MuhardiUniversity of Riau

* Published in The Electronic Journal of Geotechnical Engineering (EJGE) Vol 15, 2010

Muhardi (UNRI), Aminaton Marto (UTM), Khairul Anuar Kassim (UTM) Ahmad Mahir Makhtar (UTM), Lee Foo Wei (UTM), Yap Shih Lim (Meinhardt Pte. Ltd, Singapore)

Abstract

Tanjung Bin power station is one of the four coal power plants in Malaysia, producing180 tons/day of bottom ash and 1,620 tons/day of fly ash from 18,000 tons/day of coal burning. This paper focuses on the some engineering properties of coal ash (fly ash and bottom ash) from Tanjung Bin power station (e.g. grain size, specific gravity, compaction, shear strength, permeability and compressibility). In addition, morphology, mineralogy and chemistry of coal ash are studied using scanning electron microscope (SEM), x-ray diffraction (XRD and x-ray fluorescence (XRF). Tanjung Bin coal ashes were compacted at 95% of optimum moisture content, sealed and cured for 0, 7, and 28 days before they were analyzed for morphological and mineralogical analyses. Morphological analysis showed that the number of irregular shaped particles increased confirming change in material type with curing period. From mineralogical analysis, the crystalline compounds present in Tanjung Bin coal ash were quartz, mullite_, magnetite, hematite, and calcium oxide. From chemical analysis, Tanjung Bin fly ash is classified as class F in which fly ash has low lime, less than 10%. Its low specific gravity, freely draining nature, ease of compaction, good frictional properties, high shear strength and low compressibility can be gainfully exploited in the construction of embankments, roads, reclamation and fill behind retaining structures.

Introduction

Coal has been projected as an important resource fuel in the forthcoming in Malaysia. It is projected that the installed capacity on the coal power plant in the year 2010 will be 7,200 MW (about 40% of the total), requiring about 22.5 million tons of coal, that is for 8,200 MW capacities (Mahmud, 2003). Currently, there are four coal power plants in Malaysia namely, Tanjung Bin (2,100 MW), Jimah (1,400 MW), Sultan Salahuddin Abdul Aziz / Kapar (2,420 MW) and Sultan Azlan Shah / Manjung (2,100 MW) power plants.

Fly ash and bottom ash are two of the coal waste products. Other waste products are slag and flue gas desulfurization (FGD). It has been reported that the Tanjung Bin power plant alone needs about 18,000 tons/day of coal to generate electricity. As a result of large utilization of coal, a large volume of coal ash as waste material will be produced. The large quantity of coal ash will be a considerable disposal concern to power plants companies due to the increase requirement for ash storage space. Hence, this will increase the expenses as there will be the need to obtain large areas. Due to this, the power plants companies will be a social and environmental problem because of the magnification of disposal areas and the increased disposal expenses will be finally transferred to end users. For that reason, the utilization of coal ash in construction industry, in particular which requires large quantity materials such as in embankment construction, is greatly shows potential to answer the disposal problem of coal ash.

This paper focuses on the characterization of fly ash and bottom ash collected from Tanjung Bin power station in Malaysia that includes the investigation of morphological, mineralogical, physical and mechanical properties. Information regarding to chemical properties of coal ash is required before these materials can be safely and effectively utilized. The physical and mechanical properties, in particular, are important parameters affecting the behavior of coal ash in various engineering applications. Information concerning the morphology and mineralogy are important for addressing the potential environmental impacts associated with coal ash utilization and disposal (Abbas, 2002).

Conclusion

The detailed investigations carried out on Tanjung Bin coal ash show that fly ash and bottom ash has good potential for use in construction industry, especially for geotechnical applications. Its low specific gravity, freely draining nature, ease of compaction, good frictional properties, high shear strength and low compressibility can be gainfully exploited in the construction of embankments, roads, reclamation and fill behind retaining structures. This not only solves the problems associated with the disposal of fly ash and bottom ash (like requirement of precious land and environmental pollution) for power plants but also reduced expenses of electricity for end users.

References

Abbas, G. (2002). Handbook of Pollution Control and Waste Minimization. Published, CRC Press.

ACAA (American Coal Ash Association). (2003). Fly Ash Facts for Highway Engineers. Technical Report ACAA, USA.

ASTM (American Standard Testing Method). (2004).”Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete.” ASTM, USA.

Basak, S., Bhattacharya, A. K. and Paira, S.L.K. (2004).”Utilization Fly Ash in Rural Road Construction in India and its Cost Effectivenes.” Electronic Journal of Geotechnical Engineering (EJGE).

Das, S.K. and Yudbhir. (2006).”Geotechnical Properties of Low Calcium and High Calcium Fly Ash.” Journal of Geotechnical and Geological Engineering, Vol. 24, p 249-263.

Edil, T.B., Acosta, H.A. and Benson, C.H. (2006)”Stabilizing Soft Fine-Grained Soils with Fly Ash.” Journal of Material in Civil Engineering, Vol. 18, No. 2.

Ghosh, A. and Subbarao, C. (2007). Strength Characteristic of Class F Fly Ash Modified with Lime and Gypsum. Journal of Geotechnical and Geoenvironmental Engineering ASCE, July 2007, pp757-765.

Huang H.W. (1990). The Use of Bottom Ash in Highway Embankments, Subgrade and Subbases. Joint Highway Research Project, Final Report, FHWA/IN/JHRP-90/4 Purdue University, W. Lafayette, Indiana.

Kaniraj, S.R. and Gayathri, V. (2004).”Permeability and Consolidation Characteristics of Compacted Fly Ash.” Journal of Energy Engineering, Vol. 130, No. 1.

Kim, B.J., Prezzi, M. and Salgado, S. (2005). Geotechnical Properties of Fly and Bottom Ash Mixtures for Use in Highway Embankments. Journal of Geotechnical and Geoenvironmental Engineering, ASCE.

Kim, B.J., Yoon, S.M. and Balunaini, U. (2006). Determination of Ash Mixture Properties and Construction of Test Embankment –Part A. Joint Transportation Research Program, Final Report, FHWA/IN/JTRP-2006/24 Purdue University, W. Lafayette, Indiana.

