Lightweight Aggregate Concrete Beams Research Articles

Effect of Manufactured Sand Content on the Flexural Performance of Self-Compacting Lightweight Aggregate Concrete Beams

Effect of Manufactured Sand Content on the Flexural Performance of Self-Compacting Lightweight Aggregate Concrete Beams

Mechanical properties and flexural behaviour of green light weight concrete beams exposure to salty soils

This paper presents an experimental investigation on the mechanical properties, durability and flexural behaviour of green concrete beam when subjected to harsh environments by using recycled building materials. Concrete resistance to external aggressive environmental condition is one of the most significant characteristics to maintain the concrete durability. The fundamental goal of this study is to understanding the performance of green lightweight concrete beam of (10×10×40 cm) under two different severe saline conditions; Ground Water Condition (GWC) and Severe Saline Clay Soil Condition (SSC) that contain chlorides and sulfates at concentrations like to those existing in groundwater and soil of the southern and middle parts of Iraq. In this research, in addition to normal concrete; three basic categories of green lightweight concrete are used: structural, non-structural and moderate strength using recycled of clay bricks and themestone blocks as coarse Light Weight Concrete (LWA) by a replacement ratio of (0, 50 and 100) % volume of natural coarse aggregate. All green Light Weight Aggregate Concrete (LWAC) beams and related specimens for mechanical properties were subjected to GWC, SSC and Laboratory Air Condition (LAC) for till (3, 6 and 9 months) after twenty-eight days of curing by tap water. Compressive strength, splitting tensile strength and density were also studied. The results obtained offered that the GWC and SSC have impacted the performance of all concrete beam types negatively with exposure age. The decadence was more for non-structural green LWAC beam. It is found that the resistance of beams contains bricks aggregate to GWC and SSC was a better than the other types of the green LWAC, the percentage decreases in failure load were 15.47% and 13.31% at 9 months of exposure to GWC and SSC measured relative to concrete beam exposed to LAC, respectively. Under the effect of aggressive conditions till 3 months, the results clarified that the improvement rate in the mechanical properties of the green LWAC were increased with age in comparison with ordinary concrete. The percentage reduction in compressive, splitting tensile strength and density at 9 months were ranged between (8.70-17.05) %, (14.71-36.50) % and (0.11-3.98) %, respectively measured relative to the same specimens in LAC.

Flexure Behaviour of Using Glass Fiber Reinforced Polymer Bars on Lightweight Aggregate Concrete Beams

Flexure Behaviour of Using Glass Fiber Reinforced Polymer Bars on Lightweight Aggregate Concrete Beams

Study on shear behavior of high-performance polypropylene fiber-reinforced lightweight aggregate concrete beams

The effects of high-performance polypropylene fiber (HPPF) content, shear span to depth ratio, and stirrup ratio on the shear behavior of lightweight aggregate concrete (LWAC) beams were studied according to shear tests on eleven high-performance polypropylene fiber lightweight aggregate concrete (HPPLWC) beams and three LWAC beams under symmetrical concentrated load. The failure phenomenon, stirrup strain, shear capacity, and deflection of each specimen were analyzed, and it was determined that the failure patterns of the beams were classified as diagonal tensile failure, diagonal compression failure, shear compression failure, and bending shear failure, in which the beams without stirrups having the HPPF content of 0 kg/m3 and 3 kg/m3 were a diagonal tensile failure, the beam with the shear span to depth ratio of 1 was diagonal compression failure, the beams with the stirrup ratio of 0.38 % and the HPPF content of 6 kg/m3 and 9 kg/m3 were bending shear failure, and the rest of the specimens were shear compression failure. Adding HPPF to concrete could effectively improve its tensile strength, limit the growth of cracks, and further improve its initial cracking strength. By increasing the HPPF content and stirrup ratio, the shear capacity and ductility of the beams could be improved. Increasing the shear span to depth ratio of the beams could improve their deformability of the beams while simultaneously decreasing their shear capacity. Based on the experimental study, the contribution of each influencing factor to the shear capacity was analyzed, and the shear capacity model of the diagonal section of the HPPLWC beam was established. The model has great prediction accuracy as shown by error analysis.

