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Microstructure of Portland cement pastes containing metal nitrate salts
Waste Management 22 (2002) 147–151 www.elsevier.com/locate/wasman
Microstructure of Portland cement pastes containing metal nitrate salts S.K. Ouki*, C.D. Hills University of Surrey, Department of Civil Engineering, Centre for Environmental Health Engineering, Guildford GU2 7XH, UK
Abstract In recent years, Backscattered Scanning Electron microscopy techniques (BSE), coupled with an image analysis system have been recognised as a powerful tool for quantitative analysis. This paper investigates the effect of metal additions (Ba, Cu, Ni, Zn, Cr(III), Pb and Cd) to Portland cement to produce a solidified product which meets the durability criteria quantified by the ratio of hydrated products and porosity. In addition, other indicators of the progress of cement hydration such as the bulk density and evaporable water of the solidified products were also measured. Metal concentrations of 0.1 and 1% per weight of cement at a constant water/cement ratio of 0.4 were examined. The same measurements were conducted on control samples of different water/ cement ratio. The results have shown that the control samples at different W/C ratio showed consistent trend in residual cement porosity, density and evaporable water content. It also showed that low dosage of metal nitrate additions can reduce cement hydration by up to 50% and at the same time reduce the observable porosity. Overall, this work has shown that Scanning Electron Microscopy (SEM) and image analysis are powerful tools and could be used to quantify the observable porosity and cement hydration in solidified systems. # 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction The fixation of metallic waste species in cement systems results from the following [1] solubility reduction and precipitation, ionic substitution and incorporation in cement hydrates and sorption onto the surface area of cement hydrates. The composition of Portland cement is dominated by the anhydrous calcium silicate phases, which typically comprise 70–80% by weight. Therefore, it is sufficient to assume that the hydration products of these phases, dominated by C-S-H gel, play an important role in the retention of metals. The interaction of metal salts with C-S-H were investigated by Bhatty [2], who concluded that the following mechanisms governing addition (Eq. 1) and substitution (Eq. 2) reactions apply: C-S-H þ Metal ! Metal-C-S-H
ð1Þ
C-S-H þ Metal ! Metal-C-S-H þ Ca2þ
ð2Þ
one time to effect the immobilisation of metallic ions. Bonen and Sarkar [3] summarised the immobilisation of a number of metallic waste species in Portland cement whereas Gougar et al. [4] examined metals immobilised in C-S-H gel. Salts precipitated during solidification may accelerate or retard hydration and apparently, innocuous mineral additions are no exception [5]. Thus the interactions of waste components on cement hydration processes are complex, involve competing chemical and physical processes, and will influence the subsequent microstructural development of a solidified waste form. In general, however, when metal waste species are present as hydroxide or silicate salts they are compatible with Portland cements. This is because they form low solubility precipitates whose leachability is reduced further during solidification [3–4]. 1.1. Microstructural development
However, due to the complexity of waste systems, multiple mechanisms might also be important at any * Corresponding author. Tel.: +44-1483-686633; fax: +44-1483450984. E-mail address: [email protected] (S.K. Ouki).
Although microstructural development in cement paste and concrete has been widely studied in recent years [1,6], the same cannot be said for cement-solidified hazardous wastes. As microstructural development is known to influence the performance characteristics of Portland cement concretes [7] it follows that the same might apply to solidified waste forms.
0956-053X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0956-053X(01)00063-0
148
S.K. Ouki, C.D. Hills / Waste Management 22 (2002) 147–151
This work describes the initial results of a wider study to examine the effects of waste materials on Portland cement. Here the effects of metal nitrate salts on the microstructural development of Portland cement control samples are examined. Nitrate salts have been chosen for this work because of their general high aqueous solubility and the fact that they have been investigated elsewhere [8–16].
