Reported by ACI Innovation Task Group 10 ()() · 2020. 5. 12. · ACIITG-10.1R-18 Report on Alternative Cements Reported by ACI Innovation Task Group 10 Lawrence L. Sutter, Chair

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American Concrete Institute Always advancing

Report on Alternative Cements

First Printing August 2018

ISBN: 978-1-64195-024-4

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ACIITG-10.1R-18

Report on Alternative Cements

Reported by ACI Innovation Task Group 10

Lawrence L. Sutter, Chair

Mary U. Christiansen Jonathan E. Dongell

James K.. Hicks R. Douglas Hooton

This report addresses available and emerging alternative cements

with the intent to facilitate the adoption of these new materials.

Given the initiatives to address the sustainability of construction,

owners, architects, and engineers are actively seeking alternatives

to portland cement for concrete. An alternative cement is intended

to he a replacement for portland cement in some applications.

In some cases. alternative cements can also be used in combina

tion with portland or hlended hydraulic cements. In addition to

a reduced environmental impact associated with their production

and use, alternative cements offer improved performance over

portland cement in some applications. Various alternative cement

technologies are discussed, including their physical and composi

tional characteristics. methods of production, fresh and hardened

properties, and e.;wmple applications. Additionally, the applica

bility of existing tests methods for specifYing alternative cements is

discussed and new testing needs are identified.

Keywords: alkali-activated; altemative cementitious materials; altema

tive cements; calcium aluminate cement; calcium sulfoaluminate cement;

carbonated calcium silicate cement; geopolymer; magnesium oxychloride

cement; magnesium phosphate cement; supersulfated cement.

CONTENTS

CHAPTER 1-INTRODUCTION AND SCOPE, p. 1 1 . 1 -Introduction, p. I 1 .2-Scope, p. 2 1 .3-History, p. 2

ACI Committee Reports, Guides, and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. This document is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom.

Reference to this docmnent shall not be made in contract documents. If items found in this document are desired by the Architect/Engineer to be a part of the contract documents, they shall be restated in mandatory language for incorporation PY..th!< Architect/Engineer.

Kevin A. MacDonald

Claudio E. Manissero Anol K. Mukhopadhyay

Deepak Ravikumar

CHAPTER 2-DEFINITIONS, p. 2

CHAPTER 3-BACKGROUND, p. 3 3. 1-Petformance measures for alternative cements, p. 3 3 .2-Summary, p. 4

CHAPTER 4-ALTERNATIVE CEMENT TECHNOLOGIES, p. 4

4. 1-lntroduction, p. 4 4.2-Ciinkered alternative cements, p. 4 4.3-Calcined alternative cements, p. 8 4.4-Non-clinkered alternative cements, p. I 0 4.5-Summary, p. 1 3

CHAPTER 5-TESTING REQUIREMENTS FOR ALTERNATIVE CEMENTTECHNOLOGIES, p. 13

5 . 1 -lntroduction, p. 1 3 5.2-Testing alternative cements, p . 1 4 5 .3-Testing alternative cement concrete, p . 1 6 5.4-Summary, p . 20

CHAPTER 6-REFERENCES, p. 20 Authored docwnents, p. 21

CHAPTER 1-INTRODUCTION AND SCOPE

1.1 -Introduction This report provides a summary of a lternative cement tech

nologies currently available or emerging for construction use. This report a lso identifies the need for development of test methods to facil itate the use of altemative cements with the same level of reliabil ity expected from portland cement. The goa l of this document is to introduce the concrete construction community to a lternative cements and increase their knowledge base, experience, and confidence in their

ACJ ITG-10.1 R-18 wa adopted and published August 2018.

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2 REPORT ON ALTERNATIVE CEMENTS (ACJ JTG-10.1 R-18)

use. Because of the long histmy of using portland cement as the exclusive or primary cement for concrete construction, concrete specifications and design codes have an inherent assumption, or in some cases a requirement, that portland cement is the primary cementitious binder material to be used. Supplementary cementitious materials are commonly used but very rarely as a complete replacement for portland cement. Because alternative cements are developing and their commercial ization is increasing, it is important that engineers, architects, contractors, and owners become familiar with alternative cement properties and applications, and be knowledgeable of how to test these materials.

1.2-Scope This repot1 addresses available and emerging alternative

cements, with the intent of introducing these materials and facilitating the development of test methods to address their safe and reliable use. The discussion herein includes material properties, production methods, and testing methodologies. References made to portland cement and pm1land cement production are for comparison purposes only. An in-depth discussion of portland cement is not within the scope of this report.

1. 3-History In its simplest conception, concrete consists of aggregates

bonded together using a cohesive binder, or cement. More than �000 years ago, concrete was produced with notewm1hy ceme�t technologies such as those used by the Romans in const�ction of the Pantheon and Colosseum (Kosmatka and Wi lson 20 1 1 ). These ancient concrete mixtures relied on lime or various natural cements and pozzolans for the cohesive binder. S ince its introduction in 1 824, portland cement has universally become the most common cement for concrete given its relatively low cost, uniformity, availabil ity, and ease of use.

Portland-cement concrete (PCC) is the most widely used manmade material and is unrivaled for its versatility and durabil ity. Because of these general characteristics, PCC is an indispensable ingredient of modern civil ization, used in the construction of civil engineering and archj tectural structures, including roads, bridges, public water and sanitary systems, and buildings.

L ike many manufacturing processes, portland cement production is not without detriment to the environment with respect to the energy-intensive nature of its production and the inherent release of greenhouse gas {GHG) emissions. Production of portland cement begins with a mixture of raw materials that includes limestone, which is primarily calcium carbonate (CaC03) and shale. These materials are heated in a rotary k:j ln to temperatures of approximately 2460 to 2640°F { 1 350 to 1450°C) to produce clinker. The conversion of calcium carbonate to calcium oxide by heating is called calcining. In this process, carbon dioxide (C02) and other GHG emissions are created. The primary source of C02 is the conversion ofCaC03 to CaO. Additional C02 is released through burning fossil fuels to heat the k:j ln. The negative results of this process are a high energy demand due to the

temperatures needed for producing portland-cement cl inker and the identified GHG emissions. Although pmt land cement is a minor ingredient in PCC, it is the principal source of embodied energy and GHG emissions for the material. There are numerous papers and references discussing the environmental footprint of portland cement with a brief l ist referenced here (Hanle et al. 2009; Kosmatka and Wilson 20 I I ; RMCA 20 12; EPA 20 12) . With respect to both embodied energy and GHG emissions, the state of the at1 for pmtland cement production is approaching the point where only minimal additional reductions can be expected using existing production technologies.

Given recent initiatives to address the sustainability of everything we do as a society, owners, architects, and engineers are actively seeking alternatives to portland cement to meet the demand for concrete. It is unlikely that portland cement will be completely replaced as the primary cement for producing concrete, but there are applications in which available alternative cements can be used. Adoption of alternative cements can result in numerous environmental advantages, including the beneficial and effective incorporation of recycled and residual materials, and reductions in the embodied energy and GHG emissions associated with PCC.

In addition to environmental advantages, alternative cement concrete can perform better in specific applications when compared to PCC. Examples of performance improvements include faster setting times, increased wear resistance, and improved chemical or fire resistance.

CHAPTER 2-DEFINITIONS ACI provides a comprehensive list of definitions in

"ACI Concrete Terminology." Definitions provided herein complement that source.

alkali activation-the process of using an alkali-based solution to cause the dissolution of an alwnino-silicate precursor and to initiate the chemical reactions leading to the formation of reaction products.

alkali activator-an alkal i-based solution that causes alkali activation, such as sodium hydroxide and sodium sil icate solutions.

alternative cement-an inorganic cement that can be used as a complete replacement for portland or blended hydraulic cements, and that is not covered by applicable specifications for portland or blended hydraulic cements.

Note: An alternative cement or alternative cement blend could provide better performance than that of portland or blended hydraulic cement in some applications. An alternative cement, however, might not perform adequately as a replacement for portland or blended hydraulic cement in every application. In some cases, alternative cements can also be used in combination with portland or blended hydraulic cements.

ambient-cured-curing without the addition of heat above that available from room or the external environment.

calcined alternative cement-an alternative cement produced by calcining a raw material only, without fw1her pyroprocessing, to produce additional mineral phases within the material.

REPORT ON ALTERNATIVE CEMENTS (ACI ITG-10.1 R-18) 3

clinkered alternative cement-an alternative cement produced using technologies similar to portland cement production, with process changes that preclude production of pmtland cement but positively affect the environmental impact of production.

functional addition-a substance other than water that is added to, or combined with , a material that is not hydraulic and causes a cementitious reaction to occur or accelerate.

geopolymer-an alternative cement produced from alwnino-silicate precursors that form nonhydrated cementitious reaction products by alkali activation.

geopolymerization-a spontaneous reaction that results in the bonding of smaller inorganic polymers to form larger ones.

heat-cured uring with the addition of heat above that available from room or external environment.

non-clinkered alternative cement-an alternative cement produced using precursors that require no pyroprocessing and set after addition of an activating solution to cause reactions that are not hydration or acid-base.

precursor-a solid raw material reacted with a functional addition to form an alternative cement

CHAPTER 3-BACKGROUND

3.1-Performance measures for alternative cements

To serve as an alternative to pmtland cement, a binder technology needs to offer demonstrable improvements in one or more areas, including environmental impact, l ife-cycle cost (LCC), and performance. The cost of an alternative cement needs to be competitive when compared to pmtland cement, but most importantly, an alternative cement will be expected to meet all specified functional performance requirements. Each of these factors will be briefly discussed.

