NIST SP 1138

dx.doi.org/10.6028/NIST.SP.1138

Joseph J. Biernacki

Jeffrey W. Bullard

Daniel Constantiner

Richard C. Meininger

Maria C. G. Juenger

Josephine H. Cheung

William Hansen

R. Douglas Hooton

Andreas Lüttge  

Jeffrey J. Thomas

FHWA-HRT-13-052

Paving the W ay for 

a More Sustainable 

Concrete Infrastructure

A Vision for Developing a Comprehensive 

Description of Cement Hydration Kinetics
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NIST Special Publication 1138 

Paving the Way for a More Sustainable 

Concrete Infrastructure 

A Vision for Developing a Comprehensive Description 

of Cement Hydration Kinetics 

Joseph J. Biernacki Josephine H. Cheung 

Tennessee Technological University W.R. Grace 

Cookeville, TN Cambridge, MA 

Jeffrey W. Bullard William Hansen 

Materials and Structural Systems Division University of Michigan 

Engineering Laboratory Ann Arbor, MI 

Daniel Constantiner R. Douglas Hooton 

BASF University of Toronto 

Cleveland, OH Toronto, Canada 

Richard C. Meininger Andreas Lüttge 

Turner-Fairbanks Highway Research Center Rice University 

McLean, VA Houston, TX 

Maria C. G. Juenger Jeffrey J. Thomas 

University of Texas Schlumberger-Doll Research 

Austin, TX Cambridge, MA 

http://dx.doi.org/10.6028/NIST.SP.1138 

March 2013 

U.S. Department of Commerce 

Rebecca Blank, Acting Secretary 

National Institute of Standards and Technology 

Patrick D. Gallagher, Under Secretary of Commerce for Standards and Technology and Director 
 

 

 

 

Certain commercial entities, equipment, or materials may be identified in this 

document in order to describe an experimental procedure or concept adequately. 

Such identification is not intended to imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor is it intended to imply that the 

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Special Publication 1138 

Natl. Inst. Stand. Technol. Spec. Publ. 1138, 34 pages (March 2013) 

http://dx.doi.org/10.6028/NIST.SP.1138 

CODEN: NSPUE2 
 

This publication was simultaneously published by the U.S. Federal Highway 

Administration as J. J. Biernacki, J.W. Bullard, D. Constantiner, R. C. Meininger, M. C. G. 

Juenger, J. H. Cheung, W. Hansen, R. D. Hooton, A. Lüttge, and J. J. Thomas, Paving the way 

for a more sustainable concrete infrastructure: a vision for developing a comprehensive 

description of cement hydration kinetics, FHWA-HRT-13-052, March 2013. 

iii
 
iv
 
Foreword

Concrete is far and	away the most abundantly used	man-made material on the planet. As a construction

material, it is unique in its capacity to be formed and finished into an almost unlimited variety of shapes,

textures, and colors. It can be made on demand with portland cement and inexpensive local materials.

With correct placement and use, concrete can have a service life of 50 years to more than 200 years.

Improving the proper and efficient use of concrete and portland cement requires better understanding	

of the chemical process of hydration, and	how that process can	be characterized	and	modeled	– both	for

pure portland	systems and	for those containing admixtures and	supplemental cementitious materials

such as	fly ash, slag cement, and others. Having interactive	computer models, based on sound

experimental data, for the	chemical and physical interaction of cementing	compounds, molecules, and

ions in the concrete pore-water solutions will help both to improve cement manufacture and to

optimize sustainable concrete mixtures.

Importantly, concrete has the lowest embodied CO2 content of any	major material used in construction,

including glass, steel, and wood.	 But so much concrete is produced annually that it still accounts for

about 8 of industrial CO2 production. Therefore, reducing both	the CO2 contribution and embodied

energy of concrete is	a societal challenge that must be addressed to ensure a sustainable built

environment and transportation infrastructure. One	way to reduce	concrete’s	CO2 contribution is	to

lower its embodied CO2 and energy content and even further, typically by both more	efficient

production	of cement binder and	partial replacement with	supplementary cementitious materials or

fine mineral fillers. This approach	is already being used, but often	with	uncertainty in	the way the

binder will perform. Concrete is typically overdesigned by at least 10 % because of the inability to	

ensure	the	exact performance	of the	binder material. Therefore, the	ability to accurately model cement	

hydration	kinetics and	predict and	improve the performance of concrete as it hydrates could	lead	to	a

1 % reduction in the	mass of cement and concrete	used each year and significantly reduce	concrete’s

embodied CO2 content. Achieving these objectives will require more comprehensive and fundamental

knowledge of the hydration process that is responsible for the hardening, strength gain, and ultimate

durability of concrete.

The National Institute of Standards and Technology (NIST) and the	U.S. Federal Highway Administration

(FHWA)	recognize the importance of	obtaining that	knowledge through sustained and coordinated

research. Paving the Way for a More Sustainable Concrete Infrastructure is a joint NIST/FHWA report

that	provides a detailed	vision	for focused	experimental and	computational modeling research	that will

provide the knowledge and	translate it to	industry tools for improved	cements, mixture design, and	

service life prediction of concrete in service. The document is the direct outcome of the “International

Summit on Cement Hydration Kinetics and Modeling,”	which assembled hydration	experts from

academia, government, and industry to identify the	most important gaps in knowledge	and to formulate	

strategies	for filling those gaps. Their findings have been distilled in this document. NIST	and FHWA

therefore view this as a foundational resource and roadmap for	coordinated concrete research and to

secure the necessary sustained funding and focus	for ensuring a sustainable national infrastructure.

v
 
vi
 
Paving the	Way for a More	Sustainable	Concrete	Infrastructure

A Vision for Developing Comprehensive Description of Cement Hydration Kinetics

J. J. Biernacki1 J. W. Bullard2 D. Constantiner3 R. C. Meininger4 M. .G. Juenger5 J. H. Cheung6,

W. Hansen7, R. D. Hooton8, A. Luttge9 and J. J. Thomas10

1

Tennessee Technological University, Cookeville, TN; jbiernacki@tntech.edu 2

National Institute of Standards and	Technology, Gaithersburg, MD; bullard@nist.gov

3

BASF, Cleveland, OH; daniel.constantiner@basf.com 4

Turner-Fairbanks Highway Research Center, McLean, VA; richard.meininger@dot.gov 5

University of Texas at Austin, Austin,	TX;	mjuenger@mail.utexas.edu

6

W. R. Grace, Cambridge,	MA;	josephine.h.cheung@grace.com 7

University of Michigan, Ann Arbor, MI; whansen@umich.edu

8

University of Toronto, Toronto, Ontario, Canada;	hooton@civ.utoronto.ca

9

Rice University, Houston,	TX;	aluttge@mail.rice.edu

10Schlumberger, Cambridge, MA; jthomas39@slb.com

Abstract

Hydration of portland cement is	the cornerstone of the process	responsible for microstructure

development in	concrete and	ultimately controls the kinetics of all materials properties that make

concrete such a useful product for society	(properties	such as	setting, strength, permeability, and

durability). comprehensive understanding of, and	model for, cement hydration	will enable new

applications that require	better control of concrete	properties. Recent advances both in experimental

and in computational technology are	providing unprecedented	insights into	the nature of cement

hydration. While a comprehensive theory is not yet available, recent progress suggests that what were

once thought to	be the most elusive hurdles are now within	reach. number of simulation	platforms

are	now available, along with emerging modeling strategies that could provide	multi-scale linkages	for

the development	of	engineering models and computational research tools. Similarly, new experimental

methods are	yet to be	fully exploited, although some	are	now positioned to offer real insights and

breakthroughs. Ultimately, a more coordinated	effort must be undertaken that	will enable research

teams to assemble	and focus on specific tasks identified within a Roadmap for	developing a

comprehensive description of	cement	hydration kinetics, rather	than individual efforts being spent	on

isolated tasks.	 The objective of this document is to establish an outline for the efficient development of

data and	related	models that will enable predictive approaches for concrete materials use and	new

materials realization. This new path is needed for the continued technical leadership of the U.S. in the

development and	maintenance of a sustainable civil infrastructure.

This report is not intended	to	be scholarly review on hydration kinetics, but rather a summary	that

articulates what appears to	be some of the most important aspects of cement hydration	that currently

are limiting	our ability to	quantitatively describe an mathematically model hydration	phenomena. The	

summary herein is	being	published	in	conjunction	an as companion	to	 series of recent	scholarly

reviews [1–5].

1
 
Executive Summary

The following document is the direct outcome of an international collaboration between the US	and

Canada entitled, the “International Summit on Cement Hydration Kinetics and Modeling.”	 Funded by	

various agencies in the two countries* the summit provided	a review of the state of	knowledge on

hydration	kinetics in	the following seven	thematic areas: (1) mechanisms; (2) modeling	and simulation;

(3)	experimental techniques; (4)	chemical admixtures; (5) supplementary cementitious materials;	(6)

alternative	cements; and (7) thermochemistry. Fifty-two engineers, scientists and students from six

countries, met at Laval University	on July	27, 28 and 29, 2009. The contingent overwhelmingly	agreed

that	being able to control the process of	cement	hydration is key to the development	of sustainable

concrete materials. The term “sustainable materials” in this	context encompasses formulations based

o traditional portland	cement chemistries as	well as new emerging systems that promise smaller

carbon footprints. Collectively, the group also agreed that new instrumental and computational tools	

offer opportunities to	tackle the century long pursuit to	understand	the mechanism of portland	cement

hydration	and	to	recreate the process quantitatively and	predictably using computer models. Six

summit sub-teams were assembled to write state-of-the-art reports that comprised the seven topic

areas	of the summit. Those papers	were used to generate this document, which enumerates and maps

the 4 specific research needs or questions that if answered would enable	the	development of robust

tools for	predicting hydration kinetics and open the door	for	the development	of	next	generation

concrete infrastructure materials.

