Recipient Organization
ARIZONA STATE UNIVERSITY
660 S MILL AVE STE 312
TEMPE,AZ 85281-3670
Performing Department
School of Sustainable Engineering and the Built Environment
Non Technical Summary
The US has around 165,000 mile long reinforced concrete pavements (RCPs). Severe corrosion damage of embedded rebars due to chloride ions from road deicers necessitates expensive repair or replacement of RCPs. Americans lost around $160 billion in delays and fuel costs due to road closures in 2014. Existing stand-alone corrosion mitigation methods are found to be inadequate, highlighting the need for a comprehensive approach.In our recent studies, we found that the polyol molecules and compounds in corn and beet juice adsorb to the rebar surface, forming a molecular-scale layer lowering the corrosion rates up to 92%. We hypothesize that the corrosion in the rebars embedded in concrete can be mitigated by constantly supplying agro-derived corrosion inhibitors during the life of the RCPs. The overarching goal of this research is to develop a three-pronged synergistic bio-based corrosion inhibitor system for mitigating corrosion in RCPs. Research objectives are:1. to develop a coating, natural fiber corrosion inhibiting admixture, and a migratory corrosion inhibitor from agricultural products that can act synergistically to mitigate corrosion in RCPs2. to quantify the corrosion inhibition potential of the envisaged agricultural products, and to understand the role of synthesis design parameters3. to identify crucial design parameters and to model the corrosion inhibition potential of proposed bio-based corrosion inhibition productsCommercialization of the proposed bio-based inhibitors creates new jobs, expands the utilization of corn, soybean, beets, and wheat, generating an additional annual income to the US farmers aligning well with the priorities of the program.
Animal Health Component
20%
Research Effort Categories
Basic
80%
Applied
20%
Developmental
0%
Goals / Objectives
The long-term goal of this study is to develop low-cost, non-toxic, and scalable corrosion mitigation products from agricultural feedstocks to minimize corrosion damage in reinforced concrete pavements (RCPs).
Project Methods
Research Task-1: Synthesis of Polyol-soy Protein Coating: Besides being cost-effective and non-toxic, the main advantage of the envisaged polyol-soy protein coating is its ease of on-site application to rebars, unlike epoxy coatings. We envisage that the polyol-soy protein coating provides physical protection during the initial stages of concreting, and the polyol in the coating eventually gets adsorbed on to the metal surface as the concrete hardens while the coating comes in contact with pore water. The envisaged bio-based polyol-soy protein coating is synthesized using Method-A.Method-A: "X" weight units of soybean flour with approximately 45% protein content and 5% of moisture content will be suspended in "1.6X" weight units of 5% polyvinyl alcohol solution and "1.4X" weight units of corn polyol aqueous solution. The % weight of polyol in the aqueous solution is a design parameter (d1) and will be determined through a parametric study to achieve the best corrosion inhibition results. To this solution, 4-6% by weight ethylene diglycidyl ether is added to initiate crosslinking. Note that soybean flour is a mixture of soy proteins and carbohydrates that contain many polar functional groups like -OH, -NH2, -COOH, and -SH and hence, different commercially available agents with an epoxy group can be used for crosslinking. Based on our preliminary results, the resultant coating is proven to have low viscosity, high solid content, superior water resistance, and adhesive strength. Several other methods for the synthesis of soy adhesives/ coatings available in the literature may be pursued if they are time and cost-effective and have non-corrosive ingredients.Research Task-2: Synthesis of Bio-based Polyol Impregnated Natural Fibers: The polyol impregnated fibers when used as admixture (not as reinforcements) to fresh concrete act as time-release capsules after the concrete hardens slowly releasing polyol into the concrete pore water acting synergistically with the coating and the migratory inhibitor. The bio-based polyol impregnated fibers are manufactured employing Method-B.Method-B: Chopped wheat straw (30-50 mm length) will be soaked overnight and will be defibrillated through a compact refiner with 2-3 mm gap-width multiple times producing fibers over 20 mm length and around 100 μm diameter fibers. These fibers will be used for the synthesis of polyol impregnated fibers considering their low-cost, proven stability in the concrete environment, and polyol solute absorbability. The length of the fibers that will be used for preparing impregnated fibers is considered as a design parameter (d2) and its influence