3 . 1 . 1 Environmental impact-With respect to environmental impact such as greenhouse gas (GHG) emissions and embodied energy, alternative cement concrete typically compares favorably to PCC. The manufacture of portland cement accounts for approximately 70 percent of the total embodied energy and 88 percent of the C02 emissions for a 3000 psi (20 MPa) PCC mixture (Nisbet et al. 2002). By using alternative production techniques or precursor materials, alternative cement concretes can be produced with a reduced environmental impact.

There are nwnerous aspects to assessing environmental impact and in-depth analysis is beyond the expertise of most people in the construction industry. To summarize the environmental impacts of any product, the construction industly has responded to the need-to-know by issuing an environmental product declaration (EPD) for each product, wh ich summarizes the various impacts associated with that product. An EPD is developed within the framework of a product category rule (PCR); as alternative cements enter the market, PCRs and the associated EPDs are developed, allowing comparisons between the various cementitious systems.

3. 1 . 1 . 1 Life-cycle cost-Increasingly, construction alternatives are being considered in terms of their LCC, in addition to or in place of the initial cost. LCC considers the total cost of ownersh ip of an asset from cradle-to-grave, or when recycling and reuse is possible, cradle-to-cradle. Typical l ife-cycle aspects considered when determining the LCC include planning, design, construction and acquisition, operations and user costs, maintenance, renewal and rehabil itation, depreciation and cost of finance, and replacement or disposal costs. Note that not all costs factored into an LCC are direct monetary costs. An example for concrete is that a portion of the materials LCC will be attributed to the environmental impact of producing the cement used. In an economic environment where carbon credits/taxes exist, th is environmental impact can be assigned a monetary cost as well . In the absence of a tax or credit, converting these lifecycle aspects to monetary cost is more problematic.

The choice of binder system for a concrete will impact the LCC in various ways. As stated previously, if the material is produced with a smaller environmental footprint when compared to another material, nonmonetaty environmental impact costs will be reduced. How the material performs in service could impact operation and maintenance costs. Characteristics of the material may also impact the renewal, rehabil itation, replacement, and disposal costs. As an industry, there is considerable experience with PCC and, therefore, the individual factors that contribute to LCC are more easily estimated. Th is is not the case for some alternative cements due to a more inexperienced indushy. The LCC of a construction material is inextricably linked to its durability.

3. 1 . 1 .2 Initial cost-To be competitive with PCC, an alternative cement concrete does not necessarily need to have the same initial cost. In the past, an equal initial cost, or lower cost, would clearly be a necessmy starting point, as initial cost was the only consideration. However, with LCC increasingly being used as a decision tool in selecting materials for construction, other factors are now considered. When comparing initial costs for a project, it is important to ensure the comparisons are made on an intellectually honest basis. One cannot compare the materials cost for an alternative cement concrete to the cost of PCC if either option cannot fulfill the requirements of the project.

When considering the initial cost, it is necessa1y to consider the in-place cost, including labor, equipment, curing methods, and constmction time because performance improvements of the binder system may allow for savings in other areas of const11.1ction and ultimately reduce the total project cost. Construction contractors are constantly seeking ways to lower their total cost or improve their profitability and abil ity to compete; alternative cements provide a new oppmtunity to achieve lower project costs when all factors are considered. As one example, when rebuilding the Santa Monica Freeway after the 1 994 orthridge earthquake, the contractor received a $ 1 4.5 mil lion bonus for early completion and one factor leading to the early completion was the use of an alternative cement for pmtions of the construction (Mitchell et al . 1 995; Ph il ips 2005).

4 REPORT ON ALTERNATIVE CEMENTS (ACIITG-10. 1 R-18)

3. 1 . 1 .3 Functional pe1jormance-Although modem construction practices demand more environmentallyfriendly materials, and, to a degree, a smaller environmental footprint can offset a higher monetaty cost, functional performance will always be the key measure. If a material cannot meet project requirements, the material should not be used in construction. Many performance benefits result from the use of alternative cements in concrete, including faster set times, rapid strength gain, low permeabi lity, heat resistance, and others. However, as alternative cements seek to replace PCC in more conventional applications, unique qualities are less important and specifiers seek similar performance when alternative cement concrete is compared to PCC. This is mainly due to the empirical nature of the concrete design and construction environment.

Demonstrated petfonnance, both in the laborat01y and in practice, is required to ensw-e that life-safety considerations and performance are met when using alternative cement concrete in place of PC C. Providing this infonnation to specifiers has been a challenge for alternative cement producers largely due to the lack of a clear testing protocol or, in some cases, the lack of applicable tests. Without needed information, it is difficult to provide a demonstrated example, or even an accurate prediction, of a design life for stmctures using new types of concrete. As mentioned previously, the LCC of a construction material is inextricably linked to its durability. Therefore, developing data on long-term durability is a necessaty step to increasing use of altemative cements.

Another aspect of functional performance is constructability. To achieve the desired hardened properties, the concrete requires proper placement and curing in the field. This aspect alone may limit the application of some alternative cements, while for others it can be an advantage. Constructabil ity also depends on the availability of knowledgeable professionals to place, troubleshoot, or adjust mixture designs to achieve the desired performance. This means it will be necessary to have a workforce that is trained to proportion, test, mix, place, and cure these new materials.

3.2-Summary Concrete produced usmg alternative cements offers

numerous advantages and opportunities, which will be discussed in subsequent chapters of tlus rep011. Along with the advantages, however, is a discussion of the challenges to be resolved before alternative cements can be more commonly used in everyday construction. One challenge is the industry's desire to compare these new materials to PCC using the same metrics and methods that have historically been used, which may not be appropriate.

The general criteria of initial cost and the material's functional performance in the existing design environment are key factors but are not the only considerations. The desire for a more sustainable construction industry requires consideration of LCCs that, in turn, allows the environmental advantages of alternative cement production to be considered.

Table 4.1 a-Classification of commercially available and emerging alternative cement technologies

I Clinkered alternative cements

Calcined alternative cements

Non-clinkered alternative cements

Calcium aluminate

Reactive belite

Calcium sulfoaluminate

Carbonated calcium silicate

Magnesium oxychloride

Magnesium phosphate

Magnesium ammonium phosphate

Magnesium potassium phosphate

Alkali-activated

Fly ash

lag

Recycled glass

Supcrsulfatcd cement

CHAPTER 4-ALTERNATIVE CEMENT TECHNOLOGIES

4.1-1 ntroduction The purpose of this chapter is to introduce and discu s

the properties of the various alternative cement teclmologies. The technologies di cussed are grouped based on similar production factors. The categories used are defined in Chapter 2 and include cl inkered alternative cements, calcined alternative cements, and non-clinkered alternative cements. This chapter addresses alternative cements that are commercially available as well as those that are still in development. A summary of the state of the knowledge with re pect to all these materials is presented. A list of the alternative cements is provided in Table 4. l a. Each subsection starts with a sununaty of the technology, which may suffice for understanding the advantages and disadvantages of each technology and bow their properties compare to portland cement. Following the summary is a more in-depth synopsis of the pertinent l iterature regarding fresh and hardened properties of mixtures made using these technologies. Table 4. 1 b provides a comparison of technologies, summarizing key properties and applications for implementing alternative cement technology.

4.2-Ciinkered alternative cements Clinkered alternative cements are materials that represent

an incremental change in binder technology when compared to portland cement. However, as is discussed in thi report, the resulting materials have chemical and physical propertie that are notably different than portland cement because they offer different performance attributes and, in some cases, require varying approaches to implementation. One example i different curing regimes. Therefore, despite their sirnilatities to portland cement, these matetials that do not meet current standards for portland or blended cement are considered alternative cements.

