Reinforced Lightweight Concrete Research Articles

Hybrid Fiber Reinforced Lightweight Concrete: Vegetal and Metalized Plastic Waste Fiber Synergy and Pull-Out Behavior

Abstract Using one or more fibers in concrete is called “hybridization.” Although single-fiber concrete offers excellent performance, concrete reinforced with hybrid fibers gains speed as the synergy between the fibers results in amplified performance. This experimental work reflects the effects of incorporating 1, 2, and 3 % untreated singular and hybrid fibers on the physical and mechanical properties of lightweight concrete (LC) at 3, 28, and 90 days. Six mixture types were used: control LC, LC containing metalized plastic waste fibers (MPWFs), LC containing date palm fibers (DPFs), LC containing sisal fibers (SFs), LC with MPWFs and DPFs (Hybrid A), and LC with MPWFs and SFs (Hybrid B). In the fresh state, fiber introduction affected all mixes’ workability and wet density, and the reduction in slump and wet density was proportional to the fiber dose. However, in the hardened state, the results indicate that compressive strength (CS) and modulus of elasticity (MOE) decreased for LC containing only plastic or SFs. However, these properties increased slightly over the long term for blends containing 1 % DPF. Excepting mixtures containing MPWFs, fiber introduction improved flexural strength (FS) for all blends containing 1 % and 2 % fibers at 28 and 90 days. The most significant gains in FS were 8 % and 4 % at 28 and 90 days, respectively, for samples containing 1 % DPF. Nevertheless, fiber hybridization improved these mechanical properties and created a positive synergy in long-term bending. At 1 % fiber dosage, CS, MOE, and FS increased respectively by 3.05, 3.10, and 8 % for Hybrid A compared with the control LC. Pull-out testing provides the best means to understand typical failure modes and assess maximum tensile strength. Consequently, microstructural analysis enabled us to examine the bonding quality at the fiber-matrix interface.

Behavior of Reinforced Lightweight Concrete Slab with Initial Cracks

The flexural behavior of lightweight concrete two-way slabs repaired or strengthened with externally bonded carbon fiber-reinforced polymer (CFRP) sheets is the subject of this study. The experiment included five reinforced lightweight concrete slab specimens with dimensions of 1000 mm in length, 1000 mm in width, and 120 mm in thickness. Tested one specimen without any strengthening and reinforced another specimen with a single layer of CFRP. The other specimens were repaired with a single layer of CFRP, applying damage ratios of 50%, 60%, or 70% of the ultimate load. Intentionally designed each slab to collapse under bending forces and maintained comparable dimensions. According to the experiment results, changing the degree of damage from 70% to 50% increases the ultimate load capacity by about 17.7%, and the ultimate deflection decreases by about 31.4%. CFRPs have the potential to fix structural damage under static stress testing conditions. However, it is essential to make sure that they stick well to surfaces that do not have suitable geometric properties or have been deformed. CFRP sheets effectively repaired the specimens, increasing the failure stress of the reinforced concrete slabs and preventing the spread of cracks.

Improvements in lightweight concrete T beams CFRP strengthened and anchored with U‐wraps

AbstractThis research provides a study for an experimental program using sand‐perlite‐lightweight reinforced concrete (RC) beams strengthened and anchored with carbon fiber reinforced polymer (CFRP) materials. The main objective of this work is to showcase the efficiency of using U‐wrap anchors to secure the externally applied CFRP sheets on lightweight RC beams. A series of six full‐scale T‐beams with an increasing number of CFRP U‐wraps per shear span was prepared and tested. The use of U‐wrap anchorage enhanced the flexural performance of the sand‐lightweight concrete beams by progressively delaying the premature debonding of CFRP sheets as a direct function of the number of U‐wraps used per shear span. The beam flexural capacity gradually improved from 116 kN without the use of U‐wrap anchors to 182 kN when using six U‐wraps per shear span, which reflects a significant enhancement. Similarly, the ultimate deflection gradually improved from 56 mm for the beam without U‐wrap anchors to 94 mm when applying six U‐wraps per shear span. A design model established earlier, for normal weight concrete, has been successfully qualified to yield accurate findings against the experimental results. Also, the outcome of this study interestingly showed that the ultimate strength results of the anchored beams were close to their counterparts of normal weight concrete conducted on identical beams. This finding shows that U‐wrap anchors performed efficiently despite the lack of coarse aggregate interlock in the concrete mix.

