Project - BioCrete - Task descriptions

Task 01_Design and construction of facilities for handling of ashes at the sludge incineration plant

The task comprises the characterization and use of two different types of bio ashes. This is due to the different incinerator types at the wastewater treatment plants (WWTPs) operated by LYNIS and AWS, respectively. At LYNIS WWTP the sludge is incinerated in conventional multiple hearth furnaces; ashes production approx. 7,000 t/year. At AWS WWTP the sludge is incinerated in a fluidized bed oven, and the ashes collected as fly ashes; ashes production approx. 3,000 t/year.

At both WWTPs the bio ashes are wetted prior to the transfer to a local controlled land fill site to prevent occupational health and environmental problems with the ashes action like dust powder.

It is essential for maintaining the pozzolanic characteristics of the bio ashes to avoid wetting. Thus, an outlet system for the dry ashes has to be designed and constructed at both WWTPs, and each one allowing for a dust free transfer of dry ashes in full scale quantities to vehicles acceptable for a convenient unloading at the concrete production plant.

It is the responsibility of LYNIS and AWS, respectively, to install the two outlet systems. UNICON will contribute with expertise from the concrete industry on handling of dry powders in the design phase of the outlets. The operation of the outlets will be integrated in the SCADA systems at the WWTPs in order to obtain a user-friendly operation and on-line documentation. The method, which will be based on screw conveyors, is a well-known transport system for dry powders and a relatively simple open transfer system with dust control into a closed container.

Progress indicators – 1) outlet design approved, 2) outlets constructed and tested for functionality.

Expected results – The expected results will be two demonstration facilities for collection of dry bio ash at WWTPs with incinerator the two types: multiple hearth furnace and fluidized bed oven, respectively. These are the two predominant bio solids incinerator types in Europe. The targets are to obtain facilities, which are acceptable to the operator in terms of being user-friendly and are safe for occupational health and safety and environmental quality by preventing dust pollution.

Constraints - As there is already much expertise in the concrete industry on the handling of dry powders it assumed that a proper design is relatively straight forward in this new application. In case that the anticipated solutions will not be adequate for a dust free transfer, this will not be a constraint for the entire project. As a contingency plan transport by vacuum trucks is a possibility, however, being a more expensive solution.

Task 02_Design and construction of facilities for handling of ashes at the concrete production plant

Several different fine powder raw materials are potential for use in concrete. At least two different cement types and two other powders, fly ash and silica fume, are used on a daily basis at the average Danish ready mixed concrete plant.

In order to be able to produce concrete with an extra powder material it is necessary to establish silo facilities at the concrete production plant. To be able to handle bio ash it is essential that facilities such as storing capacity, batching equipment and conveyors are available.

As part of the present project UNICON will extend the production facilities (silo, conveyor and batching equipment) to accommodate bio ash at their large ready mixed concrete plant in Avedøre. The Avedøre plant is serving parts of the greater Copenhagen area.

Once the design planning is finished the necessary approvals will be obtained by the authorities, and a contractor will be selected to construct the ash handling facilities. When in place and tested in terms of mechanics and electrics, the ash handling facilities will be subject to trial mixing of concrete. Final approval to implement the new facilities in the daily production will be given if all tests are successful.

Progress Indicators – 1) Authority approval of construction plans, 2) Trial concrete batching using new ash handling facilities.

Expected results – Demonstration facility for production of ready mixed concrete with bio ash. The target is to obtain a facility in daily operation, which is acceptable to the operator in terms of economic feasibility, being user-friendly and are safe for occupational health and safety and environmental quality.

Constraints - As there is already much expertise in the concrete industry on the handling of dry powders it assumed that a proper design is relatively straight forward in this new application.

Task 03_White bio ash – ash production and concrete trial casting

The reddish colour of the bio ash concrete manufactured using ashes from AWS WWTP has been identified as a significant barrier, when the concrete is to be used for visible materials or constructions. The reddish colour is most probably due to the use of iron salts for the precipitation of phosphorus, and one possible solution to the problem is to substitute the iron salts by aluminium salts at the WWTP. However, these aluminium salts are more expensive than iron salts.

The task includes the following activities:

a) Collection of chemical analytical data for bio ashes from different WWTP’s in Europe with particular focus on iron content.

b) A test production of concrete using a bio ash incinerated at AWS WWTP. The bio ash is the result of incineration of dewatered digested sludge from a WWTP where aluminium salts have been used for the precipitation of phosphorus. If the colour of the cast concrete is not acceptable, there is no incentive to continue with further studies on the substitution idea.

AWS will act as task coordinator and conduct activity a).

