Abstract
Taking high geothermal tunnels as background, the deformation of concrete for shotcrete use was studied by simulating hot-humid and hot-dry environments in a laboratory. The research is made up by two parts, one is the influence of two kinds of high geothermal environments on the deformation of shotcrete, and the other is the shrinkage inhibited effect of fiber materials (steel fibers, polypropylene fibers, and the mixture of both) on the concrete in hot-dry environments. The research results show that: (1) in hot and humid environments, wet expansion and thermal expansion happened on concrete, but the deformation is smooth throughout the whole curing age. (2) In hot and dry environments, the concrete suffers from shrinkage. The deformation obeys linear relationship with the natural logarithm of curing age in the first 28 days, and it becomes stable after the 28th day. (3) The shrinkage of concrete in a hot and dry environment can be inhibited by adding fiber materials especially steel fibers, and it also obeys linear relationship with the natural logarithm of curing age before it becomes stable. However, compared with no-fiber condition, it takes 14 days, half of 28 days, to make the shrinkage become stable, and the shrinkage ratio of concrete at 180-day age decreases by 63.2% as well. (4) According to submicroscopic and microscopic analysis, there is great bond strength at the interface between steel fiber and concrete. The fiber meshes are formed in concrete by disorderly distributed fibers, which not only can effectively restrain the shrinkage, but also prevent the micro and macro cracks from extending.
Key Words
high geothermal tunnel; hot-dry environment; shotcrete; deformation; fiber material
Address
Shengai Cui, Yibin Cao and Yuezhong Ye: Department of Building Materials, School of Civil Engineerng, Southwest Jiaotong University, Chengdu 610031, China
Pin Liu and Xuewei Wang: Department of Bridge Engineering, School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China
Abstract
Technological advancements in the field of building materials are achieved day by day. In this study, a new lightweight concrete aggregate is produced by mixing certain rates of colemanite (0%, 7.5%, 12.5%, 17.5%), cement and coating the surface of pumice aggregate with this mixture. Thin aggregate sections are analyzed with specific gravity, unit weight, water absorption, impact, and crushing experiments. In this way, the production of cement and cement+colemanite coated lightweight concrete aggregates is investigated and an opinion on the likely behavior of these concrete types is provided.
Key Words
aggregates/recycled aggregates; cement; construction materials; strengthening; admixtures
Address
Alper Bideci and Özlem Salli Bideci: Department of Architecture, Faculty of Art, Design and Architecture, Duzce University, 81600, Düzce, Turkey
Sabit Oymael: Department of Architecture, Faculty of Engineering and Architecture, İstanbul Arel University, 34537, Istanbul, Turkey
Ali Haydar Gültekin: Department of Geological Engineering, Faculty of Mines, Istanbul Technical University, 34469, Istanbul, Turkey
Hasan Yildirim: Department of Civil Engineering, Faculty of Civil Engineering, Istanbul Technical University, 34469, Istanbul, Turkey
Abstract
The Taiwanese liquid crystal display (LCD) industry has traditionally produced a huge amount of waste glass that is placed in landfills. Waste glass recycling can reduce the material costs of concrete and promote sustainable environmental protection activities. Concrete is always utilized as structural material; thus, the concrete compressive strength with a variety of mixtures must be studied using predictive models to achieve more precise results. To create an efficient waste LCD glass concrete (WLGC) design proportion, the related studies utilized a multivariable regression analysis to develop a compressive strength waste LCD glass concrete equation. The mix design proportion for waste LCD glass and the compressive strength relationship is complex and nonlinear. This results in a prediction weakness for the multivariable regression model during the initial growing phase of the compressive strength of waste LCD glass concrete. Thus, the R ratio for the predictive multivariable regression model is 0.96. Neural networks (NN) have a superior ability to handle nonlinear relationships between multiple variables by incorporating supervised learning. This study developed a multivariable prediction model for the determination of waste LCD glass concrete compressive strength by analyzing a series of laboratory test results and utilizing a neural network algorithm that was obtained in a related prior study. The current study also trained the prediction model for the compressive strength of waste LCD glass by calculating the effects of several types of factor combinations, such as the different number of input variables and the relevant filter for input variables. These types of factor combinations have been adjusted to enhance the predictive ability based on the training mechanism of the NN and the characteristics of waste LCD glass concrete. The selection priority of the input variable strategy is that evaluating relevance is better than adding dimensions for the NN prediction of the compressive strength of WLGC. The prediction ability of the model is examined using test results from the same data pool. The R ratio was determined to be approximately 0.996. Using the appropriate input variables from neural networks, the model validation results indicated that the model prediction attains greater accuracy than the multivariable regression model during the initial growing phase of compressive strength. Therefore, the neural-based predictive model for compressive strength promotes the application of waste LCD glass concrete.
