CORROSION OF STEEL IN EMBEDDED CONCRETE WITH VOLCANIC AGGREGATES DUE TO SULFATE ATTACK

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 7, Issue 2, March-April 2016, pp , Article ID: IJCIET_07_02_029 Available online at Journal Impact Factor (2016): (Calculated by GISI) ISSN Print: and ISSN Online: IAEME Publication CORROSION OF STEEL IN EMBEDDED CONCRETE WITH VOLCANIC AGGREGATES DUE TO SULFATE ATTACK Abaho. G Research Scholar, Department of Civil Engineering, School of Engineering and Technology,Jain University, Bangalore M. R. Prenesh Professor, Department of Civil Engineering Engineering, School of Engineering and Technology,Jain University, Bangalore ABSTRACT The experimental tests conducted helps to study the concrete properties of volcanic concrete systems with granite replacement of river sand. The test results show that granite rock aggregates is an alternative construction material to river sand with a beneficial effect of reduced permeability properties. Compression strength, Corrosion potential and polarization resistance test results give an impression that 30% river sand replacement in volcanic concrete system is more resistant to sulfate attack as compared to same systems with no replacement. The reduced permeability property of concrete system could lead to reduced chances of corrosion of steel in reinforced concrete structures hence to increased durability of structures. Key word: Sulfate Attack, Volcanic Concrete System, Granite Rock Powder, River Sand, Corrosion of Reinforcement Cite this Article: Abaho. G and M. R. Prenesh. Corrosion of Steel In Embedded Concrete with Volcanic Aggregates Due To Sulfate Attack, International Journal of Civil Engineering and Technology, 7(2), 2016, pp INTRODUCTION Industrialization and urbanization development in Rwanda involves constructions of different types of infrastructure hence consuming large quantities of building raw materials like aggregates. The environmental impact associated with this development is high due to extraction of raw materials in quarries and carbon dioxide emissions released in the production and transport processes (Schneider et al. 2011; Shi et al. 2011; Jungle et al.2011) [1, 2, 3,]. Waste industrial materials can be used as an 328

2 Corrosion of Steel In Embedded Concrete with Volcanic Aggregates Due To Sulfate Attack alternative to natural fine aggregates in concrete mixes (Halifax AL-Jabra et al. 2009) [4]. Fly ash, siliceous stone powder, lime stone rock dust and quarry waste are examples of reported used raw materials in place of natural river sand Red DURAR (1998) [5].SciTech (2012), [6] reported the use of volcanic rock aggregates in local construction industry. This work is suspicious to the durability of the structures constructed with volcanic rock aggregates due to its porosity. Rasheeduzzafar et al. 1990) [7] found the effect of porous concrete system to cause concrete cover deterioration and the reinforcement corrosion. Reinforced concrete deterioration by sulfate attack causes the reinforcing steel exposed to aggressive agents initiate corrosion of the reinforcement and shortens its designed service life. The sulfate permeation can be controlled by: increasing compactness, lowering water-to-cement ratio, proper curing, surface treatment, and use precast concrete in place of cast-in-situ concrete (ACI Committee, 1991;Hossain, 2004; Kalousek et al., 1972; Al-Amoudi et al., 1994;Young et al.,1998) [8,9, 10, 11,15]. Research in cement chemistry over the past two decades resulted in cements with a high C3S/C2S content(rasheeduzzafar,1990).this increase in C3S/C2S ratio results in increased calcium hydroxide content in the hardened cement concrete, thereby enhancing the susceptibility to such cements to softening type of sulfate attack (Rasheeduzzafar, 1990; ACI Committee, 1991). Irassar et al. (2000) [12] reported that a low C3S/C2S ratio is a significant positive cause in the choice of cement for good sulfate resistance. However, Kalousek et al. 1972; Rasheeduzzafar, 1990; Lawrence, 1990 [13] reported that the limitation on C3A content is not the last answer to the problem of sulfate attack. Mehta (1993) [14] said that Type V cement addresses only the problem of sulfate expansion associated with the ettringite formation. Therefore, Type V cement is particularly efficacious when calcium sulfate is the attacking medium, although it could be beneficial with respect to the prevention of gypsum owing sodium sulfate attack. Thus, Type V cement is of no avail in the attack of calcium hydroxide and C-S-H and the next loss of strength (Mehta, 1993). Neville, 2004 [16] said that although significant progress has been made on the understanding of the mechanism of sulfate attack in concrete, knowledge and understanding remains inadequate. Accordingly, the role of C3A, cement content, water to binder ratio, and the role of pozzolanic materials remain controversial. Hence, the effect of ingredient materials used in the concrete material to sulfate attack and their interaction to cause corrosion of steel in concrete remains an interesting area to research. The most economic strategy, environmental friendly for sustainable development in the construction industry in Rwanda is to use the locally available construction raw materials. The abundances of volcanic rocks in northwestern part and granite rock aggregates industrial waste in the eastern part of Rwanda have motivated the conduct of this research. 2. CONCRETE MATERIALS One of the important aims of this work was to find out and compare the permeability properties of two concrete systems with granite rock aggregates and river sand fine aggregates. Some countries like Rwanda still use concrete with no admixtures. Concrete is normally a mixture of well-proportioned ingredients of cement, water, fine and coarse aggregates sometimes with chemical and mineral admixtures. Cement acts as a binding material, aggregates in general, are inert granular materials which give to 60 to 70 percent of the volume of concrete. Fine aggregates are filler materials and work as workability agent because coarse aggregates contribute to the 329

