Chemical attack on the durability of underground structures

Chemical attack on the durability of underground structures

Workshop Middle East Concrete 2015

Abu Saleh Mohammod PhD, MICT

General Manager

Pudlo Middle East Building Materials L.L.C

Concrete durability and permeation properties

Pudlo modified durable concrete

Mitigating chemical attack

Examples of durable concrete structures

Quiz

Content

Durability and permeation properties

What is durability?

“The ability of concrete to withstand the damaging effects

of the environment and of its service conditions until it

reaches a minimum level of performance”

Type of attacks on concrete durability

Corrosion of reinforcement by:

Chloride ingress

Carbonation

Sulfate attack

Delayed Ettringite Formation (DEF)

Physical salt weathering

Acid attack

Alkali Silica reaction

Multi-aggressive sea water attack

The common factor

Permeation Mechanisms

Permeation of water and gasses can be divided into three

distinct phenomena:

• Permeability

• Absorption

• Diffusion

Permeability

P1

P2

The flow property of concrete by which water will pass

through it, under a pressure differential

Fluid movement

Concrete

Absorption

Typically affects: Structures subjected to cyclic wetting and drying e.g. marine structures in the tidal zone

The process by which concrete takes in water by capillary action.

Water reservoir

Concrete

Diffusion

Cl-

Cl-

Cl-

Cl- Cl-

Cl-

Cl- Cl- Cl-

Cl-

Cl-

Cl-

C1 C2

The process by which a vapour, gas or ion can pass through

concrete under the action of a concentration gradient

Pudlo Modified Durable Concrete

What is PUDLO

A hydrophobic and micro pore blocking

admixture which additionally alters the

microstructure of concrete to stop water

and moisture transport mechanisms, thus

increasing the long term durability of

concrete.

Porosity highlighted in red scale

Comparison between control & Pudlo concrete

100 times magnification – low w/c ratio control concrete

Comparison between control & Pudlo concrete

350 times magnification – low w/c ratio Pudlo modified concrete

Hydrophobic characteristics of Pudlo concrete

Cement Particle Hydration Process

Development of the hydration process by producing hydration products The process alone does not eliminate the presence of voids within the concrete matrix

Pudlo blocks the pores by densifying the cement matrix to eliminate the voids

Attacks on concrete durability

Corrosion

Corrosion of steel

• Corrosion of steel is an electro-

chemical process

• It starts once the passive oxide

layer of steel bar is broken down,

creating microcells of :

• Anode

• Cathode

ANODE CATH

ODE

Concrete surface

Steel reinforcement

Passive oxide layer

Corrosion of steel

• The passivating layer is maintained due

to rich alkaline environment of concrete

pore solution

• This could be broken down mainly due

to the:

• Ingress of chloride ions

or

• Carbonation

ANODE CATH

ODE

Concrete surface

Ingress of moisture, oxygen & chloride / CO2

½ O2 H2O

Steel reinforcement

Cl- / CO2

Passive oxide layer

Corrosion of steel

At anode, once the passivating layer is

broken down, dissolution of steel is taken

place producing into the solution +ve Fe2+

and -ve electrons

ANODE CATH

ODE

4(OH-)

2H2O

Concrete surface


½ O2

O2

H2O

Steel reinforcement

4e - 2Fe 2+

Cl- / CO2

Passive oxide layer

Corrosion of steel

• At the cathode the liberated negative

electrons combine with H2O and O2

to form -ve OH- ion

• These -ve OH- ions then travel to the

anode to add with +ve Fe2+

ions to

form Fe2O3.H2O or rust

ANODE CATH

ODE

4(OH-)

2H2O

Concrete surface


½ O2

O2

H2O

Steel reinforcement

4e - 2Fe 2+

Cl- / CO2

Passive oxide layer

Fe2O3 H2O

Corrosion of steel

• The volume of rust is 3 to 6 times

more than the original volume of

steel

• Thus the formation of rust resulting

into an expansive pressure to the

concrete

• Concrete cracks when this pressure

exceeds the tensile strength capacity

of concrete

ANODE CATH

ODE

4(OH-)

