Concrete Mixtures Research Articles

Ultra-high performance concrete with high strength, workability, loading durability and low curing maintenance for applications in airport pavement

With the rapid development of the aviation industry, airport pavement is subjected to ever-increasing loads, posing urgent and higher demands on the mechanical performance and durability of pavement materials. This study develops a novel Ultra-High Performance Concrete (UHPC) with outstanding mechanical properties, good workability, low curing maintenance, and excellent performance in sustaining long-term load to specially designed for its potential application in airport pavement. The as-developed UHPC contains a mixed portion of fine and coarse aggregate, assuring its workability and avoiding the early-age shrinkage crack for the potential on-site construction. With a 7-day compressive strength of 140MPa, compressive strength of 155.1MPa, flexural strength of 25.4MPa at 28 days, and a wear loss per unit area of 0.043kg/m2, the mechanical properties of UHPC well outperform those of conventional C30 airport pavement concrete. Finite element simulation analysis reveals that a 10cm thick UHPC surface layer demonstrates durability and safety under aircraft taxiing and landing impact loads, with a maximum tensile stress of 4.12MPa well below its tensile strength limit of 8.75MPa. Furthermore, it is predicted that a 10cm thick UHPC overlay could support a load cycle lifespan 1014 times longer than that of conventional C30 concrete of 30cm thickness, indicating its potential to significantly extend the service life of airport pavement. This research provides a theoretical basis for the applications of UHPC in airport pavement and presents innovative perspectives on into material and structural design of airport pavement materials for the future.

Effect of steel fibers on the stress–strain behaviour of aligned steel fiber ultra-high performance concrete under uniaxial compression

The mechanical properties of ultra-high performance concrete (UHPC) can be significantly enhanced by aligning the fibers. Aligned steel fiber UHPC (ASF-UHPC) was fabricated using a uniform magnetic field, yet the corresponding stress-strain relationship has not been extensively studied, hindering accurate calculations. To address this gap, ASF-UHPC was prepared and subsequently subjected to CT scans and uniaxial compression tests to investigate its stress-strain behavior. The analysis of failure mode and stress-strain curves revealed distinct anisotropic characteristics in compressive stresses and fiber distributions. Various steel fiber parameters, including the alignment orientation, volume fraction, and length, were systematically analysed to assess their impact on the material properties. A unit-cell model was developed to elucidate the influence of the fiber alignment orientation on UHPC performance. The results demonstrate that a parallel fiber alignment significantly enhances the elastic modulus, albeit with a Poisson ratio similar to that of the matrix, owing to the limited lateral confinement. Conversely, perpendicular fiber alignment restrains lateral deformation, enhancing the material strength and toughness. Randomly distributed fibers offered a degree of horizontal confinement, whereas inclined fibers induced horizontal thrust, leading to excessive lateral deformation and consequent elevation of the Poisson ratio. Finally, predictive equations for UHPC elastic modulus and compressive strength, along with an analysis model for stress-strain characteristics, were refined taking into account the direction of fiber arrangement.

Micro-mechanical performance study of the interfacial transition zone in ultra-high performance concrete containing coarse aggregates based on digital image correlation method

To measure the mechanical properties of the interfacial transition zone (ITZ) in ultra-high performance concrete with coarse aggregates (UHPC-CA) under direct load, a mesoscopic experimental analysis is performed using a combination of an electron microscope (EM) camera and digital image correlation (DIC) technology in this study. With such a methodology, the stress-strain curve of the ITZ under compression is measured directly. Furthermore, the distribution of the nominal compressive elastic modulus (E⁎) and Poisson's ratio (v) of the ITZ is obtained. Finally, the effects of granulated blast-furnace slag (GGBS) contents (0%, 30%, 40%, and 50%) on ITZ’s properties are investigated, and their relevance to microstructure is further explored by scanning electron microscope (SEM). The results indicate that the E⁎ in the ITZ follows a 'U'-shaped distribution. In comparison to the reinforced matrix, a compaction process in ITZ is observed obviously, resulting in a smaller v in this region. Besides, as the GGBS content increases, the mesoscopic mechanical properties of the ITZ gradually decline.

