Strength and durability of cementitious binder produced from fly ash lime sludge Portland cement

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1 Indian Journal of Engineering & Materials Sciences Vol. 13, February 2006, pp Strength and durability of cementitious binder produced from fly ash lime sludge Portland cement Mridul Garg & Manjit Singh Central Building Research Institute, Roorkee , India Received 21 June 2005; accepted 23 September 2005 In this paper, investigations have been undertaken to produce cementitious binders by blending 60-70% fly ash with calcined phosphogypsum, hydrated lime sludge, Portland cement and chemical activator in different proportions. The results show that strength development of binders takes place through formation of ettringite, C-S-H and wollastonite. The durability of cementitious binder has been studied by its performance in water and by accelerated aging, i.e., alternate wetting and drying as well as by heating and cooling cycles at temperatures from 27 to 50 o C. The results indicate that the strength of the binder decreased with increasing cyclic studies at different temperatures. The maximum fall in compressive strength has been noted at 50 o C. IPC Code: C04B 7/00, B28B The advancement in science, technological and industrial revolution has resulted in the environmental pollution which has assumed alarming proportions in the developed and the developing countries. The gaseous and the liquid effluents from various industries are degrading the environment and posing hazards to both human and animal life and causing concerns for their proper disposal. Due to conventional land, disposal practice vast areas of useful land have become barren and un-productive for agricultural purpose and applications. Efforts are, therefore, being made throughout the world to effectively recycle these industrial wastes. In India, over 300 million tonnes of industrial wastes are produced per annum from the agroindustrial processes. Phosphogypsum, fly ash, fluorogypsum, lime sludges, red mud, rice husk etc. are the important industrial agricultural wastes of great interest. These waste materials contain undesirable impurities which interfere with the normal setting and hardening of the cements and cementitious materials and other building materials produced from them. Extensive researches have been carried out in Central Building Research Institute to develop a variety of building materials from different industrial solid wastes, like phosphogypsum, fluorogypsum, slag, fly ash and lime sludge 1-4. Fly ash as a partial substitute of cement has been widely used in concrete for over half a century 5-8, because of its beneficial effects in lowering the heat of hydration and sulphate resistance of concrete 9,10. Some research has indicated that fineness of fly ash is a cardinal property that effects pozzolanic reactivity, specific gravity, water requirement and strength 11,12. Increasing the fineness of a cement within acceptable bounds can improve early strength development, especially if cement contains substantial proportions of mineral admixture. In this paper, the physico-chemical properties of a cementitious binder prepared from fly ash, calcined phosphogypsum, lime sludge and Portland cement are reported 13. The durability of the binder as studied by alternate wetting and drying, and heating and cooling cycles at 27 to 50 o C 14 as well as by its performance under water are discussed. Experimental Procedure Raw materials The chemical compositions of different raw materials used for making cementitious binder are given in Table 1. The lime sludge obtained from fertilizer industry was heated at 1000 o C for 4-5 h to form lime which was used after complete hydration. Phosphogypsum contains impurities of free phosphoric acid, phosphates, fluorides and organic matter that adhere to the surface of gypsum crystals and also substituted in the crystal lattice of gypsum. Phosphogypsum also contains radioactive elements such as U 238, U 234, Ra 226, Pb 210 and Po 210 which are derived from the phosphate rocks 15,16. The contents of radioactive elements vary in a wide range depending on the composition of rock phosphate. In India, most

2 76 INDIAN J ENG. MATER. SCI., FEBRUARY 2006 of the phosphogypsum is produced out of the Morroco phosphate rock, as a result, the level of radioactivity does not accede 13.5 pcu/g maximum specified by Euratom 17. Preparation and testing of cementitious binders The cementitious binders were prepared by blending the ground fly ash, calcined phosphogypsum (β-hemihydrate and β-anhydrite), hydrated lime sludge, Portland cement and a chemical activator in different proportions followed by inter-grinding in a ball mill to the fineness of a specific surface area of 400 m 2 /kg (Blaine) (Table 2). The cementitious binders were tested and evaluated for their physical properties as per methods specified in IS: and IS:2542 (Part 1) The hydration of cementitious binder was studied by differential thermal analysis (Stanton Red Croft. U.K.). Durability studies of cementitious binder The 25 mm cubes of cementitious binders were cast at normal consistency and hardened in over 90% relative humidity at o C for a period of 28 days. The hardened cubes were subjected to durability test Table 1 Chemical composition of fly ash, phosphogypsum, lime sludge and Portland cement (Basis : Oven Dried) Constituents Fly ash Phosphogypsum Lime sludge Portland cement P 2 O F Organic matter Cl Na 2 O+K 2 O SiO R 2 O 3 (Al 2 O 3 +Fe 2 O 3 ) CaO MgO 0.80 Tr SO LOI by examining their behaviour in (i) water, (ii) wetting and drying and (iii) heating and cooling cycles. One cycle of wetting and drying comprised heating the cubes for 16 h at different temperatures (27-50 o C) followed by cooling for one hour and immersion in water for 7 h, whereas one heating and cooling cycle consisted of heating the cubes at temperatures from 27 to 50 o C separately for 6 h and cooling at room temperature for 18 h. After a certain number of cycles, the compressive strength of dry cubes was measured as per method laid down in IS: Results and Discussion The physical properties of cementitious binders are given in Table 3. Data shows an increase in the compressive strength and bulk density with curing period in all the binder compositions. It can be seen, that binder1(b) contains 70% of fly ash but no Portland cement. This binder gave higher strength values than the binders a1 and c2. While the binder d3 contains less of fly ash than the rest of binders but contains 20% of cement. Due to use of large content of fly ash, binder 1(b) was chosen for further studies. Table 2 Mix composition of cementitious binder based on fly ash, phosphogypsum plaster, lime sludge and Portland cement Binder design Fly ash Mix Composition (wt. %) Phosphogypsuement Portland- plaster Lime sludge Phospho Activator anhydrite (K 2 SO 4 ) 1 (b) (a1) (c2) (d3) Binder 1(b) 5 (a4) (b4) (c4) (d4) Table 3 Physical properties of cementitious binder prepared from ground fly ash, phosphogypsum plasters, lime sludge and Portland cement Sl. No. Binder Design Consistency (%) Physical Properties Setting time (h) Bulk density (g/cm 3 ) Compressive strength MPa Initial Final 1d 3d 7d 28d 90d 1d 3d 7d 28d 90d 1 1(b) (a1) (c2) (d3) (a4) (b4) (c4) (d4)

