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The Circular Economy in the construction sector: enhanced cementitious materials with low CO2 impact.
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Mechanical properties of mortars with waste plastic as replacement of natural aggregate
Full text linkThe use of waste plastic from Waste Electrical and Electronic Equipment (WEEE) as a substitute for natural aggregate in cementitious materials is an increasingly relevant issue. In fact, this would allow to recycle plastics destined for landfills and to decrease the use of new natural resources. However, replacing sand with plastic tends to reduce the mechanical properties of mortars due to the different mechanical properties between the natural aggregate and the waste plastic and the poor interfacial compatibility between the plastic and the cement paste. This work used several strategies to improve the mechanical properties of mortars containing waste plastic. The addition of 1 % of superplasticizer coupled with a lower w/c ratio succeeds in restoring the mechanical properties to values equal to a standard mortar prepared with the natural aggregate, thus obtaining a material that can be used in the construction field
Mechanical properties of mortar containing waste plastic (PVC) as aggregate partial replacement
Full text linkThe purpose of this work is the reuse of polyvinyl chloride (PVC) deriving from waste electrical and electronic equipment (WEEE) used as a partial substitute for the mineral aggregate to produce lightened mortars. PVC was recovered from copper electrical cables, ground and used as replacement of mineral aggregate in 5, 10, 15 and 20 % vol. in mortar. A thermal characterization of the starting material was carried out to understand its composition. The mortar samples were mechanically tested both using class G cement and ordinary Portland cement. The results showed a worsening of the mechanical properties of around 50 % for only 5 % in volume of sand substituted with PVC waste. A likely explanation to this phenomenon was found in the mechanical characteristics of the PVC used and to its poor adhesion with the matrix, that resulted in the creation of porosity. However, the mortar prepared contributes to the conservation of natural resources and maintains mechanical properties adequate for the use in non-structural applications (e.g. screed or substrate)
Recycling of WEEE plastics waste in mortar: The effects on mechanical properties
Full text linkThis work focused on the recycling of WEEE plastic waste as a partial substitute for aggregate in light mortars. The plastic mix, provided by the IREN group, was used as a replacement of aggregate in 15, 30, 45, 60, 75, and 90%vol in mortars. Worsening of the mechanical performance of around 50% was detected already at only 15%vol of mineral aggregate substituted with plastic waste. The explanation of this phenomenon was found in both the scarce mechanical properties of the used plastic and in the poor adhesion between matrix and plastics that resulted in extra-porosity formation, as also demonstrated by comparing the results with several models in the literature. However, the use of plastic waste as a partial replacement of natural aggregate contributes to the preservation of natural resources and, in any case, does not limit the application of these materials in non-structural applications
The influence of industrial biochar on mortar composites' mechanical properties
Full text linkCO2 emissions have reached record levels in recent years, and the construction and materials production industries significantly contribute to greenhouse gas emissions. To address this environmental issue, architectural design and civil engineering are trying to adopt strategies such as using less toxic and harmful building materials, controlling energy consumption throughout the structure's life cycle, and implementing new materials such as biochar, a byproduct produced through thermochemical processes that involve limited oxygen, such as pyrolysis or gasification, that have been shown to have the ability to recover energy from treated biomass and provide environmental benefits. This study examines the effects on the mechanical strength of the substitution of cement for biochar in mortar composites. The results show that substituting 1-5% of biochar does not significantly affect mortars' compressive performance, in case of cementitious conglomerates characterized by compressive strength around 50 MPa. Interestingly, results show that the fracture energy can increase up to 30% compared with the reference mortar, without biochar. The results presented in this study justify the use of this material to produce mortars for structural applications
Mechanical properties of mortar containing recycled Acanthocardia tuberculata seashells as aggregate partial replacement
