Durability of concrete: ability to resist weathering action, chemical ...

Durability 

Durability of concrete: ability to resist 

weathering action, chemical attack, 

abrasion, or any process of deterioration. 

CE 60 

Instructor: Paulo Monteiro

Water 

Water Causes: 

•Chemical processes of 

degradation 

• Physical processes of 

degradation 

CE 60 


Water in the Capillary 

CE 60 


Permeability 

• Permeability - the property that governs the rate 

of flow of a fluid into a porous solid. 

• Darcy’s law: For steady-state flow, the 

coefficient of permeability, K, is determined from 

Darcy's expression: 

dq/dt = K∙(∆H∙A)/(L∙μ) 

Where: Dq/dt = rate of fluid flow, μ = viscosity of 

the fluid, ∆H = pressure gradient, A = surface 

area, and L = thickness of the solid. 

CE 60 


Permeability of Cement Paste 

•Age (days) Permeability (cm/s 10 -11 ) 

•Fresh 20,000,000 

•5 4,000 

•6 1,000 

•8 400 

•13 50 

•24 10 

•ultimate 6 

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Permeability of Cement Paste 

•When porosity decreases from 40 to 30%, 

the permeability drops from 110 to 20 x 10 -12 

cm/sec. 

•However, a decrease in porosity from 30% 

to 20% results in a small drop in 

permeability. 

•Reasons: 

•Large pores are reduced in size and 

number. 

•There is creation of tortuosity. 

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Permeability of Aggregate 

• Compared to 30 to 40 percent capillary 

porosity of typical cement pastes in 

hardened concrete, the volume of pores in 

most natural aggregates is usually under 3 

percent, and it rarely exceeds 10 percent. 

• However, the coefficient of permeability of 

aggregates are as variable as those of 

hydrated cement pastes of water/cement 

ratios in the range 0.38 to 0.71 

CE 60 


Permeability of Aggregate 

Reason: 

• Some aggregates have much higher 

permeability than the cement paste 

because their capillary pores are much 

larger. 

• Most of the capillary porosity in a mature 

cement paste lies in the range 10 to 100 

nm, while pore size in aggregates are, on 

average, larger than 10 microns. 

CE 60 


Permeability of Aggregates 

Type of Rock Permeability (cm/sec ) 

dense trap 2.47 x 10 -12 

quartz diorite 8.24 x 10 -12 

marble 2.39 x 10 -10 

granite 5.35 x 10 -9 

sandstone 1.23 x 10 -8 

CE 60 


Physical Causes of Concrete Deterioration 

•1. Deterioration by surface wear. 

•Abrasion: dry attrition (wear on 

pavements and industrial floors by traffic) 

•Erosion: wear produced by abrasive 

action of fluids containing solid particles 

in suspension (canal lining, spillways and 

pipes). 

•Cavitation: loss of mass by formation of 

vapor bubbles and their subsequent 

collapse. 

CE 60 



Abrasion - Erosion 

•The deterioration starts at the surface, 

therefore special attentions should be given 

to quality of the concrete surface. 

•Avoid laitance (layer of fines from cement 

and aggregate). 

CE 60 



3. Deterioration by Frost Action 

•When water freezes, there is an expansion of 9%. 

However, some of the water may migrate through 

the boundary, decreasing the hydraulic pressure. 

•Hydraulic pressure depends on: 

•Rate at which ice is formed. 

•Permeability of the material. 

•Distance to an "escape boundary." 

CE 60 



Problem: 

The transformation of ice from 

liquid water generates a 

volumetric dilation of 9%. If 

the transformation occurs in 

small capillary pores, the ice 

crystals can damage the 

cement paste by pushing the 

capillary walls and by 

generating hydraulic pressure. 

CE 60 

Instructor: Paulo Monteiro 

Mehta and Monteiro: Concrete


Solution: 

Air voids can provide an 

effective escape boundary 

to reduce this pressure. 

CE 60 



Air-Entraining 

CE 60 



This image cannot currently be displayed. 

Freezing of Concrete 

CE 60 


This image cannot currently be displayed. 

Freezing of Concrete 

Does concrete freezing 

cause the air-entrained 

bubbles to get larger or 

smaller 

Answer: Smaller. Since 

the paste is expanded, the 

air-voids are compressed. 

Mehta and Monteiro: Concrete 

CE 60 


Frost Action on Aggregate 

•Aggregates likelihood to cause freezing damage depends on 

pore: 

•Sizes 

•Number 

•Continuity 

•3 classes of aggregate 

•(1) Low permeability and high strength: No problem! The rock is strong 

enough to support the hydraulic pressure. 

•(2) Intermediate permeability: Potential depending on (a) rate of 

temperature drop. (b) distance the water must travel to find an escape 

boundary – Critical Aggregate Size (a large aggregate may cause 

damage but smaller particles won't). 

•(3) High permeability: May cause problem with the transition zone. 

CE 60 


Factors Controlling Frost Resistance of Concrete 

MSA (in) air content (%) 

3/8 

1/2 

3/4 

1 

2 

3 

7.5 

7 

6 

6 

5 

4.5 

CE 60 


Deterioration by Fire 

•Concrete is able to retain sufficient strength 

for a reasonably long time. 

