Editorial

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3 pages, 148 KiB

Open AccessEditorial

Numerical Study of Concrete

by Vipulkumar Ishvarbhai Patel

Crystals 2021, 11(1), 74; https://doi.org/10.3390/cryst11010074 - 18 Jan 2021

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Abstract

This Special Issue, “Numerical Study of Concrete”, consists of 22 research articles [...] Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

Research

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17 pages, 13000 KiB

Open AccessArticle

Numerical Analysis of a Novel Shaft Lining Structure in Coal Mines Consisting of Hybrid-Fiber-Reinforced Concrete

by Xuesong Wang, Hua Cheng, Taoli Wu, Zhishu Yao and Xianwen Huang

Crystals 2020, 10(10), 928; https://doi.org/10.3390/cryst10100928 - 12 Oct 2020

Cited by 7 | Viewed by 1915

Abstract

To address the temperature cracking of concrete in frozen shaft linings in extra-thick alluvial layers in coal mines, a novel shaft lining structure of coal mines consisting of hybrid-fiber-reinforced concrete (HFRC) was developed. Using the Finite Element Method (FEM), a numerical simulation test [...] Read more.

To address the temperature cracking of concrete in frozen shaft linings in extra-thick alluvial layers in coal mines, a novel shaft lining structure of coal mines consisting of hybrid-fiber-reinforced concrete (HFRC) was developed. Using the Finite Element Method (FEM), a numerical simulation test of the HFRC shaft lining structure with four factors and three levels was carried out, and the mechanical characteristics of the shaft lining structure were obtained. The results show that under a uniform surface load, the maximum hoop stress position of the HFRC shaft lining presents a transition trend from the inside surface to the outside surface; the hoop strain of shaft lining concrete is always a compressive strain, and the inside surface is greater than the outside surface. The empirical formula for the ultimate capacity of this new type of shaft lining structure was obtained by fitting. Compared with the model test results, the maximum relative error of the calculated value is only 6.69%, which provides a certain reference value for designing this kind of shaft lining structure. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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12 pages, 2153 KiB

Open AccessArticle

Analysis of Concrete Failure on the Descending Branch of the Load-Displacement Curve

by Gennadiy Kolesnikov

Crystals 2020, 10(10), 921; https://doi.org/10.3390/cryst10100921 - 12 Oct 2020

Cited by 9 | Viewed by 5387

Abstract

In this paper, load-displacement and stress-strain diagrams are considered for the uniaxial compression of concrete and under three-point bending. It is known that the destruction of such materials occurs on the descending branch of the load-displacement diagram. The attention of the presented research [...] Read more.

In this paper, load-displacement and stress-strain diagrams are considered for the uniaxial compression of concrete and under three-point bending. It is known that the destruction of such materials occurs on the descending branch of the load-displacement diagram. The attention of the presented research is focused on the explanation of this phenomenon. Fracture mechanics approaches are used as a research tool. The method for determining effective stresses and modulus of elasticity of concrete based on the results of uniaxial compression tests has been substantiated. The ratios necessary for the calculation were obtained without any assumptions about the reinforcement of concrete and the mechanical properties of its components. However, the effect of these properties is considered indirectly, using the stress and strain peaks determined by standard concrete compression tests. It was found that the effective stresses increase both on the ascending branch and on the descending branch of the load-displacement diagram. This explains the destruction of concrete on the descending branch of the load-displacement diagram. The results of determining the stresses and modulus of elasticity under uniaxial compression are comparable with the results obtained in experiments known in the literature. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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13 pages, 1913 KiB

Open AccessArticle

Compressive Strength Forecasting of Air-Entrained Rubberized Concrete during the Hardening Process Utilizing Elastic Wave Method

by Zhi Heng Lim, Foo Wei Lee, Kim Hung Mo, Jee Hock Lim, Ming Kun Yew and Kok Zee Kwong

Crystals 2020, 10(10), 912; https://doi.org/10.3390/cryst10100912 - 09 Oct 2020

Cited by 6 | Viewed by 2247

Abstract

Conventional compressive strength test of concrete involves the destruction of concrete samples or existing structures. Thus, the focus of this research is to ascertain a more effective method to assess the compressive strength of concrete, especially during the hardening process. One of the [...] Read more.

Conventional compressive strength test of concrete involves the destruction of concrete samples or existing structures. Thus, the focus of this research is to ascertain a more effective method to assess the compressive strength of concrete, especially during the hardening process. One of the prevalent non-destructive test (NDT) methods that involves the employment of elastic wave has been proposed to forecast the compressive strength development of air-entrained rubberized concrete. The change of the properties, such as wave amplitude, velocity and dominant frequency of the wave that propagates within the concrete is investigated. These wave parameters are then correlated with the compressive strength data, obtained using the conventional compressive strength test. It has been certified that both correlation between wave amplitude and concrete compressive strength, as well as the correlation between velocity and concrete compressive strength, have high regression degrees, which are 0.9404 and 0.8788, respectively. On the contrary, dominant wave frequency has been proved imprecise to be used to correlate with the concrete compressive strength development, as a low correlation coefficient of 0.2677 is reported. In a nutshell, the correlation data of wave amplitude and velocity could be used to forecast the compressive strength development of an air-entrained rubberized concrete in the future. Full article

