tory mortar specimens have been reported for additions of 1 percent by 

 weight of the cement of lithium salts and for additions of about 2 to 7 

 percent of certain barium salts. Moderately reduced expansions were also 

 obtained with certain protein air-entraining admixtures and with some 

 water-reducing, set-retarding admixtures. It was found that some of these 

 substances were more effective in reducing expansion than others. The 

 results reported are limited and further work is needed. There is some 

 evidence that expansions due to alkali-aggregate reaction are slightly 

 lowered by air entrainment and the use of low alkali cement. 



(8) Expansion Admixtures . Admixtures, which during the hydration 

 period of concrete or grout expand themselves or react with other con- 

 stituents of the grout to cause expansion, are used to minimize the effects 

 of dry shrinkage. They are used in both restrained and unrestrained 

 placement. The most common admixtures for this purpose is finely divided 

 iron and chemicals to promote oxidation of the iron. This use is generally 

 limited to relatively small projects. Expansive cements are most often 

 used on large projects. 



(9) Shrinkage Preventing Admixtures . Three different shrinkage- 

 compensating cements are described in ASTM Standard C845 and are designated 

 as Type K, Type S, and Type M. The expansion of each of these cements when 

 mixed with sufficient water is due principally to the formation of ettrin- 

 gite. Most shrinkage-compensating cements consist of constituents of 

 conventional port land cement with added sources of aluminate and calcium 

 sulfate. The three types of expansive cements differ from each other in 

 the form of the aluminate compounds from which the expansive ettringite is 

 developed. The principal constituents of these cements are: 



(a) Type K Portland cement, calcium sulfate, and Portland-like 

 cement containing anhydrous tetracalcium trialuminate sulfate; 



(b) Type M Portland cement, calcium sulfate, and calciumaluminate 

 cement; and 



(c) Type S Portland cement high in tricalcium aluminate and 

 calcium sulfate. 



An important requirement is the selection of material proportions so 

 that the Ca, S 3 , and especially the AI2O3 become available for ettringite 

 formation during the appropriate period after the mix water is added. 

 Determination of these proportions should be based on test results in 

 accordance with ASTM Standard C806. 



(10) Bond Improvement Admixtures . Bonding admixtures are water 

 emulsions of several organic materials that are mixed with Portland cement 

 or mortar grout for application to an old concrete surface just prior to 

 placing topping or patching mortar or concrete, or are mixed with the 

 topping or patching material . Common bonding admixtures are made from 

 polymers that include polyvinyl chloride, polyvinyl acetate, acrylics, and 

 butadiene-styrene copolymer. Bonding agents usually cause entrainment of 

 air and a sticky consistency in grout mixtures. 



(11) Penetration and Plasticity Admixtures . Admixtures which 

 improve the ability of freshly mixed concrete and grout to penetrate into 

 voids and cracks also increase the plasticity of the mix. The degree of 



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