A STUDY ON APPLICATIONS OF FLYASH IN CIVIL ENGINEERING PROJECTS BY J.P.R.V.VEMKATESH K.N.A.G.K.MANIKANTA III/IV B.TECH (CIVIL) III/IV B.TECH (CIVIL) E-mail:firstname.lastname@example.org email@example.com D.M.S.S.V.H. COLLEGE OF ENGINEERING MACHILIPATNAM ABSTRACT One of the challenges of civil engineering community in near future will be to realize projects in harmony with the concept of suitable development of innovative construction materials that suit the end requirements of the structures. This involves the use of high performance materials produced at reasonable cost with lowest possible environmental impact. The most abundantly available supplementary cementing material is flyash, a by-product of thermal power stations. It has a tremendous potential to be utilized and is produced in huge quantities due to rapid industrialization .The crux of the problem is in its disposal as it requires vast areas of valuable land. Further its hazardous effects to the environment and mankind. This paper presents some of the issues that have long been problematic to the flyash producing industries as its utilization is far less than production. The suitability and superiority of flyash in various applications is also briefly discussed. Hence the knowledge and awareness of evolution of use of flyash will go a long way in building up better constructions in the future. INTRODUCTION: Flyash is a finely divided residue resulting from the combustion of pulverised coal and transported by the flue gases of boilers fired by pulverised coal as defined by IS: 3812-1981. Realisation dawned on the tremendous environmental problems being caused by large scale dumping of flyash on scarce land resource. keeping in view the health hazard, India launched the ‘Flyash Mission’, a Technology Project in Mission Mode in 1994 towards promoting safe disposal and utilization of flyash in the country. To cater this problem, flyash is used in different civil engineering constructions such as building materials, construction of ash dykes, embankments, laying of cement concrete roads etc. With the trend of development of various Building materials and application of flyash in the construction industries, it is expected that 50% of the total production of flyash could be properly utilized, provided the major constraints are removed as regards high value added suitable technology is yet to be developed and needs the research. Rough estimation of existing utilisation of flyash is around 10 % (1998) of the total generated quantity as against 3 - 5 % (1994). In absolute terms it has increased about three folds. However, countries like France, Belgium, Germany, and Netherlands have utilisation levels of 90 % or higher. This paper highlights the methods to develop proper utilisation of the flyash for the construction industries. Physical Properties of Flyash: Flyash particles can be spherical and rounded, sub-rounded, irregular and angular. Fineness is probably a single important physical characteristic which influences the activity of flyash more than any other physical factor. The surface area is found to range between 3627 and 6091 cm2/gm showing India’s flyashes to be quite fine. Carbon content in flyash influences the colour, fineness and temperature reactivity of flyash. Chemical Composition: Indian flyash is rich in SiO2, Al2O3, Fe2O3 and unburnt carbon. A typical chemical composition of Indian flyash is given in Table 1. Table 1: Chemical Composition of Indian Flyash: Constituent Percentage SiO2 35 – 62 Al2O3 19 – 28 Fe2O3 4 – 20 CaO 0.6 – 3.0 MgO 0.2 – 3.9 SO3 Trace – 2.5 LOI 0.8 – 15.81 FLYASH UTILIZATIONS: Flyash Bricks: With the fast urban development, the demand for bricks has been increasing, allowing the brick industry to exploit the top soil which is a social crime. In order to meet this demand, the flyash based bricks can be an alternative material to the conventional bricks with the improved engineering properties. In India about 25% of usage of flyash bricks envisaged to consume around 30 - 40 million tones of flyash every year. The various suggested proportions of flyash with sand, clay and lime/cement are given as: Lime based bricks:70 % flyash, 5 - 10 % lime, 20 - 25 % sand. Cement based bricks: 70 % flyash, 10% cement, and 20% sand. Clay bricks: 30 % flyash, 50 % clay, 20 % sand. Typical properties of flyash (flyash + sand + lime + gypsum) bricks and burnt clay bricks are given in Table 2 Properties of fly ash Property Burnt clay brick Flyash brick % Water absorption 21 15 Density (gm/cc) 1.44 1.80 Compressive strength (kg/cm2) 19 -42 58-78 Advantages of flyash based bricks over the conventional bricks. The main advantages of flyash based bricks over the conventional bricks are follows. Uniform and standard product size resulting in 10 % less consumption of bricks per unit constructions. Cement consumption is less in cement mortar. Compressive strength is more than conventional red bricks (>100 kg/cm2). Less load on foundation due to light weight. Due to less water absorption and no weathering effects, surfaces can be left exposed without plastering and direct application of paint is also possible. Construction of Ash Dykes: The constructional methods for an ash dyke can be grouped into three broad categories namely Upstream method, Downstream method and Centerline method. Fig.1 shows the typical configurations of embankments constructed