9 Concrete is a critical component of d eep decarbonization efforts because it impacts the building, 10 transportation, and industrial sectors. We use a bottom -up model of current and future building and 11 pavement stocks and construction in the US to contextualize the role of concrete in greenhouse gas 12 (GHG) reductions strategies under projected and ambitious scenarios, including embodied and use 13 phases of the structures’ life cycle. We show that projected improvements in the building sector result 14 in a reduction of 47% of GHG emissions in 2050 relative to 2016 levels, whereas ambitious 15 improvements result in a 56% reduction in 2050, which is 22 Gt cumulative saving. The pavements 16 sector shows a larger difference between the two scenarios wit h a 20% reduction of GHG emissions for 17 projected improvements and a 68 % reduction under the ambitious scenario, which is approximately 1.7 18 Gt. Over 70% of future emissions from new construction are from the use phase. 19 1 Introduction 20 Concrete is the most extensively used building material in the world because it possesses a unique 21 combination of attributes – strength, versatility, and durability – for a relatively low cost using raw 22 materials found all over the world. It is used in nearly every element of our built environment including 23 buildings, pavements, bridges, and water and energy systems. This ubiquity in infrastructure has also 24 made concrete use tightly linked to achieving societal sustainability goals. Thacker et al. found that 25 infrastructure, which m akes extensive use of concrete, either directly or indirectly influences the 26 attainment of every United Nations Sustainable Development Goal1. 27 On a weight -normalized basis, concrete has a lower carbon and energy footprint than nearly all 28 materials used in the built environment2. Nevertheless, the cement and concrete sec tors are deservedly 29 under scrutiny regarding their environmental footprint because of the sheer scale of production3. 30 Greenhouse gas (G HG) emissions from the production of cement (the primary driver of GHG emissions 31 for concrete) account for a little over 1% of the total US GHG emissions footprint4. Thus, the challenge of 32 sustainable development is manifest in microcosm in the use of concrete: accomplishing societal goals 33 while minimizing environmental impacts. 34 There is no question that we need to reduce the emissions associated with cement and conc rete 35 production. However, the total footprint of concrete, like any material that constitutes a complex 36 product, extends beyond production. Materials dictate the modes of manufacture and constrain the 37 operational performance of the products into which they are fashioned5. Concrete is the prime example 38 of this phenomenon. Forming the backbone of large, complex, long- lived systems, changes in the use of 39 concrete can positively or negatively impact the in -use performance and GHG emissions of these 40 systems for decades. 41 In this systems co ntext, we seek to evaluate the cost and effectiveness of a range of strategies for 42 reducing the GHG footprint of two important systems – buildings and pavements – including both 43 changes in cement and concrete production and changes in system design, mainte nance, and 44 operations. Mapping these changes for buildings and pavements is challenging, because the impact of 45 system structure is influenced by local context, the role of extant stock and its evolution, and the long 46 timeframe that needs to be considered. To overcome these challenges, we develop and apply spatially - 47 and temporally -heterogenous, life cycle models of the buildings and pavements systems. We limit our 48 analysis to the United States because of the extent of data required for modeling. In the United States, 49 PREPRINT 3 these systems account for over 60% of apparent cement usage according to data from the industry and 50 the building, transportation , and industry sectors account for 90 % of all GHG emissions4. As such, 51 changes in the structural components of these sy stems can provide influential leverage in meeting 52 climate targets. 53 1.1 Literature Review 54 There is an extensive literature on approaches to mitigate the embodied emissions of cement and 55 concrete production2,3,6 –9. Most mitigation approaches involve making cemen t with lower GHG 56 emissions or making concrete with less cement. Concrete GHG emissions can be lowered through the 57 use of cement substitutes such as low -carbon cements (blended cements or alternative clinker cements) 58 or supplementary cementitious materials (such as fly ash or granulated blast furnace slag) or through 59 active use of captured carbon to produce synthetic limestone aggregates or cure concrete3. 