Different fiber materials as reinforcement for geopolymer composite

For the last two centuries, Ordinary Portland Cement (OPC) is the most popular building material in the world due to its high mechanical properties, ease of handling and low cost. However, the concrete industry is known to leave an enormous environmental footprint. Therefore, the development of sustainable materials that could replace the OPC is essential. One of such recent developments is an aluminosilicate based material that can be activated in an alkaline medium to form a hardened sustainable product, known as ‘Geopolymer’. Geopolymers exhibit equal or better engineering properties as compared to conventional concrete with better environmental foot print. However, geopolymer\u27s main disadvantage, as concrete, is its brittleness and low tensile properties. One way to overcome this limitation is by addition of fibers, as they can control cracking by crack bridging, resulting in an increase of the tensile properties of the geopolymeric composite. The purpose of this research was to develop a high performance geopolymer composite by addition of short fibers. Three different types of fibers were added to the matrix with two different fiber contents (0.5% and 1%). The idea was to add fibers of significant difference in their chemical nature and tensile properties: PP and Carbon fibers which are both hydrophobic, but have significant differently tensile behavior, and PVA which is hydrophilic like the geopolymeric matrix, and has moderate tensile properties. Their influence on the geopolymer flexural behavior was examined. The microstructure of the composite at the fracture surface was also studied to better understand the role of the fibers. The results of this research showed that all fibers improved the ductility and toughness of the matrix. Geopolymeric composites with 1% carbon fibers showed the highest flexural strength, +216% compared to plain matrix, followed by the PVA fiber composites. Different failure modes were observed – fiber pull-out for the PP and carbon composites, and fiber rupture for the PVA fiber composite. This can be explained based on the different chemical nature of the fibers which produce a different matrix-fiber interface

Metakaolin based geopolymers as soil stabilizers

In many kinds of engineering constructions, wind-swept soils and soft weak soils are often stabilized and strengthened with ordinary Portland cement (OPC) and lime, to increase soil strength and durability. Furthermore, such soil stabilizing can also prevent erosion and dust generation. However, OPC is known to leave an enormous environmental footprint on planet Earth as its production processes are significant energy consumers with high CO2 emissions. Therefore, the development of a novel generation of cements with high durability and environmental sustainability is essential. One of these novel binders is the alkali-activated binder based on aluminosilicates materials as metakaolin or industrials by-products such as fly ash or slags, commonly referred to as geopolymer. It has been found that geopolymers can exhibit high compressive strength and higher chemical and thermal resistance than cement-based materials [1]. Therefore, due to their high strength, low cost, low energy consumption and CO2 emissions, geopolymers offers a promising alternative to OPC [2]. Geopolymers also exhibit excellent adhesion to aggregates [3], therefore it is reasonable to assume that they can serve as an effective soil stabilizer. Please click Additional Files below to see the full abstract

Development of one-part geopolymers based on industrial waste

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Retention of Re in metakaolin based geopolymer in the presence of an organic reductant – an experimental study

The goal of this research was to examine the change in redox sensitive contaminant retention and leaching behavior from a model geopolymer system, during oxidation and carbonation, in the presence of an organic reductant. The behavior of redox sensitive elements under variable environmental conditions is specifically important for understanding the leaching of radionuclides retained in geopolymeric materials (e.g. Tc) that are soluble when oxidized and insoluble under reducing conditions. An alkali-activated metakaolin geopolymer with high silica/alumina ratio was selected as a model material. Rhenium was selected as the model redox sensitive element, which exhibits a large valence (-3 to +7) and solubility range. Rhenium was introduced in its most oxidized form (VII) as Re2S7. Ascorbic acid was used as a reducing agent during geopolymer casting due to its high solubility and homogeneous distribution within the matrix. Cylindrical monoliths were cured for 90 days under an inert atmosphere (N2) and then aged for 60 days under 98% N2 + 2% CO2 or CO2 deficient air, at a constant relative humidity (68%). The samples were then subjected to EPA 1313 pH dependent leaching test and EPA 1315 monolith leaching test. Leachates were analyzed using DOC and ICP techniques. XRD and SEM – EDS imaging and analyses were used to characterizes the solids Results show that Re has precipitated as ReS2 (IV) in the matrix. The pH dependent leaching test show that Re was released homogenously throughout most of the pH range (3-12). However, the retention of the material aged under CO2 deficient air was three times lower, indicating that the main effect on leaching from this material is of the oxidation process. The natural pH values were 11.3 and 12 for the material aged under 2% CO2 and for material aged under CO2 deficient air respectively, indicating minor carbonation in the former, however, no carbonate minerals were detected in the matrix. Monolith leaching results show that the geopolymers aged under CO2 deficient air have retained significantly less Re (0.24% leaching) relative to the sample aged under 2% CO2 (0.07wt % leaching). -log(diffusivity) values were in the order of 15 and 16 for CO2 deficient air and 2% CO2 respectively. There is a clear positive correlation between the amount of Re and DOC released from the samples, where their amounts are significantly larger for the samples aged under CO2 deficient air, indicating that the main Re-release mechanism from these samples is related to chelation to organic species under oxidizing conditions