2. Experimental Nitrate salts of the following metals were examined: Ba, Cu, Ni, Zn, Cr(III), Pb and Cd at concentrations of 0.1% and 1.0% metal ion to cement (per weight). In addition, a mixed solution containing each of the salts at 0.1% and 1.0% was prepared. Each metal salt or combination of salts was dissolved in de-ionised water prior to mixing with Class 42.5N Portland cement (Rugby Cement) in a 5-l Hobart mixer. Table 1 gives details of the mix designs used. Although some nondissolved salts remained in the 1.0% Ba(NO3)2 mix solution and the 1.0% mixed metal solution these were still added to each mix. In addition, six control samples Table 1 Mix designs of the metal containing samples 0.1% w/wa
1.0% w/wa
Salt
Water/cement
Ba0.1% Cu0.1% Ni 0.1% Zn0.1% Cr0.1% Pb0.1% Cd0.1% Mix0.1%
Ba1% Cu1% Ni1% Zn1% Cr1% Pb1% Cd1% Mix1%
Ba (NO3)2 Cu (NO3)2 3H2O Ni (NO3)2 6H2O Zn (NO3)2 6H2O Cr (NO3)3 9H2O Pb (NO3)2 Cd (NO3)2 4H2O Mixed
0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40
a
Weight of metal ion addition per weight of cement.
were prepared at various water/cement ratios (0.35– 0.65). Mixes were cast into 28 mm diameter70 mm screw top polyethylene containers. The samples were vibrated for 5 s at 50 Hz to help remove included air. Immediately after sealing, samples were rotated end-over-end at 2 rpm for 3 days to eliminate settlement effects. Thereafter, samples were cured at 20 2 C for 29 days. After curing, each mix was prepared for SEM analysis. The central portion was cut away and vacuum impregnated with resin prior to polishing to 1/4 mm in non-aqueous polishing media. Off-cuts were oven dried at 60 C to constant weight in order to measure the amount of non-combined water. After oven drying, density was determined by helium pycnometry (Micrometrics, Accupic 1330). Analysis of polished samples by SEM (Jeol 5310LV) at an accelerating voltage of 20 kV, and pressure of 25 Pa, involved obtaining representative fields using back scattered electron imaging (BSE). Adjacent fields were captured in two blocks of 10 fields from the centre of each specimen to ensure that the fields are representative of the sample under investigation. Each field covered a 270 mm200 mm area. The information was recorded as PCI or TIF images for image processing (Oxford Instruments ISIS software). Using BSE, Portland cement pastes appear as contrasting light and dark areas that are related to the mean atomic number of features. Images analysis can differentiate 256 grey levels ranging from dark to brick (0–255). The higher the mean atomic number of a material, the higher the intensity of its BSE signal. Thus, porosity appears black in colour, C-S-H gel and portlandite appear in mid-grey tones whereas residual anhydrous cement grains are bright/white in colour. By applying thresholds to the grey-scale histogram of each field, it is often possible to highlight distinct features of interest [17]. By this method, illustrated in Fig. 1, the
Fig. 1. Fitting of grey-scale thresholds.
S.K. Ouki, C.D. Hills / Waste Management 22 (2002) 147–151
percentage of pores and anhydrous cement grains in each field were measured.
3. Results The results are presented relative to the 0.4 water/ cement ratio (W/C) control mix. Results for control samples are illustrated in Fig. 2. Values for residual cement were similar for W/Cs at or below 0.45 W/C. At higher W/Cs, values gradually fell to nearly 50% of the control value. Porosity increased above a W/C of 0.45 and at the highest W/C ratio examined, the value was greater than +135% of the control. Evaporable water contents also increased as W/C increased, and at a W/C of 0.75, were greater than +130% of the control. Control samples with differing W/C ratio’s showed a consistent trend in their microstructural development, density and evaporable water content.
149
Effect of metal addition on the cement hydration is illustrated in Fig. 3. All mixes showed an increase in the amount of residual cement with the exception of one sample, Mix 0.1%. The 1.0% combined addition, Mix 1%, had the lowest degree of cement hydration, as the value recorded for residual cement was 74% greater than the 0.4 W/C control. For the individual metals, except for Ba, Cd and Ni mixes, as the addition rate increased to 1.0% w/w, the residual cement content decreased. Thus for Cr and Zn mixes a reduction the region of 70% aws observed. Metal addition as illustrated in Fig. 4 decreased the amount of evaporable water. This result may simply reflect the generally lower rate of cement hydration observed in these mixes. However, at higher metal addition, all mixes, except for Cd at 1%, showed a decrease in the evaporable water contents which is contrary to what one would expect and suggests that more highly hydrated phases were produced. As illustrated in Fig. 5, values recorded for porosity were generally lower than the 0.4 W/C control mix except for the 0.1% Ba, Cu and Cr mixes. The 0.1% Cd mix, gave the lowest value for any single addition at
Fig. 2. Percentage change in control samples relative to the 0.4 W/C sample.
