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Numerical and Experimental Analysis of Advanced Concrete Materials
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Numerical and Experimental Analysis of Advanced Concrete Materials

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Construction and Building Materials".

Deadline for manuscript submissions: closed (10 June 2023) | Viewed by 27720

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Dr. Nikolina Živaljić

E-Mail Website
Guest Editor
Faculty of Civil Engineering, Architecture and Geodesy, University of Split, Split, Croatia
Interests: structural analysis; structural dynamics; earthquake engineering; finite and discrete element modeling; numerical analysis; civil engineering materials
Dr. Hrvoje Smoljanović

E-Mail Website
Guest Editor
Faculty of Civil Engineering, Architecture and Geodesy, University of Split, Split, Croatia
Interests: concrete; numerical simulation
Special Issues, Collections and Topics in MDPI journals
Dr. Ivan Balić

E-Mail Website
Guest Editor
Faculty of Civil Engineering, Architecture and Geodesy, University of Split, Split, Croatia
Interests: civil engineering; stability of structures; earthquake engineering; numerical modelling of structures
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In modern engineering practice, different types of concrete structures are used. Current applications in the construction of modern structures, or applications in the strengthening and reinforcement of existing structures, require the analysis of structures with different material properties and shapes exposed to different types of loads, such as quasi-static, dynamic, cyclic, impact, or seismic.

Advanced concrete structures, whether developed as new structures or reinforced existing structures, should satisfy a range of structural functions during operation conditions.

In practice, there are several experimental tests that provide new insights into concrete as a material at the micro, mezzo, and macro levels. The results significantly increase knowledge about the behavior of concrete as a material. Such tests are expensive, but their significance lies in the possibility of implementing material behavior in new numerical models. The development of new numerical models, if based on the results of experiments, can simulate the behavior of concrete as a building material with improved properties due to a new type of aggregate, some chemical composition, etc. Numerical models can also simulate the behavior of concrete structures whose load capacity can be an increased form of fastening.

The aim of this Special Issue is to collect and present experimental results as well as new numerical simulations of the behavior of concrete as a material and concrete structures, thus, providing a better understanding of the basic principles of cracking and crack propagation in concrete structures exposed to different types of loads. A thorough understanding, whose processes affect the reduction of strength and the formation of cracks in concrete, is key to the analysis of existing materials and the design of improved innovative materials of concrete and concrete structures.

Dr. Nikolina Živaljić
Dr. Hrvoje Smoljanović
Dr. Ivan Balić
Guest Editors

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Keywords

  • concrete materials
  • concrete structures
  • quasi-static, dynamic, cyclic loading
  • impact load
  • concrete cracking
  • damage and fracture processes
  • numerical analysis and simulation
  • experimental analysis and simulation

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Published Papers (15 papers)

