Slurry Consistency and In Situ Synchrotron X‐Ray Diffraction During the Early Hydration of Portland Cements With Calcium Chloride

Class A and H oil well cements are compared at 25 and 50 C with 0%, 1%, 2%, and 4% CaCl{sub 2}. Up to 4% CaCl{sub 2} accelerated Class A thickening, but 4% led to slower thickening than 2% for Class H. C{sub 3}S hydration in the two cements responded differently to CaCl{sub 2}. CaCl{sub 2} always accelerated aluminate hydration. For Class A, CaCl{sub 2} accelerated early Ca(OH){sub 2} precipitation, but sometimes reduced the amount at longer times. This may be coupled to C-S-H gel composition changes. For Class H, Ca(OH){sub 2} precipitation changes nonlinearly with CaCl{sub 2} concentration. Ettringite to monosulfate conversion and Friedel's salt formation were sometimes seen.