Investigating the effects of high-volume fly ash on early-age characteristics and hardening properties of concrete

Concrete production relies heavily on cement, which contributes 5%–7% of global carbon dioxide emissions, driving demand for eco-friendly, low-carbon building materials. Fly ash, a coal-fired power plant industrial byproduct, is a promising cement substitute, yet its comprehensive effects on concrete from fresh state to hardened performance remain understudied.

An international research team led by Dongguan University of Technology and Queen’s University Belfast has systematically examined how high-volume fly ash influences concrete’s early-age behavior, hydration, mechanical properties, and microstructures. Their findings, published in Lifeline Emergency and Safety, provide clear guidance for sustainable concrete design.

The team prepared concrete mixes with fly ash replacing 0%, 20%, 40%, and 60% of cement, testing flowability, setting time, compressive strength, elastic modulus, and microstructure via SEM and EDS analysis.

Test results demonstrate that fly ash can improve the workability of fresh concrete but prolongs the setting time. Notably, a 20% replacement shortens the liquid-to-solid transition phase. While high-volume fly ash significantly reduces early strength, concrete with 10%–40% fly ash replacement achieves excellent long-term strength and stiffness (up to 100 days). Microstructural imaging confirms that moderate fly ash forms dense, well-bonded hydration products, while excessive fly ash leaves unreacted spherical particles weakening the matrix.

“Our research links macro engineering performance with microstructural mechanisms, proving that fly ash can effectively green concrete without compromising structural quality,” stated Yu Zheng, corresponding author and professor at Dongguan University of Technology. “The 40% replacement rate is optimal: it reduces cement consumption, recycles industrial waste, cuts costs, and maintains excellent long-term strength and elastic modulus.”

This study supports low-carbon infrastructure development by providing a validated and practical mix design for green concrete. Future research will focus on optimizing curing regimes and combining fly ash with other supplementary cementitious materials to further improve early-age performance.

The research was published in Lifeline Emergency and Safety (2026, Volume 1, Article 9660002).

Other contributors include Lingzhu Zhou, Kaihui Hua, Zaitao Xie from Dongguan University of Technology, and Taylor Susan from Queen’s University Belfast.

This work was supported by the Guangdong-Hong Kong-Macao Greater Bay Area International Science and Technology Innovation Center Construction Fund, Guangdong Basic and Applied Basic Research Fund, and other provincial and municipal research projects.