Effects of Rice Husk Silica on microstructure and mechanical properties of Magnesium-oxychloride Fiber Cement (MOFC)

Construction and Building Materials 241 (2020) 118022

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Effects of Rice Husk Silica on microstructure and mechanical properties of Magnesium-oxychloride Fiber Cement (MOFC) Carlos Marmorato Gomes 1,⇑, Anne-Laure Garry 2, Elaine Freitas 1, Cinthya Bertoldo 3, Gustavo Siqueira 1,4 School of Civil Engineering, Architecture and Urban Design, University of Campinas, 224 Saturnino de Brito Av, Campinas, Sao Paulo, Brazil

h i g h l i g h t s
RHS has an effective contribution to the flexural behavior of MOFC.
MOFC and RHS are alternatives to development of sustainable building materials.
RHS benefically influences on magnesium oxychloride fiber cement properties.

a r t i c l e

i n f o

Article history: Received 23 September 2019 Received in revised form 11 December 2019 Accepted 2 January 2020

Keywords: Magnesium oxychloride cement Rice Husk Ash Composite

a b s t r a c t Due to growing consumption of Portland cement and high levels of CO2 emissions during its production process, this study analyzed the employment of Rice Husk Silica (RHS) as eco-friendly material and its influence on microstructural formation, flexural properties and durability of magnesium oxychloride fiber cement (MOFC). In this way, fiber-cement flat sheets with different MgO/MgCl2 and MgO/SiO2 molar ratios were made by similar Hatschek process. The effects of RHS on magnesium oxychloride cement (MOC) were analyzed by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). The mechanical properties of MOFC were analyzed by flexural tests at 28 days old and after aging by 56 days in warm water. Fractured and polished surfaces were analyzed by secondary and back-scattered electron imaging and energy dispersive X-ray spectroscopy. Evaluation of these analyses provided the microstructural informations that were related to mechanical performance obtained from flexural tests. Results indicate that RHS increase the modulus of rupture and toughness of MOFC by filler effect and M-S-H formation improving the durability of these composites. Ó 2020 Elsevier Ltd. All rights reserved.

1. Introduction Recently the use of alternative binder has been verified in several applications as roofing, sheets, panels and refractory [1]. In this way, magnesium cement is a promising material for producing lightweight insulation boards [1–3] due to its potential advantages, such as light density, good fire resistance [4,5], and low thermal conductivity [4,6,7]. Magnesium oxychloride cement(MOC) is a material prepared through the chemical reaction of magnesium oxide and magnesium chloride in a solution [4,8,9]. The bonding phases are Mg(OH)2, 5Mg(OH)2.MgCl2.8H2O (5-form), and 3Mg ⇑ Corresponding author.

1 2 3 4

E-mail address: [email protected] (C.M. Gomes). URL: http://www.fec.unicamp.br (C.M. Gomes). Department of Architecture and Construction, University of Campinas, SP, Brazil. Institut National des Sciences Appliques – INSA Lyon – France. Faculty of Agricultural Engineering, University of Campinas, SP, Brazil. Department of Structure, University of Campinas, SP, Brazil.

https://doi.org/10.1016/j.conbuildmat.2020.118022 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved.

(OH)2.MgCl2.8H2O (3-form), and 5-form is the phase with superior mechanical properties. Related to Portland cement, MOC has superior properties. It does not need wet curing, has high fire resistance, low thermal conductivity, good resistance to abrasion [10]. MOC cement can be used with different aggregates and fibers with good adherence resistance [1] and admixtures with fly ash have been studied as to MOC production [11–13] as to magnesium oxysulfate cement (MOS)[3,14–16]. Also, many studies based on MgO-SiO2 binders [1,3,17,18] and M-S-H (magnesium hydrate silicate) formation [19–23] have been reported. Within context, the Rice Husk Silica (RHS) from renewable sources can be a highly-impactful sustainable alternative in civil engineering work, allowing the industry to produce environmentally-sound fiber cement mixtures as verified in this research. It is known that Rice Husk Ash (RHA) has become a serious environmental problem due to increasing agricultural production and the amount of methane gas generated by incorrect disposal of this waste [24,25]. According to the literature, for every

