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1
Awan, Muhammad Maqbool Sadiq, Parviz Soroushian, Arshad Ali e Muhammad Yousaf Saqid Awan. "High-Performance Cementitious Matrix using Carbon Nanofibers". Indonesian Journal of Science and Technology 2, n. 1 (1 aprile 2017): 57. http://dx.doi.org/10.17509/ijost.v2i1.5989.
Testo completoAbstract (sommario):
Graphite nanomaterials would realize their reinforcement potential within cement-based materials when they are thoroughly dispersed and effectively bonded to cement hydrates. Thorough dispersion of graphite nanomaterials in the fresh cementitious matrix encounters challenges associated with the hydrophobic nature of nanomaterial surfaces and their strong tendency towards agglomeration via attractive van der Waals forces. Effective interfacial interactions with cement hydrates are further challenged by the relatively inert nature of nanomaterial surfaces. An experimental program was conducted with the objective of effectively utilizing both acid-oxidized and pristine carbon nanofibers towards reinforcement of high-performance cementitious pastes. Hybrid reinforcement systems comprising optimum volume fraction of carbon nanofibers and micro-scale fibers were also evaluated in cementitious matrices. The improvements in nanofiber dispersion and interfacial interactions resulting from acid-oxidation and use of proper dispersion techniques were found to bring about significant gains in the engineering properties of high-performance cementitious materials.
2
Al-Fakih, Amin, Ali Odeh, Mohammed Abdul Azeez Mahamood, Madyan A. Al-Shugaa, Mohammed A. Al-Osta e Shamsad Ahmad. "Review of the Properties of Sustainable Cementitious Systems Incorporating Ceramic Waste". Buildings 13, n. 8 (20 agosto 2023): 2105. http://dx.doi.org/10.3390/buildings13082105.
Testo completoAbstract (sommario):
Global carbon dioxide emissions can be attributed to Portland cement production; thus, an alternative cementitious system is essential to reduce cement demand. Ceramic waste powder (CWP), which contains high proportions of silica and alumina, has emerged as a promising alternative because of its chemical composition. This review discusses the potential of CWP as an alternative cementitious system and its effects on the physical, mechanical, and durability properties of cementitious systems. The findings revealed that the utilization of CWP in cementitious systems has positive effects on their physical, mechanical, and durability properties owing to the chemical composition of CWP, which can act as a filler material or contribute to the pozzolanic reaction. A pozzolanic reaction occurs between the silica and alumina in the CWP and calcium hydroxide in the cement, resulting in the production of additional cementitious materials such as calcium silicate hydrates and calcium aluminate hydrates. These additional materials can improve the strength and durability of cementitious systems. Various studies have demonstrated that CWP can be effectively used as a partial replacement for cement in cementitious systems. This can reduce the carbon footprint of construction activities by reducing the demand for Portland cement. However, the optimal amount and particle size of CWP have not been fully determined, and further research is required to optimize its use in cementitious systems. In addition, the technical and economic challenges associated with the use of CWP in construction must be further investigated to ensure its effective implementation.
3
Zhu, Zheyu, Zhongping Wang, Yue Zhou, Yuting Chen e Kai Wu. "Identification of Chemical Bonds and Microstructure of Hydrated Tricalcium Silicate (C3S) by a Coupled Micro-Raman/BSE-EDS Evaluation". Materials 14, n. 18 (8 settembre 2021): 5144. http://dx.doi.org/10.3390/ma14185144.
Testo completoAbstract (sommario):
Identifying the phase evolution and revealing the chemical bonds of hydrated cements accurately is crucial to regulate the performance of cementitious materials. In this paper, a coupled Raman/BSE-EDS analysis was proposed to determine the chemical bonds of tricalcium silicate hydrates and the interface transition zone (ITZ) between inner C-S-H and anhydrates. The results show that the Raman/BSE-EDS method can accurately identify the chemical bonds of inner C-S-H and inner ITZ regions, which confirms the mixed structure of inner C-S-H and nano calcium hydroxide (CH). The inner ITZ shows a lattice change region with a thickness of 700–1000 nm, which can be attributed to the pre-disassembly process of C3S crystal. The successful application of coupled Raman/BSE-EDS provides new insight into the hydration process and multi-structure features of traditional cementitious materials.
4
Takahashi, Keisuke, e Mari Kobayashi. "Utilization of Cement and Concrete for Deep Sea Infrastructure". ce/papers 6, n. 6 (dicembre 2023): 1291–94. http://dx.doi.org/10.1002/cepa.2996.
Testo completoAbstract (sommario):
AbstractThe use of cementitious materials in deep sea environments, focusing on the durability challenges of low‐temperature seawater and hydraulic pressure, are presented in this paper. The authors conducted laboratory and deep‐sea field experiments, thermodynamic calculation, and evaluated the performance of different types of binders in deep sea conditions. Durability of rebar in cementitious materials was investigated. In situ construction methods using cementitious materials was demonstrated on the deep‐sea field. Testing results revealed that deep sea conditions, especially low‐temperature seawater, can accelerate the disintegration of cement hydrates, and the use of pozzolanic admixture and calcium aluminate cement can improve its resistance. Our study provides valuable insights and applicability of cementitious materials to deep sea infrastructure construction.
5
Oproiu, Carmen-Lidia, Georgeta Voicu, Alina Bădănoiu e Adrian-Ionuţ Nicoară. "The Solidification/Stabilization of Wastewater (From a Landfill Leachate) in Specially Designed Binders Based on Coal Ash". Materials 14, n. 19 (27 settembre 2021): 5610. http://dx.doi.org/10.3390/ma14195610.
Testo completoAbstract (sommario):
The aim of this study is to assess the possibility to solidify/stabilize a liquid waste from a municipal waste landfill using binders based on coal ash (fly ash and bottom ash) and specially designed cements for waste treatment (INERCEM). The leaching test proved that all cementitious systems are efficient for the solidification/stabilization of the studied wastes and can reduce the leaching potential of heavy metals present in both liquid waste and coal ash. Therefore, these wastes cease to be a source of environmental pollution. X-ray diffraction (XRD) and thermal complex analysis (DTA-TG) were used to assess the nature and amount of compounds formed in these cementitious systems during the hydration and hardening processes; ettringite, calcium silicate hydrates and CaCO3 were the main compounds formed in these systems assessed by these methods. The microstructure of hardened specimens was assessed by scanning electronic microscopy (SEM); the presence of hydrate phases, at the surface of cenospheres present in fly ash, proved the high pozzolanic reactivity of this phase.
6
Lee, Heeyoung, Jongkyeong Seong e Wonseok Chung. "Correlation Analysis of Heat Curing and Compressive Strength of Carbon Nanotube–Cement Mortar Composites at Sub-Zero Temperatures". Crystals 11, n. 10 (28 settembre 2021): 1182. http://dx.doi.org/10.3390/cryst11101182.
Testo completoAbstract (sommario):
Concrete curing under sub-zero temperatures causes various problems, such as initial cracking and a decrease in mechanical strength. This study investigated the effect of sub-zero ambient temperature and multi-walled carbon nanotube (MWCNT) content on the heat and strength characteristics of heat-cured MWCNT cementitious composites. The experimental parameters were the application of heat curing, MWCNT content, use of an insulation box to achieve a closed system, and ambient temperature. The results showed that the internal temperature change of the MWCNT cementitious composite increased with the ambient temperature and MWCNT content. When an insulation box was installed, the maximum temperature change of the MWCNT cementitious composite during curing increased. Furthermore, heat curing increased the compressive strength of the cementitious composite. Moreover, a microstructure analysis using field-emission scanning electron microscopy verified the formation of a MWCNT network among the cement hydrates.
7
Renaudin, Guillaume, Adel Mesbah, Belay Dilnesa, Michel Francois e Barbara Lothenbach. "Crystal Chemistry of Iron Containing Cementitious AFm Layered Hydrates". Current Inorganic Chemistry 5, n. 3 (14 luglio 2015): 184–93. http://dx.doi.org/10.2174/1877944105666150420235831.
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Xu, Yue, Jian Xi Li e Li Li Kan. "Investigation on a New Hydraulic Cementitious Binder Made from Phosphogypsum". Advanced Materials Research 864-867 (dicembre 2013): 1923–28. http://dx.doi.org/10.4028/www.scientific.net/amr.864-867.1923.
