Dissertations and Theses @ UNI

Availability

Open Access Dissertation

Keywords

Concrete--Mixing; Water reuse; Concrete--Compression testing;

Abstract

Beginning with the Water Quality Act of 1987, requirements were put in place to control sediment run off from construction sites, which typically meant silt fences were installed and maintained on job sites. In 2009, when Aggregate Industries was fined $2.7 million by the Environmental Protection Agency (EPA) for poor management of concrete wash water, the disposal of concrete wash water became a significant issue. Following the EPA guidelines, the Minnesota Pollution Control Agency (MPCA) currently allows the dumping of excess concrete on the job sites, but requires control of all water used to wash concrete ready mix trucks, delivery chutes and tools used to finish concrete. Best Management Practices (BMPs) allow for containment of wash water either on the job site in a lined container or returned to the ready mix plant and stored in a lined pond. The BMPs do not suggest the reuse of the waste water. ASTM standards allow for use of concrete mixing water with up to 50,000 parts per million (ppm) suspended solids, which would allow limited reuse of the waste water. The Minnesota Department of Transportation (Mn/DOT) requires potable water in all concrete mixes used on their jobs, which means all waste water must be disposed in some manner. This study was a response to a needs statement from Mn/DOT asking for research on the environmental effects of concrete waste water. It was an investigation into a potential Best Management Practice for reuse of the water used to wash off ready mix trucks, delivery chutes and tools used to finish concrete. The research was a two by two design with two different concrete mixes, each designed to reach 4000 pounds per square inch (psi) at 28 days. One of the concrete mixes was from the American Concrete Institute (ACI) and the other mix was from the Minnesota Department of Transportation. Two different water sources, tap water and wash water from the settlement pond at the Central Concrete ready mix plant in Mankato, MN were used in the concrete mixes. Each concrete mix was paired with both tap water and wash water, making a total of four groups. Concrete was mixed using ASTM standards for materials, mixing and storage. Three separate batches of concrete were mixed in the laboratory for each group, making a total of five test cylinders per batch and a total of fifteen test cylinders per group. The 60 test cylinders were stored for 28 days in an environmental chamber, keeping both temperature and humidity within the ASTM standards. The cylinders were then tested for compressive strength using standard ASTM methodology. The three batches for each group were analyzed for mean compressive strength, variance and standard deviation within both the batch and the group. Results showed that the group with ACI mix and wash water had the highest mean compressive strength and lowest variability of the four groups. Both the Mn/DOT mix with tap water and the Mn/DOT mix with wash water had lower mean compressive strength than the ACI mixes and also showed higher variability. When compressive strength was analyzed across water source using a two-way ANOVA, the cylinders made with wash water tested at a statistically significant higher mean compressive strength than the cylinders made with tap water. The Eta² analysis placed 70% of the variability on the mix design. When the mean compressive strength of the four groups of cylinders was compared using Tukey's HSD, the results showed a statistically significant difference between the wash water and the tap water for each group.

Year of Submission

2011

Department

Department of Industrial Technology

First Advisor

Shahram Varzavand, Chair

Date Original

5-2011

Object Description

1 PDF file (ix, 112 pages)

Language

en

File Format

application/pdf

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