OSAMAT - Utilisation of oil shale ashes in road construction

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1 OSAMAT - Utilisation of oil shale ashes in road construction Marjo RONKAINEN 1, Arina KOROLJOVA 2, Aleksander POTOTSKI 2, Hendrik PUHKIM 3, Pentti LAHTINEN 1, Olli KIVINIEMI 1 1 Ramboll Finland Oy, Vohlisaarentie 2 B, Luopioinen, Finland, marjo.ronkainen@ramboll.fi, pentti.lahtinen@ramboll.fi, olli.kiviniemi@ramboll.fi 2 Eesti Energia AS, Laki tn. 24, Tallinn, Estonia, arina.koroljova@energia.ee, aleksander.pototski@energia.ee 3 Ramboll Eesti AS, Laki tn. 34, Tallinn, Estonia, hendrik.puhkim@ramboll.ee Abstract OSAMAT is an EU-Life founded project which aims in the utilisation of oil shale ashes and mining by-product in road construction. Over 90 % of the Estonian basic power supply is covered by oil shale fired thermal power plants. Every year about eleven million tonnes of oil shale is fired and about 5-7 million tonnes of oil shale ash are generated. The most serious problem today is the handling of oil shale ashes. Also oil shale mining and processing generate vast amounts of by-products. The oil shale ash contains a lot of lime, which gives the material good strength development properties. Thus the oil shale ash has potential to be used in stabilisation of soft soils as well as in layer stabilisation and other road applications. When oil shale mining by-product and oil shale ash is mixed together a potential good structure material is developed. Oil-shale ash material is registered under REACH, which is European Community Regulation on chemicals and their safe use (EC 1907/2006). The project aims in finding the ways for oil shale by-products utilisation. During the project two pilot roads will be made using oil shale ashes and mining waste. Conversion of these industrial by-products into valuable and environmentally friendly materials is important for EU as it will help to decrease the need for virgin material such as rock aggregate as well as the need for a landfill space. The success of the piloting is evaluated by follow-up studies which estimate the condition of the road after construction. During the project also LCA and LCC estimation will be done. Keywords: Industrial waste; Materials technology; Soil stabilisation; Ash Utilisation; Mining waste 1. Introduction Over 90% (as Velts O. et al.) of the basic power supply in Estonia is provided by oil-shale firing thermal power plants. Oil shale mining and processing generate vast amounts of by-products that are mostly deposited coursing environmental impacts. The most problematic industrial by-products in terms of handling are mining waste (spoil) and oil shale ash (OSA). About 40% of the industrial oil shale bed is formed of limestone beds. Rock material forming in the enrichment process of broken oil shale is deposited in open spoil dumps near the opencasts in the amount of 4.5mn tons of spoil annually. Crushed spoil could be used as a filling material on construction sites, and crushed stone made from spoil as a construction material and in concrete mixes. Despite these recycling opportunities the spoil is not so widely used because of the low quality (contain 3-20% of oil shale) (as National development plan for oil shale utilisation says). 1

2 Estonian oil shale is characterized by a high mineral matter (analysed by previous research O. Velts et al.). After combustion 45 48% of the oil shale is left over as ash, producing about 5 7 Mt of ash annually. OSA removed from the boilers is transported to the plateaus through a pipe system as water slurry (analysed by previous research R. Motlep et. al.). OSA is rich in free lime. Contacting free lime with water leads to ph values above 13 (analysed by previous research Andres Trikkela et al.). The highly alkaline leachates from the ash deposits pose an environmental risk, and the ash plateaus are considered as major pollution sources (as R. Motlep et al. says). In earlier decades, OSA has been extensively studied, that has made OSA available for usage in production of construction materials and cement, in road construction and in liming of acid soils (analysed by L. Bityukova et al.). Despite numerous studies only a small amount of oil shale ash is currently recycled, a little more than 2% of the annual amount produced (as National