Testo completoAbstract (sommario):
A new kind of high strength cementitious material is made from phosphogypsum (PG), active carbon and fly-ash. Through the orthogonal research, it was showed that the calcination temperature, retention time, dosage of active carbon and fly ash on the compressive strength of cementitious binder are the most important. The result also showed that, in the conditions of temperature 1200°C, time retention 30 min, dosage of active carbon 10%, dosage of fly ash 5%, the compressive strength of the cementitious material for 3d and 28d could reach to 46.35MPa and 92.70MPa, the content of sulfur trioxide was 11.60% accordingly. A lot of active mineral materials, such as dicalcium silicate, tricalcium silicate, tricalcium aluminate were formed in the calcination. The C-S-H gel, calcium hydroxide and ettringite were found in 3d and 28d hydrates. It is found that the lime saturation ratio and silica modulus need to be control between 0.40~0.65 and 4~8 in order to produce high strength cementitious material.
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Kaminskas, Rimvydas, e Brigita Savickaite. "Expanded Clay Production Waste as Supplementary Cementitious Material". Sustainability 15, n. 15 (1 agosto 2023): 11850. http://dx.doi.org/10.3390/su151511850.
Testo completoAbstract (sommario):
Global warming stands as one of the most significant challenges facing our planet, primarily due to the substantial emissions of greenhouse gases into the atmosphere. Among the major contributors to these emissions is the cement industry, which ranks as one of the largest sources of CO2 pollutants. To address this issue, a potential solution involves partially substituting cement with alternative materials, particularly waste generated by other industries. The aim of this study was to investigate the opportunity of using an industrial waste which originates from the cleaning of flue gas in the production of expanded clay as a supplementary cementitious material. The influence of expanded clay kiln dust on the properties of Portland cement was estimated by XRD, thermal, calorimetry and compressive strength analysis. The expanded clay kiln dust was used as received and it was additionally thermally activated at 600 °C. It was determined that the original dust can be distinguished by average pozzolanic activity; meanwhile, the pozzolanic activity of additionally activated waste increased by one third. Portland cement was replaced with both types of waste in various proportions. It was found that the additive of the investigated waste accelerates the primary hydration of Portland cement, generates the pozzolanic reaction, and incites the formation of calcium silicate hydrates and hydrates containing aluminum compounds. The addition of up to 25 wt.% of activated expanded clay kiln dust leads to a higher compressive strength of samples of Portland cement.
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Bernard, Ellina. "Research progress on magnesium silicate hydrate phases and future opportunities". RILEM Technical Letters 7 (1 settembre 2022): 47–57. http://dx.doi.org/10.21809/rilemtechlett.2022.162.
Testo completoAbstract (sommario):
This short letter summaries the latest research on the structure and thermodynamic modelling of the magnesium silicate hydrates (M-S-H) phases. M-S-H structure is comparable to hydrated clays, with a smaller and rounder microstructures compared to clay platelets. Similar to clay minerals, M-S-H can incorporate ions such as aluminium and hydrated exchangeable cations to compensate the negative surface charge. This fundamental understanding of M-S-H structure allowed to develop structure-based thermodynamic models, which can further help to optimise the conditions for M-S-H formation and its use as cementitious materials. Optimized binders containing M-S-H have the advantages of presenting: i) good mechanical properties, ii) dense microstructure and potentially good resistances to leaching and iii) low pH values. These types of binders could therefore be used for cement products with non-steel reinforcement, for the encapsulation of specific wastes, for products containing natural fibres or for the clay stabilisation, etc.
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Trochez, Jenny Johanna, Janneth Torres Agredo e Ruby Mejía de Gutiérrez. "Study of hydration of cement pastes added with used catalytic cracking catalyst (FCC) from a colombian refinery". Revista Facultad de Ingeniería Universidad de Antioquia, n. 55 (28 febbraio 2013): 26–34. http://dx.doi.org/10.17533/udea.redin.14678.
Testo completoAbstract (sommario):
This paper analyzes the effect of the incorporation of industrial waste from an oil refinery in Colombia, known as used catalytic cracking catalyst (FCC), in the hydration process of cementitious pastes. For this purpose, ordinary Portland cement pastes (OPC) added in percentages of 10 and 20% of FCC were prepared. The pozzolanic reactivity of the material and type of hydration products were determined by X-ray diffraction (XRD) and thermogravimetric analysis (TG / DTG). Additionally, the heat of hydration released was determined based on the standard ASTM C186. The results indicate that the hydration process of FCC blended cement is strongly exothermic as a consequence of its pozzolanic activity. The main phases present in the blended cement system were the calcium silicate hydrates (CSH gel), calcium aluminate hydrates (CAH) y calcium aluminosilicate hydrates (CASH), similar to the products obtained in metakaolin blended cement pastes.
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Cui, Lei. "Incorporation of Multiwalled Carbon Nanotubes to Ordinary Portland Cement (OPC): Effects on Mechanical Properties". Advanced Materials Research 641-642 (gennaio 2013): 436–39. http://dx.doi.org/10.4028/www.scientific.net/amr.641-642.436.
Testo completoAbstract (sommario):
Due to the outstanding mechanical properties, carbon nanotubes (CNTs) are considered to offer the probability to enhance the properties of high-performance cementitious composites，and to reduce ecological cost of construction materials. Recent work in the area of concrete materials research has shown the potentiality of improving concrete properties by adjusting the mic-structure of cement hydrates, addition of nanotubes and controlling the delivery of admixtures. In this study, the multiwall carbon nanotubes (MWCNTs) were effectively dispersed in the water solution by applying ultrasonic energy. The results show that small amount of effectively dispersed MWCNTs can visible increase the strength of the cementitious matrix.
13
Pyeon, Sujeong, Gyuyong Kim, Gyeongcheol Choe, Namgyu Park, Donggeun Jeong, Byungcheol Choi, Moonkyu Kim e Jeongsoo Nam. "Compressive-Strength Analysis of High-Strength Cementitious Composites Mixed with Red and Green Pigments". Applied Sciences 12, n. 15 (29 luglio 2022): 7667. http://dx.doi.org/10.3390/app12157667.
Testo completoAbstract (sommario):
We estimate the mechanical properties of pigment-containing ultra-high-strength cement composites (UHSCCs) and the pigment-induced changes in their physical properties via thermal and X-ray diffraction analyses. Hydrates in samples are analyzed using thermogravimetry. Additionally, the change in color expression with the UHSCC age is examined via the Commission Internationale de l’ Éclairage L*a*b* analysis. Correlation analysis is performed to determine linear relationships between experimental factors by calculating R2. A change in hydrate expression is confirmed as the strength increases with age. The pigment used affects the change in hydrate expression as well as color development. Correlation analysis of the results for all ages reveals that 5% red pigment mixing yields the highest R2 of 0.9858 in intensity-a*. The case of 10% red pigment mixing yields the lowest R2 of 0.5229 in intensity-b*. According to the amount of pigment used, we believe that quantitative results can be obtained by considering L* (contrast), rather than the relationship between intensity and color components. The appropriate mixing ratio based on the intensity expression of the red pigment is 3–8%, and the green pigment intensity and strength expression are inversely proportional. Our results can serve as a guideline for the performance development of pigmented cement-based composites.
14
Hlobil, Michal. "Microstructure-Based Evolution of Compressive Strength of Blended Mortars: A Continuum Micromechanics Approach". Advanced Materials Research 1144 (marzo 2017): 121–27. http://dx.doi.org/10.4028/www.scientific.net/amr.1144.121.
Testo completoAbstract (sommario):
The evolution of stiffness and strength belong to the most important properties of mortars. Motivated by an increasing demand for clinker substitution by supplementary cementitious materials (SCMs), this paper presents a multiscale model for prediction of elastic stiffness and compressive strength of blended mortars. Mortars are envisioned as hierarchically organized materials with microstructural phases spanning several orders of magnitude. On the scale of hundreds of nanometers, "CSH foam" consists of amorphous calcium silicate hydrates mixed with capillary pores which on the scale of hundreds of microns acts as a contiguous matrix reinforced by unhydrated clinker, SCM grains, and by crystalline hydration products forming "cement paste". The largest scale of observation describes mortar as quartz sand aggregate inclusions embedded into a contiguous cement paste matrix. Continuum micromechanics homogenization approach is used to upscale stiffness from calcium silicate hydrates, represented by needle-shaped ellipsoids, up to the scale of mortar. Macroscopic quasi-brittle failure of mortar is associated with a concentration of strain energy density-related microscopic stresses within a critically oriented needle-shaped hydrate in "CSH foam". Successful model validation on OPC-based and blended mortars provides strong evidence that continuum micromechanics is an efficient tool for quantification of stiffness and compressive strength.