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13 pages, 3651 KiB

Open AccessArticle

Capillary Water Absorption and Micro Pore Connectivity of Concrete with Fractal Analysis

by Xiangqun Ding, Xinyu Liang, Yichao Zhang, Yanfeng Fang, Jinghai Zhou and Tianbei Kang

Crystals 2020, 10(10), 892; https://doi.org/10.3390/cryst10100892 - 01 Oct 2020

Cited by 13 | Viewed by 2549

Abstract

This study focuses on the relationship between the complexity of pore structure and capillary water absorption of concrete, as well as the connection behavior of concrete in specific directions. In this paper, the water absorption of concrete with different binders was tested during [...] Read more.

This study focuses on the relationship between the complexity of pore structure and capillary water absorption of concrete, as well as the connection behavior of concrete in specific directions. In this paper, the water absorption of concrete with different binders was tested during the curing process, and the pore structure of concrete was investigated by mercury intrusion porosimetry (MIP). The results show that the water absorption of concrete with mineral admixtures is lower, mainly due to the existence of reasonable pore structure. The effect of slag on concrete modification is more remarkable comparing with fly ash. In addition, the analysis shows that the pore with different diameters has different fractal characteristics. The connectivity probability and water absorption of unidirectional chaotic pore are linearly correlated with the pore diameter of 50–550 nm, and the correlation coefficient reaches a very significant level, and detailed analysis was undertaken to interpret these results based on fractal theory. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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16 pages, 4485 KiB

Open AccessArticle

Numerical Investigation on Dynamic Response of RC T-Beams Strengthened with CFRP under Impact Loading

by Huiling Zhao, Xiangqing Kong, Ying Fu, Yihan Gu and Xuezhi Wang

Crystals 2020, 10(10), 890; https://doi.org/10.3390/cryst10100890 - 01 Oct 2020

Cited by 3 | Viewed by 2167

Abstract

To precisely evaluate the retrofitting effectiveness of Carbon Fiber Reinforced Plastic (CFRP) sheets on the impact response of reinforced concrete (RC) T-beams, a non-linear finite element model was developed to simulate the structural response of T-beams with CFRP under impact loads. The numerical [...] Read more.

To precisely evaluate the retrofitting effectiveness of Carbon Fiber Reinforced Plastic (CFRP) sheets on the impact response of reinforced concrete (RC) T-beams, a non-linear finite element model was developed to simulate the structural response of T-beams with CFRP under impact loads. The numerical model was firstly verified by comparing the numerical simulation results with the experimental data, i.e., impact force, reaction force, and mid-span displacement. The strengthening effect of CFRP was analyzed from the section damage evaluation. Then the impact force, mid-span displacement, and failure mode of CFRP-strengthened RC T-beams were studied in comparison with those of un-strengthened T-beams. In addition, the influence of the impact resistance of T-beams strengthened with FRP was investigated in terms of CFRP strengthening mode, CFRP strengthening sizes, CFRP layers and FRP material types. The numerical simulation results indicate that the overall stiffness of the T-beams was improved significantly due to external CFRP strips. Compared with the un-strengthened beam, the maximum mid-span displacement of the CFRP-strengthened beam was reduced by 7.9%. Additionally, the sectional damage factors of the whole span of the CFRP-strengthened beam were reduced to less than 0.3, indicating that the impact resistance of the T-beams was effectively enhanced. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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30 pages, 7451 KiB

Open AccessArticle

Constitutive Modeling of New Synthetic Hybrid Fibers Reinforced Concrete from Experimental Testing in Uniaxial Compression and Tension

by S. M. Iqbal S. Zainal, Farzad Hejazi, Farah N. A. Abd. Aziz and Mohd Saleh Jaafar

Crystals 2020, 10(10), 885; https://doi.org/10.3390/cryst10100885 - 01 Oct 2020

Cited by 12 | Viewed by 4383

Abstract

Hybridization of fibers in concrete yields a variety of applications due to its benefits compared to conventional concrete or concrete with single type-fiber. However, the Finite Element (FE) modeling of these new materials for numerical analyses are very challenging due to the lack [...] Read more.

Hybridization of fibers in concrete yields a variety of applications due to its benefits compared to conventional concrete or concrete with single type-fiber. However, the Finite Element (FE) modeling of these new materials for numerical analyses are very challenging due to the lack of analytical data for these specific materials. Therefore, an attempt has been made to develop Hybrid Fiber Reinforced Concrete (HyFRC) materials with High Range Water-Reducing Admixture (HRWRA) during the concrete mixing process and conduct experimental study to evaluate the behavior of the proposed materials. Constitutive models for each of the materials are formulated to be used as analytical models in numerical analyses. The acquired data are then used to formulate mathematical equations, governing the stress–strain behavior of the proposed HyFRC materials to measure the accuracy of the proposed models. The experimental testing indicated that the Ferro with Ferro mix-combination improved the performance of concrete in the elastic stage while the Ferro with Ultra-Net combination has the highest compressive strain surplus in the plastic stage. In tension, the Ferro with Ferro mix displayed the highest elastic behavior improvement while the Ferro with Ultra-Net designs proved superior in the plastic range, providing additional toughness to conventional concrete. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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22 pages, 6516 KiB

