Corrosion in steel can be detrimental in any steel rebar reinforced concrete as well as in the case of steel fibre reinforced concrete. The process of corrosion occurring in steel fibre incorporated concrete subjected to corrosive environment was systematically evaluated in this study. Concrete specimens were prepared with steel fibre inclusions at 1.5%
The process of corrosion in reinforced concrete elements requires more focus in the present construction practice due to the reduction in service life performance. Steel inclusion in concrete elements cannot be avoided as a result of corrosion process and necessitates more careful technique for designing the concrete elements. Right selection of concrete constituents and careful mixture proportion can provide a highly integrated concrete, which can substantially abate the process of corrosion initiation. More promising methods for protecting steel bars in concrete were found to exist. Several research studies showed the advantages of using anticorrosion agents, sacrificial anode by cathodic protection, and epoxy coating on the steel bars in civil engineering application. However, the cost of concrete construction is an important factor for executing infrastructure project and, hence, additional protection techniques can increase the cost. Hence, it is better to find a cost effective technique with the proper selection of concrete which can protect the rebar against corrosion [
The present research study evaluates the effects of ground granulated blast furnace slag and corrosion inhibitor on the process of corrosion in steel fibre reinforced concrete. The significance of filler binder materials (slag) for better improvement on the strength properties (such as compressive and flexural) of steel fibre concrete is studied. Enhanced interfacial characteristics and bonding stress between cement and the fibres are also investigated systematically.
The details of concrete making materials used in the present study are as follows.
Ordinary Portland cement of grade 53 which had a specific gravity of 3.14, fineness modulus 2.56, consistency limits 32%, initial setting time 165 min, and final setting time of cement 255 min was used.
A crushed granite waste such as manufactured sand (M-sand) conforming to zone III as per IS 383-1970 [
The physical properties of ground granulated blast furnace slag are as follows: specific gravity 3.43 and fineness modulus 3.35. The chemical properties are as follows: carbon (C) 0.24%, manganese (Mn) 0.58%, sulphur (S) 0.05%, phosphorous (P) 0.06%, free silica 6.10%, and iron (Fe) 92.97%. Slag was replaced for cement at 20%, 40%, and 60% by weight of binder.
In order to improve the workability properties of concrete and to avoid the harshness of the concrete at low water content, the addition of chemical admixtures was found to be essential. In the present study, a polycarboxylate ether based superplasticizer was used at an optimum dosage of 1.5% (by weight of cement). The mix water used for preparing concrete specimens was free from chlorides and sulphates. The study was also conducted with addition of anticorrosion inhibitors at 0.3%, 0.6%, and 0.9% by weight of steel fibres.
Glued steel fibres as shown in Figure
Glued steel fibres used in the study.
A high strength concrete grade of M40 was designed as per IS 10262-2009 [
Various concrete mixture proportions used in the study.
Mix ID | w/b ratio | Steel fibres ( |
Slag % | Anticorrosion inhibitors | SP % | Cement | Slag | Manufactured sand | Coarse aggregate | Water |
---|---|---|---|---|---|---|---|---|---|---|
kg/m3 | ||||||||||
GGC1 | 0.3 | 0 | 0 | — | 1.5 | 449 | 0 | 712 | 1165 | 135 |
GSF5 | 0.3 | 1.5 | 0 | — | 1.5 | 449 | 0 | 712 | 1165 | 135 |
GSF6 | 0.3 | 1.5 | 20 | — | 1.5 | 359 | 90 | 712 | 1165 | 135 |
GSF7 | 0.3 | 1.5 | 40 | — | 1.5 | 269 | 180 | 712 | 1165 | 135 |
GSF8 | 0.3 | 1.5 | 60 | — | 1.5 | 179 | 270 | 712 | 1165 | 135 |
AC1 | 0.3 | 0 | 0 | 0.3 | 1.5 | 449 | 0 | 712 | 1165 | 135 |
AC2 | 0.3 | 0 | 0 | 0.6 | 1.5 | 449 | 0 | 712 | 1165 | 135 |
AC3 | 0.3 | 0 | 0 | 0.9 | 1.5 | 449 | 0 | 712 | 1165 | 135 |
Note:
Alternate wetting and drying cycles are done in order to accelerate the deterioration process. Similarly, the initial loading of concrete reflects the real-time situation wherein the concrete sustains dead load and results in opening up of stress induced microcracks. This actually provides the real quantification on the process of accelerated corrosion mechanism. Hence, the initial stress on the concrete can open up the microcracks and promulgates the water and chloride ions to penetrate the concrete specimens which can initiate the corrosion process of steel fibres. Initially, the specimens were cured for required 28 days and later stressed initially up to 40% and 60% of the ultimate load. Later, the specimens were subjected to alternate wetting and drying cycle for 28 days. This process is continued up to 6 months and subsequent testing was carried on the concrete specimens. After stressing, the specimens were immersed in chloride-free water (curing tank) for 1 day and later taken out for drying in hot air oven at 100°C for 1 day. This process is continued for 28 days till testing.
