The Double C Block Project: Thermal Performance of an Innovative Concrete Masonry Unit with Embedded Insulation

The Double C Block (DCB) is an innovative composite Concrete Masonry Unit (CMU) developed to offer enhanced thermal performance over standard hollow core blocks (HCBs). The DCB features an original design consisting of a polyurethane (PUR) foam inserted between two concrete c-shaped layers, thus acting as the insulating layer and the binding agent of the two concrete elements simultaneously. The purpose of this research is to describe the results obtained when assessing the thermal transmittance (U_DCB and U_HCB) of these blocks using three different methodologies: theoretical steady-state U-value calculations, numerical simulation using a Finite Element Method (FEM), and in situ monitoring of the U-value by means of the Heat Flow method (HFM). The results obtained show that the three methodologies corroborated each other within their inherent limitations. The DCB showed a performance gap of 52.1% between the predicted FEM simulation (U_DCB was 0.71 W/(m²K)) and the values measured via HFM, which converged at 1.47 W/(m²K). Similarly, a gap of 19.9% was observed when assessing the HCB. The theoretical value via FEM of U_HCB was 1.93 W/(m²K) and the measured one converged at 2.41 W/(m²K). Notwithstanding this, the DCB showed superior thermal performance over the traditional block thanks to a lower U-value, and it complies with the Maltese building energy code. Further improvements are envisaged.