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metric ton of rice, around 200 kg of in nature husk is produced [26,27]. These figures become even more critical when we consider Brazilian production, especially in the state of Rio Grande do Sul, where it is around 8.7 million metric tons per year. Production of RHS requires the burning of the husk to be performed in controlled conditions. In Brazil, an innovative system of fluidized bed combustion (FBC) has been very efficient in the production of this pozzolana. Thus, this paper analyzes the influence of RHS on flexural properties, microstructure and durability of MOC reinforced by fibers. In this way, magnesium oxychloride fiber cements (MOFC) were produced employing carbonate filler, PVA fiber, cellulose pulp and RHS added in contents of 5% or 10% on MgO mass. Also, the effects of M-S-H formation and MgCl2 concentration on mechanical properties are investigated. According to literature, it is emphasized that the matrices analyzed can be considered as an alternative to development of sustainable building material [17,19,21].

Fig. 2. X-ray Diffraction of RHS studied.

2. Materials and methods 2.1. Raw materials This study used a light-burned magnesia (LBM), from IBAR Nordeste Ltda, with a 95% fineness passing through 75 lm (#200), density of 3.58 g/cm3 and chemical composition according to Table 1. A commercial magnesium chloride salt (MgCl2.6H2O) is used in this study. Carbonate powder was adopted as inert filler. Cellulose pulp (Unbleached Radiata pine, Chilean specie) and Chinese PVA fibers (length: 6 mm; diameter: 20 l) are employed as reinforcement. Rice husk silica with SiO2 amorphous up to 93:2%, pozzolanic activity up to 1300 mg CaðOHÞ2 =g, surface area about 21,150 m2 =kg, average diameter about 14 micron and density about 2:17 g=m3 , are adopted. Further characterization of RHS was realized by electronic microscopy Fig. 1, X-ray difraction Fig. 2 and granulometric analysis Fig. 3 to demonstrate its amorphity and fine particle dimensions.

Fig. 3. Particle size distribution of RHS studied.

2.2. Specimen preparation Chemical compositions of magnesium-oxychoride based matrices are presented in Table 2. RHS contents adopted were 5% and 10% in addition to MgO mass. PVA and cellulose fibers are used as reinforcement to all cement matrices considered. In this way, to produce the fiber cements, the contents by weight of materials Table 1 Chemical compositions of the magnesium oxide. Component Mass fraction (wt%)

MgO

SiO2

Al2O3

Fe2O3

> 92.5

< 2.5

< 0.7

< 3.0

Table 2 Chemical composition of the unreinforced magnesium-oxychloride based pastes. Sample

R1 R2 S1 S2 S3 S4

MgO (%)

Carbonate powder (%)

Salt concentration (g/L)

salt water/ rightarrow tal solids

RHS/ MgO addition (%)

25 25 15 25 25 25

75 75 85 75 75 75

84.8 154.6 84.8 84.8 154.6 154.6

0.20 0.20 0.20 0.20 0.20 0.20

– – 10 10 5 10

Fig. 1. Electronic Microscopy of RHS studied.

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C.M. Gomes et al. / Construction and Building Materials 241 (2020) 118022 Table 3 Final molar ratio of the fiber cements. Fiber cement Molar ratio MgO/MgCl2 Molar ratio MgO/SiO2 Molar ratio MgO/H2O

R1

R2

S1

S2

S3

S4

34.8

19.1

20.9

34.8

19.1

19.1

–

–

14.9

14.9

29.8

14.9

0.61

0.66

0.36

0.61

0.66

0.66

considered are 95.2% of magnesium carbonate – RHS – salt, 1.8% of PVA fiber and 3.0% of cellulose fiber. These fiber contents are close that frequently used by fiber cement industry in Portland cement matrices. Two concentrations of salt (MgCl2) were used, i.e. 84.8 g/L and 154.6 g/L. These concentrations were obtained with dilution of 20% and 40% of salt (MgCl2.6H2O) in water. All mixes were produced by the same process reported in literature [1,3,18] and it is illustrated in Fig. 4. Basically, the process steps consisted in: (i) submission of the unrefined cellulose pulp to a stirring process in water and post-refining with several passes through 300 mm disc refiner until the achievement of CSF 220 mL refinement degree; (ii) dilution of salt in water; (iii) dispersion of cellulose and PVA fiber in salt water; (iv) mixing of all these materials; (v) addition of magnesium oxide and carbonate powder; (vi) addition of RHS; (vii) high-speed mechanic mixing during 120 s; (viii) sheet molding by vacuum dewatering process and manual compression; (ix) mechanical compression about 3 MPa; after that, it is emphasized that the final amount of salt water in the sheets was maintained approximately the same and the final molar ratios obtained are shown in Table 3; 6 sheets of 150 mm  150 mm and 5 mm thick for each fiber cement composition were prepared; (x) from these sheets, three specimens were taken of 30 mm  100 mm  5 mm, one for flexural strength test at 28 days old in dry condition; one