Kim, B. (2003). Properties of Coal Ash Mixtures and their Use in Highway Embankments. PhD Thesis, Purdue University, Indiana, USA.

Lav, A.H., Lav, M.A. and Goktepe, A.B. (2006). Analysis and Design of a Stabilized Fly Ash as Pavement Base Material. Istanbul Technical University, Faculty of Civil Engineering, Turkey.

Mahmud, H.O. (2003). Coal – Fired Plant in Malaysia. The 15^th JAPAC International Symposium 19 September 2003, Tokyo.

Misra, A. (2000).”Utilization of Western Coal Fly Ash in Construction of Highways in Midwest.” Final Report, University of Missouri, Kansas City, USA.

Pandian, N.S. (2004).” Fly Ash Characterization with Reference to Geotechnical Aplications.” Journal of Indian of Institute of Science, Vol. 84, p 189-216.

Prabakar, J., Dendorkar, N. and Morchhale, R.K. (2004).”Influence of Fly Ash on Strength Bahavior of Typical Soils.” Journal of Construction and Building Materials, Vol. 18, p 263-267.

Sahu, B.K. (2001).”Improvement in California Bearing Ratio of Various Soils in Botswana by Fly Ash.” International Ash Utilization Symposium 22 – 24 October 2001, Lexington Kentucky, USA.

Sato, A. and Nishimoto, S. (2001). Effective Reuse of Coal Ash as Civil Engineering Material. International Ash Utilization Symposium 22 – 24 October 2001, Lexington Kentucky, USA.

Sear, L.K.A. (2001). The Properties and Use of Coal Fly Ash. Thomas Telford Ltd, London, UK.

Thomas, Z. (2002). Engineering Properties of Soil Fly Ash Sub-grade Mixtures. Iowa State University, Department of Civil Engineering, USA.

Tri Utomo, S.H. (1996). The Effects of Time on Properties of Pulverised Fuel Ash. PhD Thesis, University of Newcastle upon Tyne, UK.

* 6^th International Conference on Innovation in Architecture, Engineering and Construction (AEC) 2010, 9-11 June 2010, Pennsylvania State University, Philadelphia, USA

Muhardi (UNRI), Aminaton Marto (UTM), Khairul Anuar Kassim (UTM), Ahmad Mahir Makhtar (UTM), Wan Zuhairi Wan Yaacob (UKM)

Abstract

Fly ash, the by-products of coal burning to produce electricity, has been used for many years in construction. High shear strength, low compressibility, self-hardening, and relatively lightweight of compacted fly ash makes the material to be suitable as a replacement for backfill material in embankment construction. This paper investigates the effect of time on the performance of fly ash embankment model constructed on very soft soil and hard soil foundations. The model tests were carried out using mini-centrifuge modelling of 0.5m radius. Embankment, constructed using residual soils, was used as a comparison to the fly ash embankment. The paper concludes that the use of fly ash as backfill material for embankment on hard soil can give a tremendous effect in terms of decreased settlement and increased height of prototype, safety factor and time of failure, compared to the residual soils embankment. Comparing the settlement of fly ash embankment at 28 days with residual soils embankment, it is observed that the settlement was reduced by about 6% for embankments on very soft soils and 75% for embankment on hard soils.

Introduction

Fly ash is one of solid waste material resulted from coal burning in the production of electricity. As a result of large utilization of coal, a large volume of coal ash as waste material will be produced. According to Kim (2003), generally about 10% of the coal burned produces ash and up to 90% of ash is fly ash. Fly ash has been used for many years in construction as a replacement in cement, ground stabilisation as fill material in road construction, construction of embankments, reinforced soil retaining walls, and land reclamation (Kim, 2003; Meij and Berg, 2001; Sear, 2001). The relatively lightweight compacted density of fly ash makes the material very suitable as a backfill material in embankment construction. The other important property of fly ash is a self-hardening, probably due to a cementitous nature of the material. It has been well known that fly ash would become hard with time and therefore the strength increases (Kim, 2003; Pandian, 2004; Misra, 2000; Sato and Nishimoto, 2001; Basak et al., 2004; Prabakar et al., 2004; Kaniraj and Gayathri, 2004; Das and Yudbhir, 2006; Edil et al., 2006 and Marto et al., 2009).

Two full scale fly ash embankments have been successfully constructed in USA, such as Delaware and Pennsylvania embankment on hard soil (Golden et al, 2003 and Kim, 2003).  Delaware embankment was constructed approximately 20 m wide, 5 m height and 1:2 slope; Pennsylvania embankment was approximately 75 m wide, 450 m long and up to 15 m high. After two years monitoring, there were 30 mm and 75 mm of settlement measured for Delaware and Pennsylvania embankment, respectively.

Centrifuge testing has been widely used in embankment modeling such as centrifuge modeling of loose fill embankment subjected to uni-axial and bi-axial earthquakes (Charles et al., 2004), centrifuge modeling of soil reinforced systems with geogrids (Mendonsa and Lopes, 2003), dynamic behavior of a levee on saturated sand deposit (Tobita et al., 2006), post-shaking failure of sand slope in centrifuge test (Malvick et al., 2004), preliminary study of instability behavior of levee on soft ground during sudden drawdown (Xu et al., 2005) and also the centrifuge modeling of PFA embankment on hard soil foundation with and without coir fibre as reinforcement (Bhardwaj and Mandal, 2008). Research on embankment using fly ash as structural fill material is still limited especially for embankment placed on soft soils foundation.

Conclusion

Based on the theoretical calculation, the height of the prototype and scaling factor values increased significantly with time for fly ash embankment that increased about 60% from 0 day to 28 days. It is concluded that using of fly ash on hard soil show the most significant impact in terms of increased in height of prototype, safety factor and time of failure, and decreased settlement, compared to the residual soils embankment. For fly ash embankment on very soft soil, the main problem is excessive settlement of embankment and foundation. However, this is still better than residual soils embankment. Comparing the fly ash at 28 days and residual soils embankment on very soft soils at centrifuge test, the settlement was reduced by about 6%. The results confirmed the advantage of using fly ash as embankment fill materials both on hard and very soft soils foundations, over the usage of residual soils. The pozzolanic activities strengthen the fly ash with time hence stronger embankment will be achieved as the time progressed.

