Material Properties Of Concrete Research Articles

Investigating Concrete Properties Using Dielectric Constant from Ground Penetrating Radar Scans

Determining the material properties and existing capacity of concrete infrastructure using nondestructive techniques is challenging due to evolving design requirements, unknown as-built conditions, and ongoing maintenance and deterioration. Concrete’s material properties, including density, porosity, and compressive strength, are usually determined by mechanical testing, but being able to measure these properties noninvasively could aid engineers in maintaining and designing concrete infrastructure. Research into nondestructive methods for determining material properties of concrete has shown relationships between mechanical properties and ground penetrating radar (GPR) properties such as dielectric constant, attenuation, and instantaneous amplitude. We investigated direct relationships between dielectric constant and the density, porosity, and compressive strength of 23 mature concrete samples with varying mix designs using a commercial 1 GHz GPR. In normal-weight concrete, weak trends were seen between a dielectric for compressive strength (R2=0.76) and one for density (R2=0.64), whereas no significant trend was found with porosity (R2=0.52). The GPR unit used provides acceptable data but has limited resolution for analyses and utility. The dielectrics showed distinct clustering by mix type—particularly the inclusion of materials such as blast furnace slag. While demonstrating that the dielectric constant is a candidate for rapid concrete comparisons, there is also a demonstrated need for further investigation of the complex relationships between mechanical and electromagnetic properties in concrete.

A critical evaluation on nuclear safety properties of novel cadmium oxide-rich glass containers for transportation and waste management: Benchmarking with a reinforced concrete container

We examine the nuclear safety properties of a newly designed cadmium oxide-rich glass container for nuclear material to a bitumen-reinforced concrete container. Individual transmission factors, detector modelling, and energy deposition (MeV/g) in the air are calculated using MCNPX (version 2.7.0) general purpose Monte Carlo code. Two container configurations are designed with the material properties of cadmium dioxide-rich glass and Concrete + Bitument in consideration. First, individual transmission factors for 60Co and 137Cs radioisotopes are calculated. To evaluate potential environmental consequences, energy deposition amounts in the air for 60Co and 137Cs are also determined. The minimum gamma-ray transmission rates for two container types are reported for a cadmium dioxide-rich glass container. In addition, the quantity of energy deposition is varied depending on the container type, with a lower value for cadmium dioxide-rich glass container. The 40% cadmium dioxide-doped glass container provides more effective safety than the Cement + Bitumen container, according to the overall findings. In conclusion, the utilization of cadmium dioxide-doped glass material along with its high transparency and advanced material properties may be a significant and effective option in areas where concrete is required to assure the safety of nuclear materials.

Predicting transverse crack properties in continuously reinforced concrete pavement

Transverse crack properties (crack spacing and crack width) are important indicators of service life performance of continuously reinforced concrete pavements (CRCP). Crack properties are related to concrete material properties, reinforcement ratio, interface friction between both the concrete-base layer and concrete-steel, and the local climatic conditions. An improved analytical model with a bilinear concrete-base friction relationship is presented to predict crack spacing and crack width from concrete drying shrinkage and temperature contraction. The proposed 1D model was validated with test section data from a continuously reinforced concrete beam resting on asphalt base layer, which contained two reinforcement ratios, a standard paving concrete, and a lightweight aggregate concrete. A sensitivity study of model determined the bond stiffness coefficient between the concrete and reinforcement, bar spacing and diameter, elastic modulus of the reinforcement, and concrete drying shrinkage had the greatest impact on both crack spacing and crack width.

The Effects of the Addition of Polyurethane-MgO Nanohybrids on the Mechanical Properties of Ordinary Portland Cement Paste.

