cements. However, this grading is uneconomical for most work. Coarse 

 aggregates as large as the largest stones capable of being carried by a man 

 have been used with good results. 



(3) Fine Aggregate . Either crushed or natural sand may be used. 

 However, well-rounded sand grains from a natural source are preferable 

 because such sands require less water to achieve acceptable grout fluidity. 

 The sand should be hard, dense, durable, uncoated rock particles, and of a 

 uniform, stable moisture content. It should conform to current ASTM 

 Standard C33, except with respect to grading. 



(4) Pozzolan . Pozzolan is used to reduce bleeding, to improve 

 fluid properties of the mixture, and to reduce segregation of solid particles. 

 The pozzolan combines with lime liberated during hydration of the cement to 

 form strength producing compounds at later ages. The rate at which pozzolan 

 contributes the heat of hydration is much slower than that of Portland 

 cement. Both natural and manufactured pozzolans have been used, but the 

 pozzolan most generally used and preferred is fly ash conforming to ASTM 

 Standard C618, Corps of Engineers Specification CRD C255. Some pozzolans 

 have caused excessive abrasion of pumping equipment and increased water 

 requirements, so preliminary tests should be made with the selected pozzolan. 



(5) Grout Admixtures . A water-reducing, set-retarding agent, 

 known as a grout fluidifier, is commonly incorporated in the grout mixture 

 to make it more fluid, to reduce the amount of water otherwise required for 

 a given fluidity, to delay setting time for ease in handling with pumping 

 equipment and to promote better penetration of the voids in the coarse 

 aggregate. This agent is customarily a preblended material obtained 

 commercially. It normally consists of a water-reducing agent, a suspending 

 agent, aluminum powder, and a chemical buffer to assure properly timed 

 reaction of the aluminum powder with alkalies in the cement. Reaction of 

 the aluminum powder with alkalies during hydration of the cement generates 

 hydrogen gas which causes expansion of the grout while it is fluid and 

 provides small air bubbles within the grout. Normal dosage of the water- 

 reducing agent in commercially available grout fluidifiers ranges from 0.20 

 to 0.30 percent by weight of cement plus pozzolan. Aluminum powder is 

 normally employed in the range of 0.01 to 0.02 percent by weight of cement 

 plus pozzolan. The fluidifier should be so proportioned that most of the 

 expansion occurs within 3 hours after initial mixing. Preblended grout 

 fluidifiers should conform to Corps of Engineers Specification CRD C619. 



c. Grout Mix Proportioning . Grout material proportions, as in conven- 

 tional concrete practice, are influenced by structural design requirements. 

 Additionally, the grout must be so designed as to flow freely through the 

 voids of the preplaced aggregate without appreciable segregation or water 

 gain so that honeycombing is avoided and an intimate bond between grout and 

 coarse aggregate particles is ensured. The importance of selecting maximum 

 sand size, compatible with void size as determined by coarse aggregate 

 grading, is reflected in Table 26. 



Cement-to-sand ratios employed are commonly in the range of 1:1 to 1:2; 

 although ratios as lean as 1:3 cement to sand have been used. Compressive 

 strength and pumpability requirements limit the amount of sand which can be 

 used in any grout (U.S. Army Engineer, WES, 1954). The grout must be 



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