Open AccessArticle

Prediction of Properties of FRP-Confined Concrete Cylinders Based on Artificial Neural Networks

by Afaq Ahmad, Vagelis Plevris and Qaiser-uz-Zaman Khan

Crystals 2020, 10(9), 811; https://doi.org/10.3390/cryst10090811 - 14 Sep 2020

Cited by 28 | Viewed by 3157

Abstract

Recently, the use of fiber-reinforced polymers (FRP)-confinement has increased due to its various favorable effects on concrete structures, such as an increase in strength and ductility. Therefore, researchers have been attracted to exploring the behavior and efficiency of FRP-confinement for concrete structural elements [...] Read more.

Recently, the use of fiber-reinforced polymers (FRP)-confinement has increased due to its various favorable effects on concrete structures, such as an increase in strength and ductility. Therefore, researchers have been attracted to exploring the behavior and efficiency of FRP-confinement for concrete structural elements further. The current study investigates improved strength and strain models for FRP confined concrete cylindrical elements. Two new physical methods are proposed for use on a large preliminary evaluated database of 708 specimens for strength and 572 specimens for strain from previous experiments. The first approach is employing artificial neural networks (ANNs), and the second is using the general regression analysis technique for both axial strength and strain of FRP-confined concrete. The accuracy of the newly proposed strain models is quite satisfactory in comparison with previous experimental results. Moreover, the predictions of the proposed ANN models are better than the predictions of previously proposed models based on various statistical indices, such as the correlation coefficient (R) and mean square error (MSE), and can be used to assess the members at the ultimate limit state. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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16 pages, 3929 KiB

Open AccessArticle

Determination of Mohr-Coulomb Parameters for Modelling of Concrete

by Selimir Lelovic and Dejan Vasovic

Crystals 2020, 10(9), 808; https://doi.org/10.3390/cryst10090808 - 13 Sep 2020

Cited by 9 | Viewed by 8005

Abstract

Cohesion is defined as the shear strength of material when compressive stress is zero. This article presents a new method for the experimental determination of cohesion at pre-set angles of shear deformation. Specially designed moulds are created to force deformation (close to τ-axis) [...] Read more.

Cohesion is defined as the shear strength of material when compressive stress is zero. This article presents a new method for the experimental determination of cohesion at pre-set angles of shear deformation. Specially designed moulds are created to force deformation (close to τ-axis) at fixed pre-set values of angle with respect to normal stress σ. Testing is performed on series of concrete blocks of different strengths. From the compressive side, cohesion is determined from the extrapolation of the linear Mohr–Coulomb (MC) model, as the intercept on the shear stress axis. From the tensile stress side (from the left), cohesion is obtained using the Brazilian test results: first, indirect tensile strength of material σ_t^BT is measured, then Mohr circle diagram values are calculated and cohesion is determined as the value of shear stress τ^BT on the Mohr circle where normal stress (σ)t = 0. A hypothesis is made that cohesion is the common point between two tests. In the numerical part, a theory of ultimate load is applied to model Brazilian test using the angle of shear friction from the MC model. Matching experimental and numerical results confirm that the proposed procedure is applicable in numerical analysis. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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21 pages, 19065 KiB

Open AccessArticle

The Impact Resistance and Deformation Performance of Novel Pre-Packed Aggregate Concrete Reinforced with Waste Polypropylene Fibres

by Fahed Alrshoudi, Hossein Mohammadhosseini, Rayed Alyousef, Mahmood Md. Tahir, Hisham Alabduljabbar and Abdeliazim Mustafa Mohamed

Crystals 2020, 10(9), 788; https://doi.org/10.3390/cryst10090788 - 06 Sep 2020

Cited by 14 | Viewed by 2469

Abstract

Pre-packed aggregate fibre-reinforced concrete (PAFRC) is an innovative type of concrete composite using a mixture of coarse aggregates and fibres which are pre-mixed and pre-placed in the formwork. A flowable grout is then injected into the cavities between the aggregate mass. This study [...] Read more.

Pre-packed aggregate fibre-reinforced concrete (PAFRC) is an innovative type of concrete composite using a mixture of coarse aggregates and fibres which are pre-mixed and pre-placed in the formwork. A flowable grout is then injected into the cavities between the aggregate mass. This study develops the concept of a new PAFRC, which is reinforced with polypropylene (PP) waste carpet fibres, investigating its mechanical properties and impact resistance under drop weight impact load. Palm oil fuel ash (POFA) is used as a partial cement replacement, with a replacement level of 20%. The compressive strength, impact resistance, energy absorption, long-term drying shrinkage, and microstructural analysis of PAFRC are explored. Two methods of grout injection are used—namely, gravity and pumping methods. For each method, six PAFRC batches containing 0–1.25% fibres (with a length of 30 mm) were cast. The findings of the study reveal that, by adding waste PP fibre, the compressive strength of PAFRC specimens decreased. However, with longer curing periods, the compressive strength enhanced due to the pozzolanic activity of POFA. The combination of fibres and POFA in PAFRC mixtures leads to the higher impact strength energy absorption and improved ductility of the concrete. Furthermore, drying shrinkage was reduced by about 28.6% for the pumping method PAFRC mix containing 0.75% fibres. Due to the unique production method of PAFRC and high impact resistance and energy absorption, it can be used in many pioneering applications. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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15 pages, 1364 KiB

