Corrosion of AISI 316 Stainless Steel Embedded in Green Concrete with Low Volume of Sugar Cane Bagasse Ash and Silica Fume exposed in Seawater

DOI: http://dx.doi.org/10.24018/ejers.2022.7.1.2716 Vol 7 | Issue 1 | January 2022 57 Abstract — In the present research the corrosion behavior of AISI 316 Stainless Steel was analyzed, as reinforcement in Green Concrete made with Low Volume of Sugar Cane Bagasse Ash (SCBA) and Silica Fume (SF), compared to AISI 1018 steel. Four concrete mixtures were made, all with a ratio w / c = 0.65, the percentages of substitution were 0%, 10%, 20% and 30%. The specimens were exposed in seawater as an aggressive medium, corrosion was evaluated by monitoring the corrosion potential Ecorr (ASTM C-876-15) and corrosion rate icorr (ASTM G59). The results of Ecorr and icorr after 150 days of exposure show a better performance of AISI 316 steel, with a 10% of probability corrosion and a negligible level of corrosion respectively, the Green Concrete with 30% partial replacement of the CPC by the combination of SCBA-SF presented the best protection against corrosion.


I. INTRODUCTION
For a couple of decades, researchers have pointed out that the corrosion process is one of the main deteriorations of reinforced concrete, considering it as an affectation of the performance of structures [1]- [4]. The corrosion in concrete structures is a very important economic, by billions of dollars in the world [5]- [10] concentrating these repair costs mainly on the infrastructure built in marine environments [11]- [21], it is for the above that in recent years, the scientific community has worked to counteract this phenomenon with different perspectives, from innovation in concrete technology, as well as cement, special additions of inhibitors, among others, as well as studies of different media, marine, urban, both real and simulated [22]- [26]. One of the most aggressive means is where the structures are exposed in marine environments, where high concentrations of chlorides are present, and the phenomenon of corrosion is more accelerated [27]- [34] also the sulfate ions are also considered as aggressive agents [35]- [46]. To diminish this phenomenon, there is a history of the use of additions or substitutions of Submitted  portland cement for such as rice clay ash [47], fly ash [48], [49], sugar cane bagasse ash [50]- [52] and slag from blast furnace [53]. Likewise, the use of stainless steel 316 to reduce the phenomenon of corrosion and therefore increase the durability of concrete structures exposed in marine environments [54]. In this investigation, reinforced concrete specimens with sustainable concrete and reinforcement steels of 304 stainless steel and AISI 1018 steel were made. The ternary concretes were made with substitutions of sugarcane bagasse ash (SCBA) and silica fume (SF) agroindustry and industrial waste products respectively. Likewise, a conventional concrete was developed to be used as reference and comparison for ternary concrete. Results of Ecorr and Icorr from the steels of a 180-day evaluation period are presented for the sustainable concrete exposed to a marine environment as an aggressive environment and drinking water as a means of control. The main objective of this research is to contribute to the scientific society with information necessary to build sustainable concrete structures that help increase the durability of these exposed in marine environments, and likewise, that present an environmental and economic benefit to our society.

A. Materials 1) Dosage of Concrete Mixtures
The dosage of concrete mixtures was carried out according to the method of ACI 211.1 [55]. This method is based on the quality of the concrete required, taking into account mainly the resistance to strength compression (F'c), the settlement (workability or consistency), and in addition to the characterization of the physical properties of the aggregates (sand and gravel) to be used, knowing these parameters it is possible to perform the necessary concrete dosage, which determines the quantity of materials (cement, water, gravel and sand). Table I summarizes the physical characteristics of the aggregates, the tests were performed in accordance with the ASTM standards [56]- [59]. Table II summarizes the dosages of the Green Concretes produced. The study mixtures were with relation w / c = 0.65. The reference mixture (REF) with 100% composite portland cement (CPC). Subsequent mixtures were made partial portland cement substitutions from 10% to 30%, these percentages were formed by 50% of each addition used, for example, the second mixture with partial replacement of 10% CPC by SCBA and SF it contains is of 5% Sugar Cane Bagasse Ash and 5% of Silica Fume.

