PURPOSE: To prevent the solidification and to store for a long period by incorporating at least one kind of glyconic acid or sodium glyconate into coal combustion ash from a dust coal burning boiler.

CONSTITUTION: A mixture of a prescribed ratio quantity of sodium glyconate or glyconic acid and water is added to the coal combustion ash. As the addition quantity in this case, for example 300g-10kg for one ton coal combustion ash, namely 300ppm-1% is preferred. While sufficient solidification preventive effect for relatively weak solidification combustion ash is given at 100-300ppm, the effect is insufficient for strong solidification combustion ash. For use to the combustion ash at ≥1% no adverse effect is exerted but a problem at the cost remains. Without mixing the chemical with water, it may be sprayed in power form or in liquid form as it is.