4.2. 1 Calcium aluminate cement 4.2.1.1 Technology-Calcium aluminate cements (CACs)

differ significantly from p01tland cement in composition because of the raw materials and, to some extent, manufacturing proces es. Calcium aluminate cement are hydraulic

REPORT ON ALTERNATIVE CEMENTS (ACI ITG-10.1 R-18) 5

Table 4.1b-Comparison of commercially available alternative cement technologies

CAC CSA MOC Ml'C AAFA AAS sse Hydraulic I Yes Yes 0 I No I No 0 0

I Main hydration

or reaction

products

Calcium

aluminate

hydrates C3AH6

and AH3

Ettringite,

C-S-H,

CH

Insoluble

Hydro-magnesite ammonium and

phosphate phases

Variable,

C-A-S-H,

-A-S-H

Variable,

C-A-S-H Ettringitc, C-S-H

Set time relat=t"ve R .d

to PC apt

I High-early, Rapid and

expansive

High-early. -

slower rate of

late strength gain

compared to

portland

Same or longq,r Rapid H' h 1 Low-early, tg -ear y,

moderate

I Rapid +

High-early,

late strength

comparable to

Lportland

Same or faster

Low-early,

late strength

comparable to

portland

Same or faster -Low-early,

late strength

comparable to Strength

late strength 1 1 com arable to

ate strengt 1 late strength

comparable to r------Ill--portland Good sulfate, Good suI fate

resistance

- p 1 d+ompared to port an portland Good fire, Good

abrasion, ASR sulfate, ASR

Good suI fate,

acid,ASR,

resistance

Good suI fate.

corrosion, acid,

ASR. resistance

- """''"'� Key durability

attributes

ASR resistance resistance performance Good sulfate

resistance Abrasion l resistant

I ConversiOn rcacttons increase

poro ity and

reduce strength

Carbona

tion rate high

Carbona

tion affecting

corrosion

resistance

Good FT �Good ''� resistance resistance

Loses strength

Good fire Good fire

-1 resistance resistance --

Concems

Applications

I

over time

Significant heat

evoltltion

Refractory

concrete,

sulfate and acid

resistance

Possible

thaumasite

formation

Structural,

precast

cold-weather

when exposed

to water at early

ages

Significant heat

evolution

Patching,

wallboard

Significant heat Performance Performance

Limited field

evolution varies with fly varies with slag

experience ash source source

I I Fireproof I

coatings, Same as PC Same as PC Same as PC

I patching Note: Abbreviations use

cements; when CAC is placed in contact with water, hydration reactions occur and calcium aluminate (CA), a lso known as monoca lcium aluminate, quickly dissolves, followed by a rapid precipitation of hydration products. This fast reaction leads to a significant temperature rise, even in relatively sma ll volumes of cement (Scrivener 2003; Sc1ivener and Capmas 2003). Compared to portland cement, CACs have a lower C02 footprint (Juenger et al . 20 1 1 ; Henry-Lanier et a! . 20 1 4). A thorough review of calcium aluminate cements is found in severa l sources (Scrivener 2003; Scrivener and Capmas 2003; Juenger et al. 20 1 1 ).

In formulation where CAC comprises 1 00 percent of the binding materia l, conversion of the initially formed metastable hydrates to stable hydrates can result in a partia l reduction of compressive strength. This reduction in strength from an apparent maximum strength to a lower strength is called conversion. From the 1 930s to the 1 970s, the improper use of CAC resulted in several fai lures attributed to this effect. This effect led to reduced use of CAC in the structural concrete applications. Later investigation found this misuse was primarily due to a lack of education about the conversion process (Concrete Society 1 997; Scrivener and Capmas 2003). In the early 2000s, given known performance properties of CAC a renewed interest in CACs for u e in rapid repair emerged (Gossel in and Scrivener 2008;

Ideker 2008; Gossel in 2009; Gosselin et a l . 201 0; Juenger et al. 20 I I; Ideker et a l . 20 1 3) . Ca lcium aluminate cements are well known for their rapid strength ga in, especially at low temperatures, and their resistance to aggressive chemica ls.

Calcium aluminate cement is now commonly used a a rapid repa ir material , as well as in refractory applications, typica lly as I 00 percent CAC mixtures, and in ternary blends of CAC, portland cement, and gypsum. When using gypsum, the ternary blends are typica lly formulated witb unique properties such as rapid set, early strength, exparlsion, or corrosion resistance. Use in refractories and formulated products, which is its main use, has seen steady growtp since the 1 950s.

4.2.1.2 Fresh properties-Curing at a constant temperature of l00°F (38°C), immediately after casting, leads to accelerated formation of the stable hydrates; a converted strength is typica lly real ized within 5 to 7 days (EN 1 4647:2005). Figure 4.2. 1 .2 provides a schematic of the curing and strength development process. After conversion occurs and a minimum strength i reached, the water relea ed by conversion continues to react with unhydrated cement, resulting in continued long-term strength gain (Fryda et a ! . 200 1; Scrivener and Capmas 2003).

Assessing conversion is done through performance testing and can be evaluated using everal accelerated laboratory

6 REPORT ON ALTERNATIVE CEMENTS (ACJ JTG-10.1 R-18)

6CA+60H �

1. 6CAH10

I Density:

30 ·c < T < 10 ·c

� T> 1o·c �

3. 2C,AH1 + 4AH1 +36H

" Converted Strength Used for Design

CAH10 C,AH1 C1AH1 AH1 1.72 1.95 2.52 2.44

nme

Fig. 4.2.1.2-Schematic of CAC conversion and strength reduction. Density shown in units of g!cm3 (Juenger et a/. 2011). (Note: 1 g/cm3 = 62.4 lb/ftl; °F = (9/s;oc + 3 2.)

te t methods. Three accelerated conver ion te t methods are given herein. These three methods rely on ca ting concrete cylinders, subjecting the cylinders to an increa ed temperature, and monitoring their strength over a specified period to determine the converted strength.

Method 1: Direct immersion of fre hly cast cylinder in pia tic molds at 1 00°F (38°C), demoldi.ng at 24 hours, and continued immersion at 1 00°F (38°C) until the convetted strength is reached (EN 1 4647:2005) .

Method 2: Standard curing of cast cylinder in plastic molds in a 73°F (23°C) ambient environment for 24 hours then direct immersion in a 1 22°F (50°C) water bath until th� converted strength is reached (Fryda et al . 2008).

Method 3: Direct placement of cast cylinders in plastic molds in a semi-adiabatic, highly insulated curing box immediately after casting for 24 hours, followed by standard 73°F (23°C) curing thereafter (Fryda et al. 2001; Texas Department ofTransportation 20 1 0).

It is important to account for the loss of strength due to conversion through proper mixture proportioning, design, and performance testing. The water-cementitious materials ratio (w/cm) is recommended to not exceed 0.40 and the minimum CAC content is recommended to be 400 kg!m3 (674 lb/yd3) (Hanson Cement 2009).

4.2.1.3 Hardened properties-Calcium aluminate cements were originally developed to resist sulfate attack . Calcium aluminate cement concrete has also perfmmed well with respect to other forms of attack. For example, CACs are abrasion-resistant and are often combined with synthetic aggregate made from CAC to produce a highly resistant material for use in dam spil lways or industrial floor slabs �Scrivener and Capmas 2003). Alkali-silica reaction (ASR) IS thought to be unlikely when using calcium aluminate cements (Kmtis and Monteiro 1 999) . This is because the hydration products are different from those of calcium silicate cements. Specifically, because there is no calcium hydroxide fanned, the pH of the pore solution is lower ( -1 1 .5 to 1 2 .5) and, therefore, CAC by itself does not promote dissolution of si l ica (Si02) in reactive aggregates. However, blends of

CAC and portland cement may sti l l induce ASR (Kurtis and Monteiro 1 999).

Recent work by Yi and Thomas (20 14) showed that unconverted CAC concrete exposed to attificial seawater had significantly enhanced chloride ion resistance as compared to PCC. However, they also showed that in converted CAC the depth of penetration of chloride may be higher than i� unconverted specimens (Yi and Thomas 20 14). A possible reason for the observed durability of CAC concretes could be the formation of a dense, low-porosity outer layer that limits or greatly reduces the ingress of aggressive agents.

Information in the literature for CACs and corrosion is limited. Unpubl ished work indicates the rate of chloride ingress into a new, rapidly converted CAC concrete without the outer layer was rapid. Other work has shown that in unconverted CAC concrete, the electrical resistivity exceeded that of PCC by more than an order of magnitude (Juenger et al. 20 I I ).

4.2.2 Reactive belite cement 4.2.2.1 Technology-Traditional portland cement cl inker

contains four principal mineral phases known as alite belite aluminate, and ferrite, with al ite being the most abundan; phase. The chemical nomenclature and relative abundance of these phases in concrete are summarized in Table 4.2.2. 1 .

A lite reacts rapidly with water, relative to the other cl inker phases, and is responsible for most of the early strength development in portland cement. While belite is less reactive at early ages, it does contribute appreciably to strength at later ages. A reactive belite cement (RBC) has a significantly lower alite content, giving it a relatively higher belite content (Chatterjee 1 996). Production of RBC allows for a lower kiln temperature, less limestone, and lower C02 and

O. emissions (Chatterjee 1996). To achieve usable early strengths, belite is chemically modified or mineralized to improve its reactivity. Because the process of modification is complicated, the use of RBC alone has not grown. Calcium sulfoaluminate cements, however, which are a modified form of RBC, have been used in numerous applications (Burris et al. 20 1 5) . Calcium sulfoaluminate cements will be addressed further in a later section.

4.2.2.2 Fresh properties-The hydration ofRBC produces the same hydration products formed in hydrated portland cement, but with lower heat evolution and smaller quantities of calcium hydroxide (CH) formation. The hydration of RBC is expected to be somewhat slower than observed in portland cement, which may result in a lower early heat of hydration and sl ightly longer setting time as compared to portland cement. The setting time, however, is typically acceptable for use in the constmction industry for some �pplications. Additionally, hydrated RBC shows no change m volume after 28 days of hardening (Popescu et al. 2003).

