replaced by high volume of an organic-contaminated waste
glass fraction
Citation for published version (APA):
Liu, G., Florea, M. V. A., & Brouwers, H. J. H. (2017). The hydration and micro-structure characteristics of cement replaced by high volume of an organic-contaminated waste glass fraction. In The 9th International Symposium on Cement and Concrete (ISCC 2017), 31 October - 3 November 2017, Wuhan, China (pp. 1-6)
Document status and date: Published: 01/01/2017
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The Hydration and Microstructure Characteristics of Cement Replaced by High Volume of
an Organic-Contaminated Waste Glass Fraction
G. Liu1, M. V. A Florea, H. J. H Brouwers
Department of the Built Environment, Eindhoven University of Technology, P. O. Box 513, 5600MB, Eindhoven, the Netherlands. Email: g.liu@tue.nl
Abstract: The study proposes to provide data for the application of high volumes of waste glass fractions as partial replacement for
cement in building materials. Using contaminated waste glass helps to reduce the pressure on landfill and environmental pollution. Most of existing research focused on a cement replacement ratio below 30%, which still has potential to be improved. The organic contamination could cause different influences on hydration and fresh workability. The hydration characteristics of pastes mixing cement with different contents of waste glass fractions were investigated by calorimetry. The products of hydration were observed by XRD and FTIR. The microstructure properties of different waste glass content samples were identified by SEM. The influences of organics and the glass fraction on porosity and pore size distribution were investigated.
Keywords: waste glass, contamination, hydration, microstructure, cement
1 Introduction
The amount of waste glass has gradually increased in recent years because of the increasing demand for glass products. Every year, large amounts of waste glass are dumped into landfill sites. Glass is not biodegradable, which causes serious problems for environmental protection. In recent years, the recycling ratio of waste glass increased in many countries due to the concern towards natural resources protection. Parts of waste glass will be collected from urban wastes and produce containers like bottles and jars. However, some recycled glass fractions are not able to be used in the manufacturing of new glass bottles and jars or to make fiberglass. This may be because there is too much contamination or the recycled glass pieces are too small to meet manufacturing specifications. This recovered glass is then used for non-container glass products. One efficient application for these glasses is to use as building materials, because glass has the ability to be a pozzolanic or cementitious material.
There were many studies on using waste glass powder as partially replaced cement as cementitious materials. Finely ground glass powders exhibited very high pozzolanic activity. The finer the glass powder is, the higher its pozzolanic reactivity is. A mortar sample containing 25% soda lime glass powder and 75% cement as binder was found to gain about 60 MPa in compressive strength test after 90 days, which was almost equal to the 100% cement[1][2]. The durability (absorption, resistance to CL and freeze-thaw cycles) of mortars also got enhanced with glass powder addition [3]. The waste glass in this study was filter glass which is used to dry the glass and filtered out in the furnace during the glass products manufacture. This kind of glass contains considerable organic matter such as the fiber and sugar from labels and glue. There has been many investigations in the influences of fiber and sugar on the cement application. For instance, wood fiber and recycled wastepaper fiber could be used to improve the performance of cement composites [4], because the incorporation of fiber provides cement composites the lower thermal conductivity and good flexibility which increase the resistance for fire and freeze-thaw condition [5][6]. But as an organic addition, fiber acts as a role of inhibitor which has negative effect on the cement hydration because of the sugar, starches and tannins[7]. Sugar is the main reason for inhibition of cement hydration in fiber-cement composites [8]. Sugar could absorb on the surface of cement particle and hydration products, which inhibits the hydration process and hydration products growth[9][10]. The zeta potential of hydrating cement particle is positive and changed to negative after incorporation of sugar, which could explain absorption of sugar on cement particle surface [11].
There are also many studies on the application of heavy metal contaminated waste glass, such as glass from cathode ray tubes (CRT). Cement could use to immobilize the heavy metal in CRT glass[12][13][14]. However, the waste glass fractions contaminated by organics (sugar, fiber) did not have enough focus. This kind of waste glass is usually very fine and mixed with organic matter, which makes it difficult to clean and difficult to recycle for producing new glass containers. The organic contamination will influence the use of the waste glass fractions in concrete. The present study aims to study the influence of organic contaminated waste glass powder on cement hydration process, hydration
2 Material and method
2.1 Cement and waste glass
The cement in this study was CEM І 42.5N which were supplied by ENCI, Netherlands. The waste glass powder in this study was provided by a recycling plant. The glass powder is used to dry the glass and filtered out in the furnace. This type of glass usually contains cellulose fibers from labels. The particle size distribution is showed in Fig.1. The sugar and ion content of waste glass powder are showed in Table 1.
