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59 Table 3.39. Analysis of heavy metal concentration of raw material extracts. TCLP 20 x TCLP Bottom Foundry Class C Class F High-Carbon Element Limit Limit Ash Sand Fly Ash Fly Ash Fly Ash (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) a Arsenic 5.0 100 170.0 7.7 280.0a 160.0a 58.0 Barium 100.0 2000 2000.0 240.0 1300.0 320.0 1200.0 Cadmium 1.0 20 0.23 0.28 1.55 2.1 0.51 Chromium 5.0 100 10.0 18.0 87.0 96.0 16.0 Lead 5.0 100 <0.2 18.0 <0.2 37.0 <0.2 Mercury 0.2 4 <0.2 <0.2 <0.2 <0.2 <0.2 Selenium 1.0 20 <0.2 <0.2 <0.2 2.4 <0.2 Silver 5.0 100 <0.2 <0.2 <0.2 <0.2 <0.2 a Concentration exceeded the "rule of thumb" value of 20 times the TCLP limit. This systematic approach to testing leaching potential and plications where strength may be a key limiting factor, such environmental impact can be followed for any material being as in the use of excavatable CLSM. considered for use in CLSM. Although all the materials used Improvements were made to the ASTM D 4832 (uncon- in this study were deemed non-toxic, it may be possible that fined compressive strength) test method to increase its ac- certain materials considered for a given CLSM application curacy and improve its user-friendliness. may be more of an environmental concern. The effects of temperature on strength gain of CLSM mix- tures can be very pronounced, especially when using Class C fly ash. One should be aware of this increased strength Summary gain, especially when CLSM is being used in a hot climate. This chapter described a comprehensive laboratory pro- Keeping this strong temperature dependence in mind and gram focusing on CLSM, with emphasis on developing/ accounting for it in design can help to effectively produce recommending appropriate test methods to assess key CLSM excavatable CLSM. Trial batching and testing at elevated properties and understanding the impact of materials, mix- temperatures helps to gain insight into long-term strength ture proportions, and curing regime on performance. Based gain in field applications, especially when fly ash or other on the results presented in this chapter, the following general supplementary cementing materials are used. conclusions can be drawn: There is no single parameter that adequately predicts exca- vatability. Compressive strength can serve as a useful sur- Suitable test methods exist to measure most of the key rogate value in some cases, but one should try to capture the CLSM properties affecting performance in the four target long-term strength gain when applying strength as a pre- applications. The findings discussed in this chapter, cou- dictive tool. Basing long-term strength gain on short-term pled with the results from the field testing program (Chap- laboratory testing can be problematic for some CLSM mix- ter 4), helped to develop the test methods (Appendix B) tures (especially those containing fly ash). Calculating a re- and specifications (Appendix C). movability modulus (RE) shows promise in predicting ex- Models were developed to predict the water demand and cavatability. Lastly, the dynamic cone penetrometer (DCP) compressive strengths for a range of CLSM mixtures. This was found to be a valuable method of assessing CLSM in the information can be helpful in designing mixtures for ap- field and estimating ease of excavatability. Table 3.40. TCLP test results for Class C, Class F, and bottom ash. TCLP Limit Bottom Ash Class C Fly Ash Class F Fly Ash Element (mg/L) (mg/L) (mg/L) (mg/L) Arsenic 5.0 0.12 0.074 0.37 Barium 100.0 3.61 0.30 0.17 Cadmium 1.0 0.001 0.004 0.024 Chromium 5.0 0.01 0.29 0.11 Lead 5.0 <0.01 <0.01 <0.01 Mercury 0.2 <0.01 <0.01 0.11 Selenium 1.0 <0.01 0.37 0.02 Silver 5.0 <0.01 <0.01 <0.01

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60 Significant research was performed on the corrosion of in dissimilar soils, and similar precautions can be taken to metallic pipe materials embedded in CLSM. In general, ensure the desired service life. CLSM was found to be beneficial in reducing corrosion The by-product materials tested in this study were found (compared to typical compacted fill) when pipes are com- to be non-toxic. However, a testing program was pro- pletely embedded in CLSM. The reduced permeability of posed to evaluate other by-product materials that might CLSM can reduce the ingress of chlorides and the micro- be more of a concern with regard to leaching and envi- structure of CLSM can improve corrosion resistance ronmental impact. This method involves the testing of through changes in the pH and resistivity of the pore solu- total heavy metals, possibly followed by TCLP (if the total tion. There is a potential for corrosion when pipes are em- heavy metals are above certain threshold values), and pos- bedded in both CLSM and surrounding soil or conventional sibly followed by leachate testing from CLSM containing fill, setting up a galvanic cell than can increase corrosion ac- the subject material (if the TCLP values exceed certain tivity. This situation is similar in nature to metals embedded thresholds).