Observed variations suggest degrees of conservatism in the analytical methods, problems with the boundary conditions of the tests, inaccuracy with the estimate of undrained shear strength or problems with the visual identification of failure. The other difficulty was to define the constitutive failure. The failure was governed by Serviceability Limit State rather than the Ultimate Limit State. This approach appears to be very suitable to be used in research and with suitable caveats would give researchers an excellent introduction to allowable settlements and failure mechanism.

References

Basak, S., Bhattacharya, A.K. and Paira, S.L.K. (2004) “Utilization Fly Ash in Rural Road Construction in India and its Cost Effectivenes”, Electronic Journal of Geotechnical Engineering.

Bhardwaj, D.K. and Mandal, J.N. (2008) “Centrifuge Modelling on Fiber Reinforced Fly Ash Slop”, Proceedings of the 4^th Asian Regional Conference on Geosynthetics, Shanghai, China.

Charles, W.W.Ng., Li, X.S., Laak, P.A. and Hou, D.Y.J. (2004) “Centrifuge Modeling of Loose Fill Embankment Subjected to Uni-Axial and Bi-Axial Earthquakes”, Journal of Soil Dynamics and Earthquake Engineering, Vol. 24, p 305–318.

Craig, R.F. (2004) “Soil Mechanics”, E & FN Spon, London, United Kigdom.

Das, S.K. and Yudbhir. (2006) “Geotechnical Properties of Low Calcium and High Calcium Fly Ash”, Journal of Geotechnical and Geological Engineering, Vol. 24, p 249-263.

Edil, T.B., Acosta, H.A. and Benson, C.H. (2006) “Stabilizing Soft Fine-Grained Soils with Fly Ash”, Journal of Material in Civil Engineering.

Golden, D.M., and DiGioia, A.M. (2003) “Fly Ash for Highway Construction and Site Development”, Coal Combustion Product Partnership, USA.

Kaniraj, S.R. and Gayathri, V. (2004) “Permeability and Consolidation Characteristics of Compacted Fly Ash”, Journal of Energy Engineering, Vol. 130, No. 1.

Khatib, A. (2009) “Bearing Capacity of Granular Soil Overlying Soft Clay Reinforced with Bamboo-Geotextile Composite at the Interface”, PhD Thesis. Universiti Teknologi Malaysia, Skudai, Johor Bahru, Malaysia (Unpublished).

Kim, B. (2003) “Properties of Coal Ash Mixtures and Their Use in Highway Embankments”, PhD Thesis. Purdue University, Indiana, USA (unpublished).

Mahmud, H.O. (2003) “Coal – Fired Plant in Malaysia”, The 15^th JAPAC International Symposium 19 September 2003. Tokyo.

Malvick, E.J., Kutter, B.L., Boulanger, R.W. and Feigenbaum, H.P. (2004) “Post-shaking Failure of Sand Slope in Centrifuge Test”, Department of Civil and Environmental Engineering, University of California, USA.

Marto, A., Mahir, A. M., Lee, F. W., Yap, S. L. and Muhardi (2009) “Morphology, Mineralogy and Physical Characteristics of Tanjung Bin Coal Ash”, Proceedings of 4^th International Conference on Recent Advanced in Materials, Minerals and Environment (RAMM), 1-3 June 2009. Pulau Penang, Malaysia.

Meij, R. and Berg, J. (2001) “Coal Fly Ash Management in Europe Trends, Regulations and Health & Safety Aspects”, Lexington Kentucky: International Ash Utilization Symposium.

Mendonsa, A. and Lopes, M.L. (2003) “Centrifuge Modelling of Soil Reinforced Systems with Geogrids”, Research Project Report POCTI/42806/ECM/2001.Portugal.

Misra, A. (2000) “Utilization of Western Coal Fly Ash in Construction of Highways in Midwest”, Final Report, University of Missouri.

Newson, T. and White, D. (2005). “Modelling Geotechnical Problems in Soft Clays using the Mini-Centrifuge”, K.Y. Lo Symposium, 7-8 July 2005, The University of Western Ontario, Canada.

Pandian, N.S. (2004) “Fly Ash Characterization with Reference to Geotechnical Applications”, Journal of Indian of Institute of Science, Vol. 84, p 189-216.

Prabakar, J., Dendorkar, N. and Morchhale, R.K. (2004) “Influence of Fly Ash on Strength Behavior of Typical Soils”, Journal of Construction and Building Materials, Vol. 18, p 263-267.

Sato, A. and Nishimoto, S. (2001) “Effective Reuse of Coal Ash as Civil Engineering Material”, Lexington Kentucky: International Ash Utilization Symposium.

Sear, L.K.A. (2001) “The Properties and Use of Coal Fly Ash”, Thomas Telford Ltd, London, UK.

Tobita, T., Iai, S. and Ueda, K. (2006) “Dynamic Behavior of a Levee on Saturated Sand Deposit”, Annuals of Disasater Preventive Research Institute, Kyoto University.

Xu, G.M., Zhang, L. and Liu, S.S. (2005) “Preliminary Study of Instability Behavior of Levee on Soft Ground during Sudden Drawdown”, Slopes and Retaining Structures under Seismic and Static Conditions, ASCE.

* Published in Journal Science and Technology, Faculty of Engineering, University Riau

Abstract

Fly Ash (FA) has been used for many years in geotechnical engineering. The purpose of research is to examine the stress-strain behaviour for FA and applied within existing two finite element programs. In the first program, undrained triaxial tests are simulated at a pressure of 100 kPa, allow to dilatant and non-dilatant cases. For both cases, the results show similarity with the experimental in the elastic region for s₃ = 100 kPa. For the dilatant in the plastic region, the result has a higher value of deviator stress than the experimental. While for the non-dilatant, the result has a lower value. Another program is carried out to calculate the maximum displacement versus safety factor for the clay slope and an alternative solution using FA. The results of the program show the most significant impact when FA is used to re-construct the clay slope, in which the displacement is reduced.

Introduction

Fly Ash (FA) is a widely available waste material from coal burning power stations. It is created as a result of the industrial process that employs pulverised coal to produce steam power for the generation of electricity. The ash material of the parent coal shows a variation, which is dependent upon both the kind of coal and the efficiency of the burning process. The mineralogy and trace component concentration of the fly ash is influenced by the amount and rate of the subsidence, which took place in the original peat swamps. Organic and inorganic compounds were laid down to form the peat by the natural geological processes of erosion and deposition [1].