One of the most important methods of controlling the properties of concrete and cement-based materials is to control the rate and kinetics of cement hydration. In the present study, novel flexible polyurethane-decorated MgO nanohybrids were synthesized using a simple chemical method, added to cement paste in different amounts, and utilized as an effective mechanical performance-enhancing factor for cement paste. It was observed that by adding 3 wt% synthesized PU-MgO nanohybrids to cement paste, its mechanical properties were improved and its compressive strength and flexural strength were increased by up to 13% and 15%, respectively, compared to the plain cement, after 45 days. The effect mechanism of adding PU-MgO nanoparticles on the properties of the cement paste was investigated. The addition of PU-MgO nanohybrids increased the pozzolanic reactions and formed more C-S-H phases.

Overall deformation of steel-concrete-steel immersed structures during construction stage considering temperature effect

Temperature effect is one of the most significant factors to be considered in large-scale structures. For steel–concrete-steel composite immersed structures, the overall deformation is a closely watched indicator in the construction process. The main aim of this study is to investigate the overall deformation of steel–concrete-steel composite immersed structures during the construction stage, and thus a new numerical method comprehensively considering the temperature effect and material properties of early-age concrete is proposed. In the proposed method, a new finite element program for composite immersed structures, including thermal and structural modules, is developed in ANSYS. Firstly, the time-varying temperature distribution of the structure during the construction stage is accurately simulated by a transient thermal analysis, allowing for concrete hydration, solar radiation, air temperature, and changes of thermal properties comprehensively. Secondly, based on the ANSYS User-Programmable Features (UPFs), the stress–strain constitutive law of the concrete is redefined by modifying the material subroutine to consider the hardening and shrinkage of early-age concrete, then the overall structural deformation during the construction stage is estimated in the case that accurate temperature distribution and material properties are fully considered. Finally, a full-scale model of the composite immersed tunnel in Shenzhong Link is taken as an application case. The accuracy of simulation results is verified with the data of on-site monitoring. The results show that the temperature field of the composite immersed structure is obviously non-uniform and time-varying, and the overall contraction in lateral and longitudinal directions happens after the construction due to the variation of temperature and behaviors of early-age concrete.

Safety evaluation of cracked concrete structures with crack length index

Cracks always pose a great threat to the heath of concrete structures, and safety evaluation becomes an essential task during the life cycle of these cracked structures. In this study, a new safety evaluation method of cracked concrete structures is proposed based on the Boundary Effect Model (BEM). Firstly, the fracture theory is introduced to predict the constant fracture properties of concrete materials regardless the effect of specimen size and crack length. Then, the non-linear relationship between bearing capacity and crack length of cracked concrete beams is established. Next, the established equation is verified by three groups of three-point bending test results with different specimen sizes and crack lengths. Finally, combined with relevant standard, the safety evaluation method is proposed using crack length as an index. Comparing with the traditional methods adopted in standard, the newly-developed methods which use crack length as a safety evaluation index appears to be more convenient and accurate.

Impacts of climate change on long-term reliability of reinforced concrete structures due to chloride ingress

This paper presents the effect of climate change on the long-term reliability of concrete structures due to chloride ingress. The impact has been demonstrated for three regions across the globe for the best and worst-case climate change scenarios. The methodology adopted here can be divided into three main steps. The first one is the development of a machine learning regression model using CatBoost for estimation of surface chloride levels, which is a function of temperature, concrete material properties, exposure conditions, and chloride levels in the seawater. The CatBoost model fitted over the experimental data has a mean absolute error (MAE) and root mean square error (RMSE) value of 0.11 and 0.16, respectively, and a high R2 value of 0.82. The second step is solving the coupled non-linear partial differential equation for temperature, humidity, and chloride ingress in concrete with time. A parametric study considering the effect of external parameters (temperature, humidity, exposure condition, and chloride levels in water) reveals the complexity and the dependencies of the chloride ingress process on external parameters. The final step involves the reliability analysis to estimate the time for chlorides to reach threshold levels at the rebar level using the numerical model. The input for the numerical model is temperature and humidity condition for different representative concentration pathways (RCP) scenarios, the material properties of concrete, and the exposure conditions. The reliability analysis shows that, for the concrete structure located in Dubai, UAE, and Cascais, Portugal, the mean time to corrosion initiation decreases due to climate change and it increases for the structure located in Tasmania, Australia. Further, the structures that are built in the future may have lower service life compared to the structures that were built in the past. Based on the study it concluded that it is necessary to consider the impact of climate change on service life to design resilient structures.