3 GARG & SINGH: STRENGTH AND DURABILITY OF CEMENTITIONS BINDER 77 The binder 5(b 4 ) contains 80% of binder 1(b) admixed with 20% of cement attains adequate strength at 28 and 90 days of curing. The strength development in these binders 1(b) and 5 (b4) can be ascribed to the formation of C-S-H, ettringite (C z A, 3 CaSO 4, 32H 2 O) and wollastonite compounds which is amply demonstrated by DTA (Fig. 1). The thermograms show endotherms at 130 o C, 150 o C, 520 o -540 o C, 790 o C and 980 o C due to formation of tobermorite (CSH), ettringite (C 3 A.3CaSO 4.32H 2 O), Ca(OH) 2 wollastonite and CaCO 3, respectively. Durability of cementitious binder Performance in water The 25 mm cubes of cementitious binders designated as 1(b), 2(a1), 3(c2), 4(d3), 5(a4), 5(b4), 5(C4) and 5 (d4) hardened for 28 days were dried and then immersed in water for different periods to measure their water absorption and porosity. The effect of immersion in water on water absorption and porosity of cementitious binders are given in Tables 4 and 5. It can be seen that porosity and water absorption of the cementitious binders increased with increase in immersion period. Whereas in plain plaster the water absorption increases up to 3 days of immersion in water. After 3 days, the water absorption could not be measured due to leaching of the gypsum matrix. These findings manifest better stability of the cementitious binder in water than the plain plaster. The increase in water absorption with immersion period clearly indicate absence of leaching and increased level of stability of the binder towards water. Wetting and drying cycles The effect of alternate wetting and drying cycles on the compressive strength of cementitious binders 1(b), 4(d3), and 5(b4) at temperatures from 27 o C to 50 o C are shown in Figs 2-4. Fig. 2 shows that on increasing temperature from 27 o C to 40 o C, the maximum attainment of strength was found at 20 cycles at temperatures 27 o C and 50 o C and at 40 cycles at 40 o C respectively. At 27 o C and 40 o C, the strength of cubes increased to 23.77% and 30.68% of their pristine strength after 50 cycles. While 3.17% loss in strength was noted at 50 o C after 50 cycles. In case of binder 4(d3) (Fig. 3), the maximum strength was attained at 40 number of wetting and drying cycles at 27 o C and 50 o C and at 40 o C, however the maximum strength occurred at 10 wetting and drying cycles. The gain in strength after 50 cycles at 27 o C, 40 o C and 50 o C was found to be 7.84%, 21.08% and 31.54%, respectively against the pristine strength values. In Fig. 4 (Binder Table 5 Porosity of cementitious binder Binder designation Porosity 1 d 3 d 7 d 28 d 1(b) (al) (c2) (d3) (a4) (b4) (c4) Fig. 1 Differential thermograms of cementitious binders (a) binder 1(b) (b) binder 5(b 4 ) hydrated for 90 days 5(d4) POP Table 4 Water absorption of cementitious binder Mix designation Water absorption (%) 2 h 8 h 24 h 3 d 7 d 28 d 1(b) (al) (c2) (d3) (a4) (b4) (c4) (d4) POP* *Leach. Leach. * POP = Plaster of Paris, *Leach.= Leaching

