Recent studies have shown cementitious syntactic foams (CSF) to have great potential as a low den... more Recent studies have shown cementitious syntactic foams (CSF) to have great potential as a low density and high strength structural material. However, CSFs are made with hollow glass microsphere (HGM) inclusions and cementitious materials with amorphous silica inclusions such as glass are known to have a potential for the deleterious alkali silica reaction (ASR). In this study, CSFs containing HGMs are tested for ASR expansion and compressive strength along with solid particles of soda-lime and borosilicate glass to compare. Results show that in the 30-90 μm average particle size range, only solid borosilicate particles lead to more than 0.2% expansion of the composite material in an accelerated ASTM C1260 lab test for ASR, which is considered as the limit for deleterious effects. Similarly, compressive strength tests show that only solid borosilicate particles lead to reduced compressive strengths (from ~95 to ~40 MPa) in the long term, while CSFs showed no sign of loss of compressive strength even at extremely alkaline conditions. Scanning electron microscopy investigations suggest that CSFs are safe from ASR expansion of the composite and internal stresses due to their hollow geometry, which provides reservoir space for the alkaline silica gel expansion and mitigates the ASR effects.
The present work was focused on studying the strain rate sensitivity of cementitious syntactic fo... more The present work was focused on studying the strain rate sensitivity of cementitious syntactic foams (CSF), which are particulate composites reinforced with hollow glass microspheres (HMG). Different density CSFs (1.31-1.74 g/cm 3) with different volume fractions (20-40%) of HGMs were tested with a split-Hopkinson pressure bar setup. The true particle densities of the HGMs were in the range of 0.38-0.60 g/cm 3. In addition, the macro-and micro-scale failure mechanisms were investigated with high-speed camera imaging, micro-CT scanning, and electron microscopy. The results showed that both the CSFs and the baseline material (control sample), which is the cement paste matrix of the CSFs, showed strain rate sensitivity in mechanical properties in the 10 2-10 3 s −1 strain rate range. CSFs had relatively lower strain rate sensitivity in comparison to the matrix material. In the same range of strain rate, both the CSFs and the control sample showed significant changes in their macro and micro failure mechanisms depending on their age, composition and loading rate. The level of damage at the peak load for the high strain rate was higher in comparison to the same materials tested under quasi-static loading conditions for CSFs and the cement matrix.
The advancements in structural materials are guided by the desire of lowering the density and inc... more The advancements in structural materials are guided by the desire of lowering the density and increasing the strength. Composite materials show promise in tuning the density and strength to meet specific design requirements. Lightweight cementitious materials, such as foamed concretes, are generally known to show poor mechanical properties (e.g., compressive strength and elastic modulus). The lack of control over the size, shape, and distribution of air voids severely limits the improvement of mechanical properties in lightweight cementitious materials. This work is focused on manufacturing and examining the mechanical properties of cementitious syntactic foams with hollow glass microspheres. Use of hollow particles to incorporate porosity allows for the control over the size, shape, and volume fraction of voids present in the composite. Hollow glass microspheres with several different densities (0.15e0.60 g/ cm 3) are used in different volume fractions (20%e50%) to manufacture the cementitious syntactic foams. The results show that cementitious syntactic foams (CSF) have compressive strengths (32e88 MPa) and elastic moduli (10e20 GPa) for a given range of low density (1.15e1.80 g/cm 3), which are better than other cellular cementitious materials in the same density range. In-situ micro-CT scan results reveal that the micro-fracture mechanisms in CSFs under compressive loading depend on the microsphere density and aging of the material.
Structural materials with low density and high strength are of great interest to material scienti... more Structural materials with low density and high strength are of great interest to material scientists. Most of the currently available lightweight cementitious composites have a cellular structure and tend to show poor mechanical performance (1 – 10 MPa compressive strengths) especially at lower densities (0.80 – 1.80 g/cm3). Previous studies on the brittle materials show a direct relation between the size of the largest voids (D90) and the composite strength. Therefore, tailoring the microstructure of brittle composites presents an opportunity for improvements in their mechanical performance. Particulate composite materials called syntactic foams have recently gained significant interest from material scientists, showing great potential for tailoring the mechanical properties through their microstructure, which includes selecting hollow particle fillers of appropriate size, density and surface treatment for incorporation in metals and polymeric materials. However, the research conducted on cementitious syntactic foams (CSF) is limited but has great potential in civil engineering applications.