Open AccessArticle

Thermal Performance of Alginate Concrete Reinforced with Basalt Fiber

by Seyed Esmaeil Mohammadyan-Yasouj, Hossein Abbastabar Ahangar, Narges Ahevani Oskoei, Hoofar Shokravi, Seyed Saeid Rahimian Koloor and Michal Petrů

Crystals 2020, 10(9), 779; https://doi.org/10.3390/cryst10090779 - 03 Sep 2020

Cited by 13 | Viewed by 3545

Abstract

The sustainability of reinforced concrete structures is of high importance for practitioners and researchers, particularly in harsh environments and under extreme operating conditions. Buildings and tunnels are of the places that most of the fire cases take place. The use of fiber in [...] Read more.

The sustainability of reinforced concrete structures is of high importance for practitioners and researchers, particularly in harsh environments and under extreme operating conditions. Buildings and tunnels are of the places that most of the fire cases take place. The use of fiber in concrete composite acts as crack arrestors to resist the development of cracks and enhance the performance of reinforced concrete structures subjected to elevated temperature. Basalt fiber is a low-carbon footprint green product obtained from the raw material of basalt which is created by the solidification of lava. It is a sustainable fiber choice for reinforcing concrete composite due to the less consumed energy in the production phase and not using chemical additives in their production. On the other hand, alginate is a natural anionic polymer acquired from cell walls of brown seaweed that can enhance the properties of composites due to its advantage as a hydrophilic gelling material. This paper investigates the thermal performance of alginate concrete reinforced with basalt fiber. For that purpose, an extensive literature review was carried out then two experimental phases for mix design and to investigate the compressive strength of samples at a temperature range of 100–180 °C were conducted. The results show that the addition of basalt fiber (BF) and/or alginate may slightly decrease the compressive strength compared to the control concrete under room temperature, but it leads to control decreasing compressive strength during exposure to a high temperature range of 100–180 °C. Moreover, it can be seen that temperature raise influences the rate of strength growth in alginate basalt fiber reinforced concrete. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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18 pages, 3756 KiB

Open AccessArticle

Effects of Erosion Form and Admixture on Cement Mortar Performances Exposed to Sulfate Environment

by Peng Liu, Ying Chen and Zhiwu Yu

Crystals 2020, 10(9), 774; https://doi.org/10.3390/cryst10090774 - 01 Sep 2020

Cited by 4 | Viewed by 1878

Abstract

The effects of the admixtures, erosion age, concentration of sulfate solution, and erosion form of sulfate attack on the mechanical properties of mortar were investigated. Simultaneously, the microstructure, pore characteristics, kinds and morphologies of erosion products of mortar before and after sulfate attacks [...] Read more.

The effects of the admixtures, erosion age, concentration of sulfate solution, and erosion form of sulfate attack on the mechanical properties of mortar were investigated. Simultaneously, the microstructure, pore characteristics, kinds and morphologies of erosion products of mortar before and after sulfate attacks were performed by Mercury Intrusion Porosimetry (MIP), Environment Scanning Electronic Microscope and Energy Dispersive Spectrometer (ESEM-EDS). In addition, the crystal form and morphology characteristics of crystallization on mortar surfaces attacked by partial immersion form were studied. The results showed that the compressive and flexural strengths of mortar attacked by sulfate for four months decreased with the increase of the replacement of cement with fly ash, and the corresponding strength of mortar containing slag first increased and then decreased. The admixtures can improve the microstructure and mechanical properties of mortar within the replacement ratio of 10%. Although the change laws of the mortar specimens containing different admixtures were similar, the mortar containing slag had an excellent sulfate resistance under the same condition. Compared with the complete immersion form, the strength variation of the mortar containing fly ash attacked by semi-immersion form was less. The porosity and average pore diameter of mortar attacked by sulfate for four months increased, and the percentage of micropore with the pore diameter less than 200 nm increased. Plenty of rod-like and plate-like erosion products were generated in mortar attacked by a sulfate solution with a high concentration. A larger number of fibrous and flocculent crystallization covered the mortar’s surface containing fly ash, but it was a granular and dense crystallization formed on the mortar’s surface containing slag. Much dendritic erosion product was generated in the mortar attacked by semi-immersion form, and ESEM-EDS analysis revealed that it may be scawtite, spurrite, and residue of the decomposed calcium silicate hydrate (CSH) in the inner mortar; however, the crystallization sodium sulfate was crystallized on mortar surface. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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33 pages, 7071 KiB

Open AccessArticle

A Coupled Modeling Simulator for Near-Field Processes in Cement Engineered Barrier Systems for Radioactive Waste Disposal

by Steven J. Benbow, Daisuke Kawama, Hiroyasu Takase, Hiroyuki Shimizu, Chie Oda, Fumio Hirano, Yusuke Takayama, Morihiro Mihara and Akira Honda

Crystals 2020, 10(9), 767; https://doi.org/10.3390/cryst10090767 - 29 Aug 2020

Cited by 3 | Viewed by 2303

Abstract

Details are presented of the development of a coupled modeling simulator for assessing the evolution in the near-field of a geological repository for radioactive waste disposal where concrete is used as a backfill. The simulator uses OpenMI, a standard for exchanging data between [...] Read more.

