CHAPTER 4

Case Examples

Introduction

In the survey questionnaire sent to the state DOTs, the respondents were asked whether they would agree to be interviewed for the purpose of preparing case examples. Twenty-four state DOT respondents agreed to be interviewed. From this group, five states were selected based on their survey responses, which encompassed a range of information on conventional SCMs, NPs, and ASCM use; geographic location; and climatic region. The state DOTs chosen were those of California, Colorado, Louisiana, Minnesota, and Utah.

Prior to the interviews, the DOT representatives were given the following prompts that would guide the discussion:

• Please describe your agency’s history and rationale for allowing/encouraging the use of SCMs.
• Please describe your agency’s process for selecting SCM types and replacements.
• What are your agency’s specifications and practices (both initially and currently)?
• Please describe your agency’s quality assurance and acceptance in relation to SCMs and ASCMs.
• What benefits are your agency securing with SCM use in regard to infrastructure performance and sustainability?
• What challenges are your agency experiencing associated with SCM use in concrete applications?
• What opportunities associated with SCMs and ASCMs does your agency envision?

Information gathered during the interviews was used to produce the case examples. The motivation for the case example DOTs to use SCMs and ASCMs began with the desire to mitigate ASR, improve concrete durability, and capture economic benefits. However, the pathways for implementation and development of specifications differed according to the state DOTs’ needs and preferences. Industry motivation to use or promote the use of SCMs and ASCMs varies but has typically factored into each agency’s approach to implementation. These five case examples illustrate that, although there is no unique path to specification and use of SCMs and ASCMs, state DOTs are finding means to successfully capture the benefits of conventional SCMs and identify pathways for approval, specification, and use of emerging ASCMs.

Case Example 1: Caltrans

History of SCM Specification and Use

In the 1980s and 1990s, Caltrans began specifying the use of SCMs to mitigate ASR concerns for reactive aggregates. However, in recent years, Caltrans has also become interested in improving the state infrastructure’s sustainability. SCM use is one means of lowering the carbon footprint of concrete elements. In recent years, Caltrans has begun working with industry stakeholders to advance SCM use and to use blended cement, ASCMs, and other approaches.

Historically, all new products have been subject to the approval process included in Caltrans’s Product Evaluation Program (PEP). As the products are successful in the PEP, the appropriate tests and targets are added as criteria to the authorized materials list requirements. This approach allows other suppliers of the same material, as well as users and stakeholders, to know what material characteristics, test results, and performance targets must be met in order to use a material. The PEP allows the agency and users to know with confidence which suppliers are producing a product that meets these requirements. As the PEP has evolved, it has facilitated efficient selection of SCMs and ASCMs.

The PEP has also generated the test data needed to support development of Caltrans’s specification provisions associated with allowable SCM use. The Caltrans specifications provide equations that use characteristics of the SCMs to compute allowable combinations of SCMs and replacement levels. These specification provisions guide mixture design development by contractors and producers, with mixtures and calculations submitted to Caltrans for mixture/material approval. For mixture designs requiring a compressive strength exceeding 3,500 psi, the applicable equations must be satisfied in addition to the use of standard construction practices and results for acceptance. Equations supporting SCM use are provided in the addendum to this case example. Caltrans has found that the use of these equations and related specification provisions has been effective in supporting construction of concrete infrastructure with the desired performance qualities. This approach has also allowed flexibility to stakeholders who increasingly need to buffer against supply shortages or issues.

SCM Specifications and Use

Caltrans allows SCMs both as additives and in blended cements in pavements and all structures. SCMs are used in concrete classes that require low permeability to improve concrete durability, for heat management for mass concrete elements, and to improve environmental sustainability by reducing cement content. Ternary and quaternary blends are allowed in pavements and structures. Caltrans allows Class F ash, ultrafine fly ash, harvested or beneficiated fly ash meeting ASTM C618-23/AASHTO M 295, slag cement, silica fume, calcined clay, calcined shale, calcined pumice, metakaolin, and rice husk ash (although rice husk ash is not commonly used).

Instead of prescribing allowable replacement percentages for SCMs, to support stakeholders in identifying SCMs that can be used alone or combined, Caltrans has developed equations for computing the replacement percentages. These equations are shown in the addendum to this case example.

For concrete structures, individual SCMs must be proportioned in accordance with the requirements of Caltrans Construction Manual, Sec. 90-1.02B(3), which allows for the use of multiple SCMs in amounts related to the total specified cementitious material quantity. SCMs must be proportioned in accordance with Sec. 49-3.01B(2) for mass-concrete piles, 90-1.02I(2)a) for structures in freeze–thaw zones, 90-1.02I(2)(b) for concrete exposed to deicing chemicals, and 90-4.02 for precast concrete elements.

For concrete pavements, individual SCMs must be proportioned in accordance with the requirements of Sec. 90-1.02B(3), which allows for the use of multiple SCMs in amounts related to the total specified cementitious material quantity.

For minor concrete (such as precast drainage structures, culvert heads, and similar components), NPs must be proportioned in accordance with the requirements of Sec. 90-1.02B(3), which allows for the use of multiple SCMs in amounts related to the total specified cementitious material quantity. SCMs must be proportioned in accordance with Sec. 49-3.01B(2) for mass-concrete piles, 90-1.02I(2)a) for structures in freeze–thaw zones, 90-1.02I(2)(b) for concrete

exposed to deicing chemicals, and 90-4.02 for precast concrete elements. The use of rice husk ash is only allowed in minor concrete, per the requirements of Sec. 90-2.02B.

Quality Assurance Approaches

For material and mixture approval, all SCMs used must be listed on the authorized materials list and have passed all tests referenced in the standards associated with qualification of each material. Regardless of the type of SCM used, shrinkage testing in accordance with AASHTO T 160 is required for various types of concrete elements, including rapid-strength concrete, mixtures, concrete pavement, concrete bridge decks, and approach slabs. Where air-entrained concrete is specified, Caltrans also requires the air content to be measured regardless of the types or proportions of SCMs used. Concrete pavement and all concrete to be placed in designated freeze–thaw areas are subject to these requirements.

Caltrans’s specifications for acceptance are based on compressive strength, with some additional acceptance criteria for mixtures used in elements experiencing freeze–thaw cycles and conditions promoting corrosion. In some applications, the strength requirement for acceptance can be met at later ages, which helps accommodate the slower rate of strength gain of concrete containing some SCMs. Sec. 90-1.01D(5) allows concrete mixtures 42 days to attain required strength when the mixture design–specified strength is greater than 3,600 psi. For mixture designs meeting specific SCM proportions described in this section, and not for use in freeze–thaw areas, this may be extended to 56 days. The specifications require shrinkage testing and air-void system parameter testing if SCMs are used.

Benefits and Challenges Associated with SCMs and ASCMs

California has historically been a national leader in developing and implementing approaches supporting sustainability, and the use of SCMs has directly supported Caltrans’s sustainability efforts. The broad range of SCMs previously analyzed and authorized through Caltrans’s PEP have allowed suppliers and contractors to select SCMs appropriate for mitigating the reactivity of the aggregates to be used on specific projects. Depending on aggregate testing results or performance history, suppliers have different alternatives for SCMs that reflect the risk tolerance of Caltrans with that aggregate. Caltrans notes that it has not experienced significant impacts from SCMs when used with Type IL cement.

Over time, this specification approach has evolved to provide quite a bit of flexibility into both the aggregate testing requirements and SCM selection. In the past several years, California has experienced a shortage in fly ash to supply agency projects with. This program and specification approach has provided Caltrans the ability to work with producers and contractors to find approaches to address global and local shortages. One key example of when this approach proved to be useful was during the COVID-19 pandemic when supply challenges occurred. When producers or contractors experienced supply issues, they could identify potential substitutions allowed by the specifications.