2H2O

Concrete surface


½ O2

O2

H2O

Steel reinforcement

4e - 2Fe 2+

Cl- / CO2

Passive oxide layer

Fe2O3 H2O

Corrosion of steel and permeation properties

Corrosion of steel in concrete is directly related to the

permeation properties of concrete which would include

• permeability,

• absorption and

• diffusion

Corrosion of steel and permeation properties

• Water the main factors required to initiate corrosion can

permeate through concrete by all of these three mechanism

• whereas O2, CO2 and Cl- ions diffuse through concrete

cover to reach the steel surface

• It is utmost important to enhance the permeation

properties of concrete cover by reducing the permeation

properties of concrete

How Pudlo resist corrosion

By enhancing the permeation properties and reducing the

permeability, absorption and diffusion of concrete, Pudlo

makes the concrete virtually water-tight, the key factors for

steel corrosion in concrete structures.

How Pudlo Resist Corrosion

• Reduced diffusion translates into prolonged initiation period

to corrosion,

• Chloride ions take much longer time to reach the chloride

threshold level required to breakdown the oxide passivation

layer of the steel reinforcement bar

• As there is virtually no presence of moisture, therefore

possibility of corrosion initiation in Pudlo modified concrete

is almost nil

Sulfate attack

Hydration reaction

C2S/C3S + H2O C-S-H + Ca(OH)2

C3A+ H2O C-A-H + Ca(OH)2

Formation of Ettringite

C3A+ 3CaSO4.2H20+ 26H2O

Gypsum

C3A.3CaSO4.32H20

Ettringite

C3A.3CaSO4.32H20

Ettringite

C3A.CaSO4.12H20

Monosulfate

Sulfate Attack of Concrete

Dissolved sulfate in ground water can react with

certain components of the cement paste leading to

expansion, cracking and spalling of concrete

Sulfate Attack of Concrete

The most common forms of sulfate are:

Sodium sulfate Na2SO4

Potassium sulfate K2SO4

Magnesium sulfate MgSO4

Calcium sulfate CaSO4

Mechanism of Sulfate Attack

Conversion of

C3A (if present)

and expansion

Hydrated

C3A

Sulfate solution

from the

environment

Diffusion of

sulfates into

concrete

Crack

formation

Sulfate attack is characterised by the chemical reaction between sulfate ions with the Al3, Ca and OH component of hardened Portland cement The reaction leads to the formation of expansive ettringite and to a lesser extent, gypsum The reaction, with water present, will cause expansion leading to cracking This in turn will allow further ingress of sulfates and accelerate the degradation process


Sulfate attack is easily recognisable as a map

cracking on the surface, expansion of the concrete

and the appearance of a ‘soft’ white substance.

Continued attack from sulfate solutions and the

presence of water will eventually lead to complete

disintegration of the concrete


Sulfates will attack some or all of the three main hydrate components of hardened concrete: Calcium hydroxide Ca(OH)2

Calcium aluminate hydrate CaO.Al2O3.H2O

Calcium silicate hydrate CaO.SiO2.H2O

depending on the type of sulfate in solution involved.


Attack of Ca(OH)2 components SO4 will attack the Ca (OH)2 component in an ‘acid’ type attack, producing crystalline calcium sulfates (gypsum) and soluble hydroxide : e.g.

Ca(OH)2 + Na2SO4.10H2O CaSO4.2H2O + 2NaOH + 8H2O

gypsum soluble hydroxide


Attack of calcium aluminate hydrate (CaO.Al2O3.H2O) components SO4 will also attack the C-A-H component, producing ettringite, and expansive product and soluble hydroxides: e.g.

