Enhancing High Early Compressive Strength of Fly Ash Substituted Concrete through Alkali Activators and Admixtures
Shafitri Amelia, Iman Satyarno*, Suprapto Siswosukarto
1Department of Civil and Environmental Engineering, Universitas Gadjah Mada, Yogyakarta, INDONESIA
*Corresponding author: imansatyarno@ugm.ac.id
INTISARI
The construction industry increasingly demands concrete that can achieve high compressive strength within a short period to accelerate project timelines and improve efficiency. This study aims to develop high early-strength concrete (≥20 MPa within 24 hours) that is both environmentally friendly and workable. The approach involves substituting 30% of ordinary Portland cement (OPC) with fly ash and incorporating alkali activators (a combination of NaOH and Na₂SiO3) along with a type E admixture (superplasticizer), Sika® ViscoCrete®-1050 HE TH, at 0.3% of the binder weight. Concrete mix designs were calculated using the absolute volume method, with a water-to-cementitious ratio of 0.25. The alkali activator was added at varying dosages: 0%, 2.5%, 5%, and 7.5% of the fly ash weight, with adjustments made to the total water content accordingly. Compressive strength tests were conducted at 24 hours, alongside slump tests to assess workability. Results showed that concrete without alkali activator had the lowest compressive strength at 20.4 MPa. The addition of alkali activators significantly enhanced the compressive strength of the concrete, with the optimum result achieved at 5% alkali activator content, reaching 36.8 MPa an 84.2% increase compared to the control mix without alkali activator. All mixtures exhibited excellent workability with slump values exceeding 180 mm. This study demonstrates that combining fly ash, alkali activators, and superplasticizers in OPC-based concrete can produce high early-strength concrete with reduced cement usage. The findings offer a promising approach for efficient and sustainable construction practices.
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