Grantee Research Project Results
Final Report: High Albedo and Environment-Friendly Concrete for Smart Growth and Sustainable Development
EPA Grant Number: SU832477Title: High Albedo and Environment-Friendly Concrete for Smart Growth and Sustainable Development
Investigators: Reza, Farhad , Boriboonsomsin, Kanok , Stiles, Justin , Strohl, Brandon , Seals, Audrey , Schmidt, Naomi
Institution: Ohio Northern University
EPA Project Officer: Page, Angela
Phase: I
Project Period: October 1, 2005 through September 30, 2006
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2005) RFA Text | Recipients Lists
Research Category: P3 Challenge Area - Chemical Safety , Pollution Prevention/Sustainable Development , P3 Awards , Sustainable and Healthy Communities
Objective:
Concrete surfaces absorb heat from sunlight due to their low solar reflectivity (albedo). This increases the local ambient temperature in urban areas (the so-called “heat-island” effect). The heat island effect leads to a waste of energy because of increased cooling costs. It also contributes to heat-related illness and death. In addition, the heat island effect adversely affects air quality, which in turn can be detrimental to human health. Researchers in California simulated the influence of pavement albedo on air temperature in Los Angeles and predicted that increasing the albedo of 1,250 km2 of pavement by 0.25 would save cooling energy worth $15 million per year, and reduce smog-related expenses by $76 million per year. In essence, the development of an economically viable and ecologically sound alternative for concrete infrastructure will lead to major advancements towards the goal of a sustainable future.
The challenge tackled with this research project was the design of new concrete mixtures with higher solar reflectance than that of conventional concrete for use in pavement surfaces. These new concrete mixtures had to be economically viable, environment-friendly, durable, structurally sound, aesthetically acceptable and safe for traffic. The successful mixes, based on laboratory test results of albedo values, are defined as those which achieve a 60-70% increase in albedo over conventional concrete and utilize more than 10% cement replacement. Note that the manufacture of cement consumes an enormous amount of energy and contributes to greenhouse gas emissions. Worldwide, the manufacture of cement accounts for 6-7 % of the total carbon dioxide (CO2) produced by humans, adding the greenhouse gas equivalent of 330 million cars driving 12,500 miles per year. Thus, any reduction in the consumption of cement resulting from the use of alternative materials is beneficial to the environment.
Thanks to the volunteerism and enthusiasm of the excellent student team of four civil engineering students, a tremendous amount of work was accomplished in a short period of time. Under supervision of the faculty advisors, the students used multidisciplinary knowledge and skills throughout the project. They designed and performed experiments based on knowledge of concrete materials science. The students also used knowledge in pavement engineering to determine the desired properties of concrete pavements, and urban planning to quantify the environmental benefits resulting from the newly-designed concrete. The students also developed soft skills in project scheduling, marketing (to identify partners), and presentation.
Summary/Accomplishments (Outputs/Outcomes):
In this research study, it was felt that the best way to promote high reflectance concrete was to innovatively modify concrete mixtures by incorporating materials with which the concrete industry was already accustomed. The main approach was to create a whiter concrete by replacing cement, which is the darkest ingredient in concrete, with whiter constituents. The two main constituents that were used to replace cement were fly ash and ground-granulated blast furnace ‘slag’. Fly ash can vary in color from tan to gray; however, Class C fly ash is usually tan in color. Slag is of an even whiter shade than fly ash. In addition, two other alternatives namely white sand and latex were examined.
A total of 11 concrete mixtures were tested. Three standard mixes meeting Ohio Department of Transportation (ODOT) construction specifications (Mixes 1, 2, and 3) were used as control mixes. Mix 2 utilized 24% fly ash and Mix 3 used 30% slag. In order to compare the influence of fly ash and slag on concrete’s albedo, Mix 4 used the design of Mix 3 but with 30% fly ash instead. Mixes 5 and 6 increased the percent replacement by fly ash and slag to as high as 60%. Mixes 7 and 8 were ternary mixes (consisting of fly ash and slag in the proportions of 40/20 and 20/40, respectively). Mix 9 used white sand in place of ordinary sand, and Mix 10 added latex to the mixture. Mix 11 was designed later in the project after the albedo results of the first 10 mixes had been obtained. It was designed to produce further improvements in albedo of the concrete. The coarse aggregate used was #8 limestone, and the fine sand was ASTM C33 gravel.
Four cubes were created for each of the mixtures and tested for albedo at PRI Lab in Florida according to ASTM C1549. Based on the average albedo results of the 11 mixes tested (see Fig. 1(a)), the following trends can be observed:
- Concrete mixes with fly ash (Mixes 2, 4, 5) have lower albedo than the conventional mix.
- Concrete mixes with slag (Mixes 3, 6, 11) have higher albedo than the conventional mix.
- The albedo of ternary concrete mixes (Mixes 7 and 8) depends on the proportion of fly ash and slag used. A higher proportion of fly ash tends to decrease concrete’s albedo while a higher proportion of slag tends to increase concrete’s albedo.
- Whitish ingredients in concrete increase its albedo.
- The variation of albedos within a mix is higher in ternary mixes than the mixes with just one cement replacement. This is also true for concrete with white sand and latex.