Recent studies have shown cementitious syntactic foams (CSF) to have great potential as a low den... more Recent studies have shown cementitious syntactic foams (CSF) to have great potential as a low density and high strength structural material. However, CSFs are made with hollow glass microsphere (HGM) inclusions and cementitious materials with amorphous silica inclusions such as glass are known to have a potential for the deleterious alkali silica reaction (ASR). In this study, CSFs containing HGMs are tested for ASR expansion and compressive strength along with solid particles of soda-lime and borosilicate glass to compare. Results show that in the 30-90 μm average particle size range, only solid borosilicate particles lead to more than 0.2% expansion of the composite material in an accelerated ASTM C1260 lab test for ASR, which is considered as the limit for deleterious effects. Similarly, compressive strength tests show that only solid borosilicate particles lead to reduced compressive strengths (from ~95 to ~40 MPa) in the long term, while CSFs showed no sign of loss of compressive strength even at extremely alkaline conditions. Scanning electron microscopy investigations suggest that CSFs are safe from ASR expansion of the composite and internal stresses due to their hollow geometry, which provides reservoir space for the alkaline silica gel expansion and mitigates the ASR effects.
The present work was focused on studying the strain rate sensitivity of cementitious syntactic fo... more The present work was focused on studying the strain rate sensitivity of cementitious syntactic foams (CSF), which are particulate composites reinforced with hollow glass microspheres (HMG). Different density CSFs (1.31-1.74 g/cm 3) with different volume fractions (20-40%) of HGMs were tested with a split-Hopkinson pressure bar setup. The true particle densities of the HGMs were in the range of 0.38-0.60 g/cm 3. In addition, the macro-and micro-scale failure mechanisms were investigated with high-speed camera imaging, micro-CT scanning, and electron microscopy. The results showed that both the CSFs and the baseline material (control sample), which is the cement paste matrix of the CSFs, showed strain rate sensitivity in mechanical properties in the 10 2-10 3 s −1 strain rate range. CSFs had relatively lower strain rate sensitivity in comparison to the matrix material. In the same range of strain rate, both the CSFs and the control sample showed significant changes in their macro and micro failure mechanisms depending on their age, composition and loading rate. The level of damage at the peak load for the high strain rate was higher in comparison to the same materials tested under quasi-static loading conditions for CSFs and the cement matrix.
The advancements in structural materials are guided by the desire of lowering the density and inc... more The advancements in structural materials are guided by the desire of lowering the density and increasing the strength. Composite materials show promise in tuning the density and strength to meet specific design requirements. Lightweight cementitious materials, such as foamed concretes, are generally known to show poor mechanical properties (e.g., compressive strength and elastic modulus). The lack of control over the size, shape, and distribution of air voids severely limits the improvement of mechanical properties in lightweight cementitious materials. This work is focused on manufacturing and examining the mechanical properties of cementitious syntactic foams with hollow glass microspheres. Use of hollow particles to incorporate porosity allows for the control over the size, shape, and volume fraction of voids present in the composite. Hollow glass microspheres with several different densities (0.15e0.60 g/ cm 3) are used in different volume fractions (20%e50%) to manufacture the cementitious syntactic foams. The results show that cementitious syntactic foams (CSF) have compressive strengths (32e88 MPa) and elastic moduli (10e20 GPa) for a given range of low density (1.15e1.80 g/cm 3), which are better than other cellular cementitious materials in the same density range. In-situ micro-CT scan results reveal that the micro-fracture mechanisms in CSFs under compressive loading depend on the microsphere density and aging of the material.
Structural materials with low density and high strength are of great interest to material scienti... more Structural materials with low density and high strength are of great interest to material scientists. Most of the currently available lightweight cementitious composites have a cellular structure and tend to show poor mechanical performance (1 – 10 MPa compressive strengths) especially at lower densities (0.80 – 1.80 g/cm3). Previous studies on the brittle materials show a direct relation between the size of the largest voids (D90) and the composite strength. Therefore, tailoring the microstructure of brittle composites presents an opportunity for improvements in their mechanical performance. Particulate composite materials called syntactic foams have recently gained significant interest from material scientists, showing great potential for tailoring the mechanical properties through their microstructure, which includes selecting hollow particle fillers of appropriate size, density and surface treatment for incorporation in metals and polymeric materials. However, the research conducted on cementitious syntactic foams (CSF) is limited but has great potential in civil engineering applications.
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microstructure of brittle composites presents an opportunity for improvements in their mechanical performance. Particulate composite materials called syntactic foams have recently gained significant interest from material scientists, showing great potential for tailoring the mechanical properties through their microstructure, which includes selecting hollow particle fillers of appropriate size, density and surface treatment for incorporation in metals and polymeric materials.
However, the research conducted on cementitious syntactic foams (CSF) is limited but has great potential in civil engineering applications.
microstructure of brittle composites presents an opportunity for improvements in their mechanical performance. Particulate composite materials called syntactic foams have recently gained significant interest from material scientists, showing great potential for tailoring the mechanical properties through their microstructure, which includes selecting hollow particle fillers of appropriate size, density and surface treatment for incorporation in metals and polymeric materials.
However, the research conducted on cementitious syntactic foams (CSF) is limited but has great potential in civil engineering applications.