Concrete Layer Research Articles

Shotcrete 3D Printing ‐ Interaction of nozzle geometry, homogeneity and hardened concrete properties

AbstractShotcrete 3D Printing (SC3DP) applies concrete layer by layer using a wet‐spray process. The resulting hardened concrete properties of the applied SC3DP layers (e.g. height, width or mechanical strength) are largely dependent on the selected material and process parameters. In this context, the nozzle geometry is an important influencing parameter. During printing, the velocity of the shotcrete jet is significantly influenced by the nozzle outlet diameter. Therefore, in the present study, the effect of the nozzle outlet diameter (15 ‐ 30 mm) is investigated with regard to the resulting layer homogeneity, i.e. local density and aggregate distribution in the cross‐section, and hardened concrete properties, i.e. flexural strength. By analysing the manufactured specimens, an uneven distribution of the aggregate is observed horizontally across the cross‐section of the layers. An accumulation of aggregate is present in the core of the layer resulting in a cement paste‐rich region in the edge areas. This leads to increased local densities in the core of the specimen. The application of the concrete with small nozzle outlet diameters results in the highest local densities and the highest flexural strength.

Analysis of wind time-varying performance of reinforced concrete electric pole under Marine atmospheric environment

Bearing capacity calculation model of concrete electric pole considering concrete long-term performance degradation and steel corrosion is established. The horizontal bearing capacity and wind resistance of typical concrete electric pole under Marine atmospheric environment are analyzed with service time. The effects of concrete protective layer thickness, stirrup diameter and strength coefficient on the long-term wind resistance of electric pole are discussed. It is found that with the increase of service time, the shear strength of the concrete pole deteriorates faster than that of the flexural strength, and the failure mode changes from bending failure to shear failure. The wind resistance of the pole after long service can be improved by increasing the thickness of the protective layer, adopting larger diameter stirrup and higher strength coefficient. The bearing capacity calculation model of concrete electric pole considering concrete long-term performance degradation and steel corrosion is established. The horizontal bearing capacity and wind resistance of typical concrete electric pole under Marine atmospheric environment are analyzed with service time. The effects of concrete protective layer thickness, stirrup diameter and strength coefficient on the long-term wind resistance of electric pole are discussed. It is found that with the increase of service time, the shear strength of the concrete pole deteriorates faster than that of the flexural strength, and the failure mode changes from bending failure to shear failure. The wind resistance of the pole after long service can be improved by increasing the thickness of the protective layer, adopting larger diameter stirrup and higher strength coefficient.

Analysis of the correlation between the pavement structure combinations and pavement performance using experimental sections

The new generation of pavement technology with the goal of longevity is an important supporting technology that can promote the achievement of sustainable development of high-speed roadways. To further investigate the evolution trend of long-life pavement performance, this paper paved experimental sections to explore the correlations between pavement structure combinations and pavement performances. This paper presented four experimental sections with different pavement structures, asphalt concrete layer thicknesses, and pavement materials. Then, this paper analyzed the effects of the seasonal factors, pavement structure, and lanes on the deflection value and rut depth from three dimensions by the Pearson correlation coefficient (PCC). Finally, this paper used the analysis of variance (ANOVA) to analyze the relationships between the layer thickness of various materials in the pavement structure and the pavement performances, including the deflection value, international roughness index (IRI), texture depth (TD), British Pendulum Number (BPN), sideway force coefficient (SFC), rut depth, and disease area. The results showed that the seasonal factors significantly affected the deflection values of pavement structures with PCCs of 0.61, 0.72, 0.53, and 0.78. The high temperatures increased the average deflection values by 22.85%, 72.88%, 77.61%, and 88.13%, respectively. Under the influence of high temperature in summer and traffic loads, the increased ranges of average rut depth were −0.2%, 4.89%, 9.56%, and 7.31%, respectively. The results of ANOVA showed that the pavement structure type and thickness of each structural layer significantly affected the deflection value, and there also was a strong correlation between the pavement structure type, thickness, BPN, and SFC with p-values less than 0.05. Increasing the thickness of the asphalt surface was beneficial for reducing the area of defects, while laying the semi-rigid base layer was beneficial for maintaining the deflection value and rut depth at a lower level.