CE 60 


Consequence 

CE 60 


Fire in the Chunnel 

CE 60 


Effect of High Temperature 

•Effect of High Temperature on Cement Paste 

•Depends on: 

•Degree of hydration 

•Moisture state 

•Causes de-hydration: 

•Ettringite > 100 C 

•Ca(OH) 2 500-600 C 

•CSH ~ 900 C 

•Effect of High Temperature on Aggregate 

•Siliceous quartz: 573 C --sudden volume 

change ( quartz) 

•Carbonate: MgCO3 > 700 C, CaCO3 > 900 C 

CE 60 


Corrosion of Reinforced Concrete 

CE 60 


Electrochemical Process of Steel Corrosion in Concrete 

CE 60 


Volumetric Change

Carbonation of Concrete 

Painting with Phenolphthalein 

Concrete exposed to CO 2 

(accelerated test) 

CE 60 


Carbonated concrete

Alkali-Silica Reaction 

CE 60 


ASR Chemistry 

1) The high pH in the cement paste promotes the 

hydrolysis of silica: 

Si-O-Si + H OH Si-OH + Si-OH 

aggregate paste 

2) Si-OH react with the paste to form Si-O- 

3) Si-O-, adsorbs Na, K, and Ca to form a gel. 

CE 60 


ASR Optical Image 

CE 60 


ASR Optical Image 

CE 60 


Repairing ASR Damage to a Concrete 

Dam 

Typical Options: 

Monitoring 

Slot cut 

Upstream face membrane 

Roller compacted concrete 

Decrease the reservoir 

Dam Removal 

CE 60 



ASR Damage Examples 

Built in 1965, this deteriorated bridge is located 9.7 miles west of Lee 

Vining at 9400 feet elevation on the eastern slope of the Sierra Nevada. 

CE 60 



ASR Damage Examples 

Airfield parking apron at Naval Air Station Point Mugu, California . 

courtesy of U.S. Navy, NFESC 

CE 60 



Sulfate Attack 

Importance 

• Sulfate attack on concrete has been reported 

from many other parts of the world. 

• As early as 1936 the concrete construction 

manual published by the U. S. Bureau of 

Reclamation warned that concentrations of 

soluble sulfates greater than 0.1 percent in soil 

may have a deleterious effect on concrete, and 

more than 0.5 percent soluble sulfate in soil may 

have a serious effect. 

CE 60 



Origin of the problem 

• Most soils contain some sulfate in the form of gypsum 

(typically 0.01 to 0.05 percent expressed as SO 4 ); this 

amount is harmless to concrete. 

• Higher concentrations of sulfate in groundwaters are 

generally due to the presence of magnesium and 

alkali sulfates. 

• Ammonium sulfate is frequently present in agricultural 

soil and water. Effluents from furnaces that use highsulfur 

fuels and from the chemical industry may 

contain sulfuric acid. 

CE 60 


Expansion of Concrete 

• When concrete cracks, its permeability 

increases and the aggressive water 

penetrates more easily into the interior, 

thus accelerating the process of 

deterioration. 

• Sometimes, the expansion of concrete 

causes serious structural problems. 

CE 60 


Loss of Strength and Mass 

•Sulfate attack can also take the 

form of a progressive loss of 

strength and loss of mass due to 

loss of cohesiveness in the cement 

hydration products. 

CE 60 


Expansive Reaction 

• C 3 A + 3C$H 2 + 26H C 3 A∙3C$∙32H (ettringite) 

In the presence of sulfates 

C 3 A·C$·18H (monosulfate) 

CE 60 




• Gypsum formation leads to reduction of 

stiffness and strength, then by 

expansion and cracking. 

CE 60 


Sodium Sulfate Attack 

• Na 2 SO 4 +Ca(OH) 2 +2H 2 O 

CaSO 4 ∙2H 2 O + 2NaOH 

• The formation of sodium hydroxide as a byproduct 

of the reaction ensures the continuation 

of high alkalinity in the system, which is essential 

for the stability of the cementitious material 

C-S-H. 

CE 60 


Magnesium Sulfate Attack 

• MgSO 4 +Ca(OH) 2 +2H 2 O 

CaSO 4 ∙2H 2 O + Mg(OH) 2 

• 3MgSO 4 + 3CaO∙2SiO 2 ∙3H 2 O + 8H 2 O 

3CaSO 4 ∙2H 2 O + 3Mg(OH) 2 + 2SiO 2 ∙H 2 O 

• The conversion of calcium hydroxide to gypsum is 

accompanied by the simultaneous formation of 

relatively insoluble magnesium hydroxide. 

• In the absence of hydroxyl ions in the solution C-S-H 

is no longer stable and is also attacked by the sulfate 

solution. 

• The magnesium sulfate attack is, therefore, more 

severe on concrete. 

CE 60 


Factors Influencing Sulfate Attack 

• Amount and nature of the sulfate present 

• Level of the water table and its seasonal 

variation 

• Flow of groundwater and soil porosity 

• Form of construction 

• Quality of concrete 

CE 60 


ACI Building Code 318 

• Negligible attack: When the sulfate content is 

under 0.1 percent in soil, or under 150 ppm 

(mg/liter) in water, there shall be no restriction 

on the cement type and water/cement ratio. 

• Moderate attack: When the sulfate content is 

0.1 to 0.2 percent in soil, or 150 to 1500 ppm in 

water, ASTM Type II portland cement or 

portland pozzolan or portland slag cement shall 

be used, with less than an 0.5 water/cement 

ratio for normal-weight concrete. 

CE 60 


ACI Building Code 318 

• Severe attack: When the sulfate content is 0.2 

to 2.00 percent in soil, or 1500 to 10,000 ppm in 

water, ASTM Type V portland cement, with less 

than an 0.45 water/cement ratio, shall be used. 

• Very severe attack: When the sulfate content is 

over 2 percent in soil, or over 10,000 ppm in 

water, ASTM Type V cement plus a pozzolanic 

admixture shall be used, with less than an 0.45 

water/cement ratio. 

CE 60

Durability of concrete: ability to resist weathering action, chemical ...

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