Shear resistance of UHPC connection for prefabricated reinforced concrete slabs with shear grooves and dowel rebars

The shear resistance of post-cast ultra-high-performance concrete (UHPC) connections for assembled prefabricated normal strength concrete (NSC) slabs having shear grooves and dowel rebars was investigated. The effects of different factors on the failure mode and shear capacity were investigated by direct shear tests of 28 Z-shaped specimens. The influencing factors included the groove configuration, lap and anchorage length of dowel rebar (the height of UHPC connection), strength of NSC prefabricated slab, and rebar location. The failure modes, UHPC connection shear-slip behavior, dowel rebar strains, and failure mechanism were analyzed. The results indicated that two major failure modes might occur in UHPC connection, including tensile fracture within UHPC connection and shear fracture of UHPC grooves at UHPC-NSC interface. Generally, a larger UHPC connection and smaller groove key width could lead to failure in UHPC-NSC interface, otherwise in UHPC connection. Failure in UHPC connection could exhibit a relatively larger peak bearing capacity than failure in UHPC-NSC interface, but also larger post-peak degradation. In addition, increasing UHPC groove width, UHPC connection height, and prefabricated slab NSC strength could increase the shear capacity. Calculation methods of the peak and post-peak residual shear load-bearing capacity of UHPC connection under different failure modes were also proposed, exhibiting good agreement with the test results.

Damage model of NC-UHPC interface zone in UHPC wet joint based on DIC

The bond interface of the ultra-high performance concrete (UHPC) wet joint composed of normal concrete (NC) and UHPC is a weak part, which can easily damage the interface zone and affects the structure's safety. However, the damage model of the NC-UHPC interface zone in UHPC wet joint has not been carried out yet. In this study, firstly, the effects of different interfacial moisture content and interfacial roughness on the interfacial bond strengths were investigated by splitting tensile tests, NC-UHPC specimens with different interfacial bond strength were obtained, and digital image correlation (DIC) technique was used to obtain the strain evolution regulation of the NC-UHPC interface zone; Secondly, the extended interface zone damage factor Df was used to investigate the damage differences of NC-UHPC interface zone with different bond strengths; Finally, the damage model of NC-UHPC interface zone with different interfacial bond strengths was established. This research will be of great significance in improving the theoretical system of UHPC wet joint structure design.

Behavior of Hybrid Natural Fiber Reinforced Polymers Bars Under Uniaxial Tensile Strength and Pull-Out Loads with UHPC

This study evaluated the uniaxial tensile strength and bond performance of natural hybrid reinforcement bars. Hybrid FRP combines multiple fibers and matrixes, resulting in a desirable performance. Two types of hybrid bars were tested: one with natural fibers surrounded by glass fiber, and the other with a steel core surrounded by natural fiber and then glass fiber. Thirteen samples were used to assess tensile behavior, with four groups including glass fiber, flax, sisal, and jute fibers. Pull-out behavior testing was conducted on twelve samples, divided into four groups of fiberglass, flax, sisal, and jute. Each group used three types of concrete: normal, high strength, and ultra-high-performance concrete (UHPC). The results refer to flax samples that had a higher tensile strength and elastic modulus of 143MPa and 38GPa, respectively, than samples made of sisal and jute fibres. The hybrid bars with a steel core exhibited a significant improvement in elastic modulus of 206% in compared to samples made solely from glass, sisal, and jute fibers. On the other hand, the samples with UHPC showed the highest bond strength. The sample U-GFRP with ultra-high-performance concrete showed the highest bond strength 9.32MPa, while the sample N-GFRP with normal concrete showed the lowest bond strength 5.87MPa, respectively. However, this study suggests that hybridizing natural fibers can be a cost-effective and eco-friendly alternative to synthetic fibers.

