Aerated fiber cement building products and methods of making the same
Disclosed herein are low density fiber cement articles, such as fiber cement building panels and sheets, comprised of multiple overlaying fiber cement substrate layers having small and uniform entrained air pockets distributed throughout. Also disclosed herein are air entrainment systems and methods for manufacturing aerated low density fiber cement panels or sheets with consistent air void content and uniform air void distribution. Also disclosed herein are air entrainment technologies adapted to work in conjunction with the Hatschek process to produce aerated fiber cement articles having controlled air void content and distribution.
1. A building article comprising: a plurality of thin overlaying fiber cement substrate layers, each of said overlaying fiber cement substrate layer is bonded to an adjacent overlaying substrate layer thereby forming a fiber cement matrix wherein the fiber cement matrix comprises an air entrainment agent; and a plurality of closed cell air voids formed by the air entrainment agent that do not form continuous air channels with adjacent voids, the air voids defined by air pockets entrained in the fiber cement matrix such that the air voids are formed directly in the fiber cement matrix with no material separating the air voids from the fiber cement matrix, said air voids being dispersed uniformly throughout the fiber cement matrix to reduce the density of the fiber cement matrix such that the cumulative volume of the air voids is greater than 3% of the volume of the fiber cement matrix, said air voids having an average diameter greater than 20 microns.
2. The building article of claim 1 , wherein the average diameter of the air voids is between 20 microns to 100 microns.
3. The building article of claim 1 , wherein the volume of air voids is between 5% to 20% by volume of the fiber cement matrix.
4. The building article of claim 1 , wherein the density of the fiber cement matrix is between 1.0 to 1.3 grams per cubic centimeter (g/cc).
5. The building article of claim 1 , wherein at least 90% of the air voids are closed-cell.
6. The building article of claim 1 , wherein each overlaying fiber cement substrate layer has a thickness of between 20 to 450 microns.
7. The building article of claim 1 , wherein fiber cement substrate layers comprise cellulose fibers.
8. The building article of claim 1 , wherein the cumulative volume of the air voids is between 5% and 20%.