Structural Carbon Reduction: a Multi-Objective Approach at the Material, Building, and Sector-Scale

Abstract

Toward the building industry’s goal of decarbonization by 2050 at the latest, this project investigates carbon reduction at the material development, building concept-design and sector scales, which when vertically integrated yield greater results than when conducted separately. Starting at the material-level, a novel thermally-adaptive ductile cementitious composite is developed to alleviate reliance on steel reinforcement and serve as a thermal battery within building structures. This passively reduces heating and cooling energy use by 4%-7% when integrated into a shear wall and link beam building envelope. This is due to inclusion of 3% phase-change materials by mass into an engineered cementitious composite (ECC), providing a 30% increase in ECC heat capacity at indoor comfort temperature. PCM-ECC maintains a 28 MPa compressive strength, and 4% tensile strain capacity on average, 400 times the strain capacity of conventional concrete. Evaluated amongst other building materials via Ashby-style procedures, PCM-ECC shows more similarity with natural materials, such as timber, expanding the design space for concrete. Material development vectors and properties of PCM-ECC are carried into the building design workflow with a parametric multi-objective optimization (MOO) script to minimize superstructure life-cycle carbon. It is found that MOO identifies an optimal geometry to help prevent setbacks in building life-cycle carbon up to 30%, which would otherwise mask savings provided by the PCM-ECC in its structural envelope. These results, combined with data from literature and industry sources, form the basis for technology options in a sector-level simulations towards zero carbon in the US commercial structural sector. It is found that lump-sum carbon limits lead to greater carbon reductions than annual limits, and that climate compliance must begin within 4 years or face infeasibility. The results show that lump-sum embodied carbon limits, retrofit early in the time-horizon, building-scale optimization, carbon-negative material development, and a carbon tax are all essential to reach sector climate goals.