Why are kinetics so important? A number of examples should help an answer to emerge. Modern

metallurgy utilizes kinetics to manipulate ore processing and to control solidification, crystallization and

solid-state phase transformations	and, as result, has given	us super-alloys, stainless steel, lightweight

alloys, corrosion resistant metals and high temperature	refractory metallurgy. By controlling the	

kinetics of organic	synthesis, polymer science is able to produce designer macromolecules on demand

and the	pharmaceutical industry can	quickly synthesize new drugs for testing and	scale-up	to	production	

capacity	predictably. Detailed kinetic	knowledge of how trace quantities	of critical elements	react and

are	transported within semiconductors is required to reliably produce millions of computer chips yearly

with astonishing quality control specifications	measured in parts	per million or parts	per billion.	 Finally,

at the	heart of modern crude	oil refining are	numerous kinetically controlled processes including

catalytic	cracking and hydro-treating. Without	sophisticated computational modeling, it	would be

difficult to	control, design	and	operate refineries to	quickly respond	to	changing market demands and	

crude feed variations. These examples	illustrate that knowledge of kinetics leads to control of

outcomes, predictable design, engineered	decision	making and	ability to	respond	to	the changing

environmental and economic landscape. Each of the five industries mentioned above, metallurgical,

polymer, pharmaceutical, semiconductor and refining, have invested heavily in kinetics and kinetic

modeling research in an effort to establish control of product quality and the evolution of their

technology.

Equipped with extensive knowledge of cement hydration kinetics, the cement	and concrete industry

could be revolutionized. Cement manufacturers	would be able to tune their raw material proportions,

burning conditions, and	grinding to	achieve portland	cement binders with	prescribed, optimized	

reactivity for	market	demands in	different industry sectors. Chemical admixture suppliers would	be able

* National Science Foundation (NSF), Federal Highway Administration (FHWA), W. R. Grace, BASF, Mapei, Canadian

Research	Center of Concrete Infrastructure (CRIB), and	Natural Science and	Engineering Research Council of

Canada (NSERCC)

2
 
to design additives to selectively modify the rates of	different	reaction mechanisms to achieve tailored

induction periods, workability, and setting time.	 Ready-mixed suppliers would be able to forecast

exactly the	influence	of supplementary cementitious materials on early-age	behavior, and would know

how to	adjust mixture proportions and	handling in	response to	seasonal variations in	temperature at the

time of	placement. Every one of these advantages would	lead	to	more predictable behavior,

dramatically less returned	concrete and	corresponding material waste, and	the use of higher

proportions of industrial byproducts in	cementitious binders, all of which	would	translate to	a more

sustainable civil infrastructure. Unfortunately, the cements community has not put forward	a

coordinated, well-funded effort	to understand and control kinetics,	though notably there is some highquality published	research o the subject and	advances being made.	 The challenges that lie ahead,

including increasing interest in sustainable construction practices, the direct reduction in greenhouse

gas emissions and the	development of new technologies in response	to performance-based	

specifications, must be met with increased commitment to discover the fundamental principles that

govern the	transformation	of anhydrous cement phases to	hydrous materials.

In summary:	

Hydration Mechanisms – For over five decades, the prevalent	explanation for	why cement	hydration

exhibits an induction period, followed by a main hydration peak and slow hydration that	extends for	

years, has been the barrier layer-diffusion	control hypothesis. This hypothesis has never been	directly

demonstrated	and	is now seriously under question by most researchers. A layer may exist, but new

experimental evidence	and modeling results are converging in support of alternative	and simpler

explanations that involve hydroxylated surfaces, nucleation and a two-step densification, growth and

space filling processes. Models as well as new experimental evidence in support of these hypotheses	

are	also emerging. While the quest to experimentally validate or refute the barrier layer hypothesis

continues, new experimental methodologies	now offer unprecedented insights into surface	phenomena	

at the	nanometer scale with time resolutions	that will enable researchers	to isolate the factors that	

govern cement phase	dissolution, subsequent hydration and how admixtures interact at early	ages.

Techniques such as vertical scanning interferometry (VSI) and X-ray nanotomography along with	

molecular dynamic simulations and solution-phase based	chemical kinetics models can be new focal

points in	conjunction	with	traditional techniques which	include various forms of microscopy, chemical

microanalysis, calorimetry, X-ray and neutron scattering, and nuclear magnetic resonance (NMR)	

spectroscopy. These techniques can provide experimental details to	validate the modeling predictions.

Modeling and Simulation – The past two decades have been dominated by pixel-based	strategy for

generating	cement microstructure	developed at the	National Institute	of Standards and	Technology

(NIST). The well-known simulation environment, called CEMHYD3D, uses largely empirical rules and a

single, likewise empirical, global rate law with no fundamental connection to solution phase chemistry	

evolution.	 The summit participants recognize the great	contribution of this pioneering work, yet agree	

that	this strategy must	be superseded with one which links solution phase chemistry, transport

phenomena and	thermochemistry through	fundamentally sound	kinetic frameworks aligned with past

work.	 As is typical	of such endeavors, modeling is somewhat ahead of experiments,	but VSI in

combination with molecular dynamic simulation is now one route to	advance	the	understanding of basic

rate laws and reaction mechanisms. What	is clear	is that	models that	link to the basic chemical and

physical mechanisms are	being, and must continue	to be, developed and directed to connect these basic

processes to	macroscopic behavior so	that they will be useful for designing clinker phases, for mixture

proportions, for admixture optimization, and	for predicting life cycle behavior of concrete. These

3
 
connections	will inevitably require models to bridge length and time scales such that user-friendly

models	can be produced and widely adopted by the concrete industry.

Experimental Techniques –The past 5 years have been dominated by calorimetry, microscopy (optical,

electron and X-ray), microchemical X-ray analysis, X-ray and neutron scattering and, to a lesser	extent,

NMR and other forms of spectroscopy. Summit participants agree that these tools will continue to be

among the	mainstream approaches, but that new insights will	likely emerge through	the application	of

new and	developing analytical methods such as VSI, atomic force microscopy (AFM), nuclear resonance

reaction analysis (NRRA), broadband time-domain	reflectometry (BTDR), X-ray nanotomography and

nano-X-ray chemical analysis, and high	resolution	electron	microscopy. Already, high	resolution	

electron microscopy is providing support for the recent two-stage hydration hypothesis, and X-ray

nanotomography is offering a real-time window into the chemical and	microstructural changes within

cement paste. These newer techniques will complement the more traditional microstructural and

macroscopic characterization methods to enable the development of detailed	kinetic	data sets for

cement hydration.

Admixtures –Many chemical compounds are	available	for altering some	property of fresh concrete, and

each interacts with hydrating cement phases in mechanistically unique ways. Even when admixtures are	

used	for functions such	as altering rheology or controlling shrinkage, they may still effect	hydration.	

Furthermore, even within class, say set-altering admixtures, there	may be	 multiplicity of mechanisms

that	produce similar	effects. This is further	complicated by the fact	that	we do not	have a mechanistic

understanding of how cement phases hydrate, even in the	absence	of admixture	chemicals. Without

that	basic understanding it	is difficult	to determine how admixtures operate. Ultimately, a generalized

way to predict chemical interactions with cement phase surfaces and ionic species must be	sought so

that	the effect	of	any given chemical on hydration can be predicted priori. This is a challenging task,

one that will benefit greatly from molecular	simulation, computer-aided molecular design (CAMD) and

focused kinetic experimentation.

Supplementary	Cementitious Materials (SCMs) – Most high-performance cementitious systems

designed	for	improved durability characteristics and lower	CO2 consumption contain one or more SCMs

at replacement levels	ranging from 5 (silica fume) to 50 or more (ground granulated blast furnace	

slag). SCMs present many challenges	since they, like admixtures, vary	in composition and physical

characteristics. Today, each SCM is typically treated as a unique material.	 Even within classes of SCMs,

individual	sources of materials are treated as though they are unique.	 What key physical	and chemical	

features of	an SCM determine	its reactivity and how do they impact on the	reactivity of cement phases

when used as partial cement substitutes in	blended	cement systems? This question can be answered by

developing kinetic	models that incorporate solution phase chemistry	and the physical and chemical

characteristics	both	of the cement and	of the specific	SCM in question.	 However, the basic kinetic	and

thermodynamic data are not fully available at this point. Computational strategies such	as molecular

dynamic modeling,	together with the application of experimental methods such as VSI, will likely

advance progress in	this area.

Alternative Cements – Alternative cements,	several examples of which are described in Section II.7,

might be categorized as engineered variations of existing	SCMs or radical modification of clinker

chemistry	that form cements. To some extent, the chemistry of alternative cements overlaps with that

of portland	cement, and	to	some extent it broadens the field.	 For example, we	include	in this category

portland	cements that have been	modified	by the addition	of fine limestone particles to	enhance the

early-age	kinetic behavior.	 Kinetic data	are	even scarcer for	alternative cements than they are for	

4
 
portland	cement, and quantitative	models d not exist.	 The challenges facing this community are

daunting. What chemistries might be tested? What are the projected	costs o the industrial scale?

Which materials will have suitable life cycle performance characteristics? Until these questions can be

answered systematically, alternative	cements will continue to have limited	ranges	of applicability, higher

cost barriers, and/or performance concerns.

Brief History – Full appreciation of this report’s recommendations requires a brief historical review.

