Experimental and Numerical Investigation of Thermophysical, Mechanical and Fire Performance Characteristics of Novel Sustainable Composites Developed from Recycled Construction and Demolition Waste

Abstract: 

Rapid increase of Construction and Demolition Waste (CDW) generation poses big challenges to the environment globally. In Europe CDW constitute approximately one-third of the total waste generated by both economic activities and households, amounting to around 2.5-3 billion tonnes annually in the EU-28 region. Remarkably, CDW generation witnessed a staggering 300% increase between 2003 and 2013. In Cyprus, despite having a comprehensive legislative framework for CDW management in place since 2011, the actual management practices seem to be falling short. Over the past decade, construction activities in Europe have surged, driven by the need for energy-efficient refurbishments and accommodations. According to a European Union study, a significant portion of household energy consumption (63%) over the last two decades (250-300 Mtone) can be attributed to heating, cooling, and ventilation requirements, primarily due to inadequate thermal insulation. Additionally, the safety of many structures, particularly concerning fire hazards, has recently gained high attention. Shockingly, fire incidents in Europe surged by over 300% between 2010 and 2015.

Compounding these challenges, the current thermal insulation solutions available in the market have various shortcomings, including combustibility, spalling during fire incidents, high costs, and adverse environmental impacts.Top of Form The innovative aspect of this research lies in the utilization of waste ceramic tile (WCT) and waste brick (WB), achieving a 100% re-use of these raw materials, to develop novel and sustainable composite geopolymers with coupled thermal insulation and fire resistance properties by using geopolymerization technology and 3D printing technology. The geopolymerization approach involves the use of potassium hydroxide and sodium silicate as activators to develop geopolymers.

 The raw materials were mineralogically characterized, revealing that WCT contained 62%wt. SiO₂, 14.3%wt. Al₂O₃, with an apparent density of 2560 kg/m³ and water absorption of 25.6%, while WB had 54%wt. SiO₂, 14.56%wt. Al₂O₃, with an apparent density of 2810 kg/m³ and water absorption of 15.8%. In dissolution tests, a high silicon content of raw material with PSD less than 0.15mm was activated within 1 hour of reaction in KOH solution, whereas in NaOH solution, silicon activation began after 24 hours of reaction.

Experimental results demonstrate the successful production of foamed geopolymers from WCT and WB, with densities ranging from 400 to 600 kg/m³, compressive strength less than 2MPa, and thermal conductivity of 0.1Wm^-1K^-1, using expanding agents such as hydrogen peroxide and Al-powder. Hydrogen peroxide proved to be the preferable foaming agent for WB-based geopolymers, while Al-powder was feasible for WCT-based geopolymers.

Mechanical behaviour of ceramic tile fire resistance (CTFR) and brick fire resistance (BFR) geopolymers were studied. Both CTFR and BFR geopolymers exhibited high compressive strengths prior to exposure to elevated temperatures, with similar behaviour observed in post-fire tests, although compressive strength declined between 600-800^oC and rose at 1050^oC, and their density decreased by 8-9% at1050^oC while mass loss was 7-10% at this temperature. On fire test CTFR presented plastic strain without any macro-fracture at all temperature while BFR retained its elasticity with macro-fracture. Although both the BFR/CTTI and CTFR/CTTI geopolymer composites did not pass the fire resistance test based on the ISO834 standard, they fulfilled the crucial requirement of keeping the temperature at the concrete interface below 180 °C for over one hour, which is a significant achievement in the context of building fires. Additionally, both geopolymer composites maintained the temperature at the concrete interface within the range of 300-360 °C after two hours of fire exposure. Therefore, both geopolymers have potential to be used as thermal insulation and fire-resistance building materials.