for flexural strength test at 28 days old in saturated condition, and one for accelerated aging test (56 days in warm water at 60  3 °C after 7th days old in dry condition); (xi) cure in laboratory conditions at 21  2 °C and relative humidity of about 50% to prevent salt efflorescence at early ages. This condition is also described in ASTM historical standards (ASTM C 254 and ASTM C 255) to magnesium-oxide-based cements; (xii) lastly, preparation of the specimens for mechanical tests and microscopic analyses. 2.3. Testing procedure The flexural strength of the MOFC samples are determined with three-point bending test with a 100 mm span. Load-deflection curves were obtained by a servo-controlled testing machine Fig. 5. The toughnesses are obtained integrating the area below the load versus deflection curves, after the maximum load value, at the point corresponding to 95% of the peak load. Scanning electron microscopy (SEM) and X-ray diffraction were used to study the microstructure. Thus, fractured and polished surfaces were analyzed using secondary and back-scattered electron imaging and energy dispersive X-ray spectroscopy (EDX). The X-ray diffraction (DRX) used to analyze the mineralogical composition of matrices was carried out using a Universal X-ray diffractometer with Cu-K radiation source, operated at 30 kV, 20 mA, scanning rate of 3°/min and 2h range from 3° to 70°.

Table 4 Physical properties of the fiber cements. Fiber cement Void content (%) Water absorption (%) Bulk density (g/cm3)

R1

R2

S1

S2

S3

S4

28.0 16.9 1.66

29.6 18.5 1.61

29.7 18.3 1.63

27.5 16.5 1.67

22.2 12.4 1.79

22.2 12.6 1.76

Fig. 4. Production process simulating Hatschek industrial process.

Fig. 5. Flexural tenting equipment.

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3. Results and discussions 3.1. Physical properties of magnesium-oxide fiber cements Physical properties of fiber cements analyzed according to Brazilian Standard (NBR9778:2005) are shown in Table 4. Results indicate highest compactness to (S3) and (S4) composites. To unmodified fiber cements a lower density is observed. It indicates the effective role of RHS acting as filler in void contents due to its fine granulometry Fig. 3.

3.2. Effects of RHS on flexural properties

Fig. 6. Modulus of Rupture.

Fig. 6 presents the ultimate flexural strength of the MOFC’s, i.e. the modulus of rupture (MOR) calculated according ISO 8336:2009 at 95% confidence level. To flexural tests in dried condition, the highest modulus of rupture of the unmodified fiber cements was 6.38 MPa to (R2) composition. The highest salt concentration (154.6 g/L), i.e. the lowest

Fig. 7. Flexural testing of MOFCs in dried condition: (a) R1; (b) R2; (c) S1; (d) S2; (e) S3; (f) S4.

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Fig. 8. Flexural testing of MOFCs in saturated condition: (a) R1; (b) R2; (c) S1; (d) S2; (e) S3; (f) S4.

MgO/MgCl2 molar ratio furthers the 3-form and 5-form formation. It can be observed from the microscopic analyses. According to literature, the 5-form allows the increasing of mechanical properties [12,13]. In other studies, the employ of highest salt content also allowed to reach better mechanical properties to magnesium oxysulfate fiber cement [1,3]. The RHS addition increased the flexural strength to all compositions independent of MgO/MgCl2 molar ratio employed. This suggests the magnesium silicate hydrate (M-S-H) formation and also the filler effect of RHS as seen in Table 4. Although the M-S-H formation was not clearly observed in microscopic analysis, this phase can be obtained by the reaction between a magnesium source and a silica source in the presence of water [21]. Figs. 7–12 show the curves tension versus deflection to each test condition and the average curves obtained by the sum of tension values in each correspondent deflection divided by the number of samples. As seen in Fig. 7, the maximum MOR was

reached to the highest salt concentration and 5% RHS addition in dried condition. Probably, increasing RHS content up to 5% does not favor significantly the intensity of pozzolanic reaction. An excess of RHS could be seen in chemical mapping presented in Figs. 25 and 26. Figs. 8 and 9, show respectively, the curves of flexural tests in saturated condition and after warm water aging process. As observed in Fig. 8, it is clearly observed a better saturated behavior to all composites with RHS than unmodified magnesium-oxychloride fiber cements. Also, after warm water aging process, the temperature can be contributed to M-S-H formation and consequently to highest MOR to (S4) composition in which was employed lowest MgO/MgCl2 molar ratio and highest RHS content (10%) Fig. 9. In general analysis, it is evident that the lowest MgO/MgCl2 molar ratio associated with RHS addition results in the increase of flexural strength and MOFC behavior. To illustrate this,

