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TECHBRIEF
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Publication Number:  FHWA-HRT-16-017    Date:  October 2015
Publication Number: FHWA-HRT-16-017
Date: October 2015

 

The Exploratory Advanced Research Program

Novel Alternative Cementitious Materials for Development of the Next Generation of Sustainable Transportation Infrastructure

 

Abstract

Georgia Institute of Technology and collaborators from Oklahoma State University, Tourney Consulting, and the Army Corps of Engineers, for an Exploratory Advanced Research (EAR) Program project funded by the Federal Highway Administration’s (FHWA’s) Turner–Fairbank Highway Research Center, are performing a comprehensive and systematic investigation of novel alternative cementitious materials (ACMs) for applications in sustainable transportation infrastructure. These materials include calcium aluminate cement (CAC), calcium sulfoaluminate (CSA), calcium sulfoaluminate belite (CSAB), magnesium phosphate cement (MPC), and alkali-activated (AA) and carbonate-binder systems that provide potential advantages over traditional portland cement through reductions in embodied energy and greenhouse gases, as well as enhanced performance, which contributes to sustainability. The research includes evaluation of early-age and long-term material properties, in addition to multiscale durability investigations. The research team aims to provide guidance for recommended test methods and, where relevant, test limits for acceptance of ACMs for transportation infrastructure, including highway structures and rigid pavements, as well as preliminary specifications for use.

Contact: Richard Meininger, Office of Infrastructure Research and Development, FHWA. E-mail: richard.meininger@dot.gov.

Research Conclusions

In the first phase of this project, the research team investigated ACMs that were either currently commercially available or almost commercially available in the United States through review of technical and trade literature, site visits, and consultation with producers and users. This led to an increased understanding of the benefits, shortcomings, and potential changes in standard construction processes surrounding the increased use of ACMs. They are currently primarily used in pavement and bridge repairs and joints of precast panels. The research team will note additional conclusions as the research moves forward into the next phase.

Next Steps

In the next research phase, the research team will begin to conduct experimental work to better characterize the selected materials and learn about their viability for use in pavements and bridge decks throughout the United States. The research team will use this research to recommend guidelines for test methods and, where relevant, test limits for acceptance of ACMs for transportation infrastructure. Of particular interest are performance criteria that can be incorporated in preliminary specifications for use.

Background

Concrete is the world’s most widely used construction material. As a result of the vast quantities produced each year, it also represents a significant worldwide environmental impact, accounting for 4.8 percent of global anthropogenic carbon dioxide emissions (CO2e).[1] These emissions primarily result from the calcining of limestone and the burning of fuel during the manufacture of portland cement clinker, a key component of concrete. The manufacture of cement results in the emission of 830 kg (1,830 lbs) of carbon dioxide (CO2) per metric tonne of clinker because of the raw materials required for processing, in addition to further emissions resulting from the energy required to heat the cement kiln to temperatures of nearly 1,450° C (2,640°F).[2]

Increasing the use of ACMs, such as those listed in table 1, and in other publications,[3] can result in the production of concretes with equal or greater strengths and durability than traditional portland cement concrete and is one possible method for reducing the total greenhouse gas contribution of the construction industry.

Table 2 shows rough estimates of the quantity of CO2e that could be avoided by replacing portland cement with an equal quantity, by mass, of ACM binder.[3] Table 2 also shows that a substantial CO2e savings can be achieved through the use of ACMs with the greatest CO2e savings associated with the use of CSAs, CACs, and chemically-activated aluminosilicate binders.

Table 1. Binder abbreviations

BINDER SYSTEM
ABBREVIATION
Ordinary portland cement
OPC
Alkali-activated binders
AA
Calcium aluminate cement
CAC
Calcium sulfoaluminate cement
CSA
Calcium sulfoaluminate belite cement
CSAB
Magnesium phosphate cement
MPC

The numbers shown in table 2 fail to consider other aspects of these materials that may also contribute to, or detract from, increased sustainability.[4] These aspects can be difficult to quantify, and their contributions to overall sustainability of a structure are often not obvious. Material features that contribute indirectly to improvements in sustainability include increased strength and better durability. The research team is currently investigating these features for many of the alternative binders. Higher strength materials may enable the use of smaller members, reducing both the quantity of concrete required outright for the structural member, while also reducing the overall dead load of the structure. This reduction in weight could lead to further material savings. Improved durability can also result in greater time before repairs or replacement is required. For example, using a single bridge for 100 years will result in the need for less material, and will generate less CO2e when compared to building, then rebuilding, a bridge with a 50-year lifespan. Claims that these materials are of higher durability have not fully been investigated, however, leading to uncertainty about this aspect of binder sustainability. Moreover, other aspects of these materials may lead to decreased sustainability, including increased shipping distances because of the currently limited regional availability of many of these binders. With increased usage and economies of scale, these negative aspects can be reduced; therefore, although the improvements in CO2e shown in table 2 suggest that ACMs can contribute to greater sustainability in highway infrastructure, their full impact is not completely understood at this time.

Table 2. CO2 emitted in the manufacture of "pure" cement compounds.

BINDER SYSTEM
GRAMS CO2e PER GRAM OF CEMENT[3]
PERCENT CO2e v. USING OPC
OPC[5]
0.55
100%
CSA[6]
0.28
51%
CSAB[7]
0.46
84%
CAC[8]
0.29
53%
MPC[9]
0.30
55%
AA[10]
Emissions result from manufacture of alkali solutions and transportation only. Precursor materials (fly ash, slag, etc.) were assumed to contribute no CO2e as they are byproducts of other industries.
44–64%
Note: Quantities reflect emissions associated with release of CO2 from calcination of raw materials, and from coal, to heat the materials to required calcination temperatures. The research team calculated CO2e reductions assuming a 1:1 replacement of ordinary portland cement (OPC) with alternative cementitious materials.

 

In the past, most ACM users found limited (i.e., specialty) or small-scale applications for the materials, such as rapid repairs and creating joints for precast panel road replacements;[11,12] however, the research team found that there is limited understanding of the scalability of these material systems, their long-term performance and durability in a range of environments, or their structural response when subjected to transportation-relevant loading conditions. Appropriate test methods, or well-defined alternatives to standard test methods, are also required. The researchers noted that these are needed to provide pathways for specification of ACMs, which can increase their use.

 

 

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