20 Oct 2021
Low carbon applications of wheat straw building materials
The third session of the UK-China Built Environment Road to Carbon Zero Webinar, titled “Low Carbon Applications of Wheat Straw Building Materials”, took place on October 20th, with its November 1st broadcast on Sina Leju being watched by over 1.6 million. President Xi Jinping announced at the UN General Assembly that China will strive to reach peak carbon dioxide emissions by 2030 and achieve carbon neutralization by 2060, and that the Chinese government at all levels is taking more active and powerful actions to accelerate the process of decarbonization.
This time we focused on straw. The three guests invited to speak, Prof. Jihao Chen, Prof. Luming Wang and Dr. Seyed Ghaffar, gave us a step-by-step introduction from background to application and development, and gave us a general understanding of what role straw will play in the buildings of the future.
Jihao Chen's presentation was about the application and development prospects of the carbon reduction technology of straw building materials. We learned that China is a large agricultural country, with a large annual output of straw reaching 900 million tons. However, due to a the low utilization rate, waste accounts for 20%, with annual incineration reaching 81.1 million tons and accompanied carbon emissions reaching 34.5 million tons - a great burden on the environment.
However, straw itself is innocent, as it is actually a renewable resource, pollution-free and with carbon assimilation properties, as well as being light weight, strong and flexible. As a building material, it can easily be made into large blocks which improve construction efficiency, thermal insulation, costs and accessibility. Therefore, we must consider how we can utilise this waste straw after it has exhausted its agricultural uses.
Prof. Chen introduced the development and application cases of several mature straw-based building materials:
Straw brick houses
Multilayer composite straw wallboard
Plant fiber cement wallboard
Room temperature cold-pressed straw wood-based panels at room temperature
Although straw-based building materials are light, renewable and consume an ultra-low level of energy, and overcome difficulties with sound insulation, flammability, and mildew, they also face many bottlenecks. Due to seasonality, transportation distances, storage site limitations and other problems, the collection, storage and transportation of straw is a bottleneck restricting its large-scale development. Another is the issue of how to set up their product standards and construction scopes, as industry standards gatekeep the construction market.
However, straw-based building materials will show their ecological advantages and develop against the backdrop of carbon emissions reductions. Prof. Chen explained how, in China, straw is very suitable as a local material, being popularized and developed in rural areas, and how he believes that straw-based building materials with high added value (such as wood-based panels) will take the lead.
Luming Wang's presentation was about the ecological effect of the carbon reduction of straw-building materials and their ecological development. From an ecological perspective, he proposed that use of straw can protect forest resources, and using crop straw to replace wood raw materials and traditional wall materials is an effective way to realize the sustainable development of China's forestry and construction industry and alleviate raw materials supply issues. He also explained how straw has the characteristics of so-called "secondary forest resources", and how buildings built from straw can become passively ecological, defining new paradigms of "green reinforcement" and "green concrete".
As long as straw is not burned or pyrolysed, CO2 emissions can be permanently fixed. Straw building materials can also absorb atmospheric CO2, which is the most effective and realistic path to achieving a carbon peak and neutralization.
Prof. Wang introduced the Jiangsu Straw Ecological Building Materials Engineering Research Center, which is at the forefront of straw building materials research, with a focus on straw’s building characteristics, the development of plant-based building cementitious materials, the development of straw-based ecological building systems, and straw’s weather resistance and environmental coordination, so as to promote the development of local emerging industries and regional economies. As we know, the ecological environment is complex, and the use of straw as a building material faces many key scientific and technical problems, including issues with adaptability straw and modern cementitious materials.
He also introduced the synthesis of a new multifunctional inorganic composite cementitious system which can help straw overcome the technical problems of poor environmental durability, such as mildew, decay, degradation and aging, and can make it possible for straw to truly become a building resource. At the same time, he explained how:
coupling and coating technologies are adopted to solve the technical problems of interface combination and fusion between inorganic cementitious materials and biomass straw.
straw is filled with Na2SO4 10H2O brine phase-change material, greatly improving the thermal insulation performance of straw building materials.
cutting mixing and rapid solidification technologies are adopted to solve the issues with high rebound during straw homogenization mixing and cold pressing.
Seyed Ghaffar introduced his Brunel University Grow2Build bio-based building products research center and their research results. Brunel University’s Civil Engineering Department’s research in natural fiber composites is well-regarded. The Grow2Build center is a laboratory designated for technological development and has emerging biological building products on long-term display. The goal of Grow2Build is to become an authoritative consulting organization for the construction industry on all aspects of bio-based materials, from cultivation and processing to production and application.
Dr. Seyed gave an in-depth introduction to wheat straw, a seemingly simple material, teaching that if one wants to make better use of wheat straw, one must first have a comprehensive understanding of its properties. He used different experiments to show how different parts of the straw have different microfibers, and so possessing different tensile strengths. In order to make high-performance compressed straw board, the most suitable part of wheat straw with the highest tensile strength, the internode, needs to be used. Furthermore, special treatment of wheat straw, such as hot water washing and steam treatment, will greatly improve its mechanical strength, whilst also removing wax layers and impurities, so as to facilitate resin penetration and giving the resulting material higher and better interface performance and bonding qualities.
The proposal of this research result also represents a new concept of industrial efficiency, that is, how to selectively remove the defective parts of wheat straw, leaving only the internodes. Dr. Seyed hopes to develop a feasible and easy to expand process on an industrial scale.