Study of Damping of Bare and Encased Steel I-Beams Using the Thermoelastic Model

Steel I-beams are a fundamental structural component in civil construction. They are one of the main load-bearing components in a building that must withstand both the structure and any incoming external perturbations, such as seismic events. To avoid damage to the structure, the building must be designed to dissipate the maximum amount of energy possible. One way energy can be dissipated is through internal or structural damping, of which thermoelasticity is one of the causes, especially in low-frequency harmonic excitations. The main goal of this study is to analyze the amount of damping in an I-beam generated by thermoelasticity and when encased in a Portland cement concrete layer, using a Finite Element model. It was found that, due to the geometry of the I-Beam, the damping coefficient as a function of frequency has two local maxima, as opposed to the traditional single maximum in rectangular beams. Encasing an I-beam in a concrete layer decreases the overall damping. While the extra coating protects the beam, the reduction in damping leads to a lower energy dissipation rate and higher vibration amplitudes.

Study on the post-fire axial compressive performance of the lightweight ceramsite foamed concrete sandwich composite shear wall

This study is carried out to develop a new lightweight ceramsite foamed concrete sandwich composite shear wall, which is a new and affordable building system. The shear wall consists of two ordinary concrete wythes and a ceramsite foamed concrete intermediate sandwich layer between the wythes. Experimental investigation on five shear wall specimens is conducted by varying the parameters such as thickness of the ordinary concrete wythes and the insulation layer, reinforcement pattern and constrained component. Besides, by conducting fire test and axial compressive load test, the results are obtained, including the apparent phenomenon after fire, crack pattern and failure modes, load capacity, load-out of plane curve, strain distribution of the composite sandwich shear wall. The results show that sandwich ceramsite foamed concrete has good thermal insulation performance, and the compositeness of wythes and sandwich layer has reached in a certain degree. However, the compositeness of specimen using truss bars is weaken in the late loading stage and truss bars are advised to be used with the horizontal tie bars in practical engineering application. Compared with other specimens, the experiment ultimate strength has been increased by approximately 75 % by arranging the constrained component on the wall. Finite Element (FE) analysis is also conducted by ABAQUS and the results shows good agreement with experiment results, indicating that the FE model can be used to predict the behavior of the sandwich composite shear wall. Based on the existing methods, a modified method to calculate ultimate compressive bearing capacity after fire is proposed, with the maximum calculation error of 19 %, which shows that all methods can be applied to the practical engineering design.

THE EFFECT OF SEAWATER SOAKING ON THE STABILITY OF AC-WC MIXTURES USING KOYA AGGREGATE, JAYAPURA CITY

Roads are the basic infrastructure in driving the regional economy, so a good pavement structure is needed. One of the factors of road damage is standing water, for roads around the coast are likely to be inundated by sea water. Asphalt Concrete Wearing Course (AC-WC) is one of the concrete asphalt layer which is able to provide good carrying capacity and waterproof layer for road structures. Some areas in kota Jayapura such as Koya have a large number of local aggregates. This study used oil asphalt as a binder, local aggregate for hot asphalt mixture, and saw the effect of sea water immersion in the asphalt mixture. The purpose of this study is to determine the volumetric value and Marshall value of the Laston AC-WC mixture against sea water immersion and without immersion. The material used is oil asphalt from PT. Pertamina and local aggregates from the Koya area. The research carried out is an experimental test in the laboratory, where the resulting asphalt concrete mixture (AC-WC) will be treated with sea water immersion, then Marshall characteristics testing will be carried out to determine its durability value. Based on the tests carried out, the results showed that the volumetric value and the marshall value of the samples treated with immersion did not provide a significant difference in values compared to normal samples. The results of the marshall value, namely the stability of all asphalt levels meet the specifications, while for flow only the asphalt content of 5.5% and 6% both by soaking and without soaking.