Opportunities Associated with SCMs and ASCMs

Caltrans also plans to allow the use of ASCMs in the future. The agency is being approached by a variety of stakeholders with a wide range of ASCM materials. Caltrans supports and is engaged with research to support testing to evaluate the performance of these materials. One university is performing a study of some of the more unique ASCM materials, such as biochar. Another university is performing research on ASCMs that are more conventional, such as beneficiated ash, bottom ash, NP, and nano-cellular materials.

Materials showing promise in university research can be evaluated for Caltrans’s approved materials list. To be evaluated for inclusion on this list, a material sample must be submitted to Caltrans, as well as test results from a third-party laboratory. This ongoing work by Caltrans and researchers will develop the targets that need to be met for Caltrans and guide updates to the specification provisions. Material characteristics and performance targets will be transferred to the approved material list requirements, along with instructions on format, amount of testing, number of replicates, and other requirements that need to be met to request review and inclusion on the approved materials list. Caltrans believes this approach should also foster competition.

Caltrans is still considering exactly how its process should include provisions to ensure that producers can supply adequate volumes of ASCMs. For example, Caltrans is still identifying the type of information that might be needed from small operations to provide confidence that they can provide the needed quantity for different sized projects. Caltrans is trying to be helpful to producers but also be respectful of the use of taxpayer dollars. Different procurement processes are being considered, which may also be influenced by legislation.

No field trials of ASCMs have been performed, but California is considering performing at least one in the future. The field trials being considered would be for pavements, bridge structures, mass-concrete members, parking areas, or other components. Once university-provided data show promise, and Caltrans is earnestly reviewing an ASCM for inclusion in the approved product list, Caltrans will run its own field trials. These would be for low-risk applications, and the ASCM would likely be introduced through a change order. Caltrans engineers from Materials Engineering, Testing Services, Design, and other sections are members of various committees corresponding to their expertise and background. When industries suggest or submit new products for evaluation, the products and their documentation are sent to the appropriate committee for review. Within the committee, the product will be discussed and evaluated. Committees would also prepare an assessment/monitoring program, and this would be incorporated into a contract for the field trial. Caltrans intends to introduce the ASCM field trial into the project documents far enough ahead of a bid so that a contractor could address and assist with the trial, as well as account for extra effort in its bid.

As part of its effort to support the qualification and use of novel materials, Caltrans is developing approaches to assess ASCMs for suitability of use. Tests unique to ASCM concrete have not yet been provided in the specifications. However, based on the ASCMs being put forth for approval, the agency may consider requiring the same tests for ASCM concrete that are required for conventional concrete. Methods for acceptance are also being discussed as part of the actions Caltrans is taking to prepare for ASCMs to become proposed for use.

The approved materials program includes time limits for which each material is qualified for use. Reauthorization periods may vary based on the agency’s confidence in the potential variability of a product. For example, plant-produced SCMs and ASCMs may have a longer reauthorization period than NPs without extensive secondary processing (which may exhibit more variability). Caltrans believes that its system has evolved to include several controls as well as flexibility, which should provide the agency confidence in navigating the emergence of new materials and help it move these materials from research to approval to industry use. Caltrans is also open to receiving industry feedback on modifying or enhancing criteria to address emerging materials, as well as feedback concerning other needs or concerns.

For any given material that is vetted, allowed, and put in the field, there is an educational process for the suppliers, placers, and finishing crews, as well as for observation of the performance. Caltrans has learned that when new materials are proposed, there is a learning curve for users, particularly those supporting placement and finishing. Although test results support a material’s qualification for use, the information gained through field experience is critical.

Caltrans and its stakeholders have realized that since there is a learning curve for each material, mixture designs and proportions may need to be adjusted based on field performance. The wide range of temperature/weather conditions in California makes field experience critical. A single supplier near Sacramento could be placing concrete from the same stockpiles and silos in active snow conditions in the mountains and also in hot weather in the valley. The agency’s Materials Quality Management Program (MQMP) verifies means and methods, equipment accuracy, and other measures for ensuring that suppliers are capable of supplying quality concrete. The MQMP helps ensure that suppliers are capable and are using authorized materials. As new ASCMs become available, the MQMP will also play a critical role in providing Caltrans confidence in the concrete being produced.

Caltrans has found that manufacturers of precast concrete components have historically been leaders in trying novel materials, probably due to their ability to do so in a more controlled manufacturing environment. The steam curing process supports excellent curing and capture of the SCM benefits within the precasters’ ownership window. The slower strength development rate of many SCMs can also be controlled or accounted for within a precasting operation. Precasters can do cost–benefit analysis fairly readily and can justify the use of SCMs and ASCMs.

Green product procurement provisions, and particularly environmental product declarations (EPDs), are also playing an increasingly important role in how Caltrans accepts and uses ASCMs. Emerging ASCMs, if useable, could show promise to lowering the GHG emissions per an EPD. Caltrans is already constructing projects using concrete mixtures with relatively low GHG emissions compared to other states. However, Caltrans anticipates that with some of these new technologies, there may be room to improve its infrastructure sustainability even further.

Recent legislation requiring reductions in GHGs has resulted in Caltrans using concrete mixtures with a relatively low impact compared to the concrete mixtures used by many other agencies. Because Caltrans may need to continue to lower GHGs, the agency must carefully consider the baseline values to which the GHG emissions of new mixtures can be compared. California legislation may allow baseline GHG values to be determined using an earlier timeframe, when concrete mixtures typically had a higher carbon footprint. This would allow some room for improvement through lowering concrete mixture GHGs using additional SCMs and ASCMs.

Caltrans Case Example References

Caltrans. 2018. Construction Manual, State of California, California State Transportation Agency, Department of Transportation. Chapter 4: Construction Details, Section 90: Concrete. https://dot.ca.gov/programs/construction/construction-manual/section-4-90-concrete.

Addendum to Caltrans Case Example – Selected Specifications

Acceptance Strength

Sec. 90-1.01D(5)

For concrete with a described 28-day compressive strength greater than 3,600 psi, 42 days are allowed to attain the strength described. Except for concrete specified to be in a freeze–thaw area, 56 days are allowed to attain the strength described if the cementitious material satisfies the following equation:

[(41 × UF) + (19 × F) + (11 × SL)]∕TC ≥ 7.0

where:

F = natural pozzolan or fly ash complying with AASHTO M 295, Class F or N, including the quantity in blended cement, lb/cu yd. F is equivalent to the sum of FA and FB as defined in section 90-1.02B(3).

SL = GGBFS [ground granulated blast-furnace slag], including the quantity in blended cement, lb/cu yd

UF = silica fume, metakaolin, or UFFA [ultrafine fly ash], including the quantity in blended cement, lb/cu yd

TC = total quantity of cementitious material used, lb/cu yd

For concrete satisfying the equation above, test for the compressive strength at least once every 500 cu. yd. at 28, 42, and 56 days. Submit the test results to the Engineer and to METS, Attention: Office of Structural Materials, Concrete Materials Testing Branch.

Cementitious Materials

90-1.02B(1)

The cementitious materials type and brand must be on the Authorized Material List for cementitious material for use in concrete when the mix design is submitted. Unless otherwise specified, the cementitious material must be one of the following:

1. Combination of Type II or V Portland cement and SCM
2. Combination of blended cements and SCM
3. Blended cement

90-1.02B(2)

Blended cement, including Portland limestone cement, Type IL must comply with AASHTO M 240, except:

1. Maximum limits on pozzolan content do not apply
2. Sulfate resistance must be moderate (MS) or high (HS)
3. Alkali content in cement portion of blended cements must not exceed 0.60 percent by mass of alkalis as Na₂O + 0.658 K₂O when determined under AASHTO T 105

90-1.02B(3) Supplementary Cementitious Materials

Each SCM must be one of the following:

1. Fly ash complying with AASHTO M 295, Class F, and either of the following:
   1. 1.1 Available alkali as Na₂O + 0.658 K₂O must not exceed 1.5 percent when tested under ASTM C311.
   2. 1.2 Total alkali as Na₂O + 0.658 K₂O must not exceed 5.0 percent when tested under AASHTO T 105.
2. UFFA complying with AASHTO M 295, Class F, and the chemical and physical requirements shown in the following two tables.

