Effects of Bleeding on the Corrosion of Horizontal Steel Bars in Reinforced Concrete Column Specimens
Corresponding email: kkawaai@cee.ehime-u.ac.jp
Published at : 29 Jul 2019
Volume : IJtech
Vol 10, No 4 (2019)
DOI : https://doi.org/10.14716/ijtech.v10i4.2503
Sandra, N., Kawaai, K., Ujike, I., Nakai, I., Nsama, W., 2019. Effects of Bleeding on the Corrosion of Horizontal Steel Bars in Reinforced Concrete Column Specimens. International Journal of Technology. Volume 10(4), pp. 741-752
| Nevy Sandra | -Graduate School of Science and Engineering, Ehime University, 10-13,Dogo Himata, Matsuyama, Ehime 790-8577, Japan -Department of Civil Engineering, Faculty of Engineering, Universitas Negeri Padang, |
| Keiyu Kawaai | Graduate School of Science and Engineering, Ehime University, 10-13,Dogo Himata, Matsuyama, Ehime 790-8577, Japan |
| Isao Ujike | Graduate School of Science and Engineering, Ehime University, 10-13,Dogo Himata, Matsuyama, Ehime 790-8577, Japan |
| Ippei Nakai | Graduate School of Science and Engineering, Ehime University, 10-13,Dogo Himata, Matsuyama, Ehime 790-8577, Japan |
| Willick Nsama | Graduate School of Science and Engineering, Ehime University, 10-13,Dogo Himata, Matsuyama, Ehime 790-8577, Japan |
The durability
of reinforced concrete has proven to be predominantly influenced by its resistance
against the ingress of harmful substances such as chloride ions, carbon dioxide
and moisture. The corrosion of steel bars which occurs especially in marine
environments is likely to be severe, depending on the availability of oxygen
and the moisture consumed by cathodic reactions. This study aims to investigate
the effects of bleeding on the corrosion of horizontal steel bars placed in
reinforced concrete column specimens. The issue was examined through
electro-chemical tests, including half-cell potential, polarization resistance
and corrosion current density, conducted using specimens in which corrosion was
induced via dry and wet (NaCl 10%) cycles. The presence or absence of copper
slag fine aggregate and fly ash replacement was employed as an experimental parameter.
The results suggest that the corrosion of horizontal steel bars in the upper
part of the column concrete specimens was adversely affected, even in the case
of OPC specimens with relatively lower bleeding water. This was attributed to lower
resistance against the ingress of corrosive substances, especially in such
locations. In the case of fly ash mixtures, resistance to corrosion was
significantly improved owing to lower oxygen permeability of less than
1.0×10-11mol/cm²/sec, measured via the cathodic polarization
technique. The replacement of fly ash is effective in facilitating more uniform
quality in the column specimens due to a lower level of bleeding water and
higher resistance to segregation and pozzolanic reactions.
Bleeding; Chlorides; Corrosion; Horizontal steel bar; Oxygen permeability
Conventionally, reinforced concrete (RC) structures have been considered to be maintenance-free because of their highly durable. However, in recent years a decrease in the durability of RC structures caused by the corrosion of steel bars has become a major social problem. These structures are widely used for infrastructure such as tunnels and bridges, but their durability is adversely affected by such corrosion when exposed to aggressive environments, such as chloride and acid attack (Wang et al., 2014). Indonesia is an archipelagic state and many provinces are located in the coastal areas of each island. It is inevitable that corrosion of steel bars embedded in concrete occurs, and tends to be caused by chloride ions from the sea environment during the service life. The use of sea sand has also led to the corrosion of steel bars in inland areas. Massive infrastructure development, as one of the realizations of the Nawa Cita (Nine Agendas) throughout the archipelago, such as road and bridge constructions is aimed at making cities in Indonesia more interconnected. The amount of concrete produced has increased in line with the increase in construction work, which could lead to the scarcity of natural resources, such as the sand generally used as fine aggregate. The excavation of sand could have a great affect on the environment. In this regard, an alternative material to replace the main constituent of concrete should be seriously considered. In recent years, the use of industrial by-products such as construction materials has been promoted as a sustainable approach (Shi et al., 2012). For example, the amount of coal ash which produces fly ash (FA) generated from electricity utilities such as coal-fired power plants is about 8.5 million tons in Japan, and around 300,000 tons in Shikoku, according to data published in 2011, and 8.31 million tons in Indonesia in (ESDM, 2019). On the other hand, about 400,000 tons of copper slag is produced annually in Indonesia by the Freeport Company and Newmont Company according to Ministry of Energy and Mineral Resources Republic Indonesia data from 2012, while 2 million tons of copper slag is produced in Japan each year by copper refining in Shikoku (SDAR, 2003).
Much research on the
utilization of these materials to produce concrete has been conducted.
