A new study has shown that carbonated boron mud (CBM), an industrial byproduct treated through rapid carbonation, can significantly improve the performance and sustainability of basic magnesium sulfate cement (BMSC) when used as a partial replacement for magnesium oxide (MgO).
Study: Performance Optimization and Long-Term Strength of Basic Magnesium Sulfate Cement Prepared with Accelerated Carbonated Boron Mud. Image Credit: Nature Peaceful/Shutterstock.com
Background
Industrial waste management and carbon reduction are pressing challenges in cement manufacturing. Boron mud (BM), a byproduct of borax production, is produced in large quantities and has a high pollution potential. Rather than treating it as waste, researchers are exploring how to repurpose BM in construction materials, particularly magnesium-based cements.
Basic magnesium sulfate cement (BMSC) is an emerging low-carbon alternative to traditional Portland cement. It’s known for its fast setting time, low thermal conductivity, fire resistance, chemical stability, and mechanical strength. These advantages stem from its unique hydration products, which form a stable and dense microstructure.
However, the direct use of BM in BMSC is limited by its low reactivity. This is largely due to its mineral composition, which includes poorly reactive silicates and carbonates. Despite this, BM’s fine particle size and magnesium-rich content make it a promising candidate for enhancement through carbonation.
To address this challenge, the study proposed a rapid carbonation treatment of BM to improve its chemical activity and compatibility with the cement matrix. The resulting carbonated boron mud (CBM) was then evaluated as a partial MgO replacement in BMSC formulations.
Methods
The researchers began by collecting BM from local industrial sources. It was dried, ground, and sieved to a particle size of 75?μm. Its composition was analyzed using X-ray fluorescence (XRF), while its mineral phases were identified with X-ray diffraction (XRD).
To enhance its reactivity, BM underwent carbonation in a high-pressure, high-concentration CO2 reactor for 12 hours—a duration chosen based on prior efficiency trials. After treatment, the CBM was stored under controlled temperature (20 ± 1?°C) and humidity (95 %) conditions to preserve its chemical state.
To confirm the transformation of BM to CBM, the researchers conducted pH testing, particle size analysis, and further structural evaluations using XRD, Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA).
For performance evaluation, BMSC paste was prepared with a fixed mass ratio of MgO:MgSO4:H2O = 100:100:1. The paste was poured into 40 mm cubic molds using in situ compaction. Samples were made using both untreated BM and CBM to allow for direct comparison under identical curing conditions.
To assess how BM and CBM influenced BMSC behavior, the team performed a comprehensive set of tests, ranging from compressive strength and thermal performance to hydration phase identification and microstructural analysis.
Results and Discussion
The rapid carbonation process had a noticeable impact on the mineral reactivity of BM. XRD, FTIR, and TGA results indicated partial transformation of low-reactivity minerals, such as dolomite, magnesite, and enstatite, into more reactive carbonate-containing phases. This confirmed that CBM also acted as a carbon sink by capturing and storing CO2 within the cement matrix.
These changes in CBM’s chemistry directly influenced the hydration reactions in BMSC. The presence of carbonate ions led to more favorable interactions with MgO, reducing the formation of Mg(OH)2, a phase that typically weakens mechanical strength and affects dimensional stability. Instead, the hydration process favored the development of beneficial phases like hydromagnesite and the stable 5Mg(OH)2·MgSO4·7H2O, as confirmed through XRD and surface imaging with scanning electron microscopy (SEM).
Performance testing revealed that BMSC samples incorporating CBM showed marked improvements in mechanical strength, especially at around 30 % CBM content. This enhancement was attributed to a refined microstructure and better-regulated hydration kinetics. Calorimetric studies supported this by showing a delayed and moderated heat release, which likely helped reduce early-age cracking and improve long-term durability.
Microstructural analysis using SEM showed a denser, more uniform cement matrix in CBM-modified samples, with lower porosity and stronger interfacial bonding between particles. Elemental mapping further verified an increased presence of stable carbonate phases, aligning with the observed mechanical and durability improvements.
Conclusion
This study demonstrates that carbonated boron mud, produced through a simple, rapid carbonation process, can serve as a valuable partial replacement for MgO in BMSC. The integration of CBM not only enhanced hydration behavior and mechanical strength but also contributed to greater volume stability and microstructural uniformity.
Perhaps most notably, CBM enabled in situ CO2 sequestration within the cement matrix, offering environmental benefits alongside performance gains. By turning industrial waste into a useful input for sustainable construction materials, this approach addresses two major challenges: resource efficiency and emissions reduction.
The CBM-BMSC system offers a practical pathway for reducing cement-related carbon footprints while improving material performance—a promising development for both the construction industry and environmental management.
Journal Reference
Li, J. et al. (2025). Performance Optimization and Long-Term Strength of Basic Magnesium Sulfate Cement Prepared with Accelerated Carbonated Boron Mud. Materials, 18(18), 4231. DOI: 10.3390/ma18184231. https://www.mdpi.com/1996-1944/18/18/4231
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