To obtain a concrete, a mortar, etc. having high water absorption, high water retention and low shrinkage in excellent workability by incinerating a pulp sludge at a high temperature to give a burned ash and adding it to a hydraulic substance.

A pulp sludge is incinerated at a high temperature to give a burned ash, which is added to a hydraulic substance to form a modified material of a hydraulic substance. The ratio of the hydraulic substance and the burned ash is preferably 99:1 to 50:50, more preferably 70:30. A burned ash having ≤1%, unbaked carbon is preferable as the burned ash. Since a burned ash is different from sand which has been used as an aggregate, does not release water absorbed once, a produced concrete and a mortar board have a slight shrinkage and high adhesiveness and strength and excellent moldability.