Calcined marl was identified as an insulating binder substituent mate-rial for aerogel based mortars. Further synthesis of insulating organo-nanoclays through the incorporation of polyethylene glycol (PEG) or in situ polymerisation of polystyrene (PS) in clays displayed greater promises for further reduction of thermal conductivity independent of the compressive strength, unlike more con-ventional aerogel-incorporated concrete. The organo-nanoclays were characterized by Hot Disk thermal analyzer measurements. The results so far indicated the for-mation of organoclay particles from both ideal systems of bentonite and calcined marl with lowered thermal conductivities. The calcined clay appeared to maintain its binding properties, suitable for gelling excess aerogel together in the concrete matrix. Ultimately, the final hydration mix of aerogel, calcined clay-polymer binder, organo nanoclays and cements is targeted to form novel concretes with re-duced thermal conductivity comparable to existing insulating materials, while maintaining strengths of 20 MPa after 28 days of curing.
The application of superinsulation materials (SIM) reaching thermal conductivities far below 20 mW/(mK) allows the construction of relatively thin building envelopes while still maintaining a high thermal resistance, which also increases the architectural design possibilities for both new buildings and refurbishment of existing ones. To accomplish such a task without applying vacuum solutions and their inherit weaknesses may be possible from theoretical principles by utilizing the Knudsen effect for reduced thermal gas conductance in nanopores.
This study presents the attempts to develop nano insulation materials (NIM) through the synthesis of hollow silica nanospheres (HSNS), indicating that HSNS may represent a promising candidate or stepping-stone for achieving SIM. Furthermore, initial experiments with aerogel-incorporated concrete and the conceptual work concerning NanoCon are presented.
The path toward energy-efficient buildings with a low or zero carbon footprint, e.g. zero energy and zero emission buildings, involves the development of high-performance thermal insulation, aiming at reaching thermal conductivities far below 20 mW/(mK). Applying such superinsulation will allow the construction of relatively thin building envelopes yet maintaining a high thermal resistance, thus also increasing the architectural design possibilities. A vacuum insulation panel (VIP) represents a stateof-the-art thermal insulation solution with a thermal conductivity of typical 4 mW/(mK) in the pristine and non-aged condition. However, the VIPs have issues with fragility, perforation vulnerability, increasing thermal conductivity during time and lack of building site adaption by cutting as four cardinal weaknesses, in addition to heat bridge effects and relatively high costs. Therefore, the VIPs of today do not represent a robust solution. Hence, our aim is from theoretical principles, utilizing the Knudsen effect for reduced thermal gas conductance in nanopores, to develop experimentally a high-performance nano insulation material (NIM). This work presents the current status of the development of NIM as hollow silica nanospheres (HSNS) in our laboratories, from the experimental synthesis to the material characterization by e.g. thermal conductivity measurements. One attempted approach for tailor-making HSNS is the sacrificial template method and optimization of the sphere diameter and shell thickness with respect to low thermal conductivity. The results so far indicate that HSNS represent a promising candidate for achieving the high-performance thermal superinsulation for application in the buildings of tomorrow.
Improvements to concrete will have a large impact in the construction and building sector. As the attention is drawn towards energy-efficient and zero emission buildings, the thermal properties of concrete will be important. Attempts are being made to decrease the thermal conductivity of concrete composites while retaining as much as possible of the mechanical strength. In this study experimental investigations of aerogel-incorporated mortar (AIM) with up to 80 vol% aerogel are prepared utilizing a reduced ultra-high performance concrete (UHPC) recipe. It was found that at 50 vol% aerogel content, the AIM sample possessed a compressive strength of 20 MPa and a thermal conductivity of ≈0.55 W/(mK). This strength decreased by almost a factor of 4–5.8 MPa, while gaining only a 20% improvement in thermal conductivity when aerogel content increased to 70 vol%. No preferred gain in properties was observed as compared to a normal mortar system. This can be attributed to the imbalance of the particle–matrix ratio in the mortar system, causing a decrease in adhesion of the binder-aggregates. The AIM samples have been characterized by thermal conductivity and mechanical strength measurements, alongside scanning electron microscope (SEM) analyses.
The application of traditional thermal insulation materials requires thicker building envelopes in order to satisfy the requirements of the emerging zero energy and zero emission buildings. This work summarizes the steps from the state-of-theart thermal insulation materials and solutions, like vacuum insulation panels (VIP), gas-filled panels (GFP) and aerogels which all have various drawbacks, to our concepts and experimental investigations for making superinsulation materials (SIM) like e.g. nano insulation materials (NIM).