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Chemical Admixtures –Science, Technology and Applications over the Years

Dr. Bruce J. ChristensenVice President Global Technologies and Innovation ManagementBASF Construction Chemicals Ludwigshafen, Germany

The Institute of Concrete Technology - 40th Annual ConventionWarwickshire, UK22 March 2012

PRE‐HISTORIC TIMES

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Pre-historic TimesFirst Known Uses of Chemical Admixtures

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In the dawn of mankind is where it all began ...

Cave painting:The prehistoric version of construction chemicals: architectural paints

Opus CaementitiumThe precursor of concreteburned lime stone, sand, aggregate and volcanic ashplus the first admixtures:

milk, eggs, animal blood as organic binderspig fat, wax, bitumen as waterproofing agents

PRIOR TO THE 1950’s

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Prior to the 1950’sWater Reducers

First used in the 1920’s/1930’s

Sulfonated lignin from the paper making industry was one of the first chemistries

5-10% water reduction possible

Mechanism is deflocculating and dispersing the cement particles by electrostatic repulsion

Main disadvantages are retardation of set and unintentional entraining of air at high dosages

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cement grains

Prior to the 1950’sAir Entraining Admixtures

First reported uses in the 1930’s

Based upon wood resins (phenolics, carboxylic acids and other residues)

Benefits for workability and freeze-thaw protection well documented

Many factors that affect performance

Temperature

Gradation of fine aggregate

Alkali content in the concrete

Interactions with other admixtures (i.e. BNS superplasticizers)

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water

Air -Void

T0 < 0°C9% vol increase

ICE

T0 > 0°C

Prior to the 1950’sAccelerators

First reported uses in the late 1800’s, making this class likely the first class of modern admixtures

Calcium chloride is the best known, readily available, and inexpensive material

Dosages of 2% by weight of cement typically used

Main disadvantage is acceleration of steel corrosion, as well as some discoloration of the concrete when used at high dosages

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0

2

4

6

8

10

12

Control 6.5 mL/kg 13.0 mL/kg 39.1 mL/kg 58.7 mL/kg

Setti

ng ti

me,

hou

rs

-1C curing10C curing21C curing

1950 ‐ 1980

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From 1950 to 1980Retarders / Water Reducers

Despite the effects being known from the early water reducers, little is published on the topic until the 1960’s

Hydroxylated polymers or carbohydrates (sugars) most widely used

0.05-0.2% dosage typical

5-8% water reduction possible with some materials

Main issue is susceptibility to biological activity (need biocides)

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OH

MeOSO3Na

CH2OH

OHn

OH

COOHCOOH

HOOC

O

OH

CH2OH

OH

OCH2OH

OHOH

OH OHO

OCH2OH

OH

OH

On

From 1950 to 1980Alkali-Silica Reaction Mitigation Admixtures

Failure of concrete due to water-induced expansion of ASR gel

First reports of chemical solutions in the early 1950’s

Lithium salts the most common chemical admixture solution

Main disadvantage is high cost

Other potential solutions

Use alternative aggregates Reduce alkali content Use SCM’s like flyash Combinations

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2 different reactive aggregates

From 1950 to 1980Corrosion Inhibiting Admixtures Ingress of chloride into concrete causes

corrosion of the steel, with subsequent expansion and spalling of the concrete

Many materials screened until the 1970’s, but not until then was calcium nitrite identified as one of the most suitable

Passive anodic corrosion inhibitor

Does not prevent chloride ingress, but increases the threshold until initiation

Works on the anodic portion of the electrochemical cell

Best protection / durability achieved when combined with silica fume and a HRWR

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From 1950 to 1980Superplasticizer/High Range Water Reducer

One of the most significant developments in admixture history

First introduced in Japan and Germany in the late 1950’s and early 1960’s

Synthetic polymers that provide water reductions to 35% or more

Mechanism is highly effective electrostatic dispersion

BNS more widely used than SMF due to better slump retention, solution stability and cost

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SO3M

CH2 n

CH2OH

N N

N NHCH2O

NHCH2SO3M

NH

Hn

Sulfonated β-Naphthalene formaldehyde condensates

(BNS)

Sulfonated Melamine formaldehyde condensates

(SMF)

The 1980’s

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The 1980’sMid-Range Water Reducers

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First introduced in North America in the last 1980’s

Origins due to gap in performance between WR’s & HRWR’s

Based upon lignosulfonates and set-balancing ingredients

Water reductions over 15% (or slump increase to 100-125 mm)

Normal setting (<1.5 hour delay)

Finishing characteristics reported to be excellent

First introduced in Japan

Mechanism believed to be reduction of surface tension in the capillary pores

Based upon low weight alkoxylate adducts of low MW alcohols

Reductions in drying shrinkage of >50% possible

Requires use of synthetic AEA’s for adequate F/T protection

~10% reduction in early age compressive strength

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0

10

20

30

40

50

60

0 2 4 6 8 10

SRA DOSAGE (L/m3)

RE

DU

CT

ION

IN

DR

YIN

G S

HR

INK

AG

E (%

)

0

10

20

30

40

50

60

0 2 4 6 8 100 2 4 6 8 10

SRA DOSAGE (L/m3)

RE

DU

CT

ION

IN

DR

YIN

G S

HR

INK

AG

E (%

)