Fig. 4. Percentage change in evaporable water from metal doped samples relative to the 0.4 W/C control mix.
Fig. 3. Percentage change in residual cement from metal doped samples relative to the 0.4 W/C control mix.
Fig. 5. Percentage change in porosity from metal doped samples relative to the 0.4 W/C control mix.
150
S.K. Ouki, C.D. Hills / Waste Management 22 (2002) 147–151
3. Combined metal additions appeared to not always have the most important effect on microstructural development in comparison with individual additions.
Acknowledgements This work was carried out as part of a consortium project on neural network analysis for the prediction of interactions in cement systems (NNAPICS), which is being funded by the European Union Euram Brite III programme. Fig. 6. Percentage change in density from metal doped samples relative to the 0.4 W/C control mix.
about 61% of the control value. The general pattern observed, except for Cd and Zn, was for lower values at the higher addition rates. For the mixed metal additions, the decrease in the porosity compared to the 0.4 W/C control mix was almost the same. Fig. 6 demonstrated that density values for the individual metal additions were slightly higher than for the control sample. For the mixed metal additions, a modest decrease was recorded at the lower addition rate, whereas at the higher addition, an approximate 10% increase in density was recorded.
4. Discussion and conclusions Previous work dating back to the 1930s [18] has shown that the effects of individual metals and anions on cement hydration can be significant. Concentration and synergistic effects [19,20] are also important. When hydration reactions are subject to interference the degree of cement hydration, pore volume/size distribution, sample density and the amount of non-combined water are all affected. This work has shown that a number of low-dose metal nitrate salts can markedly affect the amount of cement hydration and porosity as observed by SEM and image analysis techniques. With respect to metal additions, both the type and the amount of metal appear to be important factors in determining the effect on microstructural development. However, in general, additions resulted in a reduction in cement hydration and in the total porosity observed. The following conclusions were drawn from this work: 1. Control samples with differing W/C ratios showed a consistent trend in residual cement, porosity, density and evaporable water content. 2. Low dosages of metal nitrate salts reduced the cement hydration by greater than 50% and at the same time significantly reduced observable porosity.
References [1] Bonen D, Diamond S. Interpretation of compositional patters found by quantitative energy dispersive X-ray analysis for cement paste constituents. J Am Ceram Soc 1875;77:1875. [2] Bhatty MS. Fixation of metallic ions in Portland cement. In Proc. 4th National Conf. on Hazardous Wastes and Hazardous Materials, 1987. pp. 140–5. [3] Bonen D, Sarkar SL. The present state of the art of immobilisation of hazardous heavy metals in cement-based materials. Advances in cement and concrete. In: Grutzeck MW, Sarkar SL, editors. Proc. of the Engineering Foundation Conference. New York: American Society of Civil Engineers, 1994. p. 481–98. [4] Gougar MLD, Scheetz BE, Roy DM. Ettringite and C-S-H 5% additions. Cem Conc Res 1996;20:219. [5] Barker AP. Conduction calorimetric studies of cements containing 5% additions. Cement and Concrete Research 1990;20:219. [6] Diamond S, Bonen D. Microstructure of hardened cement paste—a new interpretation. J Am Ceram Soc 1990;76:2993. [7] Garboczi EJ. Microstructure and transport properties of concrete, in: performance criteria for concrete durability. In: Kropp J, Hilsdorf HK, editors. Rilem report 12. London: E & FN Spon, 1995. [8] Hamilton IW, Sammes NM. Encapsulation of steel foundry dusts in cement mortar. Cem Concr Res 1999;29:55–61. [9] Trussell S, Spence RD. A review of solidification/stabilization interferences. Waste Manage 1994;14:507–19. [10] Mattus CH, Mattus AJ. Literature review of the interaction of select inorganic species on the set and properties of cement and methods of abatement through pre-treatment. In: Gilliam TM, Wiles CC, editors. Stabilization and solidification of hazardous, radioactive, and mixed wastes. Philadelphia: ASTM, 1996. p. 609– 33. [11] Arliguie G, Grandet J. Etude de l’hydratation du ciment en presence de zinc, influence de la teneur en gypse. Cem Concr Res 1990;20:346–54. [12] Arliguie G, Grandet J. Influence de la composition d’un ciment Portland sur son hydratation en presence de zinc. Cem Concr Res 1990;20:517–24. [13] Cullinane MJ, Bricka RM, Francingues NR. An assessment of materials that interfere with stabilization/solidification processes, Report EPA/600/9-87/015. Washington: Environmental Protection Agency, 1987. [14] Ortego JD, Jackson S, Yu GS, McWhinney H, Cocke DL. Solidification of hazardous substances. A TGA and FTIR study of Portland cement containing metal nitrates. J Environ Sci Health 1989;A24(6):589–602.
