Effects of Low Dosage Colloidal Nanosilica on Carbon Sequestration and Microstructure of Type I and Type IL Cement Paste

Abstract

Abstract Portland limestone cement (Type 1L, PLC) is widely adopted to reduce carbon emissions in cement production, yet its potential for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="upper C upper O 2" display="inline" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>CO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> sequestration through carbonation is often overlooked. This study examines the carbonation performance of PLC and ordinary portland cement (Type 1, OPC) enhanced with low-dosage colloidal nanosilica (0.3% and 0.6% by cement weight), a cost-effective approach aligned with industry recommendations. Accelerated carbonation tests reveal that nanosilica improves cement hydration, pozzolanic reactions, and pore structure, boosting <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="upper C upper O 2" display="inline" overflow="scroll"> <mml:msub> <mml:mi>CO</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math> uptake efficiency. OPC exhibits superior carbonation due to greater pore connectivity, while nanosilica enhances carbonation in PLC by stabilizing entrapped air and increasing calcium hydroxide availability. Despite increasing capillary porosity, nanosilica refines pore size and promotes carbonation efficiency. These findings demonstrate the feasibility of low-dosage nanosilica in improving the sustainability and performance of PLC, providing a practical pathway to reduce the cement industry’s carbon footprint.