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Fig. 9. Flexural testing of MOFCs after warm water aging process: (a) R1; (b) R2; (c) S1; (d) S2; (e) S3; (f) S4.

Figs. 10–12 presents a comparison of the results reached to (S3) and (S4) compared to reference compositions. Further investigations of these composites are shown in the microscopic analyses. The toughnesses values of MOFC, obtained at the point corresponding to a reduction in the load carrying capacity to 95% of the peak load, can be found in Table 5. The values corresponding to 95% confidence level calculated by average curves. The magnesium-oxide fiber cements that employed RHS have a tendency of major values to energy absorbed in both dried and saturated conditions. After aging process, these values are lower than unmodified MOFC. The possible M-S-H formation after warm water process it not discarded. The conditions for magnesium hydrated silicate formation had already been reported by literature [19–23]. In this way, the composites that employed RHS turned more brittle and harder after aging process, probably by the pozzolanic reaction as happens in Portland cement matrices [18].

3.3. Microstructure of MOC fiber cements 3.3.1. X-ray diffraction The MOC cement microstructure with and without RHS was observed by X-ray Difraction, especially (R1), (R2), (S3) and (S4) compositions. The diffractograms of the studied samples are presented in Fig. 13. It is possible to observe peaks correspondent to Mg(OH)2, Magnesium Chlorate Hydrate, 5-form phase and carbonates. In both samples the presence of carbonates can be clearly observed; besides carbonate additions on admixtures, it is also result of MgO carbonation due to the contact of the samples with the CO2 present in the air. As reported by literature, it is known that these materials undergo carbonation reactions with atmospheric carbon dioxide [28]. In this way, the carbonate phases formed on the surface can significantly influence the physical, chemical and mechanical characteristics of these materials [29].

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C.M. Gomes et al. / Construction and Building Materials 241 (2020) 118022 Table 5 Energy absorbed of the fiber cements. Fiber cement

Fig. 11. Best results of modified and unmodified magnesium-oxychloride fiber cements – Saturated condition.

S3

S4

64.3 47.0 83.2

92.9 55.9 99.6

108.7 79.4 79.8

88.4 69.0 87.6

Intensity (CPS)

Fig. 10. Best results of modified and unmodified magnesium-oxychloride fiber cements – Dried condition.

R2

Intensity (CPS)

Toughness (dried) [N.mm] Toughness (saturated) [N.mm] Toughness (aged) [N.mm]

R1

Fig. 13. Diffractograms of the studied samples: (a) R1 and R2; (b) S3 and S4.

Fig. 12. Best results of modified and unmodified magnesium-oxychloride fiber cements – Aged condition.

As shown in Fig. 14, the M-S-H formation could not be observed at 2h of 35 and 60 as showed in similar studies [21,20,23]. The M-S-H phases are poorly crystalline and they have low intensity and broad XRD signals [20]. Some studies demonstrated

that a ratio SiO2/MgO between 0.6 and 1.0 allows the formation of magnesium silicate hydrate phases [18,23], but it also depends on curing conditions and possible use of admixtures [21,23]. The RHS contents employed resulted in a higher MgO/SiO2 molar ratio. It is known that the formation and properties of M-S-H depend on several parameters such as the chemical composition and physical properties of the raw materials. Besides that, the initial Mg/Si ratio is an important conditional [21,22]. However, it is emphasized that the objective of this study is to modify the MOFC properties by RHS addition and not to produce a MgO-SiO2 binder. In this way, despite RHS contents to be significantly lower comparing to literature, they are sufficient to increase the mechanical properties of MOFC analyzed. Thus, the results indicate that is possible to adopt

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Fig. 14. Closed diffractograms of R2, S3 and S4.

the highest amount of silica, which probably will improve the behavior of fiber cement studied.