Key Words
waste LCD concrete; compressive strength; back propagation neural networks; multivariable regression analysis; input variable strategy
Address
Chih-Han Kao: Department of Civil Engineering and Engineering Management, National Quemoy University, Kinmen County, 892, Taiwan, R.O.C
Chien-Chih Wang: Department of Civil Engineering and Geomatics, Cheng Shiu University, Kaohsiung City, 83347, Taiwan, R.O.C
Her-Yung Wang: Department of Civil Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung City, 80778, Taiwan, R.O.C
Abstract
The purpose of this study is to establish a prediction model for the electrical resistivity (Er) of self-consolidating concrete by using waste LCD (liquid crystal display) glass as part of the fine aggregate and then, to analyze the results obtained from a series of laboratory tests. A hyperbolic function is used to perform nonlinear multivariate regression analysis of the electrical resistivity prediction model, with parameters such as water-binder ratio (w/b), curing age (t) and waste glass content (G). Furthermore, the relationship of compressive strength and electrical resistivity of waste LCD glass concrete is also found by a logarithm function, while compressive strength is evaluated by the electrical resistivity of non-destructive testing (NDT). According to relative regression analysis, the electrical resistivity and compressive strength prediction models are developed, and the results show that a good agreement is obtained using the proposed prediction models. From the comparison between the predicted analysis values and test results, the MAPE value of electrical resistivity is 17.0-18.2% and less than 20%, the MAPE value of compressive strength evaluated by Er is 5.9-10.6% and nearly less than 10%. Therefore, the prediction models established in this study have good predictive ability for electrical resistivity and compressive strength of waste LCD glass concrete. However, further study is needed in regard to applying the proposed prediction models to other ranges of mixture parameters.
Key Words
concrete; liquid crystal glasses; compressive strength; electrical resistivity; prediction model
Address
Chien-Chih Wang: Department of Civil Engineering and Geomatics, Cheng Shiu University, Kaohsiung, 83347, Taiwan, R.O.C.
Abstract
In this paper, an innovative technique for finite element (FE) modeling of steel tube-confined concrete (STCC) columns with active confinement under axial compressive loading is presented. In this method, a new constitutive model for the stress-strain relationship of actively-confined concrete is proposed. In total, 14 series of experimental STCC stub columns having active confinement were modeled using the ABAQUS software. The results obtained from the 3D model including the compressive strength at the initial peak point and failure point, as well as the axial and lateral stress-strain curves were compared with the experimental results to verify the accuracy of the 3D model. It was found that there existed a good agreement between them. A parametric study was conducted to investigate the effect of the concrete compressive strength, steel tube wall thickness, and pre-stressing level on the behavior of STCC columns with active confinement. The results indicated that increasing the concrete core\'s compressive strength leads to an increase in the compressive strength of the active composite column as well as its earlier failure. Furthermore, a reduction in the tube external diameter-to-wall thickness ratio affects the axial stress-strain curve and the confining pressure, while increasing the pre-stressing level has a negligible effect on the two.
Key Words
concrete constitutive models; confined concrete; finite elements method; pre-tensioned concrete; computer modeling
Address
Mahdi Nematzadeh and Akbar Haghinejad: Department of Civil Engineering, University of Mazandaran, Babolsar, Iran
Abstract
Self-Compacting Concrete (SCC) is a new technology capable to flow without segregation or any addition of energy which leads to efficient construction and cost savings. In this study, the effect of replacing the Ordinary Portland Cement (OPC) with Fly Ash (FA) on the strength, durability of the concrete was investigated experimentally, and carbon footprint and cost were also assessed. Four different replacement FA ratios (0%, 20%, 40% and 60%) were used to create four SCC mixes. Standard test methods were used to determine the workability, strength, and durability of the SCC mixes including resist chloride ion penetration, water permeability, water absorption, and initial surface absorption. The axial cube compressive strength tests were performed on the SCC mixes at 1, 7, 14, 28 and 35 days. Replacing the OPC with FA had a significant positive impact on chloride iron penetration resistance and water absorption but had a considerable negative impact on the compressive strength. The SCC mix with 60% FA had 36.7% and 15.8% enhancement in the resistance to chloride ion penetration and water absorption, respectively. Evaluation of the carbon footprint and the cost of each SCC mixes showed the CO2 emissions mixes 1, 2, 3 and 4 were significantly reduced by increasing the FA content from 0% to 60%. Compared with the control mix, the cost of all mixes increased when the FA content increased, but no significant differences were seen between the estimated costs of all four mixes.
