High Strength Concrete Materials Research Articles

Sustainability study of mix design of high-strength concrete based on fly ash

Concrete is the most widely used building material in the construction of buildings, bridges, highways, and other infrastructure. With the spread of environmental preservation ideas and technological improvement, high-strength concrete materials and their sustainable hybrid design methods have been developed. A sustainable mix design approach for high-strength concrete (HSC) is critical for the construction industry as it is one of the major emitters of CO2 emissions worldwide. Fly ash concrete is an environmentally friendly, economical and sustainable building material. This paper analyzes the sustainable mixed design method of fly ash concrete by combining past scholars' research and practical experience. By analyzing the properties of fly ash, theoretical principles, and some sustainable mixed design methods, the properties (such as durability, compressive strength, etc.) of fly ash HSC are studied. It is found that the properties of fly ash HSC and traditional HSC are similar or even stronger in some aspects, which has a good improvement on the compatibility and durability of concrete. In the future, with the progress of science and technology, people will further study fly ash and HSC, and the application of fly ash in HSC will certainly get greater development, and achieve green development and sustainable development while meeting the strength of concrete.

Evaluation of Structural Stresses of Mountain-Embedded Railway Systems

Mountain railways are constructed on terrains with steep gradients and operate under unique conditions as they climb slopes at low speeds using rack rails. Recently, mountain railway systems in the form of embedded rail systems (ERSs) have been developed to minimize environmental damage caused by the construction of new roads. However, the use of ERS in mountain railway tracks is still limited, and research on their safety and behavior is lacking. Therefore, this study was conducted to evaluate the safety profile and behavioral responses of mountain-ERS under a steep gradient condition of 180‰. The effects of using high-strength concrete materials for precast concrete panels were investigated in this study, and the safety profile and behavioral response of mountain-ERS based on changes in the gradient and after adjusting the thickness of the subgrade of mountain-ERS was assessed. Under load conditions, the maximum tensile stress in the concrete elements did not exceed the tensile strength of the concrete. In the structural behavioral analysis, the patterns of stress variation were analyzed by applying stress to the concrete elements. The safety assessment and behavioral analysis results obtained in this study are considered valuable foundational research data for analytical studies on mountain-ERSs.

Machine learning models for predicting axial compressive capacity of circular CFDST columns

Machine learning (ML), widely recognized for its advanced predictive capabilities, is progressively being employed in structural design. Concrete-filled double skin steel tubular (CFDST) members are extensively utilized due to their exceptional mechanical behavior. However, existing formulas encounter challenges in accurately calculating the axial compressive capacity of circular CFDST members, particularly when high-strength concrete and steel materials are involved, leading to complexity and low accuracy. This paper presents a data-driven framework that leverages the superior predictive performance of machine learning approaches to predict the axial compressive capacity of circular CFDST columns. Finite element models are developed through secondary development of ABAQUS using custom script, which are then validated against experimental data, confirming their effectiveness and applicability. A general database is established, comprising 226 test results and 550 finite element results obtained from the script, to facilitate the prediction of axial compressive capacity for circular CFDST columns. By incorporating the physical mechanisms of CFDST members and conducting correlation analysis, the input parameters for the machine learning models are determined. Decision Tree, Artificial Neural Network (ANN), K-nearest neighbor (KNN) and two ensemble methods including Random Forest, XGBoost, are trained and optimized using the database to provide accurate predictions. The results demonstrate that the KNN model exhibits superior performance and high accuracy, outperforming the four commonly used calculation formulas in the field, particularly for circular CFDST columns using high-strength materials. The proposed data-driven framework shows promising potential for achieving outstanding predictive performance.

