THE INFLUENCE OF SODIUM SALTS ON INTERACTION IN THE SYSTEM. PORTLAND CEMENT - GRANULATED BLAST FURNACE SLAG - FUEL ASH - SLAG BLEND R F Runova M A Kochevykh 11 Rudenko J L Nosovskii V.D. Glukhovskii Scientific Research Institute on Binders and Materials Ukraine A B S T R A C T . Among advantages of Portland cement- based binders made with industrial wastes (multi-blends) are mentioned the following: compliance of the concrete made with multi-blends working in aggressive environments with increasingly growing engineering requirements, environmental safety and low cost. Unrestricted possibilities of such concretes may be attributed, first of all, to a great variety of their compositions, and chemical modification is of special attention. There have been developed formulations of CC with Portland cement content up to 20 % by mass and strength varying between 30... 55 MPa. These properties are reached due to the use of sodium salts which take an active part in the interactions occurring in the systems containing blast furnace slag, fuel ash-slag blends and natural glassy pozzolana. The hydration products of the cementitious materials have been examined. The developed cements may be recommended for the use in road construction in making road pavement. Keywords: Calcium hydrosilicates (CHS), Composite cement (CC), Fuel ash- slag blend (ASB), Granulated blastfurnace slag (GBFS), Ordinary portland cement (OPC). Professor, DrSc(Eng) Raisa F R u n o v a is Chief Researcher of V.D.Glukhovskii Scientific Research Institute on Binders and Materials, Kyiv, Ukraine. Since 1970 she has been investigating the properties of amorphous silicates and herewith suggest of contactcondensation mechanism of hardening these systems. D r M a r i n a A Kochevykh is Research Scientist of V.D.Glukhovskii Scientific Research Institute on Binders and Materials, Kyiv, Ukraine. Her research interests include creation of new materials with determined properties based on calcium hydrosilicates. D r Igor I R u d e n k o is Research Scientist of V.D.Glukhovskii Scientific Research Institute on Binders and Materials, Kyiv, Ukraine. He is specialised in the application of fuel fly ashes and slags in cement-free concretes. J u r i L Nosovskii is an Engineer of V.D.Glukhovskii Scientific Research Institute on Binders and Materials, Kyiv, Ukraine. He specialises in developing formulations of the blended cements with low content of Portland cement clinker. Downloaded by [ Griffith University] on [25/10/17]. Copyright © ICE Publishing, all rights reserved. 342 R u n o v a , K o c h e v y k h , R u d e n k o , Nosovskii INTRODUCTION Practical experience gained from the use of blended ordinary portland cements (OPC)- based cements counts a few years and found its reflection in the European Standard ENV- 197. The role of cementitious materials which are a combination of OPC and natural and industrial pozzolanas is growing increasingly. In compliance with the norms currently in force in Ukraine DSTU B V.2.7- 46 which contain the requirements to cements intended for general application, a type of blended cement- the composite one, is introduced and specified. This allowed us to use the term «composite cements» in the present paper. According to analysis reported in , the existence of blended cement is connected with the following aspects: - technical - it is caused by a pozzolanic character of hydration which promotes the corrosion resistance enhancement to aggressive environments and the lower exothermic effect; ecological - is determined by compounding of the majority of existing industrial wastes of aluminosilicate composition with hydration products and decline in the OPC production due to a «greenhouse» effect; economical - is caused by decline in energy consumption for production of OPC, increase in lifespan of structures, decrease in expenses for repair and maintenance of concrete structures made of blended cements. One of the way of how to effect the cement activity, first of all, of the composite one, is its modification with chemical additives. From this point of view worth mentioning is the use of sodium and potassium salts. The known-in-the-art works on creation of alkali- containing cementitious materials- so-called «soil cements», which are known to differ considerably from the traditional ones in nature of the products of hardening (the presence of alkaline hydroaluminosilicates which are in their composition analogous to durable natural zeolitic materials [2, 3]. The present research performed in a continuation of the above works was dedicated at investigation of the interaction processes taking place in the blended