3 Abaho. G and M. R. Prenesh volume of concrete. In this study, the materials used were, grade 43 Portland cement (cement RW), purified drinking water, volcanic rock coarse aggregates from Ruhengeri, Kaguguriver sand and granite rock powder from East Africa granite plant at Nyagatare used as fine aggregates. The size of crushed volcanic rock coarse aggregates used ranged between (20-6.3) mm while fine aggregates ranged between 4.75mm and 150micro. Table1and Table2 below give more details on materials, sieves analysis results, grading and grading limits for all aggregates used. Table 1 shows some of the physical-chemical properties of materials. cement Materials Description Type Opc 43grade, Specific gravity , Standard consistency- 32%, Fine setting time- 300 minutes, Compressive strength- 7th day- 41N/mm2-28thN/mm2-62 N/mm2, Specific surface Average size - (μ m) 15-25, Specific surface, BET (m2/kg) Volcanic rock aggregate River sand Specific gravity-2.42, Fine modulus- 2.93, Mamum size-20 mm Bulk Density(Kg/lit)- Loose , - rounded Specific gravity-2.58, Fine modulus- 2.43, Granite powder Specific gravity-2.69, Fine modulus Chemical properties AlO3 Fe2O3 CaO SO3 K2O Na2O MgO The most proportioned fine aggregates to coarse aggregates ratio depend upon actual grading, particle shape and surface texture of both fine and coarse aggregates. For conformity with grading limit (IS: ), the granite aggregate fall in zone II of crushed aggregate and river sand aggregates fall in zone II grading limit of fine aggregates Table.2. Sieve analysis carried out on granite aggregates compared to river sand gives the results as presented in Table2. The surface index method was used to find out easily the proportion of fine to coarse aggregates (Murdock, L. J, 19 60) [31]. Figure1 Sieve analysis of fine aggregates for different sieve sizes 330

4 Corrosion of Steel In Embedded Concrete with Volcanic Aggregates Due To Sulfate Attack Sieve Size (mm) Fig 1 shows that the amount of fine particles present in granite powder is considerably higher when compared to the river sand. Water plays a critical role in the green concrete mixture, particularly in the amount used. Workability of concrete usually increases with increased water in the concrete system. Water requirement for workability of concrete increases with increase of fine aggregates but this is only true above 300micro particle size of aggregates otherwise for 300micro and below particle size the phenomena is vice versa. Table 2 Sieve Analysis results, grading limits and surface Index for coarse and fine and aggregates. Percentage Passing of the volcanic coarse aggregates Percentage Passing of the granite fine Aggregates (GP) Grading limit of crushed aggregate zone II %passing by weight Percentage Passing of the River sand Aggregates (RS) Grading limit of fine aggregate zone II % passing by weight Sieve size within which particle lie For surface Index [31] mm mm mm mm mm micron micro micron Smaller than micron micron micron micron 75 micron - - Max EXPERIMENTATION The proposed study conducted tests and their experimental setups in series to find steel corrosion behavior due to sulfate attack on a new concrete system mixture. The study utilized crushed volcanic rock aggregates as coarse aggregates and granite rock powder partly as well as full replacement. The laboratory program conducted in this investigation focused on six basic mixes. The mix designations according to the grade of concrete and the fine aggregates type used are: Mixes incorporating 0% river sand (100% granite powder), 10% granite powder (90% river sand), 30% granite powder (70% river sand), 50% granite powder (50% river sand), 70% granite powder (30% river sand), 100% granite powder (0% river sand), with no admixtures for RS100 or GP0, GP10, GP30, GP50, GP70and GP100respectively. This work adapted the Bureau of Indian Standards IS 10262:2009; 456:200 [27, 29] guidance for making M40 grade concrete specimens. Table 3 shows the resultant mixture compositions. Surface Index for particles [31] 331