using the different methods. The construction procedure of an ash dyke includes surface treatment of lagoon ash, spreading and compaction and benching. Up Stream Method Downstream Method Center line Method Fig. 1. Typical Ash Dyke Raising Configurations An important aspect of design of ash dykes is the internal drainage system. The seepage discharge from internal surfaces must be controlled with filters that permit water to escape freely and also to hold particles in place and the piezometric surface on the downstream of the dyke. The internal drainage system consists of construction of rock toe, 0.5 m thick sand blanket and sand chimney. After completion of the final section including earth cover the turfing is developed from sod on the downstream slope. Flyash as Fill Material : Large scale use of flyash as a fill material can be applied to replace another material and is therefore in direct competition with that material, flyash itself is used by the power generating company producing the flyash to improve the economics of the overall disposal of surplus flyash and at some additional cost, flyash disposal is combined with the rehabilitation and reclamation of land areas desecrated by other operations. Fills can be constructed as structural fills where the flyash is placed in thin lifts and compacted. Structural flyash fills are relatively incompressible and are suitable for the support of buildings and other structures. Non-structural flyash fill can be used for the development of parks, parking lots, playgrounds and other similar lightly loaded facilities. One of the most significant characteristics of flyash in its use as a fill material is its strength. Well compacted flyash has strength comparable to or greater than soils normally used in earth fill operations. In addition, lignite flyash possesses self-hardening properties, which can result in the development of shear strengths. The addition of illite or cement can induce hardening in bituminous flyash, which may not self-harden alone. Significant increases in shear strength can be realized in relatively short periods of time and it can be very useful in the design of embankments. Sintered light weight aggregates: The sintered light weight aggregates are one of the important constituents of cement. It produced by pyro processing, mining fly ash with water, sintering at 1000 - 13000 C. The product is finely graded into different size fractions for use as part of secondary concrete products such as pre- cast lightweight concrete panels and lightweight blocks. Portland Pozzolana cement: Pozzolana is the clay matter either natural or synthetic, which when ground with lime or clinker and mixed with water, produce cementitious compounds. Portland pozzolana cement should not contain more than 25 % of flyash. It has much lower heat of hydration and is also fairly sulphate resistant. It has all the physical properties of ordinary portland cement (OPC) but has lower shrinkage and can be used for all construction works for which OPC is used. Flyash as Partial Replacement of Cement: The flyash, a pozzolana, that is, a substance although not cementitious itself, has different constituents. This combines with the lime to form a material having cementing properties. Use of flyash in concrete started in the United States in the early 1930’s. An addition of flyash gives economic and ecological benefits in concrete improves its workability which inturn reduces segregation, bleeding, heat evolutions and permeability, inhabits alkali aggregate reaction, and enhances sulphate resistance. Flyash concretes show considerable lower rate of development of compressive strength at early ages. At 28 days and at later ages with 15 and 20 % replacement of cement by flyash exhibits comparable cube compressive strength, split-tensile strength and flexural strength. High Volume Flyash Concrete: The challenge for the civil engineering community in the near future will be to realize projects in harmony with the concept of sustainable development, and this involves the use of high performance materials produced at reasonable cost with the lowest possible environmental impact. The most available supplementary cementing material worldwide is flyash, a by-product of thermal power stations. For considerable increase in the utilization of flyash that is otherwise being wasted and to have a significant impact on the production of cement, it is necessary to advocate the use of concrete that will incorporate large amounts of flyash as a replacement for cement. In 1985, CANMAT developed a concrete incorporating large volumes of flyash that has all the attributes of high performance concrete, that is, one that has excellent mechanical properties, low permeability, superior durability, and that is environmentally friendly. Cellular Light Weight Concrete: Cellular light weight concrete can be manufactured by a process involving the mixing of flyash, cement, coarse sand, fine sand and a foaming agent in a mixer to form thin slurry. This slurry is then poured in moulds and allowed to set. The blocks are then removed from the moulds and are cured by spraying water on the stacks. The bulk density of this product varies from 0.4 - 1.8 gm/cc. These blocks are specially used in high rise construction to reduce the dead weight of the structure. Flyash in Road Projects: Researchers have already been