Editorial

2 pages, 153 KiB

Open AccessEditorial

Editorial for Special Issue Cement and Construction Materials

by Payam Hosseini and Baoguo Han

Crystals 2022, 12(10), 1490; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12101490 - 20 Oct 2022

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Cement-based materials have always been the main choice for the construction of civil engineering infrastructures [...] Full article

(This article belongs to the Special Issue Advances in Cement-Based and Construction Materials)

Research

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12 pages, 9527 KiB

Open AccessArticle

The Effect of Doping High Volume Magnesium Sulfate on Properties of Magnesium Oxychloride Cement

by Qing Huang, Weixin Zheng, Ying Li, Chenggong Chang, Jing Wen, Jinmei Dong and Xueying Xiao

Crystals 2022, 12(6), 857; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12060857 - 17 Jun 2022

Cited by 4 | Viewed by 1495

Abstract

The composite gelling system of chlorine and magnesium thioxide was prepared by mixing different mass fractions of magnesium sulfate solution into MOC. Detailed studies regarding the influences of magnesium sulfate replacing magnesium chloride on the setting time, compressive strength, and water resistance of [...] Read more.

The composite gelling system of chlorine and magnesium thioxide was prepared by mixing different mass fractions of magnesium sulfate solution into MOC. Detailed studies regarding the influences of magnesium sulfate replacing magnesium chloride on the setting time, compressive strength, and water resistance of magnesium oxychloride cement (MOC) have been carried out in this paper. The phase composition and micro morphology of the hydration products in the mixed system were analyzed by XRD and SEM. The results show that the addition of magnesium sulfate prolongs the setting time and reduces the compressive strength of the mixed MOC. Compared with the primordial MOC system, the water resistance of the mixed system improved, with the mixed system exhibiting optimal water resistance when the mass fraction of magnesium sulfate was 30%. The phases of the mixed system were composed of 5Mg(OH)₂·MgCl₂·8H₂O and 5Mg(OH)₂·MgSO₄·7H₂O phases. The microscopic morphology shows that the interior of air-cured MOC was composed of a large number of needle-like crystals, and continuous crystal structures have close contact and a strong bonding force. Cracks and pores appear on the surface after submerging in water, and the crystallization state of the internal crystals becomes worse. The compressive strength and water stability of MOC were closely related to the crystal morphology. Full article

(This article belongs to the Special Issue Advances in Cement-Based and Construction Materials)

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10 pages, 2413 KiB

Open AccessArticle

Ecofriendly and Electrically Conductive Cementitious Composites Using Melamine-Functionalized Biochar from Waste Coffee Beans

by Junyoung Jeong, Giyoung Jeon, Seongwoo Ryu and Joo Ha Lee

Crystals 2022, 12(6), 820; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12060820 - 09 Jun 2022

Cited by 4 | Viewed by 1931

Abstract

Owing to the increasing generation of waste coffee powder and the biochar from this waste being considered as alternative conductive carbon fillers, we developed eco-friendly and electrically conductive cementitious composites using biochar from waste coffee beans, which were directly pyrolyzed into eco-friendly and [...] Read more.

Owing to the increasing generation of waste coffee powder and the biochar from this waste being considered as alternative conductive carbon fillers, we developed eco-friendly and electrically conductive cementitious composites using biochar from waste coffee beans, which were directly pyrolyzed into eco-friendly and electrically conductive biochar. Via carbonization and graphitization, cyclic organic carbon precursors were transformed into sp2-bonded carbon structures and then functionalized with melamine. The non-covalent functionalization process driven by the electromagnetic process accelerated the mass production and enhanced the monodispersive properties of the cementitious composites. Thus, the melamine-functionalized biochar cementitious composites exhibited an electrical conductivity of 3.64 × 10⁻⁵ ± 1.02 × 10⁻⁶ S/cm (n = 6), which corresponded to an improvement of over seven orders of that of pure concrete. Furthermore, the percolation threshold of biochar was between 0.02 and 0.05 wt.%; thus, an effective conductive network could be formed using low additions of functionalized biochar. As a result, in this study, electrically conductive cementitious composites were developed using waste coffee powder converted into carbon nanomaterials through a newly introduced process of non-covalent functionalization with melamine. Full article

(This article belongs to the Special Issue Advances in Cement-Based and Construction Materials)

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18 pages, 4307 KiB

Open AccessFeature PaperArticle

Influence of Fineness of Wheat Straw Ash on Autogenous Shrinkage and Mechanical Properties of Green Concrete

by Muhammad Nasir Amin, Muhammad Armaghan Siffat, Khan Shahzada and Kaffayatullah Khan

Crystals 2022, 12(5), 588; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050588 - 22 Apr 2022

Cited by 5 | Viewed by 1686

Abstract

This study investigates the effectiveness of an agricultural by-product wheat straw ash (WSA) as an internal curing agent in reducing the autogenous shrinkage of high-performance concrete (HPC). After incineration under different controlled time–temperature conditions, grinding and sieving were performed to obtain two different [...] Read more.