5 Abaho. G and M. R. Prenesh NO Designation of Mix (%) Table 3Mix design with mixture compositions This study comprised of six experimental tests which are explain independently here below Workability The strength of concrete is much dependent upon water cement ratio (w/c). Leaving other factors constant, the lower the w/c ratio higher compressive strength of concrete will be. Workability of concrete with low w/cis obtained by good gradation of aggregates as it helps to reduce voids in the paste. Good gradation here means that concrete sample contains all standard fractions of aggregate in required portion to minimize voids. This study adopted the use of surface index which is an empirical number related to specific surface of the particle with more weightage given to the finer fractions (Murdock, L. J, 19 60) Compressive strength One of the most important properties of concrete is its compressive strength. The other characteristics of concrete are closely related to its compressive strength. It is one of the factors that affect the durability of the concrete structures. In this study, compressive strength test was conducted on 150mm x 150mm x150mm cube specimens using compression testing machine (CTM) of 3000kN capacity. On the specimen prepared under same condition but with different w/c ratio of 0.35, 0.4 and 0.45, the compressive strength was tested at different curing age of (1, 3, 7 and 28) days and the average test results were considered for analysis and comparison. 3.3 Weight loss In order to study the effect of sulfate environment on the weight loss of concrete and rebar corrosion of reinforcing steel, the six set up of concrete cylinder of 15 cm in diameter and 30 cm in height, with the two centrally embedded reinforcing bars, was arranged. Specimens were immersed in a 3.5% of NaSO 4 aqueous solution after dried in air for one day in a laboratory temperature (21 ± 2 C) and weighed. The reduction or increase in weight of the reinforced concrete specimens was evaluated and recorded periodically. The results for weight loss (WL) were calculated using the equation 1, %= River Sand (%) Replacement of sand with granite aggregates (%) Volcanic Coarse aggregates 1 GP GP GP GP GP G Cement (%) 332

6 Corrosion of Steel In Embedded Concrete with Volcanic Aggregates Due To Sulfate Attack Where W i = average initial weight of triplicate specimens (g); and W t. = average weight of triplicate specimens after a prescribed exposure period (g) Corrosion potential Reinforcement corrosion of the embedded steel was monitored by measuring the corrosion potentials and polarization resistance at regular intervals. The corrosion potentials (E corr ) were measured using a high impedance voltmeter and recording the potentials with respect to a copper/copper sulfate (Cu/CuSO 4 ) reference electrode Linear polarization resistance The linear polarization resistance (LPR) technique measures the polarization resistance (R) of the concrete specimen in a Potentiostat/Galvanostat of ACM Instruments. The work (Song and Saraswathy, 2007) [17] has details of electrochemical techniques. The test scan of ± 20 mv to a scan speed of mv/min gave the polarization resistance of the concrete specimen tested. The basic principle of electrochemical corrosion of reinforced concrete is well-known (Dao et al 2010; Bentur et al.1998) [18, 19] and the experimental testing is shown in Figure 2 shown below. Figure 2Experimental schemes for testing LPR With the curves for the potential against current density the R p of the systems in study was obtained and hence the basis to calculate the corrosion current density (icorr) of the systems using Equation 2 (stern and Geary, 1957) [20], where B is Tafel constant with recommended value (Dhir et al.1993; González et al.1996; Gowers and Millard, 1993; Mangat and Mollay, 1992)[21, 22, 23, 24] of V for the passive corrosion of steel in concrete. = 3.6. Slabs for water Absorption Test In general, water absorption in the concrete causes durability problems due to migration of water. In this experiment, the measurements of water rise in the slabs were performed at the age of 1 and 2 hours. The slabs were cured at 38 O C water ponding temperature for 28 days; air dried for 2 days and finally placed in a basin 10mm soaking in water, the water level was monitored to keep the water height at 10mm height. Measurements were taken using an ordinary inch tape over a cross 333

