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Methods of concrete repairing-dry packing

The dry pack consists of portland cement, sand passing sieve no:16 (1.19 mm), and water sufficiently enough to hydrate the cement. The dry pack can be used to repair holes with a depth equal or more than the least surface dimension of the repair area. Also, it can be used to fill the holes of cone bolt, core holes, and hols for the injection of the grout. Also, it can be used to fill the area removed for crack repairing. However, the dry pack should not be used to fill the relatively low depressed area in which the lateral restraint cant be achieved. Also, it should not be used to fill the area behind the reinforcement. 


Figure 1

For dry packing, the holes should be sharp and square at the surface of the member. The interior shape of the holes should be rounded, especially when the water-tightness is required. The interior of the holes should be cleaned and roughened with steel-wire rope to ensure good bonding of the dry pack.

The dry pack can be prepared by mixing one part of cement with 2.5 parts of sand passing sieve no:16. The added water should be reasonably enough to allow the hydration of cement. Excessive water can result in excessive shrinkage. The water content should be sufficient to ensure that the dry packing will just stick and will become rubbery when solidified. The lesser amount will result in an unsound dry pack. While a greater amount of water will cause excessive shrinkage and loose of repair. 

Before applying the dry pack, we should ensure that the hole is clean and free from dirt or loose aggregates. The bond between the dry pack and existing concrete can be improved by applying mortar or grout coating to all surfaces of the hole. The mix of bonding grout will be prepared by mixed  1:1 cement and fine sand to a fluid consistency. The bonding grout should be applied to all surfaces of the hole, then the dry packing should be done before the bonding grout gets dry. The presoaking of the hole with wet rags or burlap will reduce the loss of hydration water. Another method of improving the bonding strength can by the use of bonding agents. Epoxy bonding resin can be used for this purpose. The surface of the concrete should be dried before applying the bonding agent. the bonding agent should be applied thoroughly, and an excessive bonding agent should be removed. Then the dry packing should be applied immediately. 

The dry packing should be applied on layers to ensure proper compaction. Thicker layers will not be compacted at the bottom. The compaction of each layer can be done by striking a hardwood dowel or stick with a hammer, as shown in figure no:2. Hardwood sticks are used in preference to metal bars because the latter tend to polish the surface of each layer and, thus, make bonding less certain and filling less uniform. Much of the tamping should be directed at a slight angle and toward the sides of the hole to ensure maximum compaction in these areas. The holes should not be overfilled; finishing may usually be completed at once by laying the flat side of a hardwood piece against the fill and striking it several good blows with a hammer. Dry packing should be cured for 14 days. 


Figure 2

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