This study investigates the effectiveness of an agricultural by-product wheat straw ash (WSA) as an internal curing agent in reducing the autogenous shrinkage of high-performance concrete (HPC). After incineration under different controlled time–temperature conditions, grinding and sieving were performed to obtain two different grades of fine WSA (F-WSA) and superfine WSA (SF-WSA). Subsequently, material characterization tests were carried out, followed by tests for mechanical properties and autogenous shrinkage potential of concrete incorporating 10% and 20% F-WSA and SF-WSA as a partial replacement of cement. The results demonstrated slightly higher compressive and tensile strength of concrete containing SF-WSA compared to control, whereas concrete with F-WSA demonstrated comparable strength results to that of the control concrete. Moreover, a significant reduction in 7 days’ autogenous shrinkage was observed in concrete containing 10% and 20% F-WSA by 42% and 25% compared to that of control concrete, respectively. This reduction in autogenous shrinkage increased further to 57% and 40% for concrete with 10% and 20% SF-WSA, respectively. The results of microstructural investigations on paste samples such as FTIR, TGA, and N₂ adsorption analyses revealed a more refined and compact microstructure of paste samples with increasing fineness of WSA due to the formation of a more densified C-S-H phase. The improvement of the microstructure is attributable to the improved pozzolanic properties of SF-WSA compared with F-WSA. Full article

(This article belongs to the Special Issue Advances in Cement-Based and Construction Materials)

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15 pages, 4673 KiB

Open AccessArticle

Gas Permeability Prediction of Mortar Samples Based on Different Methods

by Zirui Cheng, Yiren Wang, Jihui Zhao and Chunlong Huang

Crystals 2022, 12(5), 581; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050581 - 21 Apr 2022

Cited by 5 | Viewed by 1419

Abstract

Gas permeability is one of the durability indicators of cementitious materials; permeability predictions based on pore characteristics are useful approaches to obtain gas permeability when experimental conditions are limited. In this study, the gas permeabilities of mortar are predicted by using the Hagen–Poiseuille [...] Read more.

Gas permeability is one of the durability indicators of cementitious materials; permeability predictions based on pore characteristics are useful approaches to obtain gas permeability when experimental conditions are limited. In this study, the gas permeabilities of mortar are predicted by using the Hagen–Poiseuille equation combined with a processed backscattered electron (BSE) image, the Katz–Thompson equation, and the Winland model with pore parameters obtained from MIP tests. The permeabilities calculated by the BSE method are different from the measured value because the observation range is limited and it is difficult to completely display the actual pore structure. The Katz–Thompson equation underestimates the contribution of coarse capillary pores on permeability, thus the results are two orders of magnitude lower than the measured value. The results obtained from the Winland model are close to the measured permeabilities, which indicate that the Winland model is the most suitable method for predicting gas permeability among the three methods described in this paper. Full article

(This article belongs to the Special Issue Advances in Cement-Based and Construction Materials)

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17 pages, 7418 KiB

Open AccessArticle

Experimental Study on the Influence of Dry–Wet Cycles on the Static and Dynamic Characteristics of Fiber-Modified Lime and Fly Ash-Stabilized Iron Tailings at Early Curing Age

by Ping Jiang, Xuhui Zhou, Jian Qian and Na Li

Crystals 2022, 12(5), 568; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050568 - 19 Apr 2022

Cited by 8 | Viewed by 1378

Abstract

Using fiber, lime and fly ash to modify iron tailings and apply them to a road base is an effective way to utilize iron tailings as resources. To explore the influence of fiber on lime and fly ash-stabilized iron tailings (EIT) under dry [...] Read more.

Using fiber, lime and fly ash to modify iron tailings and apply them to a road base is an effective way to utilize iron tailings as resources. To explore the influence of fiber on lime and fly ash-stabilized iron tailings (EIT) under dry and wet cycles at an early curing age, the static and dynamic characteristics of EIT and fiber-modified lime and fly ash-stabilized iron tailings (FEIT) under dry and wet cycles were studied through an unconfined compressive strength (UCS) test, splitting test and dynamic triaxial test. The results show the following. (1) EIT and FEIT still have high UCS and splitting strength after dry–wet cycles, and the dry–wet cycles can promote the static properties of FEIT. (2) The dry–wet cycle is the main factor affecting the change in the dynamic elastic modulus of EIT and FEIT. The dynamic elastic modulus of EIT first increases and then decreases with the increase in dry–wet cycles, and the dynamic elastic modulus of FEIT first decreases and then increases with the increase in dry–wet cycles. The damping ratio of EIT and FEIT decreases with the increase in dry–wet cycles, and then tends to be stable. (3) After seven dry–wet cycles, the compressive performance, tensile performance, deformation resistance and vibration resistance of FEIT are better than those of EIT. This study can provide a reference for the resource application of iron tailings in road engineering. Full article