   Chemical quality characteristic	Requirement (%)
   Sulfur trioxide (SO3) (max)	1.5
   Loss on ignition (max)	1.2
   Available alkalis as Na2O + 0.658 K2O (max)	1.5

Physical quality characteristic	Requirement (%)
Particle size distribution:
Less than 3.5 microns (min)	50
Less than 9.0 microns (min)	90
Strength activity index with Portland cement:
7 days (% of control, min)	95
28 days (% of control, min)	110
Expansion at 16 days when testing project materials under ASTM C1567a (max)	0.10

3. Raw or calcined natural pozzolans complying with AASHTO M 295, Class N, except the maximum allowable loss on ignition is 10 percent, and either of the following:
   1. 3.1 Available alkali as Na₂O + 0.658 K₂O must not exceed 1.5 percent when tested under ASTM C311.
   2. 3.2 Total alkali as Na₂O + 0.658 K₂O must not exceed 5.0 percent when tested under AASHTO T 105.
4. Metakaolin complying with AASHTO M 295, Class N, and the chemical and physical requirements for the quality characteristics shown in the following 2 tables:

   Chemical quality characteristic	Requirement (%)
   Silicon dioxide (SiO2) + aluminum oxide (Al2O3) (min)	92.0
   Calcium oxide (CaO) (max)	1.0
   Sulfur trioxide (SO3) (max)	1.0
   Loss on ignition (max)	1.2
   Available alkalis as Na2O + 0.658 K2O (max)	1.0

5. GGBFS complying with AASHTO M 302, Grade 100 or 120.
6. Silica fume complying with AASHTO M 307, with a minimum reduction in mortar expansion of 80 percent when using the cement from the proposed mix design.

Fly ash from different sources may be commingled at uncontrolled ratios if:

1. Each source produces fly ash complying with AASHTO M 295, Class F
2. At the time of commingling, each fly ash has:
   1. 2.1 Running average of relative density that does not differ from any other fly ash by more than 0.25
   2. 2.2 Running average of loss on ignition that does not differ from any other fly ash by more than 1 percent
3. Final commingled fly ash complies with AASHTO M 295, Class F
4. Fly ash supplier is responsible for testing the commingled fly ash

The quantity of cement and SCM in concrete must comply with the minimum cementitious material content specified.

The SCM content in concrete must comply with one of the following:

1. Any combination of cement and SCMs, satisfying equations 1 and 2:

   Equation 1:

   [(25 × UF) + (12 × FA) + (10 × FB) + (6 × SL)]∕MC X

   where:

   UF = silica fume, metakaolin, or UFFA, including the quantity in blended cement, lb/cu yd

   FA = natural pozzolan or fly ash complying with AASHTO M 295, Class F or N, with a CaO content of up to 10 percent, including the quantity in blended cement, lb/cu yd

   FB = natural pozzolan or fly ash complying with AASHTO M 295, Class F or N, with a CaO content of greater than 10 percent and up to 15 percent, including the quantity in blended cement, lb/cu yd

   SL = GGBFS, including the quantity in blended cement, lb/cu yd

   MC = minimum quantity of cementitious material specified, lb/cu yd

   X = 1.8 for innocuous aggregate, 3.0 for all other aggregate

   Equation 2:

   MC - MSCM - PC ≥ 0

   where:

   MC = minimum quantity of cementitious material specified, lb/cu yd

   MSCM = minimum sum of SCMs that satisfies equation 1, lb/cu yd

   PC = quantity of Type IL cement or Portland cement, including the quantity in blended cement, lb/cu yd

2. 15 percent Class F fly ash with at least 48 oz of LiNO₃ solution added per 100 lb of Portland cement or Portland limestone cement. The CaO content of the fly ash must not exceed 15 percent.

90-1.02H Concrete in Corrosive Environments

Section 90-1.02H applies to concrete specified in the special provisions to be in a corrosive environment.

The cementitious material to be used in the concrete must be a combination of Type II or V Portland cement or Type IL (MS or HS) cement and SCM.

The concrete must contain at least 675 pounds of cementitious material per cubic yard.

The reduction of cementitious material content as specified in section 90-1.02E(2) is not allowed.

The specifications for SCM content in section 90-1.02B(3) do not apply.

For pavement, the total cementitious material must be composed of one of the following options, by weight:

1. 25 percent natural pozzolan or fly ash with a CaO content of up to 10 percent and 75 percent Portland cement or Type IL cement
2. 20 percent natural pozzolan or fly ash with a CaO content of up to 10 percent, 5 percent silica fume, and 75 percent Portland cement or Type IL cement

3. 12 percent silica fume, metakaolin, or UFFA, and 88 percent Portland cement or Type IL cement
4. 50 percent GGBFS and 50 percent Portland cement or Type IL cement

For structures, the total cementitious material must be composed of one of the following options, by weight:

1. 25 percent natural pozzolan or fly ash with a CaO content of up to 10 percent and 75 percent Portland cement or Type IL cement.
2. 20 percent natural pozzolan or fly ash with a CaO content of up to 10 percent, 5 percent silica fume, and 75 percent Portland cement or Type IL cement.
3. 12 percent silica fume, metakaolin, or UFFA, and 88 percent Portland cement or Type IL cement.
4. 50 percent GGBFS and 50 percent Portland cement or Type IL cement.
5. 25 to 50 percent fly ash with a CaO content of up to 10 percent, and no natural pozzolan. The remaining portion of the cementitious material must be (1) Portland cement, (2) Type IL cement, or (3) a combination of Portland cement or Type IL cement and UFFA, metakaolin, GGBFS, or silica fume.

90-1.02I Concrete in Freeze–Thaw Areas

90-1.02I(1) General

Section 90-1.02I applies to concrete for projects specified in the special provisions to be in a freeze–thaw area.

90-1.02I(2) Materials

90-1.02I(2)(a) General

The concrete must contain at least 590 pounds of cementitious material per cubic yard unless a higher cementitious material content is specified.

Add an air-entraining admixture to the concrete at the rate required to produce an air content of 6.0 ± 1.5 percent in the freshly mixed concrete.

For concrete placed at least 2 feet below the adjacent undisturbed grade or at least 3 feet below compacted finished grade, an air-entraining admixture is not required unless the concrete will experience freezing conditions during construction.

The cementitious material must satisfy the following equation:

[(41 × UF) + (19 × F) + (11 × SL)]∕TC ≥ 7.0

where:

UF = silica fume, metakaolin, or UFFA, including the quantity in blended cement, lb/cu yd

F = natural pozzolan or fly ash complying with AASHTO M 295, Class F or N, including the quantity in blended cement, lb/cu yd. F is equivalent to the sum of FA and FB as defined in section 90-1.02I(2)(b)

SL = GGBFS, including the quantity in blended cement, lb/cu yd

TC = total quantity of cementitious material used, lb/cu yd

90-1.02I(2)(b) Concrete Exposed to Deicing Chemicals

Section 90-1.02I(2)(b) applies to concrete specified in the special provisions to be exposed to deicing chemicals.

The specifications for SCM content in section 90-1.02B(3) and the equation in section 90-1.02I(2)(a) do not apply.