2(3CaO.Al2O3.12H2O) + 3(Na2SO4.10H2O) 3CaO.Al2O3.3CaSO4.31H2O ettringite

+ 2Al(OH)3 + 6NaOH + 17H2O

soluble hydroxides


Attack of calcium silicate hydrate (CaO.SiO2.H2O) components Certain sulfates such as MgSO4 will also attack the C-S-H as well as the C-A-H and Ca(OH)2, producing very severe sulfate attack and expansive product and soluble hydroxides: e.g. 3CaO.2SiO2.aq + MgSO4.7H2O CaSO4.2H2O + Mg(OH)2 + SiO2.aq low solubility hydroxide The low solubility of the hydroxide means that the reaction proceeds until completion resulting in complete destruction of C-S H

Factors Influencing Sulfate Attack

The main parameters which influence sulfate attack are:

1. Type of sulfate

2. Concentration

3. Permeation properties of concrete

4. Cement Type

5. Mobility Rate

6. Section size

7. Environment

Sulfate ions enter into the concrete matrix as solution of

ground water

Pudlo makes the concrete virtually watertight by

significantly reducing its permeability and absorption

properties

Therefore concrete elements treated with Pudlo remain

protected against any form of sulfate attack

How Pudlo minimise the Effects of Sulfate Attack

Minimising the Effects of Sulfate Attack

Sulfate attack may also be combated by the following:

• Use of supplementary cementitious materials

• Use of Sulfate Resisting Portland Cement

• Appropriate mix design

• Provide physical barrier against sulfates


Hydration reaction

C2S/C3S + H2O C-S-H + Ca(OH)2

C3A+ H2O C-A-H + Ca(OH)2

Formation of Ettringite

C3A+ 3CaSO4.2H20+ 26H2O

Gypsum

C3A.3CaSO4.32H20

Ettringite

C3A.3CaSO4.32H20

Ettringite

C3A.CaSO4.12H20

Monosulfate


Delayed Ettringite Formation (DEF) is

associated with high concrete temperature

As a part of the hydration process, ettringite, is

normal to produce at the early stage due to the

reaction of C3A with gypsum

If the concrete temperature exceeds 70°C, the

early formation of ettringite does not occur


The formation of ettringite could be delayed,

After hardening of concrete in the prolonged

presence of water when the temperature cooled

down

As the volume of ettringite is larger than its

original hydration product, it would produce

internal stress, and induce cracks

Factors responsible for DEF

The most common factors of DEF are:

elevated temperature

prolonged exposure to water

Factors responsible for DEF

Other factors:

i) Composition of concrete

ii) Aggregate type

iii) Aggregate paste bond

iv) Cement type and chemical composition of cement

v) Exposure condition

vi) Presence of high sulfate and alkali content in the original mix is also contributed to the DEF

Combatting DEF

DEF could be a cause of concern in the Middle East due to the high ambient temperature during summer

Controlling the concrete temperature

Use of high volume GGBS to reduce the heat of hydration

Use of pozzolanic materials or reduced C3A content cement

Enhancement of permeation properties

Use of water resisting admixture such as Pudlo

Salt Weathering or Physical Salt Attack

Salt Weathering

Salt in solution from groundwater or damp soil can be transported by capillary action vertically through a concrete member.

Above ground level, the moisture is drawn to the surface and evaporates, leaving crystals of salt growing in the near surface pores.

This results in an area of deterioration just above ground level.

This form of attack is common in hot, dry areas and may also occur in marine structures.

Combatting Salt Weathering

More pronounce on porous structure by capillary rise mechanism

Reduction of porosity by densifying the concrete microstructure

Enhancing permeation properties by means of lower absorption of concrete

Pudlo CWP densify the concrete matrix by producing more C-S-H and reduce the absorption by creating a hydrophobic lining

Alkali Silica Reaction

Alkali-Silica Reaction

1. The lime saturated alkaline solution in concrete

pores contain varying amounts of alkalis such as

Na+ and K+ ions

2. Aggregates may contain reactive siliceous

components e.g. chart, flint, quartzite

Alkali-Silica Reaction

3. These reactive silica from aggregate will

deleteriously react with alkalis of concrete to form

a gel

4. In the presence of moisture the gel expands

5. Expansive products lead to internal stresses,

cracking and eventual deterioration of concrete

Alkali-Silica Mechanism

ASR can be visualised as a two-step process: 1. Alkalis within the concrete

react with siliceous components of aggregates to form a gel reaction product

2. Uptake of moisture by the gel by osmosis causes expansion of the gel leading to cracking.

Diffusion of alkalis present

in pore system

Conversion of reactive aggregate and

expansion

Reactive aggregate

Crack formation (map cracking and surface

parallel cracking)

