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3 pages, 171 KiB

Open AccessEditorial

Editorial: Microstructures and Mechanical Properties of Cement-Based Composites

by Lik-Ho Tam, Ao Zhou, Zechuan Yu and Chao Wu

Materials 2023, 16(20), 6636; https://doi.org/10.3390/ma16206636 - 11 Oct 2023

Viewed by 795

Abstract

In recent years, with the fast development of the technology and the economy associated with the growth of the global population, the construction of economical, sustainable, and eco-friendly infrastructures with improved ductility, resistance to external elements, and durability has increased the need for [...] Read more.

In recent years, with the fast development of the technology and the economy associated with the growth of the global population, the construction of economical, sustainable, and eco-friendly infrastructures with improved ductility, resistance to external elements, and durability has increased the need for the development of high-performance construction materials [...] Full article

(This article belongs to the Special Issue Microstructures and Mechanical Properties of Cement-Based Composites)

Research

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18 pages, 5508 KiB

Open AccessArticle

Preparation and Micromechanics of Red Sandstone–Phosphogypsum–Cement Composite Cementitious Materials

by Chuiyuan Kong, Bin Zhou, Rongxin Guo, Feng Yan, Rui Wang and Changxi Tang

Materials 2023, 16(13), 4549; https://doi.org/10.3390/ma16134549 - 23 Jun 2023

Cited by 7 | Viewed by 1234

Abstract

Based on the physical and chemical properties of red sandstone (RS), RS is used to produce composite cementitious materials. The flowability, mechanical strength, and micromechanics of a red sandstone–cement binary cementitious material (RS-OPC) were investigated as functions of the amount of RS replacing [...] Read more.

Based on the physical and chemical properties of red sandstone (RS), RS is used to produce composite cementitious materials. The flowability, mechanical strength, and micromechanics of a red sandstone–cement binary cementitious material (RS-OPC) were investigated as functions of the amount of RS replacing the cement (OPC). Additionally, the feasibility of producing red sandstone–phosphogypsum–cement composite materials (RS-PG-OPC) using the phosphogypsum (PG)- enhanced volcanic ash activity of RS was investigated. The products of hydration and microstructures of RS-OPC and RS-PG-OPC were analyzed by XRD, FTIR, TG-DTG, and SEM. RS enhanced the flowability of RS-OPC relative to the unmodified cement slurry but lowered its mechanical strength, according to the experiments. When the quantity of OPC replaced was greater than 25%, the compressive strength after 28 days was substantially reduced, with a maximum reduction of 78.8% (RS-60). The microscopic mechanism of RS-OPC suggested that the active SiO₂ in the RS can react with Ca(OH)₂ to produce C-S-H but can only utilize small quantities of Ca(OH)₂, confirming the low volcanic ash activity of RS. RS was responsible for dilution and filling. The incorporation of 5% PG into RS-PG-OPC slowed the hydration process compared with RS-OPC without PG but also increased the flowability and aided in the later development of the mechanical strength. This was primarily because the addition of PG provided the system with sufficient Ca²⁺ and SO₄²⁻ to react with [Al(OH)6]³⁻ to form ettringite (AFt), therefore accelerating the dissolution of Al³⁺ in RS to generate more AFt and C-(A)-S-H gels. To some extent, this excites the volcanic ash of RS. Therefore, if there is an abundance of waste RS in the region and a lack of other auxiliary cementitious materials, a sufficient quantity of PG and a finely powdered waste RS component can be used to replace cementitious materials prepared with OPC to reduce the mining of raw OPC materials. Full article

(This article belongs to the Special Issue Microstructures and Mechanical Properties of Cement-Based Composites)

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14 pages, 6552 KiB

Open AccessArticle

Study on the Performance and Mechanism of Cement Solidified Desulfurization Manganese Residue

by Shicheng Wang, Fang Wang, Jialing Che and Lihua Ma

Materials 2023, 16(11), 4184; https://doi.org/10.3390/ma16114184 - 4 Jun 2023

Cited by 3 | Viewed by 1414

Abstract

Desulfurized manganese residue (DMR) is an industrial solid residue produced by high-temperature and high-pressure desulfurization calcination of electrolytic manganese residue (EMR). DMR not only occupies land resources but also easily causes heavy metal pollution in soil, surface water, and groundwater. Therefore, it is [...] Read more.