Key Words
self-compacting concrete; durability; fly ash; resist chloride ion penetration; water permeability; water absorption; initial surface absorption
Address
Sahar Deilami, Farhad Aslani and Mohamed Elchalakani: School of Civil, Environmental and Mining Engineering, University of Western Australia, Crawley, WA 6009, Australia
Abstract
The predictive utility of a damage model depends heavily on its particular choice of a damage variable, which serves as a macroscopic approximation in describing the underlying micromechanical processes of microdefects. In the case of spatially perfectly randomly distributed microcracks or microvoids in all directions, isotropic damage model is an appropriate choice, and scalar damage variables were widely used for isotropic or one-dimensional phenomenological damage models. The simplicity of a scalar damage representation is indeed very attractive. However, a scalar damage model is of somewhat limited use in practice. In order to entirely characterize the isotropic damage behaviors of damaged materials in multidimensional space, a system theory of isotropic double scalar damage variables, including the expressions of specific damage energy release rate, the coupled constitutive equations corresponding to damage, the conditions of admissibility for two scalar damage effective tensors within the framework of the thermodynamics of irreversible processes, was provided and analyzed in this study. Compared with the former studies, the theoretical formulations of double scalar damage variables in this study are given in the form of matrix, which has many features such as simpleness, directness, convenience and programmable characteristics. It is worth mentioning that the above-mentioned theoretical formulations are only logically reasonable. Owing to the limitations of time, conditions, funds, etc. they should be subject to multifaceted experiments before their innovative significance can be fully verified. The current level of research can be regarded as an exploratory attempt in this field.
Key Words
double scalar damage variables; damage energy release rate; isotropic; irreversible thermodynamics; theoretical analysis
Address
Xinhua Xue: State Key Laboratory of Hydraulics and Mountain River Engineering, College of Water Resource and Hydropower, Sichuan University, No.24 South Section 1, Yihuan Road, Chengdu, Sichuan, 610065, P.R.China
Wohua Zhang: College of Civil Engineering and Architecture, Zhejiang University, 866 Yuhangtang Road, Hangzhou, Zhejiang, 310058, P.R.China
Abstract
Concrete retaining walls are the most common types of geotechnical structures for controlling instable slopes resulting from lateral pressure. In analytical stability, calculation of the concrete retaining walls is regarded as a rigid mass when its safety is required. When cracks in these structures are created, the stability may be enforced and causes to defeat. Therefore, identification, creation and propagation of cracks are among the important steps in control of lacks and stabilization. Using the numerical methods for simulation of crack propagation in concrete retaining walls bodies are among the new aspects of geotechnical analysis. Among the considered analytical methods in geotechnical appraisal, the boundary element method (BEM) for simulation of crack propagation in concrete retaining walls is very convenient. Considered concrete retaining wall of this paper is Pars Power Plant structured in south side in Assalouyeh, SW of Iran. This wall\'s type is RW6 with 11 m height and 440 m length and endurance of refinery construction lateral forces. To evaluate displacement and stress distributions (o1,max/o3,min), the surrounding, especially in tip and its opening crack BEM, is considered an appropriate method. By considering the result of this study, with accurate simulation of crack propagation, it is possible to determine the final status of progressive failure in concrete retaining walls and anticipate the suitable stabilization method.
Key Words
geotechnique; retaining walls; concrete; crack propagation; simulation; fracture
Address
Mehdi Azarafza and Mohammad-Reza Feizi-Derakhsh: Department of Computer Engineering, Faculty of Electrical & Computer Engineering, University of Tabriz, Tabriz, Iran
Mohammad Azarafza: Department of Geology, University of Isfahan, Isfahan, Iran
Abstract
Recent trend is to use the lightweight concrete in the construction industry because it has several advantages over normal weight concrete. The Lightweight concrete can be produced from the industrial waste materials. In South East Asian region, researchers are very keen to use the waste materials such as oil palm shell (OPS) and palm oil clinker (POC) from the palm oil producing industries. Extensive research has been done on lightweight concrete using OPS or POC over the last three decades. In this paper the aggregate properties of OPS and POC are plotted in conjunction with mechanical and structural behavior of OPS concrete (OPSC) and POC concrete (POCC). Recent investigation on the use of crushed OPS shows that OPSC can be produced to medium and high strength concrete. The density of OPSC and POCC is around 20-25% lower than normal weight concrete. Generally, mechanical properties of OPSC and POCC are comparable with other types of lightweight aggregate concrete. It can be concluded from the previous study that OPSC and POCC have the noteworthy potential as a structural lightweight concrete.
