Surface Cracking and Fractal Characteristics of Bending Fractured Polypropylene Fiber-Reinforced Geopolymer Mortar

Preparation and Research on Mechanical Properties of Eco-Friendly Geopolymer Grouting Cementitious Materials Based on Industrial Solid Wastes

Red mud (RM), a hazardous solid waste generated in the alumina production process, of which the mineral composition is mainly hematite, is unable to be applied directly in the cement industry due to its high alkalinity. With the rise of geopolymers, RM-based grouting materials play an essential role in disaster prevention and underground engineering. To adequately reduce the land-based stockpiling of solid wastes, ultrafine calcium oxide, red mud, and slag were utilized as the main raw materials to prepare geopolymers, the C-R-S (calcium oxide-red mud-slag) grouting cementitious materials. The direct impact of red mud addition on the setting time, fluidity, water secretion, mechanical properties, and rheological properties of C-R-S were also investigated. In addition, a scanning electron microscope (SEM), X-ray diffraction (XRD), three-dimensional CT (3D-CT), Fourier transform infrared spectroscopy (FT-IR), and other characterization techniques were used to analyze the microstructure and polymerization mechanism. The related results reveal that the increase in red mud addition leads to an enhanced setting time, and the C-R-S-40 grouting cementitious material (40% red mud addition) exhibits the best fluidity of 27.5 cm, the lowest water secretion rate of 5.7%, and a high mechanical strength of 57.7 MPa. The C-R-S polymer grout conforms to the Herschel-Bulkley model, and the fitted value of R2 is above 0.99. All analyses confirm that the preparation process of C-R-S grouting cementitious material not only substantially improves the utilization rate of red mud, but also provides a theoretical basis for the high-volume application of red mud in the field of grouting.

Potential utilization of waste plastic in sustainable geopolymer concrete production: A review

Plastic production has increased manifold over the last decade, with worldwide production reaching 400 million tonnes in 2021, and the trend is estimated to have a sharp rise in the future. Apart from being non-biodegradable, plastics are essentially durable, which makes waste plastic disposal extremely difficult and poses a threat to solid waste management. Disposal methods, including incinerating, landfilling, disposal into water bodies, etc., are having hazardous environmental impacts. Hence, plastic recycling is essential for ensuring sustainability. The construction industry is a major contributor to global warming primarily due to the Portland cement production emitting 6% of global CO2 production. Growing awareness has emphasized partial replacement of Portland cement with other binders, such as metakaolin, fly ash, slag, etc., to be used in conventional composites or complete replacement to yield geopolymer composites. Waste plastics can be used in geopolymer concrete (GPC) as a partial or complete replacement of natural aggregates or added as fibers. Based on the above background, various researchers have incorporated plastics in GPC in the form of aggregate replacement or fiber addition, justifying sustainability and enhancing GPC characteristics. Plastic supplementation in GPC is a relatively new research domain. An attempt has been made through the current review work to develop a comprehensive database established on various concrete characteristics through the globally available research performances involving various forms of plastic incorporation in GPC yielding plastic-supplemented GPC (PSGPC). A detailed plastic classification and varying forms are poised, with identified plastics elicited from its global acceptance so far in PSGPC production. Through various PSGPC characteristics like fresh, physical, mechanical, durability, and microstructural analysis with different plastic types and forms, the optimal waste plastic disposable range is entrenched justifying eco-friendly and sustainable concrete yield.

Experimental Study and Finite Element Analysis on the Flexural Behavior of Steel Fiber Reinforced Recycled Aggregate Concrete Beams

This paper reports on the flexural behavior of nine steel fiber reinforced-recycled aggregate concrete (SFRAC) beams through combined experimental and finite element analysis. The test parameters in this study include the steel fiber volume fraction, recycled aggregate replacement ratio, and concrete strength. The failure modes, crack development, load-deflection curves, and flexural bearing capacity of SFRAC beams are investigated in detail. The test results indicated that cracks and concrete crushing are formed in the compression zone of all specimens. The flexural bearing capacity of SFRAC beams increases with the increase of steel fiber volume fraction and concrete strength and the decrease of recycled aggregate replacement ratio. In addition, the results are compared with those of the finite element analysis. Based on the uniaxial compressive constitutive model of SFRAC, a new model for calculating the flexural bearing capacity of SFRAC beams is proposed. The prediction and test results are compared to evaluate the accuracy of the developed formula. The studies may provide a considerable reference for designing this type of structure in engineering practice.

Mechanical performance and environmental impact of normal strength concrete incorporating various levels of coconut fiber and recycled aggregates

This study presents the fresh and mechanical properties of concrete made with recycled aggregates (RAs) and coconut fibers (CFs), with an emphasis on the development of sustainable and ductile cementitious composite through the valorization of coconut and construction wastes. For this purpose, the effect of different percentages of CF, i.e., 0%, 1%, 2%, and 3% by wt. of cement, was examined on the mechanical and physical properties of concrete incorporating RA (0%, 30%, 50%, and 100%). To avoid the negative effect of CF on workability, a plasticizer was used to achieve the target workability. The performance of mixes was evaluated based on the results of workability, density, compressive strength (CS), splitting-tensile strength (STS), flexural strength (FS), and water absorption. The results showed that incorporation of 1-2% CF improved the CS and STS of concrete for each constant level of RA. The addition of 2% CF is recommended for maximum mechanical performance. Concrete incorporating 50% coarse RA with 2% CF showed CS comparable to conventional concrete. Concrete made with 100% coarse RA and 2% CF showed STS and FS comparable to that of conventional concrete. This study recommends the use of 2% CF along with plasticizer to attain the best mechanical performance. Despite comparable STS and FS, 100% RA concrete with 2% CF produced 25% lower CO₂ emissions than conventional concrete.

