GB777318A - Improvements in or relating to a process for pre-stressing concrete and like structures - Google Patents

Abstract

777,318. Reinforced concrete. COYNE, A., and BELLIER, J. Nov. 22, 1955 [Nov. 23, 1954], No. 33439/55. Class 20(4) A stone or concrete structure is prestressed by post-tensioning a stranded cable 3, sealing a portion or portions or the whole of the channel 2 through which the cable passes, injecting liquid cement grout into the sealed space or spaces, allowing excess water to pass through the interstices between the twisted cable strands to the inner parts of the cable from whence it escapes axially. In Fig. 1, the strands at one end of the cable 3 are splayed and bent into loops which are received in a tapered opening 4a in a member 5 which is acted upon by jacks 6. The opening 4a is filled with sand which jams the strands ends and transmits the force of the jacks to the cable. A ring 7 limits the length of the splaying. The required portion of the channel is sealed by cement or plastic plugs 8, 8a. The grout is injected at 9 and, by previously forcing clay, cement paste or mastic into the interstices of the cable strands at the zone of ultimate contact with the plug 8a, the passage of water axially along the cable away from the splayed end is prevented, the water thus passing as indicated by the arrow 12 to the splayed end for discharge. The cable consists of wire wound helically around a central straight rod, which may be pulled out to provide an axial water-escape channel. The inner winding is of opposite hand to the next outer winding and so on. The cement grout pipe 9 may pass through the concrete structure into the side of the channel 2. After the grout has set sufficiently to maintain the tension in the cable, the protruding end of the latter is cut off, and the stump covered by an in situ concrete cap. The member 5 may be modified by having a shouldered cylindrical opening, the smaller diameter being at the bottom. The cable ends may be crimped, instead of looped, and the sand may be replaced by an easily meltable metal or alloy, e.g. lead or tin, or a material easily soluble, e.g. mineral salts soluble in water. This permits the member 5 easily to be cleared of cable ends and jamming material for re-use.