15
Fu, Cheng Hong, Wen Ni, Hui Wu e De Zhong Li. "Hydrates and Paste Structure of Slag-Fly Ash Based Cementitious Materials". Advanced Materials Research 450-451 (gennaio 2012): 557–62. http://dx.doi.org/10.4028/www.scientific.net/amr.450-451.557.
Testo completoAbstract (sommario):
Cascade grinding mode is often applied to prepare Slag-Fly Ash Based cementitious materials with high volume of fly ash and slag and less cement clinker. This process has low water requirement and well fluidity, which is suitable to prepare HPC．When the W/C is 0.36, the 28d compressive strength is 58.93 Mpa, 28d flexural strength is 14.26 Mpa. By X-Ray diffraction analysis (XRD) and Scanning Electron Microscope (SEM) analysis the results show that main materials in grinded sample are well activated by mechanical force and chemical action; more Aft are produced and observed in 3 days hydration products and the great amount of C-S-H gel has continuously generated with the growth of hydration time. By Infrared(IR) analysis, the results show that in the hydration products, the network of Silicon Oxygen Tetrahedron and Aluminum Oxygen Tetrahedra have depolymerized significantly; in the hydration process and various raw materials mutually promoted each other to accelerate the hydration reaction. The hydrates and paste structure of slag-fly ash based cementitious materials were explained．
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Fu, Cheng Hong, Wen Ni, Hui Wu e De Zhong Li. "Hydrates and Paste Structure of Slag-Fly Ash Based Cementitious Materials". Advanced Materials Research 450-451 (gennaio 2012): 557–62. http://dx.doi.org/10.4028/scientific5/amr.450-451.557.
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Sun, Li, Hou Tian Zhang e Da Xing Qian. "Research on Performance of Concrete Made with Mineral Fillers and Fly Ash Admixed Desulphurization Gypsum". Applied Mechanics and Materials 584-586 (luglio 2014): 934–38. http://dx.doi.org/10.4028/www.scientific.net/amm.584-586.934.
Testo completoAbstract (sommario):
In order to improve the performance of concrete, reasonably use industrial waste and realize the sustainable development target of economy and environment, mineral admixtures have been widely used in concrete. But, widely using mineral admixtures reduces the overall performance of concrete, the reason is that the mineral admixtures dilutes the SO3 content in cementitious material, restricts generating the hydrates in the later concrete. If also add industrial by-products desulphurization gypsum in concrete, the added desulphurization gypsum as admixture not only improves the SO3 content in concrete, but also prime and crystal sulfate active, promote other admixtures pozzolanic effect, configuration effect and micro-aggregated effect. Experiments show that, when the desulphurization gypsum that added into cementitious material content is following 10%, in other words the desulphurization gypsum content is 3.1%, it can improve the mechanical performance of the concrete. Considering the early strength and work performance of cement, the desulphurization gypsum content that added into cementitious material should be controlled in the range of 8%, early strength increases by 16.9% and late strength also increases.
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Dai, Lei, e Xiao Xuan Deng. "The Relationship between Calcium Hydroxide Concentration in Pore Solution and the Strength of Stabilized Soils". Advanced Materials Research 989-994 (luglio 2014): 19–22. http://dx.doi.org/10.4028/www.scientific.net/amr.989-994.19.
Testo completoAbstract (sommario):
Under the same cement content, the stabilized soils, made of the soils with similar physical properties, may be significant difference in the strength. In this research, three groups of soils were selected, and the soils in each group are similar in physical properties. Strength and ions concentration in pore solution of the stabilized soils were investigated. The result reveals that calcium hydroxide (CH) concentration in pore solution of the stabilized soils might not reach to saturation due to soil consuming Ca2+and thus cause calcium silicate hydrates gels (C-S-H) and calcium aluminates hydrates gels (C-A-H) to form less. The cementitious hydrates are the main strength contributors of the stabilized soils. The Strengths of stabilized soils, the soils bearing similar physical properties, were almost identical as long as the CH concentrations in pore solution were saturated. The effect of chemical factors of soil on the strength of stabilized soil can be briefly attributed to the change of CH concentration in pore solution, and be further attributed to the influence of CH concentration on the amount of C-S-H and C-A-H formed in stabilized soils.
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Ioannidou, Katerina, Konrad J. Krakowiak, Mathieu Bauchy, Christian G. Hoover, Enrico Masoero, Sidney Yip, Franz-Josef Ulm, Pierre Levitz, Roland J. M. Pellenq e Emanuela Del Gado. "Mesoscale texture of cement hydrates". Proceedings of the National Academy of Sciences 113, n. 8 (8 febbraio 2016): 2029–34. http://dx.doi.org/10.1073/pnas.1520487113.
Testo completoAbstract (sommario):
Strength and other mechanical properties of cement and concrete rely upon the formation of calcium–silicate–hydrates (C–S–H) during cement hydration. Controlling structure and properties of the C–S–H phase is a challenge, due to the complexity of this hydration product and of the mechanisms that drive its precipitation from the ionic solution upon dissolution of cement grains in water. Departing from traditional models mostly focused on length scales above the micrometer, recent research addressed the molecular structure of C–S–H. However, small-angle neutron scattering, electron-microscopy imaging, and nanoindentation experiments suggest that its mesoscale organization, extending over hundreds of nanometers, may be more important. Here we unveil the C–S–H mesoscale texture, a crucial step to connect the fundamental scales to the macroscale of engineering properties. We use simulations that combine information of the nanoscale building units of C–S–H and their effective interactions, obtained from atomistic simulations and experiments, into a statistical physics framework for aggregating nanoparticles. We compute small-angle scattering intensities, pore size distributions, specific surface area, local densities, indentation modulus, and hardness of the material, providing quantitative understanding of different experimental investigations. Our results provide insight into how the heterogeneities developed during the early stages of hydration persist in the structure of C–S–H and impact the mechanical performance of the hardened cement paste. Unraveling such links in cement hydrates can be groundbreaking and controlling them can be the key to smarter mix designs of cementitious materials.
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Deng, Xiao Xuan, Lei Dai e Xin Huang. "Effect of Stabilizer and Molding Technics in Chemical Engineering on the Stabilization of Sulfate Rich Soil". Advanced Materials Research 577 (ottobre 2012): 65–68. http://dx.doi.org/10.4028/www.scientific.net/amr.577.65.
Testo completoAbstract (sommario):
In chemical engineering field, ettringite (AFt) formation effect the stabilization of sulfate rich soil mixed with cementitious materials. The different stabilizer compositions and twice molding technics may avoid and repair the destruction caused by AFt with decreasing the production rate of calcium silicate hydrates(C-S-H) and eliminating the void in stabilized soils. The results show that the strength of stabilized 5% sodium sulfate bearing soils, under above methods, are not less than that of the control ones, and the specimens keep steady after soaking in 5% sodium sulfate solution for 12 weeks.
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Ferreira, Walkíria Pederiva, Bacus de Oliveira Nahime, Michell Macedo Alves e Philippe Barbosa Silva. "Ecological cement: replacement of sugarcane bagasse ash derived from the sugar and alcohol industry". Concilium 24, n. 1 (12 gennaio 2024): 12–35. http://dx.doi.org/10.53660/clm-2673-24a02.
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Untreated sugarcane bagasse ash (CBCA) from two plants was investigated as a partial replacement for Portland cement (CP) with the aim of reducing environmental problems arising from clinker production by evaluating the feasibility of use as a supplementary cementitious material with pozzolanic reactivity. Mortars and pastes were produced with replacement rates of 25%, 30% and 35% of CBCA, with cures of 7, 14, 28, 90 and 180 days. The mortars were characterized in a fresh state through workability testing and in a hardened state through mechanical performance through compression and flexural tensile tests, water absorption and void index. The chemical composition, mineralogical composition, thermal analysis and formation of hydrate phases were carried out on the pastes and both ash. The ash tests showed that the CBCA-CM presented an amorphous halo and that it consumed portlandite in the process of forming the paste hydrates at 28 and 90 days. Mechanical performance tests showed that the ash has lower resistance at short ages and surpassed the control sample at long ages.
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Balopoulos, Victor D., Nikolaos Archontas e Stavroula J. Pantazopoulou. "Model of the Mechanical Behavior of Cementitious Matrices Reinforced with Nanomaterials". Journal of Engineering 2017 (2017): 1–10. http://dx.doi.org/10.1155/2017/7329540.