Fracture characteristics of sustainable crumb rubber concrete under a wide range of loading rates

The dynamic mechanical properties of concrete materials significantly influences the safety of construction under impact loads. In this study, a comprehensive experiment on the crack straight-through flattened Brazilian disc specimens of crumb rubber concrete (CRC) is undertaken. Three specific experiments were performed to obtain the wide loading-rate ranges of fracture characteristics, i.e., the quasi-static test, drop-hammer impact test, and split Hopkinson pressure bar test. The measured and calculated results are also discussed. The results reveal that the fracture toughness and energy are both positively correlated with loading rate. Moreover, a transition loading rate (around 1 GPa × m1/2/s) exists between the high and low loading rates, and the enhancing effect of high loading rate on fracture toughness cannot be neglected. The analysis of the dynamic increased factor (DIF) on the fracture toughness (DIFk) and fracture energy (DIFg) of CRC shows that DIFk and DIFg are related to the rubber content. Furthermore, the analysis demonstrates that crumb rubber particles can enhance the crack resistance of concrete under dynamic loads. Accordingly, empirical models for the DIFk and DIFg of CRC are proposed based on the experimental data. In addition, the mechanisms by which the loading-rate affects the fracture characteristics were preliminarily identified by observing the failure modes under various loading-rate loads. This study is intended to help spread the application of crumb rubber in concrete materials.

Integrated wavelet-learning method for macroscopic mechanical properties prediction of concrete composites with hierarchical random configurations

In this research, a novel integrated wavelet-learning approach with high-accuracy and efficient prediction capability is developed to predict the effective elastic properties of concrete composites with hierarchical random configurations and heterogeneous elasticity in multiple spatial scales. The significant contributions of this work include: (1) The random structural heterogeneities and material uncertainties of concrete composites in meso-scale and micro-scale are modeled on the basis of modified authors’ previous researches and Weibull probabilistic model separately. (2) Innovative stochastic three-scale asymptotic homogenization method (STAHM), background grid technique and padding strategy are presented to thoroughly acquire the doubly random geometry and material features of concrete composites with hierarchical random configurations for constructing concrete material databases. (3) The wavelet transform is utilized to preprocess the high-dimensional data features of the material databases, and the wavelet coefficients are employed as the novel input neurons for efficiently establishing more plain wavelet-neural networks that possess increasing capacity and resisting noise for approximating mappings of high complexity and nonlinearity. The numerical experiments and achieved results demonstrate that the integrated wavelet-learning approach is robust for the high-accuracy and efficient prediction of effective elastic properties of concrete materials with random heterogeneity patterns in multiple spatial scales.

Shear Strength Prediction Model for RC Exterior Joints Using Gene Expression Programming.

Predictive models were developed to effectively estimate the RC exterior joint’s shear strength using gene expression programming (GEP). Two separate models are proposed for the exterior joints: the first with shear reinforcement and the second without shear reinforcement. Experimental results of the relevant input parameters using 253 tests were extracted from the literature to carry out a knowledge analysis of GEP. The database was further divided into two portions: 152 exterior joint experiments with joint transverse reinforcements and 101 unreinforced joint specimens. Moreover, the effects of different material and geometric factors (usually ignored in the available models) were incorporated into the proposed models. These factors are beam and column geometries, concrete and steel material properties, longitudinal and shear reinforcements, and column axial loads. Statistical analysis and comparisons with previously proposed analytical and empirical models indicate a high degree of accuracy of the proposed models, rendering them ideal for practical application.