Surface electrical properties of UHPFRC with graphene

The role of graphene inclusion in ultra-high-performance concrete (UHPC) and in ultra-high-performance fiber reinforced concrete (UHPFRC) and the role of steel fibres (used in UHPFRC) have been studied. Surface electrical properties were shown as useful means to deeply investigate the properties of UHPFRC including graphene. Due to the inclusion of fibers a marked increasing of surface conductivity was shown in UHPFRC respect to UHPC. Surface conductivity has been estimated ∼20% lower than bulk conductivity in mature UHPFRC. A method for assessing the dispersion grade of graphene in concrete, based on surface electrical measurements and numerical modelling, is presented. In case of mature UHPC, increasing surface conductivity with increasing the graphene content was observed. In case of UHPFRC, graphene within the investigated range of contents (≤ 1% bwoc) was found not to greatly affect surface conductivity. With including graphene, a reduction of microstructural disorder was estimated, whereas the inclusion of fibers was estimated to increase the microstructural disorder.

Isostatic and frictional energy dissipating connecting systems for UHPC curtain walls: Design and experimental validation

Ultra-high performance concrete (UHPC) curtain wall is a new type of non-structural building envelope component. Given its large size and high cost, rational connecting systems should be employed to prevent potential seismic damage and economic losses. In this study, two novel connecting systems, including an isostatic connecting system and a frictional energy dissipating connecting system, were proposed for reinforced concrete (RC) frame with UHPC curtain walls. The design methods for these two connecting system were provided first. Then, to evaluate the feasibility of the proposed connecting systems and the corresponding design methods, three 1/2-scale RC frame structures (i.e., one bare frame without curtain walls, one with isostatic curtain wall connecting system, and one with frictional energy dissipating curtain wall connecting system) were designed and fabricated for pseudo-static tests. The damage evolution, failure mode, strength, stiffness, and energy dissipation capacity of the three test substructures were assessed. The test results demonstrated that through reasonable design, independent rocking deformation of the curtain walls was achieved in both the isostatic and frictional energy dissipating connecting systems, allowing the curtain walls to remain free from damage even under an inter-story drift of 1/36, thus validating the reliability of the proposed connecting systems and design methods. Further, compared to the bare frame, curtain walls employing the isostatic connecting system exhibited a negligible effect on the seismic performance of the frame. On the contrary, curtain walls employing frictional energy dissipating connecting system effectively enhanced the strength and energy dissipation capacity of the frame, allowing dual damage control for both walls and frame. Consequently, the frictional energy dissipating connecting system is considered to be a more rational method for enhancing the seismic performance of buildings.

Shear behavior of FRP-UHPC composite beams enhanced by FRP shear key: Experimental study and theoretical analysis

To investigate the shear behavior of FRP (fiber reinforced polymers)-UHPC (ultra-high performance concrete) composite beams, four-point bending tests were conducted on seven FRP-UHPC specimens and two FRP-NSC (normal strength concrete) specimens, having different width and depth of concrete flange as well as FRP shear key (FSK) spacing. The slip between FRP profiles and concrete flange was controlled by employing FSK and epoxy resin bonded hybrid connection. The failure pattern, load-deflection/strain curves, and sliding response of composite beams were analyzed to study the influence of concrete type, FSK spacing, width and thickness of concrete slab. The results indicate that FRP-UHPC composite beams exhibited shear failure, while FRP-NSC composite beams experienced bending-shear failure. The composite beams demonstrated shear-lag effect, which became more pronounced with the increasing of the concrete slab width. The use of UHPC, reducing FSK spacing, and increasing the size of cross-section of concrete flange can effectively enhance the shear performance and reduce interface sliding. Formulae were developed to predict the shear capacity and deflection, considering shear deformation. The results predicted by the formulae developed match well with the experimental results.

Shear performance of 25 m full-scale prestressed UHPC-NC composite I-beam without stirrups