Structural Behavior of Reinforced Lightweight Concrete Beams made of Recycled Wood Aggregates

Structural Behavior of Reinforced Lightweight Concrete Beams made of Recycled Wood Aggregates

Numerical investigation on the behavior of eccentrically loaded lightweight reinforced concrete columns at elevated temperature

AbstractIn this paper, a numerical model is presented to simulate the behavior and failure of lightweight reinforced concrete (LWRC) columns subjected to eccentric compressive load at elevated temperature using the finite element code ABAQUS. Validation of the numerical model was ensured throughout comparison numerical results with the available published experimental tests results. The validated numerical model was implemented in conducting extensive parametric study to understand the effects of important parameters on the response of eccentrically compressed LWRC column at elevated temperature. These parameters include the effect of concrete cover, the effect of exposure time, the effect of the exposed temperature, the effect of temperature distribution around column section, the effect of temperature distribution along column length, and the effect of eccentricity ratio. The numerical results indicated that increasing the concrete cover of the column section results a considerable increasing of the ultimate load capacity. In addition, there is an increase in the ultimate load capacity when the temperature exposure time is reduced to the half of the original exposure time. Whereas, if the exposure period is increased to twice and three times the original exposure time, the ultimate load shows a slight decrease. Moreover, the ultimate load capacity of the LWRC column decreases when temperature is increased. Finally, the ultimate load capacity increased of the LWRC column when the temperature is distributed over larger distance of the column length.

Lightweight Flexible Nonlinear Composite (LFNLC) and Elastic Composite, Reinforced Lightweight Concrete as an LFNLC

Lightweight Flexible Nonlinear Composite (LFNLC) and Elastic Composite, Reinforced Lightweight Concrete as an LFNLC

Mechanical Properties and Flexural Response of Palm Shell Aggregate Lightweight Reinforced Concrete Beam

This work focuses on examining the mechanical characteristics and flexural response of reinforced concrete (RC) beams by incorporating oil palm shell (OPS) lightweight aggregate from oil palm shell waste. The OPS aggregates are replaced in various percentages, such as 0 to 50% of natural coarse aggregate (NCA). Mechanical properties of OPS concrete were conducted, and these properties were used to quantify the flexural performance of RC beams. Five RC beams with several gradations of OPS aggregates were cast and tested for this investigation. The first cracking, ultimate strength, load-deflection behavior, ductility index, and failure patterns of OPS aggregate beams were investigated as the corresponding behaviors to the NCA concrete beam. The fresh properties analysis demonstrated lessening the slump test by varied concentrations of OPS concrete. Furthermore, compressive strength was reduced by 44.73%, 50.83%, 53.33%, and 57.22% compared to 10%, 15%, 20%, and 50% OPC substitution at 28 days. Increasing OPS content in concrete mixes decreased splitting tensile strength, comparable to the compressive strength test. Modulus of rupture and modulus of elasticity experiments exhibited a similar trend toward reduction over the whole range of OPS concentrations (0–50%) in concrete. It was revealed that the flexural capacity of beams tends to decrease the strength with the increased proportion of OPS aggregate. Moreover, crack patterns and failure modes of beams are also emphasized in this paper for the variation of OPS replacement in the NCA. The OPS aggregate RC beam’s test results have great potential to be implemented in low-cost civil infrastructures.