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Research

17 pages, 12126 KiB  
Article
Formulation and Performance of Model Concrete in Reduced-Scale Physical Model Tests
by Gang Zheng, Boyang Xia, Haizuo Zhou, Yu Diao, Jianyou Huang, Junbo Zhang and Xiaoxuan Yu
Materials 2023, 16(17), 5784; https://doi.org/10.3390/ma16175784 - 24 Aug 2023
Cited by 1 | Viewed by 839
Abstract
The utility of geotechnical centrifuge tests depends on how correctly they predict the physical and mechanical behaviour of concrete. In this study, a model concrete material that consisted of α-gypsum plaster, fine silica sand, and water was developed. An orthogonal test design was [...] Read more.
The utility of geotechnical centrifuge tests depends on how correctly they predict the physical and mechanical behaviour of concrete. In this study, a model concrete material that consisted of α-gypsum plaster, fine silica sand, and water was developed. An orthogonal test design was used to evaluate the effect of the mix proportion on the model concrete performance. The physical (i.e., flowability and bleeding rate) and mechanical (i.e., compressive and flexural strength) characteristics were considered as indices. Various mix ratios resulted in remarkable relative contributions to model concrete performance, and each raw material dosage exhibited positive or negative synergy. The water–plaster ratio (W/P) and aggregate–plaster ratio (A/P) strongly influenced the mechanical and physical characteristics, respectively. Multiple linear regression analysis (MLRA) was carried out to determine a forecast model for various small-scale test demands. Finally, the applicability and outlines of the presented forecasting method in proportioning design were evaluated by typical use of model concrete in small-scale model tests. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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17 pages, 2835 KiB  
Article
Optimal Design of Bubble Deck Concrete Slabs: Serviceability Limit State
by Tomasz Gajewski, Natalia Staszak and Tomasz Garbowski
Materials 2023, 16(14), 4897; https://doi.org/10.3390/ma16144897 - 8 Jul 2023
Cited by 1 | Viewed by 1735
Abstract
In engineering practice, one can often encounter issues related to optimization, where the goal is to minimize material consumption and minimize stresses or deflections of the structure. In most cases, these issues are addressed with finite element analysis software and simple optimization algorithms. [...] Read more.
In engineering practice, one can often encounter issues related to optimization, where the goal is to minimize material consumption and minimize stresses or deflections of the structure. In most cases, these issues are addressed with finite element analysis software and simple optimization algorithms. However, in the case of optimization of certain structures, it is not so straightforward. An example of such constructions are bubble deck ceilings, where, in order to reduce the dead weight, air cavities are used, which are regularly arranged over the entire surface of the ceiling. In the case of these slabs, the flexural stiffness is not constant in all its cross-sections, which means that the use of structural finite elements (plate or shell) for static calculations is not possible, and therefore, the optimization process becomes more difficult. This paper presents a minimization procedure of the weight of bubble deck slabs using numerical homogenization and sequential quadratic programming with constraints. Homogenization allows for determining the effective stiffnesses of the floor, which in the next step are sequentially corrected by changing the geometrical parameters of the floor and voids in order to achieve the assumed deflection. The presented procedure allows for minimizing the use of material in a quick and effective way by automatically determining the optimal parameters describing the geometry of the bubble deck floor cross-section. For the optimal solution, the concrete weight of the bubble deck slab was reduced by about 23% in reference to the initial design, and the serviceability limit state was met. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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19 pages, 7452 KiB  
Article
Alteration of Structure and Characteristics of Concrete with Coconut Shell as a Substitution of a Part of Coarse Aggregate
by Sergey A. Stel’makh, Alexey N. Beskopylny, Evgenii M. Shcherban’, Levon R. Mailyan, Besarion Meskhi, Alexandr A. Shilov, Diana El’shaeva, Andrei Chernil’nik and Svetlana Kurilova
Materials 2023, 16(12), 4422; https://doi.org/10.3390/ma16124422 - 15 Jun 2023
Cited by 2 | Viewed by 2920
Abstract
One of the most promising ways to solve the problem of reducing the rate of depletion of natural non-renewable components of concrete is their complete or partial replacement with renewable plant counterparts that are industrial and agricultural waste. The research significance of this [...] Read more.