The burgeoning preference for prestressed Ultra-High Performance Concrete (UHPC) I-girders without stirrups, stemming from the remarkable tensile strength of UHPC, indicating a promising trajectory for future construction endeavors. This research delved into real-world engineering scenarios, focusing on shear tests conducted on both 9.0m and 6.5m segments cut off a 25.0m full-scale prestressed UHPC-NC composite I-beam without stirrups, which had already undergone flexural failure. Employing Finite Element Models (FEM), the study scrutinized and forecasted test outcomes. In asymmetric loading shear test, the end with a lower shear span ratio and higher shear capacity fails earlier. Subsequently, a validated FEM, reflective of the tested beam, was established. Leveraging this validated model, a comprehensive analysis ensued, probing into parameters influencing the shear performance of the full-scale prestressed UHPC-NC composite I-beam without stirrups. Parameters under study encompassed the prestressed tension level, web width, and shear span ratio. Findings revealed minimal impact of prestressed tension level on the shear performance of the tested beam, with augmented web width substantially enhancing stiffness and shear capacity. Conversely, an increase in shear span ratio correlated with a decline in shear performance of the tested beam. Finally, it juxtaposed various predictive equations for the shear capacity of the beams without stirrups from disparate global locales, advocating for the utilization of equations outlined in the French equation to predict the shear capacity of the tested beams in this study, aiming for minimized margin of error and conservative estimation.

Dynamic behavior of full-scale GFRP bar-reinforced ultra-high-performance concrete-encased concrete-filled double-skin steel tubular bridge columns under lateral impact loading

In this paper, a novel full-scale glass fiber-reinforced polymer (GFRP) bar-reinforced ultra-high-performance concrete (UHPC)-encased concrete-filled double-skin steel tubular bridge column (referred to as a GFRP-UHPC-encased CFDST column) is proposed and investigated under lateral impact loading. Detailed three-dimensional nonlinear finite element models of twenty-three full-scale columns subjected to rigid vehicle impact are established and simulated, including twenty GFRP-UHPC-encased CFDST columns, one GFRP-normal strength concrete (NSC)-encased CFDST column, one GFRP bar reinforced UHPC (GFRP-UHPC) column, and one steel bar reinforced UHPC (steel-UHPC) column. The models incorporate the strain rate effects of GFRP, steel, and concrete materials, as well as the effects of concrete confinement provided by the steel tubes and stirrups. The accuracy of the numerical models is validated against test results. A full-range analysis of the dynamic response of the GFRP-UHPC-encased CFDST column, GFRP-NSC-encased CFDST column, GFRP-UHPC column, and steel-UHPC column is conducted and discussed in detail. Furthermore, the impact resistance contributions of each component of the columns are analyzed and explored. The impact resistance of the GFRP-UHPC-encased CFDST column surpasses that of the GFRP-NSC-encased CFDST column, the GFRP-UHPC column, and the steel-UHPC column, demonstrating promising cooperation between its components. Finally, parametric studies are conducted to examine the influence of impact velocity and key geometric parameters on the dynamic behavior of GFRP-UHPC-encased CFDST columns. The impact velocity, the ratio of the outer steel tube diameter to the total column diameter (do/D), the ratio of the inner steel tube diameter to the total column diameter (di/D), and the thickness of the outer steel tube significantly influence the lateral impact behavior of GFRP-UHPC-encased CFDST columns, while the effect of the inner steel tube thickness is negligible.

Laboratory Evaluation of Mechanical Properties and Noise Absorption in Magnetite-Enhanced Concrete for Pavement Applications

This paper aims to evaluate the effects of incorporating magnetite as an aggregate in concrete mixtures and as a partial replacement for Portland cement in standard mortar mixtures, focusing on performance and mechanical properties. Noise pollution from cement concrete pavements has become a significant concern for residents, making it a priority to implement effective measures to reduce traffic noise pollution. The primary goal of this research is to explore the relationship between mixture design variables with magnetite aggregates as a partial replacement for Portland cement in concrete pavement and the mixture's acoustic performance. Samples with 0, 10, 20, 30, 40, and 50% replacement of aggregates with magnetite sand were prepared initially. Subsequently, Portland cement was replaced with 0, 1, 2, 3.5, 5, 7.5, 10, 15, and 20% magnetite concentrate powder in standard mortar. Routine tests, such as slump, density, and flow table, were conducted on fresh concrete and mortar. Additionally, compressive strength, flexural strength, water absorption, electrical resistance, and impedance tube tests were performed on the concrete and mortar mixes. The impedance tube measurements demonstrated an increase in the sound absorption coefficient for concrete incorporating magnetite compared to the reference concrete. Among the tested concrete samples, the one containing 50% magnetite as aggregate exhibited the highest sound absorption coefficient, reaching a maximum value of 0.1 within the frequency range of 315 to 400Hz. This value was 2.5 times higher than the maximum sound absorption coefficient of the reference concrete.