S.K. Ouki, C.D. Hills / Waste Management 22 (2002) 147–151 [15] Tashiro C, Oba J, Akama K. The effects of several heavy metal oxides on the formation of ettringite and the microstructure of hardened ettringite. Cem Concr Res 1979;9:303–8. [16] Butcher EJ, Cheeseman CR, Sollars CJ, Perry R. Flow-through leach testing applied to stabilised/solidified wastes. In: Michael Gilliam MT, Wiles CC, editors. Stabilisation and solidification of hazardous, radioactive and mixed wastes, vol. 3. ASTM STP 1240, T. American Society of Testing and Materials, 1996. [17] Scrivener KL. Microscopy methods in cement and concrete science. World Cem Res Develop 1997:92–112.
151
[18] Forsen L. Die chemie des portlandzments in komplexchemischer darstellung. Zement 1933;6:73. [19] Hills CD, Sollars CJ, Perry R. Calorimetric and microstructural study of solidified toxic wastes: part 1-A classification of OPC/ waste interference effects. Waste Manage 1994;14:589. [20] Hills CD, Sollars CJ, Perry R. Calorimetric and microstructural study of solidified toxic wastes: part 2-A model for poisoning of hydration. Waste Manage 1994;14:601.
Microstructure of Portland cement pastes containing metal nitrate salts S.K. Ouki*, C.D. Hills University of Surrey, Department of Civil Engineering, Centre for Environmental Health Engineering, Guildford GU2 7XH, UK
Abstract In recent years, Backscattered Scanning Electron microscopy techniques (BSE), coupled with an image analysis system have been recognised as a powerful tool for quantitative analysis. This paper investigates the effect of metal additions (Ba, Cu, Ni, Zn, Cr(III), Pb and Cd) to Portland cement to produce a solidified product which meets the durability criteria quantified by the ratio of hydrated products and porosity. In addition, other indicators of the progress of cement hydration such as the bulk density and evaporable water of the solidified products were also measured. Metal concentrations of 0.1 and 1% per weight of cement at a constant water/cement ratio of 0.4 were examined. The same measurements were conducted on control samples of different water/ cement ratio. The results have shown that the control samples at different W/C ratio showed consistent trend in residual cement porosity, density and evaporable water content. It also showed that low dosage of metal nitrate additions can reduce cement hydration by up to 50% and at the same time reduce the observable porosity. Overall, this work has shown that Scanning Electron Microscopy (SEM) and image analysis are powerful tools and could be used to quantify the observable porosity and cement hydration in solidified systems. # 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction The fixation of metallic waste species in cement systems results from the following [1] solubility reduction and precipitation, ionic substitution and incorporation in cement hydrates and sorption onto the surface area of cement hydrates. The composition of Portland cement is dominated by the anhydrous calcium silicate phases, which typically comprise 70–80% by weight. Therefore, it is sufficient to assume that the hydration products of these phases, dominated by C-S-H gel, play an important role in the retention of metals. The interaction of metal salts with C-S-H were investigated by Bhatty [2], who concluded that the following mechanisms governing addition (Eq. 1) and substitution (Eq. 2) reactions apply: C-S-H þ Metal ! Metal-C-S-H
ð1Þ
C-S-H þ Metal ! Metal-C-S-H þ Ca2þ
ð2Þ
one time to effect the immobilisation of metallic ions. Bonen and Sarkar [3] summarised the immobilisation of a number of metallic waste species in Portland cement whereas Gougar et al. [4] examined metals immobilised in C-S-H gel. Salts precipitated during solidification may accelerate or retard hydration and apparently, innocuous mineral additions are no exception [5]. Thus the interactions of waste components on cement hydration processes are complex, involve competing chemical and physical processes, and will influence the subsequent microstructural development of a solidified waste form. In general, however, when metal waste species are present as hydroxide or silicate salts they are compatible with Portland cements. This is because they form low solubility precipitates whose leachability is reduced further during solidification [3–4]. 1.1. Microstructural development
However, due to the complexity of waste systems, multiple mechanisms might also be important at any * Corresponding author. Tel.: +44-1483-686633; fax: +44-1483450984. E-mail address: [email protected] (S.K. Ouki).