Fly ash has been used for many years in construction as a lightweight replacement in cement and in ground stabilisation. Fly ash is applied as a partial replacement for Portland Cements in the production of concrete, especially in high performance concrete. Fly ash is also used in ground stabilisation as fill material in road construction, construction of embankments, reinforced soil retaining walls, and land reclamation. The relatively lightweight compacted density of fly ash makes the material very suitable as a replacement in ground stabilisation. Fly ash can be used by itself to increase the mechanical properties of soil or in combination with lime or cement to form a binder. Fly ash is a pozzolan, which reacts with calcium oxide (CAO) and water to form cementitous material. Fly ash-cement or fly ash-lime stabilisation is best matched to sands and gravel with low clay content [2].

Fly ash has properties in which cover a range of behaviour and are well known chemically and mechanically. The chemical composition of fly ash differs with the source of the coal, the pre-and-post treatment processes, and the temperature at which the coal is burnt. Fly ash, forming about 80% of all ash produced, is carried out of the furnace with the flue gases. It is primarily a silt sizes material composed mainly of silicon and aluminium oxide [3]. The physically properties of fly ash are commonly influenced by the efficiency and kind of coal crushing process implemented at the power plant. Generally, the finer the coal is ground before burning, the finer the resulting fly ash [1]. It contains predominantly finely separated spherical elements mainly in the size range of 1 to 150 microns [4].

The purpose of this research is to examine the stress-strain behaviour for fly ash based on the results of some experimental work from other research, obtained from different of sources of the fly ash. Then, two cases of study are applied within an existing finite element program in Fortran; the simulation of triaxial test and plane strain slope stability analysis. The results of the finite element are compared with the results of experimental work and field tests.

Conclusions

The result from both the finite element programs, the simulation of triaxial tests and the plane strain slope stability analysis that shows similarity in the elastic region with the experimental result in simulation of triaxial tests program and fly ash can be used as replacement material for slope stabilisation in the slope stability analysis. These results suggest that for the range of conditions examined:

1. In the simulation of the dilatant undrained triaxial test, the results of the program show no limit to failure due to dilation. For the plastic region, the program result has a higher value of deviator stress than the experimental result. For the non-dilatant, the results show no plastic volume change due to dilation angle, y = 0. For the plastic region, the program result has a lower value of deviator stress than the experimental.

2. In slope stability analysis, the slope would be acceptably safety if re-constructed in fly ash with its initial condition. The slope would actually tend to a higher factor of safety due to an increase in the stiffness and strength of placed fly ash during construction. The slope takes time to re-construct and the fly ash is increasing in stiffness during this time.

3. The result of finite element program show the most significant impact when is used to re-construct the slope compared with using clay material, in which the maximum displacement is reduced after completion.

References

1. Cripwell, J.B., Pulverised Fuel Ash, National Seminar: The Use of PFA in Construction, University of Dundee, 25-27 February 1992.

2. Bell, F.G., Engineering Treatment of Soils,   London, E & FN SPON, 1993.

3. Clarke, B., Structural Fills, National Seminar: The Use of PFA in Construction, University of Dundee, 25-27 February 1992.

4. Barber, E.G., Jones, G.T., Knight, P.G.K., and Miles, M.H., PFA Utilisation, London, C.E.G.B, 1972.

5. Gatti, G. and Tripiciano, L., Mechanical Behaviour of Coal Fly Ash, Proceedings of the 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, Vol. 2, 1981.

6. Smith, I.M., Griffiths, D.V., Programming the Finite Element Method, third edition. Chichester, John Wiley & Sons, 1998.

7. Kumar, S. and Puri, V.K., Evaluation and Remediation of Slope Supporting Gasoline Tanks,EJGE,http://geotech.civen.okstate.edu/ejge/JourTOC4.htm, Vol.4, 1999.

8. Cotton,R.D., Construction of Embankments, National Seminar: The Use of PFA in Construction, University of Dundee, 25-27 February 1992.

* Published in Journal Science and Technology, Faculty of Engineering, University of Riau

Abstract

The behaviour of reinforced slope on clay has been explored using the technique of centrifuge modelling. Four clay layers were reinforced with a geotextile and the behaviour of the clay and the response of reinforcement were observed. The purpose of the reinforcement was to limit the spreading of the slope and lateral displacement of the clay. The centrifuge test was carried out to study the collapse model. This is useful since in geotechnical engineering details of pre-failure patterns of deformation are often just as valuable as factor of safety against failure. The result of test show the using of geotextile can affect the performance of the model and improve stability. Also, it prevents the formation of the circular slip surface by allowing the layers to move relative to each other.

Introduction

Centrifuge testing concerns the study of geotechnical events using small-scale models subjected to acceleration fields of magnitude many times earth’s gravity. With this technique, self weight stresses and gravity dependent processes are correctly reproduced and observations from small-scale models can be related to the full-scale prototype situation using well-established scaling laws. Because of its ability to reproduce the same stress levels in a small-scale model as those present in full-scale prototype, centrifuge is a useful tool in the investigation of geotechnical problems.

Centrifuge model tests have proved to be particularly valuable in revealing mechanism of deformation and collapse and in providing data for validation of numerical analysis. Reproducing soil behaviour both in terms of strength and stiffness is essential for two reasons. The first is that soils were originally deposited in layers and so it is possible to encounter different ways. The second is that in-situ stresses change with depth and it is well known that soil behaviour is a function of stress level and stress history [1].

Centrifuge model testing represents a major tool available to the geotechnical engineer since it enables the study and analysis of design problems by using geotechnical materials. Centrifuge model testing has found application in problem involving non-reactive contaminant transport from landfill sites and buried repositories in zones of uniform or heterogeneous soil, including problems involving unsaturated and immiscible fluid flow, density driven flow and hydrodynamic clean up, and conductive and convective heat transport. Examples, which illustrate the use of centrifuge model tests to investigate problems in civil engineering practice, are retaining wall structures, underground excavation and foundations, earthquake and dynamic loading [2].

