- Email: [email protected]
Influence of geopolymer formulation parameters on the elastic and porous properties over a one-year monitoring
Accepted Manuscript Influence of geopolymer formulation parameters on the elastic and porous properties over a one-year monitoring Julien Rouyer, Virginie Benavent, Fabien Frizon, Arnaud Poulesquen PII: DOI: Reference:
S0167-577X(17)31024-8 http://dx.doi.org/10.1016/j.matlet.2017.06.125 MLBLUE 22837
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
11 May 2017 20 June 2017 28 June 2017
Please cite this article as: J. Rouyer, V. Benavent, F. Frizon, A. Poulesquen, Influence of geopolymer formulation parameters on the elastic and porous properties over a one-year monitoring, Materials Letters (2017), doi: http:// dx.doi.org/10.1016/j.matlet.2017.06.125
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Influence of geopolymer formulation parameters on the elastic and porous properties over a one-year monitoring Julien Rouyera, Virginie Benaventb, Fabien Frizonb and Arnaud Poulesquenb*
a
Laboratoire de Mécanique et d’Acoustique, CNRS, UPR 7051, Aix-Marseille
Université, Technopôle de Château Gombert, Marseille, France b
Commissariat à l’énergie atomique et aux énergies alternatives, DEN, DTCD,
SPDE, LCBC, F-30207, Bagnols-sur-Cèze, France *
corresponding author: [email protected]
Abstract: The effects of two formulation parameters, by changing the Si/Al molar ratio and the initial water content, were studied to understand their impacts on the aging of the metakaolin-based geopolymer. Five formulations were designed and resulting samples were conditioned under 100% relative humidity. Long-term mechanical characterizations (up to 360 days) were conducted to measure the Young modulus and the compressive strength by ultrasound and compression tests, respectively. As well, porosimetry was performed using gravimetric technique (at 28-day term) and nitrogen sorption technique (up to 360 days). At fixed Si/Al ratio when increasing the initial water content, results showed a decrease of mechanical parameters and the formation of larger porous network with an increasing effective pore diameter (from 5.3 to 11.1 nm). Conversely, at fixed water content when Si/Al ratio increased, porous network characteristics were fairly identical with employed formulations, and mechanical parameters slightly increased. Also, during the seven first days, the mechanical parameter growth became slower when increasing Si/Al ratio.
Keywords: geopolymer; aging; structure; porosity; strength; elastic.
1. Introduction In the class of the alkali-activated materials, the geopolymer is a recently studied one and referrers to a lowcalcium content binder. The geopolymer properties interest fields of nuclear wastes conditioning [1] and civil engineering [2]. Geopolymerization consists primarily in a hydrolysis/dissolution and oligomerization concomitant reactions, secondly in a polycondensation process [3], [4]. Structuration mechanisms lead to a porous network formation in constant evolution from the bulk strengthening until 3-month term at least [5], [6]. Mainly open [7], the porous network consists in micro-meso and macropores [8], [7] with a wide and nonuniform pore size distribution [9]: an average pore radius below 10 nm [10], [11] and around 1-2 µm [7], respectively. Macro-elastic behaviors were linked to modifications in the microstructural arrangement when changing formulation parameters [8], [12]–[14]. The study aims to monitor both mechanical and porous properties with aging (until 360 days) using specific geopolymer formulations which emphasis the relation between macro-elastic and microstructural parameters. The Si/Al ratio and water content effects were studied using five controlled samples. Two mechanical and two porous characterization means were employed for these purposes. 2. Materials and Methods 2.1. Sample formulations The preparation of metakaolin-based geopolymers was already reported in [7]. Five geopolymer pastes were prepared with the nominal composition SiO2Na2O H2O, where
is 1.2, 1.4 or 1.6 and
was 10, 11.5 or 13,
respectively. Geopolymers had Al/Na molar ratio of 1, and H2O/Na2O of 10, 11.5 or 13 and SiO2/M2O=SiO2/Al2O3 of 3.6, 3.8 or 4 (corresponding to Si/Al of 1.8, 1.9 and 2, respectively), and the selected formulations were Na-4.0-10, Na-3.8-10, Na-3.6-10, Na-3.6-11.5, and Na-3.6-13. Samples were demolded after 24 hours and conditioned at 298 K and 100% relative humidity. 2.2. Characterization modalities 2.2.1. Mechanical characterization Shear and compressional wave speeds (
and
) in solids are related to intrinsic elastic parameters in linear
regime [15]. Through-transmission ultrasound experiment enables the wave speed measurement and the determination of the dynamic Young modulus as,
, where
is the bulk density. Using a 1-
MHz nominal frequency, both shear and compressional wave propagations were performed through a 3
4 4 16 cm samples in the transversal section. One sample per formulation was used along the measurement period thanks to this non-destructive mean. Compressive strength (
3
) measurements were performed as well on 4 4 16 cm samples using a Quantris
RP-40-400 compression machine (3R, Montauban, France). At least two specimens of each sample formulation were tested at the same age. First, the sample was broken in two parts by a three-point bending test. Then, -1
these halves of specimen undergo a compression test on lateral surfaces, with a 2.4-kN.s loading rate.
