3-mode blended fibers in an engineered cementitious composite
Disclosed herein are fiber reinforced cement composite materials incorporating a 3-mode fiber blend that includes cellulose pulp and synthetic fibers in a ratio selected to provide the composite material with improved water absorption characteristics and the same or improved mechanical properties as compared to equivalent composite materials reinforced with predominantly or all cellulose fibers. Also disclosed herein are fiber blends comprised of a combination of cellulose fibers and polypropylene fibers adapted to reinforce cementitious composite articles manufactured by the Hatschek process and autoclave cured.
1. A fiber cement composite material, comprising:
about 10%-80% by weight cementitious binder;
about 20%-80% by weight silica;
about 0%-50% by weight density modifier;
about 0%40% additives; and
about 0.5%-20% by weight of a 3 mode fiber blend that comprises refined shorter cellulose fibers, unrefined cellulose fibers, and long polypropylene fibers, wherein the average length of the refined shorter fibers is less than the average length of the unrefined cellulose fibers, and wherein the average length of the long polypropylene fibers is greater than the average length of the unrefined cellulose fibers.
2. The fiber cement composite material of claim 1 , wherein the polypropylene fibers have an average length of between 6 mm-10 mm.
3. The fiber cement composite material of claim 1 , wherein the polypropylene fibers are engineered with a hydrophilic surface and a hydrophobic bulk part.
4. The fiber cement composite material of claim 1 , wherein the percent by weight ratio of the cellulose fibers to the polypropylene fibers is between 3 to 24.
5. The fiber cement composite material of claim 1 , wherein the fiber blend comprises about 60% to 80% refined shorter cellulose fibers having an average length of less than or equal to 2 mm, about 10% to 25% unrefined cellulose fibers having an average length of between 2 to 3 mm, and about 10 to 25% long polypropylene fibers having an average length between 4 to 15 mm.
6. The fiber cement composite material of claim 1 , wherein said material having a moisture movement (MM) of less than 0.5%.
7. The fiber cement composite material of claim 1 , wherein the moisture movement of the composite material is at least 25% less than that of an equivalent fiber cement composite material containing no synthetic fibers.
8. A fiber reinforced cement composition, comprising:
a hydraulic binder;
aggregates;
cellulose fibers comprising refined shorter cellulose fibers and unrefined cellulose fibers; and
polypropylene fibers, said polypropylene fibers having irregular forms, wherein the ratio of the percent by weight of cellulose fibers to polypropylene fibers is between 3 to 24.
9. The fiber reinforced cement composition of claim 8 , wherein the composition comprises about 4% to 6% by weight cellulose fibers and about 0.25% to 1.25% polypropylene fibers.
10. The fiber reinforced cement composition of claim 8 , wherein the ratio of the weight ratio of the refined shorter cellulose fibers to the unrefined cellulose fibers is between 2.4 to 8.