High-efficient low-cost characterization of composite material properties using domain-knowledge-guided self-supervised learning

Modern AI-assisted approaches have revolutionized our abilities to better understand the properties of concrete and composite materials. However, current machine learning models such as supervised learning (SL) models usually require a large amount of training data to feed the model. Here, we introduce self-supervised learning (SSL) to address the issue of lacking labeled data in concrete material characterization. We propose a generalized SSL-based framework with domain knowledge and demonstrate its robustness to predict the properties of a commonly-used composite material (concrete) with the fewest data possible. Our numerical results show that the performance of the proposed SSL model can match the commonly-used supervised learning model with only 5 % of data, and the SSL model is also proven with ease of implementation. Our study paves the way to expand further the usability of machine learning tools for composite material fields and the broader material science community.

Bibliographic analysis on 3D printing in the building and construction industry: Printing systems, material properties, challenges, and future trends

In recent years, significant advancements in developing large-scale 3D printers and construction materials have been made to meet industrial-scale 3D printing construction demand. Constructing the buildings and structural components using 3D concrete printing is significant. The main benefits of additive manufacturing (AM) are freedom of design, construction waste reduction, mass customization, and the ability to manufacture complex structures. The major issues include optimizing the printing material with suitable properties for 3D concrete printing. However, this technology for green building construction seems to improve conventional methods by reducing human resource requirements, high investment costs, and formworks. The research community's interest in 3D printing for architecture and construction has grown significantly over the last few years. As a result, there is a need to combine existing and ongoing research in this area to understand better current problems and their potential solutions based on future research work. This paper reviews the latest trend of research and state-of-the-art technologies in 3D printing in building and construction by analyzing the publications from 2002 to 2022. Based on the above-mentioned analysis of publications, printing methods, concrete printing systems, and the influence of constituent materials and chemical admixtures on concrete material properties are briefly discussed. The challenges and recommendations of 3DCP, including reinforcement, development of new materials, multi-nozzle combinations, life cycle assessment of 3DCP, and development of hybrid systems, are then examined. This paper concluded with a discussion of the limitations of existing systems and potential future initiatives to enhance their capability and print quality.

Bibliographic analysis on 3D printing in the building and construction industry: Printing systems, material properties, challenges, and future trends

In recent years, significant advancements in the development of large-scale 3D printers and construction materials have been made to meet the demand for industrial scale 3D printing construction. It is significant to construct the buildings and structural components by using 3D concrete printing. Additive manufacturing (AM) main benefits are freedom of design, construction waste reduction, mass customization, and ability to manufacture the complex structures. The major issues including the optimization of printing material which possess the suitable properties for 3D concrete printing. However, this technology towards the green building construction seems to improve the conventional methods by reducing the requirement of human resource, high investment cost, and formworks. The research community's interest in 3D printing for architecture and construction has grown significantly over the last few years. This paper review the latest trend of research and state of the art technologies in 3D printing in building and construction by analyzing the publications from 2002 to 2022. Based on aforementioned analysis of publications, printing methods, concrete printing systems and influence of constituent’s materials and chemical admixtures on concrete material properties are briefly discussed. Finally, this paper discussed the challenges and limitations of current systems, as well as potential future work to improve their capability and print quality.

Development of Test Methods to Evaluate the Printability of Concrete Materials for Additive Manufacturing.

This study proposes test methods for assessing the printability of concrete materials for Additive Manufacturing. The printability of concrete is divided into three main aspects: flowability, setting time, and buildability. These properties are considered to monitor the critical quality of 3DCP and to ensure a successful print. Flowability is evaluated through a rheometer test, where the evolution of shear yield strength is monitored at a constant rate (rpm), similar to the printer setup. Flowability limits were set based on the user-defined maximum thickness of a printed layer and the onset of gaps/cracks during printing. Setting time is evaluated through an ultrasonic wave pulse velocity test (UPV), where the first inflection point of the evolution of the UPV graph corresponds to the setting time of the concrete specimen. The results from this continuous non-destructive test were found to correlate with the results from the discrete destructive ASTM C-191 test for measuring setting time with a maximum difference of 5% between both sets of values. Lastly, buildability was evaluated through the measurement of the early-age compressive strength of concrete, and a correlation with the UPV results obtained a predictive model that can be used in real-time to non-destructively assess the material buildability. This predictive model had a maximum percentage difference of 13% with the measured values. The outcome of this study is a set of tests to evaluate the properties of 3D printable concrete (3DP) material and provide a basis for a framework to benchmark and design materials for additive manufacturing.