2.2.2. Porosity characterization The gravimetric technique allows estimating the pore volume when pore sizes ranged between 2 nm and 2 mm. Samples were saturated in water and under vacuum for at least 72 hours. After the complete saturation, the underwater weight and the saturated sample mass were measured. Then, samples were dried in an oven at 80°C until equilibrium (mass loss less than 0.05% in twenty-four consecutive hours) and weighted again. The pore volume (
) was finally estimated using
is the mass after drying and
, where
is the mass after saturation,
is the underwater weight.
The nitrogen sorption porosimetry allows evaluating the effective pore diameter ranging from 2 up to 400 nm with the BJH model. As well, the pore volume and the specific area can be estimated with the BET method, as detailed in Supplementary Information in [7]. Nitrogen adsorption measurements were performed on a ASAP 2020 instrument (Micromeritics Instrument Corp., Norcross, GA, USA.); the corresponding experimental procedure was already reported in [7]. 3. Experimental results Mechanical results are presented in Figure 1(a,b) until 360 days, respectively. Both mechanical parameters followed a similar trend with a sharp initial strengthening between 1-day and 7-day terms. After 28-day term, the growth of mechanical moduli slowdowned while still increasing their respective values until the end of the measurement period. Gravimetric experiments were performed for a single term at 28 days. The evaluated pore volumes (
) were
39% for Na-4.0-10, 40% for Na-3.8-10, 41% for Na-3.6-10, 43% for Na-3.6-11.5, and 46% for Na-3.6-13. The evaluated pore volumes (
) by nitrogen sorption had very limited changes among samples from 7-day up to
360-day terms, as seen in Figure 2. However, a slight decrease occurred with aging. The pore volume, the pore diameter and the specific surface at the 28-day term were summarized in Table 1. Figure 3 shows the two mechanical parameters at 28-day term in function of the pore volume evaluated by gravimetric (
) and nitrogen sorption (
) techniques.
