Periodic Reporting for period 1 - W2W (Waste to Wealth (W2W): A total solution for municipal solid waste incinerated ash in geopolymer concrete)
Reporting period: 2020-09-01 to 2022-08-31
Human activities and urban lifestyle create municipal solid waste (MSW) all over the world in huge volume. Proper management of MSW is one of the important requirements/ responsibilities for a healthy environment of future generation. The proposed project aims at utilizing the MSW Incinerated (MSWI) products as secondary raw materials in geopolymer concrete, thereby converting these wastes into wealth (W2W). This also helps in satisfying the demand for raw materials in infrastructure industries.
MSW generation was estimated as 1.3 billion tonnes/year in 2012. With the growing population and increasing solid waste generated, this could reach a value as high as 2.2 billion tonnes in 2025. Currently, landfilling, incineration, recycling and composting are adopted as treatment categories for MSW. Of which, incineration is adopted for 150 kg out of 480 kg per capita generated in EU-28 countries. Incineration process reduces the mass and volume of the MSW and results in two main side streams besides electricity, viz., 20% of fly ash with hazardous heavy metals and organics, and 80% of bottom ash which is normally non-hazardous. Landfilling is the easiest solution to any non-hazardous waste. However, it has its own disadvantages such as, land requirement, sanitary maintenance, and ground water pollution. On the other side, with the growing need for infrastructure development, depletion of natural raw materials and demand for alternative materials is a well-known issue in construction industries. In specific, concrete is the second largest consumed material by mankind, just next to water. 70% of concrete is made of aggregates that are normally river sand, rock and gravel. Being the largest volume of solid material extracted aggregates are depleted in a threatening rate. Aggregate consumption on concrete production alone was estimated as 25.2 to 29.4 billion tonnes in the year 2016 and increasing with the demand, every year. This causes a demand in supply of raw materials, increasing the cost of the material. Further, transporation of the aggregate from the source to the site increases the overall project cost. The mentioned issues clearly highlight the need to identify alternatives for aggregate in concrete production. In this context, MSWI waste is also getting into limelight as an alternative material in construction industries. MSWI ash are reactive in nature due to the presence of silica and alumina which are activated by the high temperature involved in the incineration process. Hence, mainly studied as a cement replacement material. However, there is also possibility to pelletize the MSWI ash to be used as a replacement for aggregate that occupies larger volume (70%) of concrete.
The main aim of the research program is to develop treatment methods for MSWI bottom ash with minimum energy usage and to utilize 100% of the MSWI ash as a secondary raw material in concrete production. This was achieved by formulating three scientific objectives carried out as three work packages as below:
1. To optimize the treatment method for MSWI bottom ash and to understand the enhancement in the properties of treated MSWI bottom ash with advanced treatment technology (WP1)
2. To manufacture the artificial aggregate from the treated MSWI bottom ash (WP2)
3. To study the performance of the MSWI bottom ash aggregate as a secondary raw material in the geopolymer concrete application (WP3)
MSW generation was estimated as 1.3 billion tonnes/year in 2012. With the growing population and increasing solid waste generated, this could reach a value as high as 2.2 billion tonnes in 2025. Currently, landfilling, incineration, recycling and composting are adopted as treatment categories for MSW. Of which, incineration is adopted for 150 kg out of 480 kg per capita generated in EU-28 countries. Incineration process reduces the mass and volume of the MSW and results in two main side streams besides electricity, viz., 20% of fly ash with hazardous heavy metals and organics, and 80% of bottom ash which is normally non-hazardous. Landfilling is the easiest solution to any non-hazardous waste. However, it has its own disadvantages such as, land requirement, sanitary maintenance, and ground water pollution. On the other side, with the growing need for infrastructure development, depletion of natural raw materials and demand for alternative materials is a well-known issue in construction industries. In specific, concrete is the second largest consumed material by mankind, just next to water. 70% of concrete is made of aggregates that are normally river sand, rock and gravel. Being the largest volume of solid material extracted aggregates are depleted in a threatening rate. Aggregate consumption on concrete production alone was estimated as 25.2 to 29.4 billion tonnes in the year 2016 and increasing with the demand, every year. This causes a demand in supply of raw materials, increasing the cost of the material. Further, transporation of the aggregate from the source to the site increases the overall project cost. The mentioned issues clearly highlight the need to identify alternatives for aggregate in concrete production. In this context, MSWI waste is also getting into limelight as an alternative material in construction industries. MSWI ash are reactive in nature due to the presence of silica and alumina which are activated by the high temperature involved in the incineration process. Hence, mainly studied as a cement replacement material. However, there is also possibility to pelletize the MSWI ash to be used as a replacement for aggregate that occupies larger volume (70%) of concrete.
