Hollow Concrete Walls

From Swikipedia

Introduction

Hollow concrete walls are walls made of concrete which are made hollow and strengthened by twisted steel rods, sometimes called the Ransome system of concrete construction. This form of construction has the advantage of great strength, as the twisted rods tie the walls together in all directions, while the shape of the wall gives stability without waste of material. It is also superior to hollow-brick walls, as practically no moisture will pass through the concrete withes. The average cost per square foot of exterior surface, in a large building so constructed, is about 25 cents.

References:

http://chestofbooks.com/architecture/Building-Construction-V2/Hollow-Concrete-Walls.html