Research on bond behavior of CFRP-concrete interface under quasi-static cyclic loading

In order to investigate the bond behavior of CFRP-concrete interface under quasi-static cyclic loading, static and quasi-static interface shear tests were conducted on three different adhesive layer thicknesses and two concrete strength grades. From these results, it can be seen that the load-slip envelope curves of the quasi-static cyclic loading specimen is similar to the quasi-static monotonic loading curves. As the adhesive thickness increases, the interface bearing capacity increases, the maximum strain of CFRP plate increases, and the effective bond length slightly increases. The interface failure mode is related to concrete strength. The failure mode of C30 concrete bonded with CFRP plate is cohesive failure of concrete surface layer, while the failure mode of C50 interface specimen is adhesive failure between CFRP and adhesive layer interface. As the thickness of the adhesive layer and the strength of the concrete increase, the interfacial bond strength and maximum strain of CFRP plate increase. It can be seen that the bond-slip envelope curves of the quasi-static cyclic loading specimen coincide well with the curves of the quasi-static monotonic loading specimen. As the magnitude of the cyclic loading increases, the unloading/reloading stiffness degradation, residual slip at zero load increases, and the dissipated energy increases. The fitting resulted in a degradation model of interfacial stiffness during quasi-static cyclic loading.

Thermal and mechanical performance of 3D printing functionally graded concrete: The role of SAC on the rheology and phase evolution of 3DPC

In order to address the dual objectives of enhancing the mechanical and thermal performance of 3D printed concrete, this paper presents a 3D printing approach to design and prepare functional graded concrete for energy-saving sandwich structures with both thermal insulation and load-bearing functions. The 3D printing functionally graded concrete (3DPFGC) with a sandwich structure, consists of an expanded polystyrene concrete inner layer and a 3D printed concrete outer layer. In addition to the three-dimensional compressive strength and double-shearing tests, the thermal conductivity of 3DPFGC was also measured by steady-state method and compared with the transient method and verified by theoretical formulas. The influence of sulphoaluminate cement on the printability of the load-bearing layer was also comprehensively investigated by calorimetry test, rheological test, XRD and TG analysis. The addition of SAC has a significant impact on the early fresh properties, including accelerating the setting time and optimizing the rheological properties, directly improving the printing performance. 3DPFGC exhibits significantly higher compressive strength compared with other lightweight insulating concrete with similar thermal conductivities. The outcome of this research provides valuable guidance for the application of 3DPFGC in building engineering, contributing to the development of energy-efficient and structural construction materials.

Experimental and theoretical research on flexural performance of truss reinforced concrete two-way composite slab with prefabricated baseplate

This paper presents experimental and theoretical research on a novel truss reinforced composite concrete two-way slab using full-scale testing. In contrast to conventional composite slabs, the precast concrete layer with a thickness greater than 60 mm is replaced by a high toughness prefabricated inorganic baseplate with a thickness of 12 mm. The baseplate options include glass fiber and magnesium cement board, as well as fiber cement board. Four full-scale two-way slabs were subjected to eight points simulated uniform vertical loads, comprising one conventional truss reinforced concrete two-way slab (RCS) and three truss reinforced concrete composite two-way slabs with prefabricated baseplates (RCSB). The test results indicate that the failure mode of the truss reinforced concrete composite two-way slab with baseplate is similar to that of a common truss reinforced concrete two-way slab. However, a rectangular yielding region appears at the central part, instead of a single yielding line. The cracking load and ultimate load are increased due to the effect of prefabricated baseplate. Moreover, the beneficial effect of glass fiber and magnesium cement board is superior to that of fiber cement board. Finally, the calculation methods for determining the cracking load and ultimate bearing capacity of truss reinforced concrete composite two-way slabs with baseplates were improved, and the calculated results are in good agreement with experimental data.

Determination of Adiabatic Temperature in Hardening Concrete According to Different Standards

The problem of thermal cracking in mass concrete structures still remains unsolved. There are many factors that influence the thermal regime in these concrete structures, the main ones being the type and content of cement in the concrete mixture, the thickness of the concrete layer, and the ambient temperature. However, the most important factor is the cause of the heat generated. Currently, there are a large number of standards and empirical formulas for determining the origin of a heat source using adiabatic equations. This paper provides a comparison of formulas for determining the adiabatic temperature in hardening concrete as the basis for determining the thermal regime in large-sized concrete structures.

