Normal Concrete Slabs Research Articles

Behavior of zero cement reinforced concrete slabs under monotonic and impact loads: Experimental and numerical investigations

Currently, there is a shift toward the use of low-carbon construction materials to reduce global carbon dioxide emissions. Zero-cement concrete (ZCC) synthesized from alkaline activated fly ash (FA) is a promising alternative for Portland cement in the construction industry to reduce global CO2 emissions, increase the consumption of waste materials, and save energy. A substantial amount of research on the impact load behavior of ordinary reinforced concrete (RC) structural components has been conducted. However, investigations on the behavior of zero cement concrete (ZCC) slabs under impact loads have not been reported. In this work, twenty simply supported two-way flat reinforced fly ash ZCC slabs (including two normal concrete (NC) slabs as reference samples) were tested under monotonic and impact loads. The test samples were categorized into eight groups on the basis of various parameters. Twelve RC slabs (1 NC and 11 ZCCs) were prepared for repeated impact tests, and eight slabs (1 NC and 7 ZCCs) were prepared for monotonic loading tests. Various parameters were investigated herein, including slab thickness, bar spacing, molarity concentration of alkali activators, hammer height, and hammer mass. Nonlinear finite element models were also developed and validated by using ABAQUS software for additional parametric study purposes. The results revealed that the behavior of ZCC slabs is approximately similar to that of NC slabs. The results also revealed that an increase in the ZCC slab thickness, reinforcement ratio, hammer height, and hammer mass has a noticeable effect on the dynamic response of the slab. However, increasing the molarity concentration of alkali activators has clearly a slight influence on the impact loadtime history. When the slab thickness was increased or the bar spacing was reduced, the static and impact energy absorption capacities were increased by 1.5 and 2.0 times, respectively. For impact load tests, the damage degree, penetration, and cracking pattern at failure were approximately typical for all test samples at the first hit except when the hammer mass and impact height were changed. For the samples subjected to monotonic loading, a flexural response was observed for almost all the slab samples at the first loading stage, and cracking started from the midpoint of the slab and propagated toward the slab edges; ultimately, punching shear failure was observed.

Experimental study of prestressed steel-HFRC composite girders under hogging moment

To alleviate cracks in the hogging region of continuous steel-concrete composite girders, the hybrid fiber reinforced concrete (HFRC) and prestressing technique were introduced to exploit a novel type of composite girders (prestressed steel-HFRC composite girders). Four specimens with different concrete slabs (normal concrete (NC) slab, prestressed NC slab, HFRC slab, prestressed HFRC slab) were tested under hogging moment to investigate their mechanical properties. The test results showed that the prestressed steel-HFRC composite girder could take advantage of the synergy of the prestressing technique and HFRC and, therefore, its ultimate capacity, cracking load and stiffness were the biggest while the crack width was the smallest among the specimens investigated. In addition, practical equations of ultimate/crack moment and crack width were obtained based on the test results. The proposed equations could provide the reference in the design of prestressed continuous steel-HFRC composite girders.

Fire behavior of high‐contents recycled aggregate concrete composite slabs with small openings

AbstractRecycled aggregate concrete (RAC) is increasingly being used in the construction of structural elements. However, the performance of RAC elements under fire is usually considered to be inferior to that of normal concrete (NC) elements. This study investigates the fire behavior of RAC composite steel slabs with and without openings. Ten slabs of size of 1.0 m × 2.2 m were cast either with no opening, one or two circular openings, and one or two square openings. Five of the slabs were manufactured with 100% RAC, while the other five slabs were made with NC. The concrete slabs were loaded and subjected to fire tests at a temperature of about 900°C for 120 min. Test results show that RAC composite slabs have lower stiffness (thus larger mid‐span deflections) under fire exposure compared to their counterpart NC slabs. In terms of the recorded temperature–time curves, RAC slabs showed similar performance to that of NC slabs. The ratio of soffit temperature to the temperature at the top of slab was considerably smaller for RAC slabs compared to NC slabs. RAC slabs also showed more spalling than NC slabs. Experimental test results were numerically verified using PyroSim® software with the two showing good agreement. A series of new design charts for composite RAC slabs with desired fire endurance are proposed. This study is expected to promote the wider use of RAC in construction of structural elements, particularly of composite slabs exposed to extreme temperatures.