3.3.2. Scanning Electron Microscope (SEM) The analyses of fractured surfaces by secondary electrons (SE) detecting allowed to identify the principal morphology of magnesium phases formed. The MOC fiber cement microstructure with and without RHS is observed by SEM, especially for samples of compositions (R2) Fig. 15, (S3) Fig. 16 and (S4) Fig. 17. As shown

in Fig. 15, it is clear the presence of 5-form like a needles. These crystals can be observed acting on interfacial transition zone (ZTI) between PVA fiber and matrix, as shown in the analysis of (S3) composition Fig. 16. The strong adherence between the fibers employed and magnesium-oxide matrices can be observed in the images of (S3) Fig. 16 and (S4) Fig. 17 fiber cements. As reported in literature, the MOC cement shows good adherence resistance with different aggregates and fibers [1]. It explains the good flexural behavior of fiber cements analyzed in both dried and saturated conditions. After aging process, it is not observed a strong phase modifications – Fig. 18–20. The magnesium phases, specially the 5-form continued being observed as shown in Fig. 20. Also, the cellulose fibers were preserved and no alkaline attack is observed. It was attributed to lower pH of magnesium matrices comparing that traditional Portland cement composites [1,3,18]. In analysis by backscattered-electron (BSE) imaging – Figs. 21– 23, the carbonate filler shows up like light gray grains. Due to amount employed, the carbonates can be seen acting in all ZTI fiber/matrix. The effect of RHS like filler can be observed in Fig. 22 that shows a highest compactness. A percentage of no reactive silica is observed in the matrices (S3) and (S4). It is evidenced by the chemical mappings from Energy-dispersive X-ray spectroscopy (EDX) – Figs. 24–26 – where the silicon concentrations were coincident with some RHS crystal identified by BSE images. Comparing first image of Fig. 22 to silicon mapping in Fig. 25, the presence of RHS particles can be clearly observed. In this way, it is evident that the fine granulometry of RHS may have contributed to highest density of these composites and consequently better flexural results. Therefore, it is not dis-

Fig. 15. SEM images of fractured surfaces of (R2) fiber cement by secondary electrons (SE) detecting.

Fig. 16. SEM images of fractured surfaces of (S3) fiber cement by secondary electrons (SE) detecting.

C.M. Gomes et al. / Construction and Building Materials 241 (2020) 118022

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Fig. 17. SEM images of fractured surfaces of (S4) fiber cement by secondary electrons (SE) detecting.

Fig. 18. SEM images of fractured surfaces of (R2) fiber cement by secondary electrons (SE) detecting after aging process.

Fig. 19. SEM images of fractured surfaces of (S3) fiber cement by secondary electrons (SE) detecting after aging process.

carded the possibility of M-S-H formation [19–23] and the effective contribution of pozzolanic reaction. 4. Conclusions In this paper, the effects of RHS on magnesium-oxide fiber cements. The following conclusions are drawn: (i) RHS has an effective contribution to the flexural behavior of MOFC as a filler as well as a pozzolan. In this way, the addition of RHS allows a higher density and better mechanical proper-

ties. Also, lower water absorption and durability improvement can be reached. (ii) MOFC modified by RHS addition can be considered as alternative to development of sustainable building material. The possible employment of this technology can also contribute to reduce the levels of CO2 emissions related to production of Portland cement composites. (iii) RHS benefically influences on microstructural formation, mechanical properties and durability of magnesium oxychloride fiber cements.

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Fig. 20. SEM images of fractured surfaces of (S4) fiber cement by secondary electrons (SE) detecting after aging process.

Fig. 21. SEM of polished surfaces of (R2) fiber cement by Backscattered-electron (BSE) imaging.

Fig. 22. SEM of polished surfaces of (A3) fiber cement by Backscattered-electron (BSE) imaging.

Rice Husk Silica (RHS) from renewable sources can be a highlyimpactful sustainable alternative in civil engineering work, allowing the industry to produce environmentally-sound fiber cement mixtures. Thus, new studies can be encouraged, especially the possible use of other pozzolans and waste materials with and without carbonates aiming decrease the MgO content.

Writing - review editing. Anne Garry: Formal analysis, Investigation, Writing - original draft. Elaine Freitas: Data curation, Formal analysis, Investigation, Supervision, Writing - original draft, Writing review editing. Cinthya Bertoldo: Data curation, Formal analysis, Writing - original draft, Writing - review editing. Gustavo Siqueira: Formal analysis, Writing - original draft, Writing - review editing.