60 While embodied emissions of concrete are important, life cycle assessments of infrastructure systems 61 built using concrete have shown that in most cases they are much smaller than emissions that occur 62 during the use or operational phase of the structure. In most buildings , the energy consumption over 63 the building’s life dominates the total life cycle environmental impact , representing 80 -90% in many 64 cases10–13. Similarly, in most pavements , the excess fuel consumption in vehicles caused by pavement - 65 vehicle interaction (excess e nergy dissipation due to pavement roughness or deflection) is much larger 66 than the embodied impacts of paving materials. D epending on the context (i.e. the traffic and location) , 67 roughness and deflection -induced excess fuel consumption contribute 23% - 78% of the life cycle GHG 68 emissions of pavements14. Includ ing the reflectivity impact of pavements on the climate in the use phase 69 can increase the use phase impacts to approximately 90% of the total GHG impacts15. Thus, the ways in 70 which we design and maintain structures that use concrete can have much larger impacts than the 71 impact of materials. 72 Analyses of pavement systems focus on material flows16,17 or optimizing budgets and treatment 73 schedules to minimize vehicle fuel consumption and the associated life cycle GHG emission s 18,19. 74 Similarly, building system analyses concentrate on material quantities or energy consumption 20–24. Thus, 75 there is a disconnect between a nalyses of embodied GHG reductions for concrete that focus on 76 materials and do not put those reductions in the context of the full life cycle for the structures in which 77 they are used, nor the system of buildings and pavements . 78 We contextualize the role of concrete in greenhou se gas reductions in the United States building and 79 pavement sectors . This includes the potential impacts and costs of reducing the embodied impacts of 80 concrete along with changes in the design and maintenance of structures that use concrete throughout 81 their entire life cycle. To a limited extent, we examine other actions that can be used to lower GHG 82 emissions in US building and pavement systems . This allows us to evaluate concrete GHG re ductions in 83 the context of the systems and frame those opportunities based on cost and GHG reduction potential. 84 The models applied in this work consider geographic heterogeneity (at a US state level) in the 85 demographics of the current stock of buildings a nd pavements, local climate, prevailing construction 86 codes, norms for system maintenance, and, in the case of pavements, available public budgets for 87 infrastructure. Using this information, we identify a range of approaches that can be applied to bring 88 emissions from these systems to less than 50 % of current levels and how embodied and operational 89 emissions reductions strategies compare. 90 PREPRINT 4 2 Method 91 2.1 System attributes and strategies for scenarios 92 Our analysis of building and pavement systems in the US is based on attributes of those systems (e.g., 93 material or energy use) and strategies that may be used to lower GHG emissions. We estimate GHG 94 reduction potential for the strategies from 2016 to 2050 using two scenarios: projected and ambitious 95 improvements. Table 1 summarizes the building and pavement system attributes and strategies under 96 the two scenarios. Strategies are framed in terms of technical targets (e.g., % of renewab les in the grid) 97 and timing of adoption of those targets, which in some instances varies regionally. The projected 98 improvement scenario is intended to reflect a future where current trends to improve system attributes 99 will continue . For buildings this includes continued decarbonization of the electrical grid and increases in 100 energy efficiency requirements in building and appliance codes . For pavements this includes continued 101 improvement in vehicle fuel economy. For both systems, the projected improvemen t scenario evolves 102 toward the use of net zero emissions concrete ( portland -cement based and asphalt -based) through the 103 use of lower -carbon constituents (including recycled content) , carbon capture in cement production, 104 and use of captured carbon to produce aggregates and cure concrete . The ambitious i mprovement 105 scenario is intended to reflect a future where more aggressive actions to lower GHG emissions are 106 taken . In all cases, ambitious strategies are limited to technolog ies that exists today , but have not been 107 adopted at meaningful scale . Building ambitious strategies are similar to the projected actions but with 108 earlier timing of adopting technical targets. Pavements ambitious strategies are primarily tied to an 109 increase in funding for pavement maintena nce and repair . This increase is funding is important because 110 unlike buildings, there are few current policies explicitly intended to improve infrastructure GHG 111 emissions. As such, for the projected improvement scenario we assume that there is no change ov er 112 time in the pavement system’s stiffness, reflectivity, or types of maintenance, rehabilitation, and 113 reconstruction actions (referred to as MRR). The increase in available budget in the pavement ambitious 114 strategy allows for more extensive application of all pavement -related improvements , so there is more 115 of an interdependency among these ambitious strategies . Details on the technical targets and timing of 116 pavement and building sector by region are in Section 1.8 and 2.6 of the Supporting Information (SI), 117 respectively . 