196,033 research outputs found
Graphene-engineered cementitious materials: a systematic experimental study = Materiali cementizi ingegnerizzati con grafene: uno studio sperimentale sistematico
No full textCement-based composite materials (CBCMs), including mortar and concrete, are the most common and widely used materials in construction. Ordinary Portland cement (OPC) is known as a principal constituent of CBCMs acting as a binder for the other aggregates presented in the CBCMs. The quasi-brittle behavior, low toughness, and poor tensile strength of these materials are of major concerns since they are responsible for poor durability and high maintenance costs. In the last decade, on the way of the rapidly growing interest toward nanotechnology, several researchers proposed an approach based on the interaction at the nanoscale level between the cement matrix and selected nanostructures that might result in macroscopical advantageous effects. For this purpose, graphene-based materials, including graphene nanoplatelets (GNPs), nano graphite platelets (NGPs), and graphene oxide (GO), have been proposed to offset the brittleness of the CBCMs.
The main objective of this PhD research work is to develop graphene-based cementitious composites (GBCCs) using low cost and commercially available graphene nanoplatelets (GNPs), nano graphite platelets (NGPs), and graphene oxide (GO). The project further investigated the effect of these nanomaterials on the rheology, microstructure, mechanical, and physical properties of a commercial premixed mortar at both early (7 and 14 days) and later ages (28 days). A full set of graphene engineered cementitious composites has been prepared using EN-998-2 premixed mortar as matrices, two GNPs water pastes, one NGPs powder, and two GO (one water suspension and one powder). The actual impact of the different GBMs and their dosage (i.e.0.01, 0.1, or 0.2% by weight of cement) was assessed in terms of rheology of fresh admixtures along with density, microstructural features, permeability (i.e .initial surface absorption, water contact angle, volume of permeable voids and chloride ion diffusion), physical properties (i.e. thermal and electrical conductivity, damping ratio) and mechanical properties (i.e. flexural and compressive strength) of the hardened nanocomposites.
It is concluded through various characterization and experimental campaigns that all GBMs regulated the microstructure of the cementitious composites along with the densification and influenced the permeability, physical, and mechanical properties of GBCCs uniquely. A significant improvement in the permeability, physical, and mechanical properties of newly developed GBCCs has been achieved, and that could be due to the generation of distinctive microstructure generated by the pozzolanic behavior of these nanofillers. Based on the observations of test results and comprehensive characterization, the possible mechanisms of permeability barriers, conductive pathways, and microstructure developments of GBCCs have been established
Reducing the emission of climate-altering substances in cementitious materials. A comparison between alkali-activated materials and Portland cement-based composites incorporating recycled tire rubber
No full textLow carbon or near-zero carbon concrete technology is in line with the pillars of sustainable development, where industrial waste or low-carbon binders can reduce or eliminate consumption of Portland cement and natural resources, leading to less environmental pollution. This work presents an experimental study on the comparison between alkali-activated materials (also recognized as geopolymers) and a traditional cementitious matrix (Portland cement) incorporated with rubber particles, deriving from end-of-life tires, as replacement of raw mineral aggregates. To explore the potential of rubber-geopolymer compounds, an experimental comparative analysis with rubber-Portland mortars was performed. Initial investigations (microstructural/compositional analysis, porosity and water absorption measurements, and mechanical tests) were conducted on rubberized samples obtained by varying the binder, the sand-rubber replacement ratio (0 vol%, 50 vol%, and 100 vol%) and the rubber particle size (0–1 mm rubber fine aggregate and 1–3 mm rubber granules). The results revealed a greater compatibility of the alkali-activated matrix with tire rubber aggregates, resulting in better performance in terms of interfacial adhesion, reduced porosity rate, flexural strength, and toughness. However, compressive strength results showed a weaker mechanical performance of rubber-geopolymer mixes compared to Portland counterparts. As also verified by Si/Al elemental analysis, the structural quality and mechanical development of the geopolymer matrix was strongly influenced by the removal of sand as a Si-source. The potential embodied carbon emission performance and cost analysis were also estimated to evaluate the economic and environmental impact related to the use of recycled rubber as complete aggregate in Portland and geopolymer mixes. Sustainability analysis revealed the greater environmental friendliness of geopolymer formulations compared to those in ordinary cement, but higher production costs. The total addition of rubber aggregates induced an increase in emissions and costs (variable according to the type of matrix) which, however, does not directly correlate with the processing/price of the polymer fraction. Deepening the research on cleaner matrices and promoting the use of recycled materials in concrete applications could lead to a gap levelling between Portland and geopolymer rubber-based composites. Building on these findings, future study will focus on the optimization of the mix design as a function of rubber aggregates
Dataset for publication Chougan M., Ghaffar S.H., Nematollahi B., Sikora P., Dorn T., Stephan D., Albar A., Al-Kheeta M.J. Effect of natural and calcined halloysite clay minerals as low-cost additives on the performance of 3D-printed alkali-activated materials. Materials and Design (2022) 223, 111183
No full textOpen dataset for publication Chougan M., Ghaffar S.H., Nematollahi B., Sikora P., Dorn T., Stephan D., Albar A., Al-Kheeta M.J. Effect of natural and calcined halloysite clay minerals as low-cost additives on the performance of 3D-printed alkali-activated materials. Materials and Design (2022) 223, 111183. https://doi.org/10.1016/j.matdes.2022.111183
File 1 - FTIR - data of raw and calcined material - *.opj (Origin)
File 2 - Mechanical performance print vs cast - *.opj (Origin)
File 3 - Mechanical performance - *.opj (Origin)