FLEXURAL BEHAVIOR OF STEEL FIBER-REINFORCED LIGHTWEIGHT AGGREGATE CONCRETE BEAMS PRESTRESSED WITH CARBON FIBER-REINFORCED POLYMER BARS

An unbonded prestressing anchorage system for carbon fiber-reinforced polymer (CFRP) tendons was introduced. Eight lightweight aggregate concrete (LWC) beams prestressed with unbonded CFRP tendons which used CFRP auxiliary reinforcements and one fabricated using normal weight concrete (NWC) were tested under a four-point bending condition. The influences of concrete type, of prestressed degree and, of clear span length on the cracking moment, on the moment-deflection response and, on the crack width were analyzed. The existing deflection and crack width models for unbonded FRP prestressed beams with steel auxiliary reinforcements were modified from the view of equivalent axial stiffness. The applicability of the modified models was evaluated based on the test results. It is shown that the serviceability limit state of the beams is mainly governed by the crack width limit. The ratios between the moment at crack width of 0.5 mm and the ultimate moment range from 41% to 52%. With the same total reinforcement amount, the increase in the prestressed degree helps delay the cracking of the specimens. Increasing the amount of the auxiliary reinforcement and of the unbonded prestressed tendons both improve the beam stiffness and restrain the propagation of the cracks. The modified Cheng’s and modified Meng’s deflection models provide accurate deflection predictions for LWC beams with unbonded prestressed and auxiliary CFRP reinforcements.

Structural Performance of Lightweight Aggregate Concrete Reinforced by Glass or Basalt Fiber Reinforced Polymer Bars.

Lightweight aggregate concrete (LWC) and fiber reinforced polymer (FRP) reinforcement are potentially more sustainable alternatives to traditional steel-reinforced concrete structures, offering several important benefits. To further the knowledge in this area, the physical–mechanical properties of LWC produced with 0%, 50%, and 100% expanded clay aggregate were assessed. Subsequently, the flexural behavior of LWC beams reinforced with steel reinforcement and glass and basalt FRP bars was tested. The results of the experimental program allowed quantifying of the effect of expanded clay aggregate incorporation on LWC properties. The use of FRP reinforcement was also compared to steel-reinforced concrete beam behavior. The results of this study can provide additional support for the use of innovative materials such as LWA and FRP reinforcement.

Confinement in bending of high-strength lightweight aggregate concrete beams

The use of lightweight aggregate concrete (LWAC) is limited as a mainstream construction material in structural applications due to more brittle post-peak material behavior and uncontrolled crack propagation compared to normal density concrete (NWC). To improve the ductility of LWAC structures, the confinement effect from the transverse reinforcement in conjunction with longitudinal reinforcement was considered. In addition, it was tested the influence of concrete cover. The ultimate compressive strain at peak load was approximately 3.5‰ for all beams, which is like the level expected for NWC. It is possible to increase the ductility of LWAC structures by appropriate reinforcement detailing.

A Parametric Study to Assess Lightweight Aggregate Concrete for Future Sustainable Construction of Reinforced Concrete Beams

Lightweight aggregate concrete (LWC) is an attractive alternative to conventional concrete in building construction. It leads to lighter self-weight in beams and floor slabs and thus might have a positive impact on reinforcing steel consumption, also reducing the loads withstood by columns and foundations. However, LWC may increase cement consumption to maintain the required concrete compressive strength. This study presents compact equations for the design of reinforced LWC beams and subsequently applies them to a parametric analysis programmed in MATLAB. The aim of this analysis is to obtain an estimation of the equivalent carbon dioxide emissions associated with steel and cement consumption if using LWC instead of conventional concrete. The analysis involves more than 3 million beams simulating real scenarios by varying different design parameters, such as mix design, concrete strength, span length and applied loads and verifying both Ultimate and Serviceability Limit States. Whereas LWC of density equal or below 1600 kg/m3 does not seem to be feasible when trying adequately control cement content, the study shows that LWC with densities of 1800 and 2000 kg/m3 would not have a negative impact on the carbon dioxide emissions and would adequately comply with the various design restrictions.

Serviceability performance of fiber-reinforced lightweight aggregate concrete beams with CFRP bars

Six lightweight aggregate concrete (LWC) beams reinforced with carbon fiber–reinforced polymer (CFRP) bars were tested under a four-point bending load with different steel fiber contents, reinforcement ratios, and clear span lengths to investigate their flexural behavior and serviceability performance. The test results showed that using steel fiber–reinforced lightweight aggregate concrete (SFLWC) and increasing the reinforcement ratio enhanced the serviceability performance of the beams. The incorporation of 0.6% by volume of steel fibers reduced the midspan deflection by 22.70%–36.87% at the same load level in service stage. At service load, all the CFRP-reinforced beams exhibited conservative deflections when compared to the deflection limits recommended by ACI 440.1 R and GB 50608, and satisfied the crack width limit of 0.7 mm. Comparing the measured maximum crack widths with the corresponding predictions revealed that the bond-dependent coefficient value of 1.4 specified in ACI 440.1 R was reasonable yet conservative. Moreover, an energy-based method was adopted to quantify the influence of the fibers on the beam stiffness. On this basis, a rational deflection model for SFLWC beams reinforced with CFRP bars was suggested.

