Study on the pH Variation and Regulation Measures During the Cement Solidification Treatment of Dredged Material

During the cement solidification treatment of dredged material (DM) for planting use, the pH value of treated DM may be too high and impair plants growing. To lower the pH value, methods of breaking solidified DM, adding gypsum and rice straw powder (RSP) were studied, respectively. Test results show, after breaking solidified DM, the pH value can be reduced at the first two weeks, but the value still higher than 9.0. By adding gypsum, the pH value downs quickly before 5% the content of cement, when gypsum content higher than 30%, the pH value can be controlled under 9.0. After adding RSP, the pH value decrease with RSP content and curing time, when the RSP content higher than 5%, the pH value can be lower than 9.0 in one month. The mechanism for gypsum lower the pH value may be for the acidity property and reaction with calcium hydroxide which form ettringite. The mechanism for RSW action is for the acidic matter releases from organic carbon decomposition.