One of the most promising ways to solve the problem of reducing the rate of depletion of natural non-renewable components of concrete is their complete or partial replacement with renewable plant counterparts that are industrial and agricultural waste. The research significance of this article lies in the determination at the micro- and macro-levels of the principles of the relationship between the composition, the process of structure formation and the formation of properties of concrete based on coconut shells (CSs), as well as the substantiation at the micro- and macro-levels of the effectiveness of such a solution from the point of view of fundamental and applied materials science. The aim of this study was to solve the problem of substantiating the feasibility of concrete consisting of a mineral cement–sand matrix and aggregate in the form of crushed CS, as well as finding a rational combination of components and studying the structure and characteristics of concrete. Test samples were manufactured with a partial substitution of natural coarse aggregate with CS in an amount from 0% to 30% in increments of 5% by volume. The following main characteristics have been studied: density, compressive strength, bending strength and prism strength. The study used regulatory testing and scanning electron microscopy. The density of concrete decreased to 9.1% with increasing the CS content to 30%. The highest values for the strength characteristics and coefficient of construction quality (CCQ) were recorded for concretes containing 5% CS: compressive strength—38.0 MPa, prism strength—28.9 MPa, bending strength—6.1 MPa and CCQ—0.01731 MPa × m3/kg. The increase in compressive strength was 4.1%, prismatic strength—4.0%, bending strength—3.4% and CCQ—6.1% compared with concrete without CS. Increasing the CS content from 10% to 30% inevitably led to a significant drop in the strength characteristics (up to 42%) compared with concrete without CS. Analysis of the microstructure of concrete containing CS instead of part of the natural coarse aggregate revealed that the cement paste penetrates into the pores of the CS, thereby creating good adhesion of this aggregate to the cement–sand matrix. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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19 pages, 22174 KiB  
Article
Simulation of Tetrahedral Profiled Carbon Rovings for Concrete Reinforcements
by Paul Penzel, Tobias Georg Lang, Philipp Benjamin Weigel, Thomas Gereke, Lars Hahn, Arthur Hilbig and Chokri Cherif
Materials 2023, 16(7), 2767; https://doi.org/10.3390/ma16072767 - 30 Mar 2023
Viewed by 1180
Abstract
Textile reinforcements are increasingly establishing their position in the construction industry due to their high tensile properties and corrosion resistance for concrete applications. In contrast to ribbed monolithic steel bars with a defined form-fit effect, the conventional carbon rovings’ bond force is transmitted [...] Read more.
Textile reinforcements are increasingly establishing their position in the construction industry due to their high tensile properties and corrosion resistance for concrete applications. In contrast to ribbed monolithic steel bars with a defined form-fit effect, the conventional carbon rovings’ bond force is transmitted primarily by an adhesive bond (material fit) between the textile surface and the surrounding concrete matrix. As a result, relatively large bonding lengths are required to transmit bond forces, resulting in inefficient material utilization. Novel solutions such as tetrahedral profiled rovings promise significant improvements in the bonding behavior of textile reinforcements by creating an additional mechanical interlock with the concrete matrix while maintaining the high tensile properties of carbon fibers. Therefore, simulative investigations of tensile and bond behavior have been conducted to increase the transmittable bond force and bond stiffness of profiled rovings through a defined roving geometry. Geometric and material models were thus hereby developed, and tensile and pullout tests were simulated. The results of the simulations and characterizations could enable the optimization of the geometric parameters of tetrahedral profiled rovings to achieve better bond and tensile properties and provide basic principles for the simulative modeling of profiled textile reinforcements. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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14 pages, 5691 KiB  
Article
Preparation and Hydration Properties of Steel Slag-Based Composite Cementitious Materials with High Strength
by Zhiming Xu, Ying Ma, Jiahao Wang and Xiaodong Shen
Materials 2023, 16(7), 2764; https://doi.org/10.3390/ma16072764 - 30 Mar 2023