118 119 PREPRINT 5 Table 1. Building and pavement system GHG reduction strategies for system attributes under projected and ambitious 120 improvement scenarios. CCUS = carbon capture, utilization, and sequestration; US EIA = The Uni tes States Energy Information 121 Administration ; IECC = International Energy Conservation Code ; HVAC = heating, ventilation , and air conditioning. 122 Attribute Definition Projected Improvement Scenario Ambitious Improvement Scenario Buildings Concrete Production GHG emissions in concrete mix production will be reduced by lin early implementing 50% low -carbon binders by 2025 as well as CCUS by 2045 , which involves carbon capture for cement plants and utilization of captured carbon for aggregate production . GHG emissions in concrete mix production will be reduced by linearly implementing 50% low -carbon binders by 2022 as well as CCUS by 2035. Energy Codes (appliances, lighting, HVAC, insulation) Adoption of newer energy codes in newly constructed buildings. 100% IECC 2015 adoption in 2025. 100% Energy Efficient adoption in 2045. Adoption of newer energy codes in newly constr ucted buildings. 100% IECC 2015 adoption in 2025. 100% Energy Efficient adoption in 2035. Concrete Disposal Carbon uptake due to concrete carbonation after the demolition of buildings. Carbonation will be linearly implemented from 0% to 50% by 2050. Carbon uptake due to concrete carbonation after the demolition of buildings. Carbonation will be linearly impleme nted from 0% to 100% by 2050. Electricity Grid Grid decarbonization following the US EIA projection until 2050. Grid decarbonization following the US EIA projection for New York (NYLI) which based on a 33% reduction in GHG emissions. Pavements Materials Asphalt: reclaimed asphalt pavements (50% - current maximum use by states) and warm-mix asphalt (100%) usage*. Concrete: carbon capture for cemen t (100%) and low -carbon binders (50%) *. Use low impact binder, recycled asphalt, and CCUS tech nologies (including synthetic aggregates) to achieve zero -impact mixtures**. Smoothness Equivalent to the required budget for keeping surface roughness values constant (the average annual roughness is constant from 2016 -2050). 20% increase in the currently projected budget . Concrete overlay According to the regional actions already defined for each zone , some of which already include concrete overlays. Inclusion of concrete overlay action for asphalt pavement (interstates, arterials, and collectors) in the regional PREPRINT 6 2.2 Modeling approach and data sources 123 We used a bottom -up approach shown in Figure 1 to model the characteristics of individual reference 124 buildings and pavements and then scale up the results to regional networks and ultimately the entire 125 country using temporally and spatially -varying data. To capture spatial variation in building codes, 126 construction practices, structural performance , climate, and energy demand , reference designs and 127 practices were developed for climatic regions across the United States . For buildings, six reference 128 designs (representing the two most common building materials used in residential (single and multi- 129 family) and commercial buildings) were developed for each of the fourteen climate zones described by 130 the US Department of Energy (DOE). For pavemen ts, several reference designs and operating schedules 131 were estimated for four pavement types for each of the four climatic regions described by the US 132 Department of Transportation. In both cases, states were assigned to their appropriate region and the 133 prevalence of reference designs was modeled using state level data. S everal models were used to 134 establish the associated material, operational energy, and other use phase requirements for each design 135 over the course of the analysis period (2016 -2050) . A dynam ic life cycle inventory was developed to 136 capture the geographical and temporal aspects of the technologies and practices in different states to 137 precisely estimate the material, operational energy, and other use phase requirements over the course 138 of the ana lysis period (2016 -2050) . The buildings and pavements modeled