The cementitious material must be composed of any combination of (1) either Portland cement or Type IL cement and (2) at least 1 SCM satisfying the following equation:

Equation 1:

[(25 × UF) + (12 × FA) + (10 × FB) + (6 × SL)]∕TC ≥ X

The SCM must satisfy the following equations:

Equation 2:

4 × (FA + FB)∕TC ≤ 1.0

Equation 3:

(10 × UF)∕TC ≤ 1.0

Equation 4:

2 × (UF + FA + FB + SL)∕TC ≤ 1.0

The concrete mix design must satisfy the following equation:

Equation 5:

27 × (TC - MC)∕MC ≤ 5.0

where:

UF = silica fume, metakaolin, or UFFA, including the quantity in blended cement, lb/cu yd. If UF is used, the quantity of UF must be at least 5 percent.

FA = natural pozzolan or fly ash complying with AASHTO M 295, Class F or N, with a CaO content of up to 10 percent, including the quantity in blended cement, lb/cu yd. If FA is used, the quantity of FA must be at least 15 percent.

FB = natural pozzolan or fly ash complying with AASHTO M 295, Class F or N, with a CaO content of greater than 10 percent and up to 15 percent, including the quantity in blended cement, lb/cu yd. If FB is used, the quantity of FB must be at least 15 percent.

SL = GGBFS, including the quantity in blended cement, lb/cu yd

TC = total quantity of cementitious material, lb/cu yd

X = 1.8 for innocuous aggregate, 3.0 for all other aggregate

MC = minimum quantity of cementitious material specified, lb/cu yd

90-2.02B Cementitious Material

Minor concrete must contain at least 505 pounds of cementitious material per cubic yard. You may use rice hull ash as an SCM. Rice hull ash must comply with AASHTO M 321 and the requirements for the quality characteristics shown in the following tables:

Chemical quality characteristic	Requirement (percent)
Silicon dioxide (SiO2)a (min)	90
Loss on ignition (max)	5.0
Total alkalis as Na2O equivalent (max)	3.0

Physical quality characteristic	Requirement
Particle size distribution:
Less than 45 microns (min, %)	95
Less than 10 microns (min, %)	50
Strength activity index with Portland cement:
7 days (min, % of control)	95
28 days (min, % of control)	110
Expansion at 16 days when testing project materials under ASTM C1567b (max, %)	0.10
Surface area when testing by nitrogen adsorption under ASTM D5604 (min, m2/g)	40.0

^aWhen tested under AASHTO M 307 for strength activity testing of silica fume.

^bIn the test mix, Type II or V Portland cement must be replaced with at least 12 percent rice hull ash by weight.

Case Example 2: CDOT

History of SCM Specification and Use

CDOT’s use of SCMs began in the 1990s in response to ASR-related distress that was observed on Interstate projects despite the use of low-alkali cement. Following these observations, CDOT supported a research study that indicated that requiring the use of Class F fly ash at a 20% addition rate was a suitable approach to mitigating ASR for most of CDOT’s reactive aggregates. This approach worked satisfactorily for the agency through the 1990s. However, in the early 2000s, a major supplier of cement to the state indicated that it would no longer be producing low-alkali cement. In response to this change, CDOT performed ASTM C1567 testing to determine required fly ash replacement levels based on aggregate reactivity. The results of these tests determined the minimum substitution rate for the mixtures. Since ASTM C1567 testing appeared to provide satisfactory mitigation, specifications evolved to allow the mixture designer to perform this testing at the time of mixture design to determine the required minimum fly ash replacement rate for the aggregates used on a given project.

CDOT has experienced shortages in fly ash in the past, and it was also concerned about the potential implications on fly ash use when the EPA was exploring classification of fly ash as a hazardous waste. In response to this, CDOT funded research on other SCMs in the hope of providing data to support their use for ASR mitigation. This research study recommended use of AASHTO M 321, Standard Specification for High-Reactivity Pozzolans for Use in Hydraulic-Cement Concrete, Mortar, and Grout, to evaluate and qualify SCMs for use in CDOT projects. AASHTO M 321 is now used to support approval of SCMs, and substitutions are allowed if they are the same type of SCM and the ASR mitigation test data are supplied.

Silica fume was explored as an SCM to improve bridge deck performance. CDOT had a specified silica fume overlay mixture containing 7% silica fume and small-sized (pea gravel) aggregates. This mixture did not perform particularly well due to strength differences between layers. However, despite discontinuing the use of this mixture, CDOT still allows silica fume in its specifications, with mixture proportions designed using the CDOT performance approach for structural concrete. Some contractors are using silica fume with a Class F ash mixture to mitigate ASR and help achieve strength (2%–3%), reporting that they prefer this approach to the use of accelerating admixtures due to the predictable influence of silica fume on fresh concrete performance and strength gain.

CDOT allows slag in concrete mixtures. However, slag is currently not available in its market. In the 2017–2018 timeframe, the Bureau of Reclamation had a project in Wyoming that used slag, and as part of this effort, it established a delivery terminal for slag. CDOT partnered with

the supplier on this effort and had access to a supply of slag from the terminal. However, no CDOT projects incorporated the slag into mixtures. Manufacturers of metakaolin have also proposed use, but no projects containing metakaolin have been constructed to date.

Initial use of SCMs was driven by CDOT’s desire to improve durability and reduce costs. However, as time passed, CDOT specifications became influenced by material cost and availability as well as sustainability. Recently, CDOT has become a national leader in green product procurement. This movement resulted from the Buy Clean Colorado Act, which applies to state public projects for which the cost exceeds $500,000; it is effective for products solicited after January 1, 2024. This law required the Office of the State Architect to establish a maximum global warming potential (GWP) limit for each category of eligible materials, which includes concrete. Use of SCMs is a strategy to meet GWP targets for concrete.

SCM Specifications and Use

At the time of this writing, CDOT specifications allow SCMs to be used in concrete as additives alone or in blended cements. SCMs. Ternary and quaternary blends of SCMs are allowed at replacement rates of up to 50% by mass of cement in both pavements and structures. Allowable SCMs include Classes F and C fly ash, harvested or beneficiated fly ash meeting ASTM C618-23/AASHTO M 295, slag cement, silica fume, calcined clay, calcined shale, calcined pumice, metakaolin, and rice husk ash.

CDOT has not experienced challenges associated with the use of SCMs with Type IL cement. Type IL cement has been available in Colorado since 2006 and is specified using ASTM C1157 prior to its inclusion in AASHTO M 595. In many instances, CDOT has been told that the placement crews and finishers did not notice a difference when Type IL was used. Millions of square feet of pavement have been constructed using concrete containing Type IL cement paired with SCMs, and CDOT has noted no differences in performance. At the time of this writing, essentially every project using Type IL cement also uses at least 20% fly ash.

CDOT had found that fly ash characteristics and performance could be variable. However, in recent years, it has found that suppliers are better controlling the consistency of the ash or are processing the ash to reduce variability. CDOT has found that some secondary processers are also rejecting fly ash that is high in carbon or exhibits other undesirable characteristics.

Occasionally, contractors and suppliers supporting CDOT projects experience shortages of materials from certain sources. In these cases, a new mixture design must be prepared and submitted for approval. In response to shortages, CDOT has allowed temporary changes as long as ASR testing is performed and the results are satisfactory. However, if a new or substitute fly ash is to be used for more than 14 days, a new trial batch and test results are needed for mixture approval.

Quality Assurance Approaches

CDOT specifications allow concrete suppliers or producers to select the SCMs they would like to use. Mixtures must still demonstrate that the SCM used and replacement rates effectively mitigate ASR through ASTM C1567. Specifications have some prescribed requirements for sulfate mitigation, but a number of options are provided, allowing flexibility in the materials and mixture proportions that can be used to meet these requirements. Mixtures used in environments exposed to sulfates must be qualified using ASTM C1012 testing, with target test results varying depending on sulfate exposure class.