The aim of paper is to examine the behaviour of reinforced slope on clays using the technique of centrifuge modelling. Four clays layers were reinforced with geotextile and the behaviour of the clays and response of the reinforcement were observed. The purpose of the reinforcement was to limit the spreading of the slope and lateral displacement of the clay. The centrifuge test was carried out to study the collapse mode. This research was done in Centrifuge Laboratory, Manchester University.

Conclusion

The centrifuge test provided a good idea about how the reinforcement can affect the performance of the model and improve its stability. The way in which the geotextile alters the behaviour of the model is as follows: it prevents the formation of the circular slip surface by allowing the layers to move relative to each other. Therefore, the properties of the geotextile should be such that they can tolerate this relative displacement without getting damage.

The greatest difficulty was to define what constitutive failure. The failure was governed by Serviceability Limit State rather than the Ultimate Limit State.

References

[1] MSc Group Report, (2000), “Centrifuge Test”, MSc Course in Geotechnical Engineering, Manchester University and UMIST, UK.

[2] Craig, W.H. (2000), “The application of   Centrifuge Modelling in Geotechnical Engineering”, MSc Course in Geotechnical Engineering, Manchester University, UK.

[3] Craig, R.F. (1998), “Soil Mechanics”, E & FN Spon, London, UK.

[4] Taylor, R.N. (1995),“Geotechnical Centrifuge Technology”, Blackie Academic, UK.

* 1st International Conference on Suistanable Infrastructure and Built Environment in Developing Contries – SIBE 2009

Muhardi (UNRI), Aminaton Marto (UTM), Khairul Anuar Kassim (UTM), Ahmad Mahir Makhtar (UTM), Wan Zuhairi Wan Yaacob (UKM)

Abstract

Fly Ash has been used for many years in geotechnical engineering such as in embankment construction. The relatively lightweight compacted of fly ash makes the material very suitable as a replacement for backfill material in embankment construction, particularly on soft soil. Physical modelling is usually performed to study the particular aspects of the behavior of prototypes. The physical models, constructed at smaller scales than the prototypes, could give information of response more rapidly and the model details could be better controlled than the full scale testing. Geotechnical centrifuge is an example of physical modeling where all features of the prototype are reproduced at smaller scale. Large beam and drum centrifuges are now regularly used to model geotechnical engineering structures. In this research, a UKM mini-geotechnical centrifuge with 0.5m radius has been used and it has the advantage that it is cheap to manage and modify, and allow large numbers of tests to be performed rapidly. This paper discusses the components of the UKM mini-geotechnical centrifuge and its application to model fly ash embankment, constructed on hard and very soft soil foundations. Since there are no actuators or instrumentation present, tests are triggered by increasing self-weight as the acceleration is increased and settlements and failure were determined photographically. The settlement measurement method consists of a remote digital video camera together with stroboscopic lighting. It is concluded that using fly ash as fill material in embankment construction can affect the performance of the model whereby it improves stability and reduces settlement of embankment and foundation layers, as observed from mini-centrifuge model.

Introduction

Physical modelling is usually performed to study the particular aspects of the behavior of prototypes. Physical model is constructed at smaller scale than the prototype because it is expected to obtain information of response more rapidly and more control over a more details full scale testing. Centrifuge model is an example of physical modeling where all features of the prototype are reproduced at small scales. Centrifuge testing concerns the study of geotechnical events using small-scale models subjected to acceleration fields of magnitude that is many times larger than the earth gravity. With this technique, self weight stresses and gravity dependent processes are correctly reproduced and observations from small-scale models can be related to the full-scale prototype situation using well-established scaling laws (Muhardi et al., 2008).

Whilst most centrifuge facilities are aware of the teaching potential of centrifuge technology for demonstrating geotechnical problems, the cost of servicing this teaching tends to be prohibitive other than on an occasional basis. Small beam provide an alternative technique, which is more cost effective, but still requires specialist knowledge and technical expertise. Much smaller centrifuges (less than 0.5m radius) have been built for teaching and research purposes, but are described rarely in the literature. These very small centrifuge facilities have the advantage that they are cheap to operate and modify, and enable large numbers of tests to be conducted quickly (Newson et al., 2005).

Fly ash is one of solid waste material resulted from coal burning in the production of electricity. Mahmud (2003) reported that in 2002 gas has been used as main resource fuel to generate power plants in Malaysia. However coal has been projected as a possible resource fuel in the forthcoming. It is projected that the total projected installed capacity on the coal power plant will be 8,200 MW, requiring about 22.5 million tons of coal by the year 2010. As a result of large utilization of coal, a large volume of coal ash as waste material will be produced. In Malaysia, there is no report about the producing of coal ash annually. However, according to Kim (2003), generally about 10% of the coal burned produces ash and up to 90% of ash is fly ash. Fly ash has been used for many years in construction as a lightweight replacement in cement, especially in high performance concrete. Fly ash is also used in ground stabilisation as fill material in road construction, construction of embankments, reinforced soil retaining walls, and land reclamation. The relatively lightweight compacted density of fly ash makes the material very suitable as a fill material in embankment construction (Marto et al., 2009)

This paper discusses the behaviour of embankment which used fly ash as backfill materials on hard and very soft soils foundation, using the technique of centrifuge modelling. The embankment models were tested in the centrifuge equipment with the gravitational force being increased until the model failed. The failure mechanism of the embankment was also analysed. This centrifuge modelling test was carried out at the Geotechnical Centrifuge Laboratory, Universiti Kebangsaan Malaysia (UKM).

Conclusion

Two centrifuge fly ash embankment model tests were performed each on very soft soils and medium dense sand foundation. The acceleration at failure and the failure mechanisms were obtained photographically using PIV and these results were compared to the theoretical predictions. Comparing between theoretical values with centrifuge test, the prototype of embankment height matched reasonably well for embankment on very soft soils. However, for embankment on medium dense sand, the centrifuge test gave much higher value compared to theoretical calculation, in which the factor of safety is higher than 1. The allowable settlement can be accepted for embankment on medium dense sand. However, the embankment on very soft soils could not satisfy the allowable settlement for any kind of structure supported on the surface of the embankment.