in the analysis represent 139 treatment actions for regions that do not already have them. Reflectivity Average network aged albedo values: Concrete = 0.25, Asphalt = 0.1 (the average reflectivity value of all the segments will stay constant for the 2016 - 2050 period). Use reflective coating/binder to reach average network albedo = 0.3**. Stiffness Current stiffness values existing in the national road network (the average reflectivity value of all the segments will stay constant for the 2016 -2050 period). Increase the stiffness to the 95th percentile of the current frequency . Concrete carbon uptake Use: the carbon binding capacity of the mixtures will stay at 1.1 (status quo). End-of-Life: the concrete will be recycled or landfilled without carbon uptake. Use: the carbon binding capacity of the mixtures will increase to 1.3**. End-of-Life: concrete rubble will be spread and temporarily stockpiled for 18 months. Vehicle fuel efficiency According to the U.S. Energy Outlook forecast . Same as the projected improvement scenario. * The strategy was linearly implemented on repaired and reconstructed road s to 2045, and then on all repaired and reconstructed roads thereafter. ** The strategy wa s linearly implemented on repaired and reconstructed roads to 20 35, and then on all repaired and reconstructed roads thereafter. PREPRINT 7 approximately 60% of the total cement consumption in the US 25. Details of the methodology along with 140 the input data sources are described in the SI , section 1 and 2 for buildings and pavement s, respectively. 141 142 Figure 1. Summary of the bottom -up approach for investigating the life cycle GHG impact of buildings and pavement s in the US . 143 2.3 Limitations 144 Our analysis uses projected and ambitious scenarios that include a set of strategies for lowering US GHG 145 reductions. The strategies are intended to represent major points of leverage but are by no means 146 comprehensive . Indeed, other design -focused strategies could be considered including design for 147 material efficiency, longer life, increased hazard resistance, smaller size, adaptability, and recycling or 148 reuse. Furthermore, there are other actions that could be taken within the building sector such as 149 retrofits of existing buildings, lowering embodied impacts of other building materials besides concrete, 150 and increasing use of on- site renewables. Increasing recycling of all construction and demolition waste 151 would also be beneficial. Thus, the results of this analysis should not be viewed as precise since we do 152 not account for numerous sources of uncertainty in data and future trends, or comprehensive since we 153 have not evaluated the potential of all GHG reduction strategies. However, the results still provide 154 valuable insight on the potential of the strategies in both the projected and ambitious scenarios to 155 mitigate GHG emissions in the building and pavement sectors. 156 3 Results 157 3.1 Opportunities for GHG reductions 158 The original stated goal for the US in the Paris Agre ement was to lower the total anthropogenic GHG 159 emissions from 6. 5 Gt in 2017 to a range of 1.7 -2.3 Gt in 205026, a reduction of 65 – 75% . When electric 160 power emissions are allocated to end- use sectors, buildings, transportation , and industry accounted for 161 2.0, 1.9, and 1.9 Gt of US GHG emissions in 2017 , respectively4. This represents 90% of the 6.5 Gt of US 162 GHG emissions. Thus, achieving GHG reduction targets requires significant contributions from all three 163 of these sectors , and the use of concrete impacts all of them. 164 PREPRINT 8 Figure 2 shows the historical and our modeled future GHG emissions for both the buildings and 165 pavement sectors. Historical emissions increase in the 1980s and 90s due to growth in building stock 166 and the pavement network and vehicle -miles traveled . Emissions peak in the early 2000s and decrease 167 due to building energy efficiency improvements , a lack of pavement network expansion , and vehicle fuel 168 economy improvements. 169 In the buildings sector, the projected improvement scenario results in a modeled GHG emission of 170 approximately 1 Gt in 2050 , a reduction of 47% relative to 2016 levels . The ambitious improvements 171 scenario results in a 56% reduction in 2050 down to approximately 0. 