Sustainable Thermal Insulation in Cement Mortar: Optimizing Surface-Modified Silica Aerogel and Recycled PET for Energy-Efficient Masonry Applications

The construction industry is a major contributor to global energy consumption, with buildings accounting for nearly 40% of total energy use. Poor thermal insulation in traditional masonry structures exacerbates energy inefficiency, leading to increased heating and cooling demands. Conventional cement-based mortars have high thermal conductivity, resulting in significant heat loss through walls, floors, and roofs. As energy costs rise and climate change concerns intensify, the need for sustainable, energy-efficient building materials has become urgent. A key challenge in addressing this issue lies in material selection. While lightweight aggregates such as silica aerogels have demonstrated exceptional thermal insulation properties, their integration into cementitious materials is problematic due to weak adhesion with the cement matrix. This results in poor mechanical strength, limiting their practical application in construction. Furthermore, the global plastic waste crisis, particularly from polyethylene terephthalate (PET) bottles, calls for innovative recycling strategies to reduce environmental impact. This study introduces a novel approach by combining surface-modified silica aerogel with recycled PET plastic in cement mortar. Unlike previous research, which focused on aerogel or PET separately, new research paper published in Construction and Building Materials and conducted by Kaniaw Marof and led by Professor Lidija Šiller from the School of Engineering at Newcastle University investigated synergistic effects on both thermal and mechanical performance. Chemical modification of aerogel particles using KH-570 (silane coupling agent) is employed to enhance bonding with cement, addressing the long-standing adhesion issue. By integrating sustainable waste-derived materials, this research aligns with circular economy principles and contributes to reducing both energy consumption and environmental pollution.

To evaluate the feasibility of incorporating silica aerogel and PET plastic in cement mortar, a series of seven distinct mortar mixes were prepared. These included three mortar formulations with 3%, 5%, and 7% unmodified aerogel, and three additional formulations with PET plastic (3%) and surface-modified aerogel. A control sample (A1) was used for comparison. Workability assessments using the flow table test showed that adding silica aerogel and PET plastic decreased mortar flowability, mainly due to aerogel’s high surface area and PET’s hydrophobic nature. Setting time measurements indicated that aerogel reduced both initial and final setting times, while PET plastic delayed setting, likely due to its hydrophobicity affecting water absorption and cement hydration rates. Density analysis confirmed that replacing sand with aerogel and PET led to a notable decrease in bulk density, with up to a 10.4% reduction for the highest aerogel content mix. This reduction enhances mortar’s lightweight properties but also affects mechanical strength.

The authors performed compressive and flexural strength tests and found that increasing aerogel content weakened mechanical performance, with a maximum 18% reduction in compressive strength at 7% aerogel replacement. The addition of PET plastic further lowered strength values, attributed to weak interfacial bonding between PET and the cement matrix. However, all mixes met the minimum standards for N-type masonry mortar, confirming their structural suitability. Moreover, they conducted thermal conductivity testing which demonstrated a significant improvement in insulation properties. Mortars containing both aerogel and PET exhibited up to a 55% reduction in thermal conductivity, highlighting their potential in energy-efficient construction. Microstructural analysis (SEM) provided further insights, showing that chemical modification of aerogel particles improved adhesion with the cement matrix, while PET plastic remained poorly bonded, leading to localized void formation.

 In conclusion, the research work of Kaniaw Marof and Professor Lidija Šiller successfully incorporated surface-modified silica aerogel and recycled PET plastic into cement mortar, this research bridges the gap between thermal insulation and structural performance. The 55% reduction in thermal conductivity has direct applications in reducing building energy consumption, making it a promising material for walls, façades, and masonry structures in both residential and commercial buildings. Beyond thermal performance, this approach contributes to sustainable construction by offering a practical recycling solution for PET plastic waste, diverting non-biodegradable materials from landfills while reducing reliance on natural sand. The lightweight nature of aerogel-enhanced mortar also suggests potential applications in prefabricated construction elements, where load reduction and ease of transport are beneficial. While mechanical strength reductions were observed, the results confirm that the modified mortar still meets regulatory standards, demonstrating its viability for practical construction applications. Future research should focus on further improving PET-cement bonding through additional surface treatments or polymer modifications. Long-term durability assessments, including moisture resistance and freeze-thaw cycles, would also be valuable in ensuring real-world performance.