4. Discussion and Conclusion Mechanical properties were well correlated to the porous characteristics conditioned by the initial chemical formulation parameters. Indeed, at fixed Si/Al ratio and when increasing the initial water content – Na-3.610, Na-3.6-11.5 and Na-3.6-13 – these particular formulations lead to a larger pore volume with an increasing effective pore diameter – 5.3, 8.8 and 11.1 nm, respectively [16, 17]. These observations were in agreement with the sol/gel process where water is released into the system due to the polycondensation reaction [4]. In this case, the mechanical parameter decreased when increasing the initial water content (Figure 1). On the other hand, when the initial water content is constant and the Si/Al ratio increases – Na-3.6-10, Na3.8-10 and Na-4.0-10 – the characteristics of the porous network are nearly the same (Table 1), apart from the first seven days where the growth in mechanical parameters was especially slow downed when the Si/Al ratio was high (Figure 1). These results are not completely explained but we can assume that the
geopolymerization takes more time to achieve because of the higher paste viscosity [18] and the higher condensed species count at the liquid state. Therefore, the consolidation of the porous network is delayed, but the developed strength is higher (Figure 1) due to a lower pore volume (Figure 2). Over time and whatever the formulation parameters, a slight increase of mechanical properties is observed (Figure 1 after 28 days) in accordance with a slight decrease of the pore volume (Figure 2). It is important to remind here that, contrary to previous study [6], all samples have been conditioned at 100% of relative humidity. Consequently, the slight decrease in the pore volume accessible to the nitrogen may be explained by a local dissolution-reprecipitation occurring at the pore/wall solution interface which limiting the entrance nitrogen [7]. Although the quantitative evaluation of pore volume at 28 days differed between the gravimetric and the nitrogen sorption techniques due the limitation of the nitrogen sorption limitation (ink bottle effect), the interpretation of Figure 3 leads to the identical conclusion when comparing with mechanical parameters. Indeed, elastic properties decreased when the pore volume increased with an interesting fairly linear dependency in the studied sample. Among samples, the initial growth of mechanical properties at 3-day term resulted in about 80% of the final compressional strength values ranged between 45 and 75 MPa. Measured dynamic Young modulus are higher than static Young modulus values reported by [8], [12]–[14]. The differences between static and dynamic techniques arise commonly [15], [19], [20]. The differences in the strain magnitude involved in those tests (10-3 for static measurements, 10-7 for ultrasonic waves) was argued by [18] to explain the quantitative variation. Isothermal and adiabatic conditions related respectively to static and dynamic tests should have a quantitative impact influence [19].
In conclusion, the long-term monitoring of proposed samples provided new indications about the relations between microstructure and macro-elasticity. It demonstrated the continuation of one or several physicochemical processes leading to a structural remodeling under a controlled environment. Moreover, ultrasound provided a very powerful and useful tool to measure the mechanical properties changes over time due to the non-destructive character of the wave propagation in comparison with the compression ones. Indeed, a linear relationship
4.04
1.42, was obtained between the compressive strength and the
Young modulus as shown in Figure 4. Interestingly, the linear law matched well among studied formulations whatever sample ages.
Acknowledgements The authors want to thank Thomas Piallat for ultrasound and compression experiments, as well as Adrien Gerenton for nitrogen sorption experiments.
References [1]
A. Rooses, D. Lambertin, D. Chartier, and F. Frizon, “Galvanic corrosion of Mg-Zr fuel cladding and steel immobilized in Portland cement and geopolymer at early ages,” J. Nucl. Mater., vol. 435, no. 1–3, pp.
[2] [3] [4] [5] [6] [7] [8]
[9]
[10] [11] [12]
[13] [14] [15]