Influence of Steel and Polypropylene Fibers on the Structural Behavior of Sustainable Reinforced Lightweight Concrete Beams Made from Crushed Clay Bricks

Structural lightweight concrete is preferred over traditional concrete due to its ability to reduce the dead load, minimize the size of load-bearing structural members, and provide more economical solutions for foundation deteriorations. This research sheds light on sustainable lightweight concrete using waste crushed clay bricks (CCB) as a lightweight aggregate. To reduce micro-crack propagation of the developed concrete, two types of fiber were implemented and investigated. Steel fibers (SF) with amounts of 0.5% and 1.0% by volume of concrete, and polypropylene fibers (PPF) with amounts of 0.1% and 0.2% by volume of concrete, were employed. Five reinforced concrete beams were made and tested in order to precisely evaluate the structural behavior of the proposed lightweight CCB concrete. Additionally, ABAQUS software for nonlinear finite element analysis has been utilized to simulate the tested beams and compare the numerical model predictions with the experimental findings. The findings revealed that the addition of SF and PPF exhibited a notable influence on enhancing the mechanical characteristics of lightweight CCB concrete. Adding 0.2% PPF increased the ultimate load and deformation capacity at failure by approximately 16% and 24%, respectively. Furthermore, after 28 days, the addition of 0.5% and 1.0% SF enhanced the compressive strength by around 11.7% and 17.6%, respectively. Moreover, a significant level of consistency between the results obtained from the numerical model and the experimental findings was observed. In general, the use of SF and PPF in CCB concrete successfully produced high-quality lightweight concrete with interesting results for use in reinforced concrete beams.

An Introduction to Lightweight Flexible Nonlinear Composite (LFNLC) and Elastic Composite, Reinforced Lightweight Concrete (ECRLC) as the Cementitious LFNLC

Here, a new class of high-performance composites, called “Lightweight Flexible Nonlinear Composites (LFNLC)”, has been briefly introduced. This class of composites has its own structural and functional characteristics. Nonlinear behavior in bending and porous or porous-like texture are instances of such characteristics. - Cementitious LFNLC is termed “Elastic Composite, Reinforced Lightweight Concrete (ECRLC)”. The ECRLC provides lightweight beams with substantial strain capability, resilience modulus and toughness in bending, resulting in a considerable increase in bearing capacity while weighing significantly less. The failure mode in low-height and ultra-lightweight beams made of the ECRLC is not compressive and brittle. - This lightweight, flexible composite is a non-monopolistic, versatile and comparatively low-price material. Likewise, the virtues such as resilience and flexibility, workability, lightness, durability, and high formability are important in architecture. - In general, lightweight and integrated construction has a key importance in earthquake resistance. Therefore, the ECRLC can be especially beneficial in earthquake-prone regions. - By taking advantage of the resilience and flexibility of this formable system, it can also be used to build non-brittle reinforced ultra-lightweight and insulation sandwich panels, safe and lightweight guards, and shock-resistant structures. In addition, they are utilizable in some infrastructures and explosion-proof pieces with suitable behavior, resilience, and toughness. - This work presents a practical method for converting a rigid solid into a flexible material with lower density or increasing the elasticity of a flexible material while decreasing the density. Essentially, this method entails creating a porous or porous-like texture in the material, reinforcing appropriately, and providing it with the necessary integrity. (For example, properly dispersing lightweight aggregates all over the reinforced, conjoined matrix can produce a porous-like texture.) By this process, the resilience modulus and toughness in bending rise and the density reduces. - This paper briefly discusses the functional and structural characteristics of LFNLCs, some applications, and a Reproducible example of the ECRLC.

Influence of Temperature on Shear Behavior of Lightweight Reinforced Concrete Beams Using Pozzolana Aggregate and Expanded Polystyrene Beads

The innovation inherent to employing expanded polystyrene (EPS) beads lies in its transformative impact on traditional concrete practices. Through the incorporation of EPS beads in concrete mixtures, a novel approach emerges that significantly alters the material’s characteristics, and opens up new avenues for construction and design. Studying the shear behavior of RC beams made with EPS beads is essential for advancing knowledge, improving design practices, ensuring structural integrity, and promoting the effective and responsible use of innovative materials in construction. This research experimentally investigated the effect of using EPS beads and pozzolana aggregate (PA) on the shear behavior of the RC beams. A total of 27 simply supported rectangular beams were cast, using three novel distinct mix designs, and were subjected to two-point load testing until failure. These three mixes were categorized as follows: a control mix, a mix with only EPS, and a mix with EPS, along with an additive. The ultimate failure load was experimentally recorded for all specimens, and the influence of the temperature (300 °C and 600 °C) on the RC beams made with EPS was examined. The findings revealed a reduction in the concrete compressive strength and density in the beams containing EPS and EPS with superplasticizers of (21.7%, 24.9%) and (11.3%, 16.2%), respectively. Additionally, EPS played a significant role in diminishing the ultimate shear capacity of the beams, compared to the control beams, by about 19.4%. However, the addition of a superplasticizer along with the EPS helped to maintain the beam capacity, to some extent. Conversely, the beams exposed to a temperature of 300 °C exhibited an almost similar capacity to that of the control beams without heating. Nevertheless, at 600 °C, the beams displayed a noticeable decrease in the ultimate load capacity, compared to the unheated control beams.

