PRODUCTION
POLYMERIC MATERIALS AND
COMPOSITES
Development of textile reinforcements with
improved adhesion and thermal stability for
green cement
Angelika Bachinger, Peter Hellström, Anaïs Domergue,
Laurie Gaüzere, Derk de Muinck
RISE report 2021:02
Deliverable 2.3 of the project ’Green cement based on blast furnace slag’ funded by Vinnova under their programme ‘Innovationer för ett hållbart samhälle’
Development of textile reinforcements with
improved adhesion and thermal stability for
green cement
Angelika Bachinger, Peter Hellström, Anaïs Domergue,
Laurie Gaüzere, Derk de Muinck
Abstract
The present report addresses the Deliverable 2.3 of the project ‘Green cement based on blast-furnace slag’. Deliverable 2.3 aims at the development of new textile reinforcements with improved adhesion and thermal stability for green cements. Two different approaches for impregnation of textile reinforcements with materials that exhibit good adhesion to cementitious matrices as well as good thermal stability were studied: (i) impregnation with cementitious materials, (ii) impregnation with molecular precursors. Moreover, a nano-CSH impregnation system developed at Chalmers was characterized and compared to the systems developed at RISE.
Key words: Cement reinforcements, slag-based cement, thermal stability, adhesion, interfacial shear strength
RISE Research Institutes of Sweden AB RISE Report 2021:02
ISBN:978-91-89167-84-1 Mölndal 2021
Content
Abstract ... 1
Content ... 2
Preface ... 3
1 Introduction... 4
2 Materials and Methods ... 4
2.1 Materials ... 4
2.2 Methods ...5
2.2.1 Preparation of impregnation slurries ...5
2.2.2 Impregnation process ...5
2.2.3 Sample preparation for pull-out testing ... 6
2.2.4 Pull-out testing ... 7
2.2.5 Perimeter characterization ... 7
2.2.6 Calculation of the interfacial shear strength (IFSS) ... 8
3 Results and Discussion ... 8
3.1 Perimeter variations ... 8
3.2 Interfacial shear strength (IFSS) ... 9
3.2.1 Influence of perimeter variations on the calculated IFSS ... 9
3.2.2 Variation of IFSS between samples ... 9
3.2.3 Comparison of potential IFSS ... 10
3.2.4 Evaluation of stress-strain curves for each approach ... 11
3.3 Thermal properties ... 14
Preface
The present work was performed at RISE department of polymeric materials and composites, within the project ‘Green cement based on blast-furnace slag’ funded by Vinnova under their program ‘Innovationer för ett hållbart samhälle’ (Diarienummer 2016-03367).
The present report contains descriptions of earlier experiments that have been re-evaluated with new characterization methods along with new unreported experiments. The experiments have partly been reported elsewhere in more detail:
- SICOMP report TR17-001: Novel concrete reinforcements based on carbon fibres (by Anaïs Domergue), 2017.
- Internship report: Development of novel concrete reinforced with carbon fibres (by Laurie Gaüziere), 2018.
- Master thesis Derk de Muinck: Development of reinforcement structures for alkali-activated cements, 2019.
1
Introduction
Textile reinforced concrete (TRC) has been studied extensively in recent years and has been shown to be highly interesting in the development of, for instance, lightweight building applications since cost and resources can be significantly reduced. Thinner structures are possible due to improved mechanical properties and corrosion resistance of textile reinforcements allowing the reinforced structure to be exposed to the environment (as compared to steel reinforcements, which need to be protected by a thick layer of concrete). However, commercial textile reinforcements are impregnated with epoxy resin or other polymers, which leads to two main problems: (i) the adhesion of the hydrophobic polymer to the hydrophilic cement is poor, leading to poor load transfer and thus limited tensile strength. (ii) the thermal stability of the polymer impregnation is limited. Upon exposure of the structure to high temperatures or fire, softening and decomposition of the polymeric impregnation will lead to a collapse of the structure.
The present report presents investigations regarding impregnation of textile reinforcements with inorganic components with the aim of improving the adhesion to cementitious matrices as well as the thermal stability of the reinforcement.
