IRAJ conference presentation.

1. “ D E T E R I O R AT I O N O F C O N C R E T E I N
N A M R U P B V F C L P L A N T ; A C A S E
S T U D Y ”
Author
Himangshu Bhuyan
Co-Authors
Ruhul A. Mozumder
Santanu Deb

2. INTRODUCTION
The study is carried on deterioration of an RC wall with increasing age in an urea
manufacturing P.S.U (Public Sector Unit) named Brahmaputra Valley Fertilizer
Cooperation Limited (BVFCL), Namrup Assam. BVFCL is located on the bank
of the river Dilli in the south-western border of Dibrugarh District in Assam,
India. This is the first factory of its kind in India to use associated natural gas as
basic raw material for producing nitrogenous fertilizer[1].
During a visit we found spalling of concrete from the walls and formation of
crystalline Silk like compound (SLC) as shown in the Figs

3. Appearance of
Reinforced
Bars

4. DETERIORATION OF RC WALLS OF THE
TOWER LEADS TO
• Loosened concrete with reduced compressive strength
• Redistribution of the internal force
• Decrease of the reliability
• Exposes the reinforcement to environmental attack and results in
corrosion of rebar
• Hinder the normal production and also put the safety of its workers
at stake.

5. OUR EXPERIMENTAL STUDY
Determination of
Unknown SLC (Silk
Like Compound)
Cause of Spalling of
Concrete
We classify our experimental study in
two categories:

6. SLC ANALYSIS
Study shows that this compound has some similar behavior as urea. It is water
soluble and makes our hand slippery when in contact with moisture. The
chemical composition of urea (CH4N2O) is shown in table 1. Again FEG-SEM
EDX [5] of this SLC shows the following result in table 2.
Element Percentage
C 20
N 46.67
O 26.67
Table 1 Table 2

7. In order to attain a confirmed result we make two solution one
containing urea and another containing SLC. Bothe in acidic medium
forms a lemon yellow colour when few drops of para-dimethyl-
amino-benzaldehide (PDAB) is added as shown below:
SLC solution Urea Solution
According to M XiaoJie, lemon yellow material will form when
para-dimethyl-amino-benzaldehide (PDAB) will react with urea
under acidic condition [6].

8. CAUSE OF SPALLING
Urea is hydroscopic in nature [7]. It can absorb moisture resulting in the
formation of concentrated urea solution. The urea solution get absorbed by the
walls of the tower and enters the pores. When the evaporation of the absorbed
urea solution takes place, it results in the formation of urea crystals in the pores
(sub-efflorescence) of the walls and also on its surface (efflorescence). Such
formation of crystals is taking place for many years till date. C.W Correns
derived an equation [9; 10] for quantifying the crystal pressure as
P=(RT/Vs)ln(c/cs)

10. CONCLUSION
The study revealed that spalling of concrete in BVFCL‘s
Urea III prilling tower was primarily due to the formation of
urea crystals inside the pores of the walls. The Silk like
compound formed on the walls are only urea crystals due to
efflorescence. This crystal formation inside the walls exert
stress on concrete which resulted in cracks.

11. THANK YOU