Diffusion of water and alkalis into concrete

Water and alkalis from the environment

Alkali-Silica Mechanism

For ASR to take place, three fundamental conditions must be met:

1. Sufficient amount of alkali in pore fluids

2. Sufficient amount of reactive silica present in aggregates

3. Sufficient amount of water

The absence of any of the above means that ASR will not take place

Recognising Alkali-Silica Damage

ASR can be recognised by the following observations: Surface Cracking: Distinctive random ‘map’ cracking which appears after 2-3 years. Important not to confuse this with drying shrinkage cracks. Exudations: Formation and exuding silica gel at concrete surface. Concrete appears to weep as gel is forced out of the concrete Surface pop-outs: Concrete will have local pop-outs where excess expansion has taken place. Disintegration of concrete: Extensive expansion leads to complete disintegration of concrete

Alkali-Silica Damage

Microscopy shows the formation of silica gel and the network of cracks which can arise due to alkali-silica reaction

Gel formation and subsequent expansion

Local cracking

Extensive cracking due to widespread gel formation and expansion

Alkali-Silica Damage in Structures

CONCRETE RAIL ROAD TIE

BRIDGE PIER

MARINE PROMENADE

Complete disintegration of concrete

Distinctive map cracking

Longitudinal cracking

Sources of Alkalis

Portland Cement The main source is PC which contains numerous metal alkalis which contribute to the alkaline nature of the pore fluids and hydrates, the main two being:

Sodium oxide Na2O Potassium oxide K2O

During hydration, pore fluids become highly alkaline in nature, ph>12, due to the amount of sodium and potassium ions in solution.

Alkali content of Portland cement is expressed in terms of equivalent sodium oxide content:

Na2O (eq) = %Na2O + (0.658%K2O)

In the PC alkali content ranges from 0.4 – 1.0% Na2O (eq).

Sources of Alkalis

Pozzolanic Materials Certain pozzolanic materials such as fly ash and ggbs may contain alkalis Chemical Admixtures Superplasticizer, water reducer, retarder and accelerator Water Mix water or water which enters the concrete from the surrounding environment may contain alkalis, e.g. salts Aggregate Existing aggregates such as certain limestone and sandstones may contain alkaline components.

Sources of Silica

Portland Cement

Pozzolanic Materials

Aggregates

PC typically contains 20% SiO2 which is consumed by the hydration reaction to form C-S-H

Pozzolanic materials contain levels of SiO2 fly-ash (40-50%), ggbs (35-40%), metakaolin (40-50%), Silica fume (>90%) however the majority of this is consumed by the reaction with PC

Siliceous aggregates containing high levels of potentially reactive SiO2:

Gneiss, Quartz, Quartzite, Rhyolite, Sandstone, Schist contain highly strained quartz, opaline and chalcedonic silica which will react with alkalis

Aggregates are typically the main source of silica for the

reaction to take place

Factors Influencing ASR

1. Availability of alkali

2. Availability of reactive silica

3. Availability of moisture

4. Temperature

Combating ASR

There are a number of recommendations to combat the effects of ASR: 1. Limiting Alkali Content of Concrete: (i) Use of low alkali cements: Na2O (eq) < 0.6% (ii) Limit alkali content of concrete: Na2O (eq) < 3.0 kg/m³

2. Use of Pozzolanic Materials: i. Fly ash is particularly useful in combating ASR due to its ‘dilution’ effect,

reducing concentrations of hydroxyls ii. GGBS may also be used at a level of >50%

3. Limit Reactive Silica Content

4. Use of watertight concrete such as Pudlo

Pudlo to Combat ASR

The general rule in combating ASR is to curtail one or all of

the three requirements:

• Alkali content

• Content of reactive silica

• Presence of moisture

As PUDLO effectively make the concrete watertight,

therefore one of the key requirement to occur ASR is

eliminated, therefore concrete treated with Pudlo can be

effectively protected from the deleterious effect of ASR

Acid Attack

Acid Attack on Concrete

Concrete containing Portland cement, being highly

alkaline in nature (pH>11), have little inherent

resistance to attack from strong acids or compounds

which may convert to acids (pH<3).