The Center for Advanced Cement-Based	Materials (ACBM)	has provided focus for	materials science

research on cementitious materials in the US since 1989. Though	it never included	a significant thrust in	

the area of	kinetics, it	did emphasize modeling and enabled the development	of	CEMHYD3D and other	

modeling tools. In	recent years, ACBM has become an	independently funded	entity and	its emphasis

has moved	away from topics such	as the fundamental chemical interactions of cement phases. Efforts

for	more than a decade at the	National Institute	of Standards and	Technology (NIST) to develop the

Virtual Cement and Concrete Testing Laboratory (VCCTL), a platform for	the development	of	

fundamental models and their	use as practical tools, have contributed	the more recent HydratiCA	code,

the first	comprehensive effort to fuse	solution phase	chemistry, kinetics and transport processes into a

generalized modeling	environment for cementitious materials. VCCTL has also contributed model-based	

tools that	are used for	education and research in the US and around the world. The most	recent	link in

the hydration kinetics chain is the	new industry-funded Concrete Sustainability Hub (CSHub@MIT)	at	the

Massachusetts Institute of Technology (MIT). This new thrust promises to be a significant contributor to

any effort to develop generalized kinetic theories for cement hydration.

Th Path	Forward – It	is clear that the cement and concrete manufacturing sectors,	as well as the

agencies, owners, engineers, and architects using concrete, would benefit greatly from a coordinated

multidisciplinary effort o hydration	kinetics. Thus, the following single recommendation	is made – to

form an organization for	cement	hydration kinetics that	will act as focal point for relevant research

and	planning	for the	concrete	materials of the	future. The organization could	take the form of	a

consortium of stakeholders	and partners, potentially	funded by	government and industry	and involving

the academic community, National Laboratories	and private sector research and development interests.

A ambitious, cooperative structure is envisioned	wherein	industrial partners take an	active role in	the

development and	deployment of new technologies emerging from research. Industry, rather than

having the typical passive role as funder	and advisory board member, would be true research partners

and, in addition, engage	the	initiatives as test beds for transferring technology, co-developed	by the

academic and research	community, and	offer an early introduction of research findings into the	

practices of their organizations.	 Furthermore, the consortium would be the embodiment of an effort

that	combines cutting edge experimental techniques and modeling to create a process	that provides	

feedback between the two. Through the proposed organization, we hope to begin, “Paving the Way for	

More	Sustainable	Concrete	Infrastructure.”

Context of this Document – The vision for productive future research in cement hydration contained

herein	is formatted in terms of series of critical, unanswered research questions,	along with a

description	of the activities necessary to make progress on understanding and controlling the kinetics of	

the reactions in concrete. However, note that	this document does not exist in	isolation, but instead	is

tied to other	recent	roadmaps for	the concrete industry. The ACI roadmap "Vision 2030:	A Vision for the

US Concrete Industry" [6] describes four topics that link directly to	specific research	needs related	to	

kinetics: Design and Structural Systems Constituent Materials Research	Needs Concrete Production,

Delivery, and Placement and Repair an Rehabilitation. In fact,	the present document includes a series

of tables of research	needs for hydration	kinetics that are keyed	to	these four topics. In	addition, it

5
 
addresses research needs that will promote	at least two of the key goals articulated	in	the International

Concrete Repair Institute’s	“Vision 2020” roadmap [7]:	 Improve Repair Material	Design and

Performance and Develop a Means for Predicting Repair System Performance. Finally, the Federal

Highway Administration (FHWA) maintains the Concrete Pavement Road Map (called the "CP Road

Map"), which was updated in 201 [8]. Volume II of the CP Road	Map	describes	detailed research

needs categorized into 12 comprehensive "Tracks"	of research. Hydration knowledge, models, and data

are	called	for in	several of the tracks and sub-tracks -- such	as "Subtrack 1-1. Performance-Based	Mix

Design and Specifications", which recognizes that "multiscale models are needed to predict and guide

the entire concrete paving process, from microstructure to performance." Other research track

objectives in the	CP	Road Map, such as the	use of reaction	thermal proprieties, more effective curing,

and fast-track setting and strength gain for	accelerated construction would also be advanced through

understanding of hydration	kinetics.

I. Introduction

The quest to identify the underlying mechanisms that control cement hydration is among the more

enigmatic problems in modern materials science. More	importantly, the	lack of such knowledge	

appears to be	an obstacle	to the	development of next generation hydraulic construction	materials that

have sustainable characteristics and	improved	life cycle performance as compared	to	existing portland	

cement technology. Among materials, portland cement concrete is	unique in that the final product, a

complex	composite made from	aggregate (rocks and sand), water, small amounts of other additives

known in the industry	as admixtures, portland cement and SCMs are	formulated on demand and are	

processed	to	some extent at the point of use. This recipe is followed	thousands of times each	day as

this most	used engineered material on earth is applied to construct mankind’s infrastructure across the

planet. Our inherent lack of knowledge	about how to control the	hydration process makes improving,

predicting and	controlling the performance of portland	cement concrete a difficult task that	is

accomplished today by trial-and-error experimentation combined with the	experience of	engineers and

technologists. But	as concrete materials and formulations become more complex to meet	the economic

and environmental challenges of the	future, experience	with yesterday’s formulations will be	of limited

use.

It would be incorrect to say that	not	much research progress has been	made o cement hydration	

kinetics in the past three decades or so, since one might draw that conclusion based on the list of

questions that remain, a list that seems to	echo	the work of Gartner and	Gaidis [9].	 In contrast,	

advances in instrumental analysis and careful analytical chemistry have offered	considerable insights.

The inherent problem is that we simply do not have fundamental, underlying theory that describes

how portland	cement is transformed	into	the spectrum of hydrates, particularly the primary hydrates

known as calcium silicate hydrates	(C-S-H),	that make up the binder in concrete. Furthermore,	it is

unclear how or if the existing database of experimental information	can	be used	to	discover such	a

theory. Breakthroughs in our	ability to alter	and control material properties and to improve

performance have generally come along with	understanding about their synthesis and	physicochemical

behavior at the most fundamental levels. And, while such are	largely known for some	classes of

materials including metals, polymers, and semi-conductors, equivalent theories are	not available	for

concrete and its	binding matrix, portland cement.

In recent years, there have been a number	of	isolated studies of	various aspects of hydration but,

unfortunately, there has not been	a focal point for a large-scale thrust to clear the remaining hurdles. In

December of 2006, three of	the authors, Biernacki, Bullard, and Hansen met to discuss their mutual

6
 
interests in cement hydration modeling. At that time	they crafted an idea	that would eventually take	

shape as	an international workshop on hydration kinetics, now known as the	International	Summit on

Cement Hydration Kinetics and	Modeling [10].	 This vision document and	five companion papers[1–3,5,

11] o various aspects of cement hydration	are the outcomes of the Summit.

While the thematic basis of the Summit was cement hydration kinetics, the program was divided into six

subthemes that	addressed related or	enabling topics. Based upon the number	of	contributions offered

at the	Summit and the	amount of time	spent on each, the	various subtopics have	been divided into

three Primary and four	Secondary themes,	all of which are now summarized.

Primary Themes

Mechanisms – In the field of kinetics, mechanisms define	the molecular-scale processes	that control the

rate at	which something happens. Portland	cement hydration	encompasses both	chemical and	physical

changes, so explanations	of how these changes happen	likewise must incorporate both	chemical and	

physical mechanisms.	 In kinetics, mechanisms are the pathways by which chemical or	physical changes

take place. Knowledge of	mechanisms gives engineers the	insight needed to intentionally manipulate	

material behavior. Without such knowledge, engineers must use their past experience to guide them in

solving problems	and designing new formulations,	which is a trial-and-error proposition	when	

formulations change substantially.

Models and Simulations – In the past, models were mathematical devices used to explain experimental

data – without the data, models could not be calibrated and parameters could not be estimated. And,

while modern models continue to serve this purpose, new	tools such as molecular dynamic simulation

are now being used to discover	mechanisms and to estimate parameters that	can be used in other	

models. In a sense, modern models beget models. It turns out that the length and time-scale of the

desired	information	are	important in determining what kind of model is used. To predict the behavior of

“Y”	at length or time scale “x”, “Y”	must be described at a scale that is at least as small as “x and likely	

smaller. Most traditional kinetic	models	predict macroscopic	performance based on microscopic	

information. Modern modeling strategies utilize tools that can predict nanoscale events, which can then

be up-scaled as	inputs	to micro-scale models, at least in principle if not often in practice. But this	kind of

multiscale approach is likely to play a significant role in discovering and developing a universal	modeling

strategy for cement hydration.

Experimental Techniques – Experimental techniques effectively enable hypothesis generation and also

limit the extent to which new hypotheses can be validated. New	methods are continuously being

developed	and	old	ones are being used	in	new ways to	discover mechanisms and	observe hydration	

behaviors at many length	scales. Calorimetry, electron	microscopy,	thermal analysis and x-ray

diffraction	continue to	be primary	tools since they	are generally	available to all researchers in

laboratories around the world.	 Neutron and synchrotron radiation are	also being utilized to lesser

extent at larger research facilities.	NMR,	however,	is being used for cement by a still smaller number of

investigators, probably because of the highly specialized background and facilities that are required and

material limitations associated with cement (e.g., paramagnetic materials, such	as iron, interferes with

NMR).	 Similarly, transmission electron microscopy is somewhat underutilized because	it requires highly

specialized training and sample preparation. Atomic force microscopy (AFM),	despite its widespread

availability, has been somewhat underutilized technology. Newer methods, such as	VSI,	nano X-ray

tomography, broadband time-domain	reflectometry spectroscopy (BTDR)	and nuclear resonance	

reaction analysis (NRRA), are	just now emerging as potential contributors.

