Soluble Salt in Municipal Solid-Waste Incinerator Bottom Ash and Its Effect on the Performance of Cement-Stabilized Materials

The contents of soluble salts, including chloride and sulfate, were tested to use municipal solid-waste incinerator bottom ash (IBA) in cement-stabilized materials for roadbase. In addition, the effects of soluble salts on the strength properties of cement stabilized IBA and crushed stone mixture were analyzed by applying unconfined compressive and splitting strength tests, respectively. Moreover, the deformation properties of the mixture were analyzed by applying dry and temperature shrink tests, respectively. In addition, the microscopic mechanism of chloride and sulfate on the mixture was analyzed by using micro-test methods. Results show that the average contents of chloride and sulfate in IBA are 0.57% and 1.01%, respectively. The strength of the mixture that contains 30% IBA greatly decreases when the contents of chloride and sulfate in IBA are higher than 1.67% and 2.00%, respectively. The dry and temperature shrinkage deformations of the mixture greatly increase when the contents of chloride and sulfate are higher than 0.67% and 1.00%, respectively. Water treatment reduces the soluble salt content of IBA. Unlike the control mixture, the strength properties of the mixture that contained IBA with water treatment shows no remarkable difference, whereas the short and temperature shrinkage deformations increase and decrease, respectively. Microscopic analysis shows that Cl^- reacts with cement hydration products to produce Friedel salts, and the amount of hydration products increases in the mixture due to the addition of chloride and sulfate. However, some cement particles are not hydrated when the Na₂SO₄ content is 1.0%. The content of soluble salts in IBA should be limited to ensure the performance of the mixture.