CRediT authorship contribution statement

Declaration of Competing Interest

Carlos Marmorato Gomes: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Supervision, Validation, Visualization, Writing - original draft,

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

C.M. Gomes et al. / Construction and Building Materials 241 (2020) 118022

Fig. 23. SEM of polished surfaces of (A4) fiber cement by Backscattered-electron (BSE) imaging.

Fig. 24. Chemical mappings from Energy-dispersive X-ray spectroscopy (R2).

Fig. 25. Chemical mappings from Energy-dispersive X-ray spectroscopy (S3).

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C.M. Gomes et al. / Construction and Building Materials 241 (2020) 118022

Fig. 26. Chemical mappings from Energy-dispersive X-ray spectroscopy (S4).

Acknowledgments The authors would like to express their gratitude to the IBAR Nordeste Ltda, the professor Jean-Francois Georgin from INSA Lyon of France by the Student Exchange provided and the National Council for Scientific and Technological Development (CNPq – process 308881/2017-6) for supporting this research.

References [1] C.E.M. Gomes, Alternative binder for fibercement building materials, in: Materials Processing and Manufacturing III, vol. 753 of Advanced Materials Research, Trans Tech Publications, 2013, pp. 616–622.https://doi.org/10.4028/ www.scientific.net/AMR.753-755.616. [2] X. Zhou, Z. Li, Light-weight wood-magnesium oxychloride cement composite building products made by extrusion, Constr. Build. Mater. 27 (1) (2012) 382– 389, https://doi.org/10.1016/j.conbuildmat.2011.07.033. [3] C.E.M. Gomes, G. Camarini, Magnesium Oxysulfate Fibercement, Key Eng. Mater. 600 (2014) 308–318, https://doi.org/10.4028/www.scientific.net/ KEM.600.308. [4] J. Beaudoin, V. Ramachandran, Strength development in magnesium oxysulfate cement, Cem. Concr. Res. 8 (1) (1978) 103–112, https://doi.org/10.1016/00088846(78)90063-7. [5] M. Herrera, A Comparison of Critical Properties of Magnesium Oxysulfate and Magnesium Oxychloride Cements as Used in Sprayed Fire Resistive Coatings, in: M. Lieff, F. Stumpf (Eds.), Fire Resistive Coatings: The Need for Standards, ASTM International, 1983, pp. 94–94–8.https://doi.org/10.1520/STP31895S. [6] K. Kahle, Mechanism of formation of magnesium sulphate cement, Silikattecnic 23 (5) (1972) 148–151. [7] C. Wu, H. Yu, H. Zhang, J. Dong, J. Wen, Y. Tan, Effects of phosphoric acid and phosphates on magnesium oxysulfate cement, Mater. Struct. 48 (4) (2015) 907–917, https://doi.org/10.1617/s11527-013-0202-6. [8] T. Demediuk, W. Cole, A study of mangesium oxysulphates, Aust. J. Chem. 10 (3) (1957) 287–294, https://doi.org/10.1071/CH9570287. [9] E. Newman, Preparation and heat of formation of a magnesium oxysulfate, J. Res. Natl. Bureau Stand. [10] C.M. Gomes, A.D. Oliveira, Chemical phases and microstructural analysis of pastes based on magnesia cement, Constr. Build. Mater. 188 (2018) 615–620, https://doi.org/10.1016/j.conbuildmat.2018.08.083. [11] J. Chan, Z. Li, Influence of fly ash on the properties of magnesium oxychloride cement, in: Measuring, Monitoring and Modeling Concrete Properties, Springer, 2006, pp. 347–352. [12] C. Chau, J. Chan, Z. Li, Influences of fly ash on magnesium oxychloride mortar, Cem. Concr. Compos. 31 (4) (2009) 250–254, https://doi.org/10.1016/j. cemconcomp.2009.02.011. [13] Y. Li, H. Yu, L. Zheng, J. Wen, C. Wu, Y. Tan, Compressive strength of fly ash magnesium oxychloride cement containing granite wastes, Constr. Build. Mater. 38 (2013) 1–7, https://doi.org/10.1016/j.conbuildmat.2012.06.016.

