Effect of High Molar NaOH Solutions on Fly Ash

It is known that increased swell in soils with alkali solution can occur due to either increased cation exchange capacity and/or due to mineralogical changes. In the recent past lime is known to effectively control alkali induced heave in kaolinitic soils. Thus the efficiency of lime to produce pozzolanic compounds which aid in binding of soil particles increases in alkaline condition. In the search of cost effective pozzolanic materials to control the alkali induced heave, fly ash has gained due attention. Fly ash can be used if it is resistant to alkali and does not produce compounds that cause undesirable swelling. The paper attempts to understand the effect of different concentrations (1M, 2M and 4M) of sodium hydroxide (alkali) solution on the swelling and compressibility of fly ash. The results clearly indicate that no swell is observed with any concentrations of alkali solution even after allowing the samples to interact with alkali solution for longer duration. X-ray diffraction and SEM studies reveal that the pozzolanic compounds that form in fly ash due to alkali interaction can help in inhibiting the swelling. Thus fly ash seems to be a promising material to control the swelling in soils.