Application of Stochastic Finite Element Modeling to Reinforced Lightweight Concrete Beams Containing Expanded Polystyrene Beads

Limited investigations have evaluated the effect of expanded polystyrene (EPS) beads on the structural lightweight concrete properties. EPS offers many features compared to natural or artificial lightweight aggregates including the elimination of aggregate saturation prior to concrete batching, ability to be fabricated on site, consistency in size and quality, and reduced cost. The main objective of this paper is to assess the suitability of finite element (FE) modeling based on deterministic and stochastic approaches to predict the shear strength behavior of reinforced concrete (RC) beams containing EPS additions. Test results showed that the experimental load-deflection properties recorded at failure can be well reproduced using both FE approaches. Nevertheless, the damaged-zone distribution and crack patterns that occur during the loading stages of RC beams cannot be approximated using the deterministic FE approach. In contrast, the stochastic method was quite suitable as it accounted for the concrete heterogeneity and altered spatial mechanical properties (such as compressive strength, splitting tensile strength, and Young’s modulus) due to EPS additions. Such data can be of interest to civil engineers seeking to predict the failure patterns and performance of structural lightweight members while reducing the time and resources needed to account for the concrete’s strength variability during experimental testing.

Experimental investigation of mechanical behavior of lightweight RC elements under repeated loadings

Today, the use of lightweight structural concrete in earthquake-prone countries of the world has grown more and more. Therefore, it is important to study the behavior of this type of concrete against seismic loads. So far, many studies have been conducted on the behavior of reinforced concrete (RC) elements against cyclic loads caused by earthquakes, but recent observations show that many earthquakes occur consecutively. That is, structural elements and systems may experience several weak earthquakes or aftershocks during their lifetime. It is obvious that a structure that experiences several cyclic vibrations will suffer a degradation of strength and stiffness, and its behavior will change against subsequent earthquakes. The existing structural models consider the cyclic degradation resulting from the cyclic movement during an earthquake, but many of these models do not consider the effects of degradation caused by previous earthquakes; While this degradation can have significant effects on the behavior of structural elements. In this research, the degradation caused by cyclic loading in lightweight concrete structural elements was investigated first, and then their post-degradation behavior under different levels of degradation was studied; For this purpose, 12 specimens of lightweight RC beams and 4 specimens of lightweight RC columns were made with a scale of 50% and subjected to different uniform and cyclic loadings, and three levels of slight, moderate and extensive degradation were defined based on a number of constant fatigue cycles. Then, in the next step, the cyclic behavior of the specimens after degradation was tested in three levels of slight, moderate and extensive degradation. The results of the tests showed that with the increase in the degradation level, the amount of energy absorption of RC beams decreases; Especially in beams with extensive degradation level, the amount of beam energy absorption decreases by more than 40%. Comparing the cyclic behavior after the degradation of the damaged columns with the behavior of the intact specimen shows that the increase in the level of degradation reduces the ductility of the columns.

Consideration of Unidirectional Cyclic Loading on Bond in Reinforced Lightweight Concrete in Standards

The present research deals with the cyclic and standard pull-out resistance of deformed steel bars embedded in lightweight and normal concrete. This paper is a continuation of a previous paper, where the experimental results are detailed. In the present paper, the experimental results are set against the formulas and the diagrams provided by the Eurocode standard and the Model Code 1990, and then a comparative discussion is performed. In the case of cyclic loading, the damage defined by the Palmgren–Miner hypothesis, as well based on the recommendations of various national annexes of Eurocode and the Model Code, is calculated. A multiplier corresponding to the maximum load is calculated, which indicates by how much the applied load should be multiplied to obtain a damage value equal to 1.

