| 摘要 |
A core for providing noncylindrical passages in long concrete slabs comprise a multi-channel molding of laterally expansible material. A core of suitable length is provided with one or more cylindrical passages for receiving compressed air for lateral expansion purposes. The core section itself may be generally oval with flattened top and bottom faces. In addition to the cylindrical passages for inflation by air, one or more supplemental open air passages for the entire core length are provided. The shape, sectional area and orientation of such supplemental open air passages function to direct over-all lateral expansion of the molding, to maintain substantial congruence between the expanded and normal core shapes.
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