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|Title:||Use of self-stressing expansive cements in large sections of grout, mortar, and concrete. Report 1, Pumpable mortar studies|
|Authors:||U.S. Atomic Energy Commission.|
Sandia National Laboratories
United States. Defense Nuclear Agency.
Hoff, G. C. (George C.)
|Publisher:||Concrete Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Technical report (U.S. Army Engineer Waterways Experiment Station) ; C-74-6 rept.1.|
Abstract: Commercially available shrinkage-compensating cements, when used in the proper amounts in concrete, are designed to have a particular expansive potential as determined by laboratory test. In the construction of large sections of grout, mortar, or concrete, such as tunnel plugs and hydraulic structures, where low cement contents are desirable because of thermal and economic considerations and yet where some early and possibly permanent residual (non-thermal) expansions are required, the use of the standard shrinkage-compensating cements to achieve this expansion is often not feasible because the expansive potential of the cement is not adequate to overcome the effects of reduced cement content and the restraint provided by the mass of the section . In an attempt to tailor the expansive potential of a cement to the requirements and size of the section, blends of a self-stressing Type K cement and a low-heat Type II cement were studied. The self-stressing Type K cement was produced to have the greatest possible expansion within the present state-of-knowledge for this type of cement and as such could not be used by itself in an unrestrained or normally restrained cement paste as it would self- destruct. As a fractional portion of a blended cement, it performed satisfactorily, however. The effects of expansive cement content, water content, fine aggregate additions, fly ash, barite, bentonite ( "gel" ), and admixtures on the physical properties of pumpable mortars made with the blended cements were studied and are reviewed. These physical properties include unrestrained and restrained expansions, strength, modulus of elasticity, compressional wave velocity, time of set, and workability. Regarding expansive potential, special emphasis is placed on early volume changes occurring from the time water is added to the mixture. The effects of specimen size and shape on unrestrained expansion were also studied and are related to expansions obtained from standard expansion tests. The expansive potential of a mortar mixture is best described as the expansions that occur starting from a point in time occurring shortly after the mixture reaches its final set as determined from CRD-C 86. By using blends of highly expansive cement and normal portland cement, expansive potentials (restrained) of up to 0.142 percent and 0.222 per cent for normally sanded mixtures and mixtures containing fly ash, respectively, were obtained with total cementitious contents ranging between 850 and 900 lb/yd3 of mortar. With proper proportioning, any reasonable level of expansive potential can be achieved. Fly ash replacements for portions of the Type II cement without changing the amount of expansive ingredients in the mixture tend to cause an increase in expansions. Replacement of portions of the mixture sand with high density barite, in general, does not affect the expansive potential of the mixture. The replacement of up to 25 percent of the cement in a mixture with a highly expansive Type K cement, in general, produces an increase in the values of compressive strength, modulus of elasticity, compressional wave velocity, and expansions over those observed for control mixtures. Sanded mixtures containing bentonite do not experience these increases, however. Replacements of portions of the cement in a mortar mixture with highly expansive Type K cement generally result in reductions in the flowability of the mixture. These replacements do not appear to affect setting times, however. Varying the size and shape of unreinforced elements made with a mixture of a given expansive potential will affect the amount of expansion that element will undergo. Linear measurements on 3-by 6-inch and 10-by 20-inch cylinders indicated that reductions in expansions from 25 to 35 percent occurred when the cylinder size increased. A friction-reducing admixture, a water- reducing admixture, and a water-reducing-retarding admixture were studied. Expansions were not affected by the friction-reducing admixture but were reduced when the other two admixtures were use.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Technical Report|
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|TR-C-74-6-Report-1.pdf||16.1 MB||Adobe PDF|