2
Materials and Methods
2.1
Materials
For preparation of the green cement, the following materials were used: The slag was supplied by Merox with a composition as presented in Table 1. COMBIMIX cement, gypsum and sand (fine) were standard grades purchased in a local hardware store. NaOH pellets (EMPLURA®, pure), colloidal silica (LUDOX® TM-50 colloidal silica, 50 wt.% suspension in H2O), hydrochloric acid (37%, EMSURE®, reagent grade) and
kaolin (18616, particle size <2µm), Tetraethyl orthosilicate (TEOS), Glycidyloxypropyl (trimethoxysilane) (GLYMO), Vinyltrimethoxysilane (VTMOS),
Propyltrimethoxysilane (PTMOS) and 3-(Trimethoxysilyl)propyl methacrylate (MEMO) were purchased from SigmaAldrich. Unsized carbon fiber tows (IMS65-24K) were kindly supplied by Tenax®.
2.2
Methods
2.2.1
Preparation of impregnation slurries
• Geopolymer:
Kaolin was calcined for 3 hours at 800°C to obtain metakaolin. A waterglass solution was prepared by slow addition of NaOH into a silica solution in water to achieve a SiO2/Na2O molar ratio of 1 and a silica concentration of 3.3 mol/L (13.65
wt%). To this solution metakaolin was added to achieve a final SiO2/Na2O molar
ratio of 1.4. Other recipes were studied in SICOMP report TR17-001. All geopolymer-impregnated samples discussed in the present report were cured at room temperature for 72 h, followed by curing at 80°C for 4 h.
• Molecular precursors:
For TEOS-solutions, TEOS, Ethanol and deionized water were mixed in a ratio of 1/4/4. The pH was then adjusted to 1 by addition of HCl. The GLYMO slurries consisted of 5.5 ml TEOS, 1.84 ml GLYMO, 3.3 ml 0.05 M HNO3, and 0.05 ml H2O.
The VTMOS coatings consisted of 2.24 ml TEOS, 3.92 ml 0.05 M HNO3, 3.04
VTMOS and 0.84 ml MEMO. To some VTMOS coatings one ml of PTMOS were added (these experiments are called ‘PTMOS’). The impregnated bundles were cured at 70°C for 24 h. For further details, see Derk de Muinck’s master thesis.
2.2.2
Impregnation process
• Bundle impregnation
Bundle impregnation was performed in a set-up developed at RISE during the project (see SICOMP-report TR17-001 for a detailed description). The set-up allows continuous impregnation of carbon fibre bundles with viscous slurries, due to a fibre spreading unit and a 3-roller arrangement that ensure good impregnation throughout the bundle (Figure 1).
• Impregnation of weaves
Carbon fibre weaves with a water-soluble sizing obtained from Chalmers within the project were impregnated with geopolymer slurry according to the geopolymer recipe above. Bundles for impregnation were extracted from the weave prior to impregnation (geopolymer 1-3) or after impregnation and curing (geopolymer 4-6).
2.2.3
Sample preparation for pull-out testing
Samples for pull-out testing were prepared in coffee-mugs made from paper, where the impregnated bundles were kept in place (straight and ~0.5 cm above the bottom) by a plastic coffee mug lock until the cement was cured.
The different studied samples are summarized in Table 2.
Green cement mixture (38.5 g slag + 9.6 g cement + 1.9 g gypsum), sand (50 g) and waterglass (5.7 g SiO2 sol + 3.2 g NaOH + 23.6 g H2O) were mixed and then added to the coffee mugs before closing the mugs again and thus embedding the reinforcements. The samples were then stored in closed boxes. The paper mugs were placed on a wet cloth, in order to keep them moist and additional water containers were placed inside the boxes in order to ensure a high moisture environment to avoid cracking during curing (see Figure 1).
Figure 2: Samples prepared in paper-based coffee-mugs and stored in closed containers at high humidity.
After 24h, water was added to the cloth for increased moisture content. After 7 days, the wet cloth was taken away and the samples were freed from the coffee mugs. The samples were continuously stored in a box with water containers. After additional 2
days, the samples were taken out and stored at environmental conditions until pull-out testing after 1 week.
Table 2: Samples and their composition and preparation method.