7
 
Secondary	Themes

Chemical Admixtures – Chemical admixtures are materials that are added	to	the concrete mix

formulation in an effort	to alter	fresh (fluid)	or	hardened properties. Some admixtures are	deliberately

used	to	change hydration behavior, but others must be designed to change properties	such	as

flowability without	altering the rate of hydration or setting kinetics.	 Admixtures have been used since

Roman	times and were widely used in the making of	pozzolanic cement by the Romans. New admixtures

are	developed based	o a general understanding	of mechanisms involved. However, the design of	new

admixtures and the	prediction of how existing ones will behave	in various mixture formulations are	

difficult because the detailed	mechanisms required for	modeling the interaction of different admixtures

with the cementitious components are not known	with sufficient accuracy.	 Ultimately, an

understanding of how portland	cement hydrates may be obtained	through	careful study of how

admixtures interact with cement phases.

Supplementary Cementitious Materials – The use of waste or byproduct materials that have

cementitious	properties	is	an obvious	route to more sustainable concrete construction practices. This,

however, adds more degrees of freedom and	possible interactions that are often understood even less

than the hydration of	cement	clinker	phases. Nonetheless, the use of	supplementary cementitious	

materials (SCMs) as they are called, is crucially important for environmental benefits and, in some cases,

improvements in performance or service life. Much	is known	about the empirical responses of concrete

to SCMs, but mechanisms that describe the fundamental chemical and physical pathways leading to

material property changes are not known with sufficient detail to develop	predictive models.

Alternative Cements – The concept of alternatives to portland cement	has been around for	decades, but	

economic and performance	considerations have	limited alternative	cements to specialty applications

and laboratory curiosities. However, sustainable	future	for concrete	may be	found in formulations

that	are well outside of	the compositions that	we presently consider	as the norm. Assuming that	these

cements	will still require hydration to achieve their hardened properties, it stands	to reason that

mechanistic information about reaction pathways and kinetics would pave the way for quicker

development and	implementation.

Thermochemistry – All chemical and	physical transformations are driven	by thermodynamic potentials.

Without explicit knowledge of the thermochemical and thermophysical limits that	govern cement	

transformation, it	is unlikely that	we will develop corresponding rate laws that	govern the kinetic

behavior of cementitious systems. Therefore, thermochemistry and	thermodynamics in	general	is an

enabling, crosscutting	discipline. Unfortunately, this area	was underrepresented at the	Summit and will

not be reported	o here.

II.	 Hydration

II.I	Overview

This document is intended	for those with a scientific background but	who may not	necessarily be

familiar	with cement	hydration and chemistry. Therefore, we provide a brief	introduction to the key

concepts	to aid in understanding the remainder	of	the document.	 Portland cement (PC) is made	up of

8
 
five major	compounds: tricalcium silicate (C3S)† dicalcium silicate (C2S), tricalcium aluminate (C3A),

tetracalcium aluminoferrite	(C4AF) and	gypsum (calcium sulfate dihydrate, C$H2). C3 (actually the

impure form of	C3 known as alite,	a Mg,	Al and Fe bearing combination of the polymorphs)	is the major	

constituent of Type I,	II and III cements), so it is	frequently used as	a model in place of the more complex

multiphase system.	 The hydration of alite, and likewise of portland cement , is a net exothermic process

(i.e.	it releases heat) so calorimetric methods are often used to monitor the rate of hydration under

various conditions. Figure 1 is a typical isothermal calorimetry	curve for alite at 25o and	a w/c (water

to cement	mass ratio)	of	0.4. Interpreting the shape of	this curve has been the subject of debate for

decades.

Bullard	et al. [1] recently described cement	hydration as having the following five stages	shown in Figure

1: (1)	an initial fast	reaction period (Stage 1), (2)	a period of	slow reaction (Stage 2), sometimes called an

induction period, (3) period of accelerating	hydration (Stage	3), and (4) subsequent period of

progressively decelerating hydration	(Stages 4 and	5).	 While these stages have been described many

times in the literature and have become the fingerprint	for	cement	hydration, they	are the unexpected

result	of	an extremely complex process that	is yet	to be fully defined, even	for pure cement phases such	

as C3S. What follows are brief synopses of the most recent viewpoints concerning hydration of cements,

organized	by the six sub-themes listed earlier.

Figure 1. Typical alite	calorimetry curve	characteristic of C3S (triclinic)-based	hydraulic cements, data

after	Xie and Biernacki [11].

II.2 Mechanisms

† Cement hydration	shorthand	notation	is used	throughout wherein: C=CaO, S=SiO2, H=H2O, A=Al2O3, $=SO4,

M=MgO, F=Fe2O3.

9
 
Mechanisms define the fundamental steps in a process. Rate controlling mechanisms are	those	steps

that	are slowest, those that	control the observable kinetics, where “observable” is a relative term that

might be defined by a timeframe and length scale that are	relevant	to the process and the objectives of	

the observers. Thus, when studying the kinetics of cement hydration, we ultimately must define events

at	time and length scales that	suitably reconstruct	macroscopic behavior	in concrete since we, the

observers, desire to	predict and	control the properties of portland	cement concrete.

The rather simple looking calorimetry curve in Figure is actually the	result of very complex interactions

between	tricalcium silicate and	water. Understanding these events is critical to	elucidating the broader

problem of portland	cement hydration, which involves four additional major components, C2S, C3A, C$H2

and C4AF modified	by the presence of potassium and	sodium hydroxides and	other trace constituents

native to	the cement or reactive constituents added to modify the	behavior of the	concrete. Early

attempts to describe	cement hydration utilized simple	models that mostly ignored solution phase

chemistry	and assumed one, or a few at most, rate controlling mechanisms. While one could sometimes

adequately fit experimentally observed hydration behavior with these	models, none	of them could be	

used to design new material chemistries or predictably engineer new microstructures and responses in

cement or concrete.

So, where	are	the	problems and what are	the	obstacles?

Until recently, there have been no quantitative models that could adequately describe the solubility

behavior of C3S. Thermodynamic calculations unequivocally predict that C3 is extremely soluble	in

water, with equilibrium solution concentrations of calcium and silicates on the order of 102 mM

(mmoles/L). This	high solubility is	clearly responsible for the high dissolution rates	and rapid heat

liberation during Stage hydration. However, the solution	never attains concentrations as large as this

thermodynamic solubility limit. In fact, the actual activity	product is	typically	about 17 orders	of

magnitude less than the equilibrium	value. The reason for this large discrepancy is a matter of

considerable debate.

One hypothesis that has been around since at least 1964 [12] is that of the metastable barrier layer.

This hypothesis is so well known in the literature and among those having even cursory knowledge of

hydration	kinetics that it has achieved	dogmatic status with	many researchers. However, there is no

direct evidence that such	a layer actually exists. Indirect evidence, from sophisticated	experiments

involving nuclear resonance reaction analysis [13,14] and recent NMR experiments [15] is compelling

but not universally accepted.

What fuels the controversy is not the above stated hypothesis	of a low-permeability metastable layer.

Rather, the controversy is that there are altogether different hypotheses that can	explain	the observed	

behavior just as well. Barret [16],	Nonat [17] and others contend that hydroxylated surface	forms on

the C3 immediately upon contact with water, with this surface having an apparent solubility product

constant on the order of 10-17. To produce an experimentally observed peak in silicate ion

concentration, nucleation of a stable form of C-S-H	must occur within minutes, which then continues to

grow slowly during Stage (2). This has become known	as the “steady-state hypothesis.”

Notably, Bullard has demonstrated	that either the metastable barrier layer or hydroxylated	surface

hypothesis can	adequately predict alite	hydration rates, there	being only minor differences in the	

predicted	evolution	of the solution	chemistry [18]. But there were certain	assumptions or implicit

mechanistic functionality that were necessary to also make	either mechanism work;	establishing that	

10
 
such mechanisms	are present is	a challenge to be proven empirically.	 This is clear example where

modeling results may provide a clear experimental approach to resolve this difficult challenge.

Yet another hypothesis for the early-age	kinetic behavior comes from research	o the dissolution	of

various minerals other than alite, which has shown that their rates of dissolution can be abruptly	

decreased	by a change in	dissolution	mechanism from unwinding of surface defects at high	driving

forces to step flow motion below a critical driving force.	While some evidence exists that supports this

hypothesis, such	as direct observation	of etch	pits in	alite surfaces, the body of experimental data is

small at this	time.

While it is generally taught that Stage (2)	is a period in which the reaction becomes dormant, it	is

becoming increasingly clear that a true induction	period	only occurs when	something interrupts or

interferes with the ordinary progress of hydration.	 In actuality, Stage (2) is simply the point at which	

hydration	is slowest. So, the more relevant question	is, “What causes the rate of hydration	to	increase

during Stage (3)?”

The main problem with the semipermeable barrier layer hypothesis described above is that on its own,

such a layer would	suppress dissolution	rates, and	therefore hydration	rates, indefinitely. Thus, a

companion hypothesis	is	necessary. This	additional requirement demands	that the layer material be

metastable with respect to the eventual formation of a more stable form	of C-S-H	gel. This condition

would permit continuous, though slow, hydration to proceed with the layer intact until the more stable

form of	C-S-H	nucleates. How does this work? The metastable C-S-H	(C-S-H(m)) has a higher equilibrium

solubility than the more stable C-S-H, thus, once the stable form nucleates and begins to grow, the

metastable phase simply dissolves. While this seems simple enough, the metastable C-S-H(m) is an

elusive	material that has yet to be observed directly.

In this case, there are three concepts	that follow from the already mentioned mechanisms, any of which

could potentially	explain Stage	 behavior:

1.	 Nucleation and growth of a stable form of C-S-H	destabilizes the metastable C-S-H, at least at its

outer boundary, permitting large amounts of	stable C-S-H	to form.

2.	 Nucleation and growth of a stable form of C-S-H	mediated by slowly dissolving C3S.

3.	 Mechanical destabilization of a barrier layer (not necessarily chemically metastable layer).

Unfortunately, all three mechanisms can be shown to accommodate at least some of the experimental

observations and	all can	be utilized	in	part to	produce simulations that likewise are	consistent with some

of the experimental observations. Therefore, it appears that at this time there is n single model or

hypothesis that quantitatively explains all observations, nor is there unequivocal experimental evidence

to decide which, if	any, of	the hypotheses just	described most	closely describes the situation.

