Of the cost elements in concrete construction, the proportion occupied by formwork will depend on the type of structure and conditions in the field, For ordinary reinforced concrete this proportion is said to be 20 to 30 percent. In comparison, with prepacked concrete, for structures of masive plain concrete such as breakwaters, the cost is 10 to 20 percent, for breskwaters with smaller cross-section 20 to 30 percent and for reinforced concrete structures such as caissons and L-blocks about 30 to 40 percent so that the cost of formwork is relatively higher than for conventional concrete. Another feature about prepacked concrete is that bulging of forms or separation at joints often comprise causes of damaging leakage of mortar. Therefore, it is believed a proper evaluation of pressure acting on forms is an important factor governing the success and economy of the construction project.