All mixtures containing SCMs must the meet same requirements as those for straight cement mixtures. CDOT requirements for concrete mixture approval (qualification) and acceptance are provided in Division 600 of the Colorado Standard Specifications for Road and Bridge

Construction (CDOT 2017). Division 600 provides requirements for different classes of concrete used for structural, pavement, and other applications. CDOT uses a performance-based approach for mixture qualification, providing required performance tests and targets for different mixture classes as deemed appropriate for specific applications. For most mixture classes, tests for compressive strength, flexural strength, and volumetric shrinkage are required, along with either rapid chloride permeability test results or surface resistivity test results. (The approach can be chosen by the producer.) Shrinkage tests are to be performed using a modified version of the ASTM C157 test (Colorado Procedure – Laboratory 4103-15).

SCMs exhibiting slow strength gain must still meet 28-day strength requirements, although CDOT has found that contractors and suppliers are still finding ways to achieve specified strengths using significant SCM content. For example, one contractor is using 30% Class F ash with IL and still meeting 28-day strength requirements. Surface resistivity requirements must be met at 28 days. However, if the contractor elects to use the rapid chloride permeability test instead of surface resistivity, targets are for 56 days.

CDOT payment for pavement work is based on a percent within limits (PWL) approach using 28-day strength. This approach has largely been successful in supporting quality concrete construction. However, use of SCMs can have implications on pay through the PWL provisions. For example, if one type of fly ash has a lower reactivity and slower strength gain, a contractor can be penalized in pay despite the improved performance offered by the fly ash; therefore, CDOT separates different materials into new processes for pay. Contractors are, however, generally finding ways to manage the risk and meet PWL targets.

Benefits and Challenges Associated with SCMs and ASCMs

When sustainability moved to the forefront of Colorado policy, CDOT had already been using by-product and recycled materials, SCMs, and IL. Now that Buy Clean Colorado requirements are in place, SCMs are playing a role in establishing benchmarks and targets. CDOT found that it could be challenging to reduce GWP when its specifications result in production and use of concrete with a substantially lower GWP than that used in many other states. Driven by the performance-based specification provisions that allow flexibility in material selection and mixture proportioning, contractors and ready-mixed concrete suppliers are finding means to meet Buy Clean Colorado provisions and lower GWP. CDOT is finding that its paving contractors are outperforming ready-mixed concrete suppliers in terms of reducing cement content. This is likely due to the economics associated with use of SCMs, which is often viewed as smart business sense.

CDOT sees opportunities associated with ASCMs that may be available in the state, particularly as the agency has been focusing on meeting the state’s sustainable materials legislation. CDOT is considering funding a research project that would assess the credibility of products calling themselves “green” or “low carbon,” and it has personnel working with the National Transportation Product Evaluation Program (NTPEP) as it considers developing a similar program. Allowable replacement rates for ASCMs are currently not specified, but these replacement rates will be explored in further evaluation and research studies.

Over the previous 5 or 6 years, CDOT had seen ground pumice, supplied from a source located near Pueblo, used extensively on projects in the I-25 corridor. The supplier blended ground pumice with a coal ash material to develop an ASCM that has characteristics similar to Class F ash. The ground pumice product has also been used as a stand-alone material. AASHTO M 321 is used as the specification for this material. Users of this product have observed that the concrete mixtures exhibit a higher water demand than conventional mixtures. However, this has typically been accommodated by the contractor using conventional methods such as an increase in water-reducing admixtures or the use of additional water.

CDOT has been approached by producers of proprietary ASCM products and technologies but has determined that none of these emerging materials/technologies are ready for production or for implementation in a case study. Tests unique for concrete containing ASCMs are not yet included in the specifications. Rather, the supplier will likely need to qualify the material through AASHTO M 321. The approach used by CDOT will likely be to require tests for conventional concrete mixtures (based on class/application), including test results meeting CDOT’s ASR and sulfate mitigation–related specification provisions (via tests in accordance with ASTM C1567 and ASTM C1012). CDOT plans to accept test results from any AASHTO-accredited laboratory, including private testing laboratories and those of concrete producers.

The agency has been approached by several industry and university partners regarding the use of several ASCMs. Nanosilica is currently allowed as an admixture. Biochar may be investigated in partnership with a university as one potential ASCM.

CDOT Case Example References

CDOT. 2017. Colorado Standard Specifications for Road and Bridge Construction, Division 600 Miscellaneous Construction. https://www.codot.gov/business/designsupport/cdot-construction-specifications/2023-construction-specifications/2023-specs-book/2023-division-600.

Case Example 3: Louisiana DOTD

History of SCM Specification and Use

Most of the concrete used by LaDOTD is used in structural applications, although a few concrete pavement projects and concrete overlays have been constructed. Concrete mixtures currently provided for its infrastructure include high replacement rates of cement with SCMs, often in ternary blends. This has been a function of LaDOTD’s specifications moving toward use of surface resistivity to support the desired durability benefits, and also industry’s desire to use SCMs for economic and mixture workability reasons.

Prior to a 2016 specification revision, LaDOTD was allowing maximum replacement rates of 30% for ash and 50% for slag. To control temperature, the replacement rates used for mass concrete were allowed to exceed these values. However, additional approvals were required. Ternary blends were not allowed.

In the mid-2010s, research aimed at improving concrete durability through SCM use found that mixtures containing SCMs at up to a 90% replacement rate could exhibit adequate performance. Consistent, reasonable performance was seen in mixtures containing 80% to 85% replacement rates. Based on these findings, LaDOTD decided to implement a maximum SCM replacement rate of 70% for structural concrete. The agency also decided to specify a maximum SCM replacement rate of 50% in pavements to help limit potential issues associated with saw cutting.

As part of this specification update, LaDOTD decided there would be advantages to allowing the contractor or producer to design concrete mixtures, and many prescriptive provisions were removed in the 2017 specification revisions.

SCM Specifications and Use

LaDOTD’s current specifications have been in place since 2017. LaDOTD allows Classes F and C fly ash, slag, silica fume, and metakaolin. Replacement rates used in the specifications have been identified through research performed by the Louisiana Transportation Research

Center and its partnering entities. Up to 50% replacement of Portland cement (including Type IL cements) with combinations of slag and ash is allowed for pavement applications. For structural and mass concrete, LaDOTD allows up to 70% replacement of Portland cement (including Type IL cements) with SCMs. When a contractor desires to use both Classes F and C fly ash, they must be used at equal replacement rates. If ash and slag are used together, the amount of ash used must be less than or equal to the amount of slag used. Metakaolin can be used at replacement rates of up to 50%, but this NP is not often used by stakeholders. Silica fume is also allowed at replacement rates of up to 10%, but it is typically only seen in precast concrete applications.

ASTM C618 is used to guide the use of fly ash and NPs, and LaDOTD also has a slag specification. Ternary blends of SCMs are allowed in pavements and structures. In many cases, surface resistivity requirements included in LaDOTD’s specifications can only be met using ternary blends. To account for the slower strength gain of some SCMs, LaDOTD allows the strength requirements for acceptance to be met at later ages (such as 56 days) for mass-concrete applications only.

LaDOTD found that when ternary blends were allowed in mixtures in 2017, larger producers of concrete readily began supplying these mixtures for LaDOTD projects, since they were already using them for residential construction and private-sector work. This use of ternary blends was driven by these producers finding that ash and slag were cheaper than cement and resulted in very workable mixtures. As such, these larger producers had the silo capacity at plants to provide LaDOTD with ternary blend concrete. Smaller producers initially did not have the silo capacity to provide ternary blend mixtures, but now most producers have upfitted plants to support storage and use of multiple SCMs.

LaDOTD estimates that 80% to 90% of concrete structures currently being constructed, and 100% of mass-concrete structures currently being constructed, include ternary blend concrete mixtures. Concrete pavement projects are not often let for bid. However, when they are, use of ternary mixtures is dependent on producer capabilities (often silo availability and personnel experience with ternary blends).