According to a past study by Nakai et al. (2015), bleeding water tends to
increase in fresh concrete mixed with CUS because of its high density of 3.55
g/cm3. On the other hand, it has been suggested that bleeding water
could be reduced by the addition of FA, and long-term strength development is
expected from the pozzolanic reaction (Choi et al., 2006). Improving the strength
and durability of high strength concrete characteristics has been achieved by
the use of copper slag as a sand substitute at levels of up to 40–50% (by
weight of sand) (Al-Jabri et al., 2011). Moreover, the addition of slag to
high-performance concrete can increase its strength and produce an
anticorrosion effect through enhanced electrical resistivity and reduced
permeability (Hou et al., 2004). Copper slag containing 50% and 65% of slag
replacement when exposed to an aggressive environment has a more refined pore
structure than normal concrete, and better resistance to deterioration (Bouikni
et al., 2009). Therefore, studies on the durability of concrete, especially on
the corrosion of steel bars using copper slag and fly ash with partial
replacement, have been the focus of increased attention in recent years. The utilization
of copper slag and fly ash in concrete as a solution to the environmental
problem of the disposal of industrial waste in large quantities, and the sustainable
development associated with the preservation of natural resources, could be a
viable solution in Indonesia.
The corrosion
resistance of steel bars is a very important materials property in relation to
the durability of concrete structures (Hornbostel et al., 2013). Chloride-induced
corrosion is known to be most severe form, leading to a higher deterioration
rate. Chloride
attack is mainly caused by the ingress of chloride ions from the outside into
concrete cover in marine environments. The passive film is destroyed and the corrosion
of steel bars occurs when the chloride ion concentration at the depth of the bars
exceeds the threshold, i.e. 1.2 kg/m3 (Alonso et al., 2000). The
variation in chloride ion concentrations with respect to depth, i.e. their maximum
at a certain depth, especially under dry and wet actions was investigated by Andrade
and Chang (2018). Various nondestructive tests have been developed and studied to
assess corrosion
properties, as it is difficult to directly observe the corrosion processes of
steel bars embedded in concrete visually. Electrochemical methods such as the
half-cell potential method and the polarization resistance method (Bertolini et al., 2016) are promising because the corrosion of steel bars in concrete takes place
through electrochemical reactions consuming water and oxygen (Hansson et al., 2006). When corrosion of steel bars occurs, an
anodic reaction in which iron ionizes, and a cathodic reaction in which oxygen
is reduced, take place on the surface of the reinforcing bar and form a
corrosion cell. In the cathodic reaction, oxygen is consumed on the surface of
the steel bars; it has been reported that the rate of oxygen permeability is an
influencing factor which greatly affects the corrosion of steel bars in
concrete. In addition, the electrical resistivity of concrete cover is a
significant factor contributing to the corrosion processes when macrocell
formation occurs (Kawaai & Ujike, 2016; Otieno et al., 2016).
Pores
modified by bleeding water may have a great influence on durability with
respect to the ingress of harmful substances and corrosion processes owing to
chloride attack or carbonation. Bleeding in a form of segregation is
unavoidable in column specimens cast from a cast at height of 1.5 m, thus
leading to the formation of the vulnerable zones around the horizontally-
placed steel bars. The bleeding affects the integrity of the reinforced
concrete owing to the larger gaps or voids formed at the steel and concrete
interface. According to past investigation, the bleeding of fresh concrete
qualitatively diminishes the durability of horizontal steel bars embedded in
concrete structures (Mohammed et al.,
2002; Baccay et al., 2004).
Reinforced concrete column specimens were cast using various types of
aggregate, including crushed limestone, sandstone and pit sand obtained from
regional resources. The presence or absence of CUS and FA replacement was employed
as an experimental parameter. The study examined the resistance of horizontally
placed steel bars to corrosion resulting from the ingress of chloride ions in
column specimens cast with CUS and/or FA replacements, in which the bleeding
rate was varied. In particular, a detailed investigation was conducted on the
variation in chloride ion concentration in terms of height and depth, corrosion
current density, and oxygen permeability on the horizontal steel bars affected
by segregation, especially with bleeding water in the column specimens.
This
study aimed to investigate the effects of bleeding on the corrosion of
horizontal steel bars placed in reinforced concrete column specimens cast
with CUS and FA. This was examined through electro-chemical tests, including half-cell
potential, polarization resistance and corrosion current density, conducted
using specimens in which corrosion was induced via dry and wet (NaCl 10%)
cycles. The results suggest that the corrosion of the horizontal steel bars in
the upper part of the column concrete specimens was adversely affected by
bleeding water, even for the OPC specimens with a relatively lower bleeding
rate. This was attributed to less resistance against the ingress of corrosive
substances including chloride ions, water and dissolved oxygen, especially in
the upper part of the column concrete specimens. In the case of the FA
mixtures, more uniform pore structure in the column specimens was formed, which
led to higher corrosion resistance. This was subsequently improved through
pozzolanic reactions, leading to a lower rate of oxygen permeability.
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