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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