Type Impregnation recipe Impregnation method Samples
Geopolymer
SiO2 / Na2O = 1.4 Bundle impregnation Geopolymer 1-2
SiO2 / Na2O = 1.4 Weave – bundle extracted before impregnation
Geopolymer w1-3 SiO2 / Na2O = 1.4 Weave – bundle extracted
after impregnation and curing
Geopolymer w4-6
Molecular precursors
TEOS / EtOH / H2O = 1/8/4 Bundle impregnation TEOS
TEOS / GLYMO / HNO3 = 1/3/1.8 Bundle impregnation GLYMO TEOS / VTMOS / MEMO / HNO3 =
2.7/3.6/1/4.7
Bundle impregnation VTMOS
TEOS / VTMOS / MEMO / PTMOS / HNO3 = 2.7/3.6/1/1.2/4.7
Bundle impregnation PTMOS
Nano-CSH Chalmers recipe Weave – bundle extracted
after impregnation and curing
nCSH 1-3
2.2.4
Pull-out testing
The pull-out strength of the fibre bundles was tested using an AG-XK plus Shimadzu with a 50 kN grip at a speed of 1 mm/min. The set up used to place the samples in the machine is shown in Figure 2. A rubber material was placed between the grips and the cement to prevent contact stress. To reduce slippage, the fibre bundles were held between two tabs with P800 sandpaper glued to them when placed into the grip.
Figure 3: Set-up for pull-out testing and sample
2.2.5
Perimeter characterization
The perimeter of the bundles was initially characterized by microscopy, using the following procedure: The impregnated fibre bundles were cut and cast into a mix a Epofix Resin and EpoFix Hardener. The resin was mixed by hand for 1 minute, the bundles were then placed vertically in the mixture and each mixture was placed in
Thereafter each epoxy puck was grinded down using a Struers Tegramin-30. The grinding papers were used in decreasing grain size P500, P1200, P2000, and P4000. Finally the samples were polished in the same machine using a MD Dur polishing paper with a Diapro Dac 3 suspension. The samples were then examined in a Olympus BH2-UMA Universal Vertical Ilumminator Microscope. The perimeter was measured from the microscopy images at a magnification of 5 times.
Due to the limited potential of this method to detect variations in perimeter, 3D scanning was used to evaluate the perimeter at different locations of the sample.
2.2.6
Calculation of the interfacial shear strength (IFSS)
The interfacial shear strength was calculated from the pull-out force (F) measured during pull-out testing above, the perimeter of the bundles (P) and the embedded length (L) according to the following equation:
Equation 1
The shear strength is presented in force-displacement graphs and the maximum shear strength for each sample was identified along with the pull-out behaviour.
3
Results and Discussion
3.1
Perimeter variations
By 3D scanning, the perimeter of 3 different bundles was measured for each of the experiments. At each bundle, the perimeter was measured at 9 different locations. The perimeter variations from 3D scanning are presented in Figure 4.
Figure 4: Perimeter variations measured by 3D-scanning.
0 1 2 3 4 5 6 7 8 9 10 VTMOS TEOS GLYMO PTMOS Geopolymer - bundle Geopolymer - weave1 Geopolymer - weave2 nCSH1 Perimeter, mm
Perimeter of impregnated bundles and their variation measured by
3D scanning
It is concluded from 3D scanning results that the perimeter varies significantly along the bundles. This variation and its influence on the IFSS (according to Equ.1) needs to be taken into account when drawing conclusions on the most promising impregnation systems.
3.2
Interfacial shear strength (IFSS)
3.2.1
Influence of perimeter variations on the calculated IFSS
The interfacial shear strength (IFSS) was calculated according to Equation 1 from the maximum force recorded during pull-out testing. Figure 5 presents a comparison of the calculated IFSS depending on the perimeter variation (shown in Figure 4) for the different impregnation approaches. It needs to be mentioned, that Figure 5 shows the variation of the IFSS only for one sample per approach (the best performing sample), in order to visualize the influence of the perimeter variation on the IFSS (rather than the variation of the pull-out force between different samples).
Figure 5: Maximum IFSS for the different approaches and variations depending on perimeter variations.
It is seen from Figure 5 that the IFSS of most approaches exhibits significant variations due to variations in the perimeter along the bundles. However, it remains possible to draw conclusions regarding the systems with the highest potential adhesion.
3.2.2
Variation of IFSS between samples
Three samples were prepared for each approach (except for geopolymer bundle impregnation, where only 2 samples were available). The maximum pull-out force as well as the lowest detected perimeter from 3D scanning were used to calculate the maximum potential IFSS that could be detected for each sample. Figure 6 presents the resulting IFSS for each approach and the variations between individual samples.