on corrosion inhibition will be investigated in later tasks. The wheat straw fibers will be soaked in Y% wt. polyol (Y- design parameter d3) aqueous solution for time "t" which is a design parameter (d4) that has to be optimized for obtaining the desired levels of corrosion inhibition. After soaking, the fibers will be air-dried to remove excess unabsorbed polyol solution. In the next step, the polyol-soy protein coating developed in the previous step without polyol can be sprayed on the air-dried soaked fibers that will significantly prevent the immediate release of polyol from the fibers into the fresh concrete. The use of this additional coating is a design parameter (d5) and its necessity will be investigated through experiments and statistical studies.Research Task-3: Synthesis of a Polyol/ Corn/ Beet Juice Migratory Corrosion Inhibitor: The role of the migratory polyol based corrosion inhibitor is to provide protection against the highly corrosive chloride ions from the deicing salts. The migratory corrosion inhibitor is prepared by mixing a polyol or corn or beet juice to the brine solution that is applied as a deicer in the winter season. The weight fractions of the polyol/ corn, and beet juice are the design parameters d6, d7, and d8 that will be calibrated in order to obtain the maximum corrosion inhibition.Research Task-4: Characterization of Corrosion Inhibition Potential of Envisaged Products: In this task, the corrosion inhibition potential of polyol-soy protein coating, polyol impregnated fiber admixture, and migratory corrosion inhibitor will be experimentally evaluated as a function of design parameters using the Method-C and -D.Method-C: Round disk-shaped specimens will be made from commercially available uncoated US grade 40, 60, 75, 80, and 100 (grade number represents yield strength in ksi) along with epoxy coated rebars by spray coating them with polyol-soy protein coating material with the design parameter-polyol weight fraction ranging between d_1=2-16% in 2% increments. Standard three-electrode electrochemical system with a coated sample as the working electrode, standard calomel as the reference electrode, and platinum plate as the counter electrode will be built. Two electrolyte solutions: (a) 3.5% wt. NaCl in saturated calcium hydroxide solution simulating seawater exposed concrete environment, and (b) 23.4% wt. NaCl in saturated Ca(OH)2 simulating concrete exposed to deicing salts will be chosen as the electrolytes in the system. The pH of the electrolyte is maintained at 11 to simulate the alkalinity of the hardened concrete. Linear polarization resistance and potentiodynamic polarization tests will be conducted on all the specimens to characterize and compare the corrosion rates, adsorption isotherms, and inhibition in cathodic, and anodic reactions for considered values of design parameter, d1. Besides, 30-day accelerated corrosion tests will be conducted for all the coated specimens by exposing them to both 3.5%, and 23.4% wt. NaCl, Ca(OH)2 solutions to measure the mass loss due to corrosion. X-ray powder diffraction and FTIR tests will be conducted on 30-day exposed samples to characterize the chemical composition, and passivity of the corrosion products (if any) formed on the coated steel specimens.Method-D: The polyol-impregnated fibers and migratory corrosion inhibitor act by releasing polyol/ corn/ beet juice into the concrete pore water, which eventually gets adsorbed on to the metal surface. The performance of the polyol impregnated fibers and the migratory inhibitor will be measured by employing the electrochemical tests described in Method-C, albeit some changes. Instead of NaCl-Ca(OH)2 solution, 23.4% NaCl aqueous solution mixed with various weight fractions of bio-based polyol impregnated fibers (1-2% wt. of solution), polyol /corn juice/ beet juice will be used as electrolytes as these solutions are more representative of the pore solution that is contaminated by deicing salts and modified by impregnated fibers and/ or migratory corrosion inhibitor. Corrosion rates, adsorption isotherms, inhibition in cathodic, and anodic reactions will be quantified for the following ranges of design parameters: d2=10-50 mm of fiber length, d3=2-20% wt. fraction of polyol, d_4=15-60 minutes soaking time, d5= coated/ uncoated fibers, d6=0.25-1.5% wt. polyol, and d7, d8=1-4% wt. fraction of juice.Research Task-5: Experimental Data Analysis for the Determination of Crucial Design Parameters and Prediction of Corrosion Inhibition Potential: Time and cost of preparation and application of the envisaged products is of high importance to the construction industry. Moreover, it is also important to evaluate the most crucial design parameters and a data-driven model that can utilize these parameters to predict the corrosion inhibition potential of proposed products.