Multi-Scale Performance of Large-Volume Concrete under Dual Control of Temperature and Deformation

The uneven distribution of internal and external temperature stresses during casting large-volume slag/fly ash (FA) concrete (LVC) often leads to cracking. High-efficiency anti-cracking agents (HEAC) can improve structural durability by reducing the early-stage temperature rise rate of concrete hydration (CHY). However, their impact on other concrete properties remains uncertain. This study investigates the multi-scale performance of LVC under dual regulation of temperature and deformation by incorporating 0%, 4%, 6%, and 8% of HEAC. Using an ARIMA model, predictive models for temperature and deformation were developed for different concrete mixtures. The results showed that adding 8% HEAC to the concrete compared to the reference group decreased compressive strength (CS) by 11.03MPa at 7d of curing. The cumulative hydration heat (HH) at 1d decreased by 56.87J/g, the adiabatic temperature rise (ATR) at 1d was reduced by 60.92%, and the volumetric expansion at 48d reached 252.39με. The regulation of concrete temperature by the HEAC is primarily achieved by inhibiting the initial formation of C-S-H, while the reaction of hydration (HYD) products in the cement (C), along with Ca(OH)2 (CH) and Mg(OH)2 (MH) in the HEAC, generate expansive stress on the pore walls, compensating for shrinkage. The predicted values from the established models show a mean relative error of less than 1% compared to measured values, validating the model’s accuracy. The optimal HEAC dosage in LVC is determined to be between 0% and 10%.

Development and Optimization of Geopolymer-Based Artificial Angular Coarse Aggregate Using Cut-Blade Mechanism

This research introduces a novel approach to developing geopolymer-based artificial coarse aggregate using a cut-blade mechanism, providing an innovative approach to traditional aggregate. A modified concrete drum mixer equipped with additional cutting blades was employed to produce angular aggregates with consistent particle sizes ranging from 10mm to 20mm with rough surface texture. Compared to conventional techniques, this method ensures a more uniform aggregate shape, enhancing its mechanical interlocking properties in construction applications. The experimental results demonstrated abrasion values between (13.2% to 31.5%), impact value test (9.8% to 21.6%), water absorption rates of (2.62% to 4.2%), and specific gravity values ranging from (1.18 to 2.2). To further optimize the alkali activator dosage, a mathematical model was developed using the ANOVA test and Response surface methodology (RSM), achieving high regression predictive accuracy with R2 values > 0.93. The model demonstrated optimal results between experimental results and predicted results for specific gravity, impact value, abrasion value, and water absorption. Microstructural analysis via Scanning electron microscopy (SEM) reveals optimal pore distribution inside aggregates, while X-ray Fluorescence identifies significant intensities of Quartz, Ettringite, and calcium silicate hydrate gel. Overall, this research not only demonstrates the technical feasibility of producing high-performance artificial aggregate from waste materials but also underscores its potential to mitigate environmental impacts and promote sustainable construction practices.

Flexural tensile behaviour of alkali-activated slag-based concrete and Portland cement-based concrete incorporating single and multiple hooked-end steel fibres