137–140, 2013. R. Pouhet and M. Cyr, “Formulation and performance of flash metakaolin geopolymer concretes,” Constr. Build. Mater., vol. 120, pp. 150–160, 2016. V. J. Babushkin, G. M. Matveyev, and O. P. Mchedlov-Petrossyan, “Thermodynamics of Silicates,” Cryst. Res. Technol., vol. 21, no. 1, pp. 276–281, 1986. J. Rouyer and A. Poulesquen, “Evidence of a Fractal Percolating Network During Geopolymerization,” J. Am. Ceram. Soc., vol. 98, no. 5, pp. 1580–1587, May 2015. P. Steins, A. Poulesquen, O. Diat, and F. Frizon, “Structural Evolution during Geopolymerization from an Early Age to Consolidated Material,” Langmuir, vol. 28, no. 22, pp. 8502–8510, 2012. P. Steins et al., “Effect of aging and alkali activator on the porous structure of a geopolymer,” J. Appl. Crystallogr., vol. 47, no. 1, pp. 316–324, 2014. V. Benavent, F. Frizon, and A. Poulesquen, “Effect of composition and aging on the porous structure of metakaolin-based geopolymers,” J. Appl. Crystallogr., vol. 49, no. 6, pp. 2116–2128, 2016. P. Duxson, J. L. Provis, G. C. Lukey, S. W. Mallicoat, W. M. Kriven, and J. S. J. van Deventer, “Understanding the relationship between geopolymer composition, microstructure and mechanical properties,” Colloids Surfaces A Physicochem. Eng. Asp., vol. 269, pp. 47–58, 2005. C. F. Maitland, C. E. Buckley, B. H. O’Connor, P. D. Butler, and R. D. Hart, “Characterization of the pore structure of metakaolin-derived geopolymers by neutron scattering and electron microscopy,” J. Appl. Crystallogr., vol. 44, no. 4, pp. 697–707, 2011. W. M. Kriven, M. Gordon, and J. L. Bell, “Geopolymers: Nanoparticulate, Nanoporous Ceramics Made Under Ambient Conditions,” Microsc. Microanal., vol. 10, no. S02, pp. 404–405, 2004. J. L. Bell and W. M. Kriven, “Nanoporosity in Aluminosilicate, Geopolymeric Cements,” Microsc. Microanal., vol. 10, no. S02, pp. 590–591, 2004. P. Duxson, S. W. Mallicoat, G. C. Lukey, W. M. Kriven, and J. S. J. van Deventer, “The effect of alkali and Si/Al ratio on the development of mechanical properties of metakaolin-based geopolymers,” Colloids Surfaces A Physicochem. Eng. Asp., vol. 292, no. 1, pp. 8–20, Jan. 2007. M. Lizcano, H. S. Kim, S. Basu, and M. Radovic, “Mechanical properties of sodium and potassium activated metakaolin-based geopolymers,” J. Mater. Sci., vol. 47, no. 6, pp. 2607–2616, 2012. D. Yan, S. Chen, Q. Zeng, S. Xu, and H. Li, “Correlating the elastic properties of metakaolin-based geopolymer with its composition,” Mater. Des., vol. 95, pp. 306–318, 2016. E. A. Eissa and A. Kazi, “Relation between static and dynamic Young’s moduli of rocks,” Int. J. Rock Mech. Min. Sci., vol. 25, no. 6, pp. 479–482, 1988.
[16]
E. Landi, V. Medri, E. Papa, J. Dedecek, P. Klein, P. Benito, A. Vaccari, “Alkali-bonded ceramics with hierarchical tailored porosity, ” Applied Clay Science, vol. 73, no. 1, pp. 56-64, 2013.
[17]
E. Kamseu, C. Djangang, P. Veronesi, A. Fernanda, U. C. Melo, V. M. Sglavo, C. Leonelli, “Transformation of the geopolymer gels to crystalline bonds in cold-setting refractory concretes: Pore évolution, mechanical strength and microstructure, ” Materials and Design, vol. 88, pp. 336-344, 2015
[18]
A. Poulesquen, F. Frizon, and D. Lambertin, “Rheological behavior of alkali-activated metakaolin during geopolymerization,” J. Non. Cryst. Solids, vol. 357, no. 21, pp. 3565–3571, 2011.
[19]
H. Ledbetter, “Dynamic vs. static Young’s moduli: a case study,” Mater. Sci. Eng. A, vol. 165, no. 1, pp. 9–10, 1993. M. Ciccotti and F. Mulargia, “Differences between static and dynamic elastic moduli of a typical seismogenic rock,” Geophys. J. Int., vol. 157, no. 1, pp. 474–477, 2004.
[20]
Figures/Table:
Figure 1. Young modulus (top) and compressive strength (bottom) as a function of time. A log-scale for time was chosen to highlight the sharp increase occurring in the beginning of the measurement period (up to 360 days).
Figure 2. Evaluation of pore volume using the nitrogen sorption experiment in function of time.
Table 1: Pore volume (
), the mean pore diameter ( ) and the specific surface ( ) evaluated using nitrogen
sorption experiments at 28-day term. Sample
Na-4.0-10
Na-3.8-10
Na-3.6-10
Na-3.6-11.5
Na-3.6-13
18 %
21 %
22 %
27 %
31 %
5.1 nm 2
40 m /g
6.3 nm 2
45 m /g
5.3 nm 2
46 m /g
8.8 nm 2
53 m /g
11.1 nm 58 m2/g
Figure 3. Relation between the mechanical parameters and the evaluated pore volumes (a) in gravimetry and (b) in nitrogen sorption at 28-day term. Dotted and dashed lines correspond to Young modulus and compressive strength, respectively.