0 1 2 3 4 5 6 7
nCSH - weave Geopolymer - weave Geopolymer - bundle Molecular precursor - TEOS Molecular precursor - VTMOS Commercial BF - plasma Commercial CF - plasma
Interfacial Shear Strength, N/mm2
Figure 6: Variations between samples: IFSS calculated from the maximum detected pull-out force and the minimum detected perimeter.
It is seen from Figure 6 that the reproducibility of the results is rather low – large variations are detected between different samples of the same approach. It is therefore obvious, that optimization of the impregnation processes is required in order to ensure reliable performance of the impregnated reinforcements. It needs to be mentioned, however, that even the commercial reinforcements (untreated as well as treated) show large variations regarding their adhesion, as reported in RISE report 2021:01 (ISBN: 978-91-89167-83-4).
One approach that seems the be superior regarding reproducibility is the impregnation of bundles with geopolymer. This approach has been studied in detail and optimized as reported in SICOMP report TR17-001. Despite the large variation detected between individual samples, the impregnation with nano-CSH seems to provide the best adhesion to green cement of all studied systems. This impregnation system and method are described in detail in a report by Chalmers.
3.2.3
Comparison of potential IFSS
For a more detailed evaluation of the pull-out behaviour of the different experiments and samples, the stress-displacement graphs are presented below. The diagrams presented in Figure 7 show the best performing samples in order to provide an impression of the potential of each treatment method if optimized. The reliability of the different approaches has been discussed in section 3.2.2 and is therefore not considered here.
0 1 2 3 4 5 6 7
nCSH - weave Geopolymer - weave Geopolymer - bundle Molecular precursor - TEOS Molecular precursor - VTMOS Commercial BF - plasma Commercial CF - plasma
Interfacial Shear Strength, N/mm2
Variation of IFSS between samples
Figure 7: Stress-displacement diagrams for the best sample of each approach.
It is seen from Figure 7 that the best performing nano-CSH impregnation not only exhibits a high adhesion, but also enables the material to take loads after an initial debonding. This results in a toughening effect, allowing for large deformations before catastrophic failure.
The geopolymer samples exhibit a reliable moderate performance, which is still
significantly higher than the achievable adhesion for commercial reinforcements, even with plasma treatment. This approach may therefore be considered as a more cost-efficient and reliable solution compared to the nano-CSH impregnation. Moreover, geopolymer impregnation leads to stiff bundles with good handleability, compared to the n-CSH impregnation, where powder-like particles are deposited on a bundle which is difficult to handle.
Another interesting approach is the impregnation with organic precursors based on VTMOS. Even if the maximum pull-out force is significantly lower compared to nCSH or geopolymer impregnation, this system takes high loads even at extremely large deformations. In fact, this is the best performing system at deformations above 7 mm.
3.2.4
Evaluation of stress-strain curves for each approach
• Geopolymer bundle impregnation
Figure 8 presents the stress-displacement curves for the two studied samples for geopolymer bundle impregnation.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 8 9 10 Sh ear St re ss , N /m m 2 Displacement, mm
Comparison all studied systems - best of each
nCSH - weave impregnation Geopolymer - weave impregnation Geopolymer - bundle impregnation Molecular precursor - TEOS Molecular percursor - VTMOS Commercial BF - plasma Commercial CF - plasma
Figure 8: Stress-displacement curves for geopolymer bundle impregnation.
The geopolymer samples prepared by bundle impregnation are rather consistent in their pull-out behaviour: The samples exhibit a first debonding at rather low displacement but continue to take more load after this incident up to rather large displacement. Such behaviour is desired as the material does not fail catastrophically without warning.
• Geopolymer weave impregnation
Figure 9 presents the force-displacement curves for three different samples prepared by impregnation of weaves with geopolymer, where geopolymer w1-3 were impregnated by extracting a bundle prior to impregnation and geopolymer w4-6 were impregnated as a weave and bundles were extracted after curing.
Figure 9: Stress-displacement graphs for geopolymer-impregnated weaves.