Cited by 3 | Viewed by 1420
Abstract
Steel slag (SS) has been largely discharged but little utilized, causing an environmental problem in China. In this paper, SS-based composite cementitious materials with high strength were prepared by the high volume of SS (≥40%), granulated blast-furnace slag (GBFS), fly ash (FA), flue [...] Read more.
Steel slag (SS) has been largely discharged but little utilized, causing an environmental problem in China. In this paper, SS-based composite cementitious materials with high strength were prepared by the high volume of SS (≥40%), granulated blast-furnace slag (GBFS), fly ash (FA), flue gas desulfurization gypsum (FGDG) and cement to promote the effective utilization of SS. The hydration and hardening properties were studied through setting time, compressive strength, length change, isothermal calorimetry (IC), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS) tests. The results show that SS-based composite cementitious material exhibited a lower hydration heat release, an appropriate setting time, and volume stability. The SS cementitious material with 40% SS could obtain high strength of over 65 MPa at 28 days and 80 MPa at 90 days. The strength value of > 60 MPa is present in the binder, with 50% SS at 56 days. GBFS promotes hydration reactions and the formation of AFt and C-(A)-S-H gel, thus enhancing compressive strength. FA has a beneficial effect on later strength. The small and fine pore structures contribute to the development of strength. The main hydration products of SS composite cementitious materials are C-(A)-S-H gel, and ettringite (AFt), with less Ca(OH)2. The C-(A)-S-H gel with a lower Ca/Si ratio and a higher Al/Ca ratio in cementitious material, promotes mechanical properties. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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20 pages, 7168 KiB  
Article
Improved Tensile and Bond Properties through Novel Rod Constructions Based on the Braiding Technique for Non-Metallic Concrete Reinforcements
by Anwar Abdkader, Paul Penzel, Danny Friese, Matthias Overberg, Lars Hahn, Marko Butler, Viktor Mechtcherine and Chokri Cherif
Materials 2023, 16(6), 2459; https://doi.org/10.3390/ma16062459 - 20 Mar 2023
Cited by 5 | Viewed by 1335
Abstract
Textile reinforcements have established themselves as a convincing alternative to conventional steel reinforcements in the building industry. In contrast to ribbed steel bars that ensure a stable mechanical interlock with concrete (form fit), the bonding force of smooth carbon rovings has so far [...] Read more.
Textile reinforcements have established themselves as a convincing alternative to conventional steel reinforcements in the building industry. In contrast to ribbed steel bars that ensure a stable mechanical interlock with concrete (form fit), the bonding force of smooth carbon rovings has so far been transmitted primarily by an adhesive bonding with the concrete matrix (material fit). However, this material fit does not enable the efficient use of the mechanical load capacity of the textile reinforcement. Solutions involving surface-profiled rods promise significant improvements in the bonding behavior by creating an additional mechanical interlock with the concrete matrix. An initial analysis was carried out to determine the effect of a braided rod geometry on the bonding behavior. For this purpose, novel braided rods with defined surface profiling consisting of several carbon filament yarns were developed and characterized in their tensile and bond properties. Further fundamental examinations to determine the influence of the impregnation as well as the application of a pre-tension during its consolidation in order to minimize the rod elongation under load were carried out. The investigations showed a high potential of the impregnated surface-profiled braided rods for a highly efficient application in concrete reinforcements. Hereby, a complete impregnation of the rod with a stiff polymer improved the tensile and bonding properties significantly. Compared to unprofiled reinforcement structures, the specific bonding stress could be increased up to 500% due to the strong form-fit effect of the braided rods while maintaining the high tensile properties. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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15 pages, 5428 KiB  
Article
Modification Effect of Ca(OH)2 on the Carbonation Resistance of Fly Ash-Metakaolin-Based Geopolymer
by Yigang Lv, Jie Qiao, Weiwei Han, Bei Pan, Xiafei Jin and Hui Peng
Materials 2023, 16(6), 2305; https://doi.org/10.3390/ma16062305 - 13 Mar 2023
Cited by 6 | Viewed by 1641
Abstract
Compared with Portland cement, geopolymers have poor carbonization resistance, which will greatly limit the application their application. To improve the carbonization resistance of geopolymers, firstly, the carbonization behavior of the fly ash-metakaolin-based geopolymer was studied through accelerated carbonization tests. Secondly, different amounts of [...] Read more.
