为适应当前以钢带木的形势需要,北京市西城区房管局器材加工厂试制生产了预应力混凝土门框、前窗框、窗扇、后窗框、窗扇等五种规格产品。主要原料是用425号(老标号500号)水泥和中砂及少量5毫米以下的小豆石配成300号混凝土(配合比为1:1.5)。所用的钢筋 In order to adapt to the current situation of steel strip wood, the Xicheng District Housing Authority’s equipment processing plant has produced five kinds of pre-stressed concrete frames, front window frames, sashes, rear window frames and sashes. The main raw materials are No. 425 (old No. 500) cement and medium sand, and a small amount of small dolites less than 5 mm to form No. 300 concrete (the ratio is 1:1.5). Used steel bars