Cement Energy and Environment

The Blaine's finenesses of cement samples OPC-1 to OPC-5 were maintained at 320±10 m 2 /kg and were comparable to control cement OPC-C (323 m 2 /kg) (Table 3). The water requirement to prepare consistent paste of all the cement samples was in the range of 27.0-27.5% indicating insignificant effect of jarosite addition . The initial and final setting times of cement samples OPC-1 to OPC-5 showed delay in setting on addition of jarosite. However, the increase in setting time was marginal with increasing doses of jarosite. The delay in cement setting in spite of low S03 contents could be attributed to its higher rate of availability as discussed in section 3.2. The presence of alkalis derived from jarosite also contributed in amorphous ettringite formation resulting in delay in the hydration of C3A manifested in delayed setting . In a study reported (Suresh et.al, 2012; Agarwal et al , 2015), there was shortening of setting time in cement having 100% replacement level of mineral gypsum by jarosite and was attributed to the presence of higher concentration of Na 4 •, Fe 3• and Al 3- ions in the jarosite [Javed, 1987]. Table 3: Physical properties of OPC samples Properties/ OPC-C OPC-1 OPC-2 cement code (5:0)* (4:1)* (3:2)" Blaine's fineness 323 319 326 (m 2 /kg) Consistency (%) 27.0 27.0 27.0 Setting time (minutes) 1ST 215 230 240 FST 260 280 290 Compressive strength (MPa) 1-day 16.0 15.0 14.0 3-days 29.0 30.0 32.0 7-days 42.0 42.0 42.0 28-days 55.0 55.0 55.0 Soundness Le-chatlier (mm) 1.0 1.0 1.0 Autoclave (%) 0.03 0.03 0.03 Heat of hydration (KJ/Kg) 7-days 236 254 252 28-days 288 318 320 * Mineral gypsum: jarosite The delay in setting also resulted in slow gain in compressive strength development at 1-day. The values of compressive strength achieved at 3, 7 and 28-days were found to be comparable to control cement. The results of the other physical characteristics such as soundness determined as per Le-chatelier and autoclave test methods specified in Indian standards for OPC were also determined to be similar. However, the values of heat of hydration of cement samples OPC-1 to OPC-5 at 7 and 28 days were marginally higher as compared to control cement OPC-C and could be OPC-3 OPC-4 OPC-5 IS:269-2015 (2:3)* (1 :4)* (0:5)* 328 318 322 ~225 27.0 27.5 27.5 245 250 255 ~30 300 305 310 :::;;600 14.0 13.0 13.0 - 32.0 31.0 30.0 ~23 - 42.0 41 .0 41 .0 ~33 55.0 54.0 53.0 ~43 & ::;;58 1.0 1.0 1.0 :::;;10.0 0.04 0.04 0.04 :::;;0.8 248 254 267 330 317 336 attributed to accelerated hydration of silicate phases due to alkalis enrichment in cement samples. 3.4 Hydration Studies by XRD Hydration studies of cement samples OPC-C and OPC-5 containing 100% mineral gypsum and jarosite respectively was carried out by investigating the hydrated products development of above hardened cement pastes cured for 1, 3, 7, 28, 90 and 180 days by XRD. The crystalline phases such as portlandite , ettringite, calcium silicate hydrate phases such as [Ca1.sSi03s.xH20), 22