Fundamental Propertiesof Fly Ash

The fly ash produced in the thermal power plants of China amounts to 50 million tons per year, and only one-fifth of which has been utilized. Thorough investigation of the fundamental properties of fly ash is important for solving geotechnical problems related to the disposal and utilization of fly ash,. Comparisons of chemical, physical and engineering properties of fly ash at home with those aborad arc presented. Some special aspects are as follows:The patterns of sedimentation of fly ash in lagoons are described as the variations of particle size and bulk density with distance and depth;The difference of coefficients of uniformity and roundness of particles between the fly ash in silo and in lagoon is discussed;The required compaction density determined by proctor compaction test may not be consistent generally with those determined by required relative density;The permeability of various flyashes varies within a narrow range;The ratio of coefficient of permeability of fly ash along horizontal direction to that along vertical direction ranges between 2 and 6 ;Requirements for the filters to protect fly ash slurry are higher than those in compacted soils;The engineering properties of fly ash are getting better with time because of the pozzolanic action. If the fly ash is immersed under water it's engineering properties might not worsen.The dynamic shear moduli of fly ashes are about 30-60% moduli of sands at same relative density. But the modulus attenuation with strain and the damping ratio for fly ashes are similar to that for sands.The saturated loose fly ash is liable to liquefaction under dynamic or static load. However, its cyclic strength is similar to that of sands with same grain size. The aging effects on the dynamic properties of fly ash are important, especially for the fly ash coming directly from silo.