High-strength rectangular concrete-filled steel tube long columns: Parametric studies and design

High-strength steel and concrete materials (i.e., steel with yield stress Fy > 525 MPa and concrete with compressive strength f'c > 70 MPa) have been applied in various types of structures because they can increase the resistance and space efficiency of the structure. However, the AISC Specification (AISC 360-16) does not permit the use of high-strength materials in concrete-filled steel tube (CFT) members due to a lack of adequate research. This paper aims at investigating the behavior of high-strength CFT long columns and evaluating the applicability of current design equations for high-strength rectangular CFT long columns. Firstly, an experimental database including 74 tests of high-strength rectangular CFT long columns was compiled and gaps in the database were identified. Then, finite element (FE) models were developed and benchmarked for parametric studies. The effects of width-to-thickness ratio of the steel tube, yield stress of steel, compressive strength of concrete, and length-to-depth ratio of the member were investigated. Finally, new design equations for high-strength rectangular CFT long columns were proposed based on the modified slenderness reduction factor in AISC 360-16.

Experimental study on permeability of spun high strength concrete material during mechanical loading

The pretensioned spun high strength concrete pipe pile (PHC pipe pile) is widely applied in important infrastructures of off-shore zones due to its low permeability and high capacity. During the construction process and the whole service period of PHC pipe piles, the damage is inevitably caused by many reasons, which may eventually cause the early durability failure of piles. Many researches have been conducted to study the change in permeability of normal concrete due to mechanical damage. However, the relation between permeability and damage of spun high strength concrete (SHSC) is still not been studied. To quantitively investigate the change of permeability of SHSC, a series of specimens of PHC pipe piles were tested for the change of permeability during mechanical loading process in this study. As a result, the relation of stress and permeability of spun high strength concrete as well as the crack roughness of the SHSC is obtained for efficient application in engineering. Before the 40% stress ratio, the permeability of the SHSC is slightly decreased as the compressive stress increases. The mean value and standard deviation of the intrinsic permeability of the SHSC are increased as the compressive stress loading reaches the peak stress. The order of magnitude of the crack roughness ξ can be taken as 10- 4 for engineering application. Compared with the vibrate-casted concrete, the crack roughness ξ is smaller, indicating that the crack surface of SHSC is rougher than the vibrate-casted concrete.

High-Strength Building Material Based on a Glass Concrete Binder Obtained by Mechanical Activation

As part of the work, the chemical interaction of finely ground glass (~1 μm), calcium oxide, and water was studied. It is shown that an increase in the fineness of grinding makes it possible to abandon autoclave hardening in the production of products on a hydrosilicate binder. The study of chemical interaction was carried out by calculating the thermodynamic equilibrium and was also confirmed by XRD analysis. DTA analysis showed that an increase in the treatment temperature leads to an increase in the proportion of the reacted phase at the first stage. Subsequently, phase formation is associated with the presence of CaO. The carrier of strength characteristics is the CaO×2SiO2×2H2O phase. The selection and optimization of the composition make it possible to obtain a high-strength glass concrete material with a strength of about 110 MPa. The micrographs of the obtained samples correspond to classical hydrosilicate systems.

Machine learning-based evaluation of parameters of high-strength concrete and raw material interaction at elevated temperatures

High-strength concrete (HSC) is vulnerable to strength loss when exposed to high temperatures or fire, risking the structural integrity of buildings and critical infrastructures. Predicting the compressive strength of HSC under high-temperature conditions is crucial for safety. Machine learning (ML) techniques have emerged as a powerful tool for predicting concrete properties. Accurate prediction of the compressive strength of HSC is important as HSC can experience strength losses of up to 80% after exposure to temperatures of 800°C–1000°C. This study evaluates the efficacy of ML techniques such as Extreme Gradient Boosting, Random Forest (RF), and Adaptive Boosting for predicting the compressive strength of HSC. The results of this study demonstrate that the RF model is the most efficient for predicting the compressive strength of HSC, exhibiting the R2 value of 0.98 and lower mean absolute error and root mean square error values than the other applied models. Furthermore, Shapley Additive Explanations analysis highlights temperature as the most significant factor influencing the compressive strength of HSC. This article provides valuable insights into the timely and effective determination of the compressive strength of HSC under high-temperature conditions, benefiting both the construction industry and academia. By leveraging ML techniques and considering the critical factors that influence the compressive strength of HSC, it is possible to optimize the design and construction process of HSC and enhance its resilience to high-temperature exposure.