The main aim of the research program is to develop treatment methods for MSWI bottom ash with minimum energy usage and to utilize 100% of the MSWI ash as a secondary raw material in concrete production. This was achieved by formulating three scientific objectives carried out as three work packages as below:
1. To optimize the treatment method for MSWI bottom ash and to understand the enhancement in the properties of treated MSWI bottom ash with advanced treatment technology (WP1)
2. To manufacture the artificial aggregate from the treated MSWI bottom ash (WP2)
3. To study the performance of the MSWI bottom ash aggregate as a secondary raw material in the geopolymer concrete application (WP3)
The project starts with the WP1 which was to characterize the incinerated residues. Fly ash was treated at University of Oulu by two step process, 1) Sieving the material to remove the finer particles (< 0.5 mm) to remove the hazardous elements and unburnt carbon particles 2) Milling them to a D50 value <10 µm to be utilized as a binder material. This treated fly ash as a precursor for alkali activation was studied for the suitability as a binder material. Bottom ash was used as received from the industrial facility as the ash was pre-treated using a dry separation technology. Bottom ash was used as received to make granules with alkali solution as binding liquid. NaOH does not work, so sodium silicate was used as the activator liquid in this study. Granulation process was fixed based on the final granule’s particle size distribution, crushing strength and leaching values. Further, bottom ash was milled and tried to be granulated for better properties. This helped in increasing the crushing strength. Use of alternatives for sodium silicate (chemical) to improve the sustainability was tried. Here, other industrial side streams like slags were added to avoid using chemical activators
Concrete mixes were designed to utilize the incinerated fly ash and bottom ash as binder and aggregate, respectively. Importance was given to make the material sustainable and low in carbon footprint. Reference was made with all commercial material with Portland cement (OPC) and commercial lightweight aggregate. Other mixes were made with 100% bottom ash as fine aggregate instead of standard sand as in the case of reference. SCM mix was developed with partial replacement of milled bottom ash with OPC. Third mix, AABFS was made with alkali activated slag as the binder. Fourth mix, AABFS/AA was developed with equal proportion of slag and milled incinerated fly ash. All the mixes other than reference had granulated bottom ash as lightweight aggregate instead of commercial lightweight coarse aggregate.
Based on the results obtained from the concrete properties, it can be concluded that it is possible to use incinerated residues in lightweight concrete production. When slag is used as binder, the strength satisfies the criteria for these materials to be used as a structural light weight concrete (EN standards). Thermal conductivity of the produced concrete was 0.7-0.85 W/mK which would be good enough to be used as insulation materials.
Concrete mixes were designed to utilize the incinerated fly ash and bottom ash as binder and aggregate, respectively. Importance was given to make the material sustainable and low in carbon footprint. Reference was made with all commercial material with Portland cement (OPC) and commercial lightweight aggregate. Other mixes were made with 100% bottom ash as fine aggregate instead of standard sand as in the case of reference. SCM mix was developed with partial replacement of milled bottom ash with OPC. Third mix, AABFS was made with alkali activated slag as the binder. Fourth mix, AABFS/AA was developed with equal proportion of slag and milled incinerated fly ash. All the mixes other than reference had granulated bottom ash as lightweight aggregate instead of commercial lightweight coarse aggregate.
Based on the results obtained from the concrete properties, it can be concluded that it is possible to use incinerated residues in lightweight concrete production. When slag is used as binder, the strength satisfies the criteria for these materials to be used as a structural light weight concrete (EN standards). Thermal conductivity of the produced concrete was 0.7-0.85 W/mK which would be good enough to be used as insulation materials.
The project helped to understand about the incinerated residues and their present condition/quality in Finland. With minor/ simple treatment methods, it is proven to be used as a secondary source for lightweight concrete production. This also opened new research questions on applications that could benefit from these products. It was also identified, presence of minor rare earth elements/ critical raw materials in these incinerated residues could be a potential resource to be considered for remining. It was also identified to make some piloting based on the project results to convince the industries/ stake holders and policy makers, regarding the use of these materials. These ideas were proposed and funded in two different projects by Academy of Finland (https://www.oulu.fi/en/node/31770) and Horizon Europe (https://cordis.europa.eu/project/id/101058162). This opened new opportunities to continue the topic to the next level of continuous exploitation and also take the results for the economic and environmental benefits of the community/society. Future projects also involve local SMEs who are interested in developing this business, thus creating new jobs!