Sr immobilization in irradiated Portland cement paste exposed to carbonation

International audienceCement based materials are widely used as binding matrices for radionuclides in low and intermediate level waste management applications. We studied the effect of irradiation and carbonation under atmospheric condition on the leaching of Sr from Portland cement paste. Samples were exposed to gamma irradiation or subjected to thermal treatment under either inert or atmospheric conditions. Leaching tests were performed and supplemented by post-leaching characterization including local chemical analysis (LA-ICPMS) crystallographic analysis (XRD), and EPMA imaging. The combination of these methods enabled us to link between the crystallography, texture and composition of the treated samples and their ability to retain Sr ions. Results show that carbonation was the main factor determining the retention of Sr ions, whereas irradiation did not have a significant effect. Moreover, carbonation has a positive effect on the retention of Sr ions in the matrix with the formation of a carbonated zone

Retention of strontium in high- & low-pH cementitious matrices – OPC vs. model systems

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Catalytic Pyrolysis of High-Density Polyethylene: Decomposition Efficiency and Kinetics

Organic waste is generally characterized by high volume-to-weight ratios, requiring implementation of waste minimization processes. In the present study, the decomposition of high-density polyethylene (HDPE), was studied under thermal and catalytic pyrolysis conditions on two experimental systems. Firstly, pyrolytic conditions for HDPE decomposition were optimized in a laboratory-scale batch reactor. In order to maximize gas yields and minimize secondary waste, the effects of aluminosilicate catalysts, catalyst loading, and reaction temperature on decomposition efficiency were examined. Secondly, kinetics and reaction temperatures were studied on a large capacity thermobalance, especially adjusted to perform experiments under pyrolytic conditions at a larger scale (up to 20 g). The addition of catalysts was shown to enhance polymer decomposition, demonstrated by higher gas conversions. Condensable yields could be further minimized by increasing the catalyst to polymer ratio from 0.1 to 0.2. The most prominent reduction in pyrolysis temperature was obtained over ZSM-5 catalysts with low Si/Al ratios; however, this impact was accompanied by a slower reaction rate. Of the zeolites tested, the ZSM-5 catalyst with a Si/Al of 25 was found to be the most efficient catalyst for waste minimization and organic destruction, leading to high gas conversions (~90 wt%.) and a 30-fold reduction in solid waste mass

Catalytic Pyrolysis of High-Density Polyethylene: Decomposition Efficiency and Kinetics

Organic waste is generally characterized by high volume-to-weight ratios, requiring implementation of waste minimization processes. In the present study, the decomposition of high-density polyethylene (HDPE), was studied under thermal and catalytic pyrolysis conditions on two experimental systems. Firstly, pyrolytic conditions for HDPE decomposition were optimized in a laboratory-scale batch reactor. In order to maximize gas yields and minimize secondary waste, the effects of aluminosilicate catalysts, catalyst loading, and reaction temperature on decomposition efficiency were examined. Secondly, kinetics and reaction temperatures were studied on a large capacity thermobalance, especially adjusted to perform experiments under pyrolytic conditions at a larger scale (up to 20 g). The addition of catalysts was shown to enhance polymer decomposition, demonstrated by higher gas conversions. Condensable yields could be further minimized by increasing the catalyst to polymer ratio from 0.1 to 0.2. The most prominent reduction in pyrolysis temperature was obtained over ZSM-5 catalysts with low Si/Al ratios; however, this impact was accompanied by a slower reaction rate. Of the zeolites tested, the ZSM-5 catalyst with a Si/Al of 25 was found to be the most efficient catalyst for waste minimization and organic destruction, leading to high gas conversions (~90 wt%.) and a 30-fold reduction in solid waste mass