Study on flexural and shear performance of ultra‐high performance concrete prefabricated pi‐beams

AbstractUltra‐high performance concrete (UHPC) prefabricated beams are competitive in accelerated bridge construction. However, their broader application has been hindered by limited large‐scale tests and inaccurate design methods. To fill this gap, the authors conducted an experimental investigation on the shear and flexural performance of UHPC pi‐beams using two full‐scale specimens. One specimen was a precast UHPC beam, while the other was a composite beam with a normal concrete slab on the UHPC beam. The primary focus was on crack propagation, ultimate capacities, and failure modes. To complement the experimental findings, the extended finite element method (XFEM) was developed as a numerical approach. Nevertheless, relying solely on XFEM to understand real structural behavior is prone to misinterpretations. Moreover, the shear and flexural capacities were evaluated using existing codes and compared with the experimental results. The comparisons revealed that the predictions of shear capacities were at least 15% lower than the experimental values, whereas the flexural capacities showed acceptable agreement. To address this, the authors introduced the limit equilibrium method, leading to a more accurate prediction of shear capacity for UHPC beams with a deviation of <2%.

Flexural performance of prefabricated FRP-concrete hybrid beam with in-situ-cast UHPC pockets

In this study, a novel prefabricated fiber reinforced polymer (FRP)-concrete hybrid beam (HB) was proposed with the aim of reducing initial material costs and expediting construction. The proposed HB features a precast concrete slab and in-situ cast ultra-high performance concrete (UHPC) pockets around bolted connections. A comparison was made between one FRP-concrete HB with a normal concrete slab and four proposed FRP-concrete HBs with UHPC pockets through flexural testing. The results showed that the proposed bolted shear connection in UHPC pockets significantly reduced interfacial slip and increased the flexural rigidity of the HBs when compared to the FRP-concrete HB. The use of continuous UHPC pockets in the HB resulted in substantial improvements in ultimate loading capacity, with an increase between 14.2% and 40.4% compared to the traditional in-situ cast FRP-concrete HB. Continuous UHPC pockets results in higher ultimate loading capacity than that of discontinuous UHPC pockets HB. The HBs with normal concrete or discontinuous UHPC pockets failed due to concrete crushing, while the continuous UHPC pockets HB failed at shear fracture of the FRP webs. Only slight slippage (less than 0.2 mm) was observed at the FRP-concrete interface.

Punching Shear Behavior of Slabs Made from Different Types of Concrete Internally Reinforced with SHCC-Filled Steel Tubes

The punching shear failure of reinforced concrete (RC) flat slabs is an undesirable type of failure, as it is sudden and brittle. This paper presents an experimental and numerical study to explore the behavior of flat slabs made of different types of concrete under the influence of punching shear. Experimental tests were carried out on four groups of flat slabs, each group representing a different type of concrete: ordinary normal concrete (NC), high-strength concrete (HSC), strain-hardening cementitious composite concrete (SHCC), and ultra-high-performance fiber concrete (UHPFC). Each group consisted of six slabs, one representing an unreinforced control slab other than the reinforcement of the bottom mesh, and the others representing slabs internally reinforced with SHCC-filled steel tubes and high-strength bolts. An analytical equation was used to predict the punching shear capacity of slabs internally reinforced using steel assemblies. A numerical model was proposed using the ABAQUS program, and was validated by comparing its results with our experimental results. Finally, a case study was performed on large-scale slabs. The results showed that using steel assemblies inside NC slabs increased the slab's punching shear capacity but does not completely prevent punching shear failure. Internally unreinforced slabs made of UHPFC and SHCC were able to avoid punching shear failure and collapse in a ductile bending pattern due to the high compressive and tensile strength of these types of concrete. The proposed analytical method succeeded in predicting the collapse load of slabs reinforced with steel assemblies with a difference not exceeding 9%.

