Method for producing fiber reinforced cementitious slurry using a multi-stage continuous mixer

A continuous method for preparing cement composite slurry comprising the steps of:

• feeding a dry cementitious powder into a horizontal continuous fiber-slurry mixer through at least one dry cementitious powder inlet port;
• the horizontal continuous fiber-slurry mixer comprising
• a horizontally oriented elongated mixing chamber, the elongated mixing chamber defined by a horizontal housing having an interior side wall, the elongated mixing chamber having an upstream end feed section, a first mixing section, and a second downstream end mixing section, wherein the first mixing section is between the upstream end feed section and the second downstream end mixing section,
• at least a pair of horizontally oriented intermeshing self-wiping impellers traversing from an upstream end of the elongated mixing chamber to a downstream end of the elongated mixing chamber and rotating within the elongated mixing chamber,
• wherein each horizontally mounted impeller within the upstream end feed section of the elongated mixing chamber comprises an auger, wherein the dry cementitious powder is fed into the upstream end feed section of the elongated mixing chamber and conveyed by the auger to the first mixing section,
• feeding a liquid stream comprising water into the elongated mixing chamber of the continuous fiber-slurry mixer through at least one liquid stream inlet port downstream of the at least one dry cementitious powder inlet port and mixing the dry cementitious powder and the liquid stream in the first mixing section to form a cementitious slurry;
• wherein each horizontally mounted impeller within the first mixing section comprises a first plurality of mixing paddles mounted on a horizontally oriented shaft of the impeller at regular intervals and different circumferential locations, the paddles rotated about the horizontally oriented shaft within the horizontal housing, the paddles extending radially from the shaft,
• feeding a stream of reinforcement fibers through at least one reinforcement fiber inlet port into the second mixing section, and mixing the cementitious slurry and the reinforcement fibers in the second mixing section to form a fiber-slurry mixture,
• wherein at least a portion of each horizontally mounted impeller within the second mixing section of the elongated mixing chamber comprises at least one member selected from the group consisting of:
• an auger, and
• a second plurality of mixing paddles mounted on the horizontally oriented shaft of the fiber-slurry mixer at regular intervals and different circumferential locations, the paddles rotated about each respective horizontally oriented shaft within the horizontal housing, the paddles extending radially from the respective shaft,
• discharging the fiber-slurry mixture directly from the second downstream end mixing section of the fiber-slurry mixer laterally relative to the horizontal housing through an opening in the sidewall of the horizontal housing into and through a fiber-slurry mixture outlet port on the horizontal housing at a downstream end portion of the second mixing section,
• wherein the cementitious slurry and fibers are mixed in the elongated mixing chamber of the horizontal continuous fiber-slurry mixer for an average mixing residence time of about 5 to about 240 seconds while the rotating paddles apply shear force, wherein each said horizontally oriented shaft rotates at 30 to 450 RPM during mixing, to produce a uniform fiber-slurry mixture,
• wherein the fiber-slurry mixture discharged from the fiber-slurry mixer has a slump of 4 to 11 inches as measured according to a slump test using a 4 inch tall and 2 inch diameter pipe and a viscosity less than 45000 centipoise when measured using a Brookfield Viscometer, Model DV-II+ Pro with Spindle HA4 attachment running at 20 RPM speed.