Testo completoAbstract (sommario):
CNTs and CNFs have been introduced as a nanoscale reinforcing material to cementitious composites, for stiffening and strengthening the microstructure. This technology is motivated by the need to control crack initiation in the cementitious gel before it propagates into visible crack formations. Experimental evidence supports this concept; however, testing at the nanoscale may only be conducted through nanoindentation, which has a limited range only providing localized results that cannot be extrapolated to general stress states. To evaluate the restraining action of nanomaterials in the gel microstructure, a computational mechanistic model has been developed where the material phases (gel, nanotubes, and pores) are modeled explicitly allowing for natural randomness in their distribution and orientation. Repeated analysis with identical input data reproduces the statistical scatter observed in laboratory tests on identical material samples. The formulation uses a discrete element approach; the gel structure is represented by a random network of hydrates and successfully reproduces the known trends in mechanical behavior of cementitious materials (pressure and restraint sensitive material behavior) and the small ratio of tensile to compressive strength. Simulations illustrate that it is possible to computationally reproduce the measured properties and behavior of fiber-reinforced cement composites using information from simple laboratory tests.
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ANZAI, Masaki, Tatsuhiko SAEKI e Tsuyoshi SAITO. "ESTIMATION OF THE EFFECT OF HYDRATES ON MASS TRANSFER IN HARDENED CEMENTITIOUS MATERIAL". Cement Science and Concrete Technology 74, n. 1 (31 marzo 2021): 67–73. http://dx.doi.org/10.14250/cement.74.67.
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Ahn, Ji Whan, Kwang Suk You, Gi Chun Han e Kye Hong Cho. "Stabilization Behavior of Heavy Metals Derived from Wastes on Cementitious Minerals and Hydrates". Materials Science Forum 510-511 (marzo 2006): 630–33. http://dx.doi.org/10.4028/www.scientific.net/msf.510-511.630.
Testo completoAbstract (sommario):
In this paper, the application of wastes as raw materials to cementitious mineral was investigated. A rolling slag, which contains plenty of heavy metals, was used as a raw material to synthesize calcium sulfoaluminate. It was found that the suitable burning temperature of CSA clinker is between 1,250°C and 1,300°C, and the residual content of heavy metals in the CSA clinker turned out sequentially as Cu, Zn, Cr, and Pb. According to the results of the investigation, it is believed that a large amount of the Cu, Zn and Cr present in the raw materials were fixed in the CSA clinker formed during the sintering process. It was further found that the distortion of the crystal morphology of hydrate, which was ettringite, took place according to the substitution of heavy metals during the hydration process.
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Deng, Wei, Pingfeng Fu, Guiwen Fang, Wan Zhu, Shan Li, Xiaofei Wang, Tianli Xue e Yuqi Chen. "Solidification/Stabilization of MSWI Fly Ash Using a Novel Metallurgical Slag-Based Cementitious Material". Minerals 12, n. 5 (10 maggio 2022): 599. http://dx.doi.org/10.3390/min12050599.
Testo completoAbstract (sommario):
Four industrial wastes, i.e., blast furnace slag, steel slag, desulfurization ash, and phosphoric acid sludge, were used to prepare a low-carbon binder, metallurgical slag-based cementitious material (MSCM). The feasibility of solidification/stabilization of municipal solid waste incineration (MSWI) fly ashes by MSCM were evaluated, and the immobilization mechanisms of heavy metals were proposed. The MSCM paste achieved 28-day strength of 35.2 MPa, showing its high-hydration reactivity. While the fly ash content was as high as 80 wt.%, the 28-day strength of MSCM-fly ash blocks reached 2.2 MPa, and the leaching concentrations of Pb, Zn, Cr, and Hg were much lower than the limit values of the Chinese landfill standard (GB 16889-2008). The immobilization rates of each heavy metal reached 98.75–99.99%, while four kinds of MSWI fly ashes were solidified by MSWI at fly ash content of 60 wt.%. The 28-day strength of binder-fly ash blocks had an increase of 104.92–127.96% by using MSCM to replace ordinary Portland cement (OPC). Correspondingly, the lower leachability of heavy metals was achieved by using MSCM compared to OPC. The mechanisms of solidification/stabilization treatment of MSWI fly ash by MSCM were investigated by XRD, SEM, and TG-DSC. Numerous hydrates, such as calcium silicate hydrate (C-S-H), ettringite (AFt), and Friedel’s salt, were observed in hardened MSCM-fly ash pastes. Heavy metals from both MSWI fly ash and MSCM could be effectively immobilized via adsorption, cation exchange, precipitation, and physical encapsulation.
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Yang, Zhijie, De Zhang, Chengyang Fang, Yang Jiao, Dong Kang, Changwang Yan e Ju Zhang. "Hydration Mechanisms of Alkali-Activated Cementitious Materials with Ternary Solid Waste Composition". Materials 15, n. 10 (18 maggio 2022): 3616. http://dx.doi.org/10.3390/ma15103616.
Testo completoAbstract (sommario):
Considering the recent eco-friendly and efficient utilization of three kinds of solid waste, including calcium silicate slag (CSS), fly ash (FA), and blast-furnace slag (BFS), alkali-activated cementitious composite materials using these three waste products were prepared with varying content of sodium silicate solution. The hydration mechanisms of the cementitious materials were analyzed by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. The results show that the composite is a binary cementitious system composed of C(N)-A-S-H and C-S-H. Si and Al minerals in FA and BFS are depolymerized to form the Q0 structure of SiO4 and AlO4. Meanwhile, β-dicalcium silicate in CSS hydrates to form C-S-H and Ca(OH)2. Part of Ca(OH)2 reacts with the Q0 structure of AlO4 and SiO4 to produce lawsonite and wairakite with a low polymerization degree of the Si-O and Al-O bonds. With the participation of Na+, part of Ca(OH)2 reacts with the Q0 structure of AlO4 and the Q3 structure of SiO4, which comes from the sodium silicate solution. When the sodium silicate content is 9.2%, the macro properties of the composites effectively reach saturation. The compressive strength for composites with 9.2% sodium silicate was 23.7 and 35.9 MPa after curing for 7 and 28 days, respectively.
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Lin, Yonghui, Dongqiang Xu e Xianhui Zhao. "Effect of Soda Residue Addition and Its Chemical Composition on Physical Properties and Hydration Products of Soda Residue-Activated Slag Cementitious Materials". Materials 13, n. 7 (10 aprile 2020): 1789. http://dx.doi.org/10.3390/ma13071789.
Testo completoAbstract (sommario):
Soda residue (SR), the solid waste of Na2CO3 produced by ammonia soda process, pollutes water and soil, increasing environmental pressure. SR has high alkalinity, and its main components are Ca(OH)2, NaCl, CaCl2, CaSO4, and CaCO3, which accords with the requirements of being an alkali activator. The aim of this research is to investigate the best proportion of SR addition and the contribution of individual chemical components in SR to SR- activated ground granulated blast furnace slag (GGBS) cementitious materials. In this paper, GGBS pastes activated by SR, Ca(OH)2, Ca(OH)2 + NaCl, Ca(OH)2 + CaCl2, Ca(OH)2 + CaSO4, and Ca(OH)2 + CaCO3 were studied regarding setting time, compressive strength (1 d, 3 d, 7 d, 14 d, 28 d), hydration products, and microstructure. The results demonstrate that SR (24%)-activated GGBS pastes possess acceptable setting time and compressive strength (29.6 MPa, 28 d), and its hydration products are calcium silicate hydrate (CSH) gel, calcium aluminum silicate hydrates (CASH) gel and Friedel’s salt. CaCl2 in SR plays a main role in hydration products generation and high compressive strength of SR- activated GGBS pastes.
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Manzano, H., J. S. Dolado, A. Guerrero e A. Ayuela. "Mechanical properties of crystalline calcium-silicate-hydrates: comparison with cementitious C-S-H gels". physica status solidi (a) 204, n. 6 (giugno 2007): 1775–80. http://dx.doi.org/10.1002/pssa.200675359.
Testo completo
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Yoneyama, Akira, Heesup Choi, Masumi Inoue, Jihoon Kim, Myungkwan Lim e Yuhji Sudoh. "Effect of a Nitrite/Nitrate-Based Accelerator on the Strength Development and Hydrate Formation in Cold-Weather Cementitious Materials". Materials 14, n. 4 (20 febbraio 2021): 1006. http://dx.doi.org/10.3390/ma14041006.