4.2.2.3 11ardened properties-The compressive strength of hardened RBC is lower than a comparable portland cement at early ages. Reactive belite cement mortars have been shown to have higher strength gains beyond 28 days as compared to portland cement. The measured porosity after 5 years of hydration is relatively lower in RBC mortar (Chatterjee 1 996). Physical and mechanical tests performed on

REPORT ON ALTERNATIVE CEMENTS (ACI ITG-10.1 R-18) 7

Table 4.2.2.1-Chemical nomenclature and relative abundance of the principal phases in portland cement clinker (Taylor 1997)

Common name Chemical name Chemical formula Cement chemist notation' I Relative abundance, % A lite Tricalcium silicate Ca3Si0s cls I 50 to 70 Be lite Dicalcium silicate Ca2SiO. c2s I 1 5 to 30

Aluminate Tricalcium aluminate Ca3AI206 C3A I 5 to 1 0 Ferrite Tctracalcium aluminofcrritc Ca2AIFc05 C.AF I 5 to 1 5

'Abbreviations are C: CaO; A : Al203; S: Si02: F: Fe203: S: SO,.

cement mortars of sodium fluoride (NaF) mineralized belite clinker have shown the heat of hydration and compressive strength to evolve quickly to reach 28-day values like those of a lite clinker (Kacimi et al. 2009).

Given that RBC produces relatively higher amounts of C-S-H and lower CH contents, with denser, less permeable microstructures, the resulting concrete durability is expected to be good. The range of strengths of concrete made from RBC, and long-tetm durability data, have yet to be presented in the li terature.

4.2.3 Calcium su(foaluminate cement 4.2.3 . 1 Technology-As stated in 4.2.2.3, early compres

sive trength of pastes, mortars, and concretes containing RBC are generally low. Early strength, however, can be increased using several techniques. One practical technique is the addition of a reactive component such as calcium sulfoaluminate (C�3S) in some cases together with calcium sul fate (CS), tetracalcium aluminofetTite (C�F), or some combination of the ingredients (Quillin 200 1 ). This combination yields a belite-sulfoaluminate cement, commonly refetTed to a calcium ul foaluminate cement (CSA) or calcium sul foaluminate belile cement (CSAB). This cement is gaining attention from the cement and concrete industries as a lower-energy, lower-C02 alternative to portland cement. Calcium sul foaluminate cement contains as a primary pha e ye 'elimite, or C

8 REPORT ON ALTERNATIVE CEMENTS (ACJ JTG-10.1 R-18)

and H20 molecules in and out of the concrete. The finishing window for CCSC concrete is typically longer than PCC.

4.2.4.3 llardened properties-Research performed to date on concrete prepared with CCSC repmis hardened properties comparable to PCC. The Young's modulus and coefficient of thermal expansion (CTE) are similar to PCC, facilitating compatibil ity when used together (Jain et al . 20 1 5) . For CCSC-based concrete, compressive strengths of approximately I 0,000 psi (70 MPa) and flexural strengths of approximately I I 00 psi (8 MPa) have been repmied (Jain et al . 20 1 5) . Testing performed to date also indicates that CCSC concrete has good freezing-and-thawing resistance (Farnam et al. 20 1 6; Villani et al. 20 1 5 ).

4.3-Calcined alternative cements Calcined alternative cements are a combination of calcined

magnesite and a crosslinking agent that, when combined, react to form a solidified binder matrix. While water is a product of the reaction, fonnation of the hardened matrix is the result of acid/base reactions in an aqueous environment.

The calcining temperature of the magnesite detennines the reactivity of the magnesia (magnesium oxide [MgO]). Calcination at high temperatures, such as 2732 to 3632°F ( 1 500 to 2000°C), produces nonreactive dead-burned magnesia. At lower calcining temperatures of 1 832 to 2732°F ( 1 000 to l 500°C), hard-bumed magnesia is produced, which has a relatively low reactivity. Lower calcining temperatures of 1 292 to l 832°F (700 to 1 000°C) will produce light-burned magnesia-a significantly more reactive form sometimes referred to as caustic magnesia (Shand 2006). The magnesia reactivity used is dependent on the type of cement being produced, the desired plastic and hardened properties, and the nature and amount of fillers/aggregate that will be added to the binder (Matkovic et al. 1 977).

4.3. 1 Magnesium oxychloride cement 4.3. 1 . 1 Technology-The first type of magnesia cement

was developed by Stanislas Sorel in 1 867 (Sorel 1 867) and is now referred to as Sorel, magnesite, or magnesium oxychloride cement (MOC) (Phair 2006; Valek et al. 20 1 2). MOC is formed by reaction of magnesium oxide with magnesium chloride in the presence of water. A common fonnulation is to use 1 .2 parts magnesium oxide to l part of magnesium chloride hexahydrate, to 0.6 parts of water, by mass. The main bonding phase found in hardened MOC pastes is magnesium hydroxide.

4.3. 1 .2 Fresh properties-Magnesium oxychloride cement, during initial curing, is not stable in prolonged contact with water. Leaching of magnesium chloride can result, with reversal of the reaction and loss of strength (Lu et al. 1 994). Atmospheric carbon dioxide (C02) has been reported to react with magnesium oxychloride to form a surface layer that slows the leaching process. Hydromagnesite (4Mg0· 3C03 ·4H20) forms, which is insoluble and enables the cement to maintain structural integrity (Cole and Demediuk 1 955). These late carbonation reactions contribute to the claim that MOC has a low carbon footprint.

A variety of additives have been developed that will significantly slow down or block water penetration during

early ages, or expedite formation of hydromagnesite. Materials evaluated included phosphates (Deng 2003), fly ash and sil ica fume (Li and Yu 20 I 0), and alkali metal fatty acids such as magnesium stearate, metal or alkali metal sulfates such as aluminum sulfate, or magnesium sulfate. Water resistance is further enhanced by either precarbonating the mixing water or the liquid magnesium chloride phase of the cements, or by adding a carbonate into the cement powder (Rademan et al. 20 1 3) .

Neat MOC paste is generally very fluid and, as such, is not suitable for casting. The addition of fillers/aggregates and other components provides the abil ity to control viscosity and workabil ity. In general, the rheology of MOC can be control led by selection of raw materials, and the molar ratio and concentration of the magnesium chloride solution. Admixtures are not necessary for the formulation of workable mixtures, and not all concrete admixtures are effective in MOC, but some admixtures are used. Because fresh MOC tends to be thixotropic, high-range water reducers used in PCC are generally applicable depending on the flowability requirements. Another material that improves flowability is magnesium l ignosulfonate, although polyacrylates and carboxy-modified cellulose also yield good results (Zhou and Li 20 1 2) .

Because the initial stage of the reaction requires MgO dissolution, fresh mixtures start out looking dry. Mixing for a few minutes increases the fluidity, so once the two components are combined, they should be stirred for several minutes before appl ication.

The set time for neat MOC paste can vary from a few hours to 48 hours (Yadav et al . 20 1 3). Curing is affected by temperature, air flow, and humidity conditions. While heating can increase the rate of hardening, overheating the concrete may lead to cracking of the material (Yadav et al . 20 1 2). No additional curing is necessary after set.

As an acid/base reaction, neat MOC paste develops a sign ificant heat of hydration. Therefore, mixtures can develop significant temperatures. For example, 140 to 1 76°F (60 to 80°C) and temperatures above 2 1 2°F ( I 00°C) have been reported (Newman et al. 1 952). Precautions are required when handling neat paste to avoid thermal damage of substrates and forms, and to avoid personal injury. Temperature evolution is significantly decreased when fillers/aggregates are added to the paste, resulting in mixtures that are safe to handle and place. Also, the evolved heat dissipates quickly due to high thermal conductivity of the material.

Application method, material thickness, and nature of the substrate determine the applicabil ity of specific MOC mixtures. Certain fillers/aggregates, such as magnesite or dolomite, can be used in quantities up to 50 to 60 percent without significant loss in compressive strength, whereas others will result in lower strength development. Reduced heat evolution from filler addition could result in a decreased degree of reaction and a reduced strength (Yadav et al. 20 1 3).

4.3. 1 .3 l!ardened properties-Concrete mixtures prepared with MOC can have high compressive strengthfor example, 8000 to 1 0,000 psi (55 to 70 MPa within 48 hours. The compressive strength gain is achieved early

REPORT ON ALTERNATIVE CEMENTS (ACI ITG-10.1 R-18) 9

during curing so the 48-hour strength will be at least 80 percent of ultimate strength (Beaudoin and Ramachandran 1 975 ; Misra and Mathur 2007).

In general, MOC concrete is resistant to fire, mold, bacteria, and insects. It is nonshrinking and crack resistant; abrasion and wear resistant; and impact, indentation, and scratch resistant. In addition, it exhibits excellent thermal conductivity; low electrical conductivity; excellent bonding to a variety of substrates; and good resistance to acid, base, oil, and grease (Qiao et al. 20 1 4). These properties can be tailored to specific end use through the selection of appropriate components in the mixture.