Details are presented of the development of a coupled modeling simulator for assessing the evolution in the near-field of a geological repository for radioactive waste disposal where concrete is used as a backfill. The simulator uses OpenMI, a standard for exchanging data between simulation software programs at run-time, to form a coupled chemical-mechanical-hydrogeological model of the system. The approach combines a tunnel scale stress analysis finite element model, a discrete element model for accurately modeling the patterns of emerging cracks in the concrete, and a finite element and finite volume model of the chemical processes and alteration in the porous matrix and cracks in the concrete, to produce a fully coupled model of the system. Combining existing detailed simulation software in this way with OpenMI has the benefit of not relying on simplifications that might be necessary to combine all of the modeled processes in a single piece of software. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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12 pages, 6615 KiB

Open AccessArticle

The Prediction of Stiffness of Bamboo-Reinforced Concrete Beams Using Experiment Data and Artificial Neural Networks (ANNs)

by Muhtar, Amri Gunasti, Suhardi, Nursaid, Irawati, Ilanka Cahya Dewi, Moh. Dasuki, Sofia Ariyani, Fitriana, Idris Mahmudi, Taufan Abadi, Miftahur Rahman, Syarif Hidayatullah, Agung Nilogiri, Senki Desta Galuh, Ari Eko Wardoyo and Rofi Budi Hamduwibawa

Crystals 2020, 10(9), 757; https://doi.org/10.3390/cryst10090757 - 27 Aug 2020

Cited by 9 | Viewed by 2962

Abstract

Stiffness is the main parameter of the beam’s resistance to deformation. Based on advanced research, the stiffness of bamboo-reinforced concrete beams (BRC) tends to be lower than the stiffness of steel-reinforced concrete beams (SRC). However, the advantage of bamboo-reinforced concrete beams has enough [...] Read more.

Stiffness is the main parameter of the beam’s resistance to deformation. Based on advanced research, the stiffness of bamboo-reinforced concrete beams (BRC) tends to be lower than the stiffness of steel-reinforced concrete beams (SRC). However, the advantage of bamboo-reinforced concrete beams has enough good ductility according to the fundamental properties of bamboo, which have high tensile strength and high elastic properties. This study aims to predict and validate the stiffness of bamboo-reinforced concrete beams from the experimental results data using artificial neural networks (ANNs). The number of beam test specimens were 25 pieces with a size of 75 mm × 150 mm × 1100 mm. The testing method uses the four-point method with simple support. The results of the analysis showed the similarity between the stiffness of the beam’s experimental results with the artificial neural network (ANN) analysis results. The similarity rate of the two analyses is around 99% and the percentage of errors is not more than 1%, both for bamboo-reinforced concrete beams (BRC) and steel-reinforced concrete beams (SRC). Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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20 pages, 7075 KiB

Open AccessArticle

Numerical Evaluation of the Perfobond (PBL) Shear Connector Subjected to Lateral Pressure Using Coupled Rigid Body Spring Model (RBSM) and Nonlinear Solid Finite Element Method (FEM)

by Muhammad Shoaib Karam, Yoshihito Yamamoto, Hikaru Nakamura and Taito Miura

Crystals 2020, 10(9), 743; https://doi.org/10.3390/cryst10090743 - 24 Aug 2020

Cited by 12 | Viewed by 2412

Abstract

An analytical investigation focusing on the concrete damage progress of the PBL shear connector under the influence of various lateral pressures, employing a coupled RBSM and solid FEM model was carried out. The analytical model succeeded in simulating the test shear capacities and [...] Read more.

An analytical investigation focusing on the concrete damage progress of the PBL shear connector under the influence of various lateral pressures, employing a coupled RBSM and solid FEM model was carried out. The analytical model succeeded in simulating the test shear capacities and the failure modes adequately. The internal failure process was also clarified; the two horizontal cracks occurred near the top of the concrete dowels through the hole of the perforated steel plate, and afterward, the two vertical cracks also initiated and propagated along with the shear surface. In a low lateral pressure case, the shear strength was determined by the vertical cracks propagated along the shear surface. While as the amount of applied lateral pressure increased, the shear strength of the two vertical cracked surfaces was enhanced, and the shear strength of the PBL was characterized by the occurrence of the splitting cracks and caused the splitting failure into the side concrete blocks. Moreover, the combined effects of lateral pressure and hole diameters were also evaluated numerically, and it was found that the increase in shear strength was more in a large diameter case subjected to high lateral pressure because of the wide compressive regions generated around the concrete dowel. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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14 pages, 4301 KiB

Open AccessArticle

Numerical Simulation of Adsorption of Organic Inhibitors on C-S-H Gel

by Zijian Song, Huanchun Cai, Qingyang Liu, Xing Liu, Qi Pu, Yingjie Zang and Na Xu

Crystals 2020, 10(9), 742; https://doi.org/10.3390/cryst10090742 - 23 Aug 2020

Cited by 7 | Viewed by 2099

Abstract

Corrosion inhibitors are one of the most effective anticorrosion techniques in reinforced concrete structures. Molecule dynamics (MD) was usually utilized to simulate the interaction between the inhibitor molecules and the surface of Fe to evaluate the inhibition effect, ignoring the influence of cement [...] Read more.