Compared with Portland cement, geopolymers have poor carbonization resistance, which will greatly limit the application their application. To improve the carbonization resistance of geopolymers, firstly, the carbonization behavior of the fly ash-metakaolin-based geopolymer was studied through accelerated carbonization tests. Secondly, different amounts of Ca(OH)2 were introduced into the composite system, and the modification effect of the carbonization resistance of the modified geopolymer was studied. Finally, the modification effect of Ca(OH)2 on the fly ash-metakaolin-based geopolymers was analyzed, and the modification mechanism was explored. It was found that adding Ca(OH)2 to the fly ash-metakaolin-based geopolymer could significantly improve its initial compressive strength, but its strength after carbonization remained basically unchanged; meanwhile, the compressive strength of the terpolymer after carbonization clearly decreased after adding Ca(OH)2. Compared with ordinary Portland cement, the carbonization rate of fly ash-metakaolin-based geopolymer is faster, and the addition of Ca(OH)2 can inhibit the development of its carbonization depth. With increased carbonization age, the alkalinity of the geopolymer decreased, and the addition of Ca(OH)2 inhibited the decrease in the alkalinity of the geopolymer. The addition of Ca(OH)2 improved the microstructure of the geopolymers, the pore structure became denser, and the pore size became smaller size after carbonization. The hydration products of fly ash-metakaolin-based geopolymer are mainly amorphous silicaluminate gel and C–S–H gel, and Ca(OH)2 forms in the hydration products of terpolymer with the incorporation of Ca(OH)2, which is conducive to improving the carbonization resistance. In summary, Ca(OH)2 can play a good role in modifying the carbonization resistance of fly ash-metakaolin-based geopolymers. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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14 pages, 5426 KiB  
Article
Identification of Dynamic Behavior Models of Concrete B22.5
by Anatoly M. Bragov, Andrey K. Lomunov, Mikhail E. Gonov, Aleksandr Yu. Konstantinov, Leonid A. Igumnov and Victor A. Eremeyev
Materials 2023, 16(6), 2259; https://doi.org/10.3390/ma16062259 - 11 Mar 2023
Cited by 1 | Viewed by 1375
Abstract
We discuss experimental and numerical studies of the deformation and destruction of fine-grained concrete B22.5 under dynamic loading. The experiments were carried out using the Kolsky (or split-Hopkinson pressure bar) method, and its modifications in the strain rate range from 400 to 2000 [...] Read more.
We discuss experimental and numerical studies of the deformation and destruction of fine-grained concrete B22.5 under dynamic loading. The experiments were carried out using the Kolsky (or split-Hopkinson pressure bar) method, and its modifications in the strain rate range from 400 to 2000 s−1. The rate dependences of ultimate stresses and fracture energy in tension and compression are obtained. Based on experimental data, the identification of the dynamic component of two models from the LS-DYNA computational complex was carried out: *MAT_CONCRETE_DAMAGE and *MAT_CSCM. The results of a comparative analysis of the identified models based on single-element modeling and comparison with experimental data are presented. It is shown that the obtained experimental strain rate dependences of the fracture characteristics can significantly improve the predictive ability of the model compared to the default parameter set. Information about the rate dependence of the fracture energy in *MAT_CSCM model makes it possible to more realistically simulate the behavior of the material beyond the ultimate stress. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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13 pages, 4380 KiB  
Article
The Impact of Different Parameters on the Formwork Pressure Exerted by Self-Compacting Concrete
by Yaser Gamil, Andrzej Cwirzen, Jonny Nilimaa and Mats Emborg
Materials 2023, 16(2), 759; https://doi.org/10.3390/ma16020759 - 12 Jan 2023
Cited by 6 | Viewed by 1689
Abstract
Despite the advantageous benefits offered by self-compacting concrete, its uses are still limited due to the high pressure exerted on the formwork. Different parameters, such as those related to concrete mix design, the properties of newly poured concrete, and placement method, have an [...] Read more.
