Environmental performance of on-site construction processes in post-tensioned slab foundation construction: A study of production home building in the Greater Phoenix area

There is an increased movement in the construction industry towards sustainable development, understanding life-cycle environmental impacts and reducing carbon footprint. This research considers the environmental performance of on-site construction processes in the concreting phase of production home construction. This study presents a process-specific quantification of carbon emissions based on the transportation of construction crews, materials, and equipment in post-tensioned slab foundation construction, a foundation system widely used for production homes in the Greater Phoenix Arizona area. Post-tensioned slab foundation construction typically involves a concrete trade contractor, sub-trade contractors for grading aggregate base course (ABC) and post-tensioning, suppliers of ready-mix concrete, ABC and a concrete pump truck, a builder superintendent and code-compliance inspectors. This study includes multiple residential construction sites in the Greater Phoenix area, and consists of: (i) identifying all construction activities and the party responsible for each; (ii) collecting travel and fuel use data from trade contractors and through field observations; (iii) calculating CO 2 emissions for a generalized base case representative of the Greater Phoenix area and the relative contribution of various trades; (iv) studying the influence of material and equipment transportation; and (v) what-if analysis for material, equipment and crew transportation depending upon subdivision location, trade contractor location and home size. Further, CO 2 emissions of transportation in the framing phase, on-site equipment use and rework during the concreting phase are presented. The primary conclusions are: (a) ready-mix concrete transportation is a significant source of emissions in the concreting phase; other important components are transportation of the trade contractor crews and concrete pump truck; (b) the concreting phase and the framing phase are comparable in terms of transportation-based CO2 emissions even though these phases differ significantly in terms of cost and weight of materials transported; and (c) CO2 emissions for on-site equipment use are in the range of 6 to 12% of transportation-based CO2 emissions in the concreting phase. This research is valuable to home builders and specialty trade contractors who wish to measure their carbon emissions based upon on-site construction processes and compare environmental performance of different construction scenarios.