Corrosion inhibitors are one of the most effective anticorrosion techniques in reinforced concrete structures. Molecule dynamics (MD) was usually utilized to simulate the interaction between the inhibitor molecules and the surface of Fe to evaluate the inhibition effect, ignoring the influence of cement hydration products. In this paper, the adsorption characteristics of five types of common alkanol-amine inhibitors on C-S-H gel in the alkaline liquid environment were simulated via the MD and the grand canonical Monte Carlo (GCMC) methods. It is found that, in the MD system, the liquid phase environment had a certain impact on the adsorption configuration of compounds. According to the analysis of the energy, the binding ability of MEA on the surface of the C-S-H gel was the strongest. In the GCMC system, the adsorption of MEA was the largest at the same temperature. Furthermore, for the competitive adsorption in the GCMC system, the adsorption characteristics of the inhibitors on the C-S-H gel were to follow the order: MEA>DEA>TEA>NDE>DETA. Both MD and GCMC simulations confirmed that the C-S-H gel would adsorb the organic inhibitors to a different extent, which might have a considerable influence on the organic inhibitors to exert their inhibition effects. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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33 pages, 6952 KiB

Open AccessArticle

New Prediction Model for the Ultimate Axial Capacity of Concrete-Filled Steel Tubes: An Evolutionary Approach

by Muhammad Faisal Javed, Furqan Farooq, Shazim Ali Memon, Arslan Akbar, Mohsin Ali Khan, Fahid Aslam, Rayed Alyousef, Hisham Alabduljabbar and Sardar Kashif Ur Rehman

Crystals 2020, 10(9), 741; https://doi.org/10.3390/cryst10090741 - 22 Aug 2020

Cited by 93 | Viewed by 4500

Abstract

The complication linked with the prediction of the ultimate capacity of concrete-filled steel tubes (CFST) short circular columns reveals a need for conducting an in-depth structural behavioral analyses of this member subjected to axial-load only. The distinguishing feature of gene expression programming (GEP) [...] Read more.

The complication linked with the prediction of the ultimate capacity of concrete-filled steel tubes (CFST) short circular columns reveals a need for conducting an in-depth structural behavioral analyses of this member subjected to axial-load only. The distinguishing feature of gene expression programming (GEP) has been utilized for establishing a prediction model for the axial behavior of long CFST. The proposed equation correlates the ultimate axial capacity of long circular CFST with depth, thickness, yield strength of steel, the compressive strength of concrete and the length of the CFST, without need for conducting any expensive and laborious experiments. A comprehensive CFST short circular column under an axial load was obtained from extensive literature to build the proposed models, and subsequently implemented for verification purposes. This model consists of extensive database literature and is comprised of 227 data samples. External validations were carried out using several statistical criteria recommended by researchers. The developed GEP model demonstrated superior performance to the available design methods for AS5100.6, EC4, AISC, BS, DBJ and AIJ design codes. The proposed design equations can be reliably used for pre-design purposes—or may be used as a fast check for deterministic solutions. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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17 pages, 3235 KiB

Open AccessArticle

Applications of Gene Expression Programming and Regression Techniques for Estimating Compressive Strength of Bagasse Ash based Concrete

by Muhammad Faisal Javed, Muhammad Nasir Amin, Muhammad Izhar Shah, Kaffayatullah Khan, Bawar Iftikhar, Furqan Farooq, Fahid Aslam, Rayed Alyousef and Hisham Alabduljabbar

Crystals 2020, 10(9), 737; https://doi.org/10.3390/cryst10090737 - 21 Aug 2020

Cited by 118 | Viewed by 5005

Abstract

Compressive strength is one of the important property of concrete and depends on many factors. Most of the concrete compressive strength predictive models mainly rely on available literature data, which are too simple to consider all the contributing factors. This study adopted a [...] Read more.

Compressive strength is one of the important property of concrete and depends on many factors. Most of the concrete compressive strength predictive models mainly rely on available literature data, which are too simple to consider all the contributing factors. This study adopted a new approach to predict the compressive strength of sugarcane bagasse ash concrete (SCBAC). A vast amount of data from the literature study and fifteen laboratory tested concrete samples with different dosage of bagasse ash, were respectively used to calibrate and validate the models. The novel Gene Expression Programming, Multiple Linear Regression and Multiple Non-Linear Regression were used to model SCBAC compressive strength. The water cement ratio, bagasse ash percent replacement, quantity of fine and coarse aggregate and cement content were used as an input for models development. Various statistical indicators, i.e., NSE, R² and RMSE were used to assess the performance of the models. The results indicated a strong correlation between observed and predicted values with NSE and R² both above 0.8 during calibration and validation for the Gene Expression Programming (GEP). The outcomes from GEP outclassed all the models to predict SCBAC compressive strength. The validity of the model is further verified using data of fifteen tests conducted in the laboratory. Moreover, the cement content in the mix was revealed as the most sensitive parameter followed by water cement ratio form sensitivity analysis. The GEP fulfilled all the criteria for external validity. The simple formulae derived in this study could be used reliably for the prediction of SCBAC compressive strength. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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13 pages, 5042 KiB