Environmental and energy benefits assessment of alkali-activated concrete (AAC) energy pile

Energy piles provide an innovative strategy for exploiting geothermal energy in low-energy buildings, as they simultaneously provide energy for space conditioning and support structural loads. In addition to research efforts aimed at improving the energy efficiency of energy piles, a significant amount of CO2 emission from concrete production has been overlooked in energy piles’ application. This study proposes an innovative energy pile utilizing alkali-activated concrete (AAC) to reduce CO2 emissions and meanwhile improve energy extraction capacity. A systematic investigation of the energy and environmental benefits of AAC energy pile is conducted. After characterizing the material properties of AAC and traditional Portland cement concrete (PCC), the CO2 emission is evaluated. Furthermore, a numerical model for energy pile is established to study the energy harvesting potential of AAC and PCC energy piles under different operating conditions. The results show that the AAC energy pile is a promising technology that will not only extract approximately 17% more thermal energy due to its improved thermal properties, but also reduce CO2 emission by 32% compared to PCC energy pile. This study demonstrates the feasibility of AAC for energy pile construction and will provide support for the design and implementation of AAC energy piles.

Polymer Foam Concrete FC500 Material Behavior and Its Interaction in a Composite Structure with Standard Cement Concrete Using Small Scale Tests.

This paper focuses on the investigation of the material properties of FC500 foam concrete. Innovation is very important for the solution of cast-in-place concrete forms in practice today. Part of its innovative construction application is the possibility of using foam concrete in a composite structure and the use of its mechanical properties in the load-bearing parts of civil engineering structures. The method of detecting the mechanical properties of foam concrete by using non-standard cantilever test is also innovative. Here, an advanced approach of modelling specimens using powerful computational systems based on the finite element method is used. This modern material is researched especially for its use in transportation structures. For its application, it is necessary to define its resistance to mechanical loads. The main content of the research consists of correlations between experimental measurements and analytical and numerical results. This is the principle of quasi-linear identification of the non-linear behavior of polymeric cementitious porous material during tests on specimens. The focus of the research is an extensive experiment: measurements of the deformation of the specimens until failure. The following methods were chosen to investigate the material properties: small cantilever test, standard tensile test and compression test. The cantilever test was performed for the individual components of the FC500 composite and cement concrete, but also as a compact composite. Numerical simulation models were developed to correlate the individual results in order to validate the uniaxial test results. The conclusions of the research led to the definition of standardized stress–strain diagrams of the FC500 material for compression and especially tension. This is a definition of the behavior of this polymer composite, usable for the development of numerical models of full-scale structures. The results of the research will be applied in the development of national standards for the use of advanced materials in transportation structures (cycle paths, parking lots, traffic playgrounds, lightly trafficked forest roads and trails, etc.).

