Final Report: Rice Husk: A Sustainable Building Material for the PhilippinesEPA Grant Number: SU836126
Title: Rice Husk: A Sustainable Building Material for the Philippines
Investigators: Tam, Kawai , Rust, Michael , Mathaudhu, Suveen
Institution: University of California - Riverside
EPA Project Officer: Page, Angela
Project Period: September 1, 2015 through August 31, 2016
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2015) RFA Text | Recipients Lists
Research Category: P3 Awards , Pollution Prevention/Sustainable Development , Sustainability , P3 Challenge Area - Built Environment
In 2013, a 7.1-magnitude earthquake struck Bohol Island in Central Visayas, Philippines, destroying thousands of structures and displacing over 350,000 Boholanos. In response, the International Deaf Education Association (IDEA), a local non-governmental organization (NGO), built homes using coconut lumber, plywood, and bamboo. While these homes are only intended to be a temporary solution, they are unable to last for the projected 5 years. Instead, within two years of being built, IDEA’s homes are deemed uninhabitable due to extensive termite damage. Termites pose a great threat to the 12′ × 16′ coconut wood homes, and rebuilding them every few years puts a strain on materials, workers, and their limited budget. Realizing the need for an inexpensive, sustainable, structurally-sound, and termite resistant building material, IDEA reached out to our design team to find a solution.
As the seventh largest rice-producing country in the world, the Philippines generates an abundance of rice husk, a termite resistant waste product from the rice milling process that is incinerated once discarded. Our team, Husk-to-Home, intends to capitalize on this termite resistance and design a rice husk composite board with properties relevant to the Philippines’ needs: lightweight boards with strength and stiffness that will prevent side-swaying and resist forces due to earthquakes ; water resistivity which will help structures withstand humidity and tropical storms; and termite resistance that will keep structures durable and free of pests. Huskto-Home plans to innovate rice husk composite boards by using inexpensive, accessible materials, minimal machinery, and a simple production process. The project’s mission is to create a proof of concept building material, composed of rice husks and an innovative formaldehyde-free binder, to construct long-lasting homes for the Bohol Island community.
In addition to creating an environmentally-friendly building material out of waste products, Husk-to-Home formed goals to source their materials locally and partner with IDEA to facilitate implementation. Following implementation in Bohol, the team hopes to make this inexpensive, formaldehyde-free building material available throughout all of the Philippines and other rice producing countries.
The research and development of the previous team resulted in rice husk particleboard using several bio-based adhesives, the most promising of which were tannin and corn starch or casein based boards. Board manufacturing was done using a small grinder and a hydraulic hot press. The prototypes were tested for their mechanical strength by evaluating their flexural strength. Flexural tests were conducted on 8′′ × 1.5′′ × 0.5′′ board pieces using an American Society for Testing Materials (ASTM) standard three-point bend test using an Instron 1000 mechanical tester. The results were promising, but showed that there was room for improvement in the optimization phase. The tannin and corn starch bio-adhesive rice husk particleboard had a flexural strength of 24.17 lbf while the casein board’s flexural strength was 7.89 lbf. The main challenge regarding the casein board was improving the mechanical strength, which is absolutely necessary for any building material. The strength of the casein bio-adhesive was improved by the addition of rice straw, but it did not achieve the mechanical strength necessary to be a durable building material. Benchmark flexural strengths for common building materials are 34.3 lbf (1339 N) for medium-density fiberboard, 91.7 lbf (408 N) for low-quality plywood, 140 lbf (623 N) for oriented strand board, and 334 lbf (1486 N) for high-quality plywood.
