Investigation into the stabilization/solidification performance of Portland cement through cement clinker phases

摘要

This research studied the influence of individual heavy metal on the hydration reactions of major cement clinker phases in order to investigate the performance of cement based stabilization/solidification (S/S) system. Tricalcium silicate (C_3S) and tricalcium aluminate (C_3A) had been mixed with individual heavy metal hydroxide including Zn(OH)_2, Pb(OH)_2 and Cu(OH)_2, respectively. The influences of these heavy metal hydroxides on the hydration of C_3S and C_3A have been characterized by X-ray diffraction (XRD) and differential scanning calorimetry-thermogravimetry (DSC-TG). A mixture of Zn(OH)_2, Pb(OH)_2 and Cu(OH)_2 was blended with Portland cement (PC) and evaluated through compressive strength and dynamic leach test. XRD and DSC-TG data show that all the heavy metal hydroxides (Zn(OH)_2, Pb(OH)_2 and Cu(OH)_2) have detrimental effects on the hydration of C_3A, but only Zn(OH)_2 does to the C_3S at early curing ages which can completely inhibit the hydration of C_3S due to the formation of CaO(Zn(OH)_2)·2H_2O. Cu_6Al_2O_8CO_3·12H_2O, Pb_2Al_4O_4(CO_3)_4·7H_2O and Zn_6Al_2O_8CO_3·12H_2O are formed in all the samples containing C_3 A in the presence of metal hydroxides. After adding CaSO_4 into C_3A, the detrimental effect of heavy metals increases due to the coating effect of both calcium aluminate sulphates and heavy metal aluminate carbonates. The influence of heavy metal hydroxide on the hydration of C_3S and C_3 A can be used to predict the S/S performance of Portland cement.