8 Gt GHG. In either scenario, 172 modeled building sector emissions in 2050 are split evenly among residential (single and mult i-family) 173 and commercial (all other categories) buildings, with single -family buildings the largest individual 174 category of buildings by far. Both scenarios project n early identical use of concrete in the buildings 175 sector, around 240 Mt (110 Mm3) in 2050. Energy consumption in t he building stock plays a significant 176 role in the sector, which is why the largest opportunities for GHG emission reductions shown in Figure 177 2a (and the cumulative reduction quantities in Figure 3a) derive from changes to the electricity grid 178 (purple line) , appliances (orange line) , and lighting (green line) . Changes in these three attributes make 179 up over 85% of the 22 Gt of the cumulative GHG reductions projected over 34 years under the 180 Ambitious Improvements scenario ( Figure 3a). In this analysis, HVAC improvements , enhanced thermal 181 insulation, and concrete production only affect new construction, so opportunities for reduction are 182 more limited. Although the a mbitious scenario considers changes to important system attributes such as 183 electricity grid decarbonization and more intensive adoption of energy efficiency codes, its 2050 results 184 represent only an additional 10% reduction in GHG e missions from 2016 levels. Unfortunately, this 185 change is not enough to reach the 65% reduction target. This suggests that the sector will have to look 186 to other solutions or possibly much more aggressive changes to these attributes to reach the goal. 187 The p avements sector is estimated to have a 20 % reduction of GHG emissions in 2050 relative to 2016 188 levels under the projected improvement scenario . Our modeling projects the use of 90,000 t (38,000 m3) 189 of concrete in 2050. For the ambitious scenario we project both a much more intensive use of concrete 190 (260,000 t or 110,000 m3) and a much larger reduction of GHG emissions. (See Figure 2b.) 191 Pavement sector emissions reductions under the projected scenario are relatively modest because there 192 are few current efforts to systematically improve pavement network GHG intensity. R eductions within 193 the projected improvement scenario are nearly evenly split between expected improvements in vehicle 194 fuel economy and reduced materials production impacts , including increased concrete carbon uptake 195 (Figure 2b and Figure 3b). The project improvement scenario exhibits minimum emissions around 2037, 196 a behavior in contrast to all of the other analyses. This occurs because of projected vehicle fleet 197 characteristics , which are an important determinant of pavement system emissions. Current US DOE 198 projections assume fleet fuel efficiency improves until the late 2030s. Beyond th is time, fleet emissions 199 increase as vehicle -kilometers traveled continues to grow. 200 The ambitious improvement scenario makes it clear that there are significant opportunities for 201 reductions when there are changes to all pavement system attributes. This in dicates there is urgency for 202 action to shift behaviors in the pavement sector to embrace the strategies in the am bitious scenario. 203 Increasing budget is particularly important , leading to more than one quarter of the reductions seen in 204 the ambitious improv ement scenario, because it enables increased maintenance, rehabilitation, and 205 reconstruction activities, which increase smoothness and lower excess fuel consumption. Notably , for 206 PREPRINT 9 the pavements system, the materials and carbon uptake category , including the use of concrete, 207 represent the largest opportunity for reduction of GHG emissions . Materials changes account for more 208 than one third of the reductions seen in the ambitious scenario , leading to a cumulative reduction of 209 nearly 0.6 Gt over the modeled time horizon (seventh bar in Figure 3b). A relatively small but significant 210 reduction of 12.6 Mt CO 2 can be obtained from implementing strategies to elevate the carbon uptake of 211 concrete pavements during the use and end -of-life phases of the life cycle , with more than 82% of that 212 reduction stemming from stockpiling the demolished concrete temporarily. The remaining 18% of the 213 reduction comes from the uptake increase during the use phase owing to the relatively large exposed 214 surface area of concrete pavements. 215 216 PREPRINT 10 217 Figure 2. Built area and historical and future estimated GHG emissions in the (a) buildings and (b) pavements sectors. Historical 218 emissions are before 2016. 2016 levels are used as a reference for the reduction of future emissions. Projected and ambitious 219 emissions reductions for the individual attributes listed in Table 1 are plotted (with the exception of buildings ambitious 220 strategies, which are omitted for clarity) , with the cumulative total projected and ambitious emissions reduction noted . The 221 ambitious scenario GHG emissions are broken down by building and pavement types. 222 223 PREPRINT 11 224 225 Figure 3. Cumulative 2016-2050 GHG emission reductions under the ambitious scenario for (a) buildings and (b) pavements. 226 Reductions for each category are broken down into projected and ambitious scenario contributions (ambitious builds off of 227 projected). The 2016 level assumes that emissions do not change from 2016 levels over the entire 34 -year period. 