Quality Assurance Approaches

LaDOTD’s 2017 specification revision focused on resistivity requirements that support improved concrete durability performance, and as such is driving ternary blend use by contractors and suppliers. Due to the experience of many local suppliers with multiple SCMs and ternary blends, most were readily able to meet the resistivity targets. The agency specifications still include compressive strength requirements for acceptance, with flexural strength requirements used only for the (limited number of ) concrete overlay projects. Maturity is also allowed to be used for applications where high early strength is needed.

Only one producer struggled to meet resistivity targets, and the agency learned from the experience gained while supporting this producer. LaDOTD implemented e-ticketing to support quality assurance, which revealed issues associated with mixture variability at this producer’s plant. The agency compared e-tickets to the approved mixture designs provided by this producer, and after moisture adjustments, found that the concrete batched was not close to the approved mixture design. It was determined that this producer was not providing adequate quality control (QC) related to aggregate moisture content, and this lack of aggregate moisture control was the key factor influencing the low resistivity results. As such, LaDOTD realized the importance of contractor QC, particularly when more complex mixtures such as ternary blends are being produced. LaDOTD suggests that if agencies are moving toward more complex mixtures such as ternary blends, they should emphasize contractor and supplier QC. Without appropriate QC provisions and staffing, producers and suppliers may struggle.

Benefits and Challenges Associated with SCMs and ASCMs

Initially, some stakeholders did not believe that LaDOTD could successfully allow up to 70% SCM replacement rates. However, stakeholders were generally able to provide mixtures that met resistivity requirements while also meeting construction requirements. Overall, LaDOTD’s specification provisions appear to be providing the desired durability performance. Research has shown that targets are providing the desired constructability and long-term service.

Louisiana is supplied by multiple sources of ash, and fly ash shortages have not affected its projects. A brief shortage of slag occurred for 5 months due to an issue in shipping on the Chicago River, but this has since been rectified and slag is currently generally available. However, the state has recently experienced issues with consistent cement supply. Producers appear to need to switch cement suppliers more frequently than in previous years, and some suppliers are increasingly relying on a supply of cement (often Type I/II) from foreign sources. More recently, the supply has been shifting back to Type IL cement. LaDOTD has heard stakeholder complaints regarding Type IL cement but suspects the issues are being overcome by adjusting admixtures or mixture design.

From the agency’s perspective, the shift of cement supply from Type I/II to Type IL has been positive since the interground limestone can provide improved hydration, particularly when paired with SCMs. LaDOTD has observed higher long-term strength for Type IL/SCM mixtures, with only minor adjustments required to address workability, finishing, and other concerns. The agency has not observed issues with shrinkage or delayed strength with Type IL and SCM mixtures.

In moving to allow higher SCM replacement rates, LaDOTD initially thought it would see cost savings passed on in bid prices since SCMs can often be lower in price than cement. However, the cost of concrete increased slightly, likely due to the surface resistivity requirements implemented in the specifications. Suppliers have reported a 5% to 8% cost increase in the unit price of concrete due to implementation of the resistivity specifications. This cost increase has often been reflected in the suppliers’ price to contractors, and LaDOTD has generally not seen a significant increase in bid prices from contractors.

LaDOTD appreciates the sustainability benefits that are likely associated with its high SCM replacement rates. However, shipping costs to the state are also substantial for all materials, particularly aggregates. LaDOTD has funded studies that have shown that GHG emissions associated with shipping aggregates to Louisiana (often from Central America or the Caribbean) are high compared to the much lower GHG emissions associated with transport of SCMs. Cement and aggregates are typically shipped from overseas, with cement typically travelling a shorter distance than aggregates. SCMs are often trucked into the state, with the exception of slag, which is barged to Louisiana from Illinois or Alabama. Some of the impacts associated with materials can be viewed differently depending on the boundaries used within the life-cycle analysis.

In general, LaDOTD has not experienced challenges with SCM use that could not be overcome by its producers and suppliers. Silo capacity tends to be a concern for smaller producers. However, larger producers, particularly those associated with companies embracing sustainability initiatives, do not seem to have an issue with silo capacity.

In structural concrete projects, contractors often desire rapid early-age strength gain to support the desired construction schedules, often wanting to remove forms and move to the next pour within several days. Use of SCMs with slower reactivity (such as slag and fly ash) results in slower concrete strength gain, impeding the desired rapid turnaround. One approach that contractors have successfully used to support higher early-age strength is lowering the w/cm ratio of structural mixtures from the maximum allowable of 0.45 (with mixtures often proportioned at 0.42) to a lower w/cm of about 0.39. This approach has been found to support achieving the early-age strength desired to support construction schedules.

LaDOTD views the continued gasification of power plants as an issue that could result in a shortage of ash available to the state. The agency recognizes that it will need to pay for ash as a commodity needed to obtain the desired performance from its concrete infrastructure. LaDOTD recognizes that agencies willing to pay for ash will be able to secure it, while agencies not willing to pay for ash may struggle to secure a consistent supply. LaDOTD understands that the agency is essentially requiring producers to pay higher prices for ash via the resistivity specification, and these prices are then passed on to LaDOTD through bid prices.

The quality of ash that will be available in the future is also a concern, as is controlling the carbon content of the ash supplied to the state. The agency may consider supporting the use of blended ash. However, it acknowledges that most states require ash to meet ASTM C618, and therefore, it not be necessary to blend ash.

LaDOTD does not have plans to allow ASCMs. One research partner studied natural pumice in LaDOTD mixtures, but the findings did not support its use. LaDOTD supported a study of a 100% fly ash system with an acid activator. However, these mixtures did not behave as anticipated at the manufacturer’s recommended activator dosage rates, and the material did not move forward in the qualification process.

LaDOTD Case Example References

LaDOTD. 2016 Standard Specifications for Roads and Bridges Manual. Louisiana Department of Transportation and Development. Baton Rouge, LA, 2016. http://wwwsp.dotd.la.gov/Inside_LaDOTD/Divisions/Engineering/Standard_Specifications/Pages/Standard%20Specifications.aspx, accessed May 8, 2025.

Case Example 4: MnDOT

History of SCM Specification and Use

MnDOT has allowed fly ash as an SCM since the 1970s; the agency incorporated it into the 1978 MnDOT Standard Specifications for Construction (MnDOT 2024a). Initially, MnDOT allowed a maximum of 10% fly ash substitution for Portland cement in all concrete except for bridge superstructures. In 1983, a maximum of 15% Class C or 10% Class F fly ash was allowed, except 20% Class F fly ash was allowed if 3 pounds of cement were replaced with 4 pounds of fly ash. Historically, MnDOT would either limit or not allow fly ash substitutions between October and April of each year. MnDOT designed and trial batched all concrete mixture designs, providing a prescribed mix design to concrete producers, which led MnDOT to not have a 28-day compressive strength requirement but only an anticipated strength expectation until 2016 when contractor mix designs were fully implemented. In the 1990s, MnDOT started experimenting with slag as an SCM in some concrete paving and larger bridge structures, then fully allowed it beginning with the 2000 MnDOT Standard Specifications with a cement replacement of 35%. MnDOT has used higher volumes of SCMs (up to 70%) in specific applications, including mass-concrete applications, but this was not moved to general practice.

In the mid-1990s, MnDOT began to identify some material- and paste-related distresses in its concrete pavement that it had not previously observed. Prior to 1995, MnDOT supplied agency-developed mixture designs to contractors. These mixture designs typically had a w/cm ratio of 0.46, a minimum cementitious content of 530 pounds per cubic yard [450 lbs/yd³ (85%) of cement and 80 lbs/yd³ (15%) of fly ash], 244 lbs/yd³ of water, and 1,200 lbs/yd³ of fine aggregate (Sutter et al. 2018). Research on freeze–thaw durability, including pilot studies, indicated that use of w/cm lower than the 0.46 in the prescribed mixture design would likely provide improved performance and reduce permeability. Based on this work, MnDOT modified specifications to include a maximum w/cm of 0.40 and a maximum cementitious content of 600 lbs/yd³ while

requiring contractor-designed mixtures. The allowable fly ash replacement rate was increased to 25% (Sutter et al. 2018).