development plan says). Use of OSA in combination with spoil in road construction is considered as alternative to landfilling that helps to reduce the ash and spoil amounts to be deposited as well as reduce its environmental impact. Due to its chemical content OSA is considered as a valuable binder material, which could be used to improve stabilization and strength of civil-engineering structures. Based on these assumptions the OSAMAT project was initiated. The project aims at introducing, testing and promoting advanced methods of using OSA as valuable material in road construction. The scope of the project include three different applications at the two pilot sites: layer stabilization of existing road base courses with binders based on OSA, mass stabilization of peat with binders based on OSA, structural road base course by mixing different types of fractions of oil shale mining waste with OSA and verification of OSA feasibility as construction material with respect to the environmental, technical and economical criteria. The results of the project will address the challenges to the European policies and local regulation concerning waste recovery and promote sustainable recycling with a focus on life thinking and development of recyclables market. 2. Materials Different combustion technologies are applied at Estonian power plants: pulverized firing (PF) and circulating fluidized-bed combustion (CFB). PF ash from electrostatic precipitator fields (EF BL3 OBT), CFB ash from electrostatic precipitator fields (EF BL8 NBT), PF cyclone ash (CYCL) and CFB bottom ash (BOTT BL8) were chosen to be investigated in the laboratory as potential binders. The data presented in the Table 1 and Table 2 show the chemical composition and the properties of the ashes from the CFB and PF boilers used in the study. Table 1. Chemical composition of the oil shale ashes, % (A. Ots, Oil Shale Fuel Combustion, Tallinn, 2004). Component EF BL3 OBT CYCL EF BL8 NBT BOTT BL8 CaO 28,0-40,0 46,0-58,0 29,5 48,9 SiO2 20,0-35,0 20,0-28,0 38,6 11,3 Al2O3 5,0-10,0 4,0-8,0 11,9 4,4 Fe2O3 3,0-5,0 4,0-6,0 4,9 3,1 MgO 3,5-5,0 3,0-4,0 8,3 6,4 K2O 1,5-5,5 1,5-2,5 4,5 1,2 Na2O 0,1-1,0 0,1-0,2 0,2 0,1 Cl 0,40-0,42 0,1 0,18 no data CaOfree 6-12, ,4 13,9 CaSO4 8-17,0 4-7,0 4,1 16,2 2

3 Table 2. Properties of the oil shale ashes. Water Loss of Grain size ph d mean, Specific surface content [%] ignition [%] (soil type) μm area, m2/g EF BL3 OBT 0,4 3,4 Si 13,0 48 0,61 EF BL8 NBT 0,3 3,4 Si 13, CYCL 0,0 1,0 sasi 13,0 53 0,36 BOTT BL8 0,0 11,8 grsa 12, ,1 The laboratory tests showed that the better compressive strength and freeze-thaw durability could be achieved by using the mixture of ash and cement. The cement used in the study was composite cement CEM II /B-M(T-L) 42,5 R (Komp.CEM) and sulphate resistant cement CEM I 42,5 N (SR(Finnsementti)). The binder optimizing tests were done with two base materials. One was layer structure material from the pilot site road (Narva Mustajõe) and the other one was mining waste from three oil shale mines in Estonia (Tondi-Väo, Koigi and Aidu). The mining waste samples were mostly sand and gravel. The water contents of all the samples were not measured but the measures water contents were below 10 %. The stabilisation tests were done so that the some samples were mixed together in proportion of 1:1 (by volume). The properties of the tested materials are presented in table 3. Table 3. Properties of the mining waste. Sample Water content, w% Grain size distribution Notification Narva-Mustajõe 0-20 mm grsisa Tondi-Väo 0-4 mm 7 grsa Mixture of 1:1 for stabilisation Tondi-Väo 4-16 mm 2,3 sagr test (by volume) Koigi 0-8 mm 7,5 grsisa Mixture of 1:1 for stabilisation Koigi 8-16 mm 5,1 Gr test (by volume) Aidu 0-20 mm sagr 3. Methods 3.1 Environmental tests The leaching test were done to the ratio of liquid/solid (L/S) 10 using two step batch test and to the ratio L/S=2,9 using percolation test. During the percolation test ash clogged in column and the test was aborted. 3.2 Technical tests of oil shale ash as a binder The laboratory technical tests for materials were carried out for three types of stabilisation structures i.e., mining waste stabilisation, old structure (road base stabilisation) and peat stabilisation. The material tests investigated the properties of the materials and tested the stabilisation properties of the base material. The material tests were performed during the OSAMAT project in order to determine the best materials and binders and their optimal amounts for the pilot applications. Specimen making: After mixing the materials is compacted in to a cylinders having uniform diameter (~100 mm) and storing in a palace to prevent the drying of the specimens. The preparation of the peat specimens: The peat and the binders are mixed together. After mixing the mixture is compacted in to a cylinders having uniform diameter. The specimens are put in to a load 3

