Approaches For Improving Sustainability With Regard To Production Of Aggregates, Asphalt, And Concrete Materials
Some general approaches to improving pavement sustainability (and trade-offs to be considered) with regard to aggregate production, asphalt materials, and concrete materials are summarized in tables 1, 2, and 3, respectively. See Chapter 3 (.pdf) of the Reference Document for more details.
| Aggregate Materials Objective | Sustainability Improving Approach | Economic Impact | Environmental Impact | Societal Impact |
|---|---|---|---|---|
| Reduce the Amount of Virgin Aggregate Used | Use more aggregates derived from Recycled, Co-Products and Waste Materials (RCWM) sources. | Can potentially reduce cost, and preserve scarce or difficult to permit virgin sources. May increase cost depending upon availability, transportation, or processing required; reduce ability to recycle in the future; durability; special pollution problems (pH, toxicity, contaminants). | Dependent on characteristics of RCWM, considering transportation, processing, ability to recycle multiple times, special pollution problems. | Preserves virgin sources. Can reduce need for new sources and associated impacts. Reduces space in landfills. Potential for negative impacts depending upon transportation, processing requirements. |
| Use more durable aggregate, maximizing pavement life. | May increase initial cost, decrease life cycle cost. | Dependent upon transportation distance if not locally available. | Primarily dependent upon transportation. | |
| Reduce the Impact of Virgin Aggregate Acquisition and Processing | Review environmental impact and remediation plans of different aggregate sources when permitting (handled via the National Environmental Policy Act [NEPA] guidelines or equivalent environmental impact review [EIR] and permit process in many states). | Dependent upon requirements imposed by permit. Most permit processes do not consider impacts of locating quarries outside of the jurisdictional area and importing the aggregate (transfer of impacts). | More sustainable features for quarry may come from permitting process. | More sustainable features for quarry may come from permitting process. |
| Implement processing and mining operations using less or lower impact energy sources and less water. | Will often result in initial cost increase due to changeover and life cycle cost decrease due to greater energy efficiency. | Will generally reduce environmental impact. | Will often reduce societal impact. | |
| Reduce the Impact of Aggregate Transportation | Use locally available materials or those using a low impact mode for transportation (next item). | Will often reduce initial cost, may increase life cycle cost if there are significant differences in durability. | Will often reduce environmental impact. | May increase impact for those near local source production and transportation locations. |
| Minimize transportation impact by maximizing use of marine/barge and rail transport and minimizing truck transport. | Will often reduce cost. | Will usually reduce environmental impact. | Will usually reduce societal impact, focusing it on marine and rail routes reducing noise, safety issues compared with road transport. | |
| Facilitate permitting of aggregate sources and processing sites near major use areas. | Will generally reduce cost due to reduced transportation cost. | Will usually reduce environmental burden due to reduction in truck transportation. | Will increase impact on those living near mining or processing sites. |
| Asphalt Materials Objective | Sustainability Improving Approach | Economic Impact | Environmental Impact | Societal Impact |
|---|---|---|---|---|
| Reduce Virgin Binder Content in Asphalt Concrete | Use greater quantities of reclaimed asphalt pavement (RAP) if same or better performance can be realized. | Reduces cost of asphalt concrete if RAP available. | Dependent on performance, energy costs of mixing, transportation. | Extends life of petroleum resources. Reduced need for landfill. |
| Use rubberized asphalt for binder in asphalt concrete. | Some increase in initial cost, impact of mixture design higher, potential payback in less material for thin overlays, increased life. | Reduces impacts by decreasing amount of materials needed over time horizon. | Reduced exposure of public to accidents in work zones. | |
| Use recycled asphalt shingles (RAS) as partial replacement for asphalt binder if same or better performance can be realized. | Reduces cost of asphalt concrete if RAS available. | Extends life of petroleum resources. Reduced need for landfill. | ||
| Use bio-binders. | Impacts and trade-offs unknown. | Impacts and trade-offs unknown. | Impacts and trade-offs unknown. | |
