Quantitative assessment of the impact of use of Portland limestone cements in North Carolina concrete pavements.

摘要

Production of portland cement contributes significantly to global carbon emissions. In order to reduce the carbon footprint of concrete and to construct more sustainable highway infrastructure, blended cements are increasingly being utilized in pavement concrete mixtures. Blended cements, including portland limestone cements (PLC) require less clinker, and therefore, carbon emissions associated with calcinations and other production processes are reduced. PLC has been accepted as an alternative to ordinary portland cement (OPC) in many European and Latin American countries as well as in Canada. In the United States a number of state highway agencies are showing increasing interest in using PLC in highway concrete. North Carolina Department of Transportation (NCDOT) has recently enabled the use of PLC by updating its concrete specifications, but does not currently have data to support performance of concrete made with PLC and other local materials. Use of PLC in concrete pavements could have both economic and sustainability benefits, but a quantitative assessment of PLC with North Carolina materials is needed to support the state's decision to allow and potentially promote PLC use in highway concrete.;In this study, eighteen different concrete pavement mixtures were produced using three different cements (two OPC and one PLC) and two different fly ash sources, along with coarse and fine aggregates from the Mountain, Piedmont, and Coastal regions of North Carolina. Laboratory tests were performed to evaluate the mechanical properties and durability performance of the concrete, and to facilitate comparison of the performance of the OPC and PLC concretes. To quantify the potential sustainability benefits of use of PLC concrete, the web-based life cycle assessment (LCA) tool, Green Concrete, was utilized to model emissions linked to cement manufacture. Using the web-based tool, an LCA analysis was performed to evaluate the impacts of increasing limestone percentage, including fly ash with the PLC, changing the technology for finish milling/grinding/blending of portland cement, and changing the energy source for the electricity grid on the criteria air pollutant emissions.;Results from laboratory testing indicated that mechanical properties of the PLC concrete and OPC concrete batched using materials locally available to North Carolina were similar. Results from durability performance tests also tended to show similar results for OPC and PLC concrete when fly ash was not used. Enhanced durability performance of concrete, particularly reduced permeability, appears to result from the pairing of both OPC and fly ash, as well as PLC and fly ash. Results from LCA with the Green Concrete web tool show that use of PLC can result in significant reduction of criteria air pollutant emissions associated with concrete production. By increasing the limestone content in cement from 0% to 20%, criteria air pollutant emissions may be reduced up to 20%.