4 bench where the cylinders are put under a weight (18 kpa). The constant moisture content of the specimens is insured by having the bottom of the specimen cylinder under water. Unconfined Compressive Strength, UCS, is a test where a cylindrical test piece is subjected to a steadily increasing axial load until failure occurs. The axial load is the only force or stress applied. The rate of the load is 1-2 mm/min. If any noticeable failure does not occur, the maximum value of the compression strength is taken when the deformation (change of height) is 15 %. Usually, the test will be made on test pieces after at least 28 or 90 days stabilisation. Freeze-thaw durability test will determine the material s resistance to freezing and thawing cycles 12 times. After the test is completed, the strength (UCS) of the test piece will be determined. 4. Results of laboratory tests 4.1 Environmental tests The total content of the oil shale samples was determined and the leaching tests were carried out. Leaching was determined with the two step batch test and the percolation test. The results of the tests have been compared to the limit values set by the Finnish legislation: Ash utilisation of certain waste at earth construction works, using registration method. There are also limit values in the Finnish Government Regulation 403/2009 and 591/2006. Because Estonia lacks this kind of legislation, the values set by the Finnish law have been used as an informative baseline. The total content of ash is presented in Table 4. All contents are below the limit values. Table 4. Total contents of ash [mg/kg] and limit values in Finnish Government Regulation 403/2009 and 591/2006). Element/compound Ash Limit values [mg/kg] [mg/kg] As Ba Cd 0,48 15 Cr Cu < Pb Mo 9,4 50 Zn V PAH <1 20/40 covered/coated PCB <0,01 1,0 The results of the leaching tests and the limit values for leaching set by the Finnish Government Regulation 403/2009 and 591/2006 are shown in Table 5. In both test the leaching of sulphate was above the limit for both covered and coated structures. The leaching results of chloride, fluoride, chromium and molybdenum were above the limits for covered structure. Only sulphate was above the limit value in coated structure. This gives a good base for utilisation of oil shale ash because commonly both new and renovated roads are coated (asphalt). 4.2 Technical tests of oil shale ash as a binder in road base stabilisation The results for the road material (Narva-Mustajoe) are shown in Figure 1. It seems that the best results were achieved with the EF and Komposiit CEM binder mixtures. Also EF BL 8 NBT alone (without cement) worked well to some extent. EF BL3 OBT did not give good results as the freeze-thaw durability was poor. Also the bottom-cyclone ash mixture and cyclone ash alone did not work well. Although the cyclone ash gave relatively positive results together with Komp. CEM, the binder amount should be much higher to give truly satisfactory results. The frost susceptibility tests showed 4

5 that Narva-Mustajoe, base course and 6% EF BL3 OBT were slightly susceptible to frost heave, the segregation potential being 0,19 mm2/kh. Table 5. Leaching tests of ash [mg/kg]and limit values in the Finnish Government Regulation 403/2009 and 591/2006). Element/ Two step batch Percolation Limit value, Limit value, compound L/S=10 L/S=2,9 (covered) (coated) DOC 12, Chloride Fluoride 18 3, Sulfate Sb <0,020 <0,020 0,06 0,18 As <0,020 <0,020 0,5 1,5 Ba 3,7 1, Hg <0,003 <0,003 0,01 0,01 Cd <0,020 <0,020 0,04 0,04 Cr 1,7 0,53 0,5 3,0 Cu <0,020 <0,020 2,0 6,0 Pb 0,58 0,16 0,5 1,5 Mo 1,9 1,4 0,5 6,0 Ni <0,020 <0,020 0,4 1,2 Se <0,020 <0,020 0,1 0,5 Zn 0,027 <0,020 4,0 12 V <0,020 <0,020 2,0 3,0 Figure 1. Stabilisation test results of Narva-Mustajoe road material using four different oil shale ashes. "Broken" means that a test specimen has broken during freeze-thaw test. 5