In activity b) the production of Al-rich dewatered sludge will be conducted by LYNIS at the Damhusaaen WWTP by replacement of the phosphorous precipitant over a period of about three months. On this basis, AWS will incinerate a separate batch of sludge during about 2 days period, thus producing white bio ash. A concrete specimen cast will be produced by UNICON and DTI will on the white bio ash perform test according to EN 450-1 5.2 (chemical properties) and 5.3 (physical properties) and evaluate the results.

Progress indicators – 1) Aluminium salt precipitation of phosphorus initiated, 2) Incineration of Al-rich sludge completed, 3) Concrete specimens cast using the Al-rich bio ash.

Expected results
1) An overview of the iron and aluminium content in various European bio ashes
2) Verification of whether or not the substitution of iron with aluminium for the phosphorus removal results in bio ashes that are colour neutral when used in bio ash concrete
3) Indications about the correlation between iron content of bio ash and the colour of the bio ash concrete.

Constraints –
a) The data collection will depend on the data availability from the literature and / from direct contacts to other European WWTPs with sludge incineration. Contacts will be taken through existing networks.

b) The use of Al-based precipitant has earlier been conducted at the Damhusaaen WWTP so new difficulties are not to be expected. The incineration of a separate batch of dewatered Al-rich sludge is new and could possibly require special attention for tuning the incinerator plant operation.

Task 04_Documentation of the quality of the ashes

DTI is responsible for this task, which includes carrying out analyses, statistical treatment of results, evaluation and reporting. Finally, a “Product Standard” for bio ash will be drafted. The chemical and physical properties of the bio ash from each of the two WWTP will be assessed six times at regular intervals during one full year.

In order to manufacture concrete of consistent quality with bio ash, it is essential to know that the properties of the ash vary only within certain limits. It is known from past years analyses of the bio ashes that the elemental composition (including heavy metals) is rather consistent. Data from AWS show coefficients of variance (c.v.) in the range of 5-15%. However, only very few data on bio ash tested according to EN 450-1 “coal combustion fly ash” exist. The EN 450-1 tests performed on bio ash, although designed to evaluate coal combustion fly ash, are considered to provide the information needed to evaluate how well bio ash will perform in concrete. Therefore, EN 450-1 will serve a reference document for this task.

Full testing confirming to EN 450-1 5.2 (chemical properties) and 5.3 (physical properties) will be performed on six bio ash samples from each WWTP. The samples will be taken every two months over a full year at each of the two WWTPs.

In addition to the EN 450-1 analyses, the particle size distribution of the ashes will be analysed by Sedigraph for particle smaller than 100 microns, the mineralogy of the bio ashes will documented using optical microscopy, scanning electron microscopy, and X-ray diffraction, and the heavy metal content will be estimated by WDXRF-analyses. The particle size distribution of the ash will influence the workability of the concrete, and any substantial variation in particle size distribution may influence the concrete manufacturer’s ability to manufacture consistent quality concrete. Information about the mineralogy of the bio ash is essential to understanding and evaluating the bio ash in terms of strength development and reactivity in general (desirable and un-desirable).

The analysis results will be statically treated and evaluated with respect to production of consistent quality concrete. Statistical treatment of analysis results will be carried out on a semi-annual basis and a short progress reports issued. At the conclusion of the project a final report also including evaluation of the data in terms of concrete production will be issued. The report will have strong ties to Tasks 5, 6, and 8.

Progress Indicators – 1) All ash samples collected from incineration plants, 2) All chemical and physical testing initiated.

Expected results - The task is expected to provide a good overview of the variations in bio ash properties over the full production year.

Constraints - If the variations in the bio ash properties are found to be substantial it may limit the potential applications of bio ash concrete. However, the larger the plants are the less variation is to be expected, and the two plants included in this project are relatively large.

Task 05_Environmental impact of bio ash concrete

Leaching test can be conducted as tank test where a monolithic concrete block is tested for the leachabillity through the surfaces of the concrete. Leaching of heavy metals can also be measured in a column test where a column is filled with crushed concrete and then percolated with water or it can be measured in a batch test PrEn 14429 where crushed concrete is extracted with water at different pH-values. All leaching tests are designed as accelerated tests, i.e. from experiments lasting a few weeks or months, the long-term leaching is predicted.

Focus will be on the leaching of heavy metals but also the leaching of phosphor will be investigated.

In this task focus is put on the batch test where crushed concrete is extracted with water, and to a lesser extent on the tank test. Before leaching tests samples of concrete are exposed to carbon dioxide in order to accelerate the natural uptake of carbon dioxide.

The focus on the potential leaching from the concrete at the end of the lifecycle reflects the fact that concrete after demolition is going to be utilised as crushed materials for road construction or similar purposes. Currently, in Denmark 95% of all demolished concrete is used for road construction purposes. Even though the concrete recycling percentage may be lower in other parts of Europe, it is very likely that the rest Europe will obtain higher reuse rates of demolished concrete in the future.