Concrete produced with MOC is very stable to heat and freezing-and-thawing cycles and does not require air entrainment to improve durability. The literature indicates that if improvement is desired for resisance to freezing and thawing, additions of small amounts of magnesium sulfate are effective, probably due to fonnation of magnesium sui fate phases intermingled with the magnesium oxychloride matrix (Misra and Mathur 2007). However, in applications such as insulating panels or MOC wallboard, commonly referred to as Mag board, air entrainment is desirable to reduce the dead weight. This is accomplished by sparging air directly into the mixture. Air-entraining agents commonly used in PCC are also effective (Yunsong 200 1 ).

The flexural strength and flexibility of MOC panels and boards can be significantly improved by the addition of

: fibers. Magnesium oxychloride cement is compatible with : a wide variety of plastic fibers, mineral fibers such as basalt ' fibers, and organic fibers such as bagasse, wood fibers, and : hemp (Odler 2003). Due to the potential leaching of chloride · ions, direct contact with steel fibers, mild steel or other metal

subject to chloride corrosion should be avoided. If reinforcement is required, noncorrosive metals or mineral reinforcement such as basalt reinforcing bar is best suited for use with MOC cement.

Concrete using MOC does not lose strength over time. However, these cements are not vety resistant to water in early ages. Therefore, MOC is not recommended for applications where it will be in prolonged contact with water (Lu et al . 1 994). In architectural applications where the material is colored, mottling or discoloration can result from water. This can be avoided or minimized by application of sealers or other protective coatings.

4.3.2 Magnesium phosphate cement 4.3.2 . 1 Technology-Magnesium phosphate cement

(MPC) and magnesium oxysulfate cement (MOS) are variations of MOC where different acids are used to react the magnesia. Magnesium anunonium phosphate cement (MAPC) is formed by reaction of magnesia with monoammonium dihydrogen phosphate (ADP). Magnesium potassium phosphate cement (MKPC) results from the reaction of magnesia with monopotassium phosphate (MKP). Both reactions are very fast and highly exothermic. Because the reaction is very fast, typically magnesia grades used are the less-reactive dead-bumed materials. Upon reaction, a wide variety of insoluble ammonium and magnesium phosphate phases are formed. H istorically, variations of these cements

were used prior to the invention of pottland cement. Examples of use include the Great Wall of China and the Roman Pantheon (El-Gammal et al. 20 1 2).

4.3.2.2 Fresh properties-Utunodified MPCs are vety fast setting materials with low flow characteristics. Both plastic and hardened properties are affected by the other components of the mixture, the grade of MgO used, its fineness, the ratios of MgO and phosphate, and water-binder ratio (w/b). The mixtures, therefore, are developed for a specific application.

For MAPC used for fast-setting road repair mortars, set times observed ranged between 5 to 1 5 minutes for initial set, and up to 30 minutes for final set (Paceagiu and Georgescu 2008).

For MKPC, an extensive study was conducted investigating the effect of various parameters on setting times (Qiao 20 1 0). This work showed set times were significantly affected by the reactivity of the MgO used, with the more reactive grades reacting in I to 2 minutes and requiring a retarder-for example, 5 percent weight borax-to achieve I 0- to 1 5-minute initial set times.

In general, compressive strength increases as the magnesium-to-phosphate ratio (MIP) is increased from 2 to 1 0, and then begins decreasing with an optimum strength gain obtained at a ratio of 1 0. Work by Qiao (20 l 0) indicates the optimum w/b is 0. 1 8 to 0.22. A higher w/b results in a slower reaction; for example, 25 minutes at a w/b of 0.22 and 80 minutes at a wlb of 0.30. However, the higher the w/b, the lower the strength gain and ultimate compressive strength (Qiao 20 1 0).

The temperature at placement has a significant effect on set time, with mixtures that nonnal ly set in 10 to 1 5 minutes at 60°F (20°C) setting in 5 to 8 minutes at 86°F (30°C). I n some circumstances, i t may be necessary to cool the mixture water to control set times. As a note, MKPC has been shown to harden effectively down to temperatures of .0°F (-20°C) (Yue and Bing 20 1 3).

Magnesium phosphate mixtures tend to be thixotropic in nature and therefore do not flow well . However, when a shear force or vibration is applied, MPC does flow easily. This can present some issues with workability in certain applications. Due to the thixotropic nature of the binder, the material can sometimes exhibit a false set that is easily overcome by further mixing. The w/b will influence the workabil ity of MPC mixtures, as will the type and amount of sand (Solorzano 2008) or the inclusion of fly ash in the mixture (Yue and Bing 20 1 3).

As has been discussed, the reactions for these materials are exothermic and can be effectively monitored by calor imetry. The influences of w/b, MIP, and the setting retarder content on the reaction are reflected in a change of shape and intensity of the peaks on the heat flow curve.

4.3.2.3 Ilardened properties-MPC mixtures, depending on formulation, are fast setting and have a high compressive strength within the range of 5000 to l 0,000 psi (35 to 70 MPa) (Qiao 20 1 0). The material will not lose strength over time under normal exposure conditions.

1 0 REPORT ON ALTERNATIVE CEMENTS (ACJ JTG-10.1 R-18)

For MAPC, compressive strengths of 2500 psi ( 1 7 MPa) can be achieved with a typical mixture in I hour and 7500 psi (5 1 MPa) in 24 hours, with an ultimate strength of 8000 psi (55 MPa) (Paceagiu and Georgescu 2008).

For MKPC, strengths of 2000 to 2500 psi ( 14 to 1 7 MPa) in 3 hours and 3200 to 4000 psi (22 to 27 MPa) after 24 hours were obtained by varying ratios of reactants and w/b (Qiao 20 I 0) . Strength gain typically levels out in 7 days to 5000 to 7200 psi (35 to 50 MPa) and an additional strength gain of I 0 percent is observed between 28 days and I year of curing. These data are in the range of most published data on strength development, although it has been reported that by incorporating significant amounts of fly ash or wollastonite, compressive strengths of 8000 to 1 2,000 psi (55 to 83 MPa) can be obtained (Wagh 2004). Flexmal strengths of 600 to 1 000 psi (4 to 6 MPa) have been repmted with little effect on strength due to reactant ratios (Qiao 20 I 0). Others have reported flexural values in the range I 000 to 2000 psi (7 to 14 MPa) (Solorzano 2008).

Dmabil ity studies of MAPC mixtures have reported that a minor loss in strength was observed on immersion in 1 0 percent sodium sulfate solutions for 210 days. Specimens immersed in I 0 percent magnesium sulfate solution increased in strength. This indicates the material is resistant to sulfate attack and outperforms standard portland cement mixtures considerably. Wang et a! . (20 I I ) showed that shrinkage is minimal, freezing-and-thawing resistance is excellent, and permeabil ity is ve1y low. Wang et a! . (20 I I ) also conducted acid resistance testing using sulfuric acid at various concentrations by immersion of specimens for 2 1 0 days. The testing determined that MAPC performance was very good at I percent sulftuic acid, but erosion was observed at 3 and I 0 percent concentrations. For immersion in sodium hydroxide solution, a I 0 percent loss in strength was observed in a I percent solution after 2 1 0 days, and a 28 percent loss from exposme to a 5 percent solution, despite minimal visual evidence of co!Tosion.

Good adhesion to a weathered concrete substrate was observed for MAPC, but it was detem1ined that addition of sodium tripolyphosphate to the mixture improved adhesion (Paceagiu and Georgescu 2008). Also, mixtures with coarser sand performed better. This was due to absorption of water from the mixture in the substrate, starving the MAPC of water.

Research to evaluate MKPC mixtures for corrosion protection of reinforcing steel concluded the material exhibits good corrosion protection compared to portland cement mixtures (Sharkawi et a! . 20 I 0) . Recent developments have been reported on corrosion and fire protection coatings based on MKPC. These coatings do not show corrosion of the substrate or osmotic blistering even when samples are exposed for I 000 hours in a salt-spray chamber. Results from the flame spread test show no flame spread and the materials smpass all organic coatings tested in performance (Wagh 20 1 3).

4.4-Non-clinkered alternative cements Non-clinkered alternative cements are based on precursor

materials with a significant fraction of amorphous phases,

such as glass, consisting of some combination of silica (Si02) alumina (Al203), and calcia (CaO). These materials include fly ash, calcined clay, blast furnace slag, and waste glass. To form a hardened cement from these materials, some type of functional addition is required, such as an activator solution; the nature of the functional addition depends on the type of precursor material and reaction desired. ln most cases, non-clinkered alternative cements require elevated curing temperatmes-for example, I 04 to 1 76°F ( 40 to 80°C to accelerate the rate of reaction.

The type of binder created depends on the composition and combination of materials used. The predominant factor is the calcia content of the precursor. Materials that contain significant amounts of calcium-rich phases tend toward hydration reactions, like that of portland cement when exposed to water. Materials predominately rich in silica and alumina undergo a different set of reactions, refe!Ted to collectively as geopolymerization, where the resulting binder is known as a geopolymer. For more detailed backgrowld on geopolymer chemistry, refer to Petermann et al . (20 I 0) for a concise l iterature review including an annotated bibliography of other recent research.