Although microstructural development in cement paste and concrete has been widely studied in recent years [1,6], the same cannot be said for cement-solidified hazardous wastes. As microstructural development is known to influence the performance characteristics of Portland cement concretes [7] it follows that the same might apply to solidified waste forms.
0956-053X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0956-053X(01)00063-0
148
S.K. Ouki, C.D. Hills / Waste Management 22 (2002) 147–151
This work describes the initial results of a wider study to examine the effects of waste materials on Portland cement. Here the effects of metal nitrate salts on the microstructural development of Portland cement control samples are examined. Nitrate salts have been chosen for this work because of their general high aqueous solubility and the fact that they have been investigated elsewhere [8–16].
2. Experimental Nitrate salts of the following metals were examined: Ba, Cu, Ni, Zn, Cr(III), Pb and Cd at concentrations of 0.1% and 1.0% metal ion to cement (per weight). In addition, a mixed solution containing each of the salts at 0.1% and 1.0% was prepared. Each metal salt or combination of salts was dissolved in de-ionised water prior to mixing with Class 42.5N Portland cement (Rugby Cement) in a 5-l Hobart mixer. Table 1 gives details of the mix designs used. Although some nondissolved salts remained in the 1.0% Ba(NO3)2 mix solution and the 1.0% mixed metal solution these were still added to each mix. In addition, six control samples Table 1 Mix designs of the metal containing samples 0.1% w/wa
1.0% w/wa
Salt
Water/cement
Ba0.1% Cu0.1% Ni 0.1% Zn0.1% Cr0.1% Pb0.1% Cd0.1% Mix0.1%
Ba1% Cu1% Ni1% Zn1% Cr1% Pb1% Cd1% Mix1%
Ba (NO3)2 Cu (NO3)2 3H2O Ni (NO3)2 6H2O Zn (NO3)2 6H2O Cr (NO3)3 9H2O Pb (NO3)2 Cd (NO3)2 4H2O Mixed
0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40
a
Weight of metal ion addition per weight of cement.
were prepared at various water/cement ratios (0.35– 0.65). Mixes were cast into 28 mm diameter70 mm screw top polyethylene containers. The samples were vibrated for 5 s at 50 Hz to help remove included air. Immediately after sealing, samples were rotated end-over-end at 2 rpm for 3 days to eliminate settlement effects. Thereafter, samples were cured at 20 2 C for 29 days. After curing, each mix was prepared for SEM analysis. The central portion was cut away and vacuum impregnated with resin prior to polishing to 1/4 mm in non-aqueous polishing media. Off-cuts were oven dried at 60 C to constant weight in order to measure the amount of non-combined water. After oven drying, density was determined by helium pycnometry (Micrometrics, Accupic 1330). Analysis of polished samples by SEM (Jeol 5310LV) at an accelerating voltage of 20 kV, and pressure of 25 Pa, involved obtaining representative fields using back scattered electron imaging (BSE). Adjacent fields were captured in two blocks of 10 fields from the centre of each specimen to ensure that the fields are representative of the sample under investigation. Each field covered a 270 mm200 mm area. The information was recorded as PCI or TIF images for image processing (Oxford Instruments ISIS software). Using BSE, Portland cement pastes appear as contrasting light and dark areas that are related to the mean atomic number of features. Images analysis can differentiate 256 grey levels ranging from dark to brick (0–255). The higher the mean atomic number of a material, the higher the intensity of its BSE signal. Thus, porosity appears black in colour, C-S-H gel and portlandite appear in mid-grey tones whereas residual anhydrous cement grains are bright/white in colour. By applying thresholds to the grey-scale histogram of each field, it is often possible to highlight distinct features of interest [17]. By this method, illustrated in Fig. 1, the
Fig. 1. Fitting of grey-scale thresholds.