A range of bio ash concrete mixtures will be mixed (the same mixtures will be used here as in Task 6). On these samples of concrete and on samples from the highway bridge already constructed with bio ash concrete, leaching tests will be carried out.

It is expected that even if the batch leaching tests are designed for the "end of life cycle" situation (demolished concrete) it will be possible on the basis of the test to recommend if there should be any restrictions to use of the bio ash concrete. This could be the case for e.g. concrete in contact with drinking water.

The batch leaching tests including the chemical analysis are carried out at the laboratories at the DTI. The tank leaching test and the evaluation of results are carried out by the Energy Research Centre of the Netherlands ECN, who has substantial experience with concrete leaching obtained from e.g. other EU-projects.

Progress Indicators – 1) Concrete specimens casts, 2) Leaching studies initiated, 3) Leaching studies completed.

Expected results – Documentation of the amount of leaching of heavy metals from various concrete types containing bio ash. The leaching expected to similar to leaching from traditional concrete, i.e. without any significant environmental implications. There is not a tremendous amount of experience with the leaching tests on concrete, as there has only been focus on this issue for a decade or so. Nevertheless, comparing leaching form bio ash concrete with that of traditional concrete will provide a good basis for evaluating the environmental impact from heavy metals’ leaching out of bio ash concrete.

Constraints – It will constrain the use of bio ash concrete if the leaching of heavy metals is higher than from traditional concrete. However, this information is valuable as it allow for the selection of bio ash concrete products that can be manufactured without being a liability to the environment.

Task 06_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.

Task 07_Collecting data from existing bio ash concrete constructions

DTI will be responsible for this task.

Due to the approval of a Danish National Application Documents to EN206-1, bio ash concrete has been in provisional use in Denmark for concrete for passive environments since 2002. Moreover, bio ash was investigated in the Danish “Green Concrete” project, where part of a highway bridge owned by the Danish Road Directorate was cast with bio ash concrete for aggressive environment.

In co-operation with UNICON who has delivered bio ash concrete over the past few years a list of bio ash concrete structure will be compiled. The list is evaluated based on availability and diversity in concrete type and construction type, and two structures are selected for inspection – one in passive and one in aggressive environment. Already now, two candidate structures are known: i) a highway road cover exposed to ambient conditions since 2002, and ii) an underground sewage construction in connection with waste water detention tanks situated within the AWS catchment area. The inspection of the structures will include visual documentation (photos/videos), macro- and microstructure description (petrographic examination according to TI-B5), as well as documentation of concrete strength from drilled cores.

Progress indicators – 1) Structure for field inspection identified, 2) Field inspections performed.

Expected results - A report with the findings of the field inspections will be issued. In the report, possible correlation between inspection results and concrete composition, casting method, etc., are sought. The report will tentatively compare the field performance of bio ash concrete with that of traditional concrete – the comparison can only be tentative as all existing bio ash concrete structures are still very young. Nevertheless, the analyses performed will provide some indication as the expected long-term performance of bio ash concrete through traditional indicators such as strength and microstructure (e.g. carbonation depth).

Constraints - Even though bio ash concrete has been delivered almost exclusively for use in passive environment it may be difficult to locate a construction in passive environment suitable for inspection. The reason being that concrete for passive environment is often delivered in small quantities, and used in structures that are not readily accessible to inspection, i.e. there is a risk that is will not be possible to locate a structure in passive environment that can be inspected. However, access to the two structures (aggressive environment) already mentioned will be possible for completion of this task.

Task 08_Production of bio ash concrete

UNICON will be responsible for this task.

The existing information at UNICON in terms of batch information and associated concrete test results from the past years delivery of bio ash concrete will be compiled. The data will be analysed and reported.

UNICON will carry out pre-testing of concrete mixtures for environmental classes P, M, A, and E according to EN 206 and DS 2426.

Following the successful pre-testing the respective bio ash concrete mixtures will be produced and documented per 25 m³ of concrete produced. The test program will comprise the following tests:

- Slump – after mixing and at delivery (EN 12350-2)
- Density (EN 12350-6)
- Air content (EN 12350-7)
- Water separation (DS 423.18)
- Compressive strength (EN 12390-1,2,3,4 – the strength will be measured after 2, 7, 28, 56 days)

The data compiled during pre-testing and every day production will be analysed and reported in cooperation between UNICON and DTI.

Progress indicators – 1) Pre-testing of class P and M bio ash concrete performed, 2) pre-testing of class A and E bio ash concrete performed, 3) 5000 m3 of bio ash concrete produced in class P.

Expected Results – The possibility of full-scale production of bio ah concrete in all environmental classes is established through successful pre-testing. In the daily production of ready mixed concrete the variations in the properties of the fresh and hardened bio ash concrete is documented. It is expected that the variations are statistically identical to the variations of traditional concrete.