Address
Md. Nazmul Huda, Mohd Zamin Jumaat, Kh Mahfuz ud Darain, M. Obaydullah and Md. Akter Hosen: Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603, Kuala Lumpur, Malaysia
A.B.M. Saiful Islam: Department of Construction Engineering, College of Engineering, University of Dammam, 31451, Dammam, Saudi Arabia
Abstract
In this study, an aging deformation statistical model for a unique high and steep rock slope was proposed, and the aging characteristic of the slope deformation was better reflected. The slope displacement was affected by multiple-environmental factors in multiple scales and displayed the same tendency with a rising water level. The statistical model of the high and steep rock including non-aging factors was set up based on previous analyses and the study of the deformation and residual tendency. The rule and importance of the water level factor as a non-aging unit was analyzed. A partitioned statistical model and mutation model were established for the comprehensive cumulative displacement velocity with the monitoring study under multiple factors and multiple parameters. A spatial model was also developed to reflect and predict the whole and sectional deformation character by combining aging, deformation and space coordinates. A neural network model was built to fit and predict the deformation with a high degree of precision by mastering its feature of complexity and randomness. A three-dimensional finite element model of the slope was applied to approach the structure character using numerical simulations. Further, a three-dimensional finite element model of the slope and dam was developed, and the whole deformation state was analyzed. This study is expected to provide a powerful and systematic method to analyze very high, important and dangerous slopes.
Key Words
high and steep slope; statistic model; spatial model; neural network; finite element model
Address
Meng Yang and Huaizhi Su:
1) State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China
2) College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China
3) National Engineering Research Center of Water Resources Efficient Utilization and Engineering Safety, Nanjing 210098, China
Zhiping Wen: Department of Computer Engineering, Nanjing Institute of Technology, Nanjing 211167, China
Abstract
The strength and deformational capacity of slender reinforced concrete (RC) columns greatly rely on their slenderness ratios, while an additional secondary moment (i.e., the P-
Key Words
reinforced concrete; column; fire resistance; P-M interaction curve; secondary moment; slenderness ratio
Address
Hyun Kang, Deuck Hang Lee, Jungmin Lee and Kang Su Kim: Department of Architectural Engineering, University of Seoul, 163 Seoulsiripdae-ro, Dongdaemun-gu, Seoul 02504, Republic of Korea
Na-Rae Cheon: Metallic Materials and Mechanical Engineering Team, Korea Testing & Research Institute, 98 Gyoyukwon-ro, Gwacheon-si, Gyeonggi-do 13810, Republic of Korea
Heung-Youl Kim: Fire Safety Research Division, Korea Institute of Construction Technology, 182-64 Mado-ro, Mado-myeon, Hwaseong-si, Gyeonggi-do 18544, Republic of Korea
Key Words
reinforce concrete column; simplified; fire resistance; P-M interaction curve; secondary moment; slenderness ratio
Address
Deuck Hang Lee, Minsu Kim, Jungmin Lee, Jae-Yuel Oh and Kang Su Kim: Department of Architectural Engineering, University of Seoul, 163 Seoulsiripdae-ro, Dongdaemun-gu, Seoul 02504, Republic of Korea
Na-Rae Cheon: Metallic Materials and Mechanical Engineering Team, Korea Testing & Research Institute, 98 Gyoyukwon-ro, Gwacheon-si, Gyeonggi-do 13810, Republic of Korea
Abstract
Recently some efforts have been performed to combine the advantages of light-weight and self-compacting concrete in one package called Light-Weight Self-Compacting Concrete (LWSCC). Accurate prediction of hardened properties from fresh state characteristics is vital in design of concrete structures. Considering the lack of references in mixture design of LWSCC, investigating the proper mixture components and their effects on mechanical properties of LWSCC can lead to a reliable basis for its application in construction industry. This study utilizes wide range of existing data of LWSCC mixtures to study the individual and combined effects of the components on the compressive strength. From sensitivity of compressive strength to the proportions and interaction of the components, two equations are proposed to estimate the LWSCC compressive strength. Predicted values of the equations are in good agreement with the experimental data. Application of lightweight aggregate to reduce the density of LWSCC may bring some mixing problems like segregation. Reaching a higher strength by lowered density is a challenging problem that is investigated as well. The results show that, the compressive strength can be improved by increasing the of mixture density of LWSCC, especially in the range of density under 2000 Kg/m3.