Thermal Effect on the Flexural Performance of Lightweight Reinforced Concrete Beams Using Expanded Polystyrene Beads and Pozzolana Aggregate

Thermal Effect on the Flexural Performance of Lightweight Reinforced Concrete Beams Using Expanded Polystyrene Beads and Pozzolana Aggregate

Shear Capacity Analysis of Steel Reinforced Lightweight Concrete Elements Based on The Bond Strength

Push-out tests of steel reinforced lightweight concrete(SRLC) were carried out for nine specimens which were designed according to the orthogonal test method considering four influence factors including strength of lightweight aggregate concrete, stirrup ratio, thickness of protective layer and anchorage length. The curves of average bond stress and loading-end slip were drawn, the characteristics of split failure and push-out failure were analyzed, and the characteristic bond strength was obtained. Combined with the test results of other scholars on the ultimate bond strength of steel reinforced concrete(SRC), it is found that the bond strength of SRLC is not worse than that of normal concrete(NC) which can be taken the same as 0.5MPa. Then the obtained bond strength can be used to calculate the shear strength of SRLC elements which may occur two forms of shear failure-diagonal shear failure and shear bond failure, however, shear bond failure is ignored in some specifications. Shear bond failure capacity computational formula of SRLC elements is deduced into which the bond strength is introduced.To verify the reasonability and accuracy of the proposed approach, the shear capacity and failure pattern are predicted by the proposed means with previous test results and are also compared with other provisions. The analyses and calculations indicate that the proposed method can accurately predict the shear failure mode and the calculated shear capacity values are in better agreement with the experimental results.

Flexural Behaviour of Lightweight Reinforced Concrete Beams Internally Reinforced with Welded Wire Mesh

Lightweight clay aggregate (LECA) is manufactured by heating clay with no lime content in the kiln; as a result, the water evaporates and angular clay balls with pore structures are obtained. LECA possess internal curing properties as any other lightweight aggregate due to their pore structure and higher water absorption capacity. In this work, experimental and analytical behaviour using LECA as a 100% replacement for coarse aggregate to make lightweight concrete (LWC) beams was studied. The LWC beams were compared to the conventional concrete beams in load-deflection, energy absorption capacity, and ductility index. Internal mesh reinforcement using welded wire mesh (WWM) of (4 layers of 15 mm square spacing, 4 layers of 10 mm square spacing, and 4 layers of 15 mm and 10 mm mesh placed alternatively) was provided to enhance the load-carrying capacity of the LWC beam without increasing the dimensions and self-weight of the beams. The beam internally reinforced with WWM exhibited higher load carrying capacity and withstood more significant deflection without sudden failure. The internal reinforcement of WWM is provided to make steel rebars, and WWM works monolithically while loading; this will reduce the stress on tension bars and increase load-carrying capacity. Finally, the generated analytical findings agreed well with the experimental data, demonstrating that the analytical model could mimic the behaviour of LWC beams with WWM.

Behavior of Lightweight Reinforced Concrete Flat Slabs Subjected to Punching Shear

Behavior of Lightweight Reinforced Concrete Flat Slabs Subjected to Punching Shear

The Properties of Glass Fiber Reinforced Lightweight Concrete under the Effect of High Temperature