Dynamic compressive and splitting tensile characteristics of rubber-modified non-autoclaved concrete pipe piles

Non-autoclaved concrete pipe piles are gaining attention as an environmentally friendly alternative to autoclaved concrete pipe piles. The purpose of this study was to investigate the changes in the impact resistance of a non-autoclaved concrete pipe pile with the addition of rubber. To this end, various volume fractions of rubber particles were used to replace the fine sand in the non-autoclaved pipe pile concrete (0%, 5%, 10%, 15% and 20%). The dynamic and static mechanical responses of rubber-modified non-autoclaved pipe pile concrete were explored through quasi-static and dynamic compression and splitting tensile tests. The results showed that (1) The tensile-compression ratio of the rubber-modified non-autoclaved pipe pile concrete increased with the rubber content, and the brittleness of non-autoclaved concrete was improved by adding rubber. (2) When subjected to impact load, rubber particles could absorb some of the impact energy, reduce the impact load on the aggregate, and prevented the aggregate from being crushed. (3) The impact toughness index and energy consumption ratio of non-autoclaved pipe pile concrete increased with the increase of rubber content. When the rubber content was 10%, the impact toughness index and energy consumption ratio of non-autoclaved pipe pile concrete were 52.2% and 51.2% higher than those of non-autoclaved pipe pile concrete without rubber particles, respectively, and its impact resistance was the best. The impact resistance of rubber-modified non-autoclaved pipe pile concrete was better than that of traditional autoclaved pipe pile concrete, and met the mechanical performance requirements of prestressed high-strength concrete pipe pile. It could be used as a new prestressed high-strength concrete pile material, which helped to reduce energy consumption in the production process of piles. The study provided parameter basis for the subsequent drop hammer impact test and numerical simulation of pipe piles.

Synthesis and influencing factors of high-performance concrete based on copper tailings for efficient solidification of heavy metals

Copper tailings containing a large amount of heavy metals such as Pb, Cu, As, Mn, and Cr discharged from its mining are a typical bulk solid waste, which is highly hazardous to human and the environment. This research proposed a sustainable and effective method for the environmentally sound utilization of copper tailings solid waste. A high-strength concrete material with copper tailings as the main raw material was successfully prepared, with a 28-day compressive strength of up to 85.35 MPa, the flexural strength reached 12.46 MPa, and the tailings utilization rate of 60%. The mechanical properties and heavy metal stabilization properties of the prepared high-performance concrete were obtained by adding coarse aggregates such as river sand, while changing the sand rate, cementitious material admixture and water-cement ratio. A long-term leaching experiment of the high-strength concrete material with 190 day was carried and proved that the material can be made with low or no risk of heavy metal contamination in copper tailings. Incorporation of copper tailings into the high-performance concrete hydration mainly contains three mechanisms: (i) Pore sealing effect generated by the formation of tailings geopolymer prompted the hardening of the geopolymer layer to form a monolithic package structure; (ii) The active SiO2 material in copper tailings reacts with Ca(OH)2 in the hydration products to produce a strong volcanic ash effect; (iii) the primary hydration of 3CaO·SiO2(C3S) and 3CaO·Al2O3(C3A) in the cement, and the secondary hydration reaction induced by the copper tailings and silica fume. These mechanisms are blended with each other to form a dense microstructure of the slurry, which embodies extremely high mechanical properties on a macroscopic scale, providing a reference role for the bulk utilization of copper tailings.

High value-added resource treatment of antimony tailings: preparation of high-strength lightweight foam concrete materials

The continuous exploitation of global mineral resources leaves ever increasing tailings, which leads to the accumulation of antimony tailings and causes antimony pollution accidents. The complex chemical composition and associated harmful elements of antimony tailings limit their large-scale consumption and high-value comprehensive utilization. To realize the solidification/stabilization of antimony tailings with heavy metals and achieve large-scale high-value utilization, in this paper, high-strength and lightweight concrete materials based on antimony tailing powder were prepared by using antimony tailing powder as the main raw material, and cement clinker, activator, coagulant and foaming agent as the supplements. In this manner, the performance of high-strength and lightweight concrete materials were investigated and optimized in terms of mechanical properties, waterproofing properties, micromorphology, etc. The experiment results show that the decrease of the compressive strength and apparent density of the specimen slurry is due to the increased amount of antimony tailing micronized powder. Additionally, the influence of different foaming agents on the material is significant. With the addition of antimony tailing of 50% and H2O2 of 0.6% into the cementitious material of PC42.5, the material presents optimal high-strength and lightweight performance. Moreover, the compressive strength at 28 d reaches up to 36.2 MPa, and the dry apparent density is as high as 1449.2188 kg/m3. In addition, the optimal system has been optimized in terms of waterproof performance. Softening coefficient of the composite with optimized composition was increased by 55.1%, reaching 0.86, which is sufficiently high for waterproof application.