Key Words
light-weight self-compacting concrete; mixture design; components; compressive strength; density
Address
Behnam Vakhshouri and Shami Nejadi: Faculty of Engineering and Information Technology, School of Civil and Environmental Engineering, University of Technology Sydney, Australia
Abstract
This study presents investigation of the behavior of moderately thick reinforced concrete slabs having hollow cores with different parameters. The experimental part of this investigation includes testing eight specimens of solid and hollow-core slab models having (2.05 m) length, (0.6 m) width and (25 cm) thickness under two monotonic line loads. Load versus deflection was recorded during test at mid span and under load. Numerically, the finite element method is used to study the behavior of these reinforced concrete slabs by using ANSYS computer program. The specimens of slab models are modeled by using (SOLID65) element to represent concrete slabs and (LINK180) element to represent the steel bars as discrete axial members between concrete nodes. The finite element analysis has showed good agreement with the experimental results with difference of (4.71%-8.68%) in ultimate loads. A parametric study have been carried out by using ANSYS program to investigate the effects of concrete compressive strength, size and shape of core, type of applied load and effect of removing top steel reinforcement.
Key Words
experimental; finite element; reinforced concrete; hollow-core slab
Address
Adel A. Al-Azzawi and Sadeq A. Abed: Department of Civil Engineering, Al-Nahrain University, Baghdad, Iraq
Abstract
Creep and shrinkage are the main types of volume change with time in concrete. These changes cause deflection, cracking and stresses that affect durability, serviceability, long-term reliability and structural integrity of civil engineering infrastructure. Although laboratory test may be undertaken to determine the deformation properties of concrete, these are time-consuming, often expensive and generally not a practical option. Therefore, relatively simple empirically design code models are relied to predict the creep strain.
This paper reviews the accuracy of creep and shrinkage predictions of reinforced concrete (RC) shear walls structures strengthened with carbon fibre reinforced polymer (CFRP) plates, which is characterized by a widthwise varying fibre volume fraction. This review is yielded by three commonly used international \"code type\" models. The assessed are the: CEB-FIP MC 90 model, ACI 209 model and Bazant & Baweja (B3) model. The time-dependent behavior was investigated to analyze their seismic behavior. In the numerical formulation, the adherents and the adhesives are all modelled as shear wall elements, using the mixed finite element method. Several tests were used to demonstrate the accuracy and effectiveness of the proposed method. Numerical results from the present analysis are presented to illustrate the significance of the time-dependency of the lateral displacements and eigenfrequencies modes.
Key Words
RC shear walls strengthened; CFRP plates; creep and shrinkage; finite element method; seismic behavior; numerical modeling
Address
Redha Yeghnem:
1) Department of Civil Engineering and Hydraulics, University Dr. Tahar Moulay, PBox 138 City En-Nasr 20000 Saida, Algeria
2) Laboratory of Materials and Hydrology (LM&H), University Djillali Liabés, Sidi Bel Abbès, Algeria
Hicham Zakaria GUERROUDJ and Lemya HANIFI HACHEMI AMAR: Department of Civil Engineering and Hydraulics, University Dr. Tahar Moulay, PBox 138 City En-Nasr 20000 Saida, Algeria
Sid Ahmed Meftah: Laboratory of Structures et Matériaux Avancés dans le Génie Civil et Travaux Publics (SMAGCTP), University Djillali Liabés, Sidi Bel Abbès, Algeria
Samir Benyoucef and El Abbas Adda Bedia: Laboratory of Materials and Hydrology (LM&H), University Djillali Liabés, Sidi Bel Abbès, Algeria
Abdelouahed Tounsi:
1) Laboratory of Materials and Hydrology (LM&H), University Djillali Liabés, Sidi Bel Abbès, Algeria
2) Laboratory of Structures et Matériaux Avancés dans le Génie Civil et Travaux Publics (SMAGCTP), University Djillali Liabés, Sidi Bel Abbès, Algeria
Abstract
Strut-and-tie modeling method, which evolved on truss-model approach, has generally been preferred for the design of complex reinforced concrete structures and structural elements that have critical shear behavior. Some structural members having disturbed regions require exceptional detailing for all support and loading conditions, such as the beam-column connections, deep beams, short columns or corbels. Considering the general expectation of exhibiting brittle behavior, corbels are somewhat dissimilar to other shear critical structures. In this study, reinforcement layout of a corbel model was determined by the participation of structural optimization and strut-and-tie modeling methods, and an experimental comparison was performed against a conventionally designed model.
Address
Fatih Mehmet Özkal: Department of Civil Engineering, Erzincan University, 24060 Erzincan, Turkey
Habib Uysal: Department of Civil Engineering, Atatürk University, 25240 Erzurum, Turkey