It is seen from Figure 9 that the performance of the different samples varies largely. This effect is attributed to the fact that the rather viscous geopolymer slurry could not impregnate the bundles by the performed dip-coating without spreading of the bundles. However, it is also noted that the highest achieved IFSS is similar to IFSS achieved by impregnation of spread bundles, despite the seemingly worse preconditions regarding penetration of the geopolymer into the bundle. This surprisingly good adhesion may be assigned to the presence of a water-soluble sizing on
0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 0 1 2 3 4 5 6 7 8 9 10 Sh ear St re ss , N /m m 2 Displacement (mm)
Geopolymer-impregnated bundles
Geopolymer 1 Geopolymer 2 0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 0 1 2 3 4 5 6 7 8 9 10 Sh ear St re ss , N /m m 2 Displacement, mmGeopolymer-impregnated weaves with
water-soluble sizing
Geopolymer w1 Geopolymer w2 Geopolymer w3 Geopolymer w4 Geopolymer w5 Geopolymer w6the carbon fibres which after dissolution in the geopolymer slurry may reveal a carbon fibre surface that shows better compatibility with the geopolymer. However, further investigations would be required if such impregnation would be further pursued and optimized.
• Nano-CSH impregnation of weaves
Figure 10 presents the stress-displacement curves for three different samples prepared by impregnation of weaves with nano-CSH.
Figure 10: Stress-displacement diagrams for weaves impregnated with nano-CSH.
It is seen from Figure 10 that the nano-CSH impregnation exhibits high potential regarding improved adhesion of the reinforcement to cementitious matrices. However, it is also noted that the reproducibility is poor, especially regarding loads at high strains. For commercial introduction of such solutions, optimization of the impregnation process to ensure reliable quality would be required.
• Impregnation with molecular precursors
Figure 11 presents the stress-displacement curves of carbon fibre bundles impregnated with molecular precursors in comparison to geopolymer-impregnated bundles.
Figure 11: Stress-displacement diagrams of bundles impregnated with molecular precursors compared to geopolymer impregnated bundles.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 8 9 10 Sh ear St re ss , N /m m 2 Displacement, mm
Nano-CSH impregnated weaves with water-soluble
sizing
nCSH1 nCSH 2 nCSH 3 0 0,5 1 1,5 2 2,5 3 3,5 4 0 1 2 3 4 5 6 7 8 9 10 Sh ear St re ss , N /m m 2 Displacement, mmBundles impregnated with sol-gel precursors
TEOS GLYMO VTMOS VTMOS+PTMOS Geopolymersucceed to match the performance of geopolymer-impregnated bundles regarding IFSS. However, it is noted from Figure 11 that the VTMOS impregnation shows large capacity to take loads at high strains and exhibits thus a toughening effect on the material. Figure 12 below presents the stress-displacement curves of three samples of VTMOS (compared to geopolymer) to prove the consistent load-bearing capacity at high strains.
Figure 12: Stress-displacement diagrams of different VTMOS-impregnated samples compared to geopolymer bundle-impregnation.
It is seen from Figure 12 that the reproducibility of the VTMOS system requires some optimization. However, the trend to show rather high capacity to take load at high strains is consistent.
3.3
Thermal properties
Epoxy resins and SBR do not exhibit high thermal stability due to their organic nature. Even under inert atmosphere, typical epoxy resins have lost 50% of their mass at temperatures of about 360°C [1]. This is an unfortunate drawback of textile reinforcements compared to steel reinforcements, which remain stable until about 500°C, thus allowing for important evacuation time upon fire. Moreover, the rather high thermal stability of the fibre reinforcements (carbon fibres: above 500°C, 1000°C if protected from oxidation [2], basalt fibres: mass loss only 3% at 1000°C [3]) would in principle allow for increased fire safety compared to steel-reinforced concrete. However, the high thermal stability of the fibres cannot be exploited if combined with a polymeric impregnation with low thermal stability. Upon exposure to high temperatures, the polymeric material will soften and/or degrade, leaving the fibres without adhesion to the concrete. Fibre reinforcements without adhesion do not allow load transfer and can thus not take the tensile loads anymore, which will lead to collapse of the structure. Therefore, we present here several inorganic impregnation
1 Salasinska K. et al. Thermal Stability, Fire and Smoke Behaviour of Epoxy Composites
Modified with Plant Waste Fillers. Polymers 2019, 11, p.1234. doi:10.3390/polym11081234.
2 S. Feih, A.P. Mouritz. Tensile properties of carbon fibres and carbon fibre–polymer composites
in fire. Composites: Part A 43 (2012) 765–772. doi:10.1016/j.compositesa.2011.06.016.