Figure 4. Relation between the compressive strength and the Young modulus for each formulation of Nageopolymer at 1, 3, 7, 14, 28, 90, 180 days.
Highlights :
Assessment of geopolymer mechanical properties and porous network over time Dependence of mechanical properties with the porous network characteristics Linear relation between young modulus and compressive strength Evaluation of the elastic properties by ultrasound
S0167-577X(17)31024-8 http://dx.doi.org/10.1016/j.matlet.2017.06.125 MLBLUE 22837
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
11 May 2017 20 June 2017 28 June 2017
Please cite this article as: J. Rouyer, V. Benavent, F. Frizon, A. Poulesquen, Influence of geopolymer formulation parameters on the elastic and porous properties over a one-year monitoring, Materials Letters (2017), doi: http:// dx.doi.org/10.1016/j.matlet.2017.06.125
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Influence of geopolymer formulation parameters on the elastic and porous properties over a one-year monitoring Julien Rouyera, Virginie Benaventb, Fabien Frizonb and Arnaud Poulesquenb*
a
Laboratoire de Mécanique et d’Acoustique, CNRS, UPR 7051, Aix-Marseille
Université, Technopôle de Château Gombert, Marseille, France b
Commissariat à l’énergie atomique et aux énergies alternatives, DEN, DTCD,
SPDE, LCBC, F-30207, Bagnols-sur-Cèze, France *
corresponding author: [email protected]
Abstract: The effects of two formulation parameters, by changing the Si/Al molar ratio and the initial water content, were studied to understand their impacts on the aging of the metakaolin-based geopolymer. Five formulations were designed and resulting samples were conditioned under 100% relative humidity. Long-term mechanical characterizations (up to 360 days) were conducted to measure the Young modulus and the compressive strength by ultrasound and compression tests, respectively. As well, porosimetry was performed using gravimetric technique (at 28-day term) and nitrogen sorption technique (up to 360 days). At fixed Si/Al ratio when increasing the initial water content, results showed a decrease of mechanical parameters and the formation of larger porous network with an increasing effective pore diameter (from 5.3 to 11.1 nm). Conversely, at fixed water content when Si/Al ratio increased, porous network characteristics were fairly identical with employed formulations, and mechanical parameters slightly increased. Also, during the seven first days, the mechanical parameter growth became slower when increasing Si/Al ratio.
Keywords: geopolymer; aging; structure; porosity; strength; elastic.
1. Introduction In the class of the alkali-activated materials, the geopolymer is a recently studied one and referrers to a lowcalcium content binder. The geopolymer properties interest fields of nuclear wastes conditioning [1] and civil engineering [2]. Geopolymerization consists primarily in a hydrolysis/dissolution and oligomerization concomitant reactions, secondly in a polycondensation process [3], [4]. Structuration mechanisms lead to a porous network formation in constant evolution from the bulk strengthening until 3-month term at least [5], [6]. Mainly open [7], the porous network consists in micro-meso and macropores [8], [7] with a wide and nonuniform pore size distribution [9]: an average pore radius below 10 nm [10], [11] and around 1-2 µm [7], respectively. Macro-elastic behaviors were linked to modifications in the microstructural arrangement when changing formulation parameters [8], [12]–[14]. The study aims to monitor both mechanical and porous properties with aging (until 360 days) using specific geopolymer formulations which emphasis the relation between macro-elastic and microstructural parameters. The Si/Al ratio and water content effects were studied using five controlled samples. Two mechanical and two porous characterization means were employed for these purposes. 2. Materials and Methods 2.1. Sample formulations The preparation of metakaolin-based geopolymers was already reported in [7]. Five geopolymer pastes were prepared with the nominal composition SiO2Na2O H2O, where
is 1.2, 1.4 or 1.6 and
was 10, 11.5 or 13,
respectively. Geopolymers had Al/Na molar ratio of 1, and H2O/Na2O of 10, 11.5 or 13 and SiO2/M2O=SiO2/Al2O3 of 3.6, 3.8 or 4 (corresponding to Si/Al of 1.8, 1.9 and 2, respectively), and the selected formulations were Na-4.0-10, Na-3.8-10, Na-3.6-10, Na-3.6-11.5, and Na-3.6-13. Samples were demolded after 24 hours and conditioned at 298 K and 100% relative humidity. 2.2. Characterization modalities 2.2.1. Mechanical characterization Shear and compressional wave speeds (
and
) in solids are related to intrinsic elastic parameters in linear
regime [15]. Through-transmission ultrasound experiment enables the wave speed measurement and the determination of the dynamic Young modulus as,
, where
is the bulk density. Using a 1-
MHz nominal frequency, both shear and compressional wave propagations were performed through a 3
4 4 16 cm samples in the transversal section. One sample per formulation was used along the measurement period thanks to this non-destructive mean. Compressive strength (
3
) measurements were performed as well on 4 4 16 cm samples using a Quantris
RP-40-400 compression machine (3R, Montauban, France). At least two specimens of each sample formulation were tested at the same age. First, the sample was broken in two parts by a three-point bending test. Then, -1
these halves of specimen undergo a compression test on lateral surfaces, with a 2.4-kN.s loading rate.