In response to ASR distress observed in MnDOT’s concrete pavement infrastructure during the 1990s, the agency supported research to better identify appropriate approaches for ASR mitigation. These studies indicated that the agency typically needed to require a cement replacement rate of greater than 15% fly ash to mitigate ASR for some local aggregates.

In 2000, MnDOT constructed a 60-year design life high-performance concrete (HPC) pavement with a 28-day maximum permeability requirement of 2,500 coulombs, which led to construction of pavement with 35% slag replacement for cement. MnDOT has since determined that pavements with a lower w/cm ratio (0.42 or less) with higher SCM replacements, water reducers, and optimized gradations provide lower permeability, and the agency removed the permeability requirement.

In 2008, the state supported development of contractor-designed HPC bridge mixtures where reduction of cracking was desired. These mixtures had performance-based requirements for optimized gradations, shrinkage, and low permeability (measured via a rapid chloride permeability test), which could typically only be met through use of SCMs. This led to increased use of SCMs, and the agency allowed SCM replacements of slag (35%), fly ash (30%), and silica fume (5%), with a maximum of 40% SCMs for ternary mixtures. In 2012, the state implemented an HPC bridge deck mixture specification for all new bridge construction.

MnDOT began allowing contractor-submitted mixture designs for general concrete use in 2016, with a limit of 25% fly ash on flatwork and 30% fly ash for other applications.

SCM Specifications and Use

At the time of this writing, SCMs are allowed in pavements and all structures as additives alone and as a constituent in blended cements. MnDOT’s specifications particularly support use of SCMs in concrete classes that require low permeability to improve durability performance. MnDOT’s specification provisions and the contractors’ positive experiences with SCMs improving construction characteristics of the mixtures have driven use of SCMs and the replacement rates. Contractors have cited many benefits from using some fly ash sources, including reduced water demand, increased workability, and improved finishing characteristics. The contractor is typically selecting the SCM used, the replacement rate based on cost and availability, ASR mitigation requirements, and placement factors.

Based on years of testing sand sources using ASTM C1260 and C1567, when ASR mitigation of reactive aggregates is necessary, a minimum of 20% Class F fly ash, 20% to 30% Class C fly ash, 35% slag, or 20% slag/15% to 20% fly ash is required. Fly ash (both Class C and Class F) is the most used SCM in Minnesota. Class C or Class F ash is allowed at substitution rates of up to 30% for structures and up to 33% for pavements, with Class F ash more commonly used than Class C in paving and HPC bridge decks. Harvested or beneficiated fly ash meeting ASTM C618-23/AASHTO M 295 is also allowed but has not yet been used for any MnDOT projects. MnDOT has experienced challenges associated with getting fly ash in the past. When fly ash was in very limited supply, MnDOT modified its specifications to only require the use of SCMs (primarily fly ash) in concrete pavements with highly reactive aggregates and high-performance bridge deck mix designs to meet shrinkage and permeability requirements. MnDOT also had general concrete mixtures designed with 100% cement since most other SCMs are not commonly available in its market in large quantities and because of the limitations of smaller concrete producers that only have two cementitious silos at their plants.

At the time of this writing, fly ash supply is meeting demand. However, MnDOT has met with fly ash suppliers to find ways to prevent issues with both supply and consistency. One major

supplier hopes to blend 50% fly ash and 50% bottom ash, increasing the volume of material available. MnDOT would require this type of blended material to meet ASTM C618. MnDOT is also developing a performance-based specification that should allow the use of marginal and off-specification ash. MnDOT’s also has a certification process for evaluation of coal combustion ash not approved by ASTM C618 for use in concrete (MnDOT 2022).

Although slag is allowed at up to a 35% replacement rate, it is not often used in Minnesota projects. Slag cement has been used in bridge and paving projects, although many contractors reported that slag mixtures did not provide the most desirable performance from a finishing perspective.

MnDOT is expanding allowable SCM materials to include NPs, including calcined clay, calcined shale, calcined pumice, and metakaolin, even though these materials are not locally available and have not been used in MnDOT’s concrete infrastructure. At this time, MnDOT has not determined the allowable SCM substitution percentages for NPs. Recently, an NP composed of roof shingle dust has been available in the Minnesota market, but it does not provide ASR mitigation benefits. Therefore, when mitigation is required, this product needs to be blended with fly ash or slag cement.

MnDOT’s specifications allow ternary blends with a maximum of 40% SCMs for all types of concrete, except that ternary mixtures are not allowed for flatwork. Ternary blends are typically only seen in structural applications.

Quality Assurance Approaches

MnDOT requires a certification program and maintains an approved products list for cement, blended cement, fly ash, and slag cement. Also, MnDOT performs annual sampling of these materials from each concrete source supplying state projects. For informational purposes, MnDOT takes samples of the fine aggregate and all cementitious materials from each concrete paving project and performs ASTM C1567 testing to see the expected expansion of these combinations of materials. For general concrete mixtures, trial batching or strength performance data are required to provide a mixture design that contains greater than 15% fly ash or greater than 35% slag cement. Trial batching is not required for concrete paving projects; however, MnDOT specifications do require test results for rapid chloride permeability (ASTM C1202), volumetric shrinkage (ASTM C157), scaling (ASTM C672), freeze–thaw durability (ASTM C666), and air-void system parameters (ASTM C457) at the time of submittal of the HPC bridge deck mixture designs for approval.

MnDOT specifications ensure the quality of low-permeability mixtures primarily through control of the w/cm ratio. There is no strength requirement for acceptance of paving mixtures. This approach helps accommodate the slower strength gain of many SCM mixtures while still achieving the benefits associated with lower concrete permeability. However, 28-day strength test results are still required for all other concrete mixtures with and without SCMs. MnDOT has occasionally allowed HPC bridge deck mixtures up to 56 days to meet strength requirements. The agency is evaluating the feasibility of 56-day strength requirements for high-SCM mixtures (particularly structural mixtures) by fabricating and testing 56-day strength specimens. Resistivity testing is also being performed on bridge mixtures at 28 days and concrete paving mixtures at 60 days in an investigative effort, but not for acceptance. The data from this testing may be used to support development of a resistivity target for bridge mixtures.

Opportunities Associated with ASCMs

MnDOT’s standard specifications do not allow emerging and available ASCMs. However, MnDOT and its stakeholders are interested in use of ASCMs for a variety of reasons, including meeting construction demand, performance benefits, and improving durability and sustainability. Although independent test data are required for ASCM approval, MnDOT may consider

accepting test data from private laboratories or data from other state agencies to facilitate piloting the use of ASCM materials.

The agency is exploring several ASCMs, including industrial by-products, alternative materials, and other low-carbon transportation materials, at the MnROAD research facility through NRRA pooled funds. One field trial with 16 test sections constructed in 2022 (MnDOT 2024b) and three related research studies are ongoing. A second field trial with eight additional test sections will be conducted at MnROAD in 2024.

MnDOT Case Example References

MnDOT. 2022. Minnesota Department of Transportation (MnDOT) Certification Process for Evaluation of Coal Combustion Ash Not Approved by ASTM C618 for Use in Concrete.

MnDOT. 2024a. Standard Specifications for Construction and Supplemental Specifications. https://www.dot.state.mn.us/pre-letting/spec/.

MnDOT. 2024b. Development of Concrete Mix Designs/Matrix of Materials, Performance Properties, and Construction Field Sampling and Testing Expectations During Construction. https://www.dot.state.mn.us/mnroad/nrra/structure-teams/rigid/sustainable-concrete-mix-selection.html.