Mechanism of Acid Attack on Concrete

Acid attack of concrete takes the form of an aggressive substance attacking a reactive substance: Aggressive Substance Reactive Substance

Acids in solution Hydrates of hardened concrete:

(typically pH<5) Calcium hydroxide: Ca(OH)2 Calcium silicate hydrate: C-S-H Calcium aluminate hydrate: C-A-H

Calcareous aggregates (limestone)


1. Acids decompose the hydrates of cement paste to form soluble calcium salts

2. These soluble calcium salts will leach out in the presence of water


1. Acid in solution from the surrounding environment will come into contact with the surface of the concrete.

2. The acid will react with the hydrates in the cement paste and convert the cover zone concrete layer by layer

3. The most pronounced form of acid attack is the dissolution of calcium hydroxide which occurs:

2 HX + Ca(OH)2 -> CaX2 + 2 H2O

(X is the negative anion of the acid)


4. The microstructure of the cement paste is

converted into a more permeable matrix

5. The reaction products, namely calcium salts from

the interaction of acid and hydrates are then easily

removed by dissolution or abrasion

Types and Sources of Acids

Acids can be present in many forms and may attack concrete such

as:

Agricultural environments

Industrial environments

Concrete airport pavements

Sewer systems

Moorland water systems

Chemical storage tanks

Gas arising from sewage or exhaust fumes may also acid attack

concrete.

Types and Sources of Acids

Inorganic Acids Organic Acids Carbonic Acetic Hydrochloric Citric Hydrofluoric Formic Nitric Humic Phosphoric Lactic Sulfuric Tannic Other acidic substances: Aluminium chloride Ammonium salts Hydrogen sulfide Vegetable and animal fats Vegetable oils Lubricating oils

How Pudlo resist the acid attack?

Concrete can be designed to reduce the effect of acid attack by

enhancing its permeation properties by adding Pudlo

Pudlo reduces the surface tension of the capillary pore of

concrete, thus reducing the absorption of acid in solution and

increasing the acid resistant capacity of concrete

Enhanced permeability and diffusion properties of concrete

modified by Pudlo also positively contribute to the acid

resistant capacity of concrete

Multi-aggressive Seawater Attack

Multi-Aggressive Seawater Attack

Seawater contains a complexity of ions which will be detrimental to concrete in marine structures The salts which are most common in seawater are:

• Sodium chloride (NaCl)

• Magnesium chloride (MgCl2)

• Magnesium sulfate (MgSO4)

• Calcium sulfate (CaSO4)

• Potassium chloride (KCl)

• Potassium sulfate (K2SO4)

Multi-aggressive Seawater Attack

Marine structures will be subjected to both physical and chemical attack as well as corrosion of reinforcement.

There are several types of

exposure zone in marine

structures however the

submerged and low tide

zones are where the

majority

of multi-chemical attack

takes place

Multi-chemical Action

Action of CO2

• Ingress of dissolved CO2 will

react with the Ca(OH)2 and

water to form aragonite and

calcite (CaCO3).

• This will precipitate to form a

coating on the surface of the

structure.


Action of Sulfates

• Sulfates will have a limited action due to the formation of non-expansive Friedell’s salts (Calcium chloro-aluminate) in the presence of chlorides.

• However, gypsum will form leading to expansion, precipitation and the further formation of expansive ettringite.

Friedell’s salt

Gypsum


Action of Chlorides

• The presence of chlorides react with

calcium hydroxide to form soluble

calcium chloride (CaCl2)

• A secondary reaction of CaCl2 with the C-

A-H in the hydrated cement leads to the

formation of expansive chloro-aluminate,

ettringite and thaumasite

Ettringite

Thaumasite

Pudlo on multi-chemical action

• All deleterious chemical and gaseous ions enter into the

concrete microstructure through diffusion mechanism

• The densified microstructure of Pudlo treated concrete has

significantly higher resistance to diffusion of ions compared to

control

• Therefore, Pudlo effectively protect submerged marine

structures from any kind of multi-aggressive chemical attack

Examples of Durable structures

Maple Lodge Sewage treatment work, UK

More than 70 years old

No coating

The works is a fully nitrifying diffused-air activated sludge plant

with heated anaerobic sludge digestion

published data on the pH level of the raw water ranges from 4.5 to 8

Maple Lodge Sewage treatment work, UK

Construction began 1938 as above and after 70 years continuous wet/dry use no sign of corrosion