2.2.2. Porosity characterization The gravimetric technique allows estimating the pore volume when pore sizes ranged between 2 nm and 2 mm. Samples were saturated in water and under vacuum for at least 72 hours. After the complete saturation, the underwater weight and the saturated sample mass were measured. Then, samples were dried in an oven at 80°C until equilibrium (mass loss less than 0.05% in twenty-four consecutive hours) and weighted again. The pore volume (
) was finally estimated using
is the mass after drying and
, where
is the mass after saturation,
is the underwater weight.
The nitrogen sorption porosimetry allows evaluating the effective pore diameter ranging from 2 up to 400 nm with the BJH model. As well, the pore volume and the specific area can be estimated with the BET method, as detailed in Supplementary Information in [7]. Nitrogen adsorption measurements were performed on a ASAP 2020 instrument (Micromeritics Instrument Corp., Norcross, GA, USA.); the corresponding experimental procedure was already reported in [7]. 3. Experimental results Mechanical results are presented in Figure 1(a,b) until 360 days, respectively. Both mechanical parameters followed a similar trend with a sharp initial strengthening between 1-day and 7-day terms. After 28-day term, the growth of mechanical moduli slowdowned while still increasing their respective values until the end of the measurement period. Gravimetric experiments were performed for a single term at 28 days. The evaluated pore volumes (
) were
39% for Na-4.0-10, 40% for Na-3.8-10, 41% for Na-3.6-10, 43% for Na-3.6-11.5, and 46% for Na-3.6-13. The evaluated pore volumes (
) by nitrogen sorption had very limited changes among samples from 7-day up to
360-day terms, as seen in Figure 2. However, a slight decrease occurred with aging. The pore volume, the pore diameter and the specific surface at the 28-day term were summarized in Table 1. Figure 3 shows the two mechanical parameters at 28-day term in function of the pore volume evaluated by gravimetric (
) and nitrogen sorption (
) techniques.