3 Tang C. et al. Combustion Performance and Thermal Stability of Basalt Fiber-Reinforced
Polypropylene Composites. Polymers 2019, 11, p. 1826. 10.3390/polym11111826. 0 0,5 1 1,5 2 2,5 3 3,5 4 0 1 2 3 4 5 6 7 8 9 10 Sh ear St re ss , N /m m 2 Displacement, mm
Reproducibility of load-bearing capacity of VTMOS
samples at high strains
VTMOS Geopolymer VTMOS2 VTMOS3
materials that allow adhesion of the reinforcement to cementitious matrices even at temperatures above 500°C.
• Thermal properties of geopolymers:
For geopolymer materials, mechanical integrity has been proven up to 800°C [4]. • Thermal properties of sol-gel based silicates:
The thermal performance of sol-gel based silicates depends on their composition. For all systems, physical desorption of water and organic solvents takes place at temperatures above 100°C. In order to avoid cracking of the material upon exposure to elevated temperatures (or fire), it is therefore important to dry the impregnated reinforcements prior to embedding in cement. For organically modified silicas (e.g. VTMOS), the organic groups decompose at temperatures around 300°C. Depending on the organic content of the material, this may lead to some decrease in the mechanical performance and adhesion to the cement. However, the organic content studied here is not assumed to have a major influence regarding this. At higher temperatures, condensation/polymerization, volume relaxation and sintering occur [5]. These processes are assumed to influence the volume of the silica impregnation and thus reduce the adhesion to the cementitious matrix.
• Thermal properties of nano-CSH:
To our knowledge, no specific studies on the thermal properties of nano-CSH have been performed. However, it is assumed that such material behaves similar to normal CSH (cement). Despite its incombustibility, cement exhibits a degradation of mechanical properties at elevated temperatures: at 460°C, decomposition of Ca(OH)2 occurs and
around 700°C CaCO3 decomposes [6]. A debonding between reinforcements
impregnated with nano-CSH and cementitious matrices is therefore assumed to occur starting from 460°C. This early degradation is not desirable, as the load-transfer between cement and reinforcement is compromised, thus reducing the ability of the structure to take tensile loads.
It can be concluded that geopolymer impregnation provides the highest thermal stability of the studied systems according to literature. Even if the thermal stability of nano-CSH is superior to conventional textile reinforcements with polymer impregnation, it does not allow to exploit the high thermal stability of carbon or basalt fibres to provide reinforcements with improved thermal stability compared to steel reinforcements. However, experimental verification of this assumption is required (though out of scope for the present project).
4 He R., Dai N. and Wang Z. Thermal and Mechanical Properties of Geopolymers Exposed to
High Temperature: A Literature Review. Advances in Civil Engineering 2020, doi: https://doi.org/10.1155/2020/7532703
5 Zaharescu M.M, Jeanina P and Predoana L.Relevance of thermal analysis for sol–gel-derived
nanomaterials. Journal of Sol-Gel Science and Technology 2018, vol.86, p.7-23. DOI: 10.1007/s10971-018-4583-4.
6 Wang Y. et al. Effects of Highly Crystalized Nano C-S-H Particles on Performances of Portland
Cement Paste and Its Mechanism.
4
Conclusions
Several reinforcements impregnated with inorganic materials have been presented that can achieve significantly higher adhesion to cementitious materials compared to commercial reinforcements.
The present studies indicate that nano-CSH impregnation of textiles has the highest potential to achieve good adhesion to cementitious materials. However, apart from the required optimization to achieve reliable performance, the nano-CSH system exhibits additional significant drawbacks: (i) similar limitations regarding thermal stability as steel and (ii) poor handleability.
A system that could achieve more reliable results and significantly higher thermal stability to nano-CSH is geopolymer impregnation of spread tows. If the goal is to achieve good load bearing capacity at high strains, impregnation with molecular precursors based on VMTOS may be considered instead. However, this system exhibits the same thermal limitations as nano-CSH.
It is concluded that for applications with high demands regarding thermal stability and structural integrity upon fire, geopolymer impregnation may be the preferred solution. However, experimental verification of the thermal performance of the different systems is required for final recommendations regarding this aspect.
If the thermal performance of nano-CSH can meet the requirements, this solution may be preferred, provided that more reliable performance can be achieved upon
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Polymeric materials and Composites
RISE Report 2021:02 ISBN: 978-91-89167-84-1
