Thaumasite type of Sulphate attack at Dams

1. 1

2. MS Structure Engineering Fall 2019
Concrete Materials & Technology
Instructor:
Dr. Rao Arslan Khushnood
Presented by:
Muhammad khubaib Akhtar (317871)
Muhammad Ahmad Raza (319669)
2

3. 3
Analysis of Sulfates in Concrete at Rawal Dam,
Islamabad

4. Contents
■ Reconnaissance
■ Introduction
■ Preliminary Diagnoses
■ Experimental Procedure
■ Final Diagnoses
■ Mechanism in Action
■ Influencing Factors
■ Proposed Remedies
4

5. Reconnaissance
5
Rawal Lake is an artificial reservoir that provides the water demand for Rawalpindi and Islamabad. Korang
River along with some other small streams coming from Margalla Hills have been set to form this artificial lake
which covers an area of 8.8 km². Korang River is the outlet stream of Rawal Dam. Rawal Lake is located within
an isolated section of the Village Malpur, Bani Gala and Margalla Hills National Park.

6. Introduction
■ Concrete deterioration can be caused by several mechanisms among which Sulphate attack is
one of them.
■ Sulphate attack takes place where water enriched with Sulphate (SO4) comes into contact with
concrete.
6
– Moisture Content
– Waste water, soft water, fresh water, ground water
– Carbonates
– Exposure to different minerals and Soil
– Weathering conditions
– Chemical and Physical degradation
– Aggressive aqueous media
– Agricultural or agro-industrial environments

7. Preliminary Diagnoses
7
D-Cracking Surface Scaling
Cracking along Reinforcement in Spillway Piers
No binding property found
in one sample

8. Preliminary Diagnoses
8
Structure Interaction with Water and Soil
Exposed Reinforcement due Spaling out Concrete

9. Experimental Techniques
9
Ph Value Values
Concrete Sample 6.7
Concrete Sample 7.3
Water Sample 7.06
In low pH conditions unfavorable structural changes can occur in the microstructure of cement materials
which caused higher porosity in applied substances, permeability, corrosion and Sulphate attack and
eventually affect their compressive strength negatively. Corrosion of rebar in reinforced concrete because of
the dissolution of protect layer.

10. Carbonation
10
Phenolphthalein indicator solution
 If the indicator turns purple, the pH is above 8.6.
Where the solution remains colorless as in this case
study, the pH of the concrete is below 8.6, suggesting
carbonation.
 Phenolphthalein is a white or pale yellow crystalline
material. For use as an indicator it is dissolved in a
suitable solvent such as Ethanol.
 Two samples were collected from site and tested
separately by Phenolphthalein indicator. Both samples
remained color less
 Carbonation of concrete is associated with the
corrosion of steel reinforcement and with shrinkage
 Carbonation is the result of the dissolution of CO2 in
the concrete pore fluid and this reacts with calcium
from calcium hydroxide and calcium silicate hydrate to
form calcite (CaCO3).
 Thaumasite sulfate attack (TSA) is a special form of
sulfate attack typically occurring due to the availability
of carbonates/bicarbonates in the cementitious matrix
 N. B. Winter, Understanding Cement (2012)

11. X-ray Diffraction
11
394
341
1330
340
608
739
215
320
252 226
218
373
375
186
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200 1400 1600
Intensity(Counts)
2 Theta (2θ)
Quartz, syn - SiO2
Thaumasite -
Ca3Si(SO4)2(OH)6!9H2
O Thaumasite -
Ca3Si(OH)6[CO3][SO4]
!12H2O
Ca4Al2O6(SO4)!14H2O -
Calcium Aluminum
Sulfate Hydrate
Ca2SiO4!H2O - Calcium
Silicate Hydrate
Ca4Al2S2O9!xH2O -
Calcium Aluminum
Sulfate Hydrate
Ca2SiO4!3H2O -
Calcium Silicate Hydrate

12. Final Diagnoses
12
On the basis of field and experimental
inspection and literature review, it was proved
that concrete was attacked by Sulphate and
Thaumasite was detected in X-ray Diffraction
analysis. As initially indicated the possibility of
Sulphate attack or Thaumasite attack due to
exposure and carbonated concrete is now
become the major problem at Rawal Dam.
There are two possible routes for Thaumasite
formation: direct and indirect. At Rawal Dam
concrete is subjected to direct Thaumasite formation.
Thaumasite is formed through the reaction of calcium
silicate hydrate (C–S–H) with calcite in the presence
of moisture and unbound sulfate ions, according to
Eq.
SO4-2 + 3Ca+2 + Co3-2 + SiO3-2 + 15H2O
3CaO.SiO2.Co2.So3.15H2O

13. Influencing Factors
■ Presence of a sulfate, including sulfide that may decay to Sulphate.
■ pH level
■ Presence of carbonate (including carbonate in concrete aggregate)
■ Presence of moisture
■ C3A Content in Cement
■ Low temperatures (below 15°C)
■ Concentration of Sulphate ions
■ Type and quantity of cement used in concrete
■ Quality of the concrete
■ Changes to ground chemistry and water regime resulting from construction
■ Type, depth and geometry of buried concrete and Exposure Conditions
■ Porosity, Type of admixture, air entrainment quantity, Water/binder ratio of mix, Degree of hydration,
Types of ions related to carbonation also influence the coronation/corrosion of reinforcement.
13

14. Proposed Remedies
■ Curing
■ Low w/cm(<0.40)
■ Placing
■ Clear cover
■ Proper Hydration
■ Compaction
■ Admixture
14
■ Effective drainage systems
■ Improved Impermeability of Concrete
■ Use appropriate SCMs with proven
performance
■ Avoid the use of carbonate‐rich materials in
concrete (e.g. Limestone materials) under
sulfate exposures
■ Use a reliable performance test that
simulate real field conditions
■ Use type v cement in concrete
For future construction at site, It is necessary to keep in mind the following parameters to avoid or
prolong the subjected attacks in concrete:

16. DoYouHaveany
Questions??