This study aimed to produce lightweight concrete by using 50% pumice as coarse aggregate and 0.1% and 0.3% glass fiber. It is aimed to investigate the changes that will occur in the compressive strength and splitting tensile strength properties of the samples when this lightweight concrete produced is exposed to temperatures of 150 °C, 300 °C, 450 °C and 600 °C. The study was carried out in six stages. In the first stage, reference samples were produced. In the second stage, 0.1% and 0.3% glass fiber reinforced lightweight concrete samples were produced. In the third stage, unit weight, porosity, compressive strength and splitting tensile strength tests were applied to the produced samples. In the fourth step, the samples were gradually exposed to different temperatures (150 °C, 300 °C, 450 °C and 600 °C). In the fifth stage, compressive strength and splitting tensile strength tests were applied to the samples exposed to high temperature. In the sixth and final stage, SEM images of 0.1% glass fiber reinforced lightweight concrete samples were analysed. As a result, it was observed that the unit weight value decreased and the porosity values increased with glass fiber reinforcement. There was also an increase in compressive and splitting tensile strengths. In addition, it was observed that the samples exposed to 150 oC temperature had the highest compressive strength and splitting tensile strength. In the analysis of SEM images, with the increase in temperature, it was determined that the samples in microstructure changed into macrostructure as well as the cracks occurred in the sample structure. The importance of this study stem from increasing tensile strength of lightweight concrete with glass fiber reinforcement so as to prevent loss of life and property in an earthquake.This study is important because it increases the tensile strength of lightweight concrete with low tensile strength with glass fiber reinforcement. This will result in less loss of life and property in an earthquake. Keywords: Glass fiber, pumice, lightweight concrete, high temperature DOI: 10.7176/CER/14-4-07 Publication date: June 30 th 2022

Structural Behavior of Reinforced Lightweight Concrete Slabs

This paper presents an exploration of choosing the optimum density for concrete that achieves the best structural performance for two-way slabs made of concrete with fine aggregate in different proportions less than the ratio used in ordinary concrete to produce different densities, by taking advantage of the idea of fine aggregate concrete which considers as light-weight concrete to achieve lighter concrete with higher structural endurance. The experimental program includes constructing and testing five slabs, four of them made of concrete with different fine aggregate radios 75%, 50%, 25%, and 0% to get different densities (2207, 1792, 1536, 1310 kg/m3) as well as another slab made of normal concrete used as a reference slab with a density of 2414 kg/m3. The outcomes reveal that decreasing the density of the slab from 2414 kg/m3 to 1310 kg/m3 by reduction fine aggregate in concrete from 100% to 0% respectively has more effect on the first crack load than that on the ultimate load of two-way slabs as the first crack load decreases with percentages 16.7%, 33.3%, 38.9%, and 61.1% the while the ultimate load decreases with percentages 7.3%, 21.9%, 46.3%, and 56.1%, respectively as compared to the reference (normal wight concrete slab). Also, decreasing the density of the slab made the cracks form and spread quickly and the slab failure tends towards the brittleness, and the cracks diffused and grew faster and wider.

Flexural response of FRP-strengthened lightweight RC beams: hybrid bond efficiency of L‐shape ribbed bars and NSM technique

This paper presents the results of an experimental study on employing near surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement technique, and L‐shape ribbed bars, for flexural strengthening of lightweight reinforced concrete (RC) beams. 18 RC beams including 14 lightweight RC beams and four normal-weight concrete beams were designed. The beams were strengthened with glass fiber-reinforced polymer (GFRP) bars and carbon fiber-reinforced polymer (CFRP) laminate in bending tests. Test parameters included: (1) different FRP materials (glass bars and carbon sheets), (2) longitudinal steel reinforcement ratio, and (3) type of strengthening technique used (NSM reinforcement or hybrid). The ultimate tensile strength, deflection, compressive and tensile strain of concrete, and failure mode of the beams were examined under four-point flexural test. Results showed that the ultimate strength of all RC beams increased between 33 and 105% compared to the control beam. The ultimate strength of beams reinforced with CFRP in the mid-span region was 10% higher than that of beams strengthened at both ends, although the former exhibited 28% lower ultimate deflection. The ultimate strength and deflection of RC beams strengthened with combined steel reinforcing bars and GFRP bars were 10% and 108% higher, respectively, compared to those of RC beams strengthened with GFRP bars only. Hybrid L‐shape ribbed bars beams showed a considerably higher ductility (up to 170% increase in the ultimate deflection) compared to other beams. The comparison of the experimental results of the ultimate strength of the beams with ACI440-2R guidelines indicated a reasonable and conservative prediction of the code expression.