cements modified with sodium salts. The objective of the study- to achieve high activity of these cements with decreased content of the OPC . MATERIALS AND TESTING TECHNIQUE Used as basic ingredients of the CC were the OPC with a strength class of 40 MPa and a specific surface of 400 sq m/kg (by Blaine), and natural and industrial pozzolanas as aluminosilicate constituents. The chemical composition of raw materials used in the experiments is given in Table 1. Used as natural pozzolana was a perlite with a specific surface 420 sq m/kg (by Blaine). The mineralogical composition of the perlite is presented, mainly, by volcanic water-containing glass (96.71%) [ 4 , 5 ] . Used as industrial pozzolanas were a granulated blastfurnace slag (GBFS) and an ash- soda blend (ASB) with a specific surface 430 sq m/kg (by Blaine). Downloaded by [ Griffith University] on [25/10/17]. Copyright © ICE Publishing, all rights reserved. Influence of S o d i u m Salts on I n t e r a c t i o n 3 4 3 Table 1 Chemical composition of initial raw materials OXIDE CONTENT, % by mass Si0 GBFS OPC clinker ASB Perlite 2 AL 0 2 3 Fe 0 2 3 CaO MgO MnO R0 2 R0 S0 2 3 LOI 39.5 6.49 0.12 47.1 3.1 1.7 1.15 - - 0.6 51.5 42.0 3.4 0.4 0.7 - - 1.2 0.6 0.12 53.7 72.0 17.4 12.5 12.75 0.65 3.70 1.07 2.82 0.17 0.08 3.19 0.03 1.01 4.51 0.61 2.10 4.69 0.05 - The GBFS may be referred to a basic type slag is is represented, mainly, by a glass phase (75...80 % by mass) [6 ]. Its mineralogical composition is represented by melilite (gehlenite), anorthite, sulpfides, calcite. The chemical analysis data of the ASB sample show that it may be referred to the acid ones [7, 8]. The phase- mineralogical composition of the ASB is represented by a glassy component of aluminosilicate and silicate composition with inclusions of quartz and hematite [7, 8, 9]. Used as additives in the experiments were an anhydrous sodium sulfate Na S0 and sodium carbonate Na C0 as well as their blend (SSB) in which they were contained in a ratio of 2:1. This blend is a model of an industrial by product of chemical industry The additives were introduced together with a mixing water as a solution in a quantity of 6 % by mass of the cement mass. Used as a plasticiser (introduced in a quantity of 1 % by mass of the cement) was an additive selected from lignosulfonates. Used as fine aggregate was fine quartz sand with a gradation factor 1.42. CC was produced by mixing in appropriate proportions of the components ground to a certain specific surface. CC activity was determined on the beam- specimens (40x40x160 mm) made from a cement mortar (cement to slag ratio=l:3) of standard consistency allowed to harden for 3 days in normal conditions and 25 days in water. 2 4 2 3 E X P E R I M E N T A L RESULTS AND DISCUSSION Activity Taken as a criterion to assess the interaction processes in CC was its activity as the most important target property. These investigations covered a wide range of CC content varying (in % by mass) from OPC (20 - 80), ASB (5- 65), perlite ( 5 - 65), GBFS (15- 75). The dependances between activity of CC and content of the above constituents were studied on the systems «OPC-GBFS-ASB» (Figure 1, a) and «OPC-GBFS-perlite» (Figure 1, b) (for reference). As a result, it was found that the cements of the first system demonstrated the activity greater than 40 MPa with the ASB content less than 31 % by mass, and greater than 50 MPa - less than 5 % by mass. To maintain the 50 MPa activity with 25 mas.% ASB is possible by increasing the OPC content to 65 % by mass. Downloaded by [ Griffith University] on [25/10/17]. Copyright © ICE Publishing, all rights reserved. 344 Runova, Kochevykh, Rudenko, Nosovskii ui OPC, % GBFS, % ASB, % 20 75 5 20 40 40 65 3C 5 65 15 20 OPC. % 20 GBFS, % 75 Perlite, % 5 20 40 40 65 30 5 50 15 35 Figure 1 Activity of CC of the system 1 «OPC - GBFS - ASB» modified with SSB (a), of the system 2 «OPC - GBFS - perlite» modified with sodium sulfate (b) Figure 2 X-ray diffradtograms of the patterns of CC of the system 1 «OPC - GBFS - ASB» modified with SSB (a), of the system 2 «OPC - GBFS perlite» modified with sodium sulfate (b) Downloaded by [ Griffith University] on [25/10/17]. Copyright © ICE Publishing, all rights reserved. Influence of S o d i u m Salts on I n t e r a c t i o n 345 To increase the content of pozzolana in the first system may be achieved by decreasing the OPC content due to activation of the aluminosilicate component by sodium carbonate [10, 11, 12]. To optimise the first system cement formulations by a criterion of activity, a simplex- grid method planning a 3-factor experiment was applied. Taken as variables in the first system with sodium carbonate were the contents of OPC, GBFS and ASB. R = where, R x,, x , x 2 3 56XJ+18X2+27.28X3 = strength = OPC, GBFS, ASB content (for reference) Basing on analysis of the equation for further investigations have been selected the compositions given in Table 2 . The investigation of influence of an additive type on the cement activity showed high efficiency of the SSB additive. While investigating the interaction processes that take place in the system with 6 mas.