Design and performance evaluation of an electrically heated concrete panel for sustainable winter maintenance

This study focuses on developing an electrically heated concrete panel system incorporating carbon fiber (CF) and carbon nanotube (CNT) as electrical media. Properties of 8 different electrically conductive concrete mixtures, such as workability, air content, compressive strength, and electrical resistivity, were experimentally evaluated to find optimum mixture proportions. Subsequently, three laboratory specimens with different geometric designs were fabricated using a two-lift concrete placement scheme: a normal concrete (NC) layer at the bottom and a conductive concrete (CC) layer at the top. Conventional ribbed rebars were embedded as electrodes to supply electrical power. The electrical heating performance of the specimens was evaluated based on the temperature rise and thermal strain changes during the imposed heating cycles. The findings demonstrated the potential use of the developed electrical HPS for sustainable winter maintenance, which will contribute to advancing heated pavement technologies and minimize the environmental impact caused by traditional snow removal practices.

Damage and responses of two asphalt pavement structures under blast loads: A numerical simulation

The explosion accidents are threatening the service functionality of pavement structures, which puts forward new requirements such as multi-hazard resistance and resilience. Although the widely used asphalt pavement structure is vulnerable to blast loads, its dynamic behaviors under blast loads are still unclear. This research mainly focused on the damage and responses of two asphalt pavement structures, one of which was conventional asphalt pavement, and the other was the anti-blasting asphalt pavement structure with the reinforced concrete layer. The numerical simulation method, which was validated based on a real blast test, was proposed using Abaqus code with appropriate material models and simulation procedures. The finite element models of two pavement structures were built. Under various blast loads, the damage contours and dynamic responses of different pavement structure components were investigated. It was found that the total damage areas of two asphalt pavement structures were grew by 2.26 and 3.19 times, respectively, as the blast loads increased from 100 kg TNT to 2000 kg TNT. The slope of pavement structure was extremely sensitive to the changes in blast load. The proposed anti-blasting pavement structure could reduce the damage area by up to 20 %, but it would be invalidated under particularly destructive blast loads. These findings could be helpful for the further design of an anti-blasting pavement structure.

FRP-concrete-steel tubular columns with a large inner void under lateral impact loading: Experimental study and finite-element modelling

By combining two concentrically placed tubes (i.e., an FRP tube as the external sheath and a steel tube as the inner reinforcement) and a sandwiched concrete layer, FRP-concrete-steel double-skin tubular columns (DSTCs for short) are an attractive type of hollow-core columns suitable for bridge piers working in humid and corrosive environments. The very limited experimental studies on DSTCs under impact loading had one or two of the following limitations: (1) the void ratio φ was far smaller than the size with practical engineering value; (2) the column diameter Dc was too small compared with the section size used in real engineering. To supplement the existing research, DSTCs with a large inner void and a practical large column diameter (i.e., φ = 0.73 and 0.82; Dc = 300 mm) were experimentally investigated subjected to lateral impact loading, with particular research attentions on parameters including the impact velocity, the boundary conditions, as well as the void ratio of the DSTC specimen. Test results indicated that: (1) the failure mechanism was primarily controlled by the boundary condition; a bending-dominant failure mode was observed for the DSTC specimen with the top end free and the bottom end fixed; in contrast, a small global lateral displacement and severe localized dent deformation was observed for the DSTC specimen with the top end simply-supported and the bottom end fixed; (2) the peak impact force, the impact duration as well as the residual lateral displacement had a positive correlation trend with the impact velocity; (3) a DSTC specimen with a larger void ratio had a lower peak impact force and a smaller global lateral displacement. Finite element model based on ANSYS/LS-DYNA was employed to simulate DSTCs subjected to lateral impact loading, which could yield results with reasonable accuracy.

Comprehensive Investigation of the Omega-Shaped Hybrid CFRP Sheet - Concrete Slab System: Experimental, Numerical and Analytical study

Fiber Reinforced Polymer (FRP) composites have been broadly applied in substitution of steel members at rehabilitation interventions thanks to their lightweight, high strength, and high corrosion resistance. Producing novel FRP-concrete hybrid structures is the next step researchers are dealing with. In this context, the present study focuses on the numerical and analytical modeling of the experimentally obtained response of hybrid FRP-concrete slabs subjected to three points bending tests. The analyzed hybrid elements consisted of an omega shape Carbon Reinforced Polymer (CFRP) sheet on which a concrete layer was cast forming a unidirectional slab member. A Glass Fiber Reinforced Polymer (GFRP) fabric was bonded to the CFRP sheet and embedded into the concrete block to provide a connection between CFRP and concrete in one of the specimens. Simulation results showed agreement with the experimental response in terms of load-displacement curve, concrete plastic strain and failure mode. After validating the model, alternative designs (width, height, and thickness of CFRP sheet and concrete block on it) were numerically tested to study the influence of the geometry of the structural system on the load-bearing capacity. Lastly, analytical formulation assuming total compatibility and based on Euler-Bernoulli theory were implemented and contrasted with the experimental response. Overall results pointed out that the optimum design would be the one with increased height of both concrete and CFRP. For this improved configuration, the load-bearing capacity was increased by up to 44%.