Considerable attention	has been	given in the	past decade	or so to the	mechanisms causing	the	observed

second and major hydration	calorimetry peak that is associated with the	onset of Stage	(4). Since	the	

late 60’s, it had been assumed that the onset of Stage (4) signaled the transition from	nucleation and

growth kinetics to diffusion-controlled kinetics, but this	assumption is	now being questioned.	 A new

hypothesis that focuses o volume filling arguments and	a two-stage growth C-S-H	mechanism wherein

low density morphology fills the	pore	space	quickly followed by slow densification has gained

credibility	as	and alternative explanation [19].	 Most researchers still	agree, however, that diffusion is

likely to take over as the rate controlling mechanism at some later age.	 But the transition	to	diffusion	

11
 
kinetics is not clearly identifiable and little experimental	research is available upon which to draw

conclusions	or inferences	or upon which models	can be tested. To be sure, most recent modeling has	

focused on Stages (0)	through (4) in Figure	1. From different perspective, the	movement of ions from

hydrating cement grains to	form hydration	products and fill empty spaces in “dense” system (after

several days	of hydration) would be very similar to the ingress	of ions	responsible for concrete

deterioration	(sulfate, carbon	dioxide), therefore, the ability to model later-age	hydration has broader

implications.

Unfortunately, as illustrated and discussed above, there are numerous plausible mechanisms that can

explain the	observed hydration characteristics	for portland cement along with experimental evidence

that	partially supports each hypothesis.	 Furthermore, the classic framework for understanding how

cement hydrates	mechanistically	has	not changed much in the past three decades. Similarly,

mathematical modeling has been shown to render simulations that can be made to behave like

experimental observations, comply with thermodynamic constraints and yet be	controlled by any

number of hypothetical mechanisms. Thus, one can	only conclude that	there are a number	of	

fundamental questions that	must	be definitively answered before we can be confident	about	the

mechanism	of cement hydration. These questions, unfortunately, have not changed much since about

1989 [9].

At this point, it appears that	a great	deal of	effort	has focused on understanding the hydration

mechanism	for C3 and alite	since	tricalcium silicate	in the	form of alite	is the	primary component in

ordinary portland	cement. Even	then	the questions stated earlier remain. And, while it is necessary to

continue to place emphasis	on alite hydration, at some point it will become necessary	to move towards	

more complex systems including C3A, gypsum, etc. Although	this statement seems obvious, the hurdles

at this point are	high, particularly since C3 hydration	is still	not understood and there seem to be a

number of important interactions between	the silicate and	aluminate phases that can	be decisive in	

determining the time at which	hydration	begins to	accelerate.

II.3 Models and Simulations

Great strides	have been made in modeling cement hydration in the past two decades.	 The present state

of cement hydration	models might be best described	as either meso-scopic, microscopic	or nanoscopic/molecular. The meso-scale work is	predominantly driven by the recent discovery by Thomas	and

coworkers that shows	that boundary nucleation and growth (BNG) might be used to explain the

induction period (Stage 2), the onset of Stage 3 hydration and the transition to Stage 4 hydration

[20,21].	 What seems to be rather simple now was obscured for years by our attempt to work with

Avrami’s equation, which	is mechanistically incorrect [20].

Computational environments that allow modelers to simulate	microstructure	development have made a

significant contribution in the past two decades	or so. Two simulation environments are now

reasonably well developed: CEMHYD3D,	from the National Institute of	Standards and Technology (NIST),

now embedded	in	NIST’s Virtual Cement and Concrete Testing Laboratory (VCCTL) [22] and μIC [19].	

While different in many respects, both offer the opportunity to build and test various hypotheses in

frameworks that	can handle ensembles of	particles. μIC’s strength is in its rather “open architecture”

that	allows the user to build kinetic or transport rules to govern phase changes and mass migration. The

VCCTL, while primarily constructed around the NIST CEMHYD3D model which	uses semi-empirical rules

to mimic kinetic-like transformation, has been extensively disseminated	in	North	America through	

educational programs offered by NIST.

12
 
Within the newer developments from VCCTL, microscopic modeling has moved from global	kinetic and

descriptive approaches towards distributed	parameter strategies that account for	real kinetics, transport	

phenomena, solution	phase effects and	compliance with	thermodynamics. Presently, there is one

model that excels in this arena, HydratiCA [18].	 HydratiCA provides a rigorous computational

environment via	the	application of kinetic cellular automaton that mimics the complex partial

differential equations that arise from the microscopic mass continuity equations.

At the nano-scale, researchers	are beginning to simulate hydrate structures	from solution phase

chemistry	and have	strategies for combining	real-time nano-scale experiments	with computational

approaches that have	been shown to offer insights about other through-solution mineral

transformations. These new breakthroughs have generated optimism in the modeling community.

Thus, models of various forms and levels of complexity from molecular to those with simple global rate

forms are presently being used to decipher	experimentally-observed	hydration	data, which is likewise

varied and multi-scale. Though molecular work is	limited, it offers	the potential for developing insights	

that	could, to some extent, replace presently impossible-to-perform experiments and	provide inputs for

up-scaling to longer length and time scale models. It appears	that a spectrum of modeling strategies is

required since the problem is, in fact, multi-scale. Ultimately, useful engineering models	may obtain

inputs from both experimentally-derived	parameters and	those computationally-inferred.	 While this

trend is being effectively exploited in other areas of materials science, it is yet to be	well developed

within the cements community, partially because of the complexity of the problem but primarily

because the field	of concrete research	has historically been	defined	within	the context of civil

engineering	instead of materials science.

II.4 Experimental Techniques

While the bulk of the experimental work on hydration continues to depend upon calorimetry, various Xray and neutron diffraction and scattering techniques, electron microscopy, chemical analytical methods

(e.g., energy dispersive	spectroscopy) and, to much lesser extent, nuclear magnetic resonance	

spectrosocopy (NMR), there are more recently introduced techniques	that are either making or have

potential to	make novel and	critical contributions. Among the newer	methods are: vertical scanning

interferometry (VSI), atomic force microscopy, nano x-ray tomographic imaging [23],	nuclear resonance

reaction analysis (NRRA), and broadband time-domain-reflectrometry (BTDR)	dielectric spectroscopy

(DS). Unfortunately, most	of	these newer	techniques require unique facilities and unique data

processing methods that limit their widespread	use.

Vertical scanning interferometry is a technique that is being successfully used in the geochemistry	field

to unravel the complex dissolution-precipitation	kinetics of mineral interactions. The same technique

should be utilized to study the hydration of cement phases	and shows	great promise [24].	 In general,

the technique utilizes visible light, generating interference patterns caused by interaction of two

incident beams of monochromatic light.	 The interference patterns are used to produce a topological	

map	of the scanned	surface. High-resolution forms of	this technique are capable of	sub-micrometer

horizontal resolution, and	sub-angstrom vertical resolution, of surface features in real	time and in the

ambient aqueous environment. This means that samples can literally be	visualized with unprecedented

resolution as they react. Among the exciting opportunities for this technique is the direct imaging and

quantification	of rates of dissolution	at any stage of hydration, and the imaging of	the mechanisms of

dissolution	and	nuclei formation. The technique promises to	enable the discovery of the morphology of

13
 
both	dissolution	and	precipitation	events and	when	combined	with	related	modeling techniques, most

recently the use of	kinetic Monte Carlo simulations (kMC), there is hope that	intrinsic (elementary)	

kinetic	rate laws might be discovered.

Monteiro [25],	Artioli [26], and Lange [23] recently reported on a nano X-ray tomographic method

wherein individual cement grains could be directly imaged in three-dimensions without drying over a

long period of time.	 This work, while not yet quantitative, shows the evolution of	microstructure in a

volume that contains only	a few cement particles. The qualitative images clearly	show the dissolution

and conversion of some	particles into products, the	consumption of pore	space	(water filled voids), the	

relative rates of	reaction of various	particles	and various	unexpected events	such as	the production of

porosity due to	the dissolution	of particles that leave voids. If developed	into	a quantitative tool

wherein particles and products can be identified by their chemical composition	and	volumes of

individual	phases tracked as a function of time, this technique may offer new insights into the kinetics of

at least micro-scale distributed events, and thus	generate an entirely new opportunity for combining

modeling and experimental	datasets.

technique that has already shown	considerable promise as a tool for probing very near surface realtime events during hydration is nuclear	reaction resonance spectroscopy. Thus far, researchers

Livingston and Schweitzer [13] suggest that this technique provides good indirect evidence of a barrier

layer forming during the first minutes of hydration, and they have even offered an estimate of its

transport	properties and thickness. And, while the present	data may be interpreted in various ways,	the

technique may provide transport	and microstructure related inputs for	model development.

II.5 Admixtures

Admixtures are a broad	and	complex field, particularly because the range of admixture behaviors and	

their	chemical compositions vary	widely	from	simple inorganic salts such as calcium	chloride (a set

accelerator) to polycarboxylate comb polymers	(used as	superplasticizers). And, since the desired

behaviors sought from these admixtures are so	diverse (e.g., water reduction, set retardation or

acceleration, rheology-alteration,	air entrainment,	strength enhancement,	shrinkage reduction), it is

unsurprising that the modes or	mechanisms of	their effects are	likewise	diverse.	 Furthermore, since the

underlying kinetics of cement hydration	are not well understood, it becomes yet more difficult to	

interpret and predict the behavior of additives and to discover and design new substances with targeted

performance characteristics. Among the hypothesized	forms of admixture activity are surface

adsorption, nucleation	site or growth	face poisoning, ion	chelation, surface tension	reduction and

solubility alteration.	 Examples of each of these are well	documented in the literature, although in most

cases	the mechanisms of activity remains the subject	of hypothesis only. Virtually nothing has been	

done to	develop	chemical-based	models for admixture activity and	it remains an	open	field at this point.