% - content of such additive in combination with a plasticiser, some increase in activity of the cement with the increased ASB content was reported: Composition No 6 ( 4 0 mas.% ASB) is characterised by activity 4 0 MPa (Figure 1 , a), what is by 3 7 % higher as that of the additive - free analog (CC activity 2 5 MPa) and of the cement with sodium carbonate - by 1 2 % ( 3 5 MPa). Besides, the SSB additive affects greatly the activity of cement with ASB as compared with that containing GBFS. So, at the same OPC content ( 6 5 % ) , Composition No 8* ( 2 0 mas. % ASB) has an activity 5 5 MPa, what is by 2 4 % greater as compared with Composition N 7 ( 5 mas.% ASB). Table 2 CC compositions COMPOSITIONS Nos 1 2 3 4* 5 6 7 8* COMPONENTS CONTENT, mas.% OPC GBFS Perlite ASB 20 20 65 50 20 20 65 65 75 40 30 15 75 40 30 15 5 40 5 35 - _ - 5 40 5 20 Clearly followed is the influence of nature of the anion constituent of the modifying additive: the salts of sodium and weak acids are found to be the most effective in the compositions with increased calcium content (OPC) (the strong acid anion can take place in the formation of soluble calcium salts), whereas salts of sodium and strong acids - in a low- Downloaded by [ Griffith University] on [25/10/17]. Copyright © ICE Publishing, all rights reserved. 346 R u n o v a , K o c h e v y k h , R u d e n k o , Nosovskii 2+ calcium compositions due to decreased activity of the last. In the last case a lack of Ca initiates participation of the Na - ions, in the aluminosilicate glass destruction. These foundings correlate well with the comparative data on activity of the compositions with perlite containing Na . + + Worth mentioning that it is impossible to give an objective characteristic of interaction processes in the cements containing the ASB using absolut values of activity because of variable chemical and phase composition of this product which is an industrial waste. That's why, when using the ASB containing blended cements in concrete, a extremely careful approach to analysis of raw materials and, first of all, to the ASB, and their adjustment to technology should be taken. The formulations should be chosen in which the range of ASB content would provide a required stability of properties of CC. C h a r a c t e r of H y d r a t i o n P r o d u c t s The X-ray analysis data of the hydration products of the modified cement of Composition No 6 of the first system (Figure 2, a) as compared with those of an additive-free reference cement testify to a predominant formation of low-basic calcium hydrosilicates (0.305, 0,280, 0.182 nm). The intensity of the peaks of the non-reacted ASB and GBFS in a form of residual peaks of quartz (0.335, 0.251, 0.202 nm) and coinsiding with them the peaks of melilite (0.336, 0.273, 0.220 nm) and y-C S (0.336, 0.268, 0.228 nm) is by 2 times less intensive. The presence of the peaks attributed to the initial components even in the modified CC testifies to uncompleteness of the pozzolanic reaction resulted from the increased density of the aluminosilicate glass of the ASB and GBFS. This allowed to increase the OPC content up to 65% by mass. These data obtained correlate well with those of differential - thermal analysis and infra-red spectroscopy. Of interest is the comparison of these data with those obtained for the cement compositions containing perlite (the second system). 2 As the X-ray analysis data demonstrate (Figure 2, b) the hydration products of the second system cement compositions modified by sodium sulfate containing 20% by mass of the OPC (Composition No 2) at high perlite content are, in general, similar to hydration products of the Composition No 6 containing industrial pozzolana. Worth mentioning is the formation of large quantities of low-basic calcium hydrosilicates of CSH (1) type (d= 0.305, 0.280, 0.182 nm) accompanied by residual peaks of low intensity attributed to melilite and y-C S (d= 0.427, 0.335, 0.273, 0.267 nm), testifying to a more completeness of the pozzolanic reaction. The last may be also attributed to a lower, as compared with the ASB, density of watercontaining perlite glass, and its relative homogeneity. The X-ray analysis results correlate well with those obtained using the differential- thermal analysis and the infra- red spectroscopy. 