Factors Affecting Solidifcation-Stabilization

Several factors should be considered during the initial design of bench-scale tests. These factors, which are summarized below, influence the degree to which bench-scale tests are representative, workable, and cost-effective when applied to the field.

Required results. It is important that project goals be understood to ensure that appropriate data are collected during the test. Typically, these goals are based on the required engineering criteria (primarily strength and durability) and maximum contaminant concentrations of the leachate.
Availability and cost of local reagents. The reagent source should have the capability of providing a sufficient quantity of the reagent during the necessary time frame of the field effort, but it is prudent to have a secondary source. Therefore, proprietary, single-source reagents should be avoided when possible unless there are compelling reasons to use these reagents. If feasible, the reagent source should be visited and sampled, supply schedules should be developed, and contracts should be discussed early in the project. If a dual-reagent mix design is proposed (i.e., 5% cement and 2% fly ash), then the methods of uniformly field-mixing the reagents must be developed, and consideration should be given to bench-scale testing each reagent separately to determine the effects on stabilization if the field mixing fails. Bench-scale tests can help in making these decisions.
Ratio of sludge to affected soil. Soil enhances the effects of solidification, so it is advantageous to determine the field ratio of sludge to affected soil before the bench-scale program can be designed. The bench-scale test can then be conducted using this ratio to better model site conditions.
Moisture content of the waste. Wet wastes generally require a greater reagent content than dry wastes to achieve similar results in a given amount of time. This effect can be evaluated in the bench-scale tests.
Field Equipment and Methods. Bench-scale mixing methods should be conducted in a manner that approximates the typical action provided by the field equipment. The field equipment to be used often also affects the amount of reagent that is required to achieve the project goals. If the application or mixing efforts are erratic or minimal, then higher reagent contents may be required to produce the desired result. Conversely, uniform reagent applications, thorough mixing, and stringent quality control procedures can improve the test results and reduce the required amount of reagent. These variations can be accounted for in design of the bench-scale test.
Construction schedule. Many projects have a limited time frame during which construction can be conducted to avoid winter shut-downs. Higher reagent contents can expedite construction by developing a soil-like waste that cures rapidly, thereby facilitating placement of the overlying lift. Lower reagent contents may reduce the daily production rate because of the difficulties in working wetter materials and because of a longer curing time. The effect of these variations can be evaluated in the bench-scale test.
Distribution of sludge and/or soil types. Variations in the waste material should be evaluated prior to testing. If significant variations occur, the tests should be designed to ensure that the results will be appropriate for each sludge or soil type as well as a composite of the waste materials.