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 concrete material, comprising:
 a hydraulic cement;   an expansive additive;   aggregate;   water; and   substantially no internal restraint in the material.   
     
     
         2 . A shrinkage-compensating concrete structure, comprising:
 a hydraulic cement;   an expansive additive;   aggregate;   water; and   with the structure having substantially no internal restraint.   
     
     
         3 . The concrete structure of  claim 2  wherein the structure comprises a slab. 
     
     
         4 . The concrete structure of  claim 2  wherein expansive forces developed during hydration compensate for concrete shrinkage, obviating the need for internal or external restraint. 
     
     
         5 . The concrete structure of  claim 2  wherein the concrete develops internal expansive forces which at all times are lower than its tensile strength, such that the internal expansion compensates concrete shrinkage, resulting in a shrinkage-compensation without the need for reinforcement. 
     
     
         6 . The concrete structure of  claim 2  wherein the expansive cement is an ASTM Type K cement. 
     
     
         7 . The concrete structure of  claim 2  wherein the expansive additive comprises an expansive cement. 
     
     
         8 . The concrete structure of  claim 7  wherein the expansive cement comprises an oxide or sulfate that expands upon hydration. 
     
     
         9 . The concrete structure of  claim 8  wherein the expansive cement comprises calcium sulfoaluminate. 
     
     
         10 . The concrete structure of  claim 2  wherein the aggregate comprises sand. 
     
     
         11 . The concrete structure of  claim 3  with the expansive additive comprising an expansive cement such that the expansive forces developed during hydration compensate concrete shrinkage, obviating the need for restraint and resulting in a substantially crack-free slab. 
     
     
         12 . A concrete slab comprising:
 a cement developing internal expansive forces in the concrete that at all times are lower than the tensile strength of the concrete, such that internal expansion of the concrete compensates for shrinkage of the concrete, resulting in a shrinkage compensating slab without the need for infernal reinforcement.   
     
     
         13 . A method for placing substantially crack-free slabs of concrete, comprising:
 mixing an expansive cement with hydraulic cement, water and aggregate, with expansive cement causing expansion which compensates for shrinkage of the concrete, and with the concrete having no internal restraint or reinforcement.   
     
     
         14 . The method of  claim 13  wherein the concrete slab contains no metal bars or fibers. 
     
     
         15 . A shrinkage-compensating concrete or mortar provided substantially without internal restraint, in which the tensile strength of the concrete or mortar exceeds the expansive forces in the concrete or mortar. 
     
     
         16 . A self-leveling hydraulic cement-based topping, comprising:
 a hydraulic cement;   sand;   water; and   an expansive additive, resulting in a shrinkage-compensating, crack-free topping having no internal restraint.   
     
     
         17 . A method for placing a substantially crack-free self-leveling floor, comprising:
 mixing an expansive additive with a self-leveling topping composition and applying the composition onto a floor;   with shrinkage of the composition as it dries off set by expansion of the composition caused by the expansive additive; and   with the with the self-leveling floor having no internal reinforcement and no internal restraint.