Shear performance of lightweight concrete filled hollow flange cold-formed steel beams

Concrete-infilled hollow flange cold-formed steel (CF-HFCFS) beams have gained attention in the construction practices owing to many benefits in terms of their structural performances and applicability. The concrete infill ensures better structural performance by restraining the buckling instabilities of thin-walled cold-formed steel elements. However, the shear strength characteristics of CF-HFCFS are not systematically explored yet and hence there is a lack of understanding on the shear strength characteristics of CF-HFCFS beams. Therefore, in this research, shear characteristics were investigated through numerical studies by establishing and analysing three-dimensional finite element (FE) models of CF-HFCFS beams. The developed FE models were verified against the experimental data in terms of failure modes, ultimate shear capacities, and load-displacement characteristics. Then a series of parametric analyses were carried out to investigate the shear behaviour of CF-HFCFS beams against the effects of geometrical (steel thickness, beam depth) and mechanical (yield strength of steel and compressive strength of concrete) properties to further verify the shear characteristics of CF-HFCFS. Lightweight normal and lightweight high strength concrete materials were considered as infill. Also, the influence of the concrete infill on the ultimate shear capacity of the CF-HFCFS beams was evaluated through parametric studies. The ultimate shear capacities were compared against the already available design provisions. Consequently, based on the data established through of parametric analyses, modified design provisions are developed to estimate the ultimate shear capacity of CF-HFCFS beams.

Experimental investigation on the stress-strain behavior of unsaturated polyester polymer concrete subjected to monotonic and cyclic loadings

The use of polymer concrete (PC) in construction requires the development of an accurate stress-strain relationship that can accurately predict the mechanical properties of PC. Given that no constitutive equation for cyclic loading of unsaturated polyester PC (UPPC) is available in the literature, the goal of the current research has been to propose a rational analytical model for estimating the mechanical characteristics of UPPC under tensile and compressive loading. Compressive and tensile cyclic and monotonic tests were performed on specimens which had been cured for 28 days and the average monotonic stress-strain curve was obtained for the monotonic tests. The average maximum stress and strain were determined for both the compressive and tensile tests and the elastic modulus and energy absorption capacity were computed and compared with the values for normal concrete (NC) and high strength concrete (HSC) materials. Analytical models for the monotonic and skeleton curves for both tensile and compressive tests have been provided, and the proposed models were compared to experimental findings and other research results for validation. Stress-strain relationships have been proposed for the unloading and reloading paths and were compared with the cyclic test results. The ultimate stress and strain for the UPPC were three and five times higher, respectively, than for the NC in tension testing. The ultimate strain for UPPC was almost 150% greater than the final strain of HSC in compression. Under compressive loading, the UPPC absorbed to 2.33 and 5.3 times more energy, respectively, than the HSC and NC. The results showed that the skeleton curves agreed well with the monotonic curves for the compressive and tensile tests. All of the proposed models agreed well with the available experimental data and previous study results.

Study on Workability High Strength Concrete Containing Pineapple Leaf Fiber (PALF)

