Effect of Curing Temperature on the Properties of Cementitious Waste Forms
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EFFECT OF CURING TEMPERATURE ON THE PROPERTIES OF CEMENTITIOUS WASTE FORMS RYAN 0. LOKKEN. JOHN W. SHADE. AND PAUL F. C. MARTIN Pacific Northwest Laboratory* , Box 999, Richland, WA 99352 ABSTRACT Current plans for disposing various low-level radioactive and/or hazardous liquid wastes include solidification of the waste using cementitious materials. One process, known as grouting, involves mixing liquid wastes with a blend of cementitious materials and pumping the resultant slurry to lined, underground concrete vaults. As the grout slurry begins to solidify and harden, the temperature within the grout increases due to exothermic hydration reactions. Depending on the the particular grout composition and on the0 disposal conditions, the grout may be exposed to temperatures of around 90 C for extended time periods. Studies are being conducted to determine the effects of high-temperature curing on selected properties of grouts prepared with a simulated0 low-level liquid waste. Grout samples cured at temperatures up to 95 C in the laboratory absorbed water during curing. The resultant leach resistance and compressive strength of these grouts decreased with increases in curing temperature and curing time. INTRODUCTION Grout disposal is the process of mixing low-level liquid waste with cementitious powders, and pumping the resultant slurry to near-surface, concrete vaults. Once the slurry begins to solidify. exothermic hydration reactions cause the temperature of the grout to increase. Although effects of curing temperature on properties of cementitious systems have been reported in the literature, only a few studies have dealt with systems incorporating high-salt liquids in blends of cement, fly ash, and blast furnace slag [13]. These studies investigated the heat generation of various formulations for solidifying high-salt content liquid waste at the Savannah River Plant using the Saltstone process. The literature data on Saltstone and data from long-term calorimeter studies and pilot-scale tests conducted at PNL indicate that temperature rises exceeding 600C are possible with certain formulations. The grout will remain at elevated temperatures for many years because of the low heat release rates within the disposal system and the contribution from radiolytic heat generation. The effects of long-term curing at elevated temperatures on the physical and chemical characteristics of the solidified products need to be determined to provide assurance of satisfactory long-term performance of the disposed wastes. A study is currently underway to address these issues. SAMPLE PREPARATION AND CURING The nominal composition of the simulated waste used in these studies is shown in Table I [4]. The simulated waste contained approximately 32 wt% salts and precipitated solids, with the majority of the soluble salts consisting of sodium nitrate, nitrite, aluminate, and hydroxide. The solids blend, consisting of 47 wt% class F fly ash, 47 wt% ground blast furnace slag, and 6 wt% type I/II-LA portland cement, was mixed with the liquid was
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