Evaluation of Limestone from Bekhme Formation for Metakaolin, Alkaline-Resistant Glass, and Hybrid Steel Fiber Concrete Reinforcement in Kurdistan Region of Iraq

Abstract

The limestone from the Bekhme Formation within the Hareer Anticline has been utilized as a concrete aggregate. X-ray fluorescence was carried out for eighteen limestone samples to determine the major oxide compositions of CaO, SiO₂, Al₂O₃, Fe₂O₃, MgO, Na₂O, K₂O, Cl, TiO₂, SO₃, P₂O₅, MnO, and loss on ignition. The results showed that only 195m out of a 255m thickness of the Bekhme limestone met the chemical standards for concrete aggregates. Mechanical characterization using the Los Angeles abrasion test yielded a 29% wear value, which is within the acceptable range for concrete aggregate quality. Two standard concrete mix designs were adopted: 1:1.5:3 (M20) with a water content of 23–28.5 L and 1:2:4 (M15) with a water content of 22–25.5 L. A total of 32X3 concrete cubes measuring 15 cm³ were prepared for testing, using suitable proportions of cement, fine aggregate (≤ 4.75 mm), coarse aggregate (≤ 12.5 mm), and water. To enhance mechanical performance, alkali-resistant glass fiber (0.10%), hybrid steel fiber (0.50%), and metakaolin (10%) were used, the latter replacing an equivalent portion of cement by weight. The concrete comprising metakaolin exhibited higher compressive strength than that reinforced with glass or steel fibers. This improvement is attributed to the pozzolanic reactivity of metakaolin, which promotes the formation of additional calcium silicate hydrate (C–S–H) gel. An economic assessment of the upper Bekhme Formation, based on the total limestone volume, indicated that the reserve is sufficient to sustain long-term concrete production; metakaolin provides a cost-effective alternative, whereas glass and steel fibers act solely as mechanical additives without offsetting cement usage.