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## Construction and Building Materials

Volume 275, 15 March 2021, 122131

# Modification of CO2 capture and pore structure of hardened cement paste made with nano-TiO2 addition: Influence of water-to-cement ratio and CO2 exposure age

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https://doi.org/10.1016/j.conbuildmat.2020.122131
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## Highlights

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  The investigation studies how nano-TiO2 affects CO2 sequestration of hardened pastes.

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  Different nano-TiO2 percentages and water-to-cement ratios were used.

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  The use of the nanoparticles increases the CO2 uptake until a certain percentage.

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  Exposure age and w/c ratio highly influence the CO2 uptake of nano-TiO2 pastes.

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  Changes in porosity and CH reactivity modify the nano-TiO2 effect on CO2 uptake.

## Abstract

This paper studies the effects of nano-TiO2 in CO2 sequestration of hardened cement paste depending on the water-to-cement ratio (w/c) and the pore structure. Twelve cement paste mixtures were prepared with four different percentages of nano-TiO2 (0%, 0.5%, 1%, 2%) and three w/c (0.45, 0.50, 0.55). Samples were exposed for 24 h to a CO2 environment at two different ages (14 and 28 days). Thermogravimetric analysis and 3D X-Ray scans of the pore structure were performed on exposed and unexposed samples. Results showed that nano-TiO2 produces an improvement in the CO2 uptake until a certain percentage. This maximum percentage depends on exposure age and w/c. Nano-TiO2 produces a reduction in porosity and an increment of calcium hydroxide (CH) reactivity, which have opposite effects on CO2 uptake. These two competing mechanisms may explain why nano-TiO2 can be beneficial or detrimental for the CO2 uptake as a function of w/c ratio and age.

## Keywords

CO2 uptake
Cement paste
Pore structure
CO2 sequestration
TiO2 nanoparticles
Calcium hydroxide
TGA
Calcium carbonate
3D X-ray
Water-to-cement ratio

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