Observed variations suggest degrees of conservatism in the analytical methods, problems with the boundary conditions of the tests, inaccuracy with the estimate of undrained shear strength or problems with the visual identification of failure. The other difficulty was to define the constitutive failure. The failure was governed by Serviceability Limit State rather than the Ultimate Limit State. This approach appears to be very suitable for use as a research and with suitable caveats would give researchers an excellent introduction to allowable settlements and failure mechanism. The tests proved to be very quick (the test can be conducted from soil preparation to failure in less than 2 hours) and simple to perform making them suitable for demonstration tests. The whole centrifuge test is a relatively cheap as research and teaching aid. Hence, it is suggested that mini-centrifuges have a role to play in geotechnical research and education due to their ease of use, cheapness and mobility.

References

Craig, R.F. (2004), Soil Mechanics, E & FN Spon, London, United Kigdom

Khatib, A. (2009). Bearing Capacity of Granular Soil Overlying Soft Clay Reinforced with Bamboo-Geotextile Composite at the Interface. PhD Thesis, Universiti Teknologi Malaysia, Skudai, Johor Bahru, Malaysia (Unpublished)

Kim, B. (2003). Properties of Coal Ash Mixtures and Their Use in Highway Embankments. PhD Thesis, Purdue University, Indiana, USA (unpublished)

Mahmud, H.O. (2003). Coal – Fired Plant in Malaysia. The 15^th JAPAC International Symposium 19 September 2003, Tokyo

Marto, A., Mahir, A. M., Lee, F. W., Yap, S. L. and Muhardi (2009). Morphology, Mineralogy and Physical Characteristics of Tanjung Bin Coal Ash. Proceedings of 4^th International Conference on Recent Advanced in Materials, Minerals and Environment (RAMM) & 2^nd Asian Symposium on Material & Processing (ASMP), 1-3 June 2009, Pulau Penang, Malaysia

Muhardi, Marto, A., Kassim, K. A. and Craig, W. (2008). Geotechnical Centrifuge Physical Model of Reinforced Clay Slope. International Graduate Conference on Engineering (IGCES) 23-24 December 2008, Skudai, Johor Bahru, Malaysia

Newson, T. and White, D. (2005). Modelling Geotechnical Problems in Soft Clays using the Mini-Centrifuge. K.Y. Lo Symposium, 7-8 July 2005, The University of Western Ontario, Canada

* 4th International Conference on Recent Advanced in Materials, Minerals & Environment – RAMM 2009

Muhardi (UNRI), Aminaton Marto (UTM), Ahmad Mahir Makhtar (UTM), Lee Foo Wei (UTM), Yap Shih Lim (Meinhardt Pte. Ltd, Singapore)

Abstract

Coal-burning power plants in Malaysia generate more than 15.5 million tons of coal as main resource fuel in 2007 and it has been projected to 22.5 millions tons in 2010. As a result of large utilization of coal, a large volume of coal ash as waste material will be produced. Fly ash and bottom ash are two of the coal ashes by products produced from power generating plants. Direct use of these materials in construction projects exhausted large quantities of materials, not only provide a promising solution to the disposal problem, but also an alternative for fill materials. This paper focuses on the characterization of fly ash and bottom ash obtained from Tanjung Bin Power Plant, Johor, Malaysia that includes the investigation of morphological, mineralogical and physical properties. Tanjung Bin coal ash were compacted at 95% of optimum moisture content, sealed and cured for 0, 7, and 28 days before they were analyzed for morphological and mineralogical analyses. Morphological analysis showed that the number of irregular shaped particles increased confirming change in material type with curing period. From mineralogical analysis, the crystalline compounds present in Tanjung Bin coal ash were quartz, mullite_, magnetite, hematite, and calcium oxide. Some of the chemical compound disappeared with the increased of curing period. Physical properties such as specific gravity, particle size distribution and permeability were also studied. Specific gravity test result showed that Tanjung Bin coal ash exhibits lower specific gravity value than the natural soil’s. For the permeability test, in general it shows that bottom ash is a good drainage material due to high value of permeability (1.72 x 10^-4 m/s). However, fly ash is a poor drainage material due to its low permeability value (4.87 x 10^-9 m/s). The physical properties of Tanjung Bin coal ash indicate that fly ash could be used as liners while the bottom ash might be used as an alternative for fill materials such as in soil improvement work or as backfill material for road embankment.

Introduction

Coal has been projected as a possible resource fuel in the forthcoming. It is projected that the installed capacity on the coal power plant in the year 2010 will be 7,200 MW (about 40% of the total), requiring about 22.5 million tons of coal, that is for 8,200 MW capacities (1). As a result of large utilization of coal, a large volume of coal ash as waste material will be produced. Fly ash and bottom ash are two of the coal waste products. Other waste products are boiler slag and Flue Gas Desulfurization (FGD). In Malaysia, there is no specific report about the producing of coal ash annually. However, generally about 10% of the coal burned produces ash and up to 90% of ash is fly ash (2). The large quantity of coal ash will be a considerable disposal concern to power plants companies due to the increase requirement for ash storage space. Hence, this will increase the expenses as there will be the need to obtain large areas. Due to this, the power plants companies will be a social and environmental problem because of the magnification of disposal areas and the increased disposal expenses will be finally transferred to end users. For that reason, the utilization of coal ash in construction industry, in particular which requires large quantity materials such as in embankment construction, is greatly shows potential to answer the disposal problem of coal ash.

The chemical composition of coal ash varies, depending primarily on the type of coal burned, the fineness of pulverized coal and the efficiency of the coal-burning unit. Coal ash consists principally of glassy spheres together with some crystalline matter and unburned carbon. Silicon and aluminium are mainly present in glassy phase, with small amount of quartz and mullite included. The iron appears partly as the oxides magnetite and hematite, with the rest in glassy phase. Coal ash consists of silt-sized particles which are generally spherical, typically ranging in size between 10 µm and 100 µm (3). The colour of coal ash is normally tan to dark gray, depending on its chemical and mineral constituents. Tan and light colors are typically associated with high lime content. A brownish color is typically associated with the iron content. A dark gray to black color is typically attributed to elevated unburned carbon content (4).