Desulfurized manganese residue (DMR) is an industrial solid residue produced by high-temperature and high-pressure desulfurization calcination of electrolytic manganese residue (EMR). DMR not only occupies land resources but also easily causes heavy metal pollution in soil, surface water, and groundwater. Therefore, it is necessary to treat the DMR safely and effectively so that it can be used as a resource. In this paper, Ordinary Portland cement (P.O 42.5) was used as a curing agent to treat DMR harmlessly. The effects of cement content and DMR particle size on flexural strength, compressive strength, and leaching toxicity of a cement-DMR solidified body were studied. The phase composition and microscopic morphology of the solidified body were analyzed by XRD, SEM, and EDS, and the mechanism of cement-DMR solidification was discussed. The results show that the flexural strength and compressive strength of a cement-DMR solidified body can be significantly improved by increasing the cement content to 80 mesh particle size. When the cement content is 30%, the DMR particle size has a great influence on the strength of the solidified body. When the DMR particle size is 4 mesh, the DMR particles will form stress concentration points in the solidified body and reduce its strength. In the DMR leaching solution, the leaching concentration of Mn is 2.8 mg/L, and the solidification rate of Mn in the cement-DMR solidified body with 10% cement content can reach 99.8%. The results of XRD, SEM, and EDS showed that quartz (SiO₂) and gypsum dihydrate (CaSO₄·2H₂O) were the main phases in the raw slag. Quartz and gypsum dihydrate could form ettringite (AFt) in the alkaline environment provided by cement. Mn was finally solidified by MnO₂, and Mn could be solidified in C-S-H gel by isomorphic replacement. Full article

(This article belongs to the Special Issue Microstructures and Mechanical Properties of Cement-Based Composites)

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18 pages, 9281 KiB

Open AccessArticle

Mechanical and Durability Evaluation of Metakaolin as Cement Replacement Material in Concrete

by Mohammed Najeeb Al-Hashem, Muhammad Nasir Amin, Ali Ajwad, Muhammad Afzal, Kaffayatullah Khan, Muhammad Iftikhar Faraz, Muhammad Ghulam Qadir and Hayat Khan

Materials 2022, 15(22), 7868; https://doi.org/10.3390/ma15227868 - 8 Nov 2022

Cited by 8 | Viewed by 2375

Abstract

Due to the increasing prices of cement and its harmful effect on the environment, the use of cement has become highly unsustainable in concrete. There is a considerable need for promoting the use of cement replacement materials. This study investigates the effect of [...] Read more.

Due to the increasing prices of cement and its harmful effect on the environment, the use of cement has become highly unsustainable in concrete. There is a considerable need for promoting the use of cement replacement materials. This study investigates the effect of variable percentages of metakaolin (MK) on the mechanical and durability performance of concrete. Kaolin clay (KC) was used in the current research to prepare the MK by the calcination process; it was ground in a ball mill to its maximum achievable fineness value of 2550 m²/Kg. Four replacement levels of MK, i.e., 5%, 10%, 15%, and 20% by weight of cement, in addition to control samples, at a constant water-to-cement (w/c) ratio of 0.55 were used. For evaluating the mechanical and durability performance, 27 cubes (6 in. × 6 in. × 6 in.) and 6 cylinders (3.875 in. diameter, 2 in. height) were cast for each mix. These samples were tested for compressive strength under standard conditions and in an acidic environment, in addition to being subjected to water permeability, sorptivity, and water absorption tests. Chemical analysis revealed that MK could be used as pozzolana as per the American Society for Testing and Materials (ASTM C 618:2003). The results demonstrated an increased compressive strength of concrete owing to an increased percentage of MK in the mix with aging. In particular, the concrete having 20% MK after curing under standard conditions exhibited 33.43% higher compressive strength at 90 days as compared to similarly aged control concrete. However, with increasing MK, the workability of concrete decreased drastically. After being subjected to an acid attack (immersing concrete cubes in 2% sulfuric acid solution), the samples exhibited a significant decrease in compressive strength at 90 days in comparison to those without acid attack at the same age. The density of acid attack increased with increasing MK with a maximum corresponding to 5% MK concrete. The current findings suggest that the local MK has the potential to produce good-quality concrete in a normal environment. Full article