This is likely because the broader questions regarding the mechanism of alite	hydration	continue to	be

unanswered. As a result, new admixtures are most often	developed	by trial and	error, making

incremental	changes to existing known admixture chemical	scaffolds.	 This is a time-consuming, costly,

and inefficient strategy. Mechanistic insights into how cement hydrates as well as how admixtures

interject into the process would open up alternative design strategies to advance	admixture	

development, including promising new tools such as	computer aided molecular design (CAMD)

strategies	[27].

In general, the problem is not the lack of data o the impact	of admixtures nor the	lack of hypotheses to

explain some	of the	most well-characterized interactions	(e.g.	the retarding effect of sucrose), but rather

14
 
that	these hypotheses have not	been reduced to theories, nor has there been	any significant effort to	

quantitatively assemble them into	mathematical formalisms. The result is a general absence of

experiments designed to directly reveal kinetic insights in coordination with like modeling efforts in the

area	of admixture-cements	interaction. Among the pressing challenges	is	the general relationship

between	admixture chemicals, sulfates, aluminates,	ferrites and silicates in cementitious systems as well

as those containing supplementary cementitious	materials.

II.6 Supplementary Cementitious Materials (SCMs)

SCMs typically include silica fume, blast furnace slag, fly ash, and metakaolin. Notably, other natural or

synthetic	mineral-based	materials may also	be used, though	some are not	necessarily cementitious (e.g.,

fillers such as limestone powder),	yet such may interact physically or chemically with hydrating clinker

phases. The wide range of	materials used as SCMs	or as	fillers	and their likewise wide range of chemical

compositions	and physical states	makes	it difficult to	generalize their behavior. The grand	majority of

these may be mapped onto the C-S-A	(CaO-SiO2-Al2O3 ternary phase diagram, though	they range in	

crystallinity, and hence	solubility and reactivity, from pozzolanic (reactive with	CH) and	hydraulic

(reactive with water	alone)	to inert	or	very low reactivity. Adequately characterizing their composition	

and often amorphous structure, and linking these characteristics	to the reactivity, is a technical barrier	

to using these materials at	higher	replacement volumes.

II.7 Alternative Cements

There are many chemical alternatives to portland cement, that is, C3S-dominated	cement, but four	of

the most	prevalent alternatives are: (1) calcium aluminate	cements; (2) calcium sulfoaluminate	cements;

(3)	alkali-activated binders; and (4) supersulfated cements. The	chemistry of these	systems might be	

classified into two groups: (1) those related to the portland cement family, e.g. anhydrous	calcium

silicates	and aluminates	or sulfated forms	which interact with water via through-solution reaction

mechanisms to form	various stable and metastable crystalline and amorphous hydrates; and (2) those

that	are associated with glassy or	nano-structured anhydrous	phases,	such as fly ash and blast	furnace

slag, metakaolin and similar materials. However, since	each is dominated	by the hydration	of different

raw materials, C3 in	the case of calcium aluminate	cements, ash, slag and/or metakaolin in the	case	of

alkali-activated cements, it is necessary to understand the	hydration pathways likewise. And, while

there have been kinetic studies, there have been no significant	efforts to systematically reduce the

information to mathematical	models and interpretations,	not even to the extent done for C3S-based	

cementitious	systems. The primary obstacles to more widespread use of such alternative cements are

discussed	for each	of the four types individually.

Calcium aluminate cements have been	shown	to	have rapid	strength	development, to	be resistant to

abrasion and sulfate	attack and to produce	50 less CO2 than portland	cement during manufacture.	

Unfortunately, the hydration pathway passes through metastable hydrates with significant half-lives,

measured in years at ambient conditions, which ultimately convert into stable hydrates,	thereby

releasing water, AH3 gel and generating	porosity. Ways to mitigate, control and or eliminate	conversion

or its effects are	among the	most pressing challenges for calcium aluminate cement developers.	

Presently, the	value	of bauxite	sets the commercial price of	aluminum-based	cements, making it

expensive	relative	to portland cement. Therefore, modeling the processes would allow for virtual

testing of	potential solutions.

15
 
Calcium sulfoaluminate cements (CSA) are dominated	by the presence	and hydration of ye’elimite	

(C4A3$) and are generally	produced in a belitic (C2S) or ferritic (C4AF) form. In	general, CSA	cements

exhibit rapid hardening, high-strength, expansion and self-stressing behavior. Manufacture of CSA

requires temperatures that	are about	100 °C	to	200 °C	lower than	required for portland	cement. In	

addition, they require	less grinding energy to produce the cementitious powder. Overall, production of	

CSA	cement releases less than	50 of the CO2 o a finished	paste volume basis	as	compared to ordinary

portland cement. Currently, the primary obstacles to	widespread	use of CSA	cements are its high	cost

and low alkalinity (pH of 1 to 12), the	latter which may not provide	adequate	passivation against

corrosion of steel rebar.

Alkali-activated cements are	typically formulated by mixing fly ash, blast furnace	slag and/or metakaolin

with a highly alkaline solution. The resulting mixture produces gel phases, of which two forms are

generally	recognized, a C-(A)-S-H	form which is highly cross-linked and mostly amorphous and	a zeolitic

gel that resembles a zeolite	structure	on very	short length scales, but is largely	amorphous as well. By	

some estimates, the use of such binder systems	may reduce CO2 production	by as much	as 80 as

compared to portland cement. At this	time, however, this	form of cement, special class of which are	

sometime referred to as geopolymeric cement, is limited geographically and has uncertain long-term

durability properties. Although	these systems exhibit through-solution chemistries	and produce gelated

products, the reaction	mechanisms and	pathways are somewhat different than	those of the portland	

cement family	of crystalline starting materials. Not nearly	as	much work	has	been done on the kinetics	

of such	reactions; however, a well-established qualitative	reaction path process has been worked out

and to some	extent portions of the	process have	been reduced to mathematical formalisms for subsets

of materials (high	calcium containing systems). Like	portland cement, there	is no unifying	quantitative	

theory at	this time that	has been reduced to mathematical expressions. Thermodynamic models,

coupled to kinetic	expressions	via solution phase composition, have been	demonstrated	to	predict the

phase assemblage	and porosity quite	well,	though the paucity of thermodynamic data for	low calcium

systems	limits	the further development of such models	at this	time.

Supersulfated cements share	kinetic aspects of both the	portland cement family of alternative	cements

and the	alkali activated family. This class of alternative	binders almost exclusively utilizes blast-furnace

slag as	a starting raw material.	 Slags, typically containing higher alumina contents, are mixed with

calcium sulfate (or hydrated forms	or waste streams containing significant amounts of the same) and an

alkaline	activator. The	resulting products are	large	amounts of ettringite	and C-S-H	with smaller

amounts of hydrotalcite	due	to the	relatively high MgO content of the	slag. The	production of ettringite

and C-S-H	make supersulfated formulations related to portland cements, though the glass phase	

dissolution	process differs from the crystalline C3 dissolution in portland cements. Interestingly,

supersulfated cements	exhibit an initial peak, dormant stage	and main hydration peak. Once	again,

use of this alternative binder system is presently driven	by CO2 reduction. It	does not	appear	that	a

significant effort has	been directed towards	discovering mechanistic	aspects	of the hydration process or

development of mathematical models, the latter	of	which follows from the former	in most	cases.

It appears that these forms of alternative binder systems share many aspects in common with portland

cement, including through-solution reaction mechanisms, shrinkage, and metastable products.	 And,

while alkali activated systems are mechanistically different, for those binder systems that are based on

aluminate	and sulfoaluminate hydrates, there is kinetic commonality with	portland	cement. Therefore,

one might conclude that studies in	any of these areas would	be cross-cutting among the calcium-silicatealuminate-sulfate-ferrite systems. More importantly,	it is likely that a modeling tool capable of

describing the hydration	of portand	cement at fundamental chemical and physical level would be able

16
 
to accommodate any of	these alternative systems, provided	that thermodynamic and	kinetic data are

provided.

III. Reconciliation with Other Vision Statements

This vision for cement hydration kinetics does not and	must not stand	in	isolation	from other industry

visions. It must be reconciled with “Roadmap 2030,” the concrete industry’s plan for achieving a more

21st sustainable, cost effective and improved concrete for the century, published in 2002 [6].	

So, how does the vision	for cement hydration	kinetics relate to Roadmap 2030? The following four	

“critical research areas necessary	to propel the industry	forward,”	were identified by	industry	experts

and reported as the	basis of Roadmap 2030:

1. Design and Structural Systems

2. Constituent Materials

3. Concrete Production, Delivery, and	Placement

4. Repair and	Rehabilitation

Within each of these four areas, numerous subtopics and “specific research needs” were identified.

Each of these four areas will be addressed separately to illustrate	the	intimate	relationship between

hydration	and	these focal topics. Collectively, there are 130 specific research	needs identified in

Roadmap	2030. Of	these, 55 appear to be	unique	needs that are	directly related to hydration; these are	

listed in Tables I through IV.	 This tabular format	mimics the one used	in	Roadmap	2030 for easier

subsequent comparison. It is important, however, to recognize that concrete is a complex material and

that	hydration is not	the only factor	that	controls	its behavior.

Design and Structural Systems

Within Design and Structural Systems, seven research sub-topics were identified and within these seven

sub-topics, 38 specific research needs were listed in Roadmap 2030. Among these 38 specific needs, 13

would	directly benefit from having a comprehensive understanding of hydration. These 13 specific

needs cut across six of the seven	sub-topics.