Although the mechanical properties are crucial in building materials, on the island of Bohol, Philippines, the termite and humidity resistant properties of the board are equally important. Consequently, both of these prototype boards were evaluated for their termite and humidity resistance. Termite resistivity was determined by cutting the boards into 0.5′′ × 0.5′′ × 0.5′′ cubes and subjecting them to a force feeding experiment with 50 worker termites. Percent weight loss of the boards and termite mortality rates were calculated as a result of the forced feeding. Humidity resistivity was determined according to ASTM standards in which the boards were cut into 1′′ × 1′′ × 0.5′′ pieces and submerged in water at room temperature for 24-hours before thickness expansion was calculated. All of the tests were conducted in parallel to a control for reference. The main obstacle for the tannin and corn starch based board was that it lacked the humidity resistivity necessary to be a durable and sustainable building material. Efforts were made to improve the water resistivity of the board by using sodium silicate. Although the water resistivity did improve, it was determined that it would not be cost effective for the board given the target market, which consists of low-economic housing and disaster relief efforts.
A new approach was necessary and thus Husk-to-Home looked into fiber-plastic composite (FPC) boards for a solution. Recycled high-density polyethylene (HDPE) plastic was selected as the best and most sustainable plastic to incorporate into the boards due to its abundance, low cost, and recyclability. The FPC boards that were designed and optimized were evaluated for mechanical properties by conducting compression tests and preliminary screw tests, in addition to the previously mentioned three-point bend test for flexural strengths. Compression tests were performed on 2′′ × 1′′ × 0.5′′ board samples with an Instron 5969 mechanical tester in accordance to ASTM standards. Preliminary screw tests were conducted by screwing a 1” screw to the edge of the board and loading the screw until the board showed signs of cracks along the edge. The screw tests were not done according to ASTM standards but were used for comparative analysis. In the future, screw tests will be conducted in accordance to ASTM standards by accredited facilities to yield reliable results. Bioassays and soak tests were also conducted on the FPCs to evaluate termite and humidity resistance, as previously described. Again, all of the tests were conducted in parallel to a control for reference. The mechanical properties of the boards iv increased significantly. Flexural strengths reached as high as 90.67lbf (403 N), maximum compressive strengths reached 1634.58 PSI (11.27 MPa), and precursory screw tests revealed that the board could withstand a load of 60 lbf. Benchmark compressive strengths for common building materials are 4641 PSI (32 MPa) for high-quality plywood, 1740 PSI (12 MPa) for the oriented strand board, and 2321 PSI (16 MPa) for medium-density fiberboard. Soak tests indicated a percent expansion by thickness as low as 2.0% with the most recent boards. These results are excellent in comparison to the 20 to 40% expansion of formaldehyde-based adhesive rice husk particleboard that were tested in parallel. The bioassay tests determined that termites consume basswood (20.7% mortality rate), but do not consume rice husk (100% mortality rate). Bioassays for various board types are still in progress as each bioassay requires up to ten weeks to perform. In addition, although there was a low mortality rate (32%) for pure HDPE, the near zero percent weight loss means that termites do not feed on HDPE and may have been cannibalizing to stay alive.
These promising results have allowed Husk-to-Home to partner with IDEA. Future plans to replace plywood particleboard, which is currently IDEA’s main wood-based building material, with Husk-to-Home’s more durable and sustainable FPC boards have been discussed. Husk-to-Home plans to begin manufacturing the quality boards in one of IDEA’s facilities.
All tests were performed at the University of California, Riverside.
The new approach of using FPC boards instead of tannin- and casein-based adhesives proved to be promising. The recycled HDPE adhesive has improved the properties of Husk-to-Home’s rice husk composite boards substantially. The proposed board has mechanical strength near that of the plywood it will be replacing in IDEA’s homes. The team’s highest performing board has a flexural strength of 90.67 lbf (403 N), a compressive strength of 1634.58 PSI (11.27 MPa), and percent volume expansions as low as 2.0% after submerging in water for 24 hours. Although the proposed FPC board is lower in compressive strength compared to plywood, Husk-to-Home will continue optimizing its properties. As Husk-to-Home nears the finalization of their bench-scale prototyping stage, the team is ready to move forward with the implementation phase over the next two years. In collaboration with IDEA, Husk-to-Home will bring low-economic housing and disaster relief for the Bohol Island community.