| Use sulfur-modified asphalt. | Not well quantified. | Potential difficulty in future recycling. | Risks for worker health. | |
| Reduce Virgin Aggregate Content in Asphalt Concrete | Use greater quantities of RAP if the same or better performance can be realized. | Reduced cost of asphalt concrete if RAP available. | Dependent on performance, energy costs of mixing, transportation. | Extends life of aggregate resources. Reduced need for landfill. |
| Reduce Energy Consumed and Emissions Generated to Produce Asphalt Concrete | Use warm-mix asphalt (WMA) to reduce mixing temperatures. | Zero to small increase in cost. | Reduced energy and greenhouse gas (GHG) emissions to make asphalt concrete. Impact of producing WMA additives needs to be considered. | Reduced worker exposure to fumes. |
| Change fuel used for heating to reduce emissions, such as natural gas. | May increase cost. | Reduced emissions to make asphalt concrete. | Reduced worker exposure to fumes. | |
| Reduce Energy Consumed and Emissions Generated to Produce Asphalt Concrete | Employ new, more efficient plant designs to reduce energy consumption and increase the percent RAP and RAS used | Increased capital cost to upgrade existing facilities. Reduced operating cost due to decreased energy consumption as well as increased use of RAP and RAS. | Reduce emissions to make asphalt concrete through reduced fuel consumption and higher percentage use of RAP and RAS | More efficient utilization of recovered materials such as RAP and RAS |
| Extend Lives of Asphalt Concrete Materials | Increase compaction specifications, no trade-offs. | Some increase in initial cost for extra contractor effort and inspection, large payback in increased life. | Reduces impacts by decreasing amount of materials needed over time horizon. | Reduced exposure of public to accidents in work zones. |
| Use WMA to obtain better compaction. | Zero to small increase in cost, payback in increased life. | Reduces impacts by decreasing amount of materials needed over pavement life cycle. WMA additives needs to be considered. | Reduced exposure of public to accidents in work zones | |
| Improved mixture designs. | Some cost for new equipment, training, payback from longer lives. | Reduces impacts by decreasing amount of materials needed over life cycle. | Reduced exposure of public to accidents in work zones. | |
| Use polymer-modified binders. | Some increase in initial cost, impact of polymer production, potential payback in increased life. | Reduces impacts by decreasing amount of materials needed over life cycle. Impact of producing polymer additives needs to be considered. | Reduced exposure of public to accidents in work zones. Increased exposure of workers to fumes. | |
| Use rubberized asphalt. | Some increase in initial cost, impact of mixture design higher, potential payback in less material for thin overlays, increased life. | Reduces impacts by decreasing amount of materials needed over time horizon. | Reduced exposure of public to accidents in work zones. Increased exposure of workers to fumes. | |
| Extend Lives of Asphalt Concrete Materials | Use lime or liquid anti-strip to decrease risk of early failure due to moisture damage. | Slight increase in initial cost, payback from extended life where warranted. | Initial impact from manufacture of materials, potential payback if life would otherwise be shortened. | Increased worker exposure to lime or chemicals. |
| Reduce Materials Transportation Impacts | Use more locally available materials. | Lower initial cost. Potential for greater life cycle cost if perform is compromised. May have shorter lives if performance-related properties are poorer. | Reduces impacts of transportation of materials, particularly important if trucks would be used. May have shorter lives if performance-related properties are poorer. | Reduced exposure of public to trucking. |
| Extend Lives of Seal Coats | Use rubber or polymer binders. | Some increase in initial cost, impact of binder production higher, potential payback from increased life. | Increased impact due to production of polymers. Potential payback from improved life. | Polymers made from finite petroleum resources. |
| Reduce Need for Virgin Materials and Transportation | Use in-place recycling (full-depth reclamation, partial-depth recycling). May have high construction variability. | Can potentially reduce initial cost by reducing transportation of virgin materials and permitting thinner overlays, and may extend life where appropriately selected and designed. May have high construction variability. | Can reduce use of virgin materials depending on life. Can reduce transportation of materials. Energy savings dependent on technology and life. May have high construction variability. | Fewer heavy trucks on the road hauling materials. |
