In 2020, Southwest University researchers treated rice husks with acid and burned them into ash; replacing 10% of cement with the ash increased compressive strength by 16.22% after 56 days

Concrete is, of course, hard to escape when you look around in an American city; it is everywhere, in the sidewalks, the houses, the bridges, the parking lots, and the highways. However, while the use of concrete is quite widespread, it requires a lot of resources and has been the subject of studies to find ways to increase its efficiency. So when a materials-science lab in China says it has found a way to make cement stronger by mixing it with burnt rice husks, it's worth paying attention to.

The researchers, led by Jing Liu and Chunyan Xie at Southwest University in Chongqing, China, found that rice husks treated with hydrochloric acid and then burned into ash, when used to replace 10 percent of the cement, increased compressive strength by 16.22 percent after 56 days compared with plain cement. This is documented in their 2020 paper titled “Hydrochloric Acid Pretreatment of Different Types of Rice Husk Ash Influence on the Properties of Cement Paste,” published in the journal Materials. The significant leap is impressive for a material which is often thrown, buried, or burned in open fields as farm waste.

Why cement may be the villain nobody talks about


Concrete is often blamed for its carbon footprint, and cement production is a major emissions source. As the International Energy Agency explains in its 2023 report on cement, cement manufacture is one of the most difficult-to-decarbonize sectors because not only does it require high temperatures for production, but it requires a chemical process that will release carbon dioxide regardless of what kind of fuel was used. Each bag of cement sold is carrying an extra burden as a climate liability. Reducing clinker content without harming performance can be a meaningful emissions strategy, not just a marketing claim.

So what actually happened in the lab

What is remarkable about this experiment is that the ash left behind by the burning of rice husk under controlled conditions is a major component of amorphous silica. This silica is far from being inert filler; it reacts with the byproducts of cement hydration to fill in the micro-gaps in the material, thereby making it denser and tougher over time.

The Southwest University team compared rice husks from two regions of China, Inner Mongolia and Guangdong province, testing each both with and without acid pretreatment. They found that the acid treatment helped strip out potassium oxide, a compound that the paper's authors describe as acting as a crystallization "activator" that otherwise limits the ash's reactivity during combustion. The 10% replacement level performed best in this experiment, and higher amounts began to reduce the strength gain.

The part that no one may have told you

The underlying chemistry is supported by a wider review titled “Harnessing rice husk ash for sustainable construction: a comprehensive review of challenges, opportunities, and future perspectives,” published in the Journal of Material Cycles and Waste Management in 2025, which suggests that the high silica content of rice husk ash makes it a promising material for sustainable construction, while noting that inconsistent processing and limited existing infrastructure still stand in the way of it being used more widely.

This is a promising example of how agricultural waste could help reduce the carbon footprint of construction materials. If the processing of agricultural waste can continue to be improved, it could result in potentially lower costs and less environmental impact in the construction of houses in the future, without anyone having to purchase an EV or solar panels for it to occur. This is the sort of climate progress that doesn't require a marketing campaign, only improved chemistry and apparently some leftover rice husks.