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89 CHAPTER 5 Conclusions and Suggested Research Conclusions 4. There is no single parameter that adequately predicts exca- vatability. Compressive strength can serve as a useful sur- This report summarized the key findings of a multi-year re- rogate value in some cases, but one should try to capture the search project on CLSM for use in backfill, utility bedding, long-term strength gain when applying strength as a pre- void fill, and bridge approach applications. The research in- dictive tool. Basing long-term strength gain on short-term volved both a major laboratory component and field compo- laboratory testing can be problematic for some CLSM mix- nent. Through these efforts, several key deliverables have been tures (especially those containing fly ash). Calculating a re- produced, including a recommended suite of tests methods movability modulus shows promise in predicting excavata- (Appendix B), specifications (Appendix C), recommended bility. Lastly, the dynamic cone penetrometer was found to practices (Appendix D), and an implementation to drive these be a valuable method of assessing CLSM in the field and deliverables into practice (Appendix E). estimating ease of excavatability. Significant progress was made in this project to better under- 5. Significant research was performed on the corrosion of stand the behavior of CLSM and to evaluate the properties that metallic pipe materials in CLSM. In general, CLSM was most impact performance. The following list presents some of found to be beneficial in reducing corrosion (compared to the main overall findings from this project: typical compacted fill) when pipes are completely embed- ded in CLSM. The reduced permeability of CLSM can re- 1. Suitable test methods exist or were developed under this duce the ingress of chlorides and the microstructure of project to measure most of the key CLSM properties affect- CLSM can improve corrosion resistance through changes ing performance in the four target applications. Appen- in the pH and resistivity of the pore solution. A potential dix B describes the tests recommended to evaluate relevant for corrosion exists when pipes are embedded in both fresh, hardened, and durability properties of CLSM. CLSM and surrounding soil or conventional fill, because 2. Predictive models were developed to predict the water a galvanic cell is set up that can increase corrosion activ- demand and compressive strengths for a range of CLSM ity. This case is similar in nature to metals embedded in dis- mixtures. This information can be helpful in designing similar soils, and similar precautions can be taken to ensure mixtures for applications where strength may be a key lim- the desired service life. iting factor, such as in the use of excavatable CLSM. 6. The by-product materials tested in this study were found to 3. The effects of temperature on strength gain of CLSM mix- be non-toxic. However, a testing program was proposed to tures can be very pronounced, especially when using Class C evaluate other by-product materials that might be more of fly ash. One should be aware of this increased strength gain, a concern with regard to leaching and environmental im- especially when CLSM is being used in a hot climate and pact. This method involves the testing of total heavy metals, when future excavatability may be required. Keeping this possibly followed by TCLP (if the total heavy metals are strong temperature dependence in mind and accounting for above certain threshold values), and possibly followed by it in design and construction can help to effectively produce leachate testing from CLSM containing the subject material excavatable CLSM. Trial batching and testing at elevated (if the TCLP values exceed certain thresholds). temperatures help to gain insight into long-term strength 7. Due to the high fluidity of CLSM mixtures, floating of pipes gain in field applications, especially when fly ash or other or unintentional shifting of utilities may occur during place- supplementary cementitious materials are used. ment; users should take precautions to avoid this result.