Despite the advantageous benefits offered by self-compacting concrete, its uses are still limited due to the high pressure exerted on the formwork. Different parameters, such as those related to concrete mix design, the properties of newly poured concrete, and placement method, have an impact on form pressure. The question remains unanswered on the degree of the impact for each parameter. Therefore, this study aims to study the level of impact of these parameters, including slump flow, T500 time, fresh concrete density, air content, static yield stress, concrete setting time, and concrete temperature. To mimic the casting scenario, 2 m columns were cast at various casting rates and a laboratory setup was developed. A pressure system that can wirelessly and continuously record pressure was used to monitor the pressure. Each parameter’s impact on the level of pressure was examined separately. Casting rate and slump flow were shown to have a greater influence on pressure. The results also demonstrated that, while higher thixotropy causes form pressure to rapidly decrease, a high casting rate and high slump flow lead to high pressure. This study suggests that more thorough analysis should be conducted of additional factors that may have an impact, such as the placement method, which was not included in this publication. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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16 pages, 3298 KiB  
Article
A Design Process for Preventing Brittle Failure in Strengthening RC Slabs with Hybrid FRP-HPC Retrofit Systems
by Huy Q. Nguyen, Taek Hee Han, Jun Kil Park and Jung J. Kim
Materials 2023, 16(2), 755; https://doi.org/10.3390/ma16020755 - 12 Jan 2023
Cited by 2 | Viewed by 1483
Abstract
The retrofitting of existing RC slabs with an innovative system comprising FRP and HPC has been demonstrated to be effective in strengthening and overcoming the logistical challenges of installation. Nonetheless, the excessive improvement of flexural strength over shear strength would cause the sudden [...] Read more.
The retrofitting of existing RC slabs with an innovative system comprising FRP and HPC has been demonstrated to be effective in strengthening and overcoming the logistical challenges of installation. Nonetheless, the excessive improvement of flexural strength over shear strength would cause the sudden failure of rehabilitated flexural members. The literature has previously recommended failure limits to determine the additional moment strength compared with the shear strength to prevent brittle shear failure of strengthened, continuous RC slabs. This study suggests a design process for preventing shear failure and inducing the ductile-failure mode to improve the safety and applicability of retrofitted RC slabs based on the proposed failure limits. The effectiveness of the procedure in brittle-failure prevention for the end and interior spans of retrofitted RC slabs is illustrated via a case study. The outcomes showed that the retrofit system with 0.53-mm-thick-CFRP prevented brittle failure and significantly enhanced the design-factored load and ultimate failure load by up to 2.07 times and 2.13 times, respectively. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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17 pages, 3688 KiB  
Article
Engineering, Mechanical and Dynamic Properties of Basalt Fiber Reinforced Concrete
by Han Wu, Xia Qin, Xu Huang and Sakdirat Kaewunruen
Materials 2023, 16(2), 623; https://doi.org/10.3390/ma16020623 - 9 Jan 2023
Cited by 15 | Viewed by 3005
Abstract
This study investigates the engineering and mechanical properties of basalt fiber-reinforced (FRF) concrete, giving special attention to residual flexural strength and dynamic modal parameters. These properties, which have not been thoroughly investigated elsewhere, are a precursor to structural design applications for dynamic compliant [...] Read more.
This study investigates the engineering and mechanical properties of basalt fiber-reinforced (FRF) concrete, giving special attention to residual flexural strength and dynamic modal parameters. These properties, which have not been thoroughly investigated elsewhere, are a precursor to structural design applications for dynamic compliant structures (i.e., bridges, offshore platforms, railways, and airport pavement). Accordingly, the standard notched flexural tests have been carried out to assess the basalt fiber-reinforced concrete’s residual flexural strength with an additional 0.125%, 0.25%, 0.375%, and 0.5% of volume fraction of basalt fiber. In addition, dynamic modal tests were then conducted to determine the dynamic modulus of elasticity (MOE) and damping of the FRF concrete beams. The results indicate that concrete’s toughness and crack resistance performance are significantly improved with added fiber in basalt fiber reinforced concrete, and the optimum fiber content is 0.25%. It also exhibits the highest increment of compressive strength of 4.48% and a dynamic MOE of 13.83%. New insights reveal that although the residual flexural performance gradually improved with the addition of basalt fiber, the damping ratio had an insignificant change. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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21 pages, 6444 KiB  