228 PREPRINT 12 3.2 GHG Abatement Costs 229 The costs of implementing GHG mitigation strategies under the ambitious scenario are shown in the 230 abatement curves in Figure 4. Both sectors have negative abatement costs for the use of by -products 231 and recycling content (low -carbon binders and reclaimed asphalt) because they are generally lower cost 232 than virgin materials. More ambitious strategies around decarbonizing the electrical grid, improving fuel 233 economy, and captu ring carbon and using it in concrete require more investments to make them 234 feasible . For the building sector, several strategies lead to reductions in energy consumption, which 235 decreases user costs and result in negative abatement costs . 236 Estimating abateme nt costs for pavements is difficult because there is not a clear way to allocate budget 237 increase costs across the strategies . In particular, smoothness is not shown in Figure 4 b because its 238 estimated cost is over $1000/tCO 2-eq due to the fact that its cost is based entirely on an action 239 (rehabilitation or reconstruction) that is motivated by more than simply GHG miti gation. As such , the 240 abatement costs should be viewed as an incremental abatement cost assuming that sufficient budget is 241 available to treat the pavement surface, which would result in a smoother pavement. Investment in 242 concrete overlays have long -term ben efits over the life of the pavement in the instances for which they 243 are appropriate, but discounting of the benefits makes the abatement cost slightly positive. 244 Improvements in stiffness and reflectivity to asphalt pavements will be accomplished through th e use of 245 mechanisms such as added synthetic fibers and surface coatings , which are not necessary for concrete 246 due to its higher stiffness and reflectivity . The temporary stockpiling associated with the end -of-life 247 carbon uptake has a moderate abatement cos t. 248 PREPRINT 13 249 250 251 252 Figure 4. GHG abatement cost for ambitious strategy over 34 years for (a) buildings and (b) pavements. CCUS = carbon capture, 253 utilization, and sequestration. The pavement strategy smoothness is not shown because of the difficulty of estimating an 254 abatement cost that is separate from the budget increase for pavement maintenance and repair. The x -axis quantifies GHG 255 abatement potential for the strategy in CO 2-eq. The cumulative GHG abatement across all strategies is shown at the end of the 256 x-axis. 257 PREPRINT 14 3.3 Embodied and use phase GHG emissions for new construction 258 Although the existing stock of pavements and buildings have a significant influence on life cycle GHG 259 emis sions, it is important to evaluate the embodied and use phase trade -offs of new construction since 260 it is often easier to influence. As shown in the inset figures in Figure s 5a and 5b , less than 30% of the 261 cumulative life cycle emissions of new pavement s and buildings constructed after 2017 are estimated to 262 come from the embodied phase (in this figure, use phase emissions are solely from the energy 263 consumption of buildings and pavements constructed after 2017 ). In the building sector it is noteworthy 264 that embodied emissions are relatively flat and are nearly identical for both projected and ambitious 265 cases. This is the result of competing mechanisms of increasing building c onstruction, increasing 266 materials use to improve energy efficiency, and decreasing impact of concrete from use of low -carbon 267 strategies. Use phase strategies will lower overall energy consumption and GHG emissions in the sector, 268 but from a life cycle persp ective operational energy consumption will still drive emissions from new 269 construction through 2050 . For new construction, the projected and ambitious strategies do not lead to 270 notable differences in net emissions . 271 In the pavement sector, Figure 5 b shows that use phase emissions can be held relatively flat in the 272 ambitious scenario despite traffic growth and an expansion of treated pavement area. This is in stark 273 contrast to the projected scenario, which reiterates the critical importance of increased pavement 274 network budget to enable use phase reductions. As shown in the upper chart of Figure 2b, it is predicted 275 that the whole pavement network will have been treated at least on ce by 2040. Therefore, there is a 276 moderate increase in the use phase part of the life cycle GHG emissions around this time period because 277 there is an increase in traffic demand while the fuel efficiency and other solutions reach their saturation 278 point. The solutions for achieving net -zero asphalt and concrete mixtures result in zero emissions in 279 2035 in the ambitious scenario and the share of embodi ed impact in the ambitious scenario drops the 280 cumulative embodied emissions to 25% from 30% in the projected scenario . 