New mixture design approach to paper sludge ash-based stabilizers for treatment of potential irrigation earth dam materials with high water contents

In those cases where construction-generated soils with high water contents are used as filling or embankment materials, it is sometimes difficult to satisfy the specified compaction degrees. Recently, soil stabilization using a paper sludge ash-based stabilizer (PSAS) has been developed. Paper sludge (PS) ash is waste generated by the incineration of PS discharged from paper mills. It has been found that PS ash can absorb and retain excess water; and therefore, PS ash can simultaneously improve the stability of muds when it is mixed with them. However, the current mixture design approach for PSAS-treated soils is only applicable to muds with water contents exceeding the liquid limits and cannot be applied to construction-generated soils in which the coarse fraction is dominant. Therefore, this study evaluated the effects of a PSAS on the compaction and mechanical characteristics of coarse-grained soils to use them as materials for irrigation earth dams. A series of compaction tests were conducted on two types of soil samples treated with a PSAS to investigate its effects on the compaction characteristics. The compaction characteristics obtained from the tests were assessed considering the water absorption and retention performance of the PSAS. It was found that the modified optimum water content w*_opt of the treated samples, which was evaluated using the amount of water unabsorbed and unretained by the PSAS, was almost equal to the w_opt of the untreated samples. Consequently, a new mixture design approach was proposed based on the compaction characteristics. The calculated results successfully demonstrated that, if the compaction curve of an untreated sample and the water absorption and retention ratio, W_ab, of the PSAS corresponding to a certain curing period are obtained, the range in the PSAS addition amount, A_PS^1m3, required to attain the targeted compaction degree, (D_c)_target, for the curing period can be estimated without conducting compaction tests on the treated samples. Finally, the strength characteristics of the treated samples prescribed by the proposed mixture design method were investigated by conducting CBR tests and $\overline{\text{CU}}$TC tests. Based on the test results, discussions were made on the contribution of the proposed mixture design to the strength development of the treated samples and on the development mechanism.