Maple Lodge Sewage Treatment Works, UK

Southwark’s Integrated Waste Management Facility, UK

Chemical leachate

High temperature up to 85 deg C

No coating

Extreme chemical environment

Beside chemical resistant Pudlo

provided higher initial and final

compressive strength in high volume

GGBS concrete

London borough waste and recycling centre, UK

Resistance to the chemical residues -

mostly acidic -leached by the waste.

Floor needed to withstand substantial

wear and tear from heavy vehicles and

plant

Pudlo modified durable concrete with the

addition of steel and PPE fibres provided

the solution

Examples of Truly Durable Structures

London Zoo Reptile House

Designed and built in 1926-27 by Joan Beauchamp Proctor

and Sir Edward Guy Dawber, the reptile house opened in 1929.

Examples of Truly Durable Structures

1931 Now

Church at Turner’s Cross, Cork, Ireland

Royal Albert Hall, London

Building Design Partnership / Taylor Woodrow

Royal Albert Hall, London

Merchant Square, London

12 metre deep

London basement, adjoining

The Paddington Basin

Holford Associates / RJ Crockers Partnershipge

Projects in the Middle East

Fountain rises to a height of 500ft, equivalent of a 50 storey building

Over 6,600 lights and 50 colour projectors create a visual spectrum of over 1,000 different water

expressions

Burj Khalifa Fountains

900ft (275m) in length located on the 35

acre Dubai Lake

22,000 gallons of water airborne at anytime

2½ kilometres of under-ground tunnels

Burj Khalifa Fountains

Membrane free!

La Plage Jumeirah

The Gate at DIFC

Commercial Buildings

Etisalat tower Dubai

Residential towers

The Blue tower at

Sheikh Zayed Road Palladium at JLT

Trident at Dubai Marina

The Square at Mamzar

Wafi mall Dubai

New projects Mixed development at Diera, Dubai

New projects Zulekha Hospital Extension

New projects – Mont Rose Dubai

Quiz

Questions 1

Q1. What is the common factor of all problems associated with durability of concrete structures

A1. Water

Questions 2

Q. Name the 3 permeation properties by which water or vapour enter into concrete matrix.

A. Permeability, absorption and diffusion

Questions 3

Q. At what condition water enter into concrete by the mechanism of Permeability?

A. High hydrostatic pressure condition

Questions 4

Q. By what action water can be absorbed by concrete?

A. By capillary action

Questions 5

Q. When there is a presence of concentration gradient between the liquid of inside and outside of concrete, then highly concentrated ions (e.g. salt solution) will move into the lowly concentrated liquid (water) within the concrete. What is the terminology of this phenomenon?

A. Diffusion

Questions 6

Q. Why corrosion of steel creates cracks to the concrete?

A. The volume of rust is larger that the volume of the original mass of steel embedded inside hardened concrete. Therefore, the ever-growing mass of rust exert outward tensile stress to the surrounding concrete. When this stress exceeds the tensile strength of concrete, it cracks.

Questions 7

Q. Which are the component of hydration products are affected by the sulfate attack?

A. Depending on the type of sulfate all main hydration products which includes C-S-H, C-A-H and Ca(OH)2 can be affected.

Questions 8

Q. How sulfate attack can create cracks?

A. The mass of the resultant products (ettringite or gypsum) due to the chemical reaction between sulfate, hydration products and water are larger than the mass of the original hydration products. To accommodate this additional mass, internal tensile stress develops which exerts outward stress causing cracks.

Questions 9

Q. How to enhance the durability of concrete?

A. By enhancing the permeation properties by making concrete watertight.

Thank you

Engineering

Chemical attack on the durability of underground structures