Article
Experimental Study on Early Strength and Hydration Heat of Spodumene Tailings Cemented Backfill Materials
by Shunchun Deng, Lang Liu, Pan Yang, Caixin Zhang, Yin Lv and Lei Xie
Materials 2022, 15(24), 8846; https://doi.org/10.3390/ma15248846 - 11 Dec 2022
Cited by 2 | Viewed by 1564
Abstract
Spodumene tailing is the associated solid waste of extracting lithium from spodumene. With the increase in the global demand for lithium resources, its emissions increase yearly, which will become a key factor restricting the economic development of the mining area. Mechanical and hydration [...] Read more.
Spodumene tailing is the associated solid waste of extracting lithium from spodumene. With the increase in the global demand for lithium resources, its emissions increase yearly, which will become a key factor restricting the economic development of the mining area. Mechanical and hydration reactions, as well as the microstructure of early CSTB, are studied under different tailings–cement ratios (TCR) and solid mass concentration (SC) conditions. The results show that the uniaxial compressive strength of early CSTB has a negative exponential correlation with the decrease in TCR and a positive correlation with the increase in SC: when the age of CSTB increases to 7 days, the strength increases with the rise in SC in an exponential function, and the sensitivity of strength to TCR is higher than that of SC. Compared to other tailings cemented backfill materials, the addition of spodumene tailings reduces the sulfate ion concentration and leads to a new exothermic peak (i.e., the third exothermic peak) for the hydration exotherm of CSTB. Additionally, with the increase in TCR or decrease in SC, the height of the third exothermic peak decreases and the occurrence time is advanced. At the same time, the duration of induction phase was prolonged, the period of acceleration phase was shortened, and the total amount of heat released was significantly increased. The decrease in TCR or the increase in SC led to the rise in the number of hydration products which can effectively fill the internal pores of CSTB, enhance its structural compactness, and increase its compressive strength. The above study reveals the influence of TCR and SC on the early strength, hydration characteristics, and microstructure of CSTB and provides an essential reference for the mix design of underground backfill spodumene tailings. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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19 pages, 9388 KiB  
Article
Simulation and Experimental Substantiation of the Thermal Properties of Non-Autoclaved Aerated Concrete with Recycled Concrete Powder
by Xiaosong Ma, Hao Li, Dezhi Wang, Chunbao Li and Yongqi Wei
Materials 2022, 15(23), 8341; https://doi.org/10.3390/ma15238341 - 23 Nov 2022
Cited by 4 | Viewed by 1474
Abstract
Non-autoclaved aerated concrete (NAAC) is a two-phase material with a concrete matrix and air, exhibits good thermal insulation performance and shows good potential in the insulating construction industry. In this study, recycled concrete fine powder was used as an auxiliary cementing material, and [...] Read more.
Non-autoclaved aerated concrete (NAAC) is a two-phase material with a concrete matrix and air, exhibits good thermal insulation performance and shows good potential in the insulating construction industry. In this study, recycled concrete fine powder was used as an auxiliary cementing material, and the NAAC with different porosity and distribution was fabricated by the non-autoclaved method at different curing temperatures. The effect of porosity on the thermal conductivity and mechanical strength of NAAC is analyzed by experimental tests. A prediction method of thermal conductivity combining pore structure reconstruction and numerical simulation was proposed, which is established by two steps. Firstly, the pore size distributions of NAAC with different porosities were characterized by stereology image analyses. Secondly, the thermal conductivity prediction model based on the pore structure information was established by a COMSOL steady-state heat transfer module. The thermal conductivity results of COMSOL simulations were compared with the experiments and other theoretical models to verify the reliability of the model. The model was used to evaluate the effect of porosity, pore size distribution and the concrete matrix’s thermal conductivity on the thermal conductivity of NAAC; these are hard to measure when only using laboratory experiments. The results show that with the increase in curing temperature, the porosity of NAAC increases, and the number and volume proportion of macropores increase. The numerical results suggest that the error between the COMSOL simulations and the experiments was less than 10% under different porosities, which is smaller than other models and has strong reliability. The prediction accuracy of this model increases with the increase in NAAC porosity. The steady thermal conductivity of NAAC is less sensitive to the distribution and dispersion of pore size in a given porosity. With the increase in porosity, the thermal conductivity of NAAC is linearly negatively correlated with that of the concrete matrix, and the correlation is close to 1. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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17 pages, 41488 KiB  
