IMPACT OF TIME / TEMPERATURE CURING CONDITIONS AND ALUMINATE CONCENTRATIONS ON SALTSTONE PROPERTIES

Harbour, J. ; Edwards, T. ; Williams, V.

Savannah River Site (S.C.)

关键词: Slags;    Cements;    Permeability;    Waste Forms;    Processing;   

DOI  :  10.2172/957497
RP-ID  :  SRNL-STI-2009-00184
RP-ID  :  DE-AC09-08SR22470
RP-ID  :  957497

美国|英语

来源: UNT Digital Library

【 摘 要 】

This report addresses the impact of (1) the time and temperature curing conditions (profile) and (2) the impact of higher aluminate concentrations in the decontaminated salt solution on Saltstone processing and performance properties. The results demonstrate that performance properties as well as some of the processing properties of Saltstone are highly sensitive to the conditions of time and temperature under which curing occurs. This sensitivity is in turn dependent on the concentration of aluminate in the salt feed solution. In general, the performance properties and indicators (Young's modulus, compressive strength and total porosity) are reduced when curing is initially carried out under high temperature. However, this reduction in performance properties is dependent on the sequence of temperatures (the time/temperature profile) experienced during the curing process. That is, samples that are subjected to a 1, 2, 3 or 4 day curing time at 60 C followed by final curing at 22 C lead to performance properties that are significantly different than the properties of grouts allowed to cure for 1, 2, 3 or 4 days at 22 C followed by a treatment at 60 C. The performance properties of Saltstone cured in the sequence of higher temperature first are generally less (and in some cases significantly less) than performance properties of Saltstone cured only at 22 C. This loss in performance was shown to be mitigated by increased slag content or cement content in the premix at the expense of fly ash. For the sequence in which the Saltstone is initially cured at 22 C followed by a higher temperature cure, the performance properties can be equal to or greater than the properties observed with curing only at 22 C curing. The results in this report indicate that in order to meaningfully measure and report the performance properties of Saltstone, one has to know the time/temperature profile conditions under which the Saltstone will be cured. This will require thermal modeling and actual time/temperature profiles within the vaults under various pour schedules to determine (1) an average profile of time and temperature under normal processing conditions and (2) a conservative (worst case) time/temperature profile. Samples can then be cast and cured in the laboratory under these time and temperature profiles prior to measurement of the performance properties of the product waste forms From a processing perspective, a higher initial curing temperature decreased the set time to 1 day at both 40 C and 60 C and eliminated any bleed volume that was present for those samples that exhibited bleed at room temperature. However, the bleed water return system in the Saltstone Disposal Facility may remove bleed water before it can be reabsorbed. Aluminate concentrations at levels greater than 0.20 M in these salt solutions can lead to positive or negative effects on the performance properties. At a curing temperature of 22 C, aluminate increases Young's modulus and the compressive strength while reducing the total porosity. This generally corresponds to an improved (decreased) permeability (hydraulic conductivity) for Saltstone which is a positive outcome. On the other hand, with increased aluminate concentration there is a significant increase in heat of hydration that may limit pour schedule and must be considered in estimating the time/temperature profile to which Saltstone will be subjected during curing as discussed above. That is, higher temperatures in the vault (due to the higher heats of hydration) may present a greater challenge in controlling the curing time and temperature profile to achieve the desired performance properties.