The addition of fibers in concrete increases bridging force in interfacial transition zones inside the concrete matrix. Pineapple Leaf Fiber (PALF) is a natural fiber that has the potential to replace artificial fibers as reinforcement on concrete. As reinforcement fiber in concrete, PALF will undergo fibrillation and water absorption in concrete mixture and will change the mechanical properties of fresh concrete. So, the purpose of this study is to study the workability characteristics of fresh state concrete given PALF. Some variations of PALF composition are 0.04, 0.09, and 0.15 % wt. of cement is mixed into fresh concrete mixture with water-cement (w/c) ratio variations of 0.35, 0.38, and 0.41. The planned concrete is high-strength concrete, then the provisions of determination of coarse and fine aggregates using sieve analysis according to high-strength concrete material standards and concrete mixtures are given superplasticizer 0.09% wt. of cement constantly for all mixtures. A slump test method is still an option in this study, where this method becomes the standard to determine workability effectively. The results showed that an increase in concrete strength was achieved in the addition of PALF composition in concrete compared to control (normal concrete), in addition to the tendency of the relationship between w/c ratio, slump value, and compressive strength in all PALF variations achieved in this study.

Editorial: Composite Use of High Strength Steel and Concrete Materials for Sustainable Civil Engineering

The need for sustainable construction has been hastened world-widely aiming to reduce the use of construction materials and labor costs. To do so, high strength materials will be one option.The higher the strength, the smaller the member size is required. This will free up more usable floor area and require fewer materials and construction work. The composite use of them makes the aim easier to be achieved. To bridge the gap between theoretical development and practical application, a special issue with the research topic of "Composite Use of High Strength Steel and Concrete Materials for Sustainable Civil Engineering" has been organized by the Guest Surely the high temperature and cooling deteriorated the bond strength, and this would have an adverse influence on the ultimate load-carrying capacity of the composite members.The diverse nature of contributions in this collection is a testament to the cross-disciplinary research activities about the composite use of high strength materials. Nevertheless, there is a common thread running through all contributions where high strength, when properly achieved, can be the source of great creativity in achieving more sustainable construction.

Fire performance of composite columns made of high strength steel and concrete

The use of high strength steel and concrete materials for composite column construction is partly impeded by the lack of research on their fire performance. In EN1994-1-1, the highest concrete grade allowed for designing composite columns is capped at C50. This paper investigates the behaviour of concrete encased steel (CES) composite columns made of C120 concrete and S500/690 steel section under ISO834 standard fire through a series of experimental and numerical analyses. Fire tests were carried out on five high strength CES column specimens subject to varying eccentricity of loading to study their behaviours in fire. Polypropylene fibres were added into the high strength concrete mix to prevent the explosive spalling so that explicit modelling of cover spalling phenomenon can be omitted in the numerical analysis. A unified method is proposed to determine the transient strain of high strength concrete at elevated temperatures, allowing the stress-strain curves in EN1992-1-2 to be extended to high strength concrete up to C120. A numerical model, which can capture the strain reversal of concrete caused by the flexural deformation of columns at elevated temperatures, is proposed to enable a good prediction of axial displacement responses of CES columns in comparison with the test results. Finally, based on the validated numerical model and parametric studies, a new tabulated data method is proposed for the fire resistance design of CES columns with concrete class up to C90 concrete and steel section grade up to S550.

Thermal behavior of Concrete subjected to elevated temperature: Case Studies

Fire presents a significant danger to the survival of the building and inhabitants, adverse effects at the structural level. In view of this, several researchers have measured the fire efficiency and behavioural characteristics of concrete under varying temperatures. Using indirect measures such, water permeability, as chloride ion permeability absorption and sorptivity, the resilience of concrete after fire exposure is assessed. In most previous literature, residual mechanical properties mentioned may be overvalued, where cooling was typically employed. Proper assessment of concrete fire resistance requires more experimental data found under different cooling environments, such as water spraying or water quenching. Design considerations and analytical methods are provided to determine the reaction of reinforced concrete structures to elevated-temperature settings. Related studies in which reinforced concrete structural components have being exposed to cyclic loading. The purpose of this review is to provide a description of the elevated temperature characteristics of the performance of concrete ingredients and structures. The impacts of high temperatures on high-strength concrete materials are observed and their quality is compared to standard concrete strength.

