humid atmosphere if such materials are subject to any stress in the concrete. 

 Exposures in industrial atmosphere may lead to H 2 S concentrations that can 

 cause brittle fracture in the hardware. Metallizing hardware with high 

 corrosion resistant material, by flame or arc application, is an optional 

 method of protecting metal hardware. These failures are generally classi- 

 fied as one form of hydrogen embrittlement which occurs when molecular 

 hydrogen ions are able to enter between the steel molecules. This condition 

 may also develop when dissimilar metals such as aluminum or zinc are used 

 in the vicinity of steel. 



8. Joint Sealing 



a. General. Nearly every concrete structure has joints (or cracks) 

 that must be sealed to ensure its integrity and servicability. It is a 

 common experience that satisfactory sealing is not always achieved. The 

 sealant used or its poor installation usually receive the blame, whereas 

 often there have been deficiencies in the location or the design of the 

 joint that would have made it impossible for any sealant to have done a 

 good job. 



This section shows that, by combining the right sealant with the right 

 joint design for a particular application and then carefully installing 

 it, there is every prospect of successfully sealing the joint and keeping 

 it sealed. This section is a guide to what can be done rather than a 

 recommended practice because in most instances there is more than one 

 choice available. Without specific knowledge of the structure, its design, 

 service use, environment, and the amount to be spent, it is impossible to 

 prescribe a "best joint design" or a "best sealant." The information 

 contained in this guide is, however, based on current practices and experi- 

 ence judged sound by many agencies and organizations. It should therefore 

 be useful in making an enlightened choice of a suitable joint sealing 

 system and ensuring that it is then properly detailed, specified, installed, 

 and maintained. 



b. Rigid Joints and Joining Materials . Prefabricated concrete units 

 require field joining to establish structural continuity of the structure. 

 Grout material proportions, as in conventional concrete practice, are in- 

 fluenced by structural design requirements. Additionally, the grout must 

 be so designed as to flow freely into the joint space or voids without 

 appreciable segregation or water gain so that honeycombing is avoided and 

 intimate bond between the concrete surfaces is assured. Slurries of 

 Portland cement and water, with or without sand, have long been used in 

 the construction industry as a grout for filling cracks, voids, and joints, 

 Later development of epoxy formulations, uniquely suited for use as an 

 adhesive with concrete, lead to their commonly accepted use as concrete 

 grouting and joining material in concrete construction. 



(1) Cement Sand Grouts . Commonly employed grout material propor- 

 tions of cement to sand range from 1:1 to 1:2; although ratios as lean as 

 1:3 have been used. With a 1:3 proportion of cement to sand, the water to 

 cement ratio, by weight, for grout containing sand of average gradation 

 (fineness modulus of 2.75) may be approximately 1:0.9. With lower cement 

 to sand ratios, the w/c would also be lower, which increases the strength 



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