2 The new formations composition in a form of calcium hydrosilicates of the lower basicity and the gel phases, inclusive of alkaline aluminosilicate composition, explain rather high values of activity of CC modified by sodium salts additives. The identification of such phases is possible during their crystallisation for a long- term period . At the same time, the earlier reported data [ 12] on the character of micropores, suggested to assume that just a gel of such composition is of importance in the formation of material property. To the properties in support of this assumption refer, first of all, resistance to aggressive environments. Downloaded by [ Griffith University] on [25/10/17]. Copyright © ICE Publishing, all rights reserved. 347 Influence of S o d i u m Salts on I n t e r a c t i o n The results of corrosion resistance of CC compositions after they were cured for 72 days in 5% - solutions of sodium and magnesium sulfate salts are shown in Table 3. The coefficient of resistance of all CC compositions under investigation, which is expressed as a ratio of flexural strengths of the specimens kept in solutions and those reference ones kept in water, exceeds 0.8, the coefficient of their resistance in sodium sulfate solution being somewhat greater than of those stored in magnesium sulfate solution. Table3 Corrosion resistance of CC COEFFICIENT OF RESISTANCE FLEXURAL STRENGTH, MPa COMPOSITIONS Nos (See Table 2) Aggressive environments InNa S0 2 H 0 Na S0 7.0 6.0 7.5 5.4 10.7 8.3 9.8 5.3 2 2 4* 6 8* 2 4 MgS0 6.8 8.03 8.2 9.1 4 InMgS0 4 4 1.52 1.38 1.31 0.98 0.97 1.34 1.09 1.68 CONCLUSIONS 1. The interaction processes in the system "OPC-GBFS-ASB" are initiated by alkali metal salts. 2. The hydration products of the studied CC are found to be similar to those formed in the pozzolanic systems. A difference is the increased content of the gel-like new formations in a form of calcium hydrosilicates and the creation of conditions for possible formation of the products which in composition would be analogous to natural alkaline hydroaluminosilicates in a gel state. 3. The choice of the anion constituent of sodium salt which is used as an activator is determined by a nature of pozzolanic constituent of CC: sodium salts of weak acids are found to be the most efficient in the basic systems, whereas sodium salts of strong acids in low-calcium systems due to the lower activity of the last, thus causing participation of the Na ions, predominantey, in the destruction of glass of the aluminosilicate component of the system. + 4. The new formations compositions of CC modified by additives while hydration allowed to recommend them for the use in the aggressive environments, including when laying road pavements. Downloaded by [ Griffith University] on [25/10/17]. Copyright © ICE Publishing, all rights reserved. 348 Runova, Kochevykh, Rudenko, Nosovskii REFERENCES 1. DHIR, R K AND McCARTHY, M I. Optimising Binders for Concrete Construction. World Cement, 1997, Vol.28, No. 1, pp 74- 81. 2. GLUKHOVSKII, V D. Soil Silicates, UkrSSR Gosstroiizdat, Kiev, 1959, 134 pp. 3. GLUKHOVSKII, V D. Soil Silicates- Made Articles and Structures, Budivelnik., 1967, 154 pp. 4. GORIAYNOV, K E AND GORIAYNOVA, S K. Technology of Heat Insulating Materials and Articles, Stroiizdat, Moscow, 1982, 376 pp. 5. Materials and Articles from Expanded Perlite, Edit. A A Zhukov, Stroiizdat, Moscow, 1972, 249 pp. 6. KRIVENKO, P V AND PUSHKARJEVA, E K. Durability of Slag Alkaline Concrete, Budivelnik, 1993,224 pp. 7. SERGEEV, A M. Utilisation of Energy Industry Wastes in Construction, Budivelnik, Kiev 1984, 120 pp. 8. Energy Fuels of the USSR, Manual, Energia, Moscow, 1973, 128 pp. 9. Composition and Properties of the Ash and Slag from the Heat Power Stations, Code of Practice ( Edit. V A Melent'ev, Energoatomizdat, Leningrad, 1985, 285 pp. 10. Alkaline and Alkaline - Alkali-Earth Hydraulic Binders and Concretes ( Edit. V D Glukhovskii), Vyscha Shkola, Kiev, 1979, 232 pp. 11. FUNDI, Y A S. Alkaline Pozzolana Portland Cements. Proceedings of the First International Conference on Alkaline Cements and Concretes, Kiev, 1994, Vol.1, pp 181192. 12. RUNOVA, R F, KOCHEVYKH, M A AND RUDENKO, I I. Pressed Ash Containing Concrete: Activation of Structure Formation. Proceedings of the International Conference Concrete In The Service Of Mankind, Dundee, Scotland, 1996, Vol. Concrete for Environment and Protection, pp 671-676 Downloaded by [ Griffith University] on [25/10/17]. Copyright © ICE Publishing, all rights reserved.