Extruded fiber reinforced cementitious products having wood-like properties and ultrahigh strength and methods for making the same

A method of manufacturing a cementitious composite product having properties suitable for use as a substitute for wood lumber, comprising:

• mixing together water, fibers and a rheology-modifying agent to form a fibrous mixture in which the fibers are substantially homogeneously dispersed;
• adding hydraulic cement to the fibrous mixture to yield an extrudable cementitious composition having a plastic consistency and which includes the rheology-modifying agent at a concentration from about 0.1% to about 10% by wet volume, and fibers at a concentration greater than about 5% by wet volume;
• extruding the extrudable cementitious composition into a green intermediate extrudate having a predefined cross-sectional area, the green extrudate being form-stable upon extrusion and capable of retaining substantially the cross-sectional area so as to permit handling without breakage;
• heating the green extrudate to a temperature of from greater than 65° C. to less than 99° C. to allow curing of the hydraulic cement.

A cementitious composite product for use as a lumber substitute, the product comprising:

• a cured cementitious composition comprised of a hydraulic cement, a rheology modifying agent, and fibers substantially homogeneously distributed through the cured cementitious composition and included in an amount greater than about 10% by dry volume of the cured cementitious composition, said cured cementitious composition characterized by a flexural strength of at least about 1500 psi, and prepared by a process comprising:
• mixing together water, fibers and a rheology-modifying agent to form a fibrous mixture in which the fibers are substantially homogeneously dispersed;
• adding hydraulic cement to the fibrous mixture to yield an extrudable cementitious composition;
• extruding the extrudable cementitious composition into a green intermediate extrudate having a predefined cross-sectional area, the green extrudate being form-stable upon extrusion and capable of retaining substantially the cross-sectional area so as to permit handling without breakage;
• heating the green extrudate to a temperature of from greater than 65° C. to less than 99° C. to allow curing of the hydraulic cement.