7 Abaho. G and M. R. Prenesh section of the slab to determine the depth of water rise. This test measures the rate of absorption of water by capillary suction of unsaturated concrete placed in contact with water. The photographic view of the measurements of water absorption in slab specimen is shown in Fig. 3 adopted from Felix Kala (2013) [25]. Figure3Measurements of water absorption in slab specimen 4. RESULTS AND DISCUSSION 4.1. Workability Concrete workability for six mixes studied and had slump values; 70, 70, 75, 73, 71 and 70 for RS, GP10, GP30, GP50, GP70 and GP100 respectively. It shows that concrete mixes with 30% granite powder produced higher slump compared to other the mixes. This improved workability for the mix might be due to the more amounts of fine particles in granite aggregates. The very fine particle in granite aggregates i.e., 300 micron and 150 micron particles, being so fine, contribute more towards workability by acting like ball bearings to reduce the internal friction between coarse particles. However more than 30% replacement of river sand (50, 70 and 100) % by more fines made the concrete leaner which restrained the mobility of aggregates as less paste was there to provide lubrication. Other factors considered constant, it shows that a good grading was reached with 30% replacement of rivers and. It led to less total voids in concrete which caused excess paste available that effected better lubrication hence caused higher workability of concrete Compressive strength test Compressive strength test was considered important in this work because other desirable characteristic properties concrete directly or indirectly depend on its compressive strength. The effect of granite aggregates in partial and fully replacement of river sand fine aggregates is shown in Fig. 4 a), b) and c).the data show that 30% river sand replacement with granite aggregates gives the highest compressive strength in all curing days. The increased compressive strength was due to finer particles of granite aggregates that filled the pores in concrete in general which increased its density and compactness of concrete system. It is seen from the figures that the lower the w/c the more the compressive strength the concrete gained in early curing age. This possibly is due to decreased aggregate cement transition zone which increases with increase in water cement ratio. This is more likely because the cement particles are held at a closer interval in case of lower w/c ratio than higher w/c ratio. 10% of river sand replacement showed insignificant change in compressive strength. Above 30% replacement (50, 70, and 100) %, both workability and compressive strength 334

8 Corrosion of Steel In Embedded Concrete with Volcanic Aggregates Due To Sulfate Attack have a trend of decrease due to more water requirement of fine aggregates for better workability. It means that inadequate water to hydrate cement particles as well as fine aggregates left pores in concrete system. This is a line of weakness for cracking in case of compression force applied on this concrete. Also it is observed that the more the curing age, the more the compressive strength as a result of increased binding together of aggregates due to continued hydration process. a) b) c) Figure 4 a, b and c Compressive strength of 0.35, 0.4 and 0.45w/c ratio at different age of curing respectively

9 Abaho. G and M. R. Prenesh 4.2. Concrete weight loss Experimental results for weight loss of reinforced concrete specimens exposed to sulfate solution are schematically presented as a function of the exposure time in Figure 5. The data show that the concrete specimen lost weight. This was when the weight of specimens immersed in test solution was compared with their weights before immersion. It shows that the specimen gained weight on their immersion to solution. Weight loss increased considerably after three months in the RS (0% granite replacement) concrete. In comparison to others, specimens designated GP 30, the increase of weight loss was not so big and it appears after three months. This could be due to capillary pore system filled by little expansive reaction products compact the concrete matrix system and increasing the weight. Then, the expansion of these products is increased to a great extent generating fractures in the concrete matrix system, loosening of material and therefore, the weight of specimen decreased. Figure5Weight loss of concrete in sulfate environment The maximum weight loss was 2.1% in duration of six months of exposure in the RS (0% GP) volcanic concrete specimens and the minimum weight loss (0.2 %) was in GP30 concrete system. From these results, it is clear that the contribution of granite powder inporefilling of the concrete system is significant and prevents the easy penetration of sulfate ions towards and within the concrete. Again the trend in water loss in volcanic concrete system shows that the concrete becomes porous and permeable above 30% river sand replacement by granite aggregates due absorption of water by increased fines in the mix. Possibly also, 30% river sand replacement consumes some calcium hydroxide during poazzolanic reaction which reduces the amount of gypsum in the mixture. This would be the same case for mixtures more above 30% but it might be overcome by its porosity that permit the ingress of more water to concrete Corrosion potentials Figure 5 the results of corrosion potentials of evaluated test specimens. The horizontal broken lines show the limits corresponding to the corrosion probability criterion suggested in the norm ASTM C876 [26]. Figure