This paper focuses on the characterization of fly ash and bottom ash collected from Tanjung Bin Power Plant, Johor, Malaysia that includes the investigation of morphological, mineralogical, and physical properties. Tanjung Bin coal ash at 95% of optimum moisture content were compacted, sealed and cured for 0, 7, and 28 days for morphological and mineralogical analysis.

Conclusion

Tanjung Bin fly ash is composed of fine, nearly spherical particles with mostly of silt sized material. It exhibits some spherical morphological characteristic that are distinctly different from typical soils. Tanjung Bin fly ash is agglomerates of fine particles. The morphology characterization of fly ash affects their specific gravity and permeability. The coefficient of permeability of the Tanjung Bin fly ash is 4.87 x 10^-9 m/s, which is within the range of those of silty clay to clay. The permeability is low enough to enable the use of the material in the construction of impermeable liners but quite unsuitable for road embankment.

Generally, dry bottom ash and wet bottom ash are two basic types of bottom ash. The two types of bottom ash have different physical and chemical characteristics and thus different engineering properties. The samples used belong to dry bottom ash category. The non-uniformity of bottom ash is the key point to maximize the application of the material. The complex pore structure and gritty surface texture of bottom ash particles made the bottom ashes to exhibits some special characteristics that are different from those of conventional materials which influent the specific gravity and permeability of the material. Dry bottom ash tends to have low specific gravity. Based on the results of laboratory evaluations of Tanjung Bin bottom ash, it appears that this material is suitable for various uses in civil engineering constructions depending on requirements of the applications such as for fill materials in soil improvement work or backfill materials for road embankment.

References

(1)       Mahmud, H.O. (2003). Coal – Fired Plant in Malaysia. The 15^th JAPAC International Symposium 19 September 2003, Tokyo.

(2)       Kim, B. (2003). Properties of Coal Ash Mixtures and their Use in Highway Embankments. PhD Thesis, Purdue University, Indiana, USA.

(3)       Sear, L.K.A. (2001). The Properties and Use of Coal Fly Ash. Thomas Telford Ltd, London, UK.

(4)       ACAA (American Coal Ash Association). (2003). Fly Ash Facts for Highway Engineers. Technical Report ACAA, USA.

(5)       Abbas, G. (2002). Handbook of Pollution Control and Waste Minimization. Published, CRC Press.

(6)       Ghosh, A. and Subbarao, C. (2007). Strength Characteristic of Class F Fly Ash Modified with Lime and Gypsum. Journal of Geotechnical and Geoenviroment Engineering ASCE, July 2007, pp757-765

(7)       Kim, B.J., Prezzi, M. and Salgado, S. (2005). Geotechnical Properties of Fly and Bottom Ash Mixtures for Use in Highway Embankments. Journal of Geotechnical and Geoenvironmental Engineering, ASCE.

(8)       Huang H.W. (1990). The Use of Bottom Ash in Highway Embankments, Subgrade and Subbases. Joint Highway Research Project, Final Report, FHWA/IN/JHRP-90/4! Purdue University, W. Lafayette, Indiana.

(9)       Sato, A. and Nishimoto, S. (2001). Effective Reuse of Coal Ash as Civil Engineering Material. International Ash Utilization Symposium 22 – 24 October 2001, Lexington Kentucky, USA.

(10)   Misra, A. (2000).”Utilization of Western Coal Fly Ash in Construction of Highways in Midwest.” Final Report, University of Missouri, Kansas City, USA.

(11)   Sahu, B.K. (2001).”Improvement in California Bearing Ratio of Various Soils in Botswana by Fly Ash.” International Ash Utilization Symposium 22 – 24 October 2001, Lexington Kentucky, USA.

(12)   ASTM (American Standard Testing Method). (2004).”Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete.” ASTM, USA.

(13)   Pandian, N.S. (2004).” Fly Ash Characterization with Reference to Geotechnical Aplications.” Journal of Indian of Institute of Science, Vol. 84, p 189-216.

(14)   Basak, S., Bhattacharya, A. K. and Paira, S.L.K. (2004).”Utilization Fly Ash in Rural Road Construction in India and its Cost Effectivenes.” Electronic Journal of Geotechnical Engineering (EJGE).

(15)   Prabakar, J., Dendorkar, N. and Morchhale, R.K. (2004).”Influence of Fly Ash on Strength Bahavior of Typical Soils.” Journal of Construction and Building Materials, Vol. 18, p 263-267.

(16)   Kaniraj, S.R. and Gayathri, V. (2004).”Permeability and Consolidation Characteristics of Compacted Fly Ash.” Journal of Energy Engineering, Vol. 130, No. 1.

(17)   Das, S.K. and Yudbhir. (2006).”Geotechnical Properties of Low Calcium and High Calcium Fly Ash.” Journal of Geotechnical and Geological Engineering, Vol. 24, p 249-263.

(18)   Edil, T.B., Acosta, H.A. and Benson, C.H. (2006)”Stabilizing Soft Fine-Grained Soils with Fly Ash.” Journal of Material in Civil Engineering, Vol. 18, No. 2.

(19)   Kim, B.J., Yoon, S.M. and Balunaini, U. (2006). Determination of Ash Mixture Properties and Construction of Test Embankment –Part A. Joint Transportation Research Program, Final Report, FHWA/IN/JTRP-2006/24! Purdue University, W. Lafayette, Indiana.

Compaction Behaviour

Compaction is the densification of a material by the application of loads, through rolling, tamping, or vibration, with the aim of increasing the dry density of the material.  The compacted unit weight of the material depends on the amount and method of energy application, grain size distribution, plasticity characteristics and moisture content at compaction.  When it is used as a construction material, the most important engineering properties are its shear strength, its compressibility and its permeability.  In the case of an embankment, compaction is desired to improve the stability of the slope and to prevent detrimental settlement (Kim, 2003).

The compaction characteristic of PFA exhibits a similar trend to that of low plasticity cohesive soil.  Typical moisture-density curves have a mound shape.  Available data on the compaction characteristics of PFA show somewhat wide variations in both optimum water content and maximum dry density.  The large variations in the values are mainly due to the variation of PFA itself, which exhibits different chemical and physical characteristics depending on factors such as the source of coal and the condition of coal combustion (Kim, 2003).