Sutter, L., G. Moulzolf, and M. Masten. 2018. Impact of Water/Cementitious-Based Concrete Mix Design Specification Changes on Concrete Pavement Quality. Report MN/RC 2018-25. Minnesota Department of Transportation, St. Paul, MN.

Case Example 5: UDOT

History of SCM Specification and Use

UDOT began allowing fly ash, silica fume, and NPs in the 1990s. Based on the benefits offered to concrete infrastructure from use of SCMs, UDOT personnel worked to incorporate additional use of SCMs into the UDOT specifications during the 2010s. Utah has ASR-susceptible aggregates. Although they are not typically highly reactive, many exhibit moderate to low reactivity, and SCM use is necessary to mitigate reactive aggregates. Historically, fly ash has been relied on to mitigate ASR, and in most instances it has been successful.

SCM Specification and Use

UDOT allows use of SCMs as additives alone and blended in cements, in pavements, and in all structures. UDOT encourages the use of SCMs in concrete classes that require low permeability since the SCMs will typically improve concrete durability. SCMs are also desirable in mass-concrete elements for temperature management. UDOT also supports increased use of SCMs in concrete infrastructure in order to lower the environmental impact of its infrastructure through reduction of cement content in concrete mixtures.

The Utah market is proximal to several NP producers, and UDOT has several NPs that are used by suppliers and contractors. These include a natural volcanic ash, pumice, and expanded shale. The natural ash has been found to mitigate ASR and also does not adversely affect the water demand of concrete mixtures. The producer of the pumice material is not quite set up to produce the quantities needed for supplying UDOT projects, but the agency anticipates there will be a supply of this material in the future.

The expanded shale product available to UDOT has been shown to increase the water demand of mixtures, and research indicates that additional water-reducing admixture is often required to achieve the desired workability. This material is being purchased by a cement supplier that is blending it into a Type IP cement, which is being used fairly extensively by precast manufacturers and a limited number of ready-mixed concrete producers.

At the time of this writing, UDOT allows Class F fly ash at replacement rates of between 20% and 30%; silica fume at replacement rates of less than 10%; and calcined clay, shale, and pumice at replacement rates of up to 30%. Specifications require the use of 20% to 30% Class F ash or NPs in bridges/structures to support improved durability. NPs are also allowed at replacement rates of 20% to 30%. Prior to 2020, silica fume was allowed in mixtures, although recent specifications do not include silica fume as it was not being used by contractors very often. Ternary blends and quaternary blends are allowed in pavements and structures, with several restrictions. In the 2020 specifications, if fly ash and silica fume are used together in a mixture, the fly ash substitution rate must be 20%, while the silica fume content must be ≤10%. Several different ternary blends are commonly used in Utah. One particular supplier has found success using mixtures containing NPs at 25% replacement rates and fly ash at a 5% replacement rate.

UDOT has also seen increased use of blended cements, including Type IP cements. The agency has found that preblending these NPs at the cement plant likely helps with uniformity and quality control.

UDOT is developing revisions to its specifications for concrete. It is anticipated that this revision will involve reorganization of the existing specifications but that most of provisions for SCMs will remain the same. Based on observed performance and stakeholder experience, the allowable substitution rates and tests required to support approval and acceptance of these mixtures are working well and mixtures are providing the desired field performance.

Quality Assurance Approaches

UDOT requires SCMs in all concrete mixtures. For approval of mixture designs, UDOT requires that ASTM C1567 tests be performed to confirm that the cement and pozzolan combination will mitigate ASR to expansion of less than 0.1%. Additionally, low-shrinkage fiber mixtures, low-shrinkage mixtures without fibers, paving mixtures, and high early-strength mixtures require AASHTO T 160 shrinkage tests and AASHTO T 358 surface resistivity tests.

Mixtures incorporating SCMs must meet the same acceptance strength requirements as straight cement mixtures at 28 days. These include slump, strength, and air content. UDOT typically experiences good performance from SCM mixtures in service. Of note, many precast items, such as barriers that are exposed to heavy loads of deicers or to harsh conditions, are produced using SCMs. Field exposure should provide insight into the longer-term performance of these mixtures.

Benefits and Challenges Associated with SCMs and ASCMs

Utah’s concrete infrastructure has historically experienced issues with early-age shrinkage cracking. The dry Utah climate can make it challenging for contractors to provide adequate curing provisions to ensure that SCMs achieve their potential. The agency has supported a research project that is primarily focused on field study of multiple bridge decks constructed using different mixtures. Each of the bridge decks in this study includes fly ash. Two mixture designs are a focus of the study—one conventional, one with the cementitious content reduced by 80 lbs. These decks will be monitored for long-term performance, with a focus on whether cracking can be reduced by using a lower cementitious content. Wet curing of decks using a method developed in Montana is also being explored. The agency has not had success in supporting curing using fogging alone. Overall, UDOT has observed that if curing is successful, the SCM mixtures being used exhibit good performance.

To support the state’s sustainability goals, UDOT is planning on submitting an application to FHWA’s Low Carbon Transportation Materials Grant program. The agency is looking at

requesting funds for more advanced, more expensive test equipment that can run tests on the cement/pozzolan content so that UDOT can understand SCM performance better. This equipment would include a calorimeter and other testing equipment to support characterization of SCMs, ASCMs, and concrete mixtures using these materials. UDOT would like to have the capability to understand what makes a good pozzolan as more NPs become available, and it is hoping to identify the capabilities and limitations of these materials before their use in concrete.

Challenges Associated with SCM Use in Concrete Applications

One cement supplier has been encouraged by UDOT to be more environmentally responsible, which has helped drive the transition of the supplier’s cement from Type I/II to Type IL. This supplier was first to begin supplying and providing supporting data for Type IL cements. Data provided by the supplier made UDOT feel comfortable making the switch to Type IL. Minor impacts have been observed in concrete mixtures when SCMs are used with Type IL cement. However, UDOT has found that these changes can be been readily overcome by contractors and producers through conventional mixture design/proportioning approaches and construction techniques.

UDOT had experienced a shortage of fly ash in previous years. Precast concrete companies tended to be most affected by ash supply issues since they were buying in smaller quantities than ready-mix producers and contractors. Since the larger producers were purchasing the available fly ash, precast concrete manufacturers found other solutions. One solution was to use Type IP cement. Other precast operations are now using Type IL cement and blending in an NP.

The supply of ash has now increased, in part due to the commissioning of a new coal-fired power plant that recently came online. The ash supplied from this plant has exhibited a relatively high carbon content and, therefore, high LOI. However, additional processing has helped lower that carbon content (LOI) and has reduced the impact on air-entraining admixtures used in concrete. At the present time, the fly ash supply is fairly stable, also in part because a local supplier has agreed to supply ash for local needs first before selling material outside of the state.

Opportunities Associated with SCMs and ASCMs

ASCMs are allowed by UDOT at replacement rates of up to 30%. Similarly to conventional SCMs, concrete with ASCMs must be qualified through tests such as those for compressive strength of concrete, surface resistivity, shrinkage, freeze–thaw durability, and air-void system parameters. Data obtained from private laboratories are accepted.

ASCMs currently of interest in the state include ground glass and an industrial mining slag. A university partner is performing a research project on the use of ground glass in concrete, but the material has not been placed in a field trial yet. A recycler in Utah is interested in providing ground glass, but the volume a producer (or producers) can supply may be an issue in much of the state. Another issue is finding a grinder that can prepare the material to a fine enough grind.

UDOT has also been contacted by an mining company about the use of mining slag, but this has not been explored to a significant extent. The extensive mining industry in Utah may be source of ASCMs in the future, but no mining operations are currently putting forth material for consideration.

UDOT Case Example References

UDOT. 2025. 2025 Standard Specifications for Road and Bridge Construction. Utah Department of Transportation. https://www.udot.utah.gov/connect/business/standards/.