281 PREPRINT 15 282 283 Figure 5. Cumulative embodied and use phase GHG emissions for a) new buildings and b) treated pavement area . Insets show 284 the breakdown of cumulative emissions over the entire time period. 285 286 287 288 PREPRINT 16 4 Discussion 289 This analysis has provided insight on the potential role of concrete in US GHG reductions, which is 290 important given its status as the most used construction material and its relevance to building, 291 transportation, and industrial sector GHG emissions. Our results demonstrate that continuing current 292 trends in the building sector (e.g., grid decarbonization and stringent building energy codes) would be 293 expected to reap substantial benefits with per annum sector emissions dropping nearly 50% by 2050 294 even with a continued intensive use of concrete (240 Mt in 2050) . Unfortunately, even more aggressive 295 adoption of GHG reduction strategies (our ambitious scenario), does not seem to be sufficient to meet 296 stated Paris targets (modeled sector emissions drop by 56%, short of the 65 -75% reduction target). 297 Additional measures such as further grid decarbonization or extensive refurbishment of the existing 298 building stock will be needed. For pavements the story is almost completely inverted. Current trends , 299 including the use of 90,000 t of concrete, would lead to only modest reductions (20%) in per annum 300 emissions by 2050. Clearly, more significant intervention is required in pave ments in the form of 301 increased paving budgets, which increase pavement quality and durability, while enabling numerous 302 GHG reductions such as increased pavement reflectivity and stiffness. Implementing these strategies 303 (our ambitious scenario) appears to allow the pavement sector to reach Paris targets (modeled sector 304 emissions drop by 68%, reaching the 65 – 75% target) even while making use of 260,000 t of concrete 305 (nearly three times the level in the projected improvement scenario) . 306 This analysis also makes plain that use phase emissions will continue to dominate the life cycle GHG 307 emissions of buildings and pavements. As such, even the achievement of concrete with net zero 308 embodied impacts is insufficient to achieve GHG reduction targets required for m inimizing the worst 309 effects of climate change. However, this work has shown that concrete and other construction materials 310 can play a significant role by enabling reductions in the use phase by improving building energy 311 efficiency, decreasing vehicle exces s fuel consumption on pavements, and increasing radiative cooling 312 through higher albedo surfaces. To meet deep decarbonization goals we will need to pursue both 313 embodied and use phase GHG reduction strategies. In particular, we will need to continue the pu sh for 314 reducing energy consumption of vehicles and building equipment while decarboniz ing the electrical grid . 315 While the abatement cost estimates demonstrate that there are some strategies we should pursue 316 immediately because of their cost savings, partic ularly in the use of waste materials and energy - 317 efficiency improvements, investments will be required to meet the highest reduction levels. In 318 particular, the cost s associate d with CCUS pathways and constraint s in the supply of some low-carbon 319 binders mean that the cost -effectiveness of embodied GHG reduction for concrete remains a challenge. 320 The cost of capturing carbon in the cement industry is among the highest of all industries27 and the 321 production of synthetic aggregates requires a significant scale -up effort28. Hence, it is critical that these 322 embodied impact reduction strategies receive government support in much the s ame way that 323 renewable energy technologies have been supported. The key difference is that we have shown that 324 when applied wisely this will lead to both embodied and use phase GHG reductions. Such investments 325 will move us closer to the goal of sustainable development where society has the built environment 326 necessary for equitable opportunities while mitigating the impacts of climate change. 327 328 329 PREPRINT 17 Acknowledgments 330 This research was supported by the Concrete Sustainability Hub at MIT, with sponsorship provided by 331 the Portland Cement Association and the Ready Mixed Concrete Research and Education Foundation. 332 Author contributions 333 J.G., F.U., and R.K. conceived the study. J.G., H.A., E.V ., F.G, and R.K. designed the approach. E. V. 334 developed the building system model and conducted the building sector analyses. H.A. and F.G. 335 developed the pavement system model and conducted the pavement sector analyses . All authors 336 contributed to interpreting the results and writing the paper. 337