4.4. 1 Alkali-activated fly ash 4.4. 1 . 1 Technology-An alkali-activated fly ash {AAFA)

binder is composed of fly ash, water, and an alkali activator. The activator promotes dissolution of the fly ash particles and initiates chemical reactions leading to the precipitation of reaction products. The composition of the reaction products varies depending on the composition of the fly ash and activator used. Due to the heterogeneous natme of fly ash, not all fly ashes will perform the same when alkali-activated. The mineralogical and morphological variability among fly ashes should be considered and characterized when developing a mixture design (van Jaarsveld et al. 2003). These properties will affect the required type and concentration of activator to be used, curing time and temperature, and fresh and hardened properties of the concrete. Determination of pmticle size and total silica, calcia, and alwnina content in a given ash is easily detennined (Katyal et al. 2008; Font et a! . 20 I 0; Williams and van Riessen 20 I 0) . However, the exact mineralogical composition of the a h plays an impmtant role in determining the glass composition and the reactive fraction available. Both glass content and composition are difficult to determine.

4.4. 1 .2 Fresh properties-Fly ash particles typically range in size from approximately 0.5 to 1 00 microns. Rapid cooling in air and surface tension forces cause fly ash particles to maintain a spherical shape. The spherical natme of fly ash particles is particularly useful in a binder system, as it reduces both the yield stress and viscosity of the paste in shear {Pro vis et a! . 20 10). The spherical pmicle shape increases the workability of a mixture without increasing the water demand. When necessmy, high-range water reducers have shown to be useful in further improving the workabil ity of a mixture {Hardj ito et al . 2004). Like PCC, the water-solids ratio of AAFA concrete is important, where higher water content typically results in lower strength (van

. . .. . . . 3aatsvetd etaL 2003; Diaz-Loya et al . 20 I I ) . The water in a

REPORT ON ALTERNATIVE CEMENTS (ACI ITG-10.1 R-18) 11

mixture includes the mass of water in the activating solution and any extra water added for mixing. The solids in the ratio are the mass of the aluminosil icate in the fly ash plus the solids present in the activating solution.

In general, many of the same factors that affect the workabil ity of PCC also influence the workability of alkali-activated concrete made of fly ash. Examples include the ratio of coarse to fine aggregate, ratio of paste to aggregate, and water-solids ratio (Xie and Xi 200 I ) . Ashes with calcium content over 20 percent can exhibit rapid setting times when activated with high pH activator (Diaz-Loya et al. 20 1 0) .

4.4. 1 .3 llardened properties-AAFA concretes typically exhibit high early compressive strength, particularly for activated low-Ca ashes that are subjected to heat curing (Wastiels et al. I 994; Fermindez-Jimenez and Palomo 2003 ; Femandez-Jimenez et al . 2006). Most strength is typically developed within the first 24 hoW's.

Similar relationships have been documented between compressive, flexW'al, tensile strength, modulus of elasticity, and density as those that exist for nonnal PCC. Overall, AAFA concrete has been shown to perfonn similarly to PCC (Fernandez-Jimenez et al. 2006; Sofi et al. 2007; Diaz-Loya et al. 20 1 1 ).

Activated low-Ca ash concretes have also demonstrated low thermal slu·inkage (Wastiels et al . I 994), low drying shrinkage (Fernandez-Jimenez and Palomo 2003; Femandez-Jimenez et al . 2006), good resistance to sulfate attack (Wastiels et al . 1 994; Fernandez-Jimenez et al. 2007), acid attack and alkali silica reactivity {Fernandez-Jimenez et al. 2007; Garcia-Lodeiro et a l . 2007), and good bond to steel reinforcement (Femandez-Jimenez and Palomo 2003, Femandez-Jimenez et al. 2006). Activated low-Ca fly ashes have been shown to withstand very high temperatures, higher than PCCs. This is thought to be due to the lack of water chemically bound within the reaction products (Wastiels et al . 1 994).

4.4.2 Alkali-activated slag cement

4.4.2. 1 Technology-An alkali-activated slag {AAS) binder phase consists of slag cement, water, and an alkali activator. The activator promotes dissolution of slag particles and initiates the chemical reactions leading to precipitation of calcium-alumino-sil icate-hydrate phases (C-A-S-1-1 ) . AAS systems also appear in the literatW'e with a variety of names such as alkali-activated cements (Palomo and Lopez dela Fuente 2003) and alkali-slag cements (Roy 1 999).

AAS concretes have shown great promise due to their competitive cost and perfonnance when compared to PCC, including a compressive strength of up to 1 8,900 psi { 1 30 MPa) at I year (Douglas and Brandstetr 1 990; Wang and Scrivener 1 995; Fernandez-Jimenez et al. 1 999; Brough and Atkinson 2002); rapid strength gain, specifically for heatcw·ed AAS (Wang et al . 1 994; Fernandez-J imenez et al . 1 999; Shi et al . 2006); and good resistance to fire, water, and chloride penetration (Douglas et al. 1 992; Wang and Scrivener 1 995; Gifford and Gillott 1 996b) and chemical/sulfate attack (Bakharev et al . 2003) . A recent environmental lifecycle assessment study showed that AAS concrete has 73 percent lower greenhouse gas {GHG) emissions, 43 percent

less embodied energy, 25 percent less water use, and 22 to 94 percent lower values of different enviromnental toxicity impact parameters, in comparison with PCC of similar compressive strength (Jiang et al . 20 14).

4.4.2.2 Fresh properties-Before discussing the fresh and hardened prope1ties of AAS concrete, note that variability commonly observed in the composition of slag can result in significant variability in the performance of concrete produced.

Generally, the same factors that affect the workability of PCC also influence the workability of AAS concrete. Examples include aggregate size, shape and content, w/c or liquidto-binder ratio, and temperature. In addition, the nature of the alkali activator plays an important role in the slump and slwnp loss of AAS concrete (Shi et al. 2006). The viscosity and density of sodium sil icate activators are greater than water and increase with their silica content (Cartwright et al . 20 I 5) . This generally results in lower concrete slwnp. Also, a higher activator pH results in faster reactions and faster slwnp loss. Water-reducing admixtures that are used for improving the workability of PCC may not be effective in the highly alkaline environment of AAS concrete (Shi et al . 2006). Others have reported that conventional air-entraining admixtures did not work well in AAS concrete (Douglas et al. 1 992; Gifford and Gil lott I 996b).

Several factors, such as the composition, fineness and grade of slag, and the type and dosage of alkali activator, can affect the setting time of AAS concrete. Both sodium hydroxide (NaOH) and sodium carbonate aC03) activated binders often show longer setting time than mixtures activated by sodium sil icate, also known as waterglass. Also, a higher activator dosage or higher silica content of waterglass leads to shorter setting time. In comparison with portland cement, AAS binders generally set faster. Some studies suggest using solid activators that are interground with the slag to elongate the setting time (Collins and Sanjayan 1 999).

4.4.2.3 llardened properties-Activated slag concretes cured at ambient temperature typically exhibit low early compressive strength, generally less than 1 450 psi { 1 0 MPa) after I day (Shi 1 996; Collins and Sanjayan I 999; Brough and Atkinson 2002; Oh et al. 20 1 0; Chi 20 1 2). Early strength improvement can be achieved using highly concentrated activators or curing at elevated temperatures {Bakharev et al . 1 999; Collins and Sanjayan 1 999). Although strength development is often slower than occurs in PCC, later-age strengths above I 1 ,700 psi (80 MPa) have been observed by several studies (Shi 1 996; Brough and Atkinson 2002; Bernal et al. 20J I ) . Progressive strength development typically occurs within the first 5 days of curing at ambient temperature. The later-age strength of activated slag is determined mainly by the activator type and dosage (Bakharev et al. 1 999; Collins and Sanjayan 1 999; Puertas et al . 2000; Thomas et al . 20 1 4).

A few studies have investigated the elastic modulus of activated slag concrete in conjunction with broader investigations into mechanical properties and durability, finding elastic moduli in the range of 4350 to 5800 ksi (30 to 40 GPa) (Douglas et al . 1 992; Collins and Sanjayan 1 999; Cart-

1 2 REPORT ON ALTERNATIVE CEMENTS (ACJ JTG-10.1 R-18)

wright et at. 20 1 5 ; Thomas and Peethamparan 20 1 5 ). The effect of beat curing was insignificant.

A key obstacle blocking the adoption of AAS materials by the construction industry is durabil ity. Poor resistance to shrinkage cracking, carbonation corrosion, and alkali-aggregate reaction (AAR) has been reported (Shi et al . 2006) . Numerous studies have reported excessively high drying shrinkage in activated slag concrete, despite less severe weight loss than observed in comparable PCC (Coll ins and Sanjayan 2000; Melo eto et al. 2008; Duran Ati� et al. 2009) . This could be attributed to removal of water from the mesopores, which does not occur in portland cement binders. Even with the aid of a shrinkage-reducing admixture (SRA), AAS has been found to shrink substantially mor up to 2.5 times more-than pmtland cement samples (Palacios and Puertas 2007) . In sodium silicate-activated slag the increased silica in the activator was found to increase the total drying shrinkage (Melo eto et al. 2008). Despite extensive drying shrinkage, activated slag concretes are more resistant to cracking than PCC, which could be due to a higher tensile strength (Collins and Sanjayan 2000), although cracking has been observed in some durability studies (Bakharev et at . 2002).

