ACID ATTACK ON CONCRETE

Presented by

Narasimhareddy komali

PRESENTATION OUTLINE

IntroductionAttack due toH2SO4

Attack due to HNO3

Attack due to CH3COOHAttack due to HCLAttack due toH2CO3

Repair to attackConclusion references

INTRODUCTION

Concretes made of Portland cement (OPC) are highly alkaline

with pH values normally above 12.5 and are not easily attacked

by acidic solutions.

At pH values lower than 12.5 portlandite is the first constituent

starting dissolution

If pH decreases to values lower than stability limits of cement hydrates,

then the corresponding hydrate loses calcium and decomposes to

amorphous hydrogel

The final reaction products of acid attack are the corresponding calcium

salts of the acid as well as hydrogels of silicium, aluminum, and ferric

oxides

WEAK ACIDS STRONG ACIDS

ACID ATTACK

Acetic acid

Carbolic acid

Carbonic acid

Lactic acid

Phosphoric acid

Tannic acid

Hydrochloric acid

Sulphuric acid

Sulphurous acid

Nitric acid

Hydroflouric acid

Hydrobromic acid

SULPHURIC ACID ATTACK

Sulphuric acid attack causes extensive formation of gypsum in

the regions close to the surfaces, and tends to cause

disintegrating mechanical stresses which ultimately lead to

spalling and exposure of the fresh surface.

The chemical reactions involved in sulphuric acid attack on

cement based materials can be given as follows:

Ca(OH)2 + H2SO4 CaSO4.2H2O

3CaO.2SiO2.3H2O + H2SO4 CaSO4.2H2O + Si(OH)4

LOS ANGELES SANITARY SEWER SYSTEM

Deterioration of concrete pipe from H2S attack

Sulphuric acid is highly reactive and reacts with calcium compounds to form

gypsum which causes the concrete to soften, ultimately leading to roof collapse.

Organic matter + SO42- S2- + H2O + CO2

S2- + 2H+ H2S

H2S + 2O2 H2SO4

NITRIC ACID ATTACK Nitric acid usually occurs in chemical plants producing explosives,

artificial manure and similar products.

Nitric acid can be formed from the compounds and radicals of nitrates in

the presence of water

3NO2 + H2O 2HNO3 + NO

Nitric acid attack can be represented by the following equations;

2HNO3 + Ca(OH)2 Ca(NO3)2.2H2O

Ca(NO3)2.2H2O + 3CaO.Al2O3.8H2O

3CaO.Al2O3. Ca(NO3)2.10H2O

Nitric acid attack is a typical acidic corrosion for

shrinkage of the corroded layer due to leaching of highly

soluble calcium nitrate.

Such volume contractions of the corroded layer, especially

for the case of nitric acid, can result in the formation of

visually observable cracks across the corroded layer.

Variation of compressive strength with acid concentration (mix

ratio 1:1.5:3, W/C = 0.65)

ACETIC ACID ATTACK

Concrete in use in agricultural applications may be

attacked by the silage effluents containing mainly

acetic and lactic acid.

Acetic acid reacts with cement hydration products to

form calcium acetate

2CH3COOH + Ca(OH)2 Ca(CH3COO)2 + 2H2O

2CH3COOH + C-S-H SiO2 + Ca(CH3COO)2 + 2H2O

Chemical compositions of the core layers in both acetic and nitric acid

attacks are similar

The chemical composition of the corroded layer is different from that

in nitric acid solution of the same concentration due to higher pH

values of the acetic acid solution, and due to its buffering effect in

corroded layer.

In lower concentrations of both acetic and nitric acid solutions, e.g.

0.025 mol l-1, results in the formation of an additional zone, called as

core-layer, which is relatively hard and located behind the corroded

layer

HYDROCHLORIC ACID ATTACK

The chemicals formed as the products of reaction

between hydrochloric acid and hydrated cement

phases are some soluble salts and some insoluble salts

Ca(OH)2 + 2HCl CaCl2 + 2H2O

By hydroxide mixture zone, he referred to a layer

formed by undissolved salts seen as a dark brown ring.

CARBONIC ACID ATTACK

Carbonic acid attack usually occurs in the case of buried concrete

structures exposed to acidic ground water fro a long time

Atmospheric carbon dioxide absorbed by rain enters ground water

as carbonic acid

Factors affecting the rate of carbonic acid attack are;

Quality of concrete

Concentration of aggressive carbon dioxide

External exposure conditions

When concrete is exposed to carbonic acid, a reaction

producing carbonates take place which is accompanied

by shrinkage

However, continued carbonation may cause a reduction

in alkalinity of the cement paste which can be a serious

problem not only in de-passivation and corrosion of

steel bars but also in dissolution of cement hydrates.