(This article belongs to the Special Issue Microstructures and Mechanical Properties of Cement-Based Composites)

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25 pages, 10921 KiB

Open AccessArticle

Change of the Structural Properties of High-Performance Concretes Subjected to Thermal Effects

by Grzegorz Piotr Kaczmarczyk, Daniel Wałach, Eduardo Natividade-Jesus and Rui Ferreira

Materials 2022, 15(16), 5753; https://doi.org/10.3390/ma15165753 - 20 Aug 2022

Cited by 4 | Viewed by 1322

Abstract

The paper refers to studies of the structure of high-performance concrete with polypropylene fibre at different dosages. The authors see a research gap in the study of the effect of adding polypropylene fibre on the parameters of concrete exposed to high temperatures. The [...] Read more.

The paper refers to studies of the structure of high-performance concrete with polypropylene fibre at different dosages. The authors see a research gap in the study of the effect of adding polypropylene fibre on the parameters of concrete exposed to high temperatures. The study takes into account the thermal effect—groups of samples were heated to 200 °C, 400 °C and 600 °C. The authors carried out basic tests to describe the changes in density, ultrasonic tests, uniaxial compression strength tests and tensile tests by splitting. The positive effect of polypropylene fibres is mainly observed between 20 °C and 200 °C. The melting of polypropylene fibres causes a delay in the development of micro-cracks in the structure of these concretes compared to HPC. Adding polypropylene fibres to the mixtures also increased the speed of ultrasonic wave propagation in the medium. The research was deepened with tomographic imaging. A description of the splitting surface was carried out. The results of tensile by splitting tests clearly show an increase in the relative failure area for unheated concretes in proportion to the number of fibres used. Changes in splitting surfaces under the influence of temperature are graphically illustrated. Furthermore, differences in the samples under the influence of heating at high temperatures are presented. Finally, the porosity development of all sample groups before and after heating at all temperatures is described. Full article

(This article belongs to the Special Issue Microstructures and Mechanical Properties of Cement-Based Composites)

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19 pages, 8289 KiB

Open AccessArticle

Effect of Magnesium Salt (MgCl₂ and MgSO₄) on the Microstructures and Properties of Ground Granulated Blast Furnace Slag (GGBFS)-Based Geopolymer

by Kun Zhang, Kaiqiang Wang, Zhimao Liu, Zhiwu Ye, Baifa Zhang, Deng Lu, Yi Liu, Lijuan Li and Zhe Xiong

Materials 2022, 15(14), 4911; https://doi.org/10.3390/ma15144911 - 14 Jul 2022

Cited by 8 | Viewed by 1771

Abstract

The use of seawater to prepare geopolymers has attracted significant research attention; however, the ions in seawater considerably influence the properties of the resulting geopolymers. This study investigated the effects of magnesium salts and alkaline solutions on the microstructure and properties of ground-granulated-blast-furnace-slag-based [...] Read more.

The use of seawater to prepare geopolymers has attracted significant research attention; however, the ions in seawater considerably influence the properties of the resulting geopolymers. This study investigated the effects of magnesium salts and alkaline solutions on the microstructure and properties of ground-granulated-blast-furnace-slag-based geopolymers. The magnesium salt–free Na₂SiO₄-activatied geopolymer exhibited a much higher 28 d compressive strength (63.5 MPa) than the salt-free NaOH-activatied geopolymer (31.4 MPa), with the former mainly containing an amorphous phase (C-(A)-S-H gel) and the latter containing numerous crystals. MgCl₂·6H₂O addition prolonged the setting times and induced halite and Cl-hydrotalcite formation. Moreover, mercury intrusion porosimetry and scanning electron microscopy revealed that the Na₂SiO₄-activated geopolymer containing 8.5 wt% MgCl₂·6H₂O exhibited a higher critical pore size (1624 nm) and consequently, a lower 28 d compressive strength (30.1 MPa) and a more loosely bound geopolymer matrix than the salt-free geopolymer. In contrast, MgSO₄ addition had less pronounced effects on the setting time, mineral phase, and morphology. The Na₂SiO₄-activated geopolymer with 9.0 wt% MgSO₄ exhibited a compressive strength of 42.8 MPa, also lower than that of the salt-free geopolymer. The results indicate that Cl⁻ is more harmful to the GGBFS-based geopolymer properties and microstructure than SO₄²⁻ is. Full article

