A study on cement mortars incorporating plain Portland cement (PPC), ground granulated blast-furnace slag (GGBFS) and basaltic pumice

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1 Indian Journal of Engineering & Materials Sciences Vol. 12, June 2005, pp A study on cement mortars incorporating plain Portland cement (PPC), ground granulated blast-furnace slag (GGBFS) and basaltic pumice Hanifi Binici a*, Orhan Aksogan b & Hasan Kaplan c a Department of Civil Engineering, Engineering and Architectural Faculty, K.S. University, Avsar Campus, Kahramanmaras, Turkey b Department of Civil Engineering, Engineering and Architectural Faculty, Cukurova University, Adana, Turkey c Department of Civil Engineering, Engineering Faculty, Pamukkale University, Denizli, Turkey Received 7 July 2004; accepted 29 March 2005 In this paper, an experimental investigation on the effect of ternary blending on the various properties of cement paste and mortar has been reported. The ternary blended cements have been prepared by using one type of clinker and two types of pozzolans. Two types of grinding techniques, two different fineness values and varying amounts of additives have been employed. Besides these, control pastes and mortars are prepared. The influence of fineness, different grinding techniques and other parameters on the strength of the ternary blended cements has been evaluated. The chemical compositions of the pozzolans are consistent with the requirements given in both the TS 25 (a Turkish standard) and ASTM C 168 standards. The results indicate that the basaltic pumice used in this study, taken from the Osmaniye-Adana province (Southern Turkey), can be used as an admixture in cement production. SEM, XRD and thin section analyses showed that a large quantity of sheet-like CSH was formed when a combination of basaltic pumice and slag were incorporated in the mortar. IPC Code: C04B26/00 The grinding techniques and compressive strength of cements have been the subjects of interest during recent years. Natural and synthetic materials that can contribute to the formation of cement are known as additives 1. In general, the additives are introduced at the final phase of cement production and they may not be added in large amounts. The reasons for the use of these additives are due to the fact that they allow a reduction in the production cost and lead to modification of some physical and chemical properties of the cement. In the production of cement, the additives are classified as inert or active materials. In recent years, there has been some interest to compare the intergrinding and separate grinding of blast furnace slag 2,3. One of the main aims of concrete technology is to make cement based materials environmentally friendly. Therefore, not only the good workability in fresh state and excellent mechanical properties and durability but also the environmental friendliness and economic benefits must be possessed by concrete materials 4. The cement industry is one of the largest industrial energy users consuming about 1.5% of the total world fuel production and 2% of the global electricity production. The industry has been accused of wasting *For coprrespondence ( hbinici@ksu.edu.tr) energy due to the low efficiency processes that it employs, such as burning, cooling and particularly grinding 5. Turkey is rich in natural pozzolans. Almost km 2 of the country is covered by Tertiary and Quaternary age volcanic rocks, among which tuffs occupy important volumes. Although there are many geological investigations on these volcanic rocks, their potential as natural pozzolan is not wellestablished 6. In Turkey, like in most Mediterranean countries, tuffs have been used by mixing with lime since historical times. Today, the cement industry in Turkey is one of the well-established and developed industries and it has a permanent interest in new supply sources of tuffs, since almost about one-third of the total production in recent years has been pozzolan cements 7. This study is related to the pozzolanic activity of basaltic pumice and slag and their influence as additives, with varying finenesses and percentages, on the properties of ternary blends such as strength, grinding time and microstructure. The experiments were carried out employing two different grinding techniques (intergrinding and separate grinding). The control cement comprised clinker and gypsum and the ternary blends comprised clinker, basaltic pumice, slag and gypsum, which were maintained at varying amounts of basaltic pumice and slag (10, 20 and 30%