10 Corrosion of Steel In Embedded Concrete with Volcanic Aggregates Due To Sulfate Attack Fig 7 Figure 6and 7 Variation of E corr and iccorrof the reinforcement steel as a function of the exposure time respectively In the five months of specimen exposure, the corrosion potentials, of all the reinforced concrete systems, show fluctuation ranging from -696 to -380 mv/ Cu- CuSO4 with a slight decrease during the month, towards more noble values. According to ASTM C 876, these Ecorr values show that there exists a 90% chance of active corrosion during all the exposure time; but, the criterion is for partly saturated not totally saturated specimens. ASTM C 876 criterion is applied in fully merged structures or specimen environment reinforcement corrosion tests. Therefore, probably all embedded steel were in a passive state during the six months of specimen immersion in the sulfate solution. Otherwise, GP30 could have performed better in as far as resisting corrosion of steel reinforcement as shown in fig.6. Since the system with the granite rock powder presented the more noble corrosion potentials during the exposure time. The GP70 concrete samples presented corrosion potentials between to -380 mv /Cu-CuSO4 compared -696 to mV/ CuSO4 for RS (GP0) concrete systems. This shows that granite powder contribution to the inhibition of corrosion of the reinforcement has limit with percentage replacement. This testing technique provides qualitative information on reinforcement corrosion. Therefore, quantitative information on reinforcement corrosion could be developed by employing the linear polarization resistance technique presented in fig.7 shown above Polarization resistance From the curves potential against current density Rp was obtained for all the systems in study and icorr was calculated representing the results in Figure 7; the horizontal broken line point out the threshold of active to passive corrosion (Andrade and Alonso, 1996) [28]. In Figure 7; it can be observed that the system steel-concrete that presents a highest corrosion resistance induced by sulfates is GP30, because its corrosive activity was the lowest in the exposure time and decreased significantly until it reached a low level of corrosion (0.003μA/cm2) at the end of the period. The GP 70 system showed levels of corrosion between 0.03 and μa/cm2, and RS (GP0) showed levels of corrosion between 0.06 and μA/cm2 which means that GP 30 significantly inhibit the corrosion of the reinforcement in the initial six months. The significant effect of GP 30 to inhabit corrosion current density is due to reduction of pores size and pore distribution in concrete system that makes the possible dense structure of pores formed. Because of that, it is deduced that the microstructure of concrete with GP30 becomes denser than the rest of the system. Therefore, it reports a decrease in 337

11 Abaho. G and M. R. Prenesh both sulfate ion penetrability and corrosion current density. According to Powers 1958 [30], several mineral additions have also been shown to improve the resistance of concrete materials to the penetration of aggressive ions. So the research in this field may produce interesting results also regarding the durability of reinforced concrete structures Water Absorption Table 4Effect of granite powder on water absorption Hours of curing W/C Ratio Water penetration (mm) at 32 0 c water Ponding Temperature Mix Designation GP 100 GP 70 GP 50 GP30 GP 10 GP 0 1 hr hr hr hr hr hr The test results are presented in table 4 above. The absorption of the slabs 100 mm x 500 mm x500 mm containing granite powder are lower than that of RS (GP0) as presented in table 4. In the case of concrete mix GP30 the average absorption for 1 and 2 hours is 15.2 mm and 20 mm respectively. The average absorption of concrete mix RS for 1 and 2 hours is 16.9 mm and 22 mm. It is observed that the reduction in water absorption for GP30 is 5% compared to conventional concrete RS (GP0) mix presented table 4. It could be noted that the variation in absorption for different concrete mixes was found to be normal for 2 hours of curing when compared to 1 hour of curing. The interaction between permeability, volume change and micro cracking here is a challenge to the discussant, heat of hydration and internal manifestation can cause micro cracks and increase permeability of concrete system. However, based on the analysis made on the previous tests and on the water penetration comparison of GP30 and RS, the high the porosity of the specimen the higher was the water penetration in concrete. Hence, G30 was impermeable compared to RS concrete mixtures. 4. CONCLUSIONS The experimental study on steel reinforcement corrosion due to sulfate attack in concrete with volcanic rock coarse aggregates and granite aggregates to replace river sand fine aggregates is the specialty of this paper. Experimental results analysis for workability, compressive strength, weight loss, corrosion potentials, polarization resistance and water absorption characteristics of concrete systems are the basis for conclusion enclosed. It has been found that granite aggregate is an alternate construction material in volcanic concrete system with even some beneficial effects of improved workability, compression strength etc. but within certain limit. The test results show that granite powder in 30% partial replacement of river sand has an advantage of reduced permeability properties on hardened concrete over the river sand. With the results obtained in conducted test, specimens made with 30% granite rock powder (GP 30) as fine aggregates give 8% absorption decrease in the hardened 338