B. Method 1) Characterization of Fresh and Hardened of Green Concrete
In accordance with the ONNCCE and ASTM standards [60]- [63], the tests were carried out to determine the physical and mechanical characteristics of the fresh and hardened concrete. The tests performed were slump, temperature, volumetric mass, and compressive strength (F'c), the results are summarized in Table III.

2) Specifications of the test specimens
The following steel bars were embedded in the study specimens: an AISI 1018 steel bar with a 3/8 "diameter, the second 316 stainless steel bar with a 3/8" diameter and a third 304 stainless steel bar with a diameter of 1/16 ". The first two bars were used as working electrodes (WE) for the evaluation of the corrosion behavior (monitoring of Ecorr and Icorr) as indicated in the literature [64], the two bars delimit an area of exposure as shown in Fig. 1. A 304 stainless steel rod was used as the auxiliary electrode.

3) Nomenclature of the specimens
For the identification of laboratory tests and steels for electrochemical evaluation, the nomenclature presented in Table IV is established. It is mainly based on the Green Concrete mixtures, the exposure medium and the steels embedded in the concrete.

4) Specimens exposed to seawater (Electrochemical cell).
For the evaluation of the electrochemical behaviour of the steels embedded in the Green Concrete, concrete cubes were made (15×15×15 cm). The electrochemical cell was manufactured in accordance with what is established in ASTM G59 [65] to be able to use linear polarization resistance electrochemical (LPR), see Fig. 2. Technology and the results were detected by the "Analysis" of version 4 of ACM. The parameters used to perform the LPR test, they were the same as those used by other researchers [66], the sweep potential was ±20 mV with respect to the corrosion potential and the sweep rate was 10 mV/minute, the IR drop potential was considered. The corrosion current density (Icorr) was estimated from resistance to charge transference (Rct) using: Corrosion Current Density (Icorr) = B/Rct (μA/cm 2 ) where B is Stern-Geary constant (B = 26 mV for uniform corrosion) [67].
This monitoring was conducted weekly with the concrete cubes immersed in Water as Control environment and Seawater as Aggressive environment. Fig. 2. Study specimens exposed to seawater. Table V shows the values obtained according to the ASTM C876-15 [68], to interpret the results of the corrosion potential of each of the test specimens, adding a rank according to the literature [69].  Fig. 3, we can observe the behavior of the corrosion potential of AISI 316 embedded in the Green Concretes exposed to a control environment (H2O), in the stage of curing the stainless steels present Ecorr values in a range of -40 to -180 mV. Then there is a trend with a decrease in Ecorr values, which we can observe from day 28 to 63. Subsequently, the Ecorr values are maintained in an area of 10% probability of corrosion, and we can observe a better performance of the stainless steel embedded in the concrete with 20% and 30% substitution of CPC by the combinations SCBA and SF in low volume. The AISI 1018, have a greater variability in the corrosion potentials values (Ecorr), this showed more negative Ecorr values in the stage of curing (until 28 day), with Ecorr values in a range of -190 to -345 mV. The results after 28 days are in a range of -105 mV to -230 mV, the mixture that presents a best behaviour with Ecorr values located in the zone of 10% probability of corrosion, is the substitution of 20% of combination of SCBA and SF (10SCBA10FS-1-8).

A. Corrosion Potential (Ecorr)
Nevertheless, the mixtures with 10 and 30% of combination of SCBA and SF in the last days of monitoring, present Ecorr values that indicate indicating according to the ASTM C-876 standard corrosion uncertainty.
In Fig. 4, the behaviour of stainless steel 316 exposed to a seawater (Aggressive environment) is presented, a similarity of potentials in the reference mixture and with substitutions in the curing stage is observed. During the exposure time we can observe that the mixtures are maintained in an area of 10% probability of corrosion, the ranges are of the order of -160 mV and -20 mV. The stainless steels that present a greater positive tendency are those that are found within the 15SCBA15FS and 10SCBA10FS mixtures. Fig. 4. Ecorr of 316 and 1018 steel in concrete exposed to a marine environment.
In the case of AISI 1018, there is a trend of more negative Ecorr results compared with AISI 316, the AISI 1018 embedded in 05SCBA05FS and REF-2-8 concretes present more negative Ecorr values, in a range of -240 mV to -430 mV. The opposite case of the 10SCBA10FS and 15SCBA15FS mixtures at the beginning of the evaluation presented more positive Ecorr results and from day 63 they tended to an area of greater negativity to reach an area of 90% probability of corrosion. The results of the Corrosion Current Density (Icorr), were interpreted according to the criteria of the Red Durar Manual (70), see Table VI.

