# Presentation: 103221

## The Virtual Cement and Concrete

**Testing Laboratory**
**J. Bullard, D. Bentz, E. Garboczi, C. Ferraris, N. Martys,**
**and P. Stutzman**
**Materials and Construction Research Division**
**National Institute of Standards and Technology**
**Gaithersburg, Maryland**

## Virtual Testing in a Nutshell

- Physical tests on concrete require large amounts of material and long times ( ~ 28 days)
**Idea**:  Provide computer models with a virtual representation of the material and simulate the results of physical  tests
**Applications**:

- Design of new materials
- Supplant QA testing
- Understanding

## Why Concrete?

- Concrete is the **2nd** most widely consumed
- resource on the *planet* (on a mass basis)

- Concrete is fairly inexpensive on a mass  basis (compared to metals, ceramics), BUT
- It is produced in huge quantities:
-  6 billion metric tons produced globally
-  1 billion metric tons cement produced globally
- U.S. production of $8.3 billion/year in 2000
- Trimming production costs by pennies per ton is a big benefit  **streamline testing**

## What Needs To Be Tested ?

## What IS Concrete ?

**Macro-scale**

*Courtesy Portland Cement Association*

- Mix to form a 3D random composite with time-dependent chemical and physical properties

- Coarse Aggregate
- Binder
- Sand
- Cement Paste

***The clue is the glue***** (F. Ulm, MIT)**

## What IS Concrete ?

- 250 μm

- 150 μm

- 75 μm

- Up to 15 starting
- phases ...

- ... as many as 32 phases
- during hydration; at least
- half are amorphous or
- poorly crystalline

**What IS Concrete ?**

## What IS Concrete ?

**Nano-scale: C-S-H**

- 50 nm

- CaxSiO(2+x)·H2O

**Porosity**

- “IP”

- “OP”

***Micrograph courtesy of I.G. Richardson,***
***University of Leeds***

**What IS Concrete ?**

_**Silicate chemistry**_
- Only organic is more complicated
- Wide range of compositions and structural variants

- Growth by condensation of hydroxylated silicate mers in solution.  Morphology depends on temperature and composition

**Notes:**
C-S-H is a silicate-based gel.  Silicate chemistry is the most complex chemistry next to organic chemistry.
Ionic silicate tetrahedra are covalently bonded to each other in chains, sheets, or 3-D networks.  They can accommodate large amounts of ionic impurities that modify the structure (e.g. glasses).  The free energy differences between the different structures are relatively small, so that the structures that form are often sensitively dependent on local growth conditions.

## What IS Concrete ?

- Ca3SiO5 paste, 20°C, 8 yr

- Ca3SiO5 paste, 80°C, 8 d

- “IP”

- “OP”

- “IP”

- “OP”

***Micrographs courtesy of I.G. Richardson,***
***University of Leeds***

**What IS Concrete ?**

**Notes:**
Two radically different morphologies for C-S-H gel:  inner and outer product.  OP form favored when growing into free pore solution volume.  IP is denser and finer, formed in constrained volumes at the C3S/CSH interface.

## What Hope Is There ?

- Materials scientists usually target **MUCH** simpler materials for predictive modeling (Cu, MgO, etc)

- Added complexity built into models only after simpler systems are understood (e.g. metal alloy models built from models of single component metals)

- With **concrete**:
- Interdependent, multiscale phenomena
- Experiments are difficult to design and often ambiguous

## What is the Goal of Modeling ?

**Predict Behavior of Complex Materials**

**Increase complexity; repeat**

_**Science**_

- Extrapolative
- Solid foundation
- Costly

## Virtual Cement and ConcreteTesting Laboratory

**1982** – Development at NIST, under Geoff Frohnsdorff’s leadership, by Hamlin Jennings of first simple cement hydration model (continuum based)
**1989**
- NIST starts developing first (primitive) pixel-based simulation of cement hydration (Bentz & Garboczi)
- NIST starts developing finite difference methods for computing properties of pixel-based systems (Garboczi)
**January 1, 2001** – Start of **VCCTL Consortium**
- Led by NIST (BFRL and ITL)
- Charter membership of six industrial partners
- Organization and further development of user-friendly software based on 20+ years of NIST research
- Software product = VCCTL

## VCCTL Models

- Develop predictive models of real concrete by building in as much materials science, physics, and chemistry as we know:
**Hydration**           **Rheology**         **Mechanical Properties**
- Leverage computational power to apply these principles to complex chemistry and physics of concrete
- Check predictions against experiment
- Agreement:  GOOD!
- Disagreement:  Build in better science or use fitting parameters/empiricism to make predictions better

**    ****Philosophy**

## Virtual Cement and Concrete Testing Laboratory

**Vision****:****  **Integrate and enhance NIST’s state-of-the art computational materials science models into a tool that is relevant and useful to industry.

- Hydration

- Mechanical
- Properties

- Rheology

- Durability/
- Service Life

**Prediction**

- Material	 Database

- Microstructure Creation

- GUI Web
- Interface

## Integrated Modeling Approach

- 3-D Microstructure-Based
- Spatial resolution at the sub-particle level using small volume elements (1 μm cubes)

- input μ-structure
- model hydration
- of μ-structure
- predict properties
- compare w/ experiment

- Digitize

- 20 μm

- Each volume element has properties
- of the phase at that location in space

**Notes:**
A variety of WEB authoring and programming tools are utilized in the VCCTL.  The system uses HTML forms to provide a familiar interface for the users.

## K

- Ca

- Si

**K**

- Al

- ... X-ray element
-      maps ...

- ... segment image into **phases **...

- SEM/BSE Image...

- Measure autocorrelation fns on majority phases

- ... Particle Size Distribution ...

