From waste to value: Enhancing strength and CO2 sequestration of cement composites with lime mud under carbonation curing

초록

Lime mud (LM), a highly alkaline by-product from the paper industry, is usually disposed of by landfilling, causing environmental risks and resource waste. Previous attempts to use LM in cementitious materials often relied on calcination, which increases energy use and CO2 emissions, or direct blending, which leads to reduced strength and poor durability. To address these limitations, this study investigates the direct incorporation of uncalcined LM, alone or with slag, into cement-based materials (CBMs) subjected to carbonation curing. The hydration-carbonation behavior, pore structure, mechanical properties, and high-temperature resistance were comprehensively evaluated. The results show that LM provided nucleation sites and high alkalinity, accelerating CO2 uptake and enhancing early strength under carbonation curing. At 14 days, LM20 under carbonation curing reached a compressive strength of 52 MPa, 54 % higher than its normally cured counterpart. When combined with slag, the LM20A10 mixture achieved the best balance of strength and CO2 sequestration, showing a greater carbonation degree and a CO2 uptake exceeding 11 wt%. Multi-scale analyses (XRD, TG-IR, FTIR, SEM/TEM, MIP) confirmed the formation of N,C-A-S-H gels and CaCO3-SiO2 composites, which densified the matrix and linked microstructure with macroscopic performance. Furthermore, carbonation-cured specimens retained over 60 % of their compressive strength at 600 degrees C, whereas normally cured specimens showed severe degradation, indicating improved thermal resistance. This study demonstrates a sustainable strategy for LM valorization, integrating solid waste recycling, CO2 sequestration, and performance enhancement, thereby contributing to the development of low-carbon and durable construction materials.

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