1,720,979 research outputs found
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
Green High-Performance Mortars for 3D Printing Applications
No full textThe present research work focuses on the study and design of innovative mix designs of high-performance mortars with biochar, which is a waste material that gives the mortar a green connotation. Dimensional stability of the mortar at the fresh state is assessed through an extrusion test to evaluate the suitability of thematerial to be produced via 3D printing technology. In addition to the mechanical properties (flexural and compressive strength), the fracture behaviour of the mortar in crack mouth opening displacement mode is investigated. In this experimental campaign, different parameters are studied and their effect on the mechanical performance and fracture behaviour of the innovative green highperformance mortar are investigated, including aggregate/cement ratio, maximum diameter of the aggregate, and type of aggregate
Investigation on the compressive strength and durability properties of alkali-activated slag mortar: Effect of superabsorbent polymer dosage and water content
Full text linkThis paper presents the properties of alkali-activated slag (AAS) mortar additivated with a superabsorbent polymer (SAP) to improve its mechanical and durability properties. The effect of different dosages of SAP (0.0–0.3% with respect to the blast furnace slag weight) and different extra water additions on setting time, autogenous shrinkage, compressive strength, water permeability, frost resistance, heat of hydration, and porosity is presented and discussed. The results highlight the beneficial effect of adding SAP on the mechanical and durability properties of the proposed mixtures. Only at higher percentages of SAP and additional water occur performance drops due to excessive macro-porosity of the system. It is interesting to point out that, in contrast, shrinkage always decreases as the percentages of SAP addition and additional water increase, although it cannot be completely eliminated. Experimental evidence also highlights that significant benefits can be gained from using this material in harsh environments
High-strength foamed concrete for structural applications: Influence of metakaolin, superplasticizer, maximum fine sand particle size, and dry density
Full text linkAiming to minimize cement usage and carbon emissions while reducing the weight of structural elements, this work presents preliminary findings from ongoing experimental campaigns focused on foamed concrete for structural applications. This study explores the influence of dry density, superplasticizer dosage, maximum fine sand particle size, and metakaolin on the slump and mechanical properties, including flexural strength, compressive strength, and elastic modulus of foamed concrete. In detail, this experimental study involved the preparation of 90 prismatic foamed concrete specimens with fixed target densities between 1350 and 1600 kg/m3. All specimens were cured in water for 28 days and subsequently tested according to relevant UNI EN standards. The results show that mixtures containing metakaolin and higher dosages of superplasticizer demonstrate excellent flowability, a crucial characteristic for this type of material in structural applications, effectively eliminating the need for vibration. Additionally, the presence of metakaolin, smaller maximum particle size of aggregate, and higher superplasticizer content can enhance the mechanical properties of foamed concrete by promoting a denser and improved microstructure characterized by smaller micro-air-pore sizes. These conclusions are consistent with the finding related to elastic modulus. Specifically, the maximum compressive strength of the foamed concrete containing metakaolin at a target dry density of 1600 kg/m3 is approximately 58 MPa, with flexural strength exceeding 8 MPa and an elastic modulus around 20 GPa. The results are promising, in particular the compressive strength is found to be higher than that typical of lightweight aggregate concretes of the same density and is comparable to that of a conventional concrete with strength class C40/50. Additionally, these results underscore the material's strong potential for structural applications. The combination of favorable mechanical properties and reduced density can significantly enhance sustainability in the construction sector by lowering structural dead loads
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
Preliminary Study on Multi-functional Building Components Utilizing Variable Density Foamed Concrete via 3D Printing
Full text linkOver the last decades, lightweight foamed concrete has gained recognition and widespread adoption in the construction industry, owing to its intrinsic multifunctionality and versatility. Notably, the ability to achieve a broad range of densities through mix design adjustments makes this material appealing for fulfilling different essential functions, including mechanical strength and thermal insulation. Moreover, recent studies exploring the application of foamed concrete in Additive Manufacturing processes underline the considerable advantage of combining the peculiar properties of foamed concrete with the benefits associated with automated procedures.