(This article belongs to the Special Issue Microstructures and Mechanical Properties of Cement-Based Composites)

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13 pages, 3634 KiB

Open AccessArticle

Numerical Investigation of Triaxial Shear Behaviors of Cemented Sands with Different Sampling Conditions Using Discrete Element Method

by Xuqun Zhang, Zhaofeng Li, Pei Tai, Qing Zeng and Qishan Bai

Materials 2022, 15(9), 3337; https://doi.org/10.3390/ma15093337 - 6 May 2022

Cited by 4 | Viewed by 1431

Abstract

In cemented sand, the influences of the sampling factors (i.e., the curing time, cement–sand ratio, and initial void ratio) on the triaxial shear behavior were investigated using discrete element method. Cemented sand samples with different initial conditions were prepared and subjected to the [...] Read more.

In cemented sand, the influences of the sampling factors (i.e., the curing time, cement–sand ratio, and initial void ratio) on the triaxial shear behavior were investigated using discrete element method. Cemented sand samples with different initial conditions were prepared and subjected to the consolidated drained triaxial shearing test. In the simulations, the peak strength, residual strength, and pre-peak stiffness of cemented sand were enhanced by increasing the curing time and cement–sand ratio, and the enhancements could be explained by the increases in bond strength and bond number. Resulting from the increases of these two sampling factors, bond breakage emerged at a greater axial strain but lower intensity. However, some uncommon phenomena were generated; that is, the contractive but strain-softening response occurred in the sample with a curing time of 3 days, and the shear band and the strain-hardening behavior coexisted in the sample with a cement–sand ratio of 1%. The peak strength and pre-peak stiffness were also enhanced by decreasing the initial void ratio, more distinctly than by increasing the curing time and cement–sand ratio. However, the residual strength, bond breakage, and failure pattern with the persistence of shear band were insensitive to this change. Full article

(This article belongs to the Special Issue Microstructures and Mechanical Properties of Cement-Based Composites)

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13 pages, 2086 KiB

Open AccessArticle

Experimental Investigation on the Influencing Factors of Compressive Strength of Foamed Lightweight Material Utilizing Completely Decomposed Granite

by Pei Tai, Zhongkui Chen, Zhaofeng Li, Rui Chen, Hu Lu and Yongjia Li

Materials 2022, 15(3), 1060; https://doi.org/10.3390/ma15031060 - 29 Jan 2022

Cited by 4 | Viewed by 1520

Abstract

The utilization of construction waste soil to produce foamed concrete together with cement and a foaming agent is a promising method for waste recycling. Completely decomposed granite (CDG), which is widely available in southern China, was selected as a typical construction waste soil [...] Read more.

The utilization of construction waste soil to produce foamed concrete together with cement and a foaming agent is a promising method for waste recycling. Completely decomposed granite (CDG), which is widely available in southern China, was selected as a typical construction waste soil in foamed material production. The Taguchi method was applied to study the influence of various parameters on compressive strength, including cement dosage, CDG dosage, water to solid materials ratio (W/M), fine particles content, and gravel particles content. Analysis of variance (ANOVA) on a CDG-based sample showed that all factors have significant effects on compressive strength and the most effective parameter was cement dosage, followed in sequence by CDG dosage, W/M, gravel particles content, and fine particles content. However, only cement dosage and W/M influence the internal structure significantly during water/vacuum-immersion tests. The relationship between micro-pore structure and compressive strength suggested that with the decrease of open porosity, the compressive strength showed an increasing trend. This study reveals the possibility of CDG as a raw material for foamed lightweight soil and provides a technical reference of production procedure. Full article

(This article belongs to the Special Issue Microstructures and Mechanical Properties of Cement-Based Composites)

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