proved about flyash’s suitability in the road construction. A major portion of poor quality of flyash can be used in construction of the embankment of the road. Soil lime flyash stabilization can be done by different technique. Flyash when added to lime gives cementitive properties and can be used to stabilize weak soils. The thickness of lime flyash soil layer for use as sub-base or base course is designed in accordance with IRC: 37 -1984 with a minimum thickness of 150 mm. For determination of the thickness of the stabilized layer, the California Bearing Ratio (CBR) method has to be adopted. The percentage of addition of flyash and lime in the soil can be determined by the test of the specimens. For the construction of the concrete block pavement, a portion of cement can be replaced by flyash. The concrete mix incorporating upto 30 % of flyash in place of ordinary portland cement (OPC) have been utilised and observed the satisfactory result. However, resistance to surface abrasion is lower than the OPC concrete which can be improved by addition of some admixtures. In this way, a huge volume of flyash can be used in the construction of highway systems with economy and the disposal as well as ecological imbalance can be minimised upto certain level. The use of flyash in road projects is shown in Table 3. The construction of first dam in India using Roller Compacted Concrete (RCC) technology with high doses of flyash has been started near Nasik under Ghatghar Pumped Storage Scheme of Irrigation Department, Government of Maharashtra. Approximately 60 –70 % cement is being replaced by flyash. Three dams would be constructed under this project using RCC technology with high doses of fly ash, which includes a major dam of height about 90 m. Table 3 Use of Flyash in Road Projects Sl. No. Type of use Description Performance Taxi track, Pune Air field Satisfactory Cement flyash concrete 1 Taxi track, Palam Air port 1970-71 Satisfactory (wearing course) Near Govt. College Faridabad, Haryana Very satisfactory State transport workshop, Haryana, Satisfactory Lime flyash WBM 1972 Satisfactory 2 (base- course) Talcher Gopal Prasad Kaniha road, Orissa, 1976 -77 Lime flyash concrete DTC bus stop on NH-2 1977-78 -- 3 precast blocks for foot Approach road to NH-2, near CRRI, Satisfactory paths (wearing course) 1977-78 Environmental Impacts: The successful usage of flyash in concrete mix well helps in solving the wide problem of flyash disposal by thermal power plants. The other positive environmental impacts of using flyash are given as: Indian coal has high flyash content resulting in high suspended particulate matter and flyash disposal problems restricting its use. Large scale utilization of flyash can help in proper use of Indian coal. The reduction in demand for OPC production will help in conserving lime stone for future use, otherwise import of limestone /OPC to India will be required in future. Flyash contains very small quantities of heavy metals like arsenic, chromium, selinium, titanium & vanadium that can leach to ground water when disposed on land. When used in concrete mix leaching to ground water can be prevented due to hydration reaction as the heavy metals form immovable complexes in the mix. Due to the usage of flyash in concrete , the production of OPC is minimized .Hence equivalent quantum of co2 release to environment will also be avoided. CONCLUSIONS: The future poses challenges to the scientists, technologists, engineers towards sound management of flyash disposal and deposition technologies. The problem is not due to lack to technical competence but more of adoption, implementation and better management of improved and appropriate technologies. The guideline for all thermal power stations as regards disposal techniques/ strategies should ensure minimum adverse impact on the flora and fauna of a particular place. The attempt should be to consciously reduce environmental damage. To ensure more effective management of flyash in India, the country needs- (i) Guidelines, facilitation and implementation mechanism. (ii) Community participation/ raising consciousness levels of population (iii) Fiscal & Policy support for fly ash users/product manufacturers. (iv) Greater financial allocation for safe disposal & utilization. (v) Enhanced facilitation of indigenous R&D expertise for field applications. Flyash industry to be declared as "priority Industry" for all applicable concessions / support. AKNOWLEDGEMENT: This is referred by Head of the department and other Assistant professors of civil engineering department of D.M.S.S.V.H.College Of Engineering MTM. REFERENCES: 1. Metha, P.K.(1985) Influence of Flyash Characteristics on the Strength of Portland Flyash Mixtures, Cement and Concrete Research, Vol.15, 1985, pp.669-674. 2. Prabhu, C., Perumal, P., and Jeyaprakash, S.K. (2004) Effect of using Flyash in Chemical Admixtures in Plain and Reinforced Concrete Members, Proceedings of the National Conference on Recent Advances in Civil Engineering, PP.395 - 402. 3. Behera, J.P., Sarangi, B., Nayak, B.D., and Ray, H.S.(2000) Investigations on the Development of Blended Cement using Activated Flyash, The Indian Concrete Journal, Vol.74, pp.260 - 263. 4. BIS: 3812 - 1981, Influence of Flyash for use as Pozzolana and Admixture, BIS Standards, New Delhi.
Pages to are hidden for
"Fly Ash"Please download to view full document