Constituent Materials

Four sub-topics related to Constituent	Materials were identified. Thirty-nine unique specific needs

were itemized as important enabling technologies. Hydration outcomes can be directly linked to 20 of

these specific, excluding those areas that	were duplicated or	represented under	another	heading.

Concrete Production, Delivery, an Placement

The topic Concrete Production, Delivery and Placement includes four sub-topics and a total of	26 specific

research needs. Of	these, 14 are	directly related to hydration, all are	duplicated under either Design and

Structural Systems or Constituent Materials.

Repair an Rehabilitation

There are three sub-topics listed under	Repair	and Rehabilitation along with 27 specific research needs.

Eight of these specific needs are linked to hydration, and all are	duplicated under one	of the	other main

topics.

17
 
IV.	 Vision for Cement Hydration

This vision for	achieving an understanding of the kinetics of cement hydration was developed to provide

the research community with focal points for	directing immediate and short-term research that	should

be undertaken	within	the next	three to five years. Among the most	pressing issues at	hand are those

that	will impact	the design of	cementitious materials and systems that	lead to smaller carbon footprints	

and hence	improved life	cycle	performance. Although significant progress	has	been made in the past

ten years towards development	of	modeling platforms for	cement	hydration, thus far	they are mostly

limited to hydration of neat C3 (C3 in the	absence	of organic or inorganic admixtures or other cement

or mineral phases) and	even then a unique model is not yet available that describes the range of

observed	behaviors. Furthermore, the body of existing experimental information	is sometimes

contradictory	or at least can be interpreted using more than one hypothesis. In the absence of clear and

detailed	mechanistic information, the near term development of modified	and	new cementitious

systems, optimized utilization of waste and by-product materials and	discovery of new admixtures, will

continue at the present slow and costly	pace.	 The research needs identified by Summit participants are

formulated here as either	questions or	statements. The list	of	needs is not	intended to answer	the

questions, but rather to	pose them. Nor does the list represent a proposed	solution	but rather

supposed elements	of the solution. Recognizing also that the topical areas	discussed above are not

isolated from each other, but rather that they are highly interrelated, the following list is suggested in an

effort to “pave	the	way for more	sustainable concrete infrastructure via the development of a

comprehensive description of cement hydration kinetics.”

IV.I	Hydration Mechanisms

1.	 Does a semi-permeable layer actually form at early ages? A affirmative answer might lead	to	

pathways for either preventing its formation or prolonging its existence.	 If there is such a layer,

knowledge of the trigger for its disappearance (e.g. thermodynamic	or mechanical instability)

could lead to the design of admixtures	for targeting that trigger.

2.	 What role is played by surface defects, such	as stacking faults and	dislocations, in	governing the

dissolution	rates of clinker phases in	cement? Answering this question	could	lead	to	approaches

such as	annealing or chemical/mechanical pretreatments that could	optimize defect	structure

and frequency.

3.	 To what extent do species in solution adsorb on cement phases or hydration product phases and

modify the dissolution or growth rates of those phases? There is persuasive evidence that

adsorption of calcium sulfate	onto active	dissolution sites	of aluminate phases	is	responsible for

the set-controlling properties	of gypsum in cement, but understanding in this	area is	still in its	

infancy.

4.	 What are the transport properties of the bulk C-S-H	products formed and how do they evolve

with time?

5.	 Does C-S-H	form by a two-stage growth process	and what is	the bulk density of C-S-H	as a

function of	time?

6.	 When and where do C-S-H	nuclei form and what is the formation rate?

7.	 What factors are responsible for the strong interactions between silicates and aluminates in

cement clinker hydration? There is	recent experimental evidence that incorporation of

aluminate	ions in C-S-H	is highly dependent on aluminate concentration in solution, which also

can poison its growth rate.

8.	 What are the forms of the rate laws (e.g., the reaction order)?

18
 
9.	 Along with	(8), what are the elementary reactions that control the reaction	rates, not only at

early age, but at any age?

10. What is the actual morphology of C-S-H	growth and what controls the morphology since many

forms have been	observed?

11. Are there signatures in	early-age	calorimetry measurements that	indicate long-term kinetics and

performance?

IV.2 Modeling and Simulation

1.	 Continue to	develop	various solution	phase driven	models that incorporate kinetics,

thermochemistry and transport phenomena.

2.	 Develop multiple modeling paths and strategies that corroborate findings and lead towards

useful engineering tools as well as model-based	research	instruments including fast algorithms

for	PC and similar	platforms.

3.	 Continue to extend and exploit computational resources as necessary and needed	to	

accommodate	changing needs (i.e., utilize massively	parallel processing	and supercomputer

facilities as needed).

4.	 Pursue alternative	computational strategies to accelerate	the	development of rigorous models,

i.e.	fast single particle models, representative volume approaches, etc.

5.	 Exploit the body of knowledge on true multi-scale modeling.

6.	 Improve the dissemination of modeling tools to	promote their use and	development.

7.	 Incorporate more molecular-level	modeling strategies (e.g., kinetic Monte Carlo)

8.	 Develop suitable structural analogs for various anhydrous and hydrated cement phases for use

in molecular modeling.

9.	 Develop focused experimental program driven in part by	model development and designed to

provide information	for parameter estimation	and	to	answer mechanistic questions. Specific

questions that must be addressed	experimentally and	within	the construct of existing and new

models to be developed were included in Section III (Mechanisms)	above.

IV.3 Experimental Techniques

1.	 Extend as necessary and apply the vertical scanning interferometry (VSI) technique in an

attempt to answer at least portion of the	questions regarding	dissolution	mechanisms.

2.	 Further develop X-ray nanotomography into a quantitative technique and apply it	to study the

rate of	cement	phase reaction in both model systems and portland cements and for	blended

systems	containing silica fume, blast furnace slag and	fly ash.

3.	 Further explore	the	use	of nuclear resonance	reaction analysis (NRRA) as tool for elucidating

the barrier	layer	hypothesis.

4.	 Establish an open network with researchers in the broader community, both those doing

modeling and experimentation, so	that they have access to	datasets and	instrument time on

unique tools such	as VSI, X-ray nanotomography, NRRA and TDDS.

IV.4 Admixtures

1.	 Identify the paths	and kinetics of reaction for different admixtures in cements with different

amounts and availability of sulfates.

19
 
2.	 Identify the paths and kinetics of reaction for different admixtures with the	crystallographic

forms seen in typical alite, belite, aluminate and ferrite phases.

3.	 Build	computer models based	o knowledge generated	in	1 and	2 above to look at	how

hydration	kinetics is impacted	by different admixtures in	different cementitious systems.

4.	 Identify the elementary steps (reactions and kinetics)	for	classic hydration	acceleration	and	

retardation (e.g., for	CaCl2 and sucrose	activity, respectively) at dosage	rates practiced	by the

industry.

5.	 Identify the elementary steps (reactions and kinetics) for strength enhancement of different

alkanolamines and how the differences in solubility of alkanolamines in pore	solution impact the

paths and kinetics of reaction.

6.	 Isolate and identify physiochemical	interactions of different admixtures with various cement

surfaces	and quantify the rate controlling processes for	each process.

7.	 Isolate and identify chemical	interactions with various cementitious ionic species, for example,

the rate of	Ca+2 chelation by	sucrose and other admixtures, the rate of	Fe3+ chelation by	

alkanolamines, or the rate of	Al3+ chelation by	other admixtures.

8.	 Identify and model	the fates of dispersant, sulfates, and retarders whether added separately or

at the	same	time.

9.	 Understand how formation of etch pits or other defects o the silicate and	aluminate surfaces

are	impacted by the	different admixtures

10. Design experiments explicitly to be used for kinetic model development with the objective of

having quantitative outcomes than	can	be used	to	develop	and	refine models.

IV.5 Supplementary Cementitious Materials

1.	 Isolating the rate of reaction of SCMs is generally very	difficult. Most reactive SCMs	are

amorphous rather than crystalline and some, such as fly ash, contain more than one reactive

constituent; that	is, fly ashes may contain more than one reactive glassy phase each having its

own	reactivity.

2.	 So called “filler effects” are	difficult to separate	from chemical effects since both may have	

similar apparent outcomes, e.g. slightly altered size and location of the primary calorimetry peak

(Stage 3 and 4).

3.	 Generalized solubility models for the range of glassy phases are not readily available.

IV.6 Alternative Cements

1.	 While there are kinetic datasets for the various classes of cements, there is no cohesive unified

theory for the common	cement forms (i.e., those that	are indirectly derived from the portland

family of	anhydrous crystalline cements and those derived predominantly from glassy raw

materials and requiring high alkali content activator solutions).

2.	 Although	the kinetic processes share features in	common	with	those of C3S-based	cements, it

seems	that side-by-side studies	of these features	have not been conducted.

3.	 There is general lack of information regarding long-term durability for	many classes of	

alternative	cements. While	somewhat outside	of the	scope	of this document, it should be

acknowledged that	this is an obstacle to the widespread development and use of such materials.

4.	 There are number of economic hurdles at this time, including the use of bauxite as raw

material and the high cost of alkali agents.	 Further development or materials engineering might

reduce production cost and enable the introduction of alternative cements	into various	markets	

where they are presently not economically viable.

20
 
IV.7 General Comments

1.	 There is general lack of resource organization and dissemination of tools for modeling cement

hydration. national resource for hydration	data should	be considered	wherein	a database of

computer models, thermophysical properties	(thermodynamic	datasets	and thermodynamic	

models), crystallographic information files (CIF), kinetic datasets, models and modeling tools and

their	associated source codes, etc., can be easily accessed by the research community at	large.

Huge amounts of time are spent by research teams searching for, reviewing and assembling

such information independently.

