THE EXAMINATION OF HEAVY METALS LEACHING FROM FLY ASH CONCRETE
Category: Earth and Environmental Engineering
Purpose: The purpose of this project is to 1) examine the leaching of heavy metals from fly ash concrete by testing water samples for metals (found in fly ash) from concrete that is frozen, and sitting in acid rain, river water, salt water and distilled water. 2) to see if the various weathering(s) impact the amount of leaching of heavy metals and 3) to see if the results are dose dependent, meaning that the greater the proportion of fly ash in the concrete, the more the fly ash metals will leach into the water.
Hypothesis: It is hypothesized that 1) heavy metals will leach out of fly ash concrete. 2) It is hypothesized that the greatest amount of leaching will come from the concrete that is frozen and sitting in acid rain and less leaching from the concrete that is sitting in salt water, river water and distilled water. In addition, 3) the results will be dose dependent, meaning that the greater the proportion of fly ash in the concrete, the more the fly ash metals will leach into water.
Procedure: Three types of concrete were made including: a control concrete sample with 0% fly ash, a 30% fly ash sample, and a 50% fly ash sample. For each type of concrete, six samples were made. The concrete was poured tubular molds. The concrete samples were put into 18 plastic containers with 600 milliliters of water in each container. Tap water was used for the freezing samples. After 3 weeks of weathering (from freezing, salt water, distilled water, river water, and acid rain) the water samples in which the concrete was weathered were tested for heavy metals with a Sensafe heavy metals testing kit.
Data: The data shows that fly ash is leaching out of the concrete. All of the water samples that were examined had some traces of heavy metals. River water and freezing had the largest effects at 400ppb. It is thought that the freezing leached more because when freezing occurs the molecules expand. The fly ash can escape when molecules expand because larger cracks and crevices are made because the expanding water breaks apart the concrete. The 50% fly ash samples generally had more leaching of metals than the 30% sample or the 0%.
Conclusion: Hypothesis 1is accepted because heavy metals did leach out of the concrete samples. Hypothesis 2 is accept and rejected because heavy metals leached out of freezing the most. Hypothesis 3 is accepted because the results were dose dependent.