2 BINICI et al.: STUDY ON CEMENT MORTARS 215 of the weight of the clinker). The experiments were repeated for two different fineness values, kept constant in the ranges of 2800±30 cm 2 /g and 4800±30 cm 2 /g. Experimental Procedure Materials The ternary blended cements were prepared by using gypsum, clinker, basaltic pumice and slag. The basaltic pumice contained glass shards, mineral phases and less amount of volcanic rock. The essential minerals in the basaltic pumice were feldspar, quartz and biotite. Different amounts of pozzolan, such as 10, 20 and 30 percent by the weight of the clinker were used. The specimen groups and their contents are given in Table 1. The clinker used in this study was obtained from Adana Cement Plant. The chemical, mineralogical and physical characteristics of materials used are given in Table 2. The gypsum used in this study comprised 19.4% crystal water and 42.8% SO 3. Method Grinding The ball mill grindability tests were conducted in a standard Ball mill for 90 micron test sieve. The basaltic pumice and slag being finer, the clinker was also reduced down to the same fineness by crushing in roll crusher and 3.36 mm specimens were used as feed materials for tests. In the clinker grinding, the gypsum, being more rapidly grindable, tends to be concentrated in the finer particle size fractions of the product 9. Particle size distribution was measured by laser diffraction. Blaine fineness values were determined according to the ASTM-C Pozzolanic activity Pozzolanic activity test was performed according to both the Turkish Standard TS (activity with lime) and ASTM C (activity with cement). According to TS 25, the following equations were employed to find out the components of the materials used in the pozzolanic activity test: Mass of pozzolan (g) = [(Density of pozzolan) 300 (g)]/(density of lime) (1) Mass of water (g) = [Mass of pozzolan (g) +Mass of lime (g)]/2 (2) Lime (150 g) and computed amounts of ground granulated furnace slag and natural pozzolan were put together into a firm nylon bag and mixed homogeneously. Mortar specimens with dimensions 40 mm 40 mm 160 mm were produced. To prevent the leakage from the moulds, they were coated by a blend of paraffin and resin. The specimens in the moulds stayed 24 h at room temperature and then, they were kept in an oven for six days at 55 o C. After being taken out of the oven, the specimens were cooled for four hours before testing. The water/binder ratio was 0.5. Table 1 Cement specimens obtained by intergrinding and separate grinding Specimens System of additions Fineness (cm 2 /g) A 1 Clinker +4% gypsum+ 0% additions 2800 A 2 Clinker +4% gypsum+ 0% additions 4800 B 1 Separate Grinding Clinker +4% gypsum+ 5% slag +5% basaltic pumice 2800 B 2 Separate Grinding Clinker +4% gypsum+ 10% slag +10% basaltic pumice 2800 B 3 Separate Grinding Clinker +4% gypsum+ 15% slag +15% basaltic pumice 2800 C 1 Separate Grinding Clinker +4% gypsum+ 5% slag + 5% basaltic pumice 4800 C 2 Separate Grinding Clinker +4% gypsum+ 10% slag +10% basaltic pumice 4800 C 3 Separate Grinding Clinker +4% gypsum+ 15% slag +15% basaltic pumice 4800 D 1 Intergrinding Clinker +4% gypsum+ 5% slag +5% basaltic pumice 2800 D 2 Intergrinding Clinker +4% gypsum+ 10% slag +10% basaltic pumice 2800 D 3 Intergrinding Clinker +4% gypsum+ 15% slag +15% basaltic pumice 2800 E 1 Intergrinding Clinker +4% gypsum+ 5% slag +5% basaltic pumice 4800 E 2 Intergrinding Clinker +4% gypsum+ 10% slag +10% basaltic pumice 4800 E 3 Intergrinding Clinker +4% gypsum+ 15% slag +15% basaltic pumice 4800

3 216 INDIAN J. ENG. MATER. SCI., JUNE 2005 Table 2 Chemical, mineralogical and physical characteristics of materials used Specimens Oxides (%) SiO 2 Al 2 O 3 Fe 2 O 3 CaO MgO SO 3 LOI (loss on ignition) Clinker A 1= A Basaltic pumice GGBFS Cement modulus Bouge component Specimens HM SM AM LM C 3 S C 2 S C 3 A C 4 AF Clinker A 1= A Physical properties of materials Materials Specific gravity Blaine Sieve analysis (%) (g/cm 3 ) (cm 2 /g) Residue on 90μm Residue on 200μm Basaltic pumice and GGBFS and Clinker and TS standard requirements for basaltic pumice and GGBFS 8 SiO 2 + Al 2 O 3 + Fe 2 O 3 SO 3 LOI >61 <3.5 <10 HM: Hydraulic Modulus CaO =, SM: Silicate Modulus= SiO2 SiO 2+Al2O 3+Fe2O3 Al2O 3+Fe2O3 AM: Aluminate Modulus= Al2O3 Fe2O, LM: Lime Modulus= 100.CaO 3 2.8SiO 2+1.1Al2O 3+0.7Fe2O3 Compressive and flexural strengths Compressive and flexural strength tests were conducted in order to evaluate the effects of the basaltic pumice and slag percentages, the fineness of the materials and the grinding technique. The mortar specimens of the plain Portland cement (PPC) and the ternary blended cements were prepared according to the Rilem-Cembureau method in a laboratory medium of 20±2 o C temperature and 50±5% relative humidity. Demolding after 24 h, the specimens were kept in water until they were tested. Six specimens with dimensions 40 mm 40 mm 40 mm, obtained from the specimens used in the flexural strength tests, were tested under the same laboratory conditions as those applied in the flexural strength test. These compressive strength tests were carried out using a kn capacity automatic compression machine according to EN Microstructure After curing for 28 days, the specimens were investigated by polarising microscope. The hydration products were identified by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and thin section polarising microscopy. The specimens were crushed in a percussion mortar and then placed in an agate mortar. A Philips 1710 XRD was used. After curing for 28 days, the specimens were scanned at a speed of 2 2θ/min and with a step size of 0.02 in the range of θ. In order to determine the properties of the mortar incorporating basaltic pumice and slag from a micro scale view, a scanning electron microscope (SEM) was used. 10 mm cube specimens were prepared from both PPC and ternary blended cements and cured for 28 days before observing under the JEOL JEM 840 model SEM. Results and Discussion Pozzolanic activity Pozzolanic activity values, determined according to TS 25, were between 2.8 and 4.6 MPa for flexural strength and between 11 to 24 MPa for compressive strength. The results are illustrated in Fig. 1. According to TS 25, the specimens must have a compressive strength of at least 5 MPa and a flexural strength of at least 1 MPa. Compressive strength values, determined according to ASTM C 618, were found to be significantly higher