File 4 - TGA and XRD - data of raw and calcined material - *.opjuSeyed Hamidreza Ghaffar and Mehdi Chougan would like to acknowledge the funding received from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement ID: 101029471. Pawel Sikora acknowledges funds received from the National Science Centre, Poland, within Project No. 2020/39/D/ST8/00975 (SONATA-16)
The influence of nano-additives in strengthening mechanical performance of 3D printed multi-binder geopolymer composites
No full textThe weak mechanical properties the 3D printed parts can limit the competence of this technology when compared to conventionally cast-in-mold cementitious composites structures. However, experimental results in this study showed that the incorporation of nano additives could improve the mechanical property of printed structures. Six geopolymeric mixtures were designed and tested for their flow-ability, shape stability, buildability and mechanical performance. Different dosage of nano graphite platelets (NGPs) ranging from 0.1% to 1%, by the weight of geopolymer, were incorporated to the best performing geopolymer. The 3D printed geopolymer with 1% of NGPs increased the flexural strength by 89% and 46% compared to the same 3D printed and casted geopolymer without any NGPs, respectively. The same increase for compressive strength was 28% and 12%. Moreover, the geopolymer mix containing 1% of NGPs demonstrated the best shape retention and buildability
Influence of nanoceramic-plated waste carbon fibers on alkali-activated mortar performance
No full textWaste carbon fibers as reinforcing elements in construction materials have recently gained increasing interest from researchers, providing outstanding strength performance and a lower environmental footprint compared to virgin fibers. Combination with cement-free binders, namely alkali-activated materials, is becoming increasingly important for sustainable development in the construction industry. This paper presents results relating to the potential use of waste carbon fibers in alkali-activated mortars. The waste carbon fiber fraction utilized in this research is difficult to integrate as reinforcement in ceramic–cementitious matrices due to its agglomerated form and chemical inertness. For this reason, a nanoceramic coating pretreatment based on nanoclay has been implemented to attempt improvements in terms of deagglomeration, dispersibility, and compatibility with alkali-activated materials. After chemical–physical and microstructural analysis on the nanoclay-plated fibers (including X-ray diffraction, IR spectroscopy, contact angle measurements, and electron microscopy) mortars were produced with four different dosages of treated and untreated waste fibers (0.25 wt.%, 0.5 wt.%, 0.75 wt.%, and 1 wt.%). Mechanical tests and fractographic investigations were then performed. The nanoclay coating interacts compatibly with the waste carbon fibers and increases their degree of hydrophilicity to improve their deagglomeration and dispersion. Compared to the samples incorporating as-received fillers, the addition of nanoclay-coated fibers improved the strength behavior of the mortars, recording a maximum increase in flexural strength of 19% for a fiber content of 0.25 wt.%. This formulation is the only one providing an improvement in mechanical behavior compared to unreinforced mortar. Indeed, as the fibrous reinforcement content increases, the effect of the nanoclay is attenuated by mitigating the improvement in mechanical performance
Lightweight alkali-activated materials and ordinary Portland cement composites using recycled polyvinyl chloride and waste glass aggregates to fully replace natural sand
No full textPolyvinyl chloride plastic (PVC) and glass waste have proven to be significant environmental concerns considering their restricted reuse and complicated recycling procedures. Glass and PVC waste materials form a substantial portion of total solid wastes that negatively influence the environment. This study aims to fully replace natural sand with recycled PVC and waste glass aggregates in alkali-activated materials (AAMs). A comprehensive testing programme was employed to investigate the effect of 100 % aggregate replacement on the composites’ mechanical performance, water absorption, impact resistance, thermal conductivity, resistance to harsh environments, and microstructural changes. Results revealed that AAMs containing recycled PVC and glass aggregates outperformed their ordinary Portland cement (OPC)-based composite counterparts in terms of mechanical properties, energy absorption, thermal conductivity, and carbon footprint estimation. Although mixtures containing recycled aggregates cannot be deemed for load-bearing applications, these composites exhibited a promising capacity to be used in insulating applications. AAMs containing 100 vol-% PVC aggregates with flexural and compressive strengths of 9 and 11 MPa, respectively, registered the highest energy absorption of about 6 J, three times higher than the AAM control sample, and the lowest thermal conductivity of about 0.5 W/mK, with about 80 % reduction of thermal conductivity compared to the AAM control sample. With the full replacement of PVC and glass aggregates, the most significant decrease in the carbon footprint is achieved for AAM (−352.25 kg CO2-eq) and OPC (−353.94 kg CO2-eq), respectively
A systematic study on EN-998-2 premixed mortars modified with graphene-based materials
No full textGraphite nano-platelets (GNPs) and graphene oxide (GO) modify cementitious materials from the nano- to the macroscale, resulting in enhanced mechanical properties, durability and, eventually, physical multi-functionality. A systematic study on EN 998-2 premixed mortars modified with GNPs or GO is reported. Rheological properties of fresh mortars were investigated in terms of shear stress (or apparent viscosity) versus shear rate. Mortars were casted in bars and hardened for 28 or 14 days. Density, microstructure, compressive and flexural strength of hardened samples were evaluated and compared.Graphite nano-platelets (GNPs) and graphene oxide (GO) modify cementitious materials from the nanoto
the macroscale, resulting in enhanced mechanical properties, durability and, eventually, physical
multi-functionality. A systematic study on EN 998-2 premixed mortars modified with GNPs or GO is
reported. Rheological properties of fresh mortars were investigated in terms of shear stress (or apparent
viscosity) versus shear rate. Mortars were casted in bars and hardened for 28 or 14 days. Density,
microstructure, compressive and flexural strength of hardened samples were evaluated and compared
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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