Nanomaterials reduce water absorption in cement concrete

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The use of nanoparticles in concrete has gradually come to be regarded as a high-potential, quick restoration, and high-performance material.

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​​​​​​​Study: Influence of nanomaterials on the water absorption and chloride penetration of cement-based concrete. Image Credit: serato/Shutterstock.com

In a study published in the journal Materials Today, a short analysis was conducted on the impact of nano-SiO2, nano-Al2O3, graphene oxide, carbon nanotubes, nano-TiO2, nano-Fe2O3, nano-clay/metakaolin, and nano-CaCO3 usage on the water permeability and chloride infiltration of cement concrete. The possibility of employing nanomaterials in cement concrete with the requisite construction material qualities was discovered.

Cement Concrete and its Uses

Cement concrete is manufactured at a pace of 25-30 billion tons per year, representing 8-9% of total human greenhouse gas emissions. The most expensive component of concrete is the binding substance “cement”. Each year, about 5 to 6 billion tons of cement are produced worldwide, which is equivalent to a per capita use of one ton of cement.

Reduced use of Portland cement can successfully contribute to reducing greenhouse gas emissions. Carbon nanotubes (CNT), nano-SiO2 (nS), nano-Al2O3 (NA), graphene oxide (GO), nano-TiO2 (NT), nano clay (NC), nano-ZnO2 (NZ) and nano-Fe2O3 (NF) can all be used to improve the mechanical qualities and stability of concrete.

Properties of nanomaterials

Nanomaterials are particles whose dimensions range from 1 to 100 nm. The integration of nanoparticles in cement concrete composites has recently attracted a lot of interest.

The use of nanoparticles as a partial replacement for binders or as a filler material in cement concrete affects the rheological behavior and morphology at the nanoscale, significantly increasing the mechanical and durability properties of cementitious materials.

Efficiency of Nano SiO2 (nS)

Nano-SiO2 has been shown to be particularly effective in minimizing water absorption of concrete. It was reduced by 58% with 2% nano SiO2 and 36.84% with 3% nano-SiO2. According to previous research, this improvement was due to the accelerated impact that nS has on the main hydration process, which leads to densification of the matrix.

The authors also believe that the calcium hydroxide generated is lower in volume. This calcium hydroxide is absorbed much faster in the next hydration step, resulting in further improvement of the microstructure.

Compared to other nanoparticles, the use of more than 4% nano-TiO2 resulted in degradation of concrete performance. According to recent research, water absorption for control and 4% by weight of nano-TiO2 the concrete was 5.12 and 4.22%, respectively, after 168 hours of exposure. However, the water absorption capacity of blends containing 15% FA was lower than that of blends containing 4% NT.

Nano-SiO2 optimized the porous structure of concrete, lowering its conductance of chloride ions. The addition of 0.3% by weight of nano-silica lowered the migration and diffusion coefficients of chlorine significantly.

According to the authors, this decrease was caused by the nano-SiO2partially block the transport channels and therefore separate them. They also observed that any further increase in nS concentration resulted in aggregation and no further improvement in sensitivity to chloride ion passage.

Carbon nanotubes and their effects

Previous studies have shown that incorporating 0.05-0.1% carbon nanotubes reduced the chloride diffusion coefficient by 12%. This decrease was not affected by the type of carbon nanotubes (CNTs) used. Nevertheless, pure carbon nanotubes are the most effective in preventing the spread of all the carbon nanotubes studied.

The authors also revealed that the lower the e/c, the higher the effectiveness of CNTs in limiting chloride ion infiltration.

Study Highlights

It was observed that the incorporation of nanomaterials was very effective against water absorption and chloride penetration. A small amount of nano-silica was also added, which reduced water absorption by more than half. Carbon nanotubes at 0.08% by weight reduced water absorption by 35.8%. 0.8% by weight of graphene oxide reduced it by almost half. Water absorption has been reduced by two-thirds by using a smaller nano-CaCO3.

The water absorption of the concrete has been reduced using nano alumina. A small concentration of nano-silica decreased chloride migration to a quarter of its previous value, while a negligible percentage of graphene oxide halved chloride penetration depth. Carbon nanotubes decreased the diffusion coefficient of chlorides by 13%.

Reference

A. Abdalla, J., Thomas, BS, A. Hawileha, R. and Kabeer, KA (2022). Influence of nanomaterials on water absorption and chloride penetration in cement-based concrete. materials today. Available at: https://doi.org/10.1016/j.matpr.2022.06.427

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