Constraints – If successful pre-testing according to EN and DS standards is not obtained every day production of bio ash concrete cannot obviously not commence. The existing research does not indicate that insurmountable problems should be encountered with respect to obtaining pre-test results conforming to standards.

Task 09_Dissemination programme of results

DTI will be task coordinator and responsible for the dissemination of the project results in close co-operations with the project partners (AWS, LYNIS, UNICON).

The main target of the dissemination programme is to spread the knowledge obtained within the project to increase awareness of the use of bio ash in concrete in order to reduce the environmental impacts from bio ash disposal.

Based on results from the technical tasks a guideline on implementation and use of bio ash concrete will be prepared. The target group includes the entire building and construction sector from the manufacturers of bio ash concrete to the owners who have to specify the requirements to bio ash concrete, i.e. implement the environmentally improved technology. The guideline will be published in English and in Danish at a project website, and hard copies will be distributed to all Danish municipals and to other relevant parties of the Danish building and construction sector.

Based on results from the technical tasks normalizing documents will be prepared and then presented to CEN/TC 104 “Concrete and Related Products” for further actions. This contribute to the after end of project dissemination on a wider European basis.

For each task a report shall be published in English. Reports will be published on the project website.

The municipals affiliated to both LYNIS and AWS will be offered advice on how to update their instruction on tenders for construction of new building in order to accommodate the use of bio ash concrete. Such action will support the green purchase policy of the municipals. In connection with the distribution of the guideline to the municipals, the municipals will be invited to a discussion for further actions.

AWS has exhibition facilities and here samples on bio ash concrete and information on the LIFE project will be put on display. The dry ash outlets at the WWTPs and silo facilities at the concrete plant will in themselves act as interesting demonstration sites. These equipments will be on permanent display for interested people in the industry etc., and serve as up-front evidence that bio ash concrete is indeed a reality.

Owners will be encouraged to make suitable construction projects – DEMO projects – available for the present project, so that experience in use of bio ash concrete in practice can be gathered and registered. The DEMO projects will be used as future references to support the dissemination of the use of bio ash concrete in Europe.

Based on results from the technical tasks articles will be published in Danish as well as in English international journals and trade journals. A kick-off seminar will be arranged in the Copenhagen area with invitation of several stakeholders and potential end-users bio ash and bio ash concrete. The aim is to generate attention to the LIFE Project initiative and thereby facilitate the generation of useful contacts for the project period. At the end of the project international seminars for the public will be arranged inviting all European interested parties. The seminars will present the main results of the project with special focus on the guideline on use of bio ash concrete. Furthermore, AWS, LYNIS and UNICON will present the project results to their customers at “after-work meetings”. UNICON will present the project at the next meeting in the European Ready Mixed Concrete Organisation (ERMCO).

The LIFE-logo will be used at reports and at materials for presentations.

Progress indicators – 1) Kick off seminar for stakeholder held in Copenhagen, 2) Normalising documents sent to CEN-committees, 3) Agreement on first demo-project, 4) Launch of the project website.

Expected results – 1) Normalising documents concerning bio ash concrete, 2) Handbook with guidelines for use of bio ash concrete, 3) Starts-up of bio ash concrete demo-projects, 4) Articles in technical and popular journals, 5) Presentation of the project at conferences, seminars, and technical meetings in Denmark and the EU, 6) Establishing a project website.

Constraints - The success of the dissemination programme will of course depend on the results the other individual tasks. The DEMO projects depend on interested building owners who are willing to make suitable construction project available for the project and the public.

Task 10_Project management

Project coordination is the responsibility of AWS, but an Assistant Project coordinator from DTI shall be assigned to the project in order to undertake the day-to-day coordination. Task coordinators shall be assigned to all the technical tasks. Task coordinators shall report progress of the technical tasks every three month to the Assistant Project coordinator.

The Assistant Project Coordinator shall on a day to day basis evaluate the progress and results of the project. Based on quarterly progress reports from the task coordinators, the Project Coordinator and the Assistant Project Coordinator shall revise the plans if needed in order to reach the overall objectives. Every six months, the Project Coordinator produces an overall progress report, which will be discussed on a meeting for all task coordinators. The project co-ordinator is responsible for all reports except when otherwise specifically stated in the individual task descriptions.

The steering committee representing the partners at the executive level, will approve the progress reports before submission to the EU-LIFE programme officer, and will be involved for any changing in the project, requiring a commitment from the partners.

The project co-ordinator will secure that communication ways are established to the EU-LIFE programme. The project coordinator will ensure punctual delivery of reports to the EU-Commission.

During the implementation of the project continuous considerations on whether the project complies with present and coming EU legislation are made.