Open AccessArticle

Use of Flue Gas Desulfurization Gypsum, Construction and Demolition Waste, and Oil Palm Waste Trunks to Produce Concrete Bricks

by Lalitsuda Phutthimethakul, Park Kumpueng and Nuta Supakata

Crystals 2020, 10(8), 709; https://doi.org/10.3390/cryst10080709 - 18 Aug 2020

Cited by 14 | Viewed by 3279

Abstract

This research aims to study the utilization of waste from power plants, construction and demolition, and agriculture by varying the ratios of flue-gas desulfurization (FGD) gypsum, construction and demolition waste (CDW), and oil palm trunks (OPT) in concrete production. This research used these [...] Read more.

This research aims to study the utilization of waste from power plants, construction and demolition, and agriculture by varying the ratios of flue-gas desulfurization (FGD) gypsum, construction and demolition waste (CDW), and oil palm trunks (OPT) in concrete production. This research used these as the raw materials for the production of concrete bricks of 15 × 15 × 15 cm. There were 12 ratios of concrete brick, fixing 5.5 wt% of FGD gypsum to replace Portland cement and substituting coarse sand with 0 wt%, 25 wt%, 50 wt%, or 75 wt% of CDW, and gravel with 0 wt%, 0.5 wt%, and 1 wt% of OPT. The initial binder:fine aggregate:coarse aggregate ratio was 1:2:4 and the water to cement ratio was 0.5, curing in water at room temperature for 28 days. Then, all concrete brick specimens were tested for compressive strength and water absorption. From the experiment, it was found that the highest compressive strength of concrete brick specimens was 45.18 MPa, which was produced from 5.5% gypsum without CDW and OPT, while 26.84 MPa was the lowest compressive strength obtained from concrete bricks produced from 5.5% FGD gypsum, 75% CDW, and 1% OPT. In terms of usage, all proportions can be applied in construction and building work because the compressive strength and water absorption were compliant with the Thai Industrial Standard TIS 57-2530 and TIS 60-2516. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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22 pages, 72586 KiB

Open AccessArticle

A Comparative Study on Blast-Resistant Performance of Steel and PVA Fiber-Reinforced Concrete: Experimental and Numerical Analyses

by Le Chen, Weiwei Sun, Bingcheng Chen, Sen Xu, Jianguo Liang, Chufan Ding and Jun Feng

Crystals 2020, 10(8), 707; https://doi.org/10.3390/cryst10080707 - 16 Aug 2020

Cited by 5 | Viewed by 2975

Abstract

This paper deals with the blast-resistant performance of steel fiber-reinforced concrete (SFRC) and polyvinyl alcohol (PVA) fiber-reinforced concrete (PVA-FRC) panels with a contact detonation test both experimentally and numerically. With 2% fiber volumetric content, SFRC and PVA-FRC specimens were prepared and comparatively tested [...] Read more.

This paper deals with the blast-resistant performance of steel fiber-reinforced concrete (SFRC) and polyvinyl alcohol (PVA) fiber-reinforced concrete (PVA-FRC) panels with a contact detonation test both experimentally and numerically. With 2% fiber volumetric content, SFRC and PVA-FRC specimens were prepared and comparatively tested in comparison with plain concrete (PC). SFRC was found to exhibit better blast-resistant performance than PVA-FRC. The dynamic mechanical responses of FRC panels were numerically studied with Lattice Discrete Particle Model-Fiber (LDPM-F) which was recently developed to simulate the meso-structure of quasi-brittle materials. The effect of dispersed fibers was also introduced in this discrete model as a natural extension. Calibration of LDPM-F model parameters was achieved by fitting the compression and bending responses. A numerical model of FRC contact detonation was then validated against the blast test results in terms of damage modes and crater dimensions. Finally, FRC panels with different fiber volumetric fractions (e.g., 0.5%, 1.0% and 1.5%) under blast loadings were further investigated with the validated LDPM-F blast model. The numerical predictions shed some light on the fiber content effect on the FRC blast resistance performance. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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20 pages, 7485 KiB

Open AccessArticle

Enhanced Performance of Concrete Composites Comprising Waste Metalised Polypropylene Fibres Exposed to Aggressive Environments

by Rayed Alyousef, Hossein Mohammadhosseini, Fahed Alrshoudi, Mahmood Md. Tahir, Hisham Alabduljabbar and Abdeliazim Mustafa Mohamed

Crystals 2020, 10(8), 696; https://doi.org/10.3390/cryst10080696 - 12 Aug 2020

Cited by 14 | Viewed by 3094

Abstract

The utilisation of waste plastic and polymeric-based materials remains a significant option for clean production, waste minimisation, preserving the depletion of natural resources and decreasing the emission of greenhouse gases, thereby contributing to a green environment. This study aims to investigate the resistance [...] Read more.