Testo completoAbstract (sommario):
Recently, there has been increased use of calcium-nitrite and calcium-nitrate as the main components of chloride- and alkali-free anti-freezing agents to promote concrete hydration in cold weather concreting. As the amount of nitrite/nitrate-based accelerators increases, the hydration of tricalcium aluminate (C3A phase) and tricalcium silicate (C3S phase) in cement is accelerated, thereby improving the early strength of cement and effectively preventing initial frost damage. Nitrite/nitrate-based accelerators are used in larger amounts than usual in low temperature areas below −10 °C. However, the correlation between the hydration process and strength development in concrete containing considerable nitrite/nitrate-based accelerators remains to be clearly identified. In this study, the hydrate composition (via X-ray diffraction and nuclear magnetic resonance), pore structures (via mercury intrusion porosimetry), and crystal form (via scanning electron microscopy) were determined, and investigations were performed to elucidate the effect of nitrite/nitrate-based accelerators on the initial strength development and hydrate formation of cement. Nitrite/nitrate-AFm (aluminate-ferret-monosulfate; AFm) was produced in addition to ettringite at the initial stage of hydration of cement by adding a nitrite/nitrate-based accelerator. The amount of the hydrates was attributed to an increase in the absolute amounts of NO2− and NO3− ions reacting with Al2O3 in the tricalcium aluminate (C3A phase). Further, by effectively filling the pores, it greatly contributed to the enhancement of the strength of the hardened cement product, and the degree of the contribution tended to increase with the amount of addition. On the other hand, in addition to the occurrence of cracks due to the release of a large amount of heat of hydration, the amount of expansion and contraction may increase, and it is considered necessary to adjust the amount used for each concrete work.
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Brevet, Haris, Rose-Marie Dheilly, Nicolas Montrelay, Koffi Justin Houessou, Emmanuel Petit e Adeline Goullieux. "Effects of Flaxseed Mucilage Admixture on Ordinary Portland Cement Fresh and Hardened States". Applied Sciences 14, n. 9 (30 aprile 2024): 3862. http://dx.doi.org/10.3390/app14093862.
Testo completoAbstract (sommario):
France is Europe’s leading producer of flaxseed. This seed is rich in omega-3, energy, and protein for animals, but it also contains anti-nutritional factors such as mucilage. Thus, mucilage must be removed and could be used as a bio-admixture in cementitious materials development, reducing the environmental impact of cementitious materials. This study aims to valorize the usage of flaxseed mucilage (FM) in ordinary Portland cement. FM caused macroscopic and microscopic changes in the materials studied. The higher the concentration, the greater the changes were. The admixed samples showed an exponentially concentration-dependent delay in setting. FM degradation products induced by the cementitious conditions accentuated the delay. However, this delay in setting did not affect the hydrates’ growth in the material. In fact, FM showed a “delay accelerator” behavior, meaning that once hydration began, it was accelerated as compared to a reference. Macroscopically, FM induced significant flocculation, increasing material porosity and carbonation. Consequently, bulk density and thermal conductivity were reduced. At the highest amount of FM admixture (0.75% w/w), FM allowed bridge formation between Ca(OH)2 crystals, which can improve the mechanical properties of mortars. Because FM is highly hygroscopic, it has the capability to absorb water and subsequently release it gradually and under controlled conditions into the cement matrix. Therefore, regulation of water diffusion from the mucilage may induce the self-healing properties responsible for mechanical properties similar to that of the reference in the medium to long term.
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Kobayashi, Yutaro, e Tsutomu Sato. "Mineralogical Evolution of High-pH/Low-pH Cement Pastes in Contact with Seawater". Minerals 14, n. 3 (8 marzo 2024): 285. http://dx.doi.org/10.3390/min14030285.
Testo completoAbstract (sommario):
In facilities for the geological disposal of radioactive waste in coastal areas, the long-term alteration of cementitious materials in engineered barriers is expected to occur due to the ingress of groundwater derived from seawater. Although the reaction between cement and seawater has been studied, the alteration behavior caused by the reaction between seawater and low-pH cement, which is expected to be used in a disposal facility, has not yet been clarified. In this study, the effects of cement type on cement–seawater interactions were investigated, and the chemical stability and mineral evolution of cement pastes caused by reactions with seawater were determined. The dissolution of cement hydrates occurred upon increased contact with seawater, and the formation of secondary minerals, including carbonate and Mg-containing minerals, was observed. The progress of dissolution depended on the mineral composition of the initially formed cement hydrates, and low-pH cement containing pozzolanic materials showed less resistance to seawater. Differences in pH and Si concentration that are due to the type of cement used had a strong influence on the evolution of minerals (especially Mg-containing minerals), implying that the formed mineral species possibly affect the migration characteristics of radionuclide.
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Althoey, Fadi, e Yaghoob Farnam. "Reducing Damage Due to Chemical Reactions in Concrete Exposed to Sodium Chloride: Quantification of a Deleterious Chemical Phase Change Formation". MATEC Web of Conferences 271 (2019): 07004. http://dx.doi.org/10.1051/matecconf/201927107004.
Testo completoAbstract (sommario):
It has been shown that sodium chloride can react with the tricalcium aluminate (C3A) and its hydrates, leading to a formation of a deleterious chemical phase change during thermal cycling. It is believed that this chemical phase change is implicated in the premature deterioration of concrete pavements in the cold regions. This work examines the potential formation of the deleterious chemical phase change in several cementitious pastes made using different types of portland cement and supplementary cementitious materials (SCMs). The amount of the chemical phase change was quantified using a low-temperature differential scanning calorimetry. The results indicated that the formation of the chemical phase change can be reduced by using cements with low C3A content. The addition of SCMs showed different effects on the chemical phase change formation. Slag and Class F fly ash could reduce the amount of the chemical phase change due to only the dilution effect whereas silica fume could significantly reduce the amount of the chemical phase change due to the dilution effect as well as pozzolanic reactions. Adversely, the addition of Class C fly ash showed a negative effect through increasing the formation of the chemical phase change.
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Arend, Johannes, Alexander Wetzel e Bernhard Middendorf. "Fluorescence Microscopy of Superplasticizers in Cementitious Systems: Applications and Challenges". Materials 13, n. 17 (24 agosto 2020): 3733. http://dx.doi.org/10.3390/ma13173733.
Testo completoAbstract (sommario):
In addition to the desired plasticizing effect, superplasticizers used in high and ultra-high performance concretes (UHPC) influence the chemical system of the pastes and for example retardation of the cement hydration occurs. Thus, superplasticizers have to be chosen wisely for every material composition and application. To investigate the essential adsorption of these polymers to particle surfaces in-situ to overcome several practical challenges of superplasticizer research, fluorescence microscopy is useful. In order to make the superplasticizer polymers visible for this microscopic approach, they are stained with fluorescence dyes prior the experiment. In this work, the application of this method in terms of retardation and rheological properties of sample systems is presented. The hydration of tricalcium oxy silicate (C3S) in combination with different polycarboxylate ether superplasticizers is observed by fluorescence microscopy and calorimetry. Both methods can identify the retarding effect, depending on the superplasticizer’s chemical composition. On the other hand, the influence of the superplasticizers on the slump of a ground granulated blast furnace slag/cement paste is correlated to fluorescence microscopic adsorption results. The prediction of the efficiency by microscopic adsorption analysis succeeds roughly. At last, the possibility of high-resolution imaging via confocal laser scanning microscopy is presented, which enables the detection of early hydrates and their interaction with the superplasticizers.
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Homayoonmehr, Reza, Ali Akbar Ramezanianpour, Faramarz Moodi, Amir Mohammad Ramezanianpour e Juan Pablo Gevaudan. "A Review on the Effect of Metakaolin on the Chloride Binding of Concrete, Mortar, and Paste Specimens". Sustainability 14, n. 22 (14 novembre 2022): 15022. http://dx.doi.org/10.3390/su142215022.
