A recent study explores the potential of integrating surface-modified silica aerogel and recycled polyethylene terephthalate (PET) plastic to develop a cement-based thermal insulation mortar with enhanced mechanical and thermal properties.
Study: Enhancing thermal insulation in cement mortar with silica aerogel and recycled PET plastic. Image Credit: MK photograp55/Shutterstock.com
Background
Reducing energy consumption in buildings remains a key challenge for the construction industry, as conventional materials often lead to significant thermal losses due to inadequate insulation. One of the most effective strategies to improve energy efficiency and indoor thermal comfort is minimizing heat loss through walls and roofs using high-performance insulation materials.
Lightweight aggregates, known for their porous structure, offer lower density and thermal conductivity compared to traditional concrete. Materials like silica aerogel, which is highly porous, can be incorporated into cement-based composites to enhance thermal insulation and reduce energy consumption. However, there is a trade-off: while silica aerogel improves insulation, it can also weaken the mortar's compressive strength.
To counteract this, researchers are exploring the use of recycled materials as aggregates to improve the mechanical performance of cementitious composites.
Methods
In this study, researchers added 10 % styrene-butadiene rubber (SBR) by cement weight to mortar samples containing PET plastic and silica aerogel. To enhance adhesion, they treated the silica aerogel particles with silane coupling agent KH-570 (3-methacrylate propyl trimethoxy silane).
Two series of mortar samples were prepared:
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A conventional mortar mix incorporating 3 %, 5 %, and 7 % untreated silica aerogel as a volume replacement for natural sand.
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A modified mix incorporating 3 % recycled PET plastic as a sand replacement, along with surface-modified silica aerogel and 10 % SBR.
The materials were thoroughly mixed in a drum mixer to ensure uniformity before being cast into 40×40×160 mm prism molds for testing. The samples were de-molded after 24 hours and cured for 28 days.
The study evaluated compressive and flexural strength, dry density, and thermal conductivity. Additional analyses included Fourier Transform Infrared (FTIR) spectroscopy to identify functional groups in the silica aerogel, flow table tests to assess workability, and scanning electron microscopy (SEM) to examine the mortar’s microstructure.
Results and Discussion
The chemical surface modification of silica aerogel significantly improved its bonding with the cement matrix by reducing air voids and strengthening the interfacial transition zones. However, the combined presence of PET and silica aerogel reduced workability due to their hydrophobic properties, as observed in SEM images.
Despite the addition of SBR, the mortar’s flexural and compressive strength did not improve due to air voids introduced during mixing. The compressive strength of PET- and SBR-containing samples decreased due to the increased porosity caused by surfactants in the SBR, which entrained air and increased the cement mix’s lubrication.
However, the setting times of mortar specimens containing silica aerogel and recycled PET plastic remained within the acceptable standard range, ensuring their suitability for construction applications. Additionally, reducing the dry density of the samples led to a thermal conductivity decrease of up to 55 %, making the mortar highly effective for insulation.
While small amounts of silica aerogel and PET plastic had minimal impact on mechanical strength, the compressive strength remained above the minimum permissible levels for N-type masonry mortar, making it suitable for cavity walls in buildings up to 15 meters high. Similarly, the flexural strength of samples incorporating recycled PET and silica aerogel exceeded the minimum requirements for masonry units built with calcium silicate bricks. This suggests that these modified mortars meet engineering standards while offering improved thermal performance.
Conclusion
The study provides valuable insights into the impact of replacing natural sand with silica aerogel and recycled PET plastic on the thermal and mechanical properties of cement mortar. The findings indicate that this partial substitution can lower thermal conductivity by up to 55 % compared to conventional mortar while maintaining strength requirements for masonry applications.
This approach presents a sustainable solution for improving building insulation while repurposing plastic waste. By integrating recycled PET with silica aerogels, cement-based mortars can offer effective thermal insulation, contributing to both energy efficiency and environmental sustainability.
Journal Reference
Marof, K. & Šiller, L. (2025). Enhancing thermal insulation in cement mortar with silica aerogel and recycled PET plastic. Construction and Building Materials, 467, 140320. DOI: 10.1016/j.conbuildmat.2025.140320, https://www.sciencedirect.com/science/article/pii/S0950061825004684
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