The 1980’sShrinkage Reducing Admixtures

-0,06

-0,05

-0,04

-0,03

-0,02

-0,01

0,000 7 14 21 28 35 42 49 56

DAYS OF DRYING

LE

NG

TH

CH

AN

GE

(%)

Control SRA-M3 @ 2 L/m3 SRA-M3 @ 4 L/m3SRA-M3 @ 6 L/m3 SRA-M3 @ 8 L/m3

The 1980’sHydration Control / Stabilization Admixtures

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First introduced in the mid 1980’s

Based upon phosphor-containing acids and/or carboxylic acids

Able to arrest the cement hydration for days, then be re-activated by addition of accelerator or waiting for “wear off”

Mechanism is based upon retards all the clinker minerals, not just some

Used for long hauls, wash-out slurries and overnight concrete stabilization

Excellent for keeping mix drums clean

25 hours

The 1980’sCold Weather / Freeze Protection Admixtures

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Extensively research in Russia in the 1960’s

First studied and used in the west in the mid1980’s

Mixtures of inorganic salts, polymers and other ingredients

Provide both freezing point depression and acceleration

Concretes batched at 10-12 C and cast at < -10 oC set at normal times (before freezing) and gain strength

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2

4

6

8

10

12

No admixture 6.5 mL/kg 13 mL/kg 39 mL/kg 59 mL/kg

Initi

al s

ettin

g tim

e, h

ours

CWA dosage

12 C @ batch-1 C Cure

(358 kg/m3 CEMIConcrete setting time, -11 oC curing

Dosage (ml/kg) Set (hr)CWA (39.1) 3.8CWA (39.1) + HRWR (5.9) 3.4CWA (58.7) + HRWR (5.9) 3.3

The 1980’sNext generation Superplasticizers / HRWR’s

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First developed in Japan in the mid 1980’s; introduced in Europe / Americas in the late 1990’s

Polycarboxylate ethers, which provide both electrostatic and steric dispersion - highly efficient

Tunable chemistry

Excellent slump retention, water reduction, strength development, setting time, finishing, …

Can entrain unwanted amounts of air without formulation

SHRWR molecules

Improved dispersion due to electrostatic and

steric repulsion

Cement particles

The 1990’s

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The 1990’sSynthetic Air Entraining Agents

First introduced in the early 1990’s

Based upon tall oil fatty acids and other sulfonated hydrocarbons

Typically generate finer, more stable air bubbles than resin/rosin type AEA’s

Better for use in highly fluid concretes, using particularly BNS or SMF HRWR’s

Excellent freeze-thaw durability

Can give a slight compressive strength reduction in some materials

May be some very fine bubbles not detectable by pressure methods

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Volumetric Method Pressure Method

The 1990’sMixed Mechanism Corrosion Inhibitor

Introduced in the early 1990’s

Based upon amine esters

Active-Passive Type

Reduces permeability of chloride ions into the structure

Increases the threshold level to initiate corrosion

Highly effective at providing corrosion inhibition

Requires synthetic AEA to achieve necessary air contents

Slight early age strength decrease21

Polar Group Hydrocarbon (CH2) Tail

The 2000’s

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The 2000’sViscosity Modifying/Anti-Washout Admixtures

Introduced decades ago in grout and mortar applications

First significant use in concrete appears to be in anti-washout applications in the late 1990’s

Popularized in the early 2000’s for use in low fines SCC, and in lean conventional slump mixtures

Based upon starches, gums, celluloses or synthetic polymers

Latest versions have no impact on setting times or air entrainment

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The 2000’sNext Generation PCE Superplasticizers

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10

20

30

40

50

60

70

0 6 12 18 24 30 36 42 48

Time , hours

Com

pre

ssiv

e s

trengt

h , M

Pa

PCE HRWR

HES PCE HRWR

HES PCE + NCA

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0

50

100

150

200

250

0 30 60 90 120 150Time (min)

Slum

p (m

m)

PCE SP 1

PCE SP 2

SSR

High Early Strength PCE

Accelerates the hydration by highly efficient dispersion

Combinations with conventional accelerators push it even further

Super Slump Retaining PCE

Very little water reduction

Extend the slump life by 2-3 hours, even in 120 mm slump

Normal setting times

Excellent early strength

The 2000’sCrystal Seed Hardening Accelerators

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0

10

20

30

40

1 10 100 1000Time [hrs]

Stre

ngth

[MPa

]

No Accelerator

Trad. Accelerator

X-SEED

7h14h16h

7h14h16h

Crystal Seed

0

10

20

30

40

1 10 100 1000Time [hrs]

Stre

ngth

[MPa

]

No Accelerator

Trad. Accelerator

X-SEED

7h14h16h

7h14h16h

Crystal Seed

First introduced in 2009

Based upon specifically designed crystal seeds

The rate of strength development can be further increased as compared to other conventional accelerators

Acceleration achieved by nucleation of hydration products onto the seeding crystals

Best performance in concretes using high sulfate cements

No reversion in late age strength

A View of the Future

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A View of the FutureWhat is next?

Further reduction in clinker contents in cements and concretes

Utilization of poor quality aggregates (high clay contents, alkali-reactive, etc.)

Alternative binders for concrete

Reduction of stickiness in high performance concrete mixtures

Further use and modification of fibers as replacements for steel reinforcing

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Meet the demands of sustainable construction and to support the global mega trends

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