Life cycle impact comparison of different concrete floor slabs considering uncertainty and sensitivity analysis

The traditional construction industry is characterized as a labor-intensive, wasteful, and inefficient sector. Currently, prefabrication has become a common practice in residential development and has reduced energy consumption and waste generation compared to traditional on-site practices. This study investigates the differences in life cycle environmental impacts among three different floor systems (precast slab, composite slab (semi-precast slab) and cast-in-situ slab) based on two functional units (delivering the same carrying capacity and maintaining consistent floor depth) using both LCA midpoint and endpoint methods using the software tool SimaPro. This study sets a calculation boundary for the construction process: raw material production, slab production, transportation, construction activities on-site, demolition and recycling of buildings at the end-of-life stage. Moreover, uncertainty and sensitivity analysis are carried out to help decision-makers identify major environmental impact factors and develop eco-friendly plans to facilitate housing industrialization. The results indicate that (1) the environmental impact of precast slab outperforms those of cast-in-situ and composite floors regardless of different design functional units and evaluation methods. (2) While under different functional units, the environmental performance of composite and cast-in-situ floors varies considerably. (3) From the perspective of life cycle stages, the transportation sector and its supply chain make up a significant portion of the final environmental impact and are responsible for 45.2%, 50.1% and 53.6% of the total impact for the precast, composite and cast-in-situ slabs, respectively. Slab production of precast slab (it is raw material production of cast-in-situ and composite slabs) is the second largest contributor to the environmental impact

Advancing tunnelling: recognising a UK engineering legacy

Between 1760 and 1820, the Georgians pioneered modern tunnelling, constructing 47 tunnels for canals across the UK. In 1789, the then longest canal tunnel in the UK was completed after 5 years and 4 months of construction; at 3490 m, the Sapperton tunnel conveyed the Thames and Severn Canal. But there were many failures, often involving loss of life; from these, as much as from the successes, tunnelling techniques and skills were developed. The mastery of tunnelling techniques for safely traversing through the earth remains challenging for civil engineers. Since 1965, there have been over 100 reported tunnel failures across the world. While Georgian historic structures are familiar on the skylines of today’s cities, a further hidden legacy can also be discovered from the past of collective engineering experiences. This paper reviews the causes of tunnelling success and failures, bequeathed to civil engineers by their Georgian predecessors, and seeks to derive lessons for today’s civil engineers

Assessing the contribution of urban green spaces in green infrastructure strategy planning for urban ecosystem conditions and services

Maintaining ecosystem services is a key adaption option towards sustainable cities and adaptive societies in securing citizens’ health and wellbeing. This research investigates the contribution of using urban green space components as the basic units in green infrastructure strategy planning for urban ecosystem conditions and services. A total of 9 types of urban green spaces are selected and delineated from the high-resolution data. A combination of the quantification method of 6 common urban ecosystem services based on urban green spaces and the MAES framework in reference to literature data is used. A case study of Cheltenham, a typical urban town in England, is studied to present the new approach for local green infrastructure strategy development for urban ecosystem conditions and respective services in improving the resilience of a city in facing global climate change. Results show that changing the composition and spatial arrangement of urban green space components, synergy or tradeoff of various services can be stimulated easily. The small scale of urban green space components allows local detail planning and potential integrated planning among other urban settlements