2.	 There is presently no focal point for hydration	research	in	the US, but there should	be. Concrete

is	the primary building material for	the world’s infrastructure and the US must	continue to

remain competitive and be a global leader	in concrete materials technology. The lack of a

generalized, universal theory	governing	chemical transformation kinetics,	microstructure

development rates and properties of complex hydrate	synthetic mineral-based	materials

impedes the pace of development.

3.	 It appears that some alternative cement systems exhibit kinetic features that are like those of

the C3S-based	portland	cement system, including behaviors such	as an	early dissolution	peak,

dormancy and	a main	hydration	peak, i.e. super-sulfated cements	and calcium sulfoaluminate

cements. While this	is well	known among the community of researchers, it might be beneficial	

to study such systems side-by-side in an effort to resolve common or dissimilar features	that

could lead to a more refilled and clarified mechanistic	theory	of cement hydration.

21
 
Table	I. Design and Structural Systems*

Specific	Research Needs

Structural Concrete

• Chemical bonds

Altering	the strength	of such	bonds requires detailed	knowledge of the chemical structure of the surfaces involved.

• Changes du to	relaxation, creep	and	shrinkage

Current models for relaxation, creep	an shrinkage are mostly empirical or linked	to	poorly defined	material, microstructure

an hydration	definitions.

• Chemical factors such	as freeze/thaw, chlorides, and	sulfates

Interactions between concrete and	the environment are dependent upo detailed	knowledge of the pore structure an the

chemistry of the	nano- an micro-scale composite nature of hydrated cement.

• Direction,	speed,	location and cycling of external	loading or internal	forces

Multi-scale models for the prediction of load transference and resulting mechanical	properties and performance of concrete

will not be possible until a comprehensive description of hydrated cement is available.

Reinforced	Concrete

• Improved ductility of high-performance concrete

Ductility is not just a reinforcement issue, but involves understanding the nature of the matrix that supports the

reinforcement. Presently, we have almost	no way to modify the matrix. If, however, we had knowledge of	how hydration

happens an what factors can be changed to alter the chemical and physical structure of the hydrates, it may be possible to

engineer ductility	via matrix	modifications rather than depending solely	on reinforcement-based	approaches.

• Corrosion- and reinforcement-free bridge deck

The concept of corrosion	an reinforcement-free decking materials will only be possible through controlled cement	

hydration	an modification	of the concrete from the matrix (cement) perspective.

Modeling and Measurement

• Service life design models

Service	life	design models are	only	as good as the	underlying models for	prediction of properties, i.e. permeability, strength,

creep, shrinkage. While	models	are	presently available, most are	empirical and require	calibration against large	datasets	

of	experimental information.	 Ultimately, service life depends upon the chemistry and microstructure of	concrete, neither	of	

which can be adequately predicted without knowledge of hydration mechanisms.

• Durability models that predict interaction of stress and	environmental factors

Similarly, the	weakness in present durability	predictions is identical to the	weakness in present service	life	models. At the	

heart of these durability models are poorly predictive hydration models or no models whatsoever.

• Smart materials

Altering	concrete to	produce “smart” materials will be greatly accelerated	by hydration	information.

High-Performance	Concrete

• Curing	technologies

Curing	is hydration	an hydration	kinetics related	phenomena.

• HPC mixture optimization software

While there are many forms of mix optimization software, none will ever achieve predictability without detailed	knowledge

of hydration	kinetics.

Technology Transfer

• Accelerate[d] technology transfer

The ambition	here is to	reduce the time to	bring	new technology to	practice from 1 years to	two	years by 2030. Hydration	

models would enable this by making it possible to simulate material performance and to run only a limited number of

targeted field tests based on reliable predictions.

Fire-, Blast-,	and Earthquake-Resistant Materials and	Systems

• Fire-resistant, high-strength concrete

Fire resistance is complex problem for composite materials an depends upo detailed	knowledge of the composite

structure at all length-scales.

*Text in bold print matches or is paraphrased	from Roadmap	2030.
 

22
Table II. Constituent Materials Research	Needs

Specific	Research Needs

New Materials

T achieve the following	list of “specific needs” it will be critical to	understand	how to	control cement hydration. These

“needs”	can be	summarized as controlling and predicting the	performance	of concrete	and explicitly	call for manipulation of

chemical factors that	are directly linked to hydration of	the cement	matrix and its resulting structure.	

• Families of innovatively	manufactured concrete with predictable performance

Concrete will not be predictable without predictable cement hydration	kinetics.

• New materials to reduce shrinkage and cracking

Shrinkage	and cracking begin at early	age	and various forms continue	throughout the	lifecycle	of the	concrete	structure.

Both	shrinkage an cracking	are linked	to	hydration	kinetics an microstructural outcomes.

• Reduction of alkali-silica reactions	in concrete

This is fundamentally chemical an chemical kinetic problem.

• Materials for active and passive corrosion prevention

Corrosion of embedded steel is associated with the matrix chemistry and microstructure.

• Reactive	powder concretes

Reactive powder concretes begin	with	highly reactive cements that have engineered	particle distributions an in	some

cases	chemical compositions. The	performance	of such is	a classic	problem in chemical kinetics.

• New admixtures, e.g., corrosion-inhibiting,	self-consolidating	[and] leveling, reduce reinforcement

Thoug there is large body of literature o admixture behavior, it is mostly qualitative. The research	community at large

would agree that little is known	about the mechanistic interactions of admixtures an hydrating	cement. Knowledge of

such would greatly accelerate the pace of admixture discovery and design.

• Cements of specified performances

This is fundamentally chemical design	problem an cannot be	achieved until a more	mechanistic	description is available	

for	cement	hydration.

• Cement produced with improved energy efficiency and reduced environmental impact

The design	of new low-environmental impact cements will come	along with our ability	to control the properties and

performance at the hydration	stage. Producing	concrete that is more durable an lasts longer, for example, is one way to

reduce environmental impact.

• Performance-based	standards

This concept is difficult to	achieve reliably without better predictability	and control of the	materials.

• New materials from novel waste streams

The problem with	using	waste stream materials is linked to chemical	interactions with cement during hydration.	

Limitations on the	use	of fly	ash and narrow specifications for	suitable ash compositions are directly linked to our	inability

to predict	and control chemical reactions during hydration.

• Supercritical carbon dioxide research for rapid strength

The use of supercritical carbon	dioxide for modification	of cement properties is chemical reaction	an likely transport

phenomena	controlled	process.

Performance	Measurement and Prediction

Achieving	the following	“specific needs” are all dependent upo having	detailed	knowledge of hydration	an hydration	

kinetics. Predictability	of properties will only	come with confident, mechanistic-based	hydration	models. “Modeling” is a

theme throughout	these specific needs.

• Prediction methods and models for permeability, cracking, durability, and performance	(including environmental

interactions)

• Tools and	data for quantifying	benefits of using	alternative	materials

• Measurement and prediction of self-desiccation	in	concrete

• Multi-scale modeling to connect microstructure with engineering properties

• Predictive	models to augment/replace	QC	tests

Reuse and	Recycling

Hydration kinetics will ultimately govern how and if these specific needs can be addressed. At this point, most of what we

know about the	following four areas	is	qualitative	or empirical at best. Hydration kinetic	studies will	eventually provide

opportunities to	realize these needs or impose constraint which	govern	the limits of applicability.

• Reuse	of high-alkali wastewater

• Aggregate recycling

• Incorporation of waste and by-product materials from other industries

• Reuse	of cementitious materials, cement kiln	dust, and	other waste	products

Table III. Concrete Production, Delivery, and	Placement

23
Specific	Research Needs

Information and Control

• Techniques to	optimize, predict, and	verify concrete	performance	(see	Constituent Materials)

• Modeling and measurement systems to predict and control properties (see Constituent Materials)

Production, Delivery, and Placement

• Controlling curing

• DEF as relates to accelerated curing

Delayed ettringite formation is a chemical reaction and transport	problem.

Test Methods and Sensors

• Procedures and technologies for tests in the	curing process (see	Design and Structural Systems)

• Improved on-site monitoring of concrete during early age

The early age period	is dominated	by hydration	kinetics.

• Tests and	models to	predict cracking	and	strength	development immediately after setting

The period	immediately after setting	is very dynamic period	still dominated	by hydration	kinetics. The mechanical

response of concrete during	this time frame is intimately coupled	with	the rate at which	cement is hydrating.

Energy and Environment

• Aggregate and alkaline water reuse (see Constituent Materials)

• Increased use of waste streams via	the use of validated, integrated	models to	optimize	concrete	formulation	(see	

Construction Materials)

• “Cradle to grave”	assessments (see Design and Structural Systems)

• Recycling of concrete	(see	Construction Materials)

• Carbon dioxide	reduction (see	Construction Materials)

• Admixtures to	eliminate	steam cleaning/curing	precast (see	Construction	Materials)

• Frost-resistant, non air-entrained	concrete	(see	Construction	Materials)

24
 
Table IV. Repair and	Rehabilitation

Specific	Research Needs

New Repair Materials

• Self-repairing (damage-insensitive) concrete

Self healing is a chemical phenomenon which will be difficult if not impossible to predict and model without detail

microstructural, transport and kinetic information for cement paste and concrete at a broad spectrum	of ages.

• Heat-resistant pavements	(see Design and Structural Systems)

• Adhesives to improve bond between repair layers and substrate (see Design and Structural Systems)

• Repair of sulfate	damage	with sulfate-resistant concrete (see Design and Structural Systems)

Assessment Tools and	Modeling/Measurement Technologies

• Model development (see Construction Materials)

Repair Field	Process Technologies

• Mitigation of alkali-silica reactivity in existing structures	(see Construction Materials)

• Corrosion-Canceling technologies (see	Construction	Materials)

• Admixture research to stay abreast of changing performance requirements (see Construction Materials)

25
 
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