2.2 Method
The calorimetry test was performed using an isothermal calorimeter (TAM Air, Thermometric). Cement was replaced by contaminated waste glass powder with 0% (C0), 30% (C3), 50% (C5) and 70% (C7) by mass and replaced by washed waste glass powder with 0% (C0), 30% (CW3), 50% (CW5) AND 70% (CW7) by mass. Solid raw materials were mixed in advance and then mixed with distilled water, then the mixed paste was injected into the ampoule and sealed by a lid, and loaded into the calorimeter. All measurements were conducted for 160 h under a constant temperature of 20 °C.
The X-ray diffraction test was conducted to study the hydration products of samples which were cured in ambient temperature for 28d. The samples were immersed in acetone to stop the hydration reaction, then dried and milled into powder for the test. Samples contained 0%, 30%, 50% and 70% waste glass powder and washed waste glass powder were tested.
The micro structure characters of raw material and samples were observed by Scanning electron Microscope which equipped EDX detector. The EDX analyses were conducted at 10kV accelerating voltage. The SEM image of waste glass powder and cement are showed in Fig.2. Samples contained 0%, 50% and 70% waste glass powder were tested.
Fig.1 Particle size distribution of material Table 1 Sugar and ion content of waste glass powder
Sugar ug/g Ion mg/g
arabinose 12 Na+ 1.549
galactose 67.8 K+ 0.084
glucose 91.8 Ca2+ 0.109
xylose 14.8 Mg2+ 0.011
mannose 67.7 NH4+ 0.048
galacturonic acid 31.3 Chloride 0.540
glucuronic acid 37 Phosphate 0.107
Sulphate 0.235 0 10 20 30 40 50 60 70 80 90 100 0.1 1 10 100 Cu m u lativ e fin er/% Particle size / um Waste glass powder Washed glass powder
(a) (b)
Fig. 2 SEM picture of waste glass particle (a) and cement particle (b)
3 Results and discussion
3.1 Calorimetric study
The isothermal calorimetry results of cement replaced by 0% (C0), 30% (C3), 50% (C5) and 70% (C7) of waste glass powder are shown in Fig.3. It is apparent that C0, C3 and C5 have the general shape of heat flow curve which contains five stages including of initial reaction stage, induction stage, acceleration stage, reduction stage and long term reaction stage [15]. For samples incorporating waste glass powder, the duration of induction stage increased with the waste glass powder content, which indicates that the incorporation of waste glass powder in samples retards hydration
[10]. Especially for C7, the heat flow curve shows no change, which means no new phase was produced during the first
160 hours. The effects of retardation became more significant with the increase of waste glass powder content. The influences of waste glass powder not only appear on the time of heat flow peak’s appearance, but also on the height of the peak. The C0 shows the highest peak comparing with other samples incorporating waste glass powder. With the increasing of waste glass powder in the paste, less Ca2+ was dissolved in pore solution because of the low reactivity of glass particle comparing with cement particle. Less hydration products were produced during hydration process, which lower the peak of heat flow and reduces the accumulative heat as shown in Fig.3 (b). When comparing samples incorporating waste glass powder with samples contained washed waste glass powder, the accumulative heats are similar between the samples containing same amount waste glass powder and washed glass powder. The sugars in waste glass powder are responsible for the delay of the heat flow peak during the hydration. As an inhibitor of cement hydration, sugar absorbed on the surface of cement particles and surface of hydration products, which makes the growth of CH and C-S-H slower and inhibits the hydration of cement particles [16][17]. This influence became more significant when the content of waste glass powder increased, which indicates that more organic matter in the sample. The influence of sugar could be eliminated after washing as showed in Fig.4. The samples containing different content of washed waste glass powder show the peaks of heat flow almost at the same time. No obvious retardation is observed in the results of calorimetry even for CW7. From the calorimetric analysis, the influence of organic contaminated waste glass on cement hydration might be seen as two parts, glass powder incorporation reduced the heat release and sugar contamination inhibited the hydration phase production.
0.0E+00 5.0E-04 1.0E-03 1.5E-03 2.0E-03 0 50 100 150 He at flo w /(w /g ) Time/h C0 C3 0 50 100 150 200 250 300 0 50 100 150 A cc u m u lativ e h ea t/ (J/g ) Time/h C0 C3
(a) (b)
Fig. 4 Calorimetry results of cement replaced by different amount of washed waste glass powder 3.2 X-ray diffraction study
The XRD results of samples containing waste glass powder are shown in Fig. 5 (a). After curing in ambient temperature for 28 days, calcium hydroxide, ettringite, calcite, quartz and calcium silicate were found in all samples. However, with the increase of waste glass powder content, some phases are changed as shown in Fig. 5. XRD results of C0 showspeaks of calcium hydroxide and unhydrated C2S and C3S. Comparing with C7, it is noticeable that C7 shows
no significant peak of C2S and C3S. More alkali and silica released by waste glass powder during the hydration process
improved the form of C-S-H and CH, which accelerated the consumption of cement[18]. Similar results are showed in the samples with washed waste glass powder (Fig. 5 b). Another difference is that the samples containing high amount of waste glass powder begin to show the peak of hydrocalumite (3CaO · Al2O3 · CaCl2 ·10H2O). Hydrocalumite is
double layered hydroxide[19] and is the major and stable hydration products of cement subject to Cl- attack[20]. The chloride content in the waste glass powder is showed in the Table 1 is 0.54 mg/g. The higher waste powder content in the paste contributes more chloride in pore solution in the sample, which could explain that C7 has a more significant hydrocalumite peak comparing with the other samples.