In this study, three-point bending tests on notched beams according to EN 14651 have been performed to evaluate the flexural post-cracking behaviour of alkali-activated slag-based concrete (AASC) and Portland cement-based concrete (PCC) incorporating single (3D) and multiple (4D, 5D) hooked-end steel fibres in different volume fractions up to 0.75%. According to the experimental results, the post-cracking residual flexural strength increases with the increase in the fibre volume fraction for each fibre and concrete matrix type. AASC mixes incorporating 3D and 4D fibres show higher values of residual flexural strength for the same crack opening than PCC mixes with the same fibre type and dosage. Only for the mixes incorporating 5D fibres, steel fibre-reinforced PCC (SFRPCC) mixes outperform steel fibre-reinforced AASC (SFRAASC) mixes in terms of post-cracking behaviour. According to EN 14651, the values of the residual strengths and , corresponding to a crack mouth opening displacement (CMOD) of 0.5 mm and 2.5 mm, respectively, and their corresponding characteristic values and , respectively, can be derived from the experimental load-CMOD curves. Following the fib Model Code 2020, each mix can then be classified according to the values of and the ratio. As a result, empirical models have been developed for SFRPCC to predict the values of and and the applicability of such models to SFRAASC is evaluated in this study. Once the values of and are known, tensile constitutive models can be derived according to the fib Model Code 2020 and used as input parameters for finite element modelling. In this study, the accuracy of the code-based constitutive model to predict the flexural behaviour of SFRAASC and SFRPCC is evaluated using the concrete damage plasticity (CDP) model available in ABAQUS. The numerical model based on the tensile stress-strain curve in the fib Model Code 2020 can qualitatively capture the post-cracking behaviour of SFRAASC and SFRPCC incorporating 3D, 4D and 5D at 0.25% fibre volume fraction, despite overestimating their tensile strength. For higher fibre volume fractions, the CDP model, in conjunction with the mode I parameters derived from the fib Model Code 2020, is unable to adequately describe the post-hardening behaviour exhibited by the composites.

Flexural behavior of steel/GFRP reinforced concrete beams having layered sections integrated with normal and rubberized concrete

Rubberized concrete (RuC) is one of the possible sustainable solutions to the problem of quickly disposing of old tires. This study introduced a new coating material (metakaolin, MK) for crumb rubber (CR) at a controlled temperature to avoid decreasing the RuC mechanical properties. Additionally, to prevent the possible reduction in the RuC strength on the RC beam behavior, the functionally graded material (FGM) approach was applied (layered beam section with RuC at 67 % of the beam section and normal concrete (NC) at the top one). The influence of RC beams on the tensile reinforcement (glass fiber-reinforced polymer (GFRP) instead of steel) was also examined. The experimental investigation comprised several concrete combinations: conventional concrete and RuC integrated uncoated and MK-coated CR replacing sand with percentages (0 %, 5 %, 15 %, and 25 %). The mechanical characteristics of concrete mixtures under compression and splitting tension tests were examined. Moreover, fourteen RC beams were experimentally loaded in flexural to investigate the impact of proposed parameters on the beam response. Following that, Finite Element (FE) modeling was carried out to examine the influence of the additional parameters on the RC beams' performance. The results demonstrate a notable improvement in the compressive strength of concrete by 17.4 % and a 25.4 % rise in split tensile strength due to the use of MK-coated CR compared to the uncoated CR. The impact of MK-created CR was more prominent in increasing the GFRP RC beam loads than the steel RC ones. In addition, using the FGM approach could eliminate the CR effect and exhibit nearly the same NC beam load.

Numerical simulations study of concrete mix proportion based on fluidity

Numerical simulations study of concrete mix proportion based on fluidity

Concrete mix design: Optimizing recycled asphalt pavement in Portland cement concrete

Concrete mix design: Optimizing recycled asphalt pavement in Portland cement concrete

Influence of different drilling forces on drill bit wear in automated drilling of concrete with industrial robots

AbstractThis article investigates the effect of different drilling forces on drill bit wear and their effects on drilling time within the context of the development of a drilling robot for on‐site construction applications. The study explores variations in three force levels (80, 120, 160 N), three directional orientations (upwards, downwards, horizontal), four drill bit diameters (8, 10, 12, 16 mm), and two concrete strength types (C25/30, C70/85). The findings indicate that while there is little divergence in drill bit wear across force levels, the influence of concrete strength is undeniable. Furthermore, drilling time increases, by 7 % to 11 % after 37.5 m drilling depth and up to 68% after 150 m depending on the drilling configuration. In conclusion, the study reveals a notable discrepancy between the progressive increase in drilling time and the relatively stable progression of drill bit wear, particularly in achieving code‐compliant boreholes.

Performance of Various Types of Bacillus Bacteria on the Rheology and Mechanical Properties of Self-Compacting Concrete

Performance of Various Types of Bacillus Bacteria on the Rheology and Mechanical Properties of Self-Compacting Concrete