S.K. Ouki, C.D. Hills / Waste Management 22 (2002) 147–151
percentage of pores and anhydrous cement grains in each field were measured.
3. Results The results are presented relative to the 0.4 water/ cement ratio (W/C) control mix. Results for control samples are illustrated in Fig. 2. Values for residual cement were similar for W/Cs at or below 0.45 W/C. At higher W/Cs, values gradually fell to nearly 50% of the control value. Porosity increased above a W/C of 0.45 and at the highest W/C ratio examined, the value was greater than +135% of the control. Evaporable water contents also increased as W/C increased, and at a W/C of 0.75, were greater than +130% of the control. Control samples with differing W/C ratio’s showed a consistent trend in their microstructural development, density and evaporable water content.
149
Effect of metal addition on the cement hydration is illustrated in Fig. 3. All mixes showed an increase in the amount of residual cement with the exception of one sample, Mix 0.1%. The 1.0% combined addition, Mix 1%, had the lowest degree of cement hydration, as the value recorded for residual cement was 74% greater than the 0.4 W/C control. For the individual metals, except for Ba, Cd and Ni mixes, as the addition rate increased to 1.0% w/w, the residual cement content decreased. Thus for Cr and Zn mixes a reduction the region of 70% aws observed. Metal addition as illustrated in Fig. 4 decreased the amount of evaporable water. This result may simply reflect the generally lower rate of cement hydration observed in these mixes. However, at higher metal addition, all mixes, except for Cd at 1%, showed a decrease in the evaporable water contents which is contrary to what one would expect and suggests that more highly hydrated phases were produced. As illustrated in Fig. 5, values recorded for porosity were generally lower than the 0.4 W/C control mix except for the 0.1% Ba, Cu and Cr mixes. The 0.1% Cd mix, gave the lowest value for any single addition at
Fig. 2. Percentage change in control samples relative to the 0.4 W/C sample.
Fig. 4. Percentage change in evaporable water from metal doped samples relative to the 0.4 W/C control mix.
Fig. 3. Percentage change in residual cement from metal doped samples relative to the 0.4 W/C control mix.
Fig. 5. Percentage change in porosity from metal doped samples relative to the 0.4 W/C control mix.
150
S.K. Ouki, C.D. Hills / Waste Management 22 (2002) 147–151
3. Combined metal additions appeared to not always have the most important effect on microstructural development in comparison with individual additions.
Acknowledgements This work was carried out as part of a consortium project on neural network analysis for the prediction of interactions in cement systems (NNAPICS), which is being funded by the European Union Euram Brite III programme. Fig. 6. Percentage change in density from metal doped samples relative to the 0.4 W/C control mix.
about 61% of the control value. The general pattern observed, except for Cd and Zn, was for lower values at the higher addition rates. For the mixed metal additions, the decrease in the porosity compared to the 0.4 W/C control mix was almost the same. Fig. 6 demonstrated that density values for the individual metal additions were slightly higher than for the control sample. For the mixed metal additions, a modest decrease was recorded at the lower addition rate, whereas at the higher addition, an approximate 10% increase in density was recorded.
4. Discussion and conclusions Previous work dating back to the 1930s [18] has shown that the effects of individual metals and anions on cement hydration can be significant. Concentration and synergistic effects [19,20] are also important. When hydration reactions are subject to interference the degree of cement hydration, pore volume/size distribution, sample density and the amount of non-combined water are all affected. This work has shown that a number of low-dose metal nitrate salts can markedly affect the amount of cement hydration and porosity as observed by SEM and image analysis techniques. With respect to metal additions, both the type and the amount of metal appear to be important factors in determining the effect on microstructural development. However, in general, additions resulted in a reduction in cement hydration and in the total porosity observed. The following conclusions were drawn from this work: 1. Control samples with differing W/C ratios showed a consistent trend in residual cement, porosity, density and evaporable water content. 2. Low dosages of metal nitrate salts reduced the cement hydration by greater than 50% and at the same time significantly reduced observable porosity.