A. Corrosion Current Density (Icorr)
In Fig. 5 present of the results of Icorr of all specimens' study in a period of 180 days of exposure in a control medium (H2O). The 316 stainless steel has an excellent anti-corrosion behavior with values that are in a negligible area below 0.1 μA/cm 2 . In the case of AISI 1018 steels embedded in a reference concrete and in a 10% substitution, they show an activation from the beginning of the evaluation period oscillating between a high and moderate level of corrosion. The AISI 1018 steels that are found in the mixtures with 20% and 30% substitutions (10SCBA10FS and 15SCBA15FS) present an activation in the first 14 days appearing at the high and moderate level of corrosion level and later reach at the age of 63 days a passivity when positioning in a zone of negligible corrosion level. According to the above we can see a benefit to add SCBA and FS in the concrete conventional.
In Fig. 6, the Icorr results of steels embedded in Green Concrete exposed to a seawater (Aggressive environment) are presented. The specimens with AISI 316 show an excellent behavior when kept in an area of negligible corrosion level, the best behavior is contributed to the 15SCBA15FS mixture when obtaining values of 0.11 to 0.01 μA/cm 2 . Fig. 6. Icorr of 316 and 1018 steel in concrete exposed to a marine environment.
The specimens with AISI 1018 presents a greater value of Icorr, from the beginning of the evaluation to the end. The specimen made with the reference concrete (100% CPC) is maintained in a zone of high corrosion level all time. However, the Icorr results of the specimens of the Green Concretes made with 10 and 20% substitutions of SCBA and FS (5SCBA5FS and 10SCBA10FS) from the day 35 they have a tendency to a zone of moderate corrosion level. The best performance is attributed to the Green Concrete made with a 30% substitution (15SCBA15FS) present the AISI 1018 steel embedded activation in the first 14 days of exposure, later passing to an area of corrosion level moderate until day 49 and subsequently remained in a zone of negligible corrosion level to obtain 0.92 to 0.06 μA/cm 2 .

IV. CONCLUSIONS
The specimens with AISI 316 embedded in Green Concrete made with 30% (15% of Suggar Cane Bagasse Ash and 15% of Silica Fume) showed the better behavior or corrosion resistance after the 180 of exposition in Seawater (Aggressive environment), with values of Icorr below 0.10 μA/cm 2 .
The specimens with AISI 1018 steel embedded in the Green Concrete, made with 30% (15% of Suggar Cane Bagasse Ash and 15% of Silica Fume), presents a very acceptable behavior; with a moderate corrosion level until day 49, for to present values of Icorr of 0.92 to 0.06 μA/cm 2 to the end the monitoring due to the denser concrete matrix of Green Concrete.
The best percentage of substitution in Green Concretes was 30% (15% of Suggar Cane Bagasse Ash and 15% of Silica Fume), presenting the best performance against corrosion when using AISI 316 stainless steel when exposed to very aggressive media such as seawater.
The results show that Green Concretes can be used to build Civil Infrastructure in marine environments, presenting great resistance against corrosion by seawater as well as contributing to sustainability due to the use of agro-industrial and industrial waste that the least in Mexico is not used in the proportions and combinations presented in this research.
ACKNOWLEDGMENT MA Baltazar-Zamora et al., thank PRODEP for the support granted by the SEP, the Academicians UV-CA-458 "Sustainability and Durability of Materials for Civil Infrastructure" under the Call 2018 for Strengthening Academic Bodies with IDCA 28593. Thanks for the technical support to Brenda Paola Baltazar García.