A student, affiliated with UNIST has been awarded with the Excellent Presentation Award at the 2018 annual spring symposium of Korea Concrete Institute, which was held in Changwon Exhibition Convention Center from May 2 to 4, 2018.
The award has been presented to DongHo Jeon (Advisor: Professor JaeEun Oh) in the School of Urban and Environmental Engineering at UNIST in recognition of his recent study on the reapplication of fly ash in construction materials industry.
At the symposium, Mr. Bing presented his paper on the manufacturing of a high-strength Portland cement substitute, using fly ash. The new binder, introduced in the study, is made with coal fly ash with added activating agents. It is cementless and environmentally-friendly, and exhibits faster strength development comapred with the ordinary cementless binders. The results are reported in Construction and Building Materials.
Fly ash, also known as pulverished fuel ash, is produced as a byproduct in huge amounts from pulverized coal-fired power plants. Each year, about 750 million tons of fly ash are generated throughout the world, and therefore there has been great expectation on the recycling and reapplication of fly ash. However, the issue is its lower reactivity. Fly ash and calcium hydroxide obtain strength through a pozzolanic reaction, which takes a long time to develop strength due to their low reactivity.
The new binder has improved this reactivity problem with sugar. The researchers found that fly ash and calcium hydroxide actively react when added with sugar at high temperature curing conditions, resulting in higher levels of strength-producing substances. Calcium complexation effect of sugar melted more calcium hydroxide in binding material, leading to increase of pH, which led to active reaction of fly ash.
It was confirmed that the binding material can develop 40~50 MPa high strength in a day of curing. Considering that the concrete used for building generally requires compressive strength of 20~30 MPa based on 28 days curing, it is a remarkable level in both the speed and strength of the strength development.
“The Portland cement, which is the most commonly used construction material in the world, produces a large amount of carbon dioxide in the manufacturing process,” says Mr. Jeon. “The development of cement based binders using fly ash, which is an industrial byproduct, It is a way to reduce the landfill space and costs that have been used to treat existing industrial by-products.”
“The new binders is also 80% cheaper than the existing portland cement, so we can expect to commercialize them,” he said. “The development of cementless binders that can produce concrete without using existing portland cement, It is very important from a social point of view.”
Mr. Jeon plans to develop fly-ash-based lightweight aggregates, using the new binder and further proceed with research on lightweight concrete research.
Meanwhile, Professor JaeEun Oh in the School of Urban and Environmental Engineering, is conducting research on the microstructure analysis of construction materials such as concrete and cement, as well as the development of cementless concrete using fly ash and blast furnace slag powder as industrial by-products.
Dongho Jeon, et al., “The temperature-dependent action of sugar in the retardation and strength improvement of Ca(OH)2-Na2CO3-activated fly ash systems through calcium complexation,” Construction and Building Materials, (2018).