Cement Energy and Environment

• .. laumontite [Ca4(AisSh604s){H20)1s] etc were detected in both hydrated cement pastes along with un-hydrated alite and belite phases. However, the formation of crystalline ettringite was found to be improved in the hydrated cement containing mineral gypsum and this could be attributed to " " .. ....... (OPC-C) lower alkalinity as compared to cement containing jarosite as shown in Fig.3. Further, the formation of portlandite in hydrated cement sample OPC-5 was found to be improved in presence of jarosite and could be on account of accelerated hydration of silicate phases due to improved alkalinity. •:C. ~~.,--~~":-;-'--.'--.-..-,;------';.,::'--.--.l ..... .., (OPC-5) Fig 3: Monitoring of ettringite peak (28=9. 09°, d=9. 72A) marked "E" in hydrated cement pastes at different ages 3.5 Effect of Curing Under Aggressive Environments on Strength Development The compressive strength of hardened cement mortar samples OPC-5 and OPC-C cured for 3 and 6 months under chloride and sulphate solutions were found to be comparable {Fig 4) and showed that resultant cement OPC-5 prepared using 100% jarosite as set controller were resistant to chloride and sulphatic environmental conditions similar to control cement, hence indicating no deleterious effect of jarosite addition as set controller in place of mineral gypsum in cement. Water Sulphate Curing medium ll!l OPC-C 9 OPC·51 3 months Chloride CONCLUSIONS • Presence of S03 bearing mineral phases such as natrojarosite, bessenite and anhydrite in by– product jarosite showed its suitability for use as set controller in cement. • The availability of sulphate ions from jarosite in cement during early ages of hydration was found to be higher as compared to mineral gypsum resulting in relative increase in setting time as compared to cement containing mineral gypsum. Water Sulphate Curing medium ll!l OPC-C 9 OPC·51 6 months Chloride Fig 4: Effect of curing medium on compressive strength of OPC samples 23