Finite Element Modelling of Bolt Shear Connections in Prefabricated Steel Lightweight Aggregate–Concrete Composite Beams

Steel lightweight aggregate–concrete composite beams (SLACCBs) with bolted shear connections provide several advantages, such as reducing the overall self-weight, shortening the construction period, and improving the structural seismic performance. However, current research on the mechanical behavior of bolted connections is primarily concentrated on composite structures with normal concrete (NC), and there is no investigation focused on the shear performance of bolt connections embedded in lightweight aggregate concrete (LAC) slabs. Therefore, this paper developed a three-dimensional (3D) numerical model to study the shear properties of the bolt connections embedded in SLACCBs by utilizing ABAQUS software. Nonlinear geometric effects and material nonlinearities were considered in the finite element (FE) modelling. The accuracy and reliability of the FE modelling were initially calibrated and validated against the push-off tests described in the literature. Subsequently, the basic shear properties of the bolted connection embedded in SLACCBs were studied and compared with those of the bolted connection embedded in the NC slab by applying the verified FE modelling. Meanwhile, the effects of the concrete strength, concrete density, bolt diameter, and bolt tensile strength on the shear behavior of the bolt connections embedded in SLACCBs were also investigated using extensive parametric studies. Finally, some design formulae were proposed to predict the bolt connection shear strength.

Experimental investigation of ultra-early-strength cement-based self-compacting high strength concrete slabs (URCS) under contact explosions

In this paper, UR50 ultra-early-strength cement-based self-compacting high-strength concrete slabs (URCS) have been subjected to contact explosion tests with different TNT charge quality, aiming to evaluate the anti-explosive performance of URCS. In the experiment, three kinds of ultra-early-strength cement-based reinforced concrete slabs with different reinforcement ratios and a normal concrete slab (NRCS) were used as the control specimen, the curing time of URCS is 28 days and 24 h respectively. The research results show that URCS has a stronger anti-explosion ability than NRCS. The failure mode of URCS under contact explosion is that the front of the reinforced concrete slab explodes into a crater, and the back is spall. With the increase of the charge, the failure mode of the reinforced concrete slab gradually changed to explosive penetration and explosive punching. The experiment results also show that the reinforcement ratio of URCS has little effect on the anti-blast performance, and URCS can reach its anti-blast performance at 28 days after curing for 24 h. On this basis, the damage parameters of URCS for different curing durations were quantified, and an empirical formula for predicting the diameter of the crater and spalling was established.

Numerical Investigation of Performance of Continuous Composite Girders with UHPC slab at Hogging Moment

This paper intends to investigate the behavior of continuous composite girders with of ultra-high-performance concrete (UHPC) slab at hogging moment zone utilizing the nonlinear finite element (FE) modeling. A nonlinear three-dimensional FE model of the continuous composite girder was developed utilizing the commercial software ABAQUS. The model considers both material and geometric nonlinearities. Behavior of normal concrete (NC) and UHPC was modeled utilizing damage plasticity model. Tied, normal friction behavior, embedded contacts were used to simulate the interfacial zones between contacted elements. Four different models were developed and validated with experimental results. The verified model showed satisfactory behavior and is capable of predicting the loading history for continuous composite girders. The model can capture the modes of failure either in normal concrete slab at sagging moment zone or delaminating of UHPC layer at hogging moment zone. A parametric study was carried out to investigate the effect of length of UHPC slab at hogging moment zone on the behavior of the continuous composite girders. The findings of the parametric study showed that the length of UHPC slab slightly affects the ultimate capacity, yielding load, and stiffness of the composite girders. However, significant enhancement in cracking loads was obtained as increasing the length of UHPC slab.

Study on mechanical behavior of rockfall impacts on a shed slab based on experiment and SPH–FEM coupled method