References [1] Bonen D, Diamond S. Interpretation of compositional patters found by quantitative energy dispersive X-ray analysis for cement paste constituents. J Am Ceram Soc 1875;77:1875. [2] Bhatty MS. Fixation of metallic ions in Portland cement. In Proc. 4th National Conf. on Hazardous Wastes and Hazardous Materials, 1987. pp. 140–5. [3] Bonen D, Sarkar SL. The present state of the art of immobilisation of hazardous heavy metals in cement-based materials. Advances in cement and concrete. In: Grutzeck MW, Sarkar SL, editors. Proc. of the Engineering Foundation Conference. New York: American Society of Civil Engineers, 1994. p. 481–98. [4] Gougar MLD, Scheetz BE, Roy DM. Ettringite and C-S-H 5% additions. Cem Conc Res 1996;20:219. [5] Barker AP. Conduction calorimetric studies of cements containing 5% additions. Cement and Concrete Research 1990;20:219. [6] Diamond S, Bonen D. Microstructure of hardened cement paste—a new interpretation. J Am Ceram Soc 1990;76:2993. [7] Garboczi EJ. Microstructure and transport properties of concrete, in: performance criteria for concrete durability. In: Kropp J, Hilsdorf HK, editors. Rilem report 12. London: E & FN Spon, 1995. [8] Hamilton IW, Sammes NM. Encapsulation of steel foundry dusts in cement mortar. Cem Concr Res 1999;29:55–61. [9] Trussell S, Spence RD. A review of solidification/stabilization interferences. Waste Manage 1994;14:507–19. [10] Mattus CH, Mattus AJ. Literature review of the interaction of select inorganic species on the set and properties of cement and methods of abatement through pre-treatment. In: Gilliam TM, Wiles CC, editors. Stabilization and solidification of hazardous, radioactive, and mixed wastes. Philadelphia: ASTM, 1996. p. 609– 33. [11] Arliguie G, Grandet J. Etude de l’hydratation du ciment en presence de zinc, influence de la teneur en gypse. Cem Concr Res 1990;20:346–54. [12] Arliguie G, Grandet J. Influence de la composition d’un ciment Portland sur son hydratation en presence de zinc. Cem Concr Res 1990;20:517–24. [13] Cullinane MJ, Bricka RM, Francingues NR. An assessment of materials that interfere with stabilization/solidification processes, Report EPA/600/9-87/015. Washington: Environmental Protection Agency, 1987. [14] Ortego JD, Jackson S, Yu GS, McWhinney H, Cocke DL. Solidification of hazardous substances. A TGA and FTIR study of Portland cement containing metal nitrates. J Environ Sci Health 1989;A24(6):589–602.
S.K. Ouki, C.D. Hills / Waste Management 22 (2002) 147–151 [15] Tashiro C, Oba J, Akama K. The effects of several heavy metal oxides on the formation of ettringite and the microstructure of hardened ettringite. Cem Concr Res 1979;9:303–8. [16] Butcher EJ, Cheeseman CR, Sollars CJ, Perry R. Flow-through leach testing applied to stabilised/solidified wastes. In: Michael Gilliam MT, Wiles CC, editors. Stabilisation and solidification of hazardous, radioactive and mixed wastes, vol. 3. ASTM STP 1240, T. American Society of Testing and Materials, 1996. [17] Scrivener KL. Microscopy methods in cement and concrete science. World Cem Res Develop 1997:92–112.
151
[18] Forsen L. Die chemie des portlandzments in komplexchemischer darstellung. Zement 1933;6:73. [19] Hills CD, Sollars CJ, Perry R. Calorimetric and microstructural study of solidified toxic wastes: part 1-A classification of OPC/ waste interference effects. Waste Manage 1994;14:589. [20] Hills CD, Sollars CJ, Perry R. Calorimetric and microstructural study of solidified toxic wastes: part 2-A model for poisoning of hydration. Waste Manage 1994;14:601.