4 78 INDIAN J ENG. MATER. SCI., FEBRUARY (b4)), the maximum strength was obtained at 40, 30 and 20 cycles at temperatures 27 o C, 40 o C and 50 o C respectively and then fall in strength was observed. Fig. 1 Schematic- diagram of the proposed method However, the strength measured at 50 cycles at 27 o C, 40 o C and 50 o C was 5.93%, 11.20% and 7.15% respectively of the pristine strength values. Heating and cooling cycles The effect of alternate heating and cooling cycles at temperatures from 27 o C to 50 o C on the compressive strength of cementitious binders 1(b), 4(d3) and 5(b4) is shown in Figs 5-7. Data show (Fig. 5), that the compressive strength of cementitious binder 1(b) decreased with an increase in temperature and heating and cooling cycles. The compressive strength of binder reduced to 33.89% and 35.14% at 40 o C and 50 o C, respectively of the original strength value after 50 cycles. However, gain in strength was observed at 27 o C. Whereas data of the cementitious binder 4(d3) (Fig. 6) showed 24.25% gain in strength at 50 cycles at 27 o C. However, at 40 o C and 50 o C, the gain of strength was 3.47% and 8.2% after 50 cycles of heating and cooling. In case of binder 5(b4) (Fig. 7), the maximum strength was achieved at 40, 20 and 10 heating and cooling cycles at 27 o C, 40 o C and 50 o C followed by Fig. 2 Effect of wetting and drying cycles on compressive strength of binder 1(b) Fig. 5 Effect of heating and cooling cycles on compressive strength of binder 1(b) Fig. 4 Effect of wetting and drying cycles on compressive strength of binder 5(b4) Fig. 6 Effect of heating and cooling cycles on compressive strength of binder 4(d3)

5 GARG & SINGH: STRENGTH AND DURABILITY OF CEMENTITIONS BINDER 79 Fig. 7 Effect of heating and cooling cycles on compressive strength of binder 5(b4) fall in strength. However, gain in strength of the order of 5.56%, 11.93% and 5.6% was noticed at 27 o C, 40 o C and 50 o C, respectively at 50 cycles of heating and cooling over the original strength. Conclusions From the above studies, following conclusions can be drawn: (i) The cementitious binder can be produced by blending industrial wastes like fly ash, phosphogypsum plaster (β-hemihydrate), lime sludge with OPC in suitable proportions. (ii) Ettringite, CSH and Wollastonite were identified as the major hydraulic products responsible for strength development of the cementitious binders. (iii) Water absorption and porosity of cementitious binders increased with increase in curing period, indicating, thereby absence of leaching and increased level of stability towards water. (iv) When subjected to alternate wetting and drying cycles at 27 o C, 40 o C and 50 o C, variation in strength development was observed due to variable hydration of the binders. (v) When subjected to alternate heating and cooling cycles at 27 o C, 40 o C and 50 o C, the strength is reduced with an increase in temperature. The maximum fall in strength occurs at 50 o C. References 1 Singh Manjit & Garg Mridul, Indian Concr J, 77 (5) (2003) Singh Manjit & Garg Mridul, Cem Concr Res, 29 (1999) Singh Manjit & Garg Mridul, Civil Engg Construct Rev, 8 (10) (1995) Singh Manjit & Garg Mridul, Cem Concr Res, 25 (4) (1995) Bouzoubaa N, Zhang M H, Bilodeau A & Malhotra V M, Mechanical properties and durability of concrete made with high volume fly ash blended cements, fly ash, silica fume, slag and natural pozzolanas in concrete, Sixth CANMET/ACI Int Conf, SP-178 edited by V.M. Malhotra, American Concrete Institute, Farmington Hills, Mich., 1998, pp Berry E E & Malhotra V M, Fly ash in concrete, Publ. SP85-3, CANMET, Aimin Xu, Cem Concr Res, 21 (1991) Alvarez M, Salas J & Veras I., Int J Cement Compos Lightweight Concr, 10, (2) (1988) Mehta PK, Proc. First Intl. Conf on the use of fly ash, silica fume, slag and other mineral by-products in Concrete, Montebello, 1983, ACISP-79, pp Dinstan ER, Cem Concr Agreegates, 2 (1980) Hobbs DW, Mag Concr Res, 32 (1980) Paya J, Monjo J, Borrachero, M V, Cem Concr Res, 26 (2) (1996) Singh Manjit, Garg Mridul, Somani K K & Verma C L, Lime pozzolana masonry cement from industrial wastes, Cement Expo th Int Exhibition and Seminar, Mumbai October Singh Manjit, Garg Mridul & Rehsi S S, Cem Concr Res, 20 (2) (1990) St Rihanek, Tonindustrie Zeitung, 95 (9) (1971) R Taha & K S Roger, Phosphogypsum literature review IRM Report, LSU, Baton Rouge. 17 UNIDO Report, Review of Environmental Issues, Fertilizer Manual, (Kluwer Academic Publishers, Dordrecht, The Netherlands), 1998, IS: 4031: Specification for methods of physical tests of hydraulic cements, Bureau of Indian Standards, New Delhi, India, IS:2542 (Part 1) : Specification for methods of tests for gypsum plaster, concrete and products, Part I Gypsum plaster, concrete and products, Bureau of Indian Standards, New Delhi, India, 1981.