Chloride and sulfate resistance of LC3 with reduced clinker content using low-grade local clay

The demand for low-carbon construction materials is driving the development of alternative binders such as limestone calcined clay cement (LC3). LC3 is a low-carbon ternary binder based on clinker, calcined clay, limestone, and small fraction of gypsum. The use of locally available low-grade clay can broaden the application of LC3. However, its durability at clinker content below the conventional LC3 mixture requires further evaluation. This study investigated the use of locally available low-grade Trenggalek clay, characterized by a low kaolinite with 33.3% of the identified crystalline phases by Rietveld XRD analysis and 32.62% by thermogravimetry analysis (TGA), while reducing clinker content from 50% to 35%. The chloride migration and sulfate resistance of the resulting mixtures were comparatively evaluated against metakaolin-based mixtures and Portland Pozzolan Cement (PPC) using accelerated laboratory methods based on NT Build 492 and ASTM C1012M-18. Material characterization was conducted using X-ray fluorescence (XRF), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Despite its relatively low kaolinite content, the local clay-based LC3 exhibited lower chloride migration coefficients and lower sulfate-induced expansion than PPC under the investigated conditions. At 180 days, the 35% clinker mixture showed a chloride migration coefficient of 9.74 × 10⁻¹ ² m²/s and sulfate expansion of 0.134%. These findings provide experimental evidence of feasibility and limitations of using lower-grade regional clay resources in reduced-clinker LC3 systems. However, the results represent separate accelerated laboratory exposures. Combined chloride-sulfate exposure and long-term field validation are required before performance under actual marine conditions can be established.