The mechanical behavior of rockfall impacts on shed slabs was studied in three aspects: the rockfall impact force, the inertia effect coefficient, and the structural damage evaluation. A test model composed of a concrete slab and a cushion layer was constructed. Nine batches of impact experiments with energies ranging from 50 to 250 kJ were conducted. The dynamic impact model was established using LS-DYNA to analyze the dynamic impact response characteristics and inertia effect based on the SPH–FEM coupled method. Moreover, random sample expansions were calculated, and methods for assessing the impact force and inertia effect coefficient were proposed. In addition, the applicability of the proposed equation was verified by comparing the calculated results with relevant published experimental data and the Japanese calculation method of impact force. Furthermore, the velocity and mass of the rockfall were selected as the main control variables for damage assessment. A damage assessment index based on punching bearing capacity was established, and the level of damage was classified. Additionally, the influence of the parameters of the concrete slab and cushion layer thickness on damage assessment was analyzed. The impact resistances of the Ultra-High Performance Concrete (UHPC) and normal concrete slab were compared. The results demonstrated that the effect of impact force and the concurrent impact-induced inertia effect should be considered in structural designs. The larger the mass rockfall, the greater the damage sustained by the slab under the same impact energy. The compressive strength of concrete and the yield strength of steel have the greatest and least influence on the damage degree, respectively. A 90 cm-thick sand cushion on a slab increases the impact resistance of the slab by 25%–30%, compared with a 60 cm-thick sand cushion layer. Moreover, it was found that the UHPC concrete slab has good impact resistance, which is approximately twice that of the C40 concrete slab. One of the highlights in this paper is that the SPH–FEM coupled method is proposed to reproduce the physical phenomenon of sand pit-forming. Compared with FEM, SPH–FEM generates a simulated value that is closer to the experimental value.

Fatigue behavior of steel fiber reinforced concrete composite girder under high cycle negative bending action

Tensile concrete crack is a critical factor in the negative flexural region of a steel–concrete composite girder, which could influence the entire structural safety and durability dramatically. The steel fiber reinforced concrete (SFRC) has been utilized for constraining these cracks because of its good tensile performance and low cost in practice. But the practical application of SFRC is still hindered by the unclear fatigue performance of SFRC composite girder. To this end, four 3.3 m-long composite girder tests were executed for investigating the static and cyclic effects of SFRC and connector arrangement. About 3 million load cycles with a monolithic ultimate loading process were applied on each specimen. Generally, the fatigue load cycles in tests resulted in about 10–30% reduction of girders’ global bending stiffness without interlay bonding, and the effect of SFRC on it was not obvious. Even though there were more fatigue load induced cracks found on SFRC slabs than on the normal concrete slabs during loading, the SFRC crack width was smaller. Moreover, the steel–concrete interlayer slip development was found to be slower in SFRC composite girders, while arranging stud connectors in groups resulted in faster slip development. In addition, the test simulation and parametric analysis with material damage plasticity models were carried out, which showed a higher longitudinal reinforcement ratio in SFRC could further reduce fatigue damage on concrete.

Effect of Free Water on the Mechanical Properties and Blast Resistance of Concrete

This study investigates the effect of free water on the mechanical properties and blast resistance of concrete. For this purpose, comparative experiments on saturated and normal concretes subjected to quasi-static compression, cyclic loading-unloading, quasi-static splitting, and dynamic compression are conducted. Thereafter, contact explosion tests are performed on saturated and normal concrete slabs. The results show that free water reduces the blast resistance of concrete slabs. This is primarily because free water alters the mechanical properties of concrete, including its compressive strength, tensile strength, damage evolution rate, and strain rate effect. Therefore, the material parameters of saturated concrete differed from those of normal concrete. It is unreasonable to employ the material parameters of normal concrete for simulating the cracks and damage modes in hydraulic concrete structures subjected to underwater explosions. Then, the material parameters of Holmquist-Johnson-Cook constitutive model for the saturated and normal concrete slabs are determined based on experimental data, respectively. Finally, the numerical simulation of concrete slabs subjected to contact explosions was carried out. The results show that the numerical predictions and the test data both for the saturated and normal concrete slabs subjected to contact explosions were in good agreement.

Structural behavior of multifunctional inhomogeneous infra‐lightweight concrete elements

AbstractThe reduction of energy and resources consumption in the building sector is of crucial importance. One way to approach this challenge is the development of high‐performance materials to increase efficiency. In the research project “MultiLC” (Multifunctional lightweight concrete elements with inhomogeneous properties) highly efficient Infra‐Lightweight Concrete (ILC) elements with varying properties over the cross‐section and further functions, for example, active thermal insulation or photocatalytic air purification, were developed. Besides investigations in concrete technology and building physics, the structural behavior of inhomogeneous ILC‐elements was examined. This paper summarizes the analytical and experimental methods used to investigate the structural behavior of wall and beam specimens and wall‐to‐slab connections. It was found that the stiffness method is a reasonable approach to calculate the maximum load‐bearing capacity of the inhomogeneous ILC elements. Recommendations could be formulated for ultimate design values. Also, the feasibility of a fixed connection between a normal concrete slab and a multi‐layered ILC‐wall was shown.