6 4.3 Tests of oil shale ash as a binder in peat stabilisation The stabilisation tests were carried out for three samples from there points at the Simuna-Vaiatu road. The samples were collected from the depth of 0,5-4,0 metres. The compressive strengths were measured after 28 days for all the samples and after 90 days for only some of the samples. The index properties of peat samples are shown in Table 6. The stabilisation tests were done for the three peat samples presented in Figure 2. The compressive strengths were measured at an age of in 28 days. The targeted strength for the stabilised peat was above 100 kpa. It seems that the peat samples need cement and oil shale ash binder mixture for reaching the target strength. Oil shale ash binder alone is not enough. After the above mentioned tests the optimal amount of binder has not yet been established, therefore tests will be continued before piloting stabilisation. There were also very different results in points S-7, S-9 and S-10). Table 6. Index properties (water content, LOI, density and ph) of peat samples. Sample Water Loss of Density ph content [%] ignition [%] [kg/m3] S , ,2 S , ,1 S , , Simuna Vaiatu S 7 0,5 4,0 m Simuna Vaiatu S 9 0,5 4,0 m Simuna Vaiatu S 10 0,5 4,0 m EF BL3 OBT 250 kg/m3 EF BL3 OBT 200 kg/m3 + Komp. CEM 100 kg/m3 EF BL8 NBT 250 kg/m3 EF BL8 NBT 200 kg/m3 + Komp. CEM 100 kg/m3 BOTT BL8 100 kg/m3 + CYCL 100kg/m3 + Komp. CEM 100 kg/m3 CYCL. 250 kg/m3 CYCL. 200 kg/m3 + Komp. CEM 100 kg/m3 CYCL. 200 kg/m3 + Komp. CEM 200 kg/m3 EF BL3 OBT 350 kg/m3 EF BL3 OBT 200 kg/m3 + Komp. CEM 150 kg/m3 EF BL8 NBT 350 kg/m3 EF BL8 NBT 200 kg/m3 + Komp. CEM 150 kg/m3 BOTT BL8 100 kg/m3 + CYCL 100kg/m3 + Komp. CEM 150 kg/m3 CYCL. 350 kg/m3 CYCL. 200 kg/m3 + Komp. CEM 150 kg/m3 CYCL. 200 kg/m3 + SR (Finnsementti) 150 kg/m3 Figure 2. Peat stabilisation test results (Unconfined compression strength in kpa) using OSA or mixture of OSA and cement binders (age 28 days). 4.4 Technical tests of mining wastes Stabilisation of mining waste was tested with four samples from three different deposits (Tondi-Väo, Koigi and Aidu). The results of the Tondi-Väo mining waste stabilisation test are presented in Figure 3. The best compressive strengths were achieved with the EF+Komp. CEM binder mixtures. These samples gave good results of the freeze-thaw durability studies. Electric filter ash block 8 (new burning technology) gave also alone good results. However, the electric filter ash block 3 (old burning 6

7 technology) did not work well alone as the Freeze-thaw durability was poor. The test results exhibited that the bottom ash and cyclone ash binder mixture as well as cyclone ash alone did not give good results and did not have any freeze-thaw durability. However, the cyclone ash and Komp. CEM binder mixture gave quite good results with good compressive strengths and freeze-thaw durability. The frost susceptibility tests showed that Tondi-Väo (0-4mm+4-16mm) + 6% OSA EF BL3 OBT was not susceptible to frost heave, the segregation potential being 0,01 mm2/kh. The results of the Koigi mining waste stabilisation tests are presented in Figure 3. The 28 days compressive strength results of the Koigi mining waste were similar to the results of the Tondi-Väo mining waste, although not equally high values were achieved. The best binder mixtures were the EF and Komp. CEM binder mixtures and EF BL8 NBT. However, the rest of the specimens did not have any freeze-thaw durability but were broken during the test procedure. The results of the last binder mixture (Cyclone ash and Komp. CEM 3%+3%) showed that the Koigi 0-32mm gave better results than the Koigi 0-8mm which was more tested. The frost susceptibility tests showed that Koigi (0-8 mm+8-16 mm) + 3% bottom ash BL8 + 3% cyclone ash was not susceptible to frost heave, the segregation potential being 0,11 mm2/kh. The results of the Aidu mining waste stabilisation tests are presented in Figure 3. The results of the Aidu mining waste were similar to the Koigi mining waste results when only EF was used as a binder. However, the EF and Komp. CEM did not have as high compressive strength as with Koigi mining waste and did not differ much from the binder option where only EF was used. On the basis of the results, it is can be stated that it is possible to stabilise mining waste using only oil shale electric filter ash as a binder. Figure 3. Unconfined compression test results (MPa) using OSA or mixture of OSA and cement binders (age 28 days or Freeze-thawing durability) using mining wastes from Tondi-Väo, Koigi and Aidu. 7

