epoxy concrete. Epoxy grouts or mortars usually consist of four to seven 

 parts of aggregate (by weight) to one part of binder. 



The ease and effectiveness of epoxy application is greatly influenced 

 by the temperature of surfaces on which the epoxy compound is applied. 

 Commonly available epoxy compounds in use today react most favorably when 

 temperatures are in the range of 16 to 38 Celsius (60 to 100 Farenheit) . 

 If temperatures below 16 Celsius but above 5 Celsius exist, application 

 of epoxy compounds can be accomplished provided a compound is formulated 

 for use within this range and an increased hardening period is not objection- 

 able. At temperatures above 32 Celsius (90 Farenheit) difficulties may 

 be experienced in application owing to acceleration of the reaction and 

 hardening rates. 



c. Flexible Joint Requirements . 



(1) Why Joints are Necessary . Concrete is normally subject to 

 changes in length, plane or volume caused by changes in its moisture 

 content or temperature, reaction with atmospheric carbon dioxide, or by the 

 imposition or maintenance of loads. The effect may be permanent contrac- 

 tions due to, for example, initial drying shrinkage, carbonation, and 

 irreversible creep. Other effects are cyclical and depend on service 

 conditions such as environmental differences in humidity and temperature or 

 the application of loads and may result in either expansions or contrac- 

 tions. In addition, abnormal volume changes, usually permanent expansions, 

 may occur in the concrete due to sulphate attack, reactions between alkali 

 (from the cement) and certain aggregates, and other causes. 



The results of these changes are movements, both permanent and transient, 

 of the extremities of concrete structural units. If, for any reason, con- 

 traction movements are excessively restrained, then cracking may occur 

 within the unit. The restraint of expansion movements may result in 

 distortion and cracking within the unit or crushing of its ends and the 

 transmission of unanticipated forces to abutting units. In most concrete 

 structures these effects are objectionable from a structural or an appearance 

 viewpoint. One means of minimizing these effects is to provide joints at 

 which movement can be accommodated without loss of integrity of the struc- 

 ture. 



There may be other reasons for providing joints in concrete structures. 

 In many buildings the concrete serves to support or frame curtain walls, 

 cladding, doors, windows, partitions, mechanical and other services. To 

 prevent development of distress in these it is often necessary for them to 

 move to a limited extent independently of overall expansions, contractions 

 and deflections occurring in the concrete. Joints may also be required to 

 facilitate construction without serving any structural purpose. 



(2) Why Sealing is Needed . The introduction of joints creates 

 openings which must usually be sealed in order to prevent passage of gases, 

 liquids, or other unwanted substances into the openings or through them. 



In buildings, it is important to prevent intrusion of wind and rain. In 

 tanks, most canals, pipes, and dams, joints must be sealed to prevent the 

 loss of contents. Moreover, in most structures exposed to the weather the 

 concrete itself must be protected against the possibility of damage from 



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