Grantee Research Project Results
Final Report: Using hazardous byproduct of mining industry as a corrosion inhibitor
EPA Grant Number: SU836119Title: Using hazardous byproduct of mining industry as a corrosion inhibitor
Investigators: Nossoni, Goli
Institution: Manhattan College
EPA Project Officer: Page, Angela
Phase: I
Project Period: November 1, 2015 through August 31, 2016 (Extended to October 31, 2017)
Project Amount: $14,830
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2015) RFA Text | Recipients Lists
Research Category: P3 Awards , Pollution Prevention/Sustainable Development , Sustainable and Healthy Communities , P3 Challenge Area - Sustainable and Healthy Communities
Objective:
The objective of this research project is to determine the efficacy of a new sustainable concrete to alleviate corrosion of steel reinforcement in the presence of chloride. The sustainable concrete will utilize the industrial waste product “chat” as a mineral additive and/or aggregate with positive environmental effects.
Chat is a byproduct of mining and milling operations in lead and zincs mines. Commutation of chat piles in lead and zinc mining sites is one the main environmental challenges in the three states of Missouri, Kansas and Oklahoma. Federal agencies have suggested that chat be used in concrete and asphalt as aggregates for environmental protection purposes since it contains varying concentrations of lead. However, a relatively unrealized positive potential of adding chat into concrete is that of chloride fixing, which can significantly reduce and perhaps even eliminate corrosion of reinforcing steel. When chloride diffuses into concrete it can chemically bond to the free lead (Pb) in chat and form PbOHCl (ksp = 2 × 10-14) and possibly PbCl2 (ksp =1.17 × 10-5). The solubility of both products in water is very low and this bonding prevents further movement of chloride inside concrete. This project will develop a sustainable concrete that will keep the [Cl-]/[OH-] ratio below the threshold value required to initiate corrosion, thereby keeping steel reinforcement corrosion free.
The proposed project intends to improve the health and welfare of the people, especially in the three states of Missouri, Kansas and Oklahoma, by using the hazardous waste byproduct of the mining industry in an application that enhances sustainability and improves environmental quality. Also, this application promises to increase economic prosperity by resulting in more corrosion resistant infrastructure and annually saving a considerable fraction of the $5.2 billion spent on maintaining our aging infrastructure. Further, the research will contribute to preserving the future environment of the planet by reducing the demand on natural aggregate and replacing it with a waste and unavoidable byproduct of the mining industry.
Summary/Accomplishments (Outputs/Outcomes):
The purpose of phase I of the proposed research was to investigate the feasibility of using chat as a corrosion inhibitor in concrete. The potential bonding capacity of chat to chloride ions was investigated through laboratory experimentation. Also, the effect of using chat as replacement for aggregate on the concrete compressive strength, which is the most important mechanical property of concrete, was investigated. The results from phase I of the project were very encouraging and showed the tremendous promise of this approach. Chat was able to reduce the free chloride ions inside concrete by chloride bonding capacity of concrete. Also, using chat as a replacement of aggregate increased the compressive strength of concrete.
1) Using Chat to Replace Aggregates Increased Chloride Binding Capacity
A basic screening test was done to determine the possible binding capacity of chat when it is used as coarse aggregate in concrete. This test examined the effectiveness of the approach when chat reacts chemically with other ingredients in concrete. The experiments studied the binding capacity of concrete samples exposed to 3.5% salt solution for 10 days when 25%, 50% and 75% of coarse aggregate by weight was replaced by chat. The chloride binding capacity was measured using both ASTM C1218 (Standard Test Method for Water-Soluble Chloride in Mortar and Concrete) and ASTM C1152 (Standard Test Method for Acid-Soluble Chloride in Mortar and Concrete). The non-water soluble chloride content of the concrete is the difference between the water soluble and acid soluble chloride contents and shows the capacity of concrete to bind diffused chloride. The initial screening results were very promising. Figure 1 shows that as the percentage of chat replacing coarse aggregate was increased, the capacity of concrete to bind diffused chloride also increased. Although the amount of free chloride removed was relatively low, it is expected that as the size of chat incorporated in concrete is reduced, e.g., fine aggregate is replaced with chat or chat is added as mineral additive, the capacity of concrete to bind diffused chloride will increase.
Figure 1. Percent of Coarse Aggregate Replaced with Chat
2) Using Chat to Replace Aggregates Increased Concrete Strength
Given the positive results of the initial screening on chloride binding capacity, the effect of using chat to replace coarse aggregate on the compressive strength of concrete was investigated. The compressive strength tests were done according to ASTM C39 (Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens) for the concrete samples in which 25% and 50% of coarse aggregate by weight was replaced with chat. The results were compared with the compressive strength of concrete with the same mix design and normal coarse aggregate. Figure 2 shows the 1-week and 10-week compressive strength of the concrete samples. The compressive strength generally increased as the percentage of coarse aggregate that was replaced by chat increased.
Figure 2. Compressive strength of concrete without and with coarse
aggregate replaced by chat.
Conclusions:
The purpose of the phase I research was to investigate the feasibility of using chat, a hazardous byproduct of zinc and lead mining industry, as a corrosion inhibitor in concrete. Chat contains varying amounts of lead which has a potential to increase the diffused chloride binding capacity of concrete. Two main tests of (1) concrete chloride binding capacity, and (2) concrete compressive strength were performed during phase I. The chloride binding capacity test was performed to verify the potential of the approach and the compression strength test was performed to assure that chat does not affect the concrete’s most important mechanical property.
Both tests showed positive results indicating that as the percentage of coarse aggregate replaced by chat increased: (1) the chloride binding capacity of concrete increased, and (2) the compressive strength of concrete increased. These findings verify that chat can be used intelligently to create a more sustainable concrete infrastructure, thereby providing environmental benefits.
Journal Articles:
No journal articles submitted with this report: View all 1 publications for this projectSupplemental Keywords:
concrete, chat, coarse aggregate, chloride removal, corrosion inhibitors, compressive strengthProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.