Process of improving the strength of existing concrete support columns

In a vertically-oriented column, having a base end resting on a supporting surface and an upper end spaced thereabove in contact with an overhead load, to provide support thereto, a process of strengthening the column to increase its ability to withstand increased physical loading accompanying an earthquake, comprising the steps of:

• a) defining a work area by spaced-apart upper and lower marginal edges arranged circumferentially about the column and over the surface thereof, to which said strengthening is to be accomplished;
• b) forming at least one vent channel in the surface of the column extending from within said work area upward above said upper marginal edge;
• c) forming at least one injection channel in the surface of the column extending from within said work area downward below said lower marginal edge;
• d) applying a flexible, liquid-impermeable membrane against the surface of the column over said work area and sealing same to form a liquid-impermeable barrier surrounding the entire column between said upper marginal edge and said lower marginal edge of said work area;
• e) inserting injection means in said injection channel between the surface of the column and said membrane including one end extending outward therefrom;
• f) inserting vent means in said vent channel between the surface of the column and said membrane including one end extending outward therefrom;
• g) overwrapping said membrane with at least one layer of high-strength, stretchable fibers wherein said fibers are oriented at an angle with respect to the vertical axis of the column;
• h) applying over said layer of fibers, a layer of hardenable material, having a tensile elongation at least as great as the tensile elongation of said fibers and being capable of expanding and stretching with said fibers, and hardening said layer to form a hard shell over said fibers and said work area;
• i) applying pressure-retaining means circumferentially about the column over said layer of hardened material adjacent said upper and said lower marginal edges of said work area to form a pressure-retaining area over said work area;
• j) injecting a quantity of a hardenable, low-shrinkable liquid material in through said injection means, between the surface of the column and said membrane over said work area, in an amount sufficient to fill the area therebetween and simultaneously exhaust any air trapped between said membrane and the surface of the column;
• and,
• k) closing said vent means, after exhaustion of all air trapped between said membrane and the column, and continuing to inject a further quantity of said material under pressure in an amount sufficient to cause said fibers to undergo about 1/2% to about 4% elongation.