New type of lightweight high-strength foamed concrete blocks

Lightweight high-strength concrete materials have been paid increasing attention with the development of the civil engineering technology. This study tested the effects of the admixture ratio on the properties of lightweight high-strength foamed concrete (LWHSFC) samples in a laboratory. The results demonstrated that a type of foamed concrete with 1200 kg/m3 density and >15 MPa uniaxial compressive strength can be produced by chemical foaming and by adding three types of materials (i.e., silica fume, slag, and fly ash) to the cement–fine sand matrix at an optimized mix ratio. The laboratory tests also showed that the failure mechanism of the LWHSFC was similar to ordinary concrete (i.e., longitudinal splitting failure). The angle between the failure surface and the vertical load direction was 53°–76°, indicating the material’s brittleness. The decreasing order of the compressive strength of the LWHSFC with one type of mineral powder when tested 28 days after casting was: silica fume to slag to fly ash. Moreover, the decreasing order of the compressive strength of the LWHSFC with two types of mineral powder admixtures when tested 28 days after casting was silica fume + slag to silica fume + fly ash to slag + fly ash.

Improving the Durability of High Early Strength (HES) Concrete Patching Materials for Concrete Pavements

High early strength (HES) concrete patching materials are increasingly used to repair damaged pavements. The use of HES concrete enables the repaired pavement to be opened to traffic shortly after the repair has been installed; for example, opening pavements to traffic 4–6 h after the concrete is placed is becoming more common. HES concrete mixtures are typically designed with a low water-to-cement ratio and a high cement content; they contain accelerating admixtures and limited supplementary cementitious materials. As a result, these HES patches may be susceptible to self-desiccation, causing autogenous shrinkage and early age cracking. Self-desiccation can lead to reduced hydration, limited strength gain, and overestimation of strength development in maturity-based predictions. The objectives of this study are threefold. First, the paper will illustrate how self-desiccation can lead to the premature cessation of hydration and increased potential for shrinkage cracking. Second, the paper will illustrate how maturity-based predictions can be modified to account for self-desiccation. Third, internal curing is discussed as a way to mitigate self-desiccation and shrinkage ultimately improving the performance of HES concrete patching materials.

Validation of Micromechanical Model for Prediction of ITZ Thickness of High-Strength Concrete Containing Secondary Cementitious Materials

The mechanical properties of a cementitious composite are strongly affected by interfacial transition zone (ITZ) between the matrix and the aggregates, mainly by its strength and thickness. A micromechanical model based on Mori-Tanaka scheme coupled with an estimation of deviatoric stress in ITZ was developed for evaluation of the effect of selected secondary cementitious materials (SCMs – silica fume, fly ash and metakaolin) on the properties of ITZ in high-strength concrete (HSC). The model was validated by means of comparison of predicted ITZ thickness with direct ITZ thickness measurements performed by a combination of scanning electron microscopy and grid nanoindentation. Very good agreement between the theoretical and experimental results was reached, therefore the developed micromechanical model can be used for further research and optimization of HSC containing SCMs. Silica fume was determined to be the most efficient supplementary cementitious material from the point of view of ITZ thickness reduction.

3D non-linear finite element analysis of concentrically loaded high strength reinforced concrete column with GFRP bar

The use of High Strength Concrete (HSC) material in Reinforced Concrete (RC) column has become widely used. HSC was found to be durable, strong in compression, but it has low ductility. This low ductility of HSC can be improved by providing confinement. However, for HSC with concrete strength higher than 70 MPa, additional clause for confinement in ACI 318-19 generates denser arrangement of transverse bars and eventually creates weak planes between the concrete core and the cover. These weak planes can trigger early cover spalling. To reduce the utilization of confining bars, high-strength Glass Fiber Reinforce Polymer (GFRP) bar can be used. However, the performance of GFRP bar varies significantly from their uniaxial behavior in tension or compression to the real performance when it is used as the main reinforcement. For that reason, this paper tries to investigate the behavior of HSC RC column with bars made of conventional steel rebar and with GFRP bars. Due to limited data on the strain gauge reading on the GFRP bars from the available test result, an inverse analysis is carried out to determine the best stress-strain curve for GFRP bars used as the main reinforcement. For that purpose, an inhouse finite element package called 3D-NLFEA is used. From the comparisons, it was found out that the peak load, softening behavior, and the concrete core enhancement prediction agrees well with the test result. From the inverse analysis, only 25% and 45% of the GFRP bar yield strength can be deployed when loaded under compression and tension, respectively.