Regulating High-Temperature Hydration Sensitivity of Calcium Aluminate Cement through CO2 Curing and MgO Modification

Abstract Calcium aluminate cement (CAC) exhibits severe strength regression due to the conversion of metastable hydrates ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>CAH</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">/</mml:mo> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">C</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi>AH</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>8</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ) and marked sensitivity to temperature variations. This study introduces a synergistic strategy that couples light-burned MgO modification (0–15 wt.%) with accelerated <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>CO</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> curing (1 MPa, 4 h, 20°–50°C) to suppress phase conversion while simultaneously sequestering <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>CO</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> . Comprehensive experiments combining X-ray diffraction (XRD), thermogravimetric and differential thermogravimetric (TG-DTG) analysis, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) analysis show that 10 wt.% MgO delays the transformation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>CAH</mml:mi> <mml:mn>10</mml:mn> </mml:msub> </mml:mrow> </mml:math> into <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi mathvariant="normal">C</mml:mi> <mml:mn>3</mml:mn> </mml:msub> <mml:msub> <mml:mi>AH</mml:mi> <mml:mn>6</mml:mn> </mml:msub> </mml:mrow> </mml:math> through hydrotalcite stabilization and generates Mg-bearing carbonates (nesquehonite, magnesite) that densify the matrix. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>CO</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> curing at 35°C refines the pore structure (median diameter reduced from 308 to 6.94 nm; porosity from 26.6% to 16.4%), eliminating strength inversion and yielding 44.3 MPa at 90 days, matching the peak value of the uncarbonated reference. However, under elevated carbonation at 50°C, the long-term strength showed a moderate reduction, though it remained superior to untreated CAC. MgO modification coupled with accelerated <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>CO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> curing effectively mitigates the pronounced temperature sensitivity of CAC.