12 Corrosion of Steel In Embedded Concrete with Volcanic Aggregates Due To Sulfate Attack concrete system compared to river sand aggregates. Polarization resistance test has proved that volcanic concrete system with 30 % granite rock powder replacement is more resistant to corrosion of steel reinforcement compared to 100 % volcanic river sand system. The addition of 30% of granite rock powder as partial replacement river sand reduced weight loss by around 1.9%. Granite rock powder increases densification of the concrete system and reduces pore size as well as poredistribution in volcanic concrete systems as justified by an average of 14.75MPa difference in compressive strength GP30 as compared to RS. Therefore, corrosion of steel reinforcement due to sulfate attack in volcanic concrete systems could be reduced with the use of GP30 granite rock powder fine aggregates than using RS (GPO). This work opens for more research to find out the exact limit for river sand replacement which lies between (10-50) percent as per present finding. ACKNOWLEDGEMENT The authors thank Jain University for its support in the Ph.D. Program with its scholarship. Thanks for the government of Rwanda to the support extended to the research scholar through His Excellency president Kagame scholarship. Thanks for the University of Rwanda for the study leave given to the research scholar. Authors are also thankful to support given by Civil-Aid Techno clinic P.V.T. Ltd in conducting experiments and other laboratory tests. REFERENCE [1] Schneider, M, Romer, M, Tschudin, M, Bolio. H. Sustainable cement production: Present and future. Cem. Concr. Res, 41, 2011, pp [2] Shi, C, Fernandez-Jiménez, A, Palomo, A. New cements for the 21st century: The pursuit of an alternative to Portland cement. Cem.Concr.Re s., 41, 2011, pp [3] Juenger, M.C.G.; Winfield, F.; Provis, J.L.; Ideker, J.H. Advances in alternative cementitiousbinders.cem.concr. Res, 41, 2011, pp [4] Khalifa Al-Jabri, S; Makoto Hisada, K. Salem Al-Oraimi and H. Abdullah Al- Saidy, Copper slag as the sand replacement for high-performance concrete, Cement &Concrete Composites, 31,2009, pp [5] Red DURAR, Manual de Inspección, Evaluación y Diagnostico de Corrosiónenestructuras de HormigónArmado, CYTED, España, [6] Schittich, C, Building simply two: Sustainable, cost-efficient, local, Walter de Gruyter, Architecture, [7] Rasheeduzzafar, Dakhil F. H, Al-GahtaniA. S, Al-Saadoun S.S, Bader M. A. Influence of cement composition on corrosion of reinforcement and sulfate resistance of concrete. ACI Mater J, 87(2), 1990, pp [8] ACI committee 201, proposed revision of: Guide to durable concrete, ACI Mater. J. 88(2): 1991, pp [9] Hossain K.M. A Properties of volcanic scoria based lightweight concrete. Mag. Concr. Res.56 (2), 2004, pp [10] Kalousek GL, Porter LC, Benton EJ Concrete for long-time service in sulfate environment.cem.concr. Res. 2(1), 1972, pp [11] Al-Amoudi OSB, Maslehuddin RM, Abduljauwad SN, Influence of chloride ions on sulphate deterioration in plain and blended cement, Mag.Concr. Res. 46(167), 1994, pp

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