10 20 30 40 50 60 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2 C0 C3 C5 C7 CH CH CH CH CH CH C C C CH CH Q Q H E E E CS CS E C CH CH CH CH H Q CS 10 20 30 40 50 60 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Q Q CS CS CS H C C C C CH CH CH CH CH CH CH CH CH CH CH CH CH E E E E E 2 C0 CW3 CW5 CW7 Q
Fig. 5 XRD of samples cured in ambient temperature for 28d (a) paste incorporated waste glass powder (b) paste incorporated washed waste glass powder (E-ettringite. H-hydrocalumite, CH-calcium hydroxide, C-calcite, CS-C2S and C3S, Q-quartz) 3.3 Scanning electric microscopy and energy dispersive X-ray study
The Scanning electric microscopy and Energy dispersive X-ray were used to study the microstructure and chemical composition of hydration products in samples with different amount of waste glass powder (C0, C5 and C7). Fig. 6 shows the SEM of the sample C0 with no waste glass powder incorporation. The dense hydration products are fully filled between the unhydrated cement particles. The location 1 is on the unhydrated cement particle after 28 days ambient curing related to C2S. As shown in the SEM image, the cement particle is tightly connected with the hydration
products. The location 2 is the hydration product of cement. The EDX result (Fig. 6 (c)) shows that the hydration product between cement particles is consisted of large amounts of Si and Ca with the Ca/Si ratio about 1.67. It is notable that Fig. 7 (a) shows that C5 had porosity products around the waste glass particle. There is a significant space around the waste glass particle, which may indicate that the connection between hydration products and glass particles is weak or no reaction happened on the surface of glass powder. Fig. 7 (c) shows the elements in hydration products near the waste glass powder. High content of Si and Ca are found in this point, which is similar as C0. Besides that, higher amounts of Na are shown. And the Ca/Si ratio decreased to 1.39. Fig. 8 shows the microstructure and EDX details of C7, the weak connection between hydration products and glass powder like in C5, which related to the lower surface area and reactivity of glass powder comparing with the cement particle. The EDX result of hydration products of point 1 which is located on the waste glass powder surface indicates that more Na appears in hydration product. At
the same time, Ca/Si keeps decreasing to 0.94 when comparing with C0 and C5. The waste glass powder contains lower amounts of Ca and higher amounts of Na and Si than cement, the increase of waste glass powder content in the samples contributes less Ca2+ but more Na+ and SiO4
in the pore solution. As a consequence, hydration products showed low Ca/Si ratio with the increasing content of glass powder in the samples.
(a) (b) (c)
Fig. 6 SEM image of C0 (a), EDX of point 1-unhydrated cement particle (b), EDX of point 2-hydration products (c)
(a) (b) (c)
Fig. 7 SEM image of C5 (a), EDX of point 1-glass fraction in C5 (b), EDX of point 2-hydration products (c)
(a) (b) (c)
Fig. 8 SEM image of C7 (a), EDX of point 1-hydration products (b), EDX of point 2-hydration products (c)
4 Conclusion
observed.
3) The incorporation of waste glass powder improved the production of hydrocalumite which is related to the alkali and Cl- released by waste glass powder in the samples. The addition of waste glass powder improved the hydration of cement particle.
4) The XRD and EDX results indicates that, with the increase of the waste glass content, sample showed higher porosity than C0. The Ca/Si ratio of hydration products decreased with the increase of the waste glass powder amount in the samples.
Acknowledgement
This research was carried out under the funding of China Scholarship Council and Eindhoven University of Technology. Furthermore, the authors wish to express their gratitude to the following sponsors of the Building Materials research group at TU Eindhoven: Rijkswaterstaat Grote Projecten en Onderhoud; Graniet-Import Benelux; Kijlstra Betonmortel; Struyk Verwo; Attero; Enci; Rijkswaterstaat Zee en Delta-District Noord; Van Gansewinkel Minerals; BTE; V.d. Bosch Beton; Selor; GMB; Icopal; BN International; Eltomation, Knuaf Gips; Hess AAC Systems; Kronos; Joma; CRH Europe Sustainable Concrete Centre; Cement & Beton Centrum; Heros; Inashco; Keim; Sirius International; Boskalis; NNERGY; Millvision; Sappi and Studio Roex (in chronological order of joining).
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