- Reconstruct 3D Image

_**Contributors**_**:  D. Bentz and P. Stutzman**

## “Extract” particle/aggregate shapes,

- “Extract” particle/aggregate shapes,
- then mathematically analyze
- and store them

_**Contributor**_**:  E. Garboczi**

## 3-D image 

- 3-D image
- of model
- cement
- particles

- Captures
-  Volume fractions
-  Surface fractions
-  PSD
-  w/s ratio

## Module forCement Paste Hydration

_**Contributor**_**:  D. Bentz**

**Notes:**
To have any chance of simulating microstructure development and predicting performance, quantitative and extensive characterization of the raw materials (particularly the cement) is critical.

Only when we have characterized the starting materials can we have any hope of predicting what will happen when water is added to the system.

## CCRL Proficiency Sample 135w/c = 0.4, T = 25° C

**CCRL Proficiency Sample 135****w/c = 0.4, T = 25****°**** C**

**Degree of Hydration**

## CCRL Proficiency Sample 135w/c = 0.25, T = 25° C

**CCRL Proficiency Sample 135****w/c = 0.25, T = 25****°**** C**

**Setting Time**

**Vicat****Needle**

**Gilmore****Needle**

## CCRL Proficiency Sample 135w/c = 0.3, T = 25° C

**CCRL Proficiency Sample 135****w/c = 0.3, T = 25****°**** C**

**Chemical Shrinkage**

## Module forRheological Properties ofFresh Concrete

_**Contributors**_**:  N. Martys, C. Ferraris**

**Notes:**
To have any chance of simulating microstructure development and predicting performance, quantitative and extensive characterization of the raw materials (particularly the cement) is critical.

Only when we have characterized the starting materials can we have any hope of predicting what will happen when water is added to the system.

## 
Micro:  cement in water	         (Cement Paste)
Milli:    sand in cement paste       (Mortar)
Macro: coarse aggregates           (Concrete) 

**Micro**:  cement in water	         (Cement Paste)
**Milli**:    sand in cement paste       (Mortar)
**Macro**: coarse aggregates           (Concrete)

**Concrete Rheology is a Multiscale Problem**

**Approach**:
- Experiments on simplified, model systems
- Simulations based on Dissipative Particle Dynamics

## DPD Simulation ofConcrete Rheometers 

- Parallel Plate

- Coaxial

- Top Plate

- Bottom Plate

- Top View

## Self-consolidating Concrete

**Self-consolidating Concrete**

**Notes:**
Prenons comme cas d’étude un béton autoplaçant, qui par définition s’écoule à travers les obstacles sans aucune vibration. Le béton est simulé dans un premier temps par une suspension concentrée de granulats sphériques monodisperses dans un mortier. Le mortier est considéré comme un fluide newtonien homogène et est caractérisé par sa viscosité plastique. La distance entre les armatures est fixe mais la viscosité du médium (mortier), la dimension des granulats et la concentration en granulats sont variables.
Les mécanismes de blocage peuvent ainsi être étudiés. Les informations qui peuvent être alors être déduites de cette simulation sont: 1) la vitesse d’écoulement; 2) la granulométrie optimale des granulats (gravillons); 3) la viscosité idéale du mortier; 4) la concentration idéale en granulats; et 5) l’influence de la forme des granulats (sphériques, concassés...). L’opérateur peut ainsi étudier numériquement différents scénarios (sans avoir à gâcher de béton). 
Cette figure et la suivante montre deux exemples de résultats obtenus. Un film captant les images successives du flux fut produit  et on peut voir le flux de particules
Differents points de vue peuvent être visualisés soit en représentation 2-D soit en 3-D sur un écran RAVE (Reconfigurable Advanced Visualization Environment) au NIST. 

## Module forMechanical Properties of Concrete

_**Contributor**_**:  E. Garboczi**

**Notes:**
To have any chance of simulating microstructure development and predicting performance, quantitative and extensive characterization of the raw materials (particularly the cement) is critical.

Only when we have characterized the starting materials can we have any hope of predicting what will happen when water is added to the system.

## Elastic Properties of Cement Paste

## Cement Paste Elastic Moduli

**Cement Paste Elastic Moduli**

## Moduli and Strength of Concrete

**Effective Medium Theory (EMT)**
- Provides estimate of **elastic moduli** of mortar and concrete

- _Input_:
- volume fractions of air, aggregate
- elastic properties of paste and aggregate
- thickness and elastic properties of ITZ

**5 %**

**1 %**

**12 %**

**5 %**

- Compressive strength estimated from empirical relation (Neville)

## VCCTL Consortium:  5th Year

## VCCTL Consortium: Year 5

**Rheology**

**User**
**Interface**

**HydratiCA:  Next-generation hydration model**

**Systematic validation effort underway**

**Influence of aggregate size distribution on viscosity**

**Real-shape aggregate effects**
**Influence of lubrication and inter-particle forces on rheology of fresh concrete**

**Menu driven**
**Graphical output **
**Rebuild for v6.0, enable better session management & database interactivity**

** ****Version 5.0:**

**Thermodynamic and kinetic framework for microstructure development**

**VCCTL Consortium: Year 5**

- Restructured for better administration and communication
- Industrial Advisory Board
- Focused working groups
- Narrower scope to accelerate research in two key areas
- Hydration modeling
- Rheology modeling

## Final Remarks

- VCCTL software can be used to
- Streamline testing and save $$
- Two industry projects which realized cost savings
** ****~ $1M** in one month (Dyckerhoff)
** ****~ $700K** in several weeks (Cemex)
- Expedite design of new materials and admixtures
- Help educate students and professionals
- Drive changes in standard test methods