Optimized Alkali-Activated Slag-Based Concrete Reinforced with Recycled Tire Steel Fiber

This study employed Taguchi-Grey relational analysis to optimize the influences of binder content, the molarity of sodium hydroxide (SH) solution, alkaline solution to binder content (Al/Bi) ratio, water to alkali-activated solids (W/S) ratio, and sodium silicate to sodium hydroxide solution (SS/SH) ratio on the workability, setting time, and compressive strength of alkali-activated slag-based concrete (AASC). Then, the recycled tire steel fibers (RTSF) were introduced into the optimized mixture in different dosages, and the physical and mechanical properties of fiber-reinforced AASC (FR-AASC) were evaluated. RTSF inclusion negatively affected the workability and increased the density while slightly reducing the water absorption. Additionally, the compressive strength and flexural behavior of FR-AASC improved by increasing the RTSF content. The analysis of images taken from flexural specimens through the Digital Image Correlation technique (DIC) revealed that higher RTSF dosage caused a curved macro crack with several branches alongside, leading to a better post-cracking performance in terms of strength and toughness.

Editorial for Special Issue “Fractal and Fractional in Cement-Based Materials”

Cement-based materials, including cement paste, mortar, and concrete, are the most widely used construction materials in the world [...]

Influence of MgO on the Hydration and Shrinkage Behavior of Low Heat Portland Cement-Based Materials via Pore Structural and Fractal Analysis

Currently, low heat Portland (LHP) cement is widely used in mass concrete structures. The magnesia expansion agent (MgO) can be adopted to reduce the shrinkage of conventional Portland cement-based materials, but very few studies can be found that investigate the influence of MgO on the properties of LHP cement-based materials. In this study, the influences of two types of MgO on the hydration, as well as the shrinkage behavior of LHP cement-based materials, were studied via pore structural and fractal analysis. The results indicate: (1) The addition of reactive MgO (with a reactivity of 50 s and shortened as M50 thereafter) not only extends the induction stage of LHP cement by about 1–2 h, but also slightly increases the hydration heat. In contrast, the addition of weak reactive MgO (with a reactivity of 300 s and shortened as M300 thereafter) could not prolong the induction stage of LHP cement. (2) The addition of 4 wt.%–8 wt.% MgO (by weight of binder) lowers the mechanical property of LHP concrete. Higher dosages of MgO and stronger reactivity lead to a larger reduction in mechanical properties at all of the hydration times studied. M300 favors the strength improvement of LHP concrete at later ages. (3) M50 effectively compensates the shrinkage of LHP concrete at a much earlier time than M300, whereas M300 compensates the long-term shrinkage more effectively than M50. Thus, M300 with an optimal dosage of 8 wt.% is suggested to be applied in mass LHP concrete structures. (4) The addition of M50 obviously refines the pore structures of LHP concrete at 7 days, whereas M300 starts to refine the pore structure at around 60 days. At 360 days, the concretes containing M300 exhibits much finer pore structures than those containing M50. (5) Fractal dimension is closely correlated with the pore structure of LHP concrete. Both pore structure and fractal dimension exhibit weak (or no) correlations with shrinkage of LHP concrete.

Sustainable High-Performance Hydraulic Concrete

Concrete has always been indispensable as a material for the engineering and construction of hydraulic structures (e [...]

Investigation and Application of Fractal Theory in Cement-Based Materials: A Review

Cement-based materials, including cement and concrete, are the most widely used construction materials in the world. In recent years, the investigation and application of fractal theory in cement-based materials have attracted a large amount of attention worldwide. The microstructures of cement-based materials, such as the pore structures, the mesostructures, such as air voids, and the morphological features of powders, as well as the fracture surfaces and cracks, commonly present extremely complex and irregular characteristics that are difficult to describe in terms of geometry but that can be studied by fractal theory. This paper summarizes the latest progress in the investigation and application of fractal theory in cement-based materials. Firstly, this paper summarizes the principles and classification of the seven fractal dimensions commonly used in cement-based materials. These fractal dimensions have different physical meanings since they are obtained from various testing techniques and fractal models. Then, the testing techniques and fractal models for testing and calculating these fractal dimensions are introduced and analyzed individually, such as the mercury intrusion porosimeter (MIP), nitrogen adsorption/desorption (NAD), and Zhang’s model, Neimark’s model, etc. Finally, the applications of these fractal dimensions in investigating the macroproperties of cement-based materials are summarized and discussed. These properties mainly include the mechanical properties, volumetric stability, durability (e.g., permeability, frost and corrosion resistance), fracture mechanics, as well as the evaluation of the pozzolanic reactivity of the mineral materials and the dispersion state of the powders.