sufficiently fluid so that it will penetrate and fill all the voids in the 

 aggregate mass, yet he of such consistency that the suspended sand and 

 cementing materials do not settle out. For normal structural work, the 

 ratio of cementitious materials (cement plus pozzolan) to sand should be 

 approximately 1:1. Usually, the proportions of cement to pozzolan are 2:1, 

 although ratios as low as 1:1 and up to 9:1 have been used on various jobs. 

 Occasionally, the pozzolan may be omitted entirely. For a structural grout, 

 it is usually not desirable to exceed a cement to sand ratio of 1:2 by weight 

 because higher ratios produce lower strengths and excessive segregation of 

 sand in the grout mixture may occur. Mix proportions may be determined by 

 Corps of Engineers Specifications CRD C615. 



d. Physical Properties . For structural preplaced aggregate concrete 

 where strength and other physical properties are a consideration, the grout 

 should be proportioned and test specimens, using the contemplated coarse 

 aggregate grading, should be made to determine the grout mix proportions 

 which will produce preplaced aggregate concrete of the required physical 

 properties. Such tests will also provide information as to the quantity of 

 materials needed for the work. Where necessary, the information on physical 

 properties of the structural preplaced aggregate concrete should include 

 strength, resistance to freezing and thawing exposure, modulus of elasticity, 

 drying shrinkage, volume change, or other structural criteria. Physical 

 properties of preplaced aggregate concrete made with a grout containing 

 pozzolan and a fluidifier have been determined and compared with conventional 

 concrete in a number of laboratory tests. This data can be found in pub- 

 lished reports (U.S. Army Engineer, WES, 1954) (U.S. Bureau of Reclamation, 

 1949). 



Compressive strength of concrete with a given maximum size aggregate, 

 grout fluidifier, and pozzolan is slightly lower at 28 days' age than that 

 of conventional concrete containing entrained air and an equal amount of 

 cementing materials. At 90 days' age and later, its strength is equivalent 

 to that of conventional air entrained concrete (U.S. Army Engineer, WES, 

 1954). Concrete containing aluminum powder or a grout fluidifier, and 

 pozzolan develops a higher bond strength with old concrete than does new, 

 conventional concrete. This may be explained because of the greater fluidity 

 of the grout as compared with mortar and the expansion of the grout which 

 develops a slight pressure during the formation of the hydrogen gas. 



e. Placement . 



(1) Foundation Preparation . Foundation preparation is important in 

 underwater placement. For example, if extremely fine material is left on 

 the foundation or in heavy suspension just above the foundation, it will be 

 displaced upward into the aggregate. The dispersed fine material then coats 

 the aggregate or settles and becomes concentrated in void spaces in the 

 aggregate, thus precluding proper intrusion and consolidation. Therefore, 

 all loose fine material must be removed insofar as possible before placement 

 of aggregate. Alternatively, if structural conditions permit, a layer of 

 sand and gravel may be first deposited to serve as a filter bed to prevent 

 contamination of preplaced coarse aggregate. 



(2) Aggregate Placement . Coarse aggregate should be washed and 

 screened immediately before placing in the forms so that it will be surface 



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