Overall, Mix 11, which contains 70% slag, has the highest albedo value of 0.582. This is equivalent to an increase in albedo of 71% over the conventional mix (albedo = 0.341). These results verify the success of the project relative to the defined objectives. It should be noted that the use of white sand, which is intuitively promising, does not improve the albedo as much as the use of 60% or more slag. This finding, coupled with the fact that white sand is more expensive than slag, affirms the use of high slag content as a very attractive solution to produce high albedo and environment-friendly concrete.
Figure 1. Albedo test results
In order to ensure a quality end product, all of the concrete mixtures were tested for engineering properties, and their properties were checked against the performance specifications of ODOT. The target specifications for the concrete were a minimum compressive strength of 4000 psi at 28 days, and a modulus of rupture (flexural strength) of 600 psi at 7 days. The compressive strength was tested at 7 and 28 days according to ASTM C39. The flexural strength was tested at 7 and 28 days according to ASTM C78. The results show that the average compressive strength of three test cylinders of all mixes meets the specification in just 7 days. Also, the 7-day modulus of rupture of a beam sample of every mix meets the specification except for Mixes 5 and 8. Additionally, the setting time of the cement paste was measured according to ASTM C266. All mixes except Mix 10 (with latex) equaled or had shorter setting times than the conventional mix.
Based on the results obtained, the high-slag-content concrete is the champion. It increases concrete’s albedo significantly while preserving or even improving the engineering properties. It is also possible to develop a relationship between the slag content in concrete and the albedo value. As shown in Fig. 1(b), this relationship is linear, with a high coefficient of determination (R2). The use of slag contents higher than 70% might further increase the albedo of concrete; however, this will require careful consideration of impacts on engineering and other properties of the resulting concrete.
The benefits of using cement replacement materials can be determined from a life cycle inventory (LCI) of concrete production. LCI is a compilation of the materials, energy inputs (in the form of electricity, natural gas, diesel fuel, and other fuel oils), and emissions outputs associated with the production of one cubic yard of concrete from cement manufacture, transport of materials, to concrete plant operations. It is determined that while the material cost is about the same, the use of high-slag concrete helps decrease net energy consumption by 43.5%. It also reduces pollutant emissions in the order of 40-60%. The largest emissions reduction is in CO2. For example, if this high-slag-content concrete is used in place of conventional concrete to place 160 lane miles (a 20-mile divided highway segment with 4 lanes in each direction) of a typical 10-inch-thick concrete pavement, the result would be approximately 228,400 million Btu (315,000 GJ) of energy saving and 106 million lbs (48,250 metric ton) of CO2 reduction.
The use of high-slag concrete can also benefit people and prosperity. Higher albedos will mitigate the heat island effect, save cooling energy costs, alleviate smog, and improve human comfort. Researchers in Arizona showed that an increase in albedo of 0.1 reduces pavement surface temperature by about 4.7 °C (8.5 °F); therefore, the 70% slag concrete could reduce pavement surface temperature by 11.3 °C (20.4 °F). This would certainly help lower air temperature, but this also depends on many other factors including surface composition, climatological conditions, and other anthropogenic heat sources in an area. Increase in the albedo of 1,250 sq km of roadways in Los Angeles by 0.25 could reduce smog-related medical and lostwork expenses by $76 million per year, and produce cooling energy savings worth $15 million per year.
Conclusions:
The success of this project shows considerable potential to improve the quality of life and to bring about several positive improvements toward sustainability. Concrete mixtures utilizing 70% slag as cement replacement achieved 71% higher albedo than conventional concrete, while preserving or even improving other desirable properties. This design is broadly applicable and transferable to concrete and construction industries in both the developed and developing world. Since the end product is knowledge, it can easily be disseminated across a variety of end users. To further enhance the knowledge and understand any possible issues of using high albedo concrete, it is recommended that comprehensive evaluations be conducted on: other desirable properties of concrete e.g. permeability and freeze-thaw durability; changes of concrete albedo in real world conditions; and its impacts on surface temperature in different climate conditions, both hot and cold.
High albedo concrete can be used in many applications including pavements. There are some market barriers to the use of high reflectance concrete pavement, for example, lack of information and knowledge, lack of contractors with experience, and lack of standards. The first two barriers can be overcome by the dissemination of the results from this and future research studies. With regards to the third barrier, many public agencies currently put a limit on the allowable percentage of slag to be used in concrete. The findings from this and future studies should serve as a basis for these agencies to reconsider their specifications. Of course, it is not possible to repave several hundreds square kilometers of roadways in a short period of time. However, if education and policy are put in place today to guide the development toward sustainability, future generations will benefit tremendously from our energy conservation, pollution reduction, and environment preservation.
Journal Articles:
No journal articles submitted with this report: View all 1 publications for this projectSupplemental Keywords:
ambient air, atmosphere, ozone, global climate, life-cycle analysis, alternatives, sustainable development, clean technologies, innovative technology, renewable, waste reduction, waste minimization, environmentally conscious manufacturing, engineering, measurement methods, Midwest, Ohio, OH, transportation, RFA, Scientific Discipline, Sustainable Industry/Business, Sustainable Environment, Technology for Sustainable Environment, Chemistry and Materials Science, Environmental Engineering, green design, sustainable development, alternative building technology, environmental conscious construction, fly ash, alternative materials, concrete , albedo, engineering, solar reflectivity, pollution preventionThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.