Techno-Market Survey on Flyash Bricks

 

Organization of Report

 

The main body of the report is preceded by detailed contents including lists of figures, tables, and annexes followed by units used in the report. This is followed by executive summary giving briefly the scope and objectives of the study, importance of the topic, methodology, limitations, major observations / findings, and recommendations & action plan.

Chapter 1 explains the importance of the topic, scope, methodology of data collection and analysis.
Chapter 2 discusses the properties of fly ash. An overview of the utilization potential of fly ash is presented in
Chapter 3. In chapter 4, the utilization potential of fly ash in construction sector, of which fly ash bricks is a sub-set, is the focus.
Chapter 5 discusses the fly ash brick technologies and
Chapter 6 the specific case studies / projects related to manufacture of fly ash bricks. In some quarters, concerns are being expressed regarding possible radioactive effects of fly ash. Studies are underway in India and some other countries. This aspect is considered in
Chapter 7. Chapter 8 gives the conclusions, recommendations & action plan.

All chapters are preceded by a brief synopsis of the chapter, and key words. The main report is followed by glossary, giving the acronyms and abbreviations used in the report, a listing of all the key words corresponding to various chapters. References which have been used for certain inputs are listed after the key words. Wherever these references have been quoted / data or technical specifications taken in the text, these have been cross-referred by their serial number (appearing as superscripts in the report) in the list of References.



 

Conclusions

  • The total fly ash generation at TPPs by the turn of the century is estimated at about 90 million tonne.
  • Utilization of fly ash while reducing the environmental problems is a resource for value added products.
  • Utilization of fly ash in building materials is of special importance. Considerable short-fall in production of various building materials is anticipated in the near future. The short-fall in the annual production of bricks is expected to be of the order of 25 billion bricks by the turn of the century.
  • The control and information of variability of fly ash properties especially the fineness, carbon content and other chemicals / minerals are necessary for facilitating more specified uses of fly ash.
  • The correlation of the pozzolanic properties of fly ash with its constituents has been established. However, this has not enabled to standardize product or process designs.
  • The technologies for the manufacture of fly ash bricks can be classified into the following main technology routes:
  • Clay – fly ash bricks
  • Red mud – fly ash bricks
  • Sand-fly ash bricks
  • Fly ash – lime bricks
  • Fly ash – lime/gypsum bricks

Advantages of clay-fly ash bricks are:

  • Fuel saving in the range of 15%-35% (coal consumption) or coal saving upto 3-7 tonne per lakh bricks.
  • Drying losses are checked in case of plastic black and red soils. Excessive linear drying shrinkage is reduced.
  • Higher strength.
  • 30-40 tonne of fly ash per lakh bricks can be utilized in case of alluvial soils, and 100-125 tonne per lakh bricks in case of red and black soils.
  • Clay, a valuable and irreplaceable economic resource, is conserved to the extent of 40% by weight.
  • ricks conforming to IS:3102-1976 can be manufactured.
  • Uniformly in shape and size.
  • Comparatively less quantity of cement mortar by 20%-25% is required.
  • Water absorption is 13% to 15% as compared to 20% for conventional bricks.
  • Outside wall plastering could be avoided as these bricks are smooth.
  • Fly ash lime bricks are more resistant to salinity and water seepage.
  • Lower bulk density of fly ash bricks help in minimizing the resultant load on load-bearing walls.

Selection of fly ash brick manufacturing technology should be based on the availability of raw materials, financial strength of the entrepreneur, and the market characteristics (size and nature of applications required for the strength of the bricks / blocks etc.). Clay fly ash brick manufacturing is most suitable for transition with minimum changes from existing practices and manual moulding of bricks which is most common. Red-mud should be used share this industrial waste is available. CBRI technology is welltried and tested. These can also have semi-mechanized operations, but manual operations are most effective cost. Sand-fly ash bricks, which need chemical accelerator, are conductive to manual or semi-mechanized operations. Technologies are available from CBRI, CFRI, AEC, SAIL, NCBM. Fly ash –lime bricks are superior and are more cost effective for semi-mechanized / mechanized operations. NCB, ACC and CBRI technologies are available. Fly ash-lime-gypsum bricks / blocks are very good products giving the highest strength among various bricks. These require relatively higher investment and expensive raw materials to give a range of high strength products. This is most suitable for mechanized operation, though semi-mechanized operations are also possible. AEC, ITC-B, NLC, INSWAREB, Bhanu International have developed technologies which are in operation.

  • Due to transportation cost, the use of fly ash beyond 40-50 km from the TPP becomes uneconomical. Also, appropriate technologies for fly ash handling and transportation are not available.
  • Fly ash of consistent quality and of desired grade is often not available on a long term basis. The difficulty in obtaining the fly ash in dry state from TPPs adds to the problems.
  • Absence of technology transfer efforts and extension services/technological back-up support have rendered fly ash brick technologies unusable.
  • Brick moulders and manufacturers do not readily agree to diversify from the conventional practices without incentives to cover the risks.
  • The indigenous availability of good quality machines like brick press, mould equipment, cutting machines, sintering strand or kiln along with spare parts which are required for large commercial scale production of fly ash based building materials is till not guaranteed. The cost of importing these machineries is very high, which often makes the project economically not viable.
  • When coal is brunt, most of its mineral mater is fused into ash, and majority of its radioactive substances get concentrated in ash. Fly ash applications could lead to irradiating those who may be residing in closed buildings, with fly ash products. This aspect needs a further study. Otherwise, it is quite safe to use fly ash in building construction.                                                                                                                                                                             Back