4 BINICI et al.: STUDY ON CEMENT MORTARS 217 Fig.1 Pozzolanic activity of basaltic pumice and slag according to TS 25 Table 3 Pozzolanic activity according to ASTM C 618 Specimens 28-d Compressive strength (MPa) Activity (%) Control-A 1 (250 m 2 /kg) Control-A 2 (500 m 2 /kg) NP(250 m 2 /kg) NP(500 m 2 /kg) GBFS (250 m 2 /kg) GBFS (500 m 2 /kg) Note: Pozzolanic activity percentage has to be greater than 70% of the compressive strength of the control specimens than those mentioned above, namely between 39.5 and 53.2 MPa (see Table 3). These results show that the strength of the mortar increased with an increase in the specific surface of the additive for both the basaltic pumice and slag. This increase is greater for the slag compared to the basaltic pumice. It is mentioned in the literature that pumice can be evaluated as an admixture in Turkish cement industry 15. The results of the present study, concerning the pozzolanic activities of the additives, slag has the higher potential as an active material than basaltic pumice. However, both additives should be evaluated as admixtures for the Turkish cement industry, since they both fulfill the strength requirement of the TS 25 and ASTM C 168. Grindability of the clinker and additives It is well-known that the clinker (with admixtures, especially gypsum) has to be ground to suitable fineness in order to produce cement that will react readily with water in the hydration process. The clinker will achieve better and more rapid strength development as it is more finely ground and acquires a large specific surface. It has been mentioned in the literature 14 that for every additional 100 cm 2 /g of specific surface, the increase in strength of the mortar Fig. 2 Grinding times of materials Table 4 Compressive strength of control and ternary blended specimens (MPa) Specimens Days A A B B B C C C D D D E E E is in the interval from 0.5 to 2 MPa. It is also reported that the average increase in 28 days compressive strength is approximately 1 MPa. The results of the present study are somewhat higher, falling in the interval from 0.7 to 2.5 MPa. It can be seen from Fig. 2 that the grinding time for the basaltic pumice is much less than that for the slag. The sieve analysis showed that the 45µ residue of all the cements and additives were lower than 3.3%. Compressive and flexural strengths The compressive strength is the main feature that allows an appreciation of the cement quality. The results of the mechanical tests obtained for the ternary blended and control mortars are shown in Tables 4 and 5. These results show a clear decrease in the compressive strength with an increase in the percentage of the additives. However, in the case of