Airfield pavement resiliency assessment against extreme dynamic events by explicit axisymmetric finite element models

Infrastructure resiliency has become an essential element in ensuring community recovery after unexpected events. In airfield pavement, resilience can be achieved through an improved design approach by understanding the fundamental elements of damage mitigation and thus allowing rapid recovery. The objective of this study was to numerically evaluate easy-to-implement alternatives for mitigating damage in rigid airfield layered pavement systems when subjected to dynamic events such as blasts or high-velocity impacts. This was accomplished by developing an efficient axisymmetric explicit finite element model, which served as an analytical tool for the study. The model was developed in LS-DYNA and the methodology consisted of a comprehensive parametric analysis. The results showed that the concrete pavement layer parameters—mass density and compressive strength—have the most significant effect on the damage to the pavement when subjected to extreme dynamic events. The material parameters for the pavement layers were optimized to minimize the damage, caused by dynamic loads, achieving more than 70% damage mitigation. Furthermore, adding a granular base layer to the rigid airfield pavement design reduces the concrete pavement layer damage by almost 40%. An asphalt concrete overlay reduces the concrete pavement layer damage by about 55%. Moreover, adding an asphalt concrete overlay to the optimized rigid airfield pavement design reduces the damage by 10%. In contrast, adding a granular base layer to the optimized rigid airfield pavement design is ineffective.

Studi Karakteristik Marshall Pada Campuran Lapis Aspal Beton (Laston) dengan Bahan Tambah Limbah Kain Nilon

The use of nylon fabric waste as adding material for concrete asphalt layers can be one of the solutions, because it can reduce pollution in the environment.The level of variation in adding nylon fabric waste is 0%, 5%, 10% and 15%. Sample testing as many as 24 test specimens. . The purpose of this study is to determine the physical properties of the asphalt with the added material of the nylon fabric waste and to determine the properties of the concrete asphalt layer mixture (Laston) with the added material of the nylon fabric waste. The results of testing the addition of nylon fabric waste levels as added material to the asphalt show that the value of the physical properties of asphalt is penetration, soft point, specific gravity, flame point and fuel point and asphalt dactality meets the standard specifications of the 2018 SNI Marga. As well as the addition of nylon substitution waste a number of asphalt at 5%, 10% and 15% content can affect the nature of concrete asphalt layers (Laston). In variations of 5%, 10% and 15% density value of 2,336 gr/cm, 2,327 gr/cm, 2,343 gr/cm, stability of 1892,4 kg, 2239,0 kg, 1953,6 kg, VMA of 15,9%, 16,2%, 15,6%, VIM of 4,4%, 4,7%, 4,1%, VFB of 73,6%, 70,9%, 74,0%, melting of 3,93 mm, 3,43 mm, 3,02 mm and MQ of 480,1 kg/mm, 652,9 kg/mm, 691,5 kg/mm.

Flexural behavior of composite ribbed slabs employing cold-formed steel lipped channels

By means of a series of full-scale laboratory tests, this research studied the flexural behavior of a composite ribbed slab employing cold-formed steel profiles as formwork before and after concrete casting. An experimental program was devised and separated in two sets of tests. The first set consisted of the execution of four-point bending tests on eight specimens to represent the system during construction, featuring three specimen types; isolated profile, profile with plastic spacers along the channel and a full assembly including the profile, the plastic spacers and a rebar truss. Displacement and strain as a function of load were measured and the data was used to analyze the influence of the different components on the flexural strength and stiffness of the system. On the second set of tests, three ribbed composite slab specimens featuring steel profiles were subjected to four-point bending. Displacement was registered along with strain on the concrete layer. A formulation to determine the flexural strength of the slabs based on Eurocode is presented and compared to experimental observations. The first phase indicates significant increases of flexural strength and stiffness by coupling a truss to the profile and varying the height of the former, namely a maximum increase of 708% in stiffness and 357% in strength. Isolated profiles and profiles with plastic spacers all failed by distortional buckling, while the full assembly specimens failed by instability of the top chord on the trusses. Second phase results show that the analytical prediction is adequate to determine the flexural strength of the prototype slabs, with approximately 95% accuracy for this sample size. All slab specimens failed by plastic hinge formation within the pure moment span. Furthermore, strain measurements on the concrete indicate that the formulae chosen to determine the effective width of the concrete “tee” section is also adequate.