DWORSHAK NATIONAL FISH HATCHERY

ACI 210.1R-94

Deterioration of concrete surface of a tank carbonic acid

Repaired area

The Dworshak reservoir collects snow melt runoff

and releases the pure water during the seasonal

incubation and rearing phase of the hatchery

production

There was high concentration of dissolved carbon

dioxide in the collected water

pH of the collected water was 6.5-7.4

FALLING OF COVER DUE TO CORROSION OF REINFORCEMENT

Concrete Corrosion Above Water Level at Adjoining Effluent Trough Segments

19

Concrete Corrosion on Exposed Effluent Trough Surfaces

Concrete Corrosion in Sludge Valve Box

21

Corroded Drain Pipe

22

For deteriorated concrete

For non-deteriorated concrete and new concrete

Repair Systems and Procedures

23

Clean and remove loose concrete from the surface with high pressure water jetting, 10,000 psi, or sandblasting.

If reinforcing bars are exposed and corroded, chip out concrete to expose around the bars.

Apply a migrating corrosion inhibitor on the surface.

For Deteriorated Concrete

24

Rebuild the deteriorate surfaces:

Apply an underlayment with a fast-setting, high early strength, Portland-based resurfacing material to restore damaged concrete surfaces where required.

Underlayment should be trowelable or sprayable formulation for dimensional rebuilding.

25

Apply an epoxy aggregate filled mortar intermediate coat (125 mils) by trowelling on the rebuilt surfaces.

Provide final lining with spray apply sealer over aggregate filled epoxy base layer. Minimum thickness of lining should be two (2) coats of 30-mils each. The sealer provides the substrate for chemical and water resistance.

Perform spark testing to check for voids or defects in coating. Repair defects.

26

Troweling underlayment to restore damaged concrete surfaces.

Underlayment with broom finish.

Underlayment with spray finish.

Spray apply final lining (sealer) on ceiling and walls.30

Application of final lining (sealer coat) on ceiling.31

Clean the concrete surface with with high pressure water jetting, 10000 psi, or sandblasting.

Apply a migrating corrosion inhibitor on the surface.

Trowel in an epoxy filler compound specifically designed to fill small voids, bugholes and irregularities in concrete surfaces to provide a smooth surface.

For Non-Deteriorated Concrete and New Concrete

32

Filler compound must be compatible with the protective lining.

Provide final lining with spray apply sealer over aggregate filled epoxy base layer. Minimum thickness of lining should be two (2) coats of 30-mils each. The sealer provides the substrate for chemical and water resistance.

Perform spark testing to check for voids or defects in coating. Repair defects.

33

Surface preparation by sandblasting and grinding. 34

Application of filler epoxy compound to fill small voids, bug holes and irregularities on beam. 35

Application of filler epoxy compound to fill small voids, bug holes and irregularities on trough walls. 36

Hand rolling of final lining (sealer coat) on walls.

Partial coating of final lining (sealer coat). 38

Pinholes in sealer coating. 39

Spark testing to detect defects and pinholes in sealer coating. 40

CONCLUSIONS

In the case of sulphuric acid attack, although the formation of gypsum has been reported frequently, there is no agreement on its consequences

Attack by Acetic acid resembles the process of corrosion in nitric acid. However the growth of the corroded layer in solutions of acetic acid is relatively slower than that in the same concentrations of nitric acid solution

The chemical composition of the corroded layer is different from that in nitric acid solution of the same concentration due to higher pH values of the acetic acid solution

REFERENCES

Mark G. Richardson, Fundamentals of Durable Reinforced Concrete, 2002

Ali Allahverdi and Frantisek skvara, Acidic corrosion of hydrated cement based materials, 2000, Institute of chemical technology, Department of glass and ceramics

Compendium of Case Histories on Repair of Erosion-Damaged Concrete in Hydraulic Structures, ACI 210.1 R-94 (reapproved 1999)

Kolapo O. Olusola and Opeyemi Joshua, Effect of Nitric Acid Concentration on the Compressive Strength of Laterized Concrete, Vol. 2, No. 10, 2012

Emmanuel K. Attiogbe and Sami H. Rizkalla, Response of concrete to sulphuric acid attack, 1989, ACI Material journal, Title no. 85-M46