In the present study the application of multi-density foamed concretes in the fabrication of multifunctional engineered building components through 3D Concrete Printing (3DCP) processes is investigated. The possibility of employing medium-density foamed concrete for 3D printing topologically optimized structural sections and ultra-lightweight foamed concrete for filling these sections with thermal insulation purpose is proposed. This innovative solution allows for the fulfillment of multiple performance requirements - high mechanical performance and excellent thermal insulation - within a single cohesive cementitious element, thus eliminating the need to assemble numerous monofunctional layers of different materials.
The primary properties of the two proposed foamed concrete mixes were investigated. Compressive strengths of 7.04 MPa and 5.40 MPa were achieved for cast and 3D-printed medium-density foamed concrete, respectively. Thermal conductivities of 0.205 W/mK and 0.072 W/mK were obtained for medium-density and ultralight-density foamed concrete, respectively. A successful 3D printing application with medium-density foamed concrete was executed using a collaborative robotic arm, and the possible pouring of ultralight-density foamed concrete to produce multi-density building components was assessed
3D-printed multi-functional foamed concrete building components: Material properties, component design, and 3D printing application
Full text linkThe use of multi-density foamed concretes (FCs) to produce multi-functional building components by 3D Concrete Printing (3DCP) is investigated. The use of medium-density 3D-printed foamed concrete (3DPFC_800), primarily serving a load-bearing role, and ultra-lightweight foamed concrete (ULFC_300), as thermal insulation material poured in the voids defined by the former, is proposed. This enables meeting diverse performance requirements within a single cementitious matrix, eliminating the need for multiple materials. The main properties of the proposed mixes are investigated. The compressive strength and thermal conductivity are equal to 7.04 MPa and 0.205 W/mK, and 1.43 MPa and 0.072 W/mK for 3DPFC_800 and ULFC_300, respectively. A successful 2D-printing test validates the suitability of 3DPFC_800 for 3DCP, and a robotic arm is employed for 3DCP tests. The proposed application allows for further knowledge on the use of FC in 3DCP and the identification of some issues and challenges that still need to be addressed
Investigation on the fracture behavior of foamed concrete
Full text linkThe fracture behavior of lightweight foamed concrete (LWFC) is significantly influenced by microstructural properties, which are ascribed to the arrangement of air bubbles and pores as well as to the presence of different hydration products. In this contribution, an experimental investigation on the fracture behavior of LWFC is performed. Notched beams made of LWFC were tested in three-point bending to determine the fracture energy based on the load-CMOD (Crack Mouth Opening Displacement) curve. The influence of the dry density is explored considering one density for non-structural purposes (equal to 800 kg/m3) and another density for structural applications (1600 kg/m3). Moreover, two curing conditions are considered (air and water). The load-CMOD curves reveal that for lower dry densities the fracture behavior of LWFC is particularly affected by the curing conditions, with better results achieved in air curing conditions, but this influence decreases with higher dry densities. The improved performance in air curing conditions for lower dry densities is also observed in terms of flexural strength, but is not particularly evident for the compressive strength. Micrographs across the crack surface determined via Scanning Electron Microscopy (SEM) are finally presented to analyze the experimental findings and justify the results in terms of microstructural configuration of the specimens
CRITICAL ASSESSMENT OF CO2EMISSION OF DIFFERENT CONCRETES: FOAMED, LIGHTWEIGHT AGGREGATE, RECYCLED AND ORDINARY CONCRETE
Full text linkConstruction materials contribute to about 75% of the CO2 emission of all the construction processes. Concrete is one of the most widely used construction materials and is thus primarily responsible for CO2 emission. In particular, 8 − 9% of global greenhouse gas (GHG) emission are produced by concrete. CO2 emissions can be considerably reduced in the construction phase through a careful selection of materials with low environmental impact or through specific admixtures. In this study, different concretes are taken into consideration, including foamed concrete, lightweight aggregate concrete, recycled concrete and ordinary concrete. A series of mix designs of these four classes of concrete, characterized by a comparable mechanical strength or a comparable density, are taken from the relevant literature and compared to one another in terms of CO2 emission. Some guidelines or possible research lines aimed at reducing CO2 emission are finally outlined in this contribution
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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