Structural behavior of out-of-plane loaded precast lightweight EPS-foam concrete C-shaped slabs

This study aimed to develop optimum lightweight expanded polystyrene foam (LEPSF) concrete with a compressive strength of 35 MPa at a density of 1980 kg/m3, to produce precast LEPSF concrete C-shaped slabs with different parameters. LEPSF beads and quarry dust were used as partial replacements for coarse and fine aggregates at different percentages of (15%, 22.5%, and 30%) and (7.5%, 15%, and 22.5%), respectively. From the findings of this investigation, it was noticed that the use of LEPSF beads resulted in acceptable early age strength; however, a reduction in strength was observed at a mature age. Meanwhile, the use of quarry dust improved the compressive strength of LEPSF concrete by more than 30% compared to the mixtures with EPS alone. Totally, 256 samples were prepared to examine the physical and engineering properties of LEPSF concrete mixtures. Results revealed that the deflection of the full-scale LEPSF concrete C-shaped slabs was 31.5%–45.7% more than that recorded in comparable normal concrete slabs. Meanwhile, results have shown that the ductility of the precast LEPSF concrete C-shaped slabs improved in comparison to the normal concrete samples and they also exhibited 20% reduction in the self-weight. It was also seen that precast LEPSF concrete C-shaped slabs give more warning time before failure occurs. As such, it was concluded that the developed precast LEPSF concrete C-shaped slabs have a significant potential to be adopted in flooring systems of modern buildings today.

Value of Concrete Compressive Strength on 28 days with Variation of Candlenut Shell Applicated to Plate on a Non-destructive Test Using Hammer Test

Concrete compressive strength is one of the parameters used to control the quality of a concrete. Concrete compressive strength testing method which is considered the highest level of reliability is a destructive test using a compressive testing machine. Testing requires quite high costs and a longer processing time. But sometimes testing must be done in the scene. Based on the case, a testing tool is needed to measure or determine the compressive strength of concrete without spoil, which is known as the non-destructive test. The tool commonly used for this test is the hammer test. The type of research is experimental. The purpose of this research is to get the compressive strength value of a concrete plate variation of 30% candlenut shells from the test results using a hammer test so as the results can be close to the results of testing using a compressive testing machine (destructive test). The research variable is the testing method (3 point of testing with angle 0°), the age of concrete plate curing, the method of curing (wet curing and dry curing). The number of samples of reinforced concrete slabs is 8 pieces measuring 50cm x 25 cm x 12cm. The research results are Compressive strength of concrete slabs of 30% candlenut shell variations using a Hammer test showed that the concrete strength reached 23-27 Mpa both in wet curing and dry curing or equivalent to the quality of K250 concrete at 28 days. The results also indicate higher values compared to normal concrete slabs.

Study on composite beams with prefabricated steel bar truss concrete slabs and demountable shear connectors

In the conventional steel-concrete composite beams, the composite action is achieved by welded stud connectors which are encased into the cast-in-place concrete slab. This makes the deconstruction and reuse of the structural components almost impossible. A sustainable and prefabricated composite structural system was developed in this study wherein the steel beam is attached to the prefabricated steel-bars truss concrete slab using the demountable bolted connectors. Twelve push-out specimens were designed and tested to assess the shear behavior of the bolted connectors. The test results showed that the shear bearing capacity of the bolted connectors with the prefabricated steel-bars truss concrete slab increased 7.0% over that of the bolted connectors with the prefabricated normal concrete slab. Three full-scale composite beams with various shear connection ratios were constructed and loaded to failure. For direct comparison, a similar composite beam was constructed with the same section size and shear connectors, but using the cast-in-place concrete slab. The flexural capacity of the composite beams with 68% shear connection and full shear connection increased 9.8% and 15.8% compared to the composite beam with 46% shear connection, respectively. The mechanical behavior of the composite beam with the prefabricated concrete slab was comparable with that of the composite beam with cast-in-place concrete slab. The load carrying capacity of the composite beam can be predicted by the simplified model in Eurocode 4 and the plastic model.