8 5. Results of piloting tests on site During this project, three different methods to utilise oil shale ash and mining waste have been planned. These include: - in-situ road base mixer stabilisation of existing road base with oil shale fly ash based binding agent, - replacement of existing road base with oil shale mining waste based aggregate, and - mass stabilisation of peat under a road structure with oil shale ash based binding agent. Peat stabilisation test construction will be done during summer In Narva-Mustajoe road, in the eastern part of Estonia, mining waste was used for the existing road base stabilisation and construction of other structures. In the future, also peat stabilisation will be done. The Narva-Mustajoe road poses a challenge as it is considerably uneven in terms of longitudinal roughness. When the old paving was milled out, an old cracked concrete layer was found below. The concrete layer had quite constant horizontal cracks and the adjacent blocks seemed to have moved in time so that the surface of the concrete layer was far from even. The estimate of the longitudinal structure based on the samples taken in preliminary investigations from piloting site. The structure below the asphalt concrete and stabilised ash (was actually concrete) layers vary a lot. The sandy gravel layer below them was degraded over time and contained a considerably high portion of fine particles and hence was frost-susceptible. The pilot construction was started by performing in-situ road base stabilisation mixer of existing road base. Part of the existing road structure was replaced with oil shale mining waste aggregate and part of it was left there and covered with the same material. The thickness of road base stabilisation is 0,25 m and the length of section is 900 m. After road base stabilisation, asphalt concrete pavement was done. The thickness of asphalt layer is 40 mm (surface) and 50 mm (base). Type profile of road base stabilisation stabilisation structure is shown in Figure 4. Figure 4. Type profile of road base stabilisation structure in Narva-Mustajoe road. The pilot construction was carried out using Aidu mining waste (16-32 mm) and two binder mixtures: 6 % OSA EF BL3 OBT and 3 % Komposiit cement 5 % OSA Cyclone ash and 5 % Komposiit cement. The structures were finished in September For this reason, the results of the follow-up studies from the road are not yet available. 8

9 The road base stabilisation method consists of the following steps: The old pavement of the road section to be stabilised is milled using a rotary mixer before spreading the mining waste aggregate layer; The mining waste aggregate layer is spread on the top of the milled pavement layer with defined layer thickness and width. Water is also spread onto the base material for optimal moisture; The binder mixture (from mixing plant) used in stabilisation is transported to the stabilisation site in ready-to-use form; The binder mixture is spread onto the surface with an asphalt distributor or similar machine; The binder is mixed into the body material using a rotary mixer within defined depth; The mixed layer is compacted immediately after the mixing using a vibratory roller on the stabilised layer and must be shaped to its form by a grader. During construction work the quality controlling was carried out. The water content and its changes, the optimal content of water and target density were measured. The proctor curve of the material is shows that optimal water content is 8 % and the maximum dry density is 2080 kg/m 3. It presents the results for the material in site and it could be a little different from the laboratory curve. Test specimens were collected at the construction site for the unconfined compression strength test (UCS). There are results of these tests in a Table 7. The comparison to the preliminary laboratory results reveals that the obtained strength