Effect of truck and train loading on permanent deformation and fatigue cracking behavior of asphalt concrete in flexible pavement highway and asphaltic overlayment track

Abstract This research investigated the largest magnitude of displacement and horizontal tensile strain in several critical locations within the asphalt concrete (AC) layer in both the flexible pavement highway (FPH) and asphaltic overlayment track (AOT) structure using the numerical modeling method. The role of the hauling loads, speed, and loading cycles of freight truck’s dumps and freight train’s wagons on the mechanical behavior of FPH and AOT in terms of the permanent deformation and fatigue cracking was examined. Furthermore, the performance of the FPH and AOT in terms of permanent deformation and fatigue cracking characteristics due to various magnitudes of hauling loads, speed, and loading cycles of freight truck’s dumps and freight train’s wagons was compared to determine the optimum infrastructure for the freight coal transportation, based on the hauling capacity as well as the magnitude of permanent deformation and the horizontal tensile strain of the AC layer. According to the findings of this study, it is suggested to choose the AOT structure with fourth or sixth loading systems to run the freight coal transportation with the highest magnitude of the hauling capacity of 360,000 tons, since it produces the minimum magnitude of the permanent deformation and fatigue cracking of the AC layer. Future research should be conducted to examine the potential and the characteristics of fatigue cracking due to the contact between the edge of the sleeper and the surface of the AC layer in AOT.

Case Study: Validation of the Spectral-Analysis-of-Surface-Waves Method for Concrete Pavement Condition Evaluation

Before conducting pavement rehabilitation, the concrete pavement performance evaluation is more than necessary to assess the strength and analyze the internal condition. To evaluate the modulus performance of concrete pavement and provide theoretical support for subsequent maintenance and rehabilitation, the SASW (Spectral-Analysis-of-Surface-Waves) method, a non-destructive testing method based on surface waves, was used to determine the modulus of three in-service concrete pavements. At the same time, FWD (Falling Weight Deflectometer) testing and on-site coring were carried out at the measuring points. Through the analysis of modulus results measured in the field, it was found that the SASW method can accurately obtain the elastic modulus of the concrete layer and base layer. Compared with the concrete modulus measured by FWD, the modulus measured by the SASW method was closer to the uniaxial compressive modulus. Moreover, since the SASW method has the ability to provide gradient modulus varying with depth and determine the pavement thicknesses, it is reasonable to recognize the location of the inherent distress based on the region where the modulus suddenly decreases within one layer. The comprehensive evaluation of concrete pavement condition, including the modulus value and internal distress recognition, has the capability to assist in determining the design of overlay asphalt thickness and material.

AC layer fatigue damage analysis and reflective cracking control of CRC + AC composite pavement

The current continuous reinforced concrete composite asphalt pavement (CRC + AC) design method in China does not consider the effect of the asphalt concrete (AC) layer on the longitudinal reinforcement rate of the continuous reinforced concrete (CRC) layer. To address such issues, a finite element model of CRC + AC using continuum damage mechanics theory and finite element method was established. The most unfavorable working condition and the location of the greatest damage by comparing the damage distribution under different working conditions were determined. To resolve the limitations of traditional design methods of CRC + AC composite pavement, criteria for the microcrack width of the CRC layer under different AC layer thicknesses were proposed, based on the combined effects of AC layer thickness and CRC layer microcrack width on the damage of the AC layer. The results suggest that the left lane vehicles braking and the right lane vehicles driving at a constant speed are the most unfavorable working conditions, with the greatest degree of damage found on the lane divider of AC layer. meanwhile, the microcrack width should be below 0.64 mm to mitigate the risk of Top-Down cracking and reflective cracking. Additionally, the CRC plate crack width control standards are provided for AC layer thicknesses ranging from 4 cm to 14 cm.