(This article belongs to the Special Issue Advances in Cement-Based and Construction Materials)

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18 pages, 9825 KiB

Open AccessArticle

Use of Bacteria Externally for Repairing Cracks and Improving Properties of Concrete Exposed to High Temperatures

by Milad Nimafar, Bijan Samali, Saied Jalil Hosseini and Alireza Akhlaghi

Crystals 2021, 11(12), 1503; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11121503 - 03 Dec 2021

Cited by 7 | Viewed by 2323

Abstract

The current paper presents the results of an experimental study on the application of calcium carbonate precipitation bacteria as a new approach to repairing damaged concrete when exposed to high temperatures. To do so, cylindrical and cubic concrete specimens were initially exposed to [...] Read more.

The current paper presents the results of an experimental study on the application of calcium carbonate precipitation bacteria as a new approach to repairing damaged concrete when exposed to high temperatures. To do so, cylindrical and cubic concrete specimens were initially exposed to heat in a furnace for 1 h, after reaching two different temperatures of 600 and 800 °C. A heat rate of 5.5 °C per minute was used to achieve the target temperatures. Then, two types of bacteria, namely Sporosarcina pasteurii and Bacillus sphaericus, with cell concentration of 10⁷ cells/mL, were utilized externally, to repair the thermal cracks, enhancing the mechanical properties and durability of the damaged concrete. The efficiency of the bacterial remediation technique was then evaluated through compressive strength, ultrasonic pulse velocity (UPV), and electrical conductivity tests on the control specimens (unexposed to heat), and those exposed to high temperature with or without bacterial healing. The experimental results demonstrate that the compressive strength of the test specimens exposed to temperatures of 600 and 800 °C decreased by about 31–44% compared with the control ones. However, compared to those damaged at 600 and 800 °C, the compressive strength of specimens repaired by the S. pasteurii and the B. sphaericus showed increases of 31–93%. This increase is associated with the precipitation of calcium carbonate in the deep and superficial cracks and pores of the damaged specimens. Furthermore, the ultrasonic pulse velocity of the specimens subjected to bacterial remediation had a significant increase of about 1.65–3.47 times compared with the damaged ones. In addition, the electrical conductivity of repaired specimens decreased by 22–36% compared with the damaged specimens. Full article

(This article belongs to the Special Issue Advances in Cement-Based and Construction Materials)

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13 pages, 4026 KiB

Open AccessArticle

Effect of Curing Conditions on the Strength Development of Alkali-Activated Mortar

by Lijuan Kong, Zirui Fan, Wenchen Ma, Jiatao Lu and Yazhou Liu

Crystals 2021, 11(12), 1455; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11121455 - 25 Nov 2021

Cited by 5 | Viewed by 1439

Abstract

In this study, the strength development and microstructure evolution of alkali-activated fly ash (AAF), granulated blast furnace slag (AAG), and metakaolin (AAM) mortars under standard curing, steam curing, and oven curing conditions were investigated. The results show that 80 °C steam curing was [...] Read more.

In this study, the strength development and microstructure evolution of alkali-activated fly ash (AAF), granulated blast furnace slag (AAG), and metakaolin (AAM) mortars under standard curing, steam curing, and oven curing conditions were investigated. The results show that 80 °C steam curing was more suitable for AAF mortar. Although oven curing was not as good as steam curing under the same temperature, the water evaporation increased the volume density of the N-A-S-H gel and refined the pore structure. For AAG mortar, the strength developed according to a Boltzmann function with time under steam curing conditions, which increased rapidly in the first 8 h, but grew little after about 15 h. Moreover, the strength development was severely limited by steam curing at 60 °C, and decreased under oven curing conditions due to the formation of microcracks that were induced by temperature stress and chemical shrinkage. For AAM mortar, the strength developed according to an Allometric power function with time under steam curing conditions, and the N-A-S-H gel formed in AAM had a higher polymerization degree and denser structure compared to that in AAF. The compressive strength of AAM mortar was 31.7 MPa after 80 °C steam curing for 4 h, and the standard curing time required to reach the same strength was less than 24 h, indicating that the standard curing was more suitable. Full article

(This article belongs to the Special Issue Advances in Cement-Based and Construction Materials)

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