Flexural behavior of two-layer beams made with normal and lightweight concrete layers

In this paper, twelve concrete beams with two different layers of concrete were evaluated as a simply supported beam under four-points loading. The beams assembled of two different types of concrete layers, one of which was normal-weight concrete (NWC) and the other was lightweight aggregate concrete (LWAC). The investigated parameters were the thickness of the lightweight concrete to the overall depth of beams (hLW/h), and the compressive strength of normal and lightweight concrete. Due to the weak lightweight aggregates used, lightweight aggregate concrete exhibits more brittleness and lower stiffness. Therefore, the viability of compensating for this degradation and providing a layer of normal concrete seems to be very interesting in such beams. The behavior of beams was evaluated based on cracking, failure mode, flexural strength, maximum deflection, stiffness, and toughness. The results showed slight variations on the majority of the above-mentioned performance aspects of two-layer beams compared to fully normal concrete beams. While there were great enhancements compared to fully LWAC beams. The variants were mainly attributable to the efficacy of using LWAC in providing lower stiffness and lower tensile strength. The experimental results have been compared to predicted values using the ACI 318-19, with some modifications for the equations to be matched with two-layer beams, the comparison was in terms of the deflection due to service load, moment capacity, and cracking moment.

CALCULATION METHOD FOR CRACK WIDTH OF STEEL FIBER-REINFORCED LIGHTWEIGHT AGGREGATE CONCRETE BEAMS REINFORCED WITH FRP BARS CONSIDERING BOND-SLIP BEHAVIOR

Regarding the crack development of concrete beams reinforced with fiber-reinforced polymer (FRP) bars as a process wherein the FRP bars are pulled out from concrete on both sides, a differential equation of crack width of lightweight aggregate concrete beams reinforced with FRP bars considering bond-slip behavior was established. According to the crack width limits provided by the design codes, the upper limit of slip was reasonably determined and constitutive models for bond-slip relationship between FRP bars and steel fiber reinforced-lightweight aggregate concrete in ‘low slip’ stage which were suitable to the service stage of the beams were proposed and introduced. The maximum crack spacing, lmax, amplification factor of crack width, h2/h1, and residual stress of fiber reinforced-concrete in cracked sections, σfib, were specified. On this basis, a crack width model of steel fiber reinforced-lightweight aggregate concrete beams reinforced with FRP bars was proposed using iterative algorithm and its accuracy was evaluated based on measured data of maximum crack width in service stage. It is shown that within crack width limit of 0.5 mm, the proposed model generates accurate maximum crack width predictions for steel fiber-reinforced lightweight aggregate concrete beams reinforced with FRP bars.

Experiment on the bonding performance of the lightweight aggregate and normal weight concrete composite beams

Aiming at the bonding performance of the casting interface in the composite ceramsite lightweight aggregate concrete (LWAC) and normal weight concrete (NWC), the experiment on the shear bonding blocks and bending composite beams were designed for progressive study. The Z-shaped composite blocks were first made by the LWAC and NWC with different strength grades considering the variation of the casting interval time and the interface preparing method. The bending composite beams were designed considering the variation of the casting interval time, the relative position between the casting interface and the calculated sectional neutral axis in the LWAC and NWC composite beam. The result indicates that, the bonding shear performance of the casting interface decreases most obviously within 2 days of the casting interval time. The shear strength of the casting interface with 14 days casting interval time for considered different interface preparing methods is higher than that calculated according to the specification. Although there is no bonding sliding failure happening on the casting interface in the composite beam during the experimental loading, a certain influence exists on the crack developing near the casting interface, the load-deflection curve developing, the strain developing of the mid-span section and the subtle damage variation considering the variation of the casting interval time, the relative position between the casting interface and the calculated neutral axis in the composite beam.