A general unified method for calculating fire resistance of CFST columns considering various types of steel and concrete

Due to the advantages of CFST structures, various types of steel (e.g., ordinary/high strength/stainless steel, etc.) and concrete (e.g., ordinary/high strength/ultra-high performance/recycled concrete, etc.) are used in them, and fire safety design is an indispensable part in the structural design of CFST. However, there is still a lack of a simple unified fire design method that can consider different materials and their combinations at the same time. Based on the unified calculation method of fire resistance of CFST based on average temperature proposed by the authors, this paper focuses on enhancing the generality and accuracy of the unified method, with specific attention paying to the prediction of material properties degradation effect and cross-sectional average temperature under fire. For the prediction of material properties degradation effect with considering various types of steel and concrete, two methods, namely the global equivalent method and the segmented equivalent method, are proposed to convert arbitrary temperature reduction factor models defined at material level to the corresponding equivalent models defined at CFST section level. After validating with various types of steel and concrete material properties reduction factor models given in the previous literature, it turns out that the equivalent models generated by the two methods can well approximate the temperature-induced degradation effect at CFST section level. As for the prediction of average temperature with considering various types of steel and concrete, an incremental calculation method to calculate the average temperature of steel tube and concrete core is proposed, which is compatible with various thermal property models for different types of steel and concrete without any intermediate conversion techniques. In the meantime, this incremental calculation method can be adopted for CFST members with or without protection and is also consistent with the temperature calculation formulas for steel structures given in Code. In conclusion, the improvements made in this paper can expand the application scope of the previously proposed unified method to various types of concrete materials and thus enhance the generality of the method.

Regularisation methods for modelling flexural dominant lightly reinforced concrete walls

Localisation can occur in distributed plasticity fibre models when a strain-softening response at the section restricts the spread of damage due to the unloading of stress in adjacent sections/elements. Past studies have developed regularisation schemes for the concrete compression response and reinforcement tension response to achieve mesh objective simulations for the failure of reinforced concrete (RC) walls. However, for walls designed with low amounts of longitudinal reinforcement, the response and failure are controlled by the tensile behaviour, including concrete cracking and reinforcement fracture. The aim of this study was to develop reliable regularisation approaches that could be implemented into fibre models to simulate the cracking and reinforcement fracture response for lightly reinforced concrete walls. Methods for regularisation of both the reinforcement and concrete material properties using a fracture energy method were proposed to minimise the effect of element size on the strain localisation during nonlinear analysis of lightly reinforced concrete walls. The proposed regularisation techniques were validated against the measured response of tested lightly reinforced walls subjected to both monotonic and cyclic loading to ensure that both the cracking strength, ultimate strength, and ultimate drift capacity could be accurately simulated. The local strain response was also investigated to highlight the post-processing of model outputs required to achieve objective simulation results. The results indicate that the models implementing the proposed regularisation of concrete and reinforcement constitutive models could accurately predict the global hysterical response as well as the local strain response of lightly reinforced concrete walls.

The Complexity of Virtual Reality Technology in the Simulation and Modeling of Civil Mathematical Models

Abstract Because civil engineering structures include stressed structural members and unstressed non-structural members, it isn’t easy to obtain the true parameters of the model when modeling. The article uses a virtual reality fuzzy random modeling to establish a steel bearing force model in civil engineering operations. We determined the relevant bearing capacity parameters based on the corrosion of steel bars in civil engineering. The research found that the numerical simulation method determined in this paper has grasped the essence of stress rate, concrete material properties, and dynamic load effect to a considerable extent.

Impact of drying on concrete and concrete structures

This study reviews research showing changes in the performance of reinforced concrete structures and members caused by drying conditions, and aims to contribute to evaluating the structural safety in the long-term use of concrete. Additionally, to build a consensus on the changes in the physical properties of concrete materials after drying, the review focused on experiments intended to produce a uniform distribution of moisture-induced material property changes in the interior of the cross-section.
 There is generally no effect on the change in the maximum loading capacity of a structure when the design is based on the flexural performance of the components. However, in the case of structures dominated by members determined by the shear capacity of the components, the reduction of the maximum loading capacity can be a problem. The decrease in stiffness is largely due to the opening of shrinkage cracks and the reduction of the Young’s modulus of concrete after drying. The change in the compressive strength of concrete due to drying is governed by the specific strength change of hardened cement paste caused by the colloidal nature, but it is also affected by the shrinkage of the aggregate, which changes the damage in concrete under drying.