Method and apparatus for forming longitudinal joints in concrete

Abstract

A method and apparatus for forming a longitudinal joint in a concrete surface. A vertical knife is mounted on a concrete slip-forming machine and extends to a predetermined depth in the concrete surface. As the knife is pulled through the formed concrete by the machine, aggregate or reinforcing fibers are deflected to either side of the knife. An aggregate- or fiber-free strip of concrete paste fills in the gap behind the knife creating a weakened zone which acts to constrain the formation of cracks in the concrete surface to the formed joint. The longitudinal joint in the roadway is formed without sawing, cleaning, or sealing and does not require maintenance.

1 . A method for forming a longitudinal joint during a concrete forming operation, comprising the steps of: 
 (a) pulling an upright knife through plastic concrete that has been at least partially formed into a surface;    (b) creating a strip of aggregate-free concrete paste by deflecting aggregate in the concrete to either side of the knife; and    (c) allowing the concrete paste to cure thereby forming a weakened strip in the roadway which constrains crack formation in the surface to the path of the knife.    
   
   
       2 . A method as defined in  claim 1 , further comprising the step of vibrating the knife to assist in deflection of the aggregate to either side of the knife.  
   
   
       3 . A method as defined in  claim 1 , further comprising the step of smoothing the concrete surface adjacent either side of the joint formed by the knife.  
   
   
       4 . Apparatus for forming a longitudinal joint in a concrete surface being formed by a concrete slip-forming machine, comprising: 
 (a) a knife member mounted on the machine; and    (b) a knife extending downwardly from the trowel through the surface of the concrete to a predetermined depth;    (c) wherein the machine pulls the knife through the concrete to deflect aggregate to either side of the knife creating a strip of aggregate-free concrete paste which, upon curing of the concrete forms a weakened zone which constrains the formation of a crack comprising a longitudinal joint in the concrete surface.    
   
   
       5 . Apparatus as defined in  claim 4 , further comprising a vibrator mounted on the knife member to assist in deflecting the aggregate to either side of the knife.  
   
   
       6 . Apparatus as defined in  claim 4 , further comprising a float for smoothing the concrete surface to either side of the formed joint.  
   
   
       7 . Apparatus as defined in  claim 4 , wherein the knife comprises a leading edge that is sloped relative to horizontal between about 20 degrees and about 80 degrees.  
   
   
       8 . A method for forming a longitudinal joint during a fiber-reinforced concrete forming operation, comprising the steps of: 
 (a) pulling an upright knife through plastic concrete that has been at least partially formed into a surface;    (b) creating a strip of fiber-free concrete paste by deflecting fibers in the concrete to either side of the knife; and    (c) allowing the concrete paste to cure thereby forming a weakened strip in the roadway which constrains crack formation in the surface to the path of the knife.    
   
   
       9 . Apparatus for forming a longitudinal joint in a fiber-reinforced concrete surface being formed by a concrete slip-forming machine, comprising: 
 (a) a trowel mounted on the machine; and    (b) a knife extending downwardly from the trowel through the surface of the concrete to a predetermined depth;    (c) wherein the machine pulls the knife through the concrete to deflect fibers to either side of the knife creating a strip of fiber-free concrete paste which, upon curing of the concrete forms a weakened zone which constrains the formation of cracks in the concrete surface to the path of the knife.