Permeability

Permeability is an important parameter in the design of liners to contain leachate migration, dykes to predict the loss of water as well as the stability of slopes and as a sub-base material.  The coefficient of permeability of ash depends upon the grain size, degree of compaction and pozzolanic activity (Pandian, 2004).

Shear Strength

An important engineering property that is necessary for using PFA in many geotechnical applications is its shear strength.  In soil mechanics, shear strength is the fundamental characteristic that determines the ability of soils to resist loading without failing.  The evaluation of the shear strength is important for the stability assessment of all soil structures including embankment slopes, foundations, and soil retaining structures.

Class F PFA is basically only frictional materials. The class F PFA may develop an apparent cohesion due to capillary tension when it becomes wet.  However, the effect is completely lost when it is either dried or saturated.  In contrast to this behavior, class C PFA can exhibit considerable cohesive strength due to cementitious reactions, which is the dominant source of shear strength of class C PFA (Kim, 2003)

Compressibility

Compressibility characteristics of PFA depend on its initial density, degree of saturation, self-hardening characteristics and pozzolanic activity.  Partially saturated ashes are less compressible compared to fully saturated ones.  To estimate the settlement of structures placed on PFA embankments or fills, one-dimensional consolidation test results are required (Pandian, 2004).

PFA is a fine-grained material and more permeable than compacted cohesive soils. Consequently, the deformation behavior is likely to be similar to that of a granular soil. For a granular soil, the deformation undergone is the result of deformation in the particles themselves and relative inter particle movement.  In granular soils, deformation is caused by distortion and crushing of individual particles, and relative motion between particles as the result of sliding or rolling.  While the sliding between the particles occurs at all stress levels, the crushing and fracturing of particles begins in a minor way at very low stresses, but becomes evident when some critical stress is reached (Kim, 2003).

Appearance and Shape

PFA is typically finer than Portland cement and lime. PFA consists of silt-sized particles which are generally spherical, typically ranging in size between 10 and 100 micron.  As the coal is burnt producing temperature in region of 1400⁰ C, the minerals associated with it become molten and form a spherical shape.  Because of rapid cooling experienced by the fine ash particles as they pass out of the furnace, they solidify as an amorphous, glassy material in this shape (Sear, 2001).

Fineness is one of the important properties contributing to the pozzolanic reactivity of PFA. PFA can be tan to dark gray, depending on its chemical and mineral constituents.  Tan and light colors are typically associated with high lime content.  A brownish color is typically associated with the iron content.  A dark gray to black color is typically attributed to elevated unburned carbon content (ACAA, 2003).

Specific Gravity

The specific gravity of ash varies largely depending on its chemical composition and particle structure.  Generally, the ashes with high iron contents will have higher specific gravities.  Likewise, the ashes that have solid structures will be denser than those that are porous or hollow, and have correspondingly high specific gravities.  Comparing between specific gravity of PFA (1.73 – 2.71) and natural soils (2.5 – 2.7), specific gravity of PFA have more range variety and average lower than natural soils.  This caused by differing chemical content and particle structure.

Particle Size Distribution

PFA is a fine, powder-like material.  The grain sizes range from 0.6 mm (No. 40 sieve) to 0.001 mm, which spans the range from fine sands and silt to large clay particles.  The gradation characteristics of PFA differ by type.  The particle-size distributions of PFA are mainly silt sized.  In most cases, however, the PFA is relatively uniform, falling in the range passing the No. 200 sieve (0.075 mm).

The chemical composition of PFA varies, depending primarily on the type of coal burned, the fineness of pulverized coal and the efficiency of the coal-burning unit.  PFA consists primarily of oxides of silicon, aluminum iron and calcium. Magnesium, potassium, sodium, titanium, and sulfur are also present to a lesser degree.  When used as a mineral admixture in concrete, PFA is classified as either Class C or Class F ash based on its chemical composition (ACAA, 2003).

PFA consists principally of glassy spheres together with some crystalline matter and unburned carbon.  Silicon and aluminium are mainly present in glassy phase, with small amount of quartz and mullite (3Al₂O₃, 2SiO₂) included.  The iron appears partly as the oxides magnetite (Fe₃O₄) and heamatite (Fe₂O₃), wit the rest in glassy phase (Sear, 2001).

ASTM C 618 defines the chemical composition of Class C and Class F PFA.  Class C ashes are generally derived from sub-bituminous coals and consist primarily of calcium alumina-sulfate glass, as well as quartz, tricalcium aluminates, and free lime (CaO).  Class C ash is also referred to as high calcium PFA because it typically contains more than 20 percent CaO. Class F ashes are typically derived from bituminous and anthracite coals and consist primarily of an alumina-silicate glass, with quartz, mullite, and magnetite also present. Class F, or low calcium PFA has less than 10 percent CaO (ACAA, 2003).

Coal is one of energy source to generate power stations.  Coal is a primary energy supply in some of country in the world.  Coal plays a central role in producing energy of China and US. China is the world’s largest producer of the coal, followed by US, India, and Australia (Fujitomi, et al., 2005).

Pulverised Fuel Ash (PFA) is known by variety of names including coal fly ash, fly ash, and as a coal combustion product (CCP).  Within the UK, the accepted term and the most descriptive one is PFA.  However, in general usage in many countries the term fly ash is used for pulverized coal ash but it can also cover ashes from burning other materials (Sear, 2001).

PFA is one of the coal ash products obtained from coal burning power stations.  Others waste products are Furnace Bottom Ash (FBA), boiler slag and Flue Gas Desulfurization (FGD).  The coal is crushed and blown into the combustion by a spurt of air.  Then it is destroyed by fire and the resulting ash is in the form of small part spheres, small amounts of which are hollow.  Some 75% – 85% of these ashes are passed away in the pipe gases and are then taken out from the gas by electronic precipitators.  This product is known as pulverised fuel ash (PFA).  The residual 15% – 25% agglomerates fall to the underneath of the combustion compartment and are accumulated from there.  This residue is named furnace bottom ash (FBA) and is a coarser material (Muhardi, 2002).

Coal ash have been used beneficially in a number of areas, primarily in cement and concrete, structural fills, waste stabilizations, road base/sub base, and mining applications.  The components of coal ash have different uses since they have distinct chemical, physical and mechanical properties.  Most of PFA applications are in cement and structural fills area.