콘크리트 단위용적중량을 고려한 경량골재 콘크리트 보의 소성회전능력 모델의 제시

이 연구의 목적은 단위용적중량(ρ<SUB>c</SUB>)에 따른 철근 콘크리트(reinforced concrete, RC) 보의 곡률(μ<SUB>∅</SUB>) 및 변위(μ<SUB>Δ</SUB>) 연성비에 대한 단순 모델을 제시하는 것이다. 철근 콘크리트(RC) 보의 소성회전능력은 위험단면에서 변형률 적합조건 및 힘의 평형조건과 보 길이에 따라 이상화된 곡률 분포로부터 유도된 μ<SUB>∅</SUB>와 μ<SUB>Δ</SUB>의 개념으로 평가되었다. 분석결과 RC 보의 μ<SUB>∅</SUB>와 μ<SUB>Δ</SUB>는 ρ<SUB>c</SUB>이 2,300 kg/m³에서 1,400 kg/m³으로 감소할 때 각각 47 % 및 28 % 감소하였다. 이는 동일한 주절근 지수(ω<SUB>8</SUB>)에서 경량골재 콘크리트(light-weight aggregate concrete, LWAC) 보의 소성회전 능력이 보통 콘크리트(normal-weight concrete, NWC) 보보다 낮음을 의미한다. 기존 문헌에서 구축된 120개 실험결과와의 비교에서, Pam et al.과 Arslan and Cihanli의 모델은 LWAC 보의 변위 연성비를 불안 전측으로 예측하였다. 그 불안전측의 정도는 ρ<SUB>c</SUB>가 감소함에 따라 증가하였다. 반면, 제시된 μ<SUB>Δ</SUB>의 모델은 ρ<SUB>c</SUB>와 ω<SUB>8</SUB>에 관계없이 실험 결과를 잘 예측하였는데, 실험결과 값 대비 예측값의 비의 평균 및 표준편차가 0.98 및 0.20이었다.

Comparative study of the flexural behavior of steel fiber-reinforced lightweight aggregate concrete beams reinforced and prestressed with CFRP tendons

A comparative experimental investigation of flexural behavior of lightweight aggregate concrete (LWC) beams reinforced and prestressed with carbon fiber reinforced polymer (CFRP) bars was presented and an unbonded prestressing anchorage system for CFRP tendons was introduced. A total of four beams prestressed with unbonded CFRP bars and four reinforced with CFRP bars were tested under four-point bending, taking into account the effect of steel fiber content and clear span length. Based on the experimental results, the application of prestressing force and the addition of steel fibers reduced the deflection and crack width of the beams. The larger clear span length resulted in wider crack width and lower tendon stress increment in the prestressed specimens. A geometry-based model was proposed to calculate the tendon stress increment in terms of deflection. Accordingly, decomposing analytical procedure into a bonded beam analysis and an unbonded member analysis, an iterative algorithm for the deflection of beams prestressed with unbonded FRP tendons was developed. The proposed models yielded reasonable stress increment and deflection predictions at service load level.

Ductility and internal forces redistribution in lightweight aggregate concrete beams

Lightweight Aggregate Concrete (LWAC) is typically defined as concrete having a density smaller than or equal to 2200kg/m3 and can be obtained by mixing natural or artificial lightweight aggregates. There is a general scepticism regarding the use of lightweight aggregate concrete (LWAC) for structural applications. This concern is attached to the more brittle material behaviour which leads to lower ductility.&#x0D; This article presents a numerical parametric analysis of the behaviour of the reinforced LWAC cross-sections under the immediate load taking into account the density of the LWAC concrete, concrete strength and tensile reinforcement ratio.&#x0D; Numerical analysis of the beams was conducted in OpenSees, an open–source nonlinear finite element method framework. One-dimensional elements, with three degrees of freedom at each end, were used. Bending stiffness in the integration points was calculated based on the sectional moment – curvature relationship.&#x0D; The analysis showed that there is a relationship between the ductility of the cross-sections made of lightweight concrete and its density class. It is associated with limited compressive strains and the brittle behavior of LWAC. The limited rotation capacity of the reinforced concrete sections made of LWAC also affects the ability of redistribution of internal forces in statically indeterminate beams

경량골재를 사용한 철근콘크리트 보의 최대 주철근 비 평가

경량골재를 사용한 철근콘크리트 보의 최대 주철근 비 평가

Flexural cracks in steel fiber-reinforced lightweight aggregate concrete beams reinforced with FRP bars

Fourteen plain and steel fiber-reinforced lightweight aggregate concrete (LWC) beams with two types of fiber-reinforced polymer (FRP) