Investigating the Pozzolanic Reaction of Post-Consumption Glass Powder
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Investigating the pozzolanic reaction of post-consumption glass powder and the role of portlandite in the formation of sodium-rich C-S-H Mehdi Mejdi, Wiliam Wilson, Mickael Saillio, Thierry Chaussadent, Loïc Divet, Arezki Tagnit-Hamou To cite this version: Mehdi Mejdi, Wiliam Wilson, Mickael Saillio, Thierry Chaussadent, Loïc Divet, et al.. Investi- gating the pozzolanic reaction of post-consumption glass powder and the role of portlandite in the formation of sodium-rich C-S-H. Cement and Concrete Research, Elsevier, 2019, 123, 8 p. 10.1016/j.cemconres.2019.105790. hal-02181573 HAL Id: hal-02181573 https://hal.archives-ouvertes.fr/hal-02181573 Submitted on 25 May 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. 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Version of Record: https://www.sciencedirect.com/science/article/pii/S0008884619302728 Manuscript_8cccda46c02afc8e437c2bf6dcd461cd 1 Investigating the pozzolanic reaction of post-consumption 2 glass powder and the role of portlandite in the formation 3 of sodium-rich C-S-H 4 Mehdi Mejdi a,b , William Wilson b, Mickael Saillio a, Thierry Chaussadent a, Loic Divet a, and 5 Arezki Tagnit-Hamou b 6 7 a Université de Paris-Est, MAST, CPDM, IFSTTAR F-77447 Marne-La-Vallée, France 8 b Département de Génie Civil, Université de Sherbrooke, Sherbrooke (Québec), J1K 2R1, Canada 9 10 Abstract 11 The use of glass powder (GP) as an alternative SCM offers a viable opportunity to partially substitute 12 OPC, and therefore provides economic and environmental benefits. Moreover, the predominant 13 siliceous amorphous phase provides the required component for its use as pozzolanic material. In this 14 work, the mechanism and the products of the finely ground GP reaction with lime are investigated. 15 The released silica, from glass dissolution, reacts with calcium hydroxide (CH) to form C-(N)-S-H 16 with different compositions depending on the system. In the studied CH-GP binder systems, the 17 fineness of GP ensures a higher surface for silica to react, leaving time for the pozzolanic reaction to 18 take place. However, the glass continues to react even after the consumption of CH, which may lead to 19 the apparition of alkali-silica gels around the particles in the long term. 20 Keywords 21 Soda-lime glass powder, pozzolanic reaction, alkali-silica reaction, C-(N)-S-H, lime-pozzolan binder 22 © 2019. This manuscript version is made available under the Elsevier user license https://www.elsevier.com/open-access/userlicense/1.0/ 23 1. Introduction 24 25 Socio-economic and environmental benefits could be drawn from the use of locally available 26 resources. For the case of concrete, various by-product supplementary cementitious materials (SCM) 27 have been studied to assess their potential use as reactive addition or cement replacement. Some of 28 them have led to improvements of some concrete properties and have been widely used for many years 29 such as silica fume, fly ash, and slag. Additional alternative materials are currently being studied for 30 similar applications, especially in regions where well known and standardised SCMs are not available. 31 Among them, post-consumption soda-lime glass, for which the predominant siliceous amorphous 32 phase, mainly composed of silica, makes this material very suitable for cement based materials as it 33 can react due to pozzolanic reaction. Yet, the presence of alkalis in soda-lime glass (typically 12-16 34 wt.% [1]) limits its use as pozzolanic material due to concerns about the possible formation of 35 expansive and deleterious alkali silica gels (N,K–(C)–S–H) formation [2]. 36 It is well documented that partial replacement of aggregates by waste glass can lead to expansion due 37 to the formation of alkali-silica reaction (ASR) gels while fine glass powder (GP) acts as pozzolanic 38 material [3,4]. Schwarz et al. [5] have demonstrated that for a substitution of 5 to 20% of cement and 39 diameters smaller than 100 μm, the glass powder has higher levels of pozzolanicity than fly ash. 40 Similarly, the results of [6–9] showed that for glass powder with a diameter of less than 75 μm the 41 pozzolanic reaction is largely privileged over ASR. Further studies [10–12] agreed that for GP below 42 #100 sieve (150 μm) and used at cement replacement levels below 30%, glass mortar bars expansion 43 satisfies the reference value (maximum value of 0.1% at 16 days) in accordance with ASTM C1567 44 [13]. Overall, several studies have associated ASR with coarse glass particles while finely ground 45 glass reduces this risk significantly and exhibits more pozzolanic activity [5,7,11,14]. In the case of 46 coarse glass cullet in cement pastes, the particles progressively dissolve and the released silica ions 47 react with calcium to form calcium silicate hydrates (C-(N,K)-S-H) with low Ca/Si ratios and 48 containing alkalis. However, the deficit of calcium near GP grains eventually induces the formation of 49 silica gel preferably than C-S-H [10]. Even though this behaviour could be expected to be the same for 50 different particle size, it is well recognised that fine glass powder does not undergo ASR and rather 51 improve the long-term mechanical and durability properties of concrete [10,14,15]. 52 Former studies have proposed different explanations of the relationship between the size of glass 53 particles and their behaviour in the cementitious matrix. While it is commonly accepted that the 54 pozzolanic reaction takes place faster than the ASR gel formation [5,10], Bazant et al. [16] have 55 shown, using a mathematical model, that below a given pessimum size (around 1-2 mm), the swelling 56 pressure generated by alkali-silica gel decreases with the size of reactive particles. Thus, based on this 57 assumption, fine glass powder will not lead to any expansion of concrete. On the other hand, Tang et 58 al. [17] have correlated the expansion with the CaO/(Na 2O+SiO 2) ratio of gels formed. When this ratio 59 is higher than 0.3, the gels have no significant effect on the expansion. In the case of small hydrating 60 glass particles, the products have a locally lower alkali to calcium ratio as reported by Shi [18]. 61 Another explanation proposed by Maraghechi et al. [19] suggests that the internal residual cracks in 62 the glass grains are responsible for the development of ASR reaction in the glass while the thin micro- 63 cracks of small particles are innocuous. 64 Even though the pozzolanic reactivity of GP is recognized, its mechanisms of reaction are still unclear. 65 This might be due to the fact that SCMs and cement hydration reactions occur at the same time but at 66 different rates, which is a complication for the fine distinction between the hydration products of each 67 compound [20][21]. Therefore, the present work focuses on the pozzolanic reaction of fine particles of 68 soda-lime glass with calcium hydroxide (Ca(OH) 2, abbr. CH) in order to provide a better 69 understanding of the mechanism of GP hydration. It should be emphasized, as detailed in this study, 70 that lime-pozzolan reaction conditions are different from those encountered in cementitious pore 71 solutions. As such, additional research is needed to investigate the behaviour of glass powder in 72 hydrated blended cements. 73 74 2. Materials and methods 75 76 2.1 Materials 77 The conducted investigation focuses mainly on the reaction of post-consumption soda-lime glass 78 powder (GP) and portlandite (CH, chemical grade with 95% purity). The physico-chemical properties 79 of the materials used in this study are reported in Table 1,2 . The oxide and mineral compositions (wt. 80 %) were obtained by X-ray fluorescence (XRF) and X-ray diffraction (XRD), respectively. The 81 physical properties were measured by laser granulometry, pycnometry, Blaine and N 2 adsorption tests. 82 83 2.2 Sample preparation 84 Three sets of pastes were prepared with a propeller mixer (2min, 2000rpm) in a glove box under 85 nitrogen atmosphere in order to limit the carbonation of the portlandite. The GP/CH weight ratios were 86 set to 1/1, 3/1 and 1/3, while the water (distilled) to binder (GP+CH) ratio was fixed to w/b=0.75 87 (Table 3 ). The pastes were cast in plastic containers, sealed and stored in a desiccator with soda-lime 88 to avoid CO 2 contamination before testing at the ages of 7, 14, 28, 56, and 91 days of hydration. At 89 each age of testing, the pastes were manually coarsely ground (d 50 of ~600 µm) and placed 90 immediately in isopropanol for 15 min to stop the hydration. The isopropanol was removed first using 91 a Buchner funnel, then by solvent exchange with diethyl ether, which can be easily removed by a short 92 vacuum drying process without affecting the hydrate assemblage [22]. Finally, the powders were 93 manually ground to reach d 50 ≈40 µm. The resulting powders were tested at each age using 94 thermogravimetric analysis (TGA) and XRD. 95 96 2.3 Thermogravimetric analyses (TGA) 97 The apparatus used for the TGA investigations was a TA instrument SDT Q600.