Testo completoAbstract (sommario):
Chloride binding is a complex phenomenon in which the chloride ions bind with hydrated Portland cement (PC) phases via physical and chemical mechanisms. However, the current utilization of clays as (Al)-rich supplementary cementitious materials (SCMs), such as metakaolin (MK), can affect the chloride-binding capacity of these concrete materials. This state-of-the-art review discusses the effect of clay-based SCMs on physical and chemical chloride binding with an emphasis on MK as a high-reactivity clay-based SCM. Furthermore, the potential mechanisms playing a role in physical and chemical binding and the MK effect on the hydrated cement products before and after exposure to chloride ions are discussed. Recent findings have portrayed competing properties of how MK limits the physical chloride-binding capacity of MK-supplemented concrete. The use of MK has been found to increase the calcium silicate hydrates (CSH) content and its aluminum to silicon (Al/Si) ratio, but to reduce the calcium to silicon (Ca/Si) ratio, which reduces the physical chloride-binding capacity of PC-clay blended cements, such as limestone calcined clay cements (LC3). By contrast, the influence of MK on the chemical chloride capacity is significant since it increases the formation of Friedel’s salt due to an increased concentration of Al during the hydration of Portland cement grains. Recent research has found an optimum aluminum to calcium (Al/Ca) ratio range, of approximately 3 to 7, for maximizing the chemical binding of chlorides. This literature review highlights the optimal Al content for maximizing chloride binding, which reveals a theoretical limit for calcined clay addition to supplementary cementitious materials and LC3 formulations. Results show that 5–25% of replacements increase bound chloride; however, with a higher percentage of replacements, fresh and hardened state properties play a more pivotal role. Lastly, the practical application of four binding isotherms is discussed with the Freundlich isotherm found to be the most accurate in predicting the correlation between free and bound chlorides. This review discusses the effects of important cement chemistry parameters, such as cation type, sulfate presence, carbonation, chloride concentration, temperature, and applied electrical fields on the chloride binding of MK-containing concretes—important for the durable formulation of LC3.
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Reiterman, Pavel, Ondřej Holčapek, Ondřej Zobal e Martin Keppert. "Freeze-Thaw Resistance of Cement Screed with Various Supplementary Cementitious Materials". REVIEWS ON ADVANCED MATERIALS SCIENCE 58, n. 1 (1 aprile 2019): 66–74. http://dx.doi.org/10.1515/rams-2019-0006.
Testo completoAbstract (sommario):
Abstract This paper describes a study of the effect of partial replacement of ordinary Portland cement (OPC) by various mineral additives in the screed mixtures. Ceramic powder, blast furnace slag and fly ash were gradually employed in increments of 12.5 wt.% up to 50 wt.% to replace OPC. The mixtures were designed to a constant consistency. The influence of mineral additives was evaluated in terms of the air content in the fresh mixtures, the compressive strength, the flexural strength and the freeze-thaw resistance and using non-destructive measurements after 28 and 90 days. The accompanied paste sampleswere analysed using thermogravimetry to monitor the hydration process by means of total bound water content. The decrease in the mechanical properties and the frost resistance of the mixtures with the mineral additives were recorded, because of the necessity for a larger addition of water. According to the valid standards for concrete screed related to the frost resistance, it could be concluded that maximal suitable cement replacement contents are 12.5, 37.5 and 50 wt.% for ceramic powder, fly ash and blast furnace slag, respectively. The freeze-thaw resistance of the studied materials was found to be strongly related to the content of CSH and CAH hydrates.
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Kim, Hayeon, e H. M. Son. "Effects of Air Entrainment on Bacterial Viability in Cement Paste". Materials 15, n. 6 (15 marzo 2022): 2163. http://dx.doi.org/10.3390/ma15062163.
Testo completoAbstract (sommario):
This study investigated the effect of air entrainment (AE) on bacterial viability in cementitious materials. Specimens were fabricated with Portland cement, urea, calcium lactate, and ureolytic bacteria, and with varying amounts of an AE agent. Specimens with different amounts of the AE agent were fabricated, and then a compressive strength test, quantitative polymerase chain reaction, X-ray diffraction, and thermogravimetry were used to investigate the mechanical properties, viability of bacteria, and hydrates of the specimens. The highest compressive strength was achieved by the specimen with 0.3% AE agent, while the compressive strength of the specimens decreased considerably when the incorporated AE agent was over 0.6%, due to increased porosity. The quantitative polymerase chain reaction result showed that the cell number of the viable bacteria was increased by incorporation of the AE agent, which also corresponded with an increase in CaCO3 due to microbial mineral formation. The obtained result confirmed the positive effect of AE agent incorporation in cementitious materials containing bacterial admixtures, as the viability of bacteria, which play a vital role in self-healing efficiency of concrete, was increased by the space provided by the AE agent in the cement matrix. In addition, the quantity of CaCO3 and the compressive strength were highest when 0.3% AE agent was incorporated.
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Cho, Byoung Hooi. "Exploring the Potential of Sr2+ for Improving the Post-Hardening Strength and Durability Characteristics of Cement Paste Composites". Applied Sciences 14, n. 5 (23 febbraio 2024): 1841. http://dx.doi.org/10.3390/app14051841.
Testo completoAbstract (sommario):
This study investigates the effects of strontium ions on enhancing the post-hardening strength and durability characteristics of hydrated cement composites, exploring their potential use as a rehabilitation method for aging concrete structures. A 30% strontium nitrate solution served as the source of strontium ions. Cement paste specimens with a water-to-cement ratio of 0.5, cured for 28 days, were submerged in the 30% strontium nitrate solution to facilitate strontium ion penetration. Compressive and flexural strength tests were conducted on the specimens and compared to those cured in deionized water. Moreover, the durability performance, including surface abrasion resistance, water sorptivity, and porosity, was examined. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffractometry (XRD) analyses were also carried out to investigate the microscopic morphology and chemical characteristics of the specimens. Results indicated that the strontium-treated specimens exhibited notable enhancements in both compressive and flexural strengths, especially in flexural strength. The specimens also demonstrated improved surface abrasion resistance, decreased water absorption, and a marked reduction in porosity. SEM analysis revealed a densified microstructure in the strontium-treated cement paste specimens, and EDS and XRD analyses showed changes in their morphology and chemical compositions and structures, indicating the formation of new types of hydrates. Accordingly, this study suggests that the strontium ion treatment method has significant potential for the maintenance and restoration of aging cementitious materials.
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Tang, Kangwei, Feng Zeng, Liang Shi, Long Zhu, Zining Chen e Feng Zhang. "Mechanical Behavior of Hydrated-Lime–Liquid-Stabilizer-Treated Granular Lateritic Soils". Sustainability 15, n. 6 (22 marzo 2023): 5601. http://dx.doi.org/10.3390/su15065601.
Testo completoAbstract (sommario):
Granular lateritic soil is commonly used for road construction in humid tropical and subtropical regions. However, the high plastic clay content and poor particle distribution of some laterite materials make them unsuitable for bases and subbases. Lime treatment is a widely used method for improving problematic lateritic soil, and liquid ionic stabilizers are considered an environmentally friendly solution for reinforcing such soils. However, using only lime or only stabilizers may not be optimal. This study investigated the effect of treating granular lateritic soil with hydrated lime and a new liquid stabilizer, Zhonglu-2A (ZL-2A). A series of indoor tests, including compaction, California bearing ratio, and unconfined compressive strength tests, were conducted to evaluate the effects of hydrated lime content and stabilizer content on the mechanical properties, mineralogical composition, and microstructure of the soil. The results show that an increase in hydrated lime dosage increases the optimal moisture content and decreases the maximum dry density. The CBR of lime-stabilizer-treated laterite was at least 2–3 times higher than that of the only-lime-treated soil. The highest CBR was observed in samples treated with 0.2‰ ZL-2A stabilizer. The sample with 6% lime and 0.2‰ ZL-2A stabilizer exhibited the highest unconfined compressive strength, and a nearly linear increase was observed between the unconfined compressive strength and CBR. Further investigation of the stabilization mechanism using X-ray diffraction mineralogy analysis and scanning electron microscopy revealed that the inorganic substances of the ZL-2A stabilizer and the hydrated lime provided the basic conditions for the reaction and generated cementitious hydrates on the clay particles. The mixture of granular lateritic soil and hydrated lime was wrapped by the ZL-2A stabilizer, forming a complex spatial structure and improving the strength of the soil. To improve the bearing capacity of subgrades in actual subgrade engineering, a combination of a liquid ionic stabilizer and lime should be used to treat laterite.
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Marsiske, Maximilian R., Christian Debus, Fulvio Di Lorenzo, Ellina Bernard, Sergey V. Churakov e Cristina Ruiz-Agudo. "Immobilization of (Aqueous) Cations in Low pH M-S-H Cement". Applied Sciences 11, n. 7 (26 marzo 2021): 2968. http://dx.doi.org/10.3390/app11072968.
