Ultra-high-performance concrete (UHPC), despite its superior mechanical and durability properties, has a high ${\mathrm{CO}}_2$ footprint owing to its high portland cement content. This drawback can be offset to a notable extent if a high volume of supplementary cementitious materials can be utilized to produce UHPC while maintaining mechanical and durability properties that are comparable to those of conventional UHPC. In this study the effects of high-volume cement replacement by Class-F fly ash (up to 70% by mass) on the mechanical, durability, and microstructure properties of UHPC are investigated, with the aim of encouraging moderate- to low-volume cement use in UHPC (from 600 down to $300\mathrm{kg}/{\mathrm{m}}^3$ ). Environmentally friendly-UHPC (ECO-UHPC) mixes, which have ${\mathrm{CO}}_2$ footprint intensities of less than $5\mathrm{kg}/{\mathrm{m}}^3/\mathrm{MPa}$ , have been synthesized with different replacements of cement by Class-F fly ash. Results suggest that concretes with ultrahigh strength ($>150\mathrm{MPa}$ ) and a strength greater than 100 MPa can be prepared with up to 40% and 70% replacements, respectively, without employing any special curing or fibers. A model has been developed to predict the compressive strength of fly ash–based UHPC from the contents and chemical compositions of its binders. UHPCs made with up to 60% cement replacement by Class-F fly ash exhibit durability properties comparable to that of UHPC without fly ash, in terms of water absorption, initial rate of water absorption, and corrosion risk. The depth of carbonation remains below the detection limit of 0.5 mm, up to 70% replacement.

Low- and middle-income countries have the largest health burdens associated with air pollution exposure, and are particularly vulnerable to climate change impacts. Substantial opportunities have been identified to simultaneously improve air quality and mitigate climate change due to overlapping sources of greenhouse gas and air pollutant emissions and because a subset of pollutants, short-lived climate pollutants (SLCPs), directly contribute to both impacts. However, planners in low- and middle-income countries often lack practical tools to quantify the air pollution and climate change impacts of different policies and measures. This paper presents a modelling framework implemented in the Low Emissions Analysis Platform - Integrated Benefits Calculator (LEAP-IBC) tool to develop integrated strategies to improve air quality, human health and mitigate climate change. The framework estimates emissions of greenhouse gases, SLCPs and air pollutants for historical years, and future projections for baseline and mitigation scenarios. These emissions are then used to quantify i) population-weighted annual average ambient PM2.5 concentrations across the target country, ii) household PM2.5 exposure of different population groups living in households cooking using different fuels/technologies and iii) radiative forcing from all emissions. Health impacts (premature mortality) attributable to ambient and household PM2.5 exposure and changes in global average temperature change are then estimated. This framework is applied in Bangladesh to evaluate the air quality and climate change benefits from implementation of Bangladesh's Nationally Determined Contribution (NDC) and National Action Plan to reduce SLCPs. Results show that the measures included to reduce GHGs in Bangladesh's NDC also have substantial benefits for air quality and human health. Full implementation of Bangladesh's NDC, and National SLCP Plan would reduce carbon dioxide, methane, black carbon and primary PM2.5 emissions by 25%, 34%, 46% and 45%, respectively in 2030 compared to a baseline scenario. These emission reductions could reduce population-weighted ambient PM2.5 concentrations in Bangladesh by 18% in 2030, and avoid approximately 12,000 and 100,000 premature deaths attributable to ambient and household PM2.5 exposures, respectively, in 2030. As countries are simultaneously planning to achieve the climate goals in the Paris Agreement, improve air quality to reduce health impacts and achieve the Sustainable Development Goals, the LEAP-IBC tool provides a practical framework by which planners can develop integrated strategies, achieving multiple air quality and climate benefits.