The Effects of Pressure on the Freeze-Thaw Durability of Fiber-Reinforced Cement Board

摘要

Fiber-Reinforced Cement Board (FRCB) is used in residential construction applications as an alternative to wood for siding, roofing and backerboard products. The material is gaining in consumer popularity because it is more durable than wood products. However, the freeze-thaw resistance of the product is still unknown. Due to its laminated structure, high porosity and cellulose fiber reinforcement, concerns exist about its durability. In an attempt to improve the freeze-thaw durability of FRCB, some manufacturers have started pressing the material after it is formed, thereby expelling excess water and possibly improving the interlaminar bond. The objective of this project is to determine the effects of this pressure on the freeze-thaw resistance of FRCB. FRCB produced by a single manufacturer that were pressed at a range of pressures, and commercially available pressed and nonprossed products were investigated. Materials were subjected to as many as 300 freeze-thaw cycles based on a modified version of ASTM Standard C1185. Mechanical properties, including flexural and Interlaminar Bond (ILB) strength, were measured. In addition, microstructural properties were evaluated using mercury intrusion porosimetry and scanning electron microscopy. The results indicate that, for the FRCB produced by a single manufacturer, pressure treatment improves the flexural and ILB strength, and decreases the porosity. After freeze-thaw cycling, however, pressure treatment appears to improve the ILB strength, but does not affect the flexural strength or porosity of the FRCB. Examination of commercially available pressed and nonpressed products showed that there may be an improvement in performance, but that other factors including board composition and processing parameters are also influential.