The utilisation of waste plastic and polymeric-based materials remains a significant option for clean production, waste minimisation, preserving the depletion of natural resources and decreasing the emission of greenhouse gases, thereby contributing to a green environment. This study aims to investigate the resistance of concrete composites reinforced with waste metalised plastic (WMP) fibres to sulphate and acid attacks. The main test variables include visual inspection, mass loss, and residual strength, as well as the microstructural analysis of specimens exposed to aggressive environments. Two sets of concrete mixes with 100% ordinary Portland cement (OPC) and those with 20% palm oil fuel ash (POFA) were made and reinforced with WMP fibres at volume fractions of 0–1.25%. The results revealed that the addition of WMP fibres decreased the workability and water-cured compressive strength of concrete mixes. The outcomes of the study suggest that the rate of sulphate and acid attacks, in terms of mass losses, was controlled significantly by adding WMP fibres and POFA. The mutual effect of WMP fibre and POFA was detected in the improvement in the concrete’s resistance to sulphate and acid attacks by the reduction in crack formation, spalling, and strength losses. Microstructural analysis conducted on the test specimens elucidates the potential use of POFA in improving the performance of concrete in aggressive environments. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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28 pages, 4774 KiB

Open AccessArticle

Effect of Aggregate Type and Specimen Configuration on Concrete Compressive Strength

by Sherif Yehia, Akmal Abdelfatah and Doaa Mansour

Crystals 2020, 10(7), 625; https://doi.org/10.3390/cryst10070625 - 19 Jul 2020

Cited by 22 | Viewed by 5170

Abstract

In this paper, concrete mixes utilizing two sizes of natural aggregate and two sources of lightweight and recycled aggregates were used to investigate the effect of aggregate type and specimen size and shape on the compressive strength of concrete. In addition, samples from [...] Read more.

In this paper, concrete mixes utilizing two sizes of natural aggregate and two sources of lightweight and recycled aggregates were used to investigate the effect of aggregate type and specimen size and shape on the compressive strength of concrete. In addition, samples from ready-mix concrete producers with different strengths were evaluated using standard size cylinders and cubes. Results were obtained on the 7th, 28th, and 90th day. In addition, flexural strength, split tension, and modulus of elasticity were evaluated on the 28th and 90th day. Statistical analyses were conducted to examine the significance of the difference between the compressive strength values for each two mixes using tests of hypotheses. Moreover, other mechanical properties as a function of compressive strength were discussed and compared to those predicated by the American Concrete Institute (ACI) specifications. Results indicate specimen shape has a noticeable effect on the compressive strength as the Cylinder/Cube ratio on the 90^th day was ranging between 0.781 and 0.929. The concrete compressive strength and modulus of elasticity were significantly affected by the aggregate type. The flexural strength and split tensile strength were less affected by the aggregate type, which was also confirmed by the values predicted with the ACI equations. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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18 pages, 3619 KiB

Open AccessArticle

Durability Assessment of PVA Fiber-Reinforced Cementitious Composite Containing Nano-SiO₂ Using Adaptive Neuro-Fuzzy Inference System

by Ting-Yu Liu, Peng Zhang, Qing-Fu Li, Shao-Wei Hu and Yi-Feng Ling

Crystals 2020, 10(5), 347; https://doi.org/10.3390/cryst10050347 - 28 Apr 2020

Cited by 7 | Viewed by 2456

Abstract

In this study, the durability of polyvinyl alcohol fiber-reinforced cementitious composite containing nano-SiO₂ was evaluated using the adaptive neuro-fuzzy inference system (ANFIS). According to the structural characteristics of the cementitious composite material and some related standards, the classification criteria for the evaluation [...] Read more.

In this study, the durability of polyvinyl alcohol fiber-reinforced cementitious composite containing nano-SiO₂ was evaluated using the adaptive neuro-fuzzy inference system (ANFIS). According to the structural characteristics of the cementitious composite material and some related standards, the classification criteria for the evaluation indices of cementitious composite materials were clarified, and a corresponding structural framework of durability assessment was constructed. Based on the hypothesis testing principle, the required test data capacity was determined under a certain degree of accuracy, and durability experimental data and expert evaluation results were simulated according to statistical principles to ensure that there were sufficient datasets for ANFIS training. Using an environmental factor submodule as an example, 14 sets of actual test data were used to verify that the ANFIS can quickly and effectively mimic the expert evaluation reasoning process to evaluate the durability of cementitious composites. Compared with other studies related to the durability of cementitious composites, a systematic evaluation system for the durability of concrete was established. We used a polyvinyl alcohol fiber-reinforced cementitious composite containing nano-SiO₂ to conduct a comprehensive evaluation of cementitious composites. Compared with the traditional expert evaluation method, the durability evaluation system based on the ANFIS learned expert experience, stored the expert experience in fuzzy rules, and eliminated the subjectivity of expert evaluation, thereby making the evaluation more objective and scientific. Full article

(This article belongs to the Special Issue Numerical Study of Concrete)

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