Similar methodology was also adopted for the other set of concrete specimens wherein the specimens were cured in sodium chloride solution prepared at 3% concentration and the snapshot of cubes and beams immersed in the solution are shown in Figures
(a) Cube specimens cured in NaCl (3%) solution. (b) Beam specimens cured in NaCl (3%) solution.
Compressive test was conducted in universal compressive testing machine of capacity 2000 kN at a loading rate of 2.5 kN/sec (as shown in Figure
Initial stress applied to concrete specimens.
Snapshot of flexural test setup.
Test results of various steel fibre concrete specimens subjected to initial stress and cured in water and salt solution are provided in Figure
Compressive strength of concrete for alternate wetting and drying of concrete specimens in chloride-free water (stressed at 40% ultimate load).
Failure pattern of corroded steel fibre concrete specimen.
Compressive strength of concrete cured in NaCl (3%) solution for various mixes (40% stressed).
Compressive strength of concrete cured in NaCl (3%) solution for various concrete mixes (60% stressed).
The flexural strength test results for various steel fibre concretes are presented in Figure
Flexural strength of concrete specimens for alternate wetting and drying cycles for various concrete mixes (subjected to 40% initial stress).
Plain concrete specimens exposed to sodium chloride solution (3%).
Flexural testing of corroded steel fibre concrete specimens.
Flexural strength of concrete specimens cured in sodium chloride solution for various concrete mixes (subjected to 40% initial stress).
The effects of corrosion in different concrete mixes were analyzed after failure and the degree of corrosion occurring in concrete specimens were shown in Figure
Snapshot of corroded steel fibres in different concrete mixes containing slag and corrosion inhibitor.
Variation of flexural strength with respect to % of reduction in thickness of steel fibres.
Variation of reduction in steel fibre diameter and the percentage reduction in steel fibre diameter for various concrete mixes.
Based on the experimental investigation, the following conclusions are drawn within the limitations of the test results. Compressive properties of steel fibre concrete specimens were found to be affected when exposed to accelerated corrosion process due to rapid deterioration. Alternate wetting and drying cycles of all plain steel fibre concrete mixes in normal water curing and salt curing showed rapid corrosion process after 28 days of curing period. The influence of initial stress on the steel fibre concrete specimens reported faster initiation of corrosion process in steel fibres present in the concrete system. This provides a reliable estimate for predicting the corrosion potential in different concrete systems. Compressive properties were found to be favourably improved in slag incorporated steel fibre concretes compared to plain steel fibre concretes. Compared to concrete specimens subjected to normal water curing, the specimens immersed in salt solution showed faster deterioration in terms of concrete surface deterioration as well as corrosion of steel fibres. Strength increase was noticed in all steel fibre concrete specimens incorporating slag and corrosion inhibitors. This could be possibly due to improved micostructural properties of slag concrete and the corrosion inhibitors possibly reduced the intensity of steel fibre corrosion. Compressive strength was found to be higher (54.49 MPa) in 40% slag substituted concretes as well as with the addition of corrosion inhibitor at 0.6% showing 52.50 MPa. Flexural strength results also showed improvement with the slag substitution (60%) as well as corrosion inhibitor (0.9%) added steel fibre concrete mixes. A maximum flexural strength of 5.89 Mpa was noticed in slag substituted concrete mixes subjected to severe wetting and drying cycles accompanied with initial stress up to 40%. The intensity of corrosion was measured with the reduction of steel fibre diameter and can predict the degree of corrosion measured in terms of percentage of corrosion potential. A maximum reduction in corrosion percentage up to 25.33% and 6.67% was noticed in slag and corrosion inhibitor substituted concrete mixes, respectively. Corrosion potential was found to be reduced in the case of slag substituted steel fibre concrete mixes up to a maximum of 25.33%.
The authors declare that there is no conflict of interests regarding the publication of this paper.