4. Discussion and Conclusion Mechanical properties were well correlated to the porous characteristics conditioned by the initial chemical formulation parameters. Indeed, at fixed Si/Al ratio and when increasing the initial water content – Na-3.610, Na-3.6-11.5 and Na-3.6-13 – these particular formulations lead to a larger pore volume with an increasing effective pore diameter – 5.3, 8.8 and 11.1 nm, respectively [16, 17]. These observations were in agreement with the sol/gel process where water is released into the system due to the polycondensation reaction [4]. In this case, the mechanical parameter decreased when increasing the initial water content (Figure 1). On the other hand, when the initial water content is constant and the Si/Al ratio increases – Na-3.6-10, Na3.8-10 and Na-4.0-10 – the characteristics of the porous network are nearly the same (Table 1), apart from the first seven days where the growth in mechanical parameters was especially slow downed when the Si/Al ratio was high (Figure 1). These results are not completely explained but we can assume that the
geopolymerization takes more time to achieve because of the higher paste viscosity [18] and the higher condensed species count at the liquid state. Therefore, the consolidation of the porous network is delayed, but the developed strength is higher (Figure 1) due to a lower pore volume (Figure 2). Over time and whatever the formulation parameters, a slight increase of mechanical properties is observed (Figure 1 after 28 days) in accordance with a slight decrease of the pore volume (Figure 2). It is important to remind here that, contrary to previous study [6], all samples have been conditioned at 100% of relative humidity. Consequently, the slight decrease in the pore volume accessible to the nitrogen may be explained by a local dissolution-reprecipitation occurring at the pore/wall solution interface which limiting the entrance nitrogen [7]. Although the quantitative evaluation of pore volume at 28 days differed between the gravimetric and the nitrogen sorption techniques due the limitation of the nitrogen sorption limitation (ink bottle effect), the interpretation of Figure 3 leads to the identical conclusion when comparing with mechanical parameters. Indeed, elastic properties decreased when the pore volume increased with an interesting fairly linear dependency in the studied sample. Among samples, the initial growth of mechanical properties at 3-day term resulted in about 80% of the final compressional strength values ranged between 45 and 75 MPa. Measured dynamic Young modulus are higher than static Young modulus values reported by [8], [12]–[14]. The differences between static and dynamic techniques arise commonly [15], [19], [20]. The differences in the strain magnitude involved in those tests (10-3 for static measurements, 10-7 for ultrasonic waves) was argued by [18] to explain the quantitative variation. Isothermal and adiabatic conditions related respectively to static and dynamic tests should have a quantitative impact influence [19].
In conclusion, the long-term monitoring of proposed samples provided new indications about the relations between microstructure and macro-elasticity. It demonstrated the continuation of one or several physicochemical processes leading to a structural remodeling under a controlled environment. Moreover, ultrasound provided a very powerful and useful tool to measure the mechanical properties changes over time due to the non-destructive character of the wave propagation in comparison with the compression ones. Indeed, a linear relationship
4.04
1.42, was obtained between the compressive strength and the
Young modulus as shown in Figure 4. Interestingly, the linear law matched well among studied formulations whatever sample ages.
Acknowledgements The authors want to thank Thomas Piallat for ultrasound and compression experiments, as well as Adrien Gerenton for nitrogen sorption experiments.
References [1]
A. Rooses, D. Lambertin, D. Chartier, and F. Frizon, “Galvanic corrosion of Mg-Zr fuel cladding and steel immobilized in Portland cement and geopolymer at early ages,” J. Nucl. Mater., vol. 435, no. 1–3, pp.
[2] [3] [4] [5] [6] [7] [8]
[9]
[10] [11] [12]
[13] [14] [15]
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[20]
Figures/Table:
Figure 1. Young modulus (top) and compressive strength (bottom) as a function of time. A log-scale for time was chosen to highlight the sharp increase occurring in the beginning of the measurement period (up to 360 days).
Figure 2. Evaluation of pore volume using the nitrogen sorption experiment in function of time.
Table 1: Pore volume (
), the mean pore diameter ( ) and the specific surface ( ) evaluated using nitrogen
sorption experiments at 28-day term. Sample
Na-4.0-10
Na-3.8-10
Na-3.6-10
Na-3.6-11.5
Na-3.6-13
18 %
21 %
22 %
27 %
31 %
5.1 nm 2
40 m /g
6.3 nm 2
45 m /g
5.3 nm 2
46 m /g
8.8 nm 2
53 m /g
11.1 nm 58 m2/g
Figure 3. Relation between the mechanical parameters and the evaluated pore volumes (a) in gravimetry and (b) in nitrogen sorption at 28-day term. Dotted and dashed lines correspond to Young modulus and compressive strength, respectively.
Figure 4. Relation between the compressive strength and the Young modulus for each formulation of Nageopolymer at 1, 3, 7, 14, 28, 90, 180 days.
Highlights :
Assessment of geopolymer mechanical properties and porous network over time Dependence of mechanical properties with the porous network characteristics Linear relation between young modulus and compressive strength Evaluation of the elastic properties by ultrasound