Testo completoAbstract (sommario):
Incorporation of heavy metal ions in cement hydrates is of great interest for the storage and immobilization of toxic, hazardous, and radioactive wastes using cementitious matrix. Magnesium silicate hydrate (M-S-H) is a low pH alternative cementitious binder to commonly used Portland cement. Low pH cements have been considered as promising matrix for municipal and nuclear waste immobilization in the last decades. It is however crucial to assure that the incorporation of secondary ions is not detrimental for the formation of the hydration products. Herein, we investigate the early stages of formation of M-S-H from electrolyte solutions in presence of a wide range of metal cations (LiI, BaII, CsI, CrIII, FeIII, CoII, NiII, CuI, ZnII, PbII, AlIII). The final solid products obtained after 24 h have been characterized via powder X-ray diffraction (PXRD), attenuated total reflectance-Fourier transformed infrared spectroscopy (FTIR-ATR), elemental analysis via energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM). In all the experiments, the main precipitated phase after 24 h was confirmed to be M-S-H with a ratio (total metal/Si) close to one. The obtained M-S-H products showed strong immobilization capacity for the secondary metal cations and can incorporate up to 30% of the total metal content at the early stages of M-S-H formation without significantly delaying the nucleation of the M-S-H. It has been observed that presence of Cr, Co, and Fe in the solution is prolonging the growth period of M-S-H. This is related to a higher average secondary metal/total metal ratio in the precipitated material. Secondary phases that co-precipitate in some of the experiments (Fe, Pb, Ni, and Zn) were also effectively trapped within in the M-S-H matrix. Barium was the only element in which the formation of a secondary carbonate phase isolated from the M-S-H precipitates was detected.
40
Galan, Isabel, Lukas Briendl, Maria Thumann, Florian Steindl, Rudolf Röck, Wolfgang Kusterle e Florian Mittermayr. "Filler Effect in Shotcrete". Materials 12, n. 19 (1 ottobre 2019): 3221. http://dx.doi.org/10.3390/ma12193221.
Testo completoAbstract (sommario):
The effects of fine limestone powder on the early hydration of cementitious systems accelerated by means of alkali-free aluminum sulfate based products, commonly used for shotcrete applications, were investigated in the course of laboratory and real scale tests. In binary (CEM I + limestone) and ternary (CEM I + limestone + slag) systems the addition of fine limestone led to an enhancement of the hydration degree and strength development at early times (<24 h). The formation of ettringite, aluminate hydrates, and C–S–H is affected by the joint action of the setting accelerator and the fine limestone. Accelerator and limestone, in combination with the cement, can be optimized to enhance ettringite and silicate reaction, in some cases coupled with aluminate reaction inhibition, to produce mixes suitable for sprayed concrete applications. Such optimization can help to reduce the cement content in the mixes without compromising the early strength development of the shotcrete.
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Wang, Qing, Zhao Yang Ding, J. Zhang, L. G. Qiu e Zhi Tong Sui. "Study on Slag-Based Geopolymer Hydration Process". Key Engineering Materials 477 (aprile 2011): 67–71. http://dx.doi.org/10.4028/www.scientific.net/kem.477.67.
Testo completoAbstract (sommario):
As environment-friendly or green cement, the geopolymer cementitious material has high early age strength, good volume stability and durability. In this paper, the mechanical properties of geopolymer hydrates at different hydrating ages were studied by changing the oxide content of raw material. The results showed that the chemical-combined water kept increasing as hydrating age prolonged, and reached the maximum at n(SiO2)/n(Al2O3)=3.9, n(H2O)/n(SiO2)=2.3 and n(Na2O)/n(Al2O3)=0.6. With the development of hydration, the pH value of geopolymer paste showed fluctuated: pH value kept increased at the age of 1d～3d, then decreased at the age of 3d～7d, at the age of 7d～14d the pH value increased again and at last it remained constant at the age of 14d～28d. 28d compressive strength of geopolymer paste reached the maximum as chemical-combined water content was 0.09g～0.10g and pH value was 10～11.
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El Bitouri, Youssef. "The Effect of Temperature on the Structural Build-Up of Cement Pastes". CivilEng 4, n. 4 (28 novembre 2023): 1198–213. http://dx.doi.org/10.3390/civileng4040066.
Testo completoAbstract (sommario):
The structural build-up of cementitious materials is the subject of more and more attention since it conditions several processes such as formwork pressure and multi-layer casting. However, this phenomenon originating from flocculation and chemical changes is complex and its reversibility is not clearly elucidated. The aim of this paper is to examine the effect of temperature on the reversibility of structural build-up. The results show that irreversible structural build-up remains negligible despite a rise in temperature. It represents between 0.5–7.3% of the total structural build-up. The addition of SCMs allows for a decrease in this irreversible structural build-up. Therefore, a large part of the chemical contribution is expected to be reversible. The effect of temperature can be explained by the increase in the dissolution rate leading to an increase in flocculation and to the bridging effect induced by early hydrates. Finally, the results suggest that the interparticle distance could be the key parameter governing the irreversibility of structural build-up.
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Gameiro, André, António Santos Silva, R. Veiga e Ana Velosa. "Phase and Microstructural Characterization of Lime-MK Blended Mixes". Materials Science Forum 730-732 (novembre 2012): 135–40. http://dx.doi.org/10.4028/www.scientific.net/msf.730-732.135.
Testo completoAbstract (sommario):
Metakaolin (MK) is nowadays a well-known pozzolanic material used in cement-based materials. Its benefits are related to its great pozzolanic reactivity when compared with some others pozzolanic materials, like fly ash or ground-granulated blast furnace slag. When MK reacts with calcium hydroxide, cementitious products are formed. It is known that the main phases produced during its pozzolanic reaction at ambient temperature are calcium silicate hydrates (CSH), stratlingite (C2ASH8) and calcium aluminate hydrate (C4AH13). However, in literature there are several discrepancies regarding these phases stability, namely the transformation of stratlingite and C4AH13 into hydrogarnet (C3AH6) at long term. The consequences of that instability are a reduction in the porosity and a loss of microstructural strength that can induce a complete material degradation. The MK is a material with great potential in Portugal, since there is a large abundance of kaolinitic clays, however its development is not yet achieved. In order to answer this demand a research project was initiated with the aim of optimizing the production of MK in Portugal and enhancing the durability of aerial calcitic lime mortars, to be mainly used in conservation and restoration of historical buildings. With the objective of studying the compounds formed in lime/MK and their stability during time, we have prepared different lime/MK ratio pastes (molar ratios). These lime/MK pastes were stored at saturated conditions (RH > 95%) and 23 ± 2 °C temperature being analysed at several ages by TGA-DTA, XRD and SEM-EDS. In this paper the results obtained are presented and discussed.
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Jabbar, Adil. "Using Cementitious Materials to Enhance Concrete Properties and Improve the Environment: A Review". Wasit Journal of Engineering Sciences 11, n. 3 (1 dicembre 2023): 140–54. http://dx.doi.org/10.31185/ejuow.vol11.iss3.482.
Testo completoAbstract (sommario):
Cement production significantly contributes to carbon dioxide emissions, which increase global warming. Therefore, reducing cement consumption can support efforts to reduce that risk. On the other hand, the consumption of industrial wastes in concrete production contributes to improving the environment. Industrial waste can be used as supplementary cementitious materials (SCMs) to enhance concrete properties. This paper reviews the effects of SCMs, such as silica fume, fly ash, metakaolin, and ground granulated blast furnace slag (GGBFS), on the properties of fresh and hardened concrete. The findings show that SCMs enhance packing density and reduce permeability. The impact of SCMs on concrete properties appears after a period of curing depending on the availability of calcium hydroxide and activity index. Calcium hydroxide produced from cement hydration reacts with silicates of SCMs to produce additional calcium-silicate hydrates that enhance concrete strength and minimize the relatively large size of calcium hydroxide, which lowers porosity. Silica fume and metakaolin raise water demands and reduce workability, while GGBFS and fly ash improve workability. Silica fume, metakaolin, and (10) μm particle size of GGBFS increase early-age strength, (10-45) μm particle size of GGBFS enhances strength after 28 days, while fly ash raises the strength after 90 days. For low cement content, 10 % or less silica fume, (10-30) % fly ash, (10-20) % GGBFS or metakaolin are considered the perfect percentage to arrive at best strength. For high cement content, (25-30) % silica fume or 40 % fly ash is considered the optimum ratio to reach the highest strength.