AAS concrete has been shown to have enhanced resistance to acid attack (Bakharev et al. 2003), sulfate attack (Bakharev et al. 2002), and chloride penetration (Douglas et at . 1 992) as compared to PCC. AAS concrete is, however, inherently susceptible to AAR due to the high alkalinity of the pore solution because of the alkali activation (Gifford and Gil lott I 996a; Yang et at . 1 999; Bakharev et at . 200 1 a; Lloyd et at . 20 I 0). In addition, AAS can carbonate rapidly when exposed to drying, due to the ab ence of solid calcium hydroxide to serve as a pH buffer (Wang and Scrivener 1 995 ; Bakharev et al. 200 1 b; Criado et at . 2005 ; Shi et at . 2006). As such, carbonation shrinkage and the risk of carbonation corrosion could be significant (Aperador et al. 2009; Lloyd et at. 20 1 0). Increased binder content has been shown to reduce the severity of carbonation (Bernal et al. 20 I 1 ).

4.4.3 Activated recycled glass 4.4.3. 1 Technology-Two well-known hurdles facing

alkali-activated cements and geopolymers are the availability of aluminosilicate materials and variability within these materials. Most product development bas focused on using slag cement and fly ash as the primary precursor. However, another significant material reserve is found in waste glass.

Glass has increasingly been the focus of development for new alternative cements (Cyr et at. 20 1 2; Christiansen 20 1 3 ; Christiansen and Sutter 20 1 3) . For use in a geopolymer, the alumina content of glass is low, which leads to the presence of excess alkalis and instability in water. An additional source of alumina is required to balance the alkalis and increase water stabil ity (Christiansen 20 1 3 ; Redden and Neithalath 20 1 4). The composition of the glass precmsor has a significant impact on the mechanical performance and stability of the geopolymer (Cbristiansen 20 1 3) .

4.4.3.2 Fresh properties-Because glass-based geopolyni"ers ·require .. he.at . curing, setting time depends a great deal

on the temperature at which the specimens are cured. Glassbased geopolymers cured at ambient temperature have been found to exhibit very little compressive strength (Cyr et al . 20 1 2; Clu·istiansen 20 1 3) .

Research has shown that addition of metakaolin to a glass-based mixture as a supplemental source of alumina resulted in a temperature peak under adiabatic calorimetry that was not present when glass alone was reacted (Christiansen 20 1 3). Higher compressive strength was shown to correlate to a longer delay in the second temperature peak, which is usually considered to represent polycondensation (Zhang et at. 20 1 2) . The water/solids ratio also affects the magnitude of the peaks measured on adiabatic calorimetry (Christiansen 20 1 3) .

4.4.3.3 llardened properties-A high early compressive strength-for example, 1 to 3 days-of approximately 5000 to 6000 psi (34 to 4 1 MPa) was found in the work of Christiansen (20 1 3) and Redden and eithalath (20 1 4). Christiansen (20 1 3) also noted a sl ight decrease in strength from 1 to 7 days, but this was recovered by 28 days with the strength continuing to increase after that. Cyr et at . (20 1 2) and Li et al . (20 1 4) found similar or higher strengths at 7 days.

Christiansen (20 1 3 ) found strength to increase over time, up to 1 80 days, in all the glass-based geopolymer mixtures tested, with an especially significant increase in those mixtures made with very fine glass having a 3 to 4 J.liD median particle size, higher activator molarity such as I OM, and higher curing temperatures of 1 76°F (80°C) (Christiansen 20 1 3) . Those geopolymers made with a highalumina glass of 1 2.2 percent Al203 showed the most drastic strength gain over time, with some mixtures gaining nearly 5500 psi (38 MPa) from 7 to 28 days.

Stabil ity in water is a significant issue for high-silica glass-based geopolymers. Geopolymer matrixes consisting primarily of sodium and silica are unstable in water, but can be strengthened through the addition of alumina or calcia in the form of metakaolin, slag, or fly ash. Redden and

eithalath (20 14) found that geopolymers based primarily on low-alumina glass resulted in a sodium silicate gel that was susceptible to shrinkage and cracking (Redden and

eithalath 20 1 4). This was combatted through the addition of metakaolin and slag, where the additional alumina and calcia were considered to transfonn the reaction products to more stable phases.

4.4.4 Supersu(fated cement 4.4.4.1 Technology-Supersulfated cement (SSC)

consists of blast-furnace slag activated by means of calciwn sulfate. The cement is 80 to 85 percent slag, I 0 to 1 5 percent anhydrite, and approximately 5 percent alkaline activator, usually portland cement cl inker. After Kiihl first patented SSC in 1 908 (Kuhl 1 908), it was standardized in Germany, France, and Belgiwn (DI 42 1 0: 1 959), and Great Britain (BS 4248:2004). Production of SSC increased after World War I l , from 1 940 to 1 960 because of a portland cement shmtage (Lea I 970). Production was abandoned, however, due to changes in iron production that yielded slags that did not meet the minimum 1 3 percent Al203 requirement (Lea

REPORT ON ALTERNATIVE CEMENTS (ACI ITG-10.1 R-18) 1 3

1 970). The German standard was subsequently withdrawn in 1 970. Supersulfated cements are attracting renewed attention due to a low C02 footprint and unique characteristics, such as sulfate resistance and low heat of hydration. A new European standard for SSCs was issued in 20 10 (E 1 5743 :20 1 0).

4.4.4.2 Fresh properties-Compared to normal portland cement or normal slag cement, the water uptake of sse is much higher during curing. The w/c of concrete with such cements should be at least 0.50. Wet curing of not less than 3 days is required to avoid formation of an undesirable powdery surface layer because of premature drying. Water reducers can be used to reduce the amount of water available, as anhydrite and high-alumina slags can take up excessive amounts of water, thus increasing the w/c. Retardation of the initial setting was observed on using a water-reducing admixture (Bijen and iel 1 98 1 ).

The initial setting time for SSC is typically less than 45 minutes and the final setting time typically does not exceed I 0 hours (Lea 1 970) . E 1 5743 :20 1 0 specifies different initial setting time, depending on the strength class ranging from 45 to 75 minutes. E 1 5743 :20 1 0 states that SSC has a low heat of hydration-approximately 1 66 to 1 88 J/g ( 1 8.0 to 20.4 kcalllb) at 7 days and 1 88 to 209 J/g (20.4 to 22.7 kcalllb) at 28 days-making sse desirable for use in mass concrete structures.

There is limited research and published work on the airentrainment requirements of SSC. However, Setzer ( 1 997) reports that non-air-entrained sse has a low frost resistance, and that the addition of an air-entraining admixture to sse did not lead to any significant improvements.

4.4.4.3 llardened properties-In the l iterature, low earlyage compressive strength development of sse is commonly reported. This is mainly due to the slow reaction rate of slag. Matschei et al. (2005) repotted that only 26 percent of slag reacts after 56 days of hydration.

The compressive strength of mortars made with SSC increases rapidly up to approximately 7 days, when it then begins to slow down (Midgley and Pettifer 1 97 1 ).

Supersulfated cement is resistant to sulfate-laden waters, seawater, weak organic acids, and chlorides, according to a study by Lea ( 1 970) of the Beervlei Dam in South Africa, which was built in 1 956. The concrete of this dam was examined in 2000 and found to have a strength of 1 8,000 psi ( 1 24 MPa) with minimal carbonation of 0.2 to 0.08 in. (2 to 5 mm), leaving it in good condition.

4.5-Summary The variety of technologies discussed in this chapter is

indicative of diversity and growth of this broad group of binder systems. ot only do the raw materials differ for each binder, but the mixture proportioning, chemical reactions, curing, placement techniques, and fresh and hardened properties all vary as well. There is no standard procedure for working with these novel materials; the nuances of each technology should be well understood to fully capitalize on the advantages of each technology.

CHAPTER 5-TESTING REQUIREMENTS FOR ALTERNATIVE CEMENT TECHNOLOGIES

5.1-lntroduction In most cases, when a cementitious material is to be used

in concrete construction, it requires compliance with architectural or engineering specifications. Material specifications establish limits for key properties and typically define the testing required to measure those properties. Current specifications for portland cement contain a mixture of prescriptive-compositional and quasi-performance property l imits. By this approach, novel materials often cannot meet these requirements due to having a significantly different composition, having different sample preparation or curing needs for testing, or due to other limits imposed by the test methods specified.

To circwnvent issues caused by prescriptive specificat ions, another approach is development of purely performance-based specifications that could potentially apply to all cementitious binder materials and combinations, and allow for direct comparisons of different materials. Barriers to this approach include a general lack of agreement regarding the performance properties that require testing, and lack of appropriate test methods that could better l ink a material's properties to performance when used in concrete. This holds true for alternative cements and portland cement alike.

