretes. Strength measured at 2, 7, 28 and 56 days according to EN 12390-1, 2, 3, 4.

Progress indicators - 1) Concrete specimens cast, 2) Durability tests initiated, 3) Strength development tests initiated.

Expected Results
Reports with documentation on whether the durability and strength development of bio ash concrete are comparable with traditional concrete types.

Constraints – Substantial adverse effects on either strength development or durability may naturally reduce the incitement to use bio ash in concrete production. Research has so far not provided indications that substantial adverse effects are to be expected.