Researchers at Kansas State University have demonstrated that certain bioethanol and other biofuel byproducts can be converted into a cementitious material that can work well as a replacement for part of the Portland cement used in concrete. The idea is that the waste material could potentially reduce some of the energy requirements and subsequent CO2 production of cement production.
It should be noted first that, while this is an example of “waste-not” smart thinking, the use of byproducts as supplementary cementitious materials (SCMs) will always be fairly limited because the world demand for cement and concrete is extremely high (because of its relatively low cost and high utility). Nevertheless, like the use of fly ash, incorporating into the concrete mix what heretofore has been dumped in landfills is obviously a good idea—especially when it improves the concrete mix and reduces energy consumption and CO2 production.
Much of the work at KSU has been done by Feraidon Ataie, a doctoral student in civil engineering from Kabul, Afghanistan, who is being mentored by Kyle Riding, an assistant professor of civil engineering. Ataie’s research has focused on byproducts from the production of cellulosic ethanol made from agricultural residue, such as wood chips and wheat straw.
To be clear, there is a separate process that also can be used to make bioethanol that involves edible feedstock, such as grains. The byproducts from the grain process can be used as cattle feed. However, the process for agricultural residue that Ataie focused on produces a ”high-lignin” residue (HLR) that has struggled to find a subsequent use. Riding say in a KSU news release, “Your choices of how to use it are a lot lower. The most common choices would be to either burn it for electricity or dispose of the ash” in a landfill.
The first step to make the material into a usable SCM is to convert it to ash by burning. The agricultural residues ash (ARA) cannot be used directly, and much of Ataie’s and Riding’s research has involved looking at how best to convert it to make it as reactive (i.e., accelerating hydration) as possible. While other researchers already had shown that that dilute acid pretreatment could improve the reactivity of ARA in concrete materials, he went a step farther and examined the pozzolanic property of the ARA if acid pretreatment is followed by enzymatic hydrolysis.
According to an abstract of some of the duo’s work, they concluded
Based on heat of hydration, calcium hydroxide consumption, and compressive strength experiments, it was concluded that the ash produced by burning HLR is a very reactive pozzolanic material that can be used as a partial replacement of cement in concrete materials. Thus, HLR which are byproducts of biochemical conversion of [agricultural residue] can be utilized as valuable materials for SCMs production for concrete.
Indeed, Ataie and Riding found that replacing 20 percent of the cement with cellulosic SCM increased the compressive strength of the concrete by 32 percent.
“The utilization of this byproduct is important in both concrete materials and biofuel production,” Ataie says in the release. “If you use this in concrete to increase strength and quality, then you add value to this byproduct rather than just landfilling it. If you add value to this byproduct, then it is a positive factor for the industry. It can help to reduce the cost of bioethanol production.”
Ataie also was one of two Kansas State University graduate students named a winner at the 2013 Capitol Graduate Research Summit in Topeka, Kansas, based on his poster about the SCM research.