results are a little lower in this case. The same effect has also been seen in Vuosaari Harbour base course stabilisation case (Lahtinen P. et al. 2007). Table 7. Results of unconfined compression strength tests (UCS). Sampling place w [%] 7 d UCS [MPa] 28 d UCS [MPa] 28 d FT-UCS* [MPa] ,1 1,4 3, ,0 3,9 3, ,8 1, ,1 0,5 0, ,2 1,3 1,2 *FT-UCS = Freeze-thawing test (UCS) 6. Discussion As a result of laboratory investigation, it is possible to determine suitable binders, mixture recipes and the amounts of ingredients. They give the potential mixtures for the site tests. It is important to find proper parameters for comparing the quality controlling tests and the target values and they are possible to approximate from the test sections. Mining waste and oil shale ash stabilisation constitutes a very promising material for replacing natural rock and sand. In this way, the consumption of the non-renewable resources of Estonia can be diminished. Also the lack of natural sand and rock resources means longer transporting distances from far away locations. Together with its test results and follow-up studies, is expected to raise the knowledge and the awareness of the possibilities of utilising mining waste and oil shale ash. There is also a very good possibility use more oil shale ash instead of cement or any other binders in the soft soil stabilisation. Later than more studies during this project will be carried out it is possible to do life cycle assessment (LCA) and life cycle costs (LCC) studies and scenarios. 7. Conclusions According to the Development Plan of Estonian electricity economy, oil shale will continue to be the primary fuel of energy production in Estonia until This states that oil shale ash and mining waste amounts will remain at least at the same level of generation for several years. OSAMAT-project results will help to promote the recycling of oil shale by-products in effective way, to acquire know- 9

10 how of using OSA in civil-engineering application, to propose efficient and low-cost additive to the society substituting natural aggregates from non-renewable sources and reducing CO2-emissions. Conclusions in EU Life+ OSAMAT project has been so far: It is possible determine optimal binders and mixtures in laboratory before the site test. It is important to find quality control parameters in laboratory before the site test. Mining waste is a potential material for utilisation in road construction, because there is a lack of natural sand and rock resources in Estonia. Oil shale ash is a potential binder in binder mixtures for soft soil stabilisation. It can replace a part of cement. Acknowledgements Many thanks to EU Life+ program for funding the OSAMAT-project (Life+ 09/ENV/227). It gives great possibilities to demonstrate new technology and binder materials of oil shale ash. References Bityukova L., Mõtlep R., Kirsimäe K., The composition of oil shale ashes from pulverized firing (PF) and circulating fluidized-bed boiler combustion (CFB) systems at Narva Thermal Power Plants, Estonia, Oil Shale, 2010, Vol. 27, No. 4, pp Mõtlep R., Sild T., Puura E., Kirsimäe K., Composition, diagenetic transformation and alkalinity potential of oil shale ash sediments, Journal of Hazardous Materials 184 (2010) Finnish Government Regulation 403/2009 and 591/2006. Utilisation of certain waste at earth construction works. Registration method. Lahtinen P., Ronkainen M., Sikiö J., Fly ash and FGD as stabilisation binder components for the base course. Case: Vuosaari Harbour. 6 th International Conference in Sustainable Aggregates, Asphalt Technology and Pavement Engineering, Liverpool, UK, February National development plan of oil shale utilisation Ministry of the Environment. Internet: va_+en.pdf Ots A., Oil Shale Fuel Combustion, Tallinn, 2004 Ramboll Finland Oy. LIFE+ 09/ENV/227 OSAMAT Material Report. Intermediate report. Unpublished Ramboll Finland. LIFE+ 09/ENV/227 OSAMAT Applications, Narva-Mustajoe pilot, Intermediate report. Unpublished Trikkela Andres, Kuusik Rein, Martins Ants, Pihu Tõnu, Stencel John M., Utilization of Estonian oil shale semicoke, Fuel processing technology ( ). Velts O, Uibu M., Rudjak I., Kallas J., Kuusik R, Utilisation of oil shale ash to prepare PCC: leachibility dynamics and equilibrium in the ash-water system, Energy Procedia I (2009)