| Increase Pavement Albedo where Warranted (See Chapter 6) | Use lighter colored aggregates, place light colored chip seals, other reflective surface treatments. | Cost may be greater if reflective treatment not otherwise needed. Can potentially reduce risk of rutting of asphalt concrete. More materials used if additional coating applied that is not otherwise needed. | Needs to be evaluated on a case by case basis (see Chapter 6). If warranted, specific impacts that are positively impacted must be noted. Unintended consequences should also be examined. | Needs to be evaluated on a case by case basis (see Chapter 6). If warranted, specific impacts that are positively impacted must be noted. Unintended consequences should also be examined. |
| Concrete Materials Objective | Sustainability Improving Approach | Economic Impact | Environmental Impact | Societal Impact |
|---|---|---|---|---|
| Reduce Non-Renewable Energy Consumption and GHG Emissions in Cement Manufacturing | Improved cement plant efficiency through better energy harvesting and improved grinding | High capital cost but lower cost of manufacturing | Reduced energy consumption and GHG emissions | Less fuel consumed and emissions generated |
| Utilization of renewable energy including wind and solar | High capital cost but lower cost of manufacturing | Reduced non-renewable energy consumption and GHG emissions | Less non-renewable fuel consumed and GHG generated | |
| Utilization of more efficient fossil fuels | Lowers manufacturing costs | Reduces emissions per unit of energy used | Cleaner burning fuel | |
| Utilization of waste fuels | Lowers manufacturing costs | Beneficial use of waste material | Reduces materials in landfills | |
| Utilization of biofuels | Reduces cost to cost neutral | Reduces GHG emissions | Reduces dependency on fossil fuels | |
| Minimize clinker content in portland cement through allowable limestone additions and inorganic processing additions | Reduces cost to cost neutral | Reduces GHG emissions and consumption on fuel | Reduces dependency on fossil fuels and lowers emissions | |
| Increase production of blended cements containing limestone or supplementary cementitious materials (SCMs) | Reduces cost | Significant reduction in energy consumption and GHG emissions. Redirects RCWMs from landfill | Reduces dependency on fossil fuels and less material sent to landfill | |
| Increase concrete mixing plant efficiency and reduce emissions | Increased capital cost but decrease production costs | Reduced emissions | Reduced local emissions including noise and particulate | |
| Utilization of renewable energy | Cost neutral to increase cost | Reduced emissions | Reduced emissions | |
| Use electrical energy from the grid | Depends on proximity to grid - should save cost | Reduced emission, better emission controls | Reduced local emissions | |
| Reduce Energy Consumption and Emission in Concrete Production | Use less cement in concrete mixtures without compromising performance | Reduce cost of concrete | Reduced emissions and energy | Longer lasting pavements - less delays |
| Use more blended cements without compromising performance | No impact on cost | Reduced emissions and energy | Longer lasting pavements - less delays | |
| Increase addition rate of SCMs at concrete plant without compromising performance | Reduce cost of concrete | Reduced emissions and energy | Longer lasting pavements - less delays | |
| Reduce Water Use in | Recycle washout water | Cost neutral to slightly added cost | Use less water resources | Improved water quality |
| Hydraulic Cement Concrete (HCC) Production | Recycle water used to process aggregates | Cost neutral to slightly added cost | Use less water resources | Improved water quality |
| Increase Use of RCWMS and Marginal Materials as Aggregate in Concrete | Change specifications to allow greater amounts of RCWMs to be used in concrete without compromising performance | Reduced cost | Less landfill material, less transportation | |
| Use RCWMs and marginal aggregates in lower-lift of two-lift pavement | Cost neutral to slightly added initial cost; potential for reduced life cycle costs | Less landfill material, less transportation | ||
| Improve the Durability of Concrete | Lower w/cm through admixture use | Cost neutral to slightly added cost | Longer lasting pavements | Less delays over life cycle |
| Utilize an effective QA program throughout material production phase | Slightly added initial cost - save cost on litigations | Longer lasting pavements | Less delays over life cycle |