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KAWABATA, Yuichiro, Kazuo YAMADA e Hiromichi MATSUSHITA. "RELATION OF PHASE COMPOSITION OF CEMENT HYDRATES WITH SUPPLEMENTARY CEMENTITIOUS MATERIALS TO THE SUPPRESSING EFFECT ON ASR EXPANSION". Journal of Japan Society of Civil Engineers, Ser. E2 (Materials and Concrete Structures) 69, n. 4 (2013): 402–20. http://dx.doi.org/10.2208/jscejmcs.69.402.
Testo completo
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Izadifar, Mohammadreza, Jorge S. Dolado, Peter Thissen e Andres Ayuela. "Interactions between Reduced Graphene Oxide with Monomers of (Calcium) Silicate Hydrates: A First-Principles Study". Nanomaterials 11, n. 9 (31 agosto 2021): 2248. http://dx.doi.org/10.3390/nano11092248.
Testo completoAbstract (sommario):
Graphene is a two-dimensional material, with exceptional mechanical, electrical, and thermal properties. Graphene-based materials are, therefore, excellent candidates for use in nanocomposites. We investigated reduced graphene oxide (rGO), which is produced easily by oxidizing and exfoliating graphite in calcium silicate hydrate (CSHs) composites, for use in cementitious materials. The density functional theory was used to study the binding of moieties, on the rGO surface (e.g., hydroxyl-OH/rGO and epoxide/rGO groups), to CSH units, such as silicate tetrahedra, calcium ions, and OH groups. The simulations indicate complex interactions between OH/rGO and silicate tetrahedra, involving condensation reactions and selective repairing of the rGO lattice to reform pristine graphene. The condensation reactions even occurred in the presence of calcium ions and hydroxyl groups. In contrast, rGO/CSH interactions remained close to the initial structural models of the epoxy rGO surface. The simulations indicate that specific CSHs, containing rGO with different interfacial topologies, can be manufactured using coatings of either epoxide or hydroxyl groups. The results fill a knowledge gap, by establishing a connection between the chemical compositions of CSH units and rGO, and confirm that a wet chemical method can be used to produce pristine graphene by removing hydroxyl defects from rGO.
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Lefever, Gerlinde, Dimitrios G. Aggelis, Nele De Belie, Marc Raes, Tom Hauffman, Danny Van Hemelrijck e Didier Snoeck. "The Influence of Superabsorbent Polymers and Nanosilica on the Hydration Process and Microstructure of Cementitious Mixtures". Materials 13, n. 22 (17 novembre 2020): 5194. http://dx.doi.org/10.3390/ma13225194.
Testo completoAbstract (sommario):
Superabsorbent polymers (SAPs) are known to mitigate the development of autogenous shrinkage in cementitious mixtures with a low water-to-cement ratio. Moreover, the addition of SAPs promotes the self-healing ability of cracks. A drawback of using SAPs lies in the formation of macropores when the polymers release their absorbed water, leading to a reduction of the mechanical properties. Therefore, a supplementary material was introduced together with SAPs, being nanosilica, in order to obtain an identical compressive strength with respect to the reference material without additives. The exact cause of the similar compressive behaviour lies in the modification of the hydration process and subsequent microstructural development by both SAPs and nanosilica. Within the present study, the effect of SAPs and nanosilica on the hydration progress and the hardened properties is assessed. By means of isothermal calorimetry, the hydration kinetics were monitored. Subsequently, the quantity of hydration products formed was determined by thermogravimetric analysis and scanning electron microscopy, revealing an increased amount of hydrates for both SAP and nanosilica blends. An assessment of the pore size distribution was made using mercury intrusion porosimetry and demonstrated the increased porosity for SAP mixtures. A correlation between microstructure and the compressive strength displayed its influence on the mechanical behaviour.
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Jiang, Ruixin, e Zhengjun Wang. "Performance and Heavy Metal Analysis of Graphite Tailings Cured Using Cementitious Materials". Buildings 14, n. 2 (17 febbraio 2024): 537. http://dx.doi.org/10.3390/buildings14020537.
Testo completoAbstract (sommario):
The massive accumulation of graphite tailings causes serious environmental pollution, mainly from heavy metal pollution. Therefore, this article introduces a method of using graphite tailings as a high-content main material, cement as a small component of the auxiliary cementitious material, and clay as a substitute for cement. The compressive strength and permeability of graphite tailing–solidified material (GT, GT–Clay) were tested, and the effect of clay partially replacing cement as an auxiliary cementitious agent on GT–Clay performance was compared. In addition, inductively coupled plasma mass spectrometry (ICP) was used to analyze the effect of the graphite tailing placement time on the heavy metal content, as well as the changes in the GT heavy metal leaching concentration and its heavy metal content under outdoor freeze–thaw conditions. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to elucidate the microstructural changes in the GT–Clay. The experimental results show that, as the substitution of clay for cement increased from 0 to 50%, the compressive strength of the 90% GT–Clay gradually decreased, and the permeability also increased. The compressive strength of 95% GT–Clay did not show significant changes, but the permeability increased, and when mixed with quicklime, gypsum, and silica fume, the permeability decreased. The Ni and As in graphite tailings fluctuated significantly with the placement time. The heavy metal leaching concentrations of the 90% GT and 95% GT were below the standard limit, and Cd, As, and Ni in GT were potential sources of pollution. The analysis of the microscopic test results showed that the hydration products of the GT–Clay included ettringite, Ca(OH)2, and calcium silicate hydrates. The hydration product stabilized and filled the gaps between the tailing particles, thereby cementing them together. Not only did it improve the mechanical strength of GT, it also reduced the permeability and heavy metal leaching rate. This study provides a new analytical approach to applying graphite tailings for environmental treatment.
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Wang, Yunfeng, Bo Jiang, Ying Su, Xingyang He, Yingbin Wang e Sangkeun Oh. "Hydration and Compressive Strength of Activated Blast-Furnace Slag–Steel Slag with Na2CO3". Materials 15, n. 13 (21 giugno 2022): 4375. http://dx.doi.org/10.3390/ma15134375.
Testo completoAbstract (sommario):
Alkali-activated materials (AAMs) are regarded as an alternative cementitious material for Portland cement with regards to sustainable development in construction. The purpose of this work is to investigate the properties of activated blast-furnace slag (BFS)–steel slag (SS) with sodium carbonate (NC), taking into account BFS fineness and Na2O equivalent. The hydration was investigated by rheological behavior and pH development. The hydrates were characterized by TG-DTG and XRD, and the microstructure was analyzed by SEM and MIP. Results showed that the rheology of activated BFS-SS pastes was well-fitted with the H-B model and affected by BFS fineness and NC mixture ratio. It was found that BFS fineness and NC ratio played a crucial role in the initial alkalinity of SS-BFS-based pastes. As such, lower BFS fineness and higher NC ratio can dramatically accelerate the formation of reaction products to endow higher mechanical strength of BFS-SS pastes. However, the effect of NC ratio on the microstructure development of BFS-SS based AAMs was more obvious than BFS fineness.
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Xu, Linglin, Siyu Liu, Peiming Wang e Zhenghong Yang. "Influence of Mineral Additives on the Efflorescence of Ettringite-Rich Systems". Materials 14, n. 18 (21 settembre 2021): 5464. http://dx.doi.org/10.3390/ma14185464.
Testo completoAbstract (sommario):
Efflorescence is aesthetically undesirable to all cementitious materials products and mainly results from the carbonation of hydrates and salt precipitation. Alternative binders without portlandite formation theoretically have much lower efflorescence risk, but in practice, the efflorescence of ettringite-rich systems is still serious. This study reports the impacts of mineral additives on the efflorescence of ettringite-rich systems and the corresponding microstructural evolution. The effects of silica fume, limestone powder, and diatomite on efflorescence and the capillary pore structure of mortars were investigated from a multi-scale analysis. The composition and microstructure of efflorescent phases were revealed by optical microscope (O.M.), in-situ Raman spectroscopy, and Scanning Electron Microscopy (SEM). Results indicate that the addition of mineral additives can efficiently inhibit the efflorescence of reference, especially with silica fume. Similar to the ettringite-rich system, the efflorescence substances of all modifies are composed of ettringite and CaCO3, indicating that the addition of mineral admixture does not lead to chemical reactions, lower capillary absorption coefficient of mineral additives modified specimen, the denser pore structure and the lower efflorescence degree.