[14] C. Wu, H. Zhang, H. Yu, Preparation and properties of modified magnesium oxysulfate cement derived from waste sulfuric acid, Adv. Cem. Res. 28 (3) (2016) 178–188, https://doi.org/10.1680/jadcr.15.00011. [15] Z.-G. Li, S.-P. Chen, J.-Z. Li, J. Li, Y.-D. Sun, Influences of fly ash on the compressive strength and hydration products of magnesium oxysulfate cement, in: Future Generation Communication and Networking (FGCN), 2014 8th International Conference on, IEEE, 2014, pp. 139–141.https://doi. org/10.1109/FGCN.2014.41. [16] Z.-G. Li, Z.-S. Ji, L.-L. Jiang, S.-W. Yu, Effect of additives on the properties of magnesium oxysulfate cement, J. Intell. Fuzzy Syst. 33 (5) (2017) 3021–3025, https://doi.org/10.3233/JIFS-169353. [17] T. Zhang, E. Dieckmann, S. Song, J. Xie, C. Cheeseman, Properties of magnesium silicate hydrate (m-s-h) cement mortars containing chicken feather fibre, Constr. Build. Mater. 180 (2018) 692–697, https://doi.org/10.1016/ j.conbuildmat.2018.05.292. [18] G. Marmol, H. Savastano, Study of the degradation of non-conventional mgosio2 cement reinforced with lignocellulosic fibers, Cem. Concr. Res. 80 (2017) 258–267, https://doi.org/10.1016/j.cemconcomp.2017.03.015. [19] E. Bernardi, B. Lothenbach, C. Chlique, M. Wyrzykowski, A. Dauzeres, I. Pochard, C. Cau-Dit-Coumes, Characterization of magnesium silicate hydrate (m-s-h), Cem. Concr. Res. 116 (2019) 309–330, https://doi.org/10.1016/j. cemconres.2018.09.007. [20] C. Roosz, S. Grangeon, P. Blanc, V. Montouillout, B. Lothenbach, P. Henocq, E. Giffaut, P. Vieillard, S. Gaboreau, Crystal structure of magnesium silicate hydrates (m-s-h): The relation with 2:1 mg-si phyllosilicates, Cem. Concr. Res. 73 (2015) 228–237, https://doi.org/10.1016/j.cemconres.2015.03.014. [21] C. Sonat, C. Unluer, Development of magnesium-silicate-hydrate (m-s-h) cement with rice husk ash, J. Clean. Prod. 211 (2019) 787–803, https://doi.org/ 10.1016/j.jclepro.2018.11.246. [22] T. Zhang, Zhenlin Vandeperre, C. Cheeseman, Formation of magnesium silicate hydrate (m-s-h) cement pastes using sodium hexametaphosphate, Cem. Concr. Res. 65 (2014) 8–14, https://doi.org/10.1016/j.cemconres.2014.07.001. [23] T. Zhang, J. Zou, B. Wang, Z. Wu, C. Cheeseman, Characterization of magnesium silicate hydrate (msh) gel formed by reacting mgo and silica fume, Materials 909 (2018) 1–15, https://doi.org/10.3390/ma11060909. [24] W. Oosterkamp, Use of volatile solids from biomass for energy production, Bioenergy Res.: Adv. Appl. 1 (2014) 203–217, https://doi.org/10.1016/B978-0444-59561-4.00013-9. [25] R. Pode, Potential applications of rice husk ash waste from rice husk biomass power plant, Renew. Sustain. Energy Rev. 53 (2016) 1468–1485, https://doi. org/10.1016/j.rser.2015.09.051. [26] P. Metha, A unique suplementary cementing material. in: Advances in concrete technology, Proceedings: CANME (1992) 407–431. [27] P. Metha, N. Pitt, A new process of rice utilization, in: International conference on the utilization of rice by-products, Proceedings: IATA, 1977, pp. 45–58. [28] L. Black, C. Breen, J. Yarwood, K. Garbev, P. Stemmermann, B. Gasharova, Structural features of C-S-H(I) and its carbonation in air-a raman spectroscopic study. Part ii: Carbonated phases, J. Am. Ceram. Soc. 90 (2007) 908–917, https://doi.org/10.1111/j.1551-2916.2006.01429.x. [29] T. Runcˇevski, C. Wu, H. Yu, B. Yang, R.E. Dinnebier, Structural characterization of a new magnesium oxysulfate hydrate cement phase and its surface reactions with atmospheric carbon dioxide, J. Am. Ceram. Soc. 96 (11) (2013) 3609–3616, https://doi.org/10.1111/jace.12556.