5 218 INDIAN J. ENG. MATER. SCI., JUNE 2005 Table 5 Flexure strength of control and ternary blended specimens (MPa) Specimens Days A A B B B C C C D D D E E E separate grinding the ternary blended cements for fineness 4800 cm 2 /g containing 20% additives (i.e. specimen C2) showed the highest strength development at the age of 180 days. Furthermore, the ternary blends containing 30% pozzolan showed a slow strength development as compared to those containing 10% and 20% pozzolan at early ages. The compressive and flexural strengths of all the ternary blends were found to be higher than the minimum value stated by TS Microstructure The analysis showed that the ternary blends had pozzolanic activity in addition to their cementitious property and the best results were obtained by adding 20% of additives. Some characteristic thin section images are presented in Figs 3-5. These images show that some of the hydrated particles are surrounded by rims of hydration products. The XRD results for all the specimens were very similar. Hence, only one of them is presented in Fig. 6. As seen from Figs 5 and 6, poorly formed crystalline CSH coats mineral and aggregate surfaces as a dominant binder. SEM images of the specimens which show the distribution of ettringite crystals and portlandite in the microstructure are presented in Figs 7 and 8. In the thin sections, CSH, ettringite crystals, alite, belite, free CaO, ferrite and other minerals and, as a surprise, some conglomerations of oval and spheroidal belite grains are observed (see Fig. 3). The fineness of the ternary blends has an effect on the pore size of the mortar (see Fig. 4). The more refined pore structure observed in the thin sections is probably due to the homogeneous distribution of the Fig. 3 Thin section of PPC mortar (A1), (A: alite, F: ferrite, C: calcite and CSH: calcium silicate hydrate). Fig. 4 Thin section of ternary blended cement mortar (C1), (A: alite, B: belite and P: pore). Fig. 5 Thin section of ternary blended cement mortar (C2), (E: ettringite and CSH: calcium silicate hydrate). hydration products. Other workers also support these observations 16. Fine ettringite crystals were observed in voids in conjunction with formations like heaps of needles. This reveals a clear improvement in the performance characteristics of the cement obtained using basaltic pumice and slag. The aforementioned SEM, X-ray and thin section analyses showed that a large quantity of sheet-like CSH was formed when a

6 BINICI et al.: STUDY ON CEMENT MORTARS 219 of the cement is an activating property for its compressive strength, especially during the early ages. Although this tendency shows itself in the flexural strengths, also, it is not strictly true during the ages after 28 days for the specimens obtained by intergrinding. Fig. 6 XRD patterns of ternary blended cement mortar (C2, 28 days). Fig. 7 SEM image of PPC cement mortar (A1, mag. 2500x). Conclusions The following conclusions can be drawn from this study: 1 Both basaltic pumice and slag used in this study had more than 61% of major chemical components, SiO 2 + Al 2 O 3 + Fe 2 O 3, conforming with the chemical requirements of the ASTM and Turkish Standards. They also fulfilled the mechanical requirements concerning compressive and flexural strengths. 2 The fineness of cement is an activating property for the mortar strength, especially during the early ages. 3 The addition of basaltic pumice and slag leads to an increase in the amount of the CSH gel in the mortars. (This may be the reason for the improvement in the performance characteristics of the mortar obtained using basaltic pumice and slag.) 4 Finally, it can be said that, the basaltic pumice cone deposits, located in the Osmaniye-Adana province (Southern Turkey), with an estimated reserve of approximately million tonnes is a perfect potential for the cement industry. Acknowledgements The authors wish to acknowledge the valuable assistance given by the Iskenderun Cement Manufacturers Association, which is gratefully appreciated. Fig. 8 SEM image of ternary blended cement mortar (B1, mag. 3000x). combination of basaltic pumice and slag were incorporated in the mortar. Influence of the fineness The results given in Tables 4 and 5 show clearly that the strength of the mortar improves with an increase in the fineness of the additives. The fineness References 1 Barahma A, Compared influences of the physical and chemical properties of the Portland cement, presented at Cement and Concrete Technology, Istanbul, Turkey, Erdogdu K, Tokyay M & Turker P, Cem Conc Res, 29 (1999) Schubin W I & Entin S B, Zement Kalk Gips (English Version), 2 (1993) Guangcheng L, Xinyonu W & Youjun X, Cem Conc Res, 32 (2002) Benzer H, Ergun L, Lynch A J, Oner M, Gunlu A, Celik I B & Aydogan N, Min Eng, 14 (2000) Kaplan H & Binici H, Çimento Beton Dünyasi, 1 (1996) 23. (in Turkish) 7 Türkmenoglu A G & Tankut A, Cem Conc Res, 32 (2002) TS 12142, Cement-composite, Turkish Standards Institute, 1997, (in Turkish).

7 220 INDIAN J. ENG. MATER. SCI., JUNE Bouge R H, The chemistry of Portland cement, (Van Nastrand, Reinhold Company, New York), ASTM C 204, Standard test method for fineness of hydraulic cement by air permeability apparatus, ASTM standards, TS 25, Trass, Turkish Standards Institute, 1975, (in Turkish). 12 ASTM C618, Standard specification for coal fly ash and raw or calcined natural Pozzolan for use as a mineral admixture in Portland cement concrete, ASTM Standards, EN 196-1, Methods of testing cement, determination of strength, European Standards, Oney M, Cem Conc Res, 30 (2000) Türkmenoglu A, Tankut A, Tokyay M & Turan C, Pozzolanic activities of tuffs from Ankara region, Turkey, presented at Cement and Concrete Technology, Istanbul, Turkey, Begimgil M, Cement Concrete World, 5 (2000) 47, (in Turkey).