Probabilistic approaches to the measurement of embodied carbon in buildings

The measurement of embodied carbon in buildings or building components encounters many problems of uncertainty, which are increased for life cycle measurement. The level of uncertainty for a measurement varies on a spectrum from precise knowledge to total ignorance. The most rudimentary way of measuring an uncertain variable is to use a single-value ‘best guess’. Methods that acknowledge uncertainty and give a probabilistic measurement of the variable include: a range, a three-point estimate, an empirical distribution, or a mathematical distribution. Life cycle measurement subject to uncertainty can be represented by a tree of possible future values, or by Monte Carlo simulation of sampled future values. When measurements are probabilistic, decision makers’ choices respond to their degree of risk aversion and time preference. In situations of uncertainty, flexible strategies that adapt to unfolding events can mitigate the risk of damaging outcomes. A worked example compares deterministic and probabilistic measurement of the embodied carbon of a construction system with reusable steel modules. The system reduces embodied carbon if the modules are reused. For the probabilistic measurement, the length of the service life of the modules and the probability of reuse are uncertain variables. The steel module system is compared with conventional reinforced concrete construction. The probabilistic approach provides additional information and understanding for decision makers

Soil-steel composite bridge: An alternative design solution for short spans considering LCA

In a bridge project, several alternative design solutions can be functionally equivalent for the designated location. Today’s bridge constructions highly rely on the non-renewable resources, the consumption of fossil fuels, and the intensive usage of concrete. This urges designers to explore the new design options to mitigate the associated environmental burdens. When comparing to the concrete slab frame bridges (CFB), the soil-steel flexible culverts (or soil-steel composite bridge, SSCB) show advantages in ease erection, low maintenance as well as the competitive cost. However, its environmental performance has never been studied. This paper intends to compare the environmental performance of these two bridge types through the whole life cycle, based on 8 selected cases in Sweden. Unlike previous studies only limited to few impact indicators, this study comprehensively covers a wide range of indicators: including eleven types of mid-point impact categories, the cumulative energy demand (CED) and the associated cost. The construction phase, which seldom included previously, is a specific focus in this paper. The results find that: 1) the SSCBs show advantages over the CFBs in most of the investigated indicators; 2) the construction phase, when explicitly evaluated, may take up to 34% of the total life cycle environmental burdens; 3) the environmental performance of a bridge is closely linked with the bridge type selection, multiple indicators in the environmental domain, designers' preference, the construction phase, as well as the time schedule constraints