Full text linkWaste management is a most current topic, and as such, numerous articles in literature discuss over the recycling and re-use of waste materials from various fields. A common solution is the to use these materials as partial substituent of the inert fraction in concretes and mortars. This work focuses on the possibility of using Acanthocardia tuberculata seashells, which constitute a food waste destined to landfilling, as partial substituents of inert in mortars. The results obtained evidenced that the reduction in mechanical properties (in terms of toughness and flexural stress) is mainly due to the water absorption properties of seashells aggregates, which affect the hydration of the cement. However, as experimentally demonstrated, such decrease in mechanical properties in any case does not compromise the performance of the material when used for civil applications
The influence of biochar shape in cement-based materials
Full text linkBiochar-containing cement composites are gaining interest in the last years due to the possibility of reducing the environmental impact linked to cement. It can also improve the mechanical properties and the electrical conductivity of cement-based materials. A parameter that can affect mechanical performance of biochar-containing cement composites is the morphology of biochar. While it is reasonable to expect a different behavior for different shapes (rod-like, spherical or sheet), a full understanding is yet to be achieved of the competing effects of aspect ratio, morphology, and composition linked to the specific biochar source. This study shows that biochar can improve the mechanical properties of cement-based composites. 1 wt. % of biochar improves of 7 % the compression strength and 15 % the flexural strength. The results presented in this work confirm that biochar has a positive effect on both the mechanical and environmental behavior of cement-based materials
Concrete Waste and CDW Powders as Portland Cement Replacement in Mortar: A Preliminary Study
No full textThe construction industry’s heavy reliance on Ordinary Portland Cement (OPC) significantly contributes to global CO2 emissions, prompting the search for sustainable alternatives. This study investigates the partial substitution of Portland cement with construction and demolition waste (CDW) powder and concrete waste (CON) powder in mortar mixes. Replacement levels of 5%, 10%, 15%, and 20% by weight were tested following EN 196-1 standards to evaluate the mechanical performance of the resulting materials. X-ray diffraction (XRD), X-ray fluorescence (XRF), and thermo-gravimetric analyses confirmed that CDW and CON powders consist mainly of quartz and calcite, with chemical compositions compatible with cementitious systems. Mechanical testing revealed that compressive strength was maintained or slightly improved at replacement levels up to 10%, while higher substitutions led to moderate reductions due to dilution effects. The use of CDW and CON powders effectively transformed a 52.5 R Type I cement into a 42.5 R Type II equivalent, demonstrating the feasibility of producing sustainable binders with acceptable performance
Oxidation of Carbon Nanotubes for Improving the Mechanical and Electrical Properties of Oil-Well Cement-Based Composites
Full text linkCarbon nanotubes are used to improve both the mechanical properties and electrical conductivity of cement, allowing the preparation of a strengthened and toughened cement that can be used for self-monitoring applications. Functionalization by reaction with acid is necessary to guarantee both a good dispersion in water and a strong interaction with cement. Sulfonitric acid (a solution of sulfuric acid and nitric acid) is the best oxidation treatment to decorate the surface of carbon nanotubes with polar groups. The time of treatment influences the mechanical and electrical properties of the composites, and in this work, the effect of the length of the treatment on both CNTs and composites was thoroughly analyzed. It was shown that a long-time oxidation treatment (90 min) was very effective to obtain well-dispersed carbon nanotubes that allow us to obtain cement-based composites with a large improvement of mechanical properties with respect to plain cement: 213% for flexural strength, 90% for fracture energy, and 20% for compressive strength. Furthermore, the electrical resistivity of cement-based composites was reduced to only 3% of the value of plain cement
Modified Fine Recycled Concrete Aggregates with a Crystallizing Agent as Standard Sand Replacement in Mortar
Full text linkThis study aimed to evaluate mortar performance by substituting part of standard sand with recycled fine aggregates sourced from concrete waste, aiming to assess mechanical properties and durability. Moreover, this study examined the use of crystallizing agents to understand their impact on mortar properties. Four mortar series were prepared with sand substitution percentages ranging from 25% to 100% while adhering to the diverse fraction proportions within the standardized sand particle size distribution. Mechanical results indicate that incorporating recycled concrete sand significantly enhances mechanical properties with respect to standard sand. The study showed the technical feasibility of producing mortars with up to 100% recycled fine concrete aggregate with enhanced compressive strength, albeit requiring higher superplasticizer dosages. The addition of crystallizing agents provided an increase in flexural strength in specific conditions, while they did not provide a significant improvement to compressive strength
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