Article
Strength, Frost Resistance, and Resistance to Acid Attacks on Fiber-Reinforced Concrete for Industrial Floors and Road Pavements with Steel and Polypropylene Fibers
by Željko Kos, Sergii Kroviakov, Vitalii Kryzhanovskyi and Daria Hedulian
Materials 2022, 15(23), 8339; https://doi.org/10.3390/ma15238339 - 23 Nov 2022
Cited by 17 | Viewed by 1874
Abstract
A comparison of the effect of steel and polypropylene fibers on the strength, frost resistance, abrasion, and corrosion resistance in an acidic environment of fiber-reinforced concrete for industrial floors and road pavements was carried out. Steel fibers with a length of 50 mm [...] Read more.
A comparison of the effect of steel and polypropylene fibers on the strength, frost resistance, abrasion, and corrosion resistance in an acidic environment of fiber-reinforced concrete for industrial floors and road pavements was carried out. Steel fibers with a length of 50 mm and a diameter of 1 mm and polypropylene fibers with a length of 36 mm and a diameter of 0.68 mm were used. The amount of steel fiber varied from 15 to 25 kg/m3, and the amount of polypropylene fiber varied from 2 to 3 kg/m3. It has been established that steel fiber more significantly increases the concrete compressive strength, and both types of dispersed reinforcement increase the flexural strength equally by 27–34%. Also, dispersed reinforcement reduces the concrete abrasion resistance by 15–35% and increases its frost resistance by 50 cycles, which helps to improve the durability of industrial floors and road pavements. The use of steel fiber in an amount of 20 kg/m3 and polypropylene fiber in an amount of 2.5 kg/m3 also increases the concrete corrosion resistance in an acidic environment. In general, dispersed reinforcement with both fiber types has approximately the same technological effect concerning the mentioned applications. However, the use of polypropylene fibers is economically more profitable since an increase in the cost of 1 m3 of concrete with steel fiber reinforcement is from $22.5 to $37.5, and an increase in cost with polypropylene fiber is from $10 to $15. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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11 pages, 3764 KiB  
Article
Incorporation of Silica Particles Attached to Nylon 66 Electrospun Nanofibers with Cement
by Tri N. M. Nguyen, Do Hyung Lee and Jung J. Kim
Materials 2022, 15(19), 7011; https://doi.org/10.3390/ma15197011 - 10 Oct 2022
Viewed by 1394
Abstract
In this study, a modified version of electrospun nylon 66 nanofibers by silica particles were blended into ordinary Portland cement to investigate the microstructure and some mechanical properties of cementitious material. The addition of silica into the nanofibers improved the tensile and compressive [...] Read more.
In this study, a modified version of electrospun nylon 66 nanofibers by silica particles were blended into ordinary Portland cement to investigate the microstructure and some mechanical properties of cementitious material. The addition of silica into the nanofibers improved the tensile and compressive properties of the hardened cement pastes. The observations from the mechanical strength tests showed an increase of 41%, 33% and 65% in tensile strength, compressive strength, and toughness, respectively, when modifying the cement pastes with the proposed nanofibers. The observations from scanning electron microscopy and transmission electron microscopy showed the morphology and microstructure of the fibers as well as their behaviors inside the cement matrix. Additionally, X-ray diffraction and thermal gravimetric analysis clarified the occurrence of the extra pozzolanic reaction, as well as the calcium hydroxide consumption by the attached silica inside the cement matrix. Finally, the observations from this study showed the successful fabrication of the modified nanofibers and the feasibility of improving the tensile and compressive behaviors of cement pastes using the proposed electrospun nanofibers. Full article
(This article belongs to the Special Issue Numerical and Experimental Analysis of Advanced Concrete Materials)
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