Standards for conventional materials have been developed and revised over time as industry has obtained experience with their use. Examples of this path of acceptance include pottland cement, blended cements, fly ash, and slag cement. A notable exception, discussed herein as an example, is the development of specifications for silica fume. In the early 1 980s, si l ica fume started to be used in Notth American concrete because it was recognized to provide special propetties, including segregation resistance in fluid concrete and development of high-early strength. There were, however, no specifications for sil ica fume; standards were developed after industry adoption of the material . In 1 983, the Canadian Standards Association was the first to include requirements for si l ica fume in CSA A23.5, which was later withdrawn and incorporated into CSAA3000. The ASTM C l 240 specification for silica fume was not approved until 1 993. Industry developed confidence in the use of silica fume without a materials standard, but rather based on in-field experience and documentation of that experience in the literature.

The adoption of alternative cements has followed a path l ike that described for sil ica fume. Although not yet receiving broad acceptance, alternative cements have established niche markets or applications where the existing knowledge base supports that application. Unlike sil ica fume, however, which is an additive to PCC, alternative cements are a direct replacement for pottland cement. As such, a higher level of scrutiny exists and a comprehensive battety of tests and performance data are expected for these materials to be fully incorporated into design specifications. The challenge for the concrete construction industry is to develop this necessary information in a timely manner. The knowledge base supporting specifications for PCC has been developed over

1 4 REPORT ON ALTERNATIVE CEMENTS (ACJ JTG-10.1 R-18)

the past 1 00 years or more; to embrace the perfonnance and sustainability benefits of alternative cements, a relatively faster path to implementation is desirable.

L isted are some of the main issues that should be demonstrated in the development of standards for new concrete materials where field experience and long-tenn performance data are not available (Hooton 20 1 5). ew concrete materials should:

(a) Have required, predictable, and reproducible fresh and hardened properties so they can, for example, be airentrained, and maintain adequate workabi l ity during delive1y, placement, and finishing

(b) Be sufficiently robust to perfom1 as expected over the range of temperature and humidity encountered in practice

(c) Have an established relationship between different strength properties, including compressive, tensile, shear, flexure, and bond as well as elastic modulus. The relationships often assumed in building codes may differ from those of commonly used hydraulic cements at different temperatures and humidities

(d) Exhibit short- and long-term volume stabil ity l ike thermal, drying shrinkage, and creep

(e) Remain durable in vmying environmental exposures (f) Demonstrate sufficient uniformity in workabil ity,

setting time, and strength development in performance properties

Assembling the information described requires a combination of separately testing the alternative cement as well as the concrete produced using the alternative cement. Each of these steps will be discussed in the following sections.

5.2-Testing alternative cements Like portland cement, an alternative cement will be tested

for the purposes of quality assurance (QA) and quality control (QC). Because alternative cements are often specified for their inherent sustainability benefits, other details are requested by specifiers that are not directly measured by testing. Examples include greenhouse gas emissions and embodied energy associated with the final product. This additional information is typically found in the environmental production declaration (EPD) for the alternative cement and is not considered part of the specification environment, although specifiers are increasingly considering these sustainabil ity traits when selecting materials. Selected examples of the properties to be measured will be discussed in detail as follows. They include:

(a) Chemical composition (b) Particle size (c) Density (d) Strength (e) Yolmne stability (f) Setting time (g) Heat of hydration (h) Admixture compatibil ity 5.2. 1 Chemical composition-Determination of chemical

composition is invariably the starting point for testing and specification of cementitious materials. Qualitative chemical analysis can be used to identify the chemical components of

a material, both desired and deleterious. Quantitative analysis will determine the quantity of each component present. Chemical requirements are often used in a material specification because they can be readily measured and provide a value that can be compared to a specification limit. Unfortunately, chemical composition by itself rarely provides an insightful measure of desired perfonnance. Plus, given the inherent variability in producing cementitious materials, the specification limits for composition are typically very broad or, in many cases, such as with ASTM C l 50/C l 50M, only l imiting in a small number of elements that dictate performance for that specific cement.

Chemical analysis such as loss on ignition (LOI) and MgO content can serve to identify deleterious components. However, what is deemed deleterious in one material may be desirable in a different material. Therefore, prescriptive chemical composition limits in material specifications generally make that specification pertinent to only one nan·ow class of material. Again, as an example, when ASTM C l 50/ C 1 50M cement is specified, the chemical requirements of ASTM C 1 50/C 1 50M serve to exclude most other materials from qualifying.

Pe1formance specifications typically do not stipulate chemical requirements and for that reason are preferred by those promoting use of alternative cements. However, in the absence of chemical requirements, demonstrating uniformity is a challenge. Most recognized performance tests require significant time to complete and are therefore performed less frequently, making the possibility of variation between tests potentially significant. As tests and specifications evolve for alternative cements, measuring chemical requirements that relate to uniformity will be desired, and rapid performance tests should be developed. As a minimmn, required chemical tests should be used to identify and quantify any deleterious components specific to an alternative cement.

Methods for chemical characterization used for portland cement can readily be applied to altemative cements, including X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), thermo-gravimetric analysis/differential thennal analysis (TGA/DTA), various wet-chemistry methods, and LOI. However, specification l imits remain to be developed.

5.2.2 Particle size-Particle size is critical to performance, as smaller particles react more quickly than relatively coarser particles due to a relatively higher specific surface area for the smaller particles. Particle size distribution, which affects both uniformity and overall perfonnance, should be measured but does not necessarily need to be specified.

There are currently no tests used in cementitious material specifications for direct measurement of patticle size distribution. Pa11icle size distributions, however, are often measured by manufacturers using laser-based or X-raybased particle size analyzers. A more common approach to specifying particle size distribution is air permeabi l ity or Blaine smface area (ASTM C204).

Minimum limits on the Blaine surface area are specified in ASTM C 1 50/C 1 50M along with maximum limits for Type

REPORT ON ALTERNATIVE CEMENTS (ACI ITG-10.1 R-18) 1 5

I I and IV cements. ASTM C595/C595M, ASTM C l l 57/ C l l 57M, ASTM C 1 600/C l 600M, and ASTM C989/C989M specifications do not have limits on Blaine fineness but require it to be reported. Alternatively, in the ASTM C6 1 8, ASTM C989/C989M, and ASTM C 1 240 specifications for fly ash, slag, and silica fume, there are limits placed on the maximum residue retained on the 45 Jlm sieve. The implication is that particles larger than 45 J..Lm are of little value as a binder material. ASTM C595/C595M and ASTM C l l 57/ C l l 57M only require the fineness values be reported. These same methods for determining particle size distribution may be applicable to alternative cements.

5.2.3 Density--Knowing the particle bulk density, or specific gravity, is essential for mixture design. Density also provides a useful measure of uniformity, pa�iicularly when combined with bulk chemical analysis. The current standard for measuring the density of portland cement isASTM C l 88, the Le Chatelier flask using kerosene or naphtha as the fluid. However, recent advances in helium pycnometers have provided easy-to-use, benchtop devices that are extremely accurate and have a high level of precision. Any new specification regarding alternative cements should require some measure of density for use in volwnetric mixture design calculations, and currently available methods are all suitable for use with alternative cements.

5.2.4 Strength-Strength is arguably the most critical characteristic to measure, if for no other reason than it being the characteristic most specifiers will turn to fu·st when evaluating a cementitious material. Compressive strength provides a measure of uniformity that is universally accepted and, most importantly, links directly with concrete perfonnance and the key measures to be examined when developing concrete specifications for use in construction codes and specifications. Although the actual measurement of strength is easily accomplished, it is a challenge to do so for a wide range of alternative cements in a manner that al lows each to be directly compared to portland cement. The challenge is to develop mixture designs using each type of cementitious material that can be directly compared. This includes providing a curing regime for each alternative cement mixture that results in comparable mixture design strength. The rate of strength development a lso varies greatly among alternative cements, especially with respect to different curing regimes. Therefore, an age at which the strength should be measured and recorded should be established, or a minimum strength at any age specified. Note that many alternative cements gain strength more rapidly than potiland cement, so comparing strengths at a nominal 28 days diminishes a positive attribute of the altemative cement.

For portland cement, the ASTM C l 09/C 1 09M mortar cube strength test is used. With portland cement, w/c is critical; the test normally uses a w/c = 0.485 for portland cement. For other matetials, the test allows mixtures to be cast to a flow of I L O ± 5 percent. This al lows for alternative cements that require a different water-cementitious materials ratio (wlcm) for equal flow to be used (ASTM C l600/C l 600M). Although this is a possible solution for alternative cements that are hydraulic, for many materials, the w/cm does not relate to strength, the

alternative cement is not hydraulic, or the measurement of flow may be not applicable. Also, the mixing sequence in ASTM C305 may not be suitable and may require modification for some alternative cements. For geopolymers, heat curing is typically required to achieve full strength, although questions will l ikely arise when comparing heat-cured with ambient-cw-ed materials.

A major challenge, therefore, for testing and specifying alternative cements is to develop a robust approach for measuring strength. A universal approach is needed for measuring the absolute strength of a cementitious material and reconci ling the measured strength