Shrinkage-compensating concrete

Abstract

A shrinkage compensating concrete does not require restraint. The expansive forces developed during hydration compensate for concrete shrinkage, obviating the need for any added internal or external restraint element. Using this new shrinkage compensating concrete, substantially crack-free slabs may be built without using restraining steel bars, fibers, or other separate restraining element. The shrinkage compensating concrete includes a cement that develops internal expansive forces that never exceed the tensile strength of the concrete, such that the internal expansion compensates for the concrete shrinkage. The expansive cement may be an ASTMS, M or S cement, or other expansive cements may also be used.

1 . A shrinkage-compensating mortar, comprising:
 a hydraulic cement;   an expansive additive;   sand;   water; and   substantially no internal restraint in the mortar.   
     
     
         2 . The mortar of  claim 1  wherein expansive forces developed during hydration compensate for shrinkage, obviating the need for internal or external restraint. 
     
     
         3 . The mortar of  claim 2  wherein internal expansive forces are at all times lower than its tensile strength, such that internal expansion compensates for shrinkage, resulting in shrinkage-compensation without the need for reinforcement. 
     
     
         4 . The mortar of  claim 1  wherein the expansive cement is an ASTM Type K cement. 
     
     
         5 . The mortar of  claim 1  wherein the expansive additive comprises an expansive cement. 
     
     
         6 . The mortar of  claim 5  wherein the expansive cement comprises an oxide or sulfate that expands upon hydration. 
     
     
         7 . The mortar of  claim 6  wherein the expansive cement comprises calcium sulfoaluminate. 
     
     
         8 . The mortar of  claim 7  having an expansion exceeding the limits of ASTM C 845. 
     
     
         9 . The mortar of  claim 7  wherein the hydraulic cement comprises Portland cement. 
     
     
         10 . A shrinkage-compensating mortar, comprising:
 a hydraulic cement;   an expansive additive including an ASTM Type K cement;   sand, water, and   substantially no internal restraint in the mortar.   
     
     
         11 . The mortar of  claim 10  wherein the expansive additive comprises an oxide or sulfate that expands upon hydration. 
     
     
         12 . The mortar of  claim 11  wherein the expansive cement comprises calcium sulfoaluminate. 
     
     
         13 . The mortar of  claim 12  wherein expansive forces developed during hydration compensate for shrinkage, obviating the need for internal or external restraint. 
     
     
         14 . The mortar of  claim 13  wherein internal expansive forces are at all times lower than its tensile strength, such that internal expansion compensates for shrinkage, resulting in shrinkage-compensation without the need for reinforcement. 
     
     
         15 . The mortar of  claim 12  having an expansion exceeding the limits of ASTM C 845. 
     
     
         16 . The mortar of  claim 10  wherein the hydraulic cement comprises Portland cement.