Flexural Strength of Modified Reactive Powder Concrete One Way Slabs

Background: Over the last three decades, the interest in using advanced high-performance materials in the construction industry has been increasing worldwide. Recently, a very high strength cement-based composite with high ductility called Reactive Powder Concrete (RPC) has been developed. The RPC concept is based on the principle that a material with a minimum of defects such as micro-cracks and voids will be able to achieve greater load-carrying capacity and durability. Methods: In the present paper, an experimental program of sixteen reinforced concrete one-way slabs was conducted to investigate their behavior under flexural loading. Four of these slabs were with Normal Concrete (NC) and the others of Modified Reactive Powder Concrete (MRPC). All slabs were identical in the dimension of its length and width (1000×500) mm, respectively, and its thickness was varied as one of the variables used in the present work. Other parameters for a one-way slab are concrete type, steel fibers content and flexural steel reinforcement ratio (0.33 and 0.66)%. Results: The results showed that the MRPC slabs with steel fibers failed in a ductile manner and had ultimate load capacity more than that of non-fibrous MRPC with an improvement percentage that reaches up to (66) %. This percentage became (212) % in comparison with normal concrete slabs. Conclusions: Moreover, the results showed that slabs, for both concrete types, reinforced with lower steel ratio failed by tension mode, otherwise, the slabs of higher reinforcement steel ratio failed by combined tension-shear mode. However, an improvement was observed in the ultimate load capacity up to (53 and 98) % when the ratio of steel reinforcement and slab thickness increased, respectively.

Punching Shear Behavior on High Strength Concrete

An experiment was conducted to investigate the behavior of punching shear on connection between column and slab as the effect of axial loading. Four test specimens that consist of high strength concrete slab and normal concrete slab were tested with axial loading. Test result indicated that the capacity of load deflection as behavior of punching shear on a connection of column and slab as the effect of axial loading on high strength concrete slabs higher than load deflection on normal strength concrete slab.

Experimental Study of Blast Resistance on BFRP Bar‐Reinforced Cellular Concrete Slabs Fabricated with Millimeter‐Sized Saturated SAP

An innovative cellular concrete procured with sat‐SAP (superabsorbent polymer) is introduced. Combined with BFRP bars, this concrete may play a role as protective structures in marine applications. Eight BFRP‐reinforced cellular concrete slabs (BSs) and three steel‐reinforced normal concrete slabs (SPs) are exposed to simulated blast loadings in a shock tube device. Low‐modulus cellular concrete and BFRP bars cause BSs to exhibit distinctive behaviours compared to those of SPs. BSs, which are more flexible at the same reinforcement ratio, have more intensive vibrations and larger deformations compared to SPs under various blast loadings. In addition to the porous structure of cellular concrete, BSs demonstrate better wave‐attenuating and energy‐absorbing abilities. More severe damage such as cracks, deflections, and breaches is observed for BSs. In the current research, a comprehensively superior blast resistance can be achieved through improving reinforcement ratio to promote serviceability.

Experimental and numerical study of rubber concrete slabs with steel reinforcement under close-in blast loading

We conducted explosion field tests on rubber concrete slabs with steel reinforcement, including four kinds of concretes with different mix proportions of volume fractions of rubber particles (0%, 10%, 30%, and 50%, termed NC, RC10, RC30, and RC50, respectively). In addition, we compared the measured overpressure at the center of a slab with some empirical models to verify the accuracy our model. Field testing results showed that the tensile zone damage of rubber concrete slabs is smaller than that of normal concrete slabs under large explosive charges. Additionally, we validated a numerical simulation employing Multi-Material ALE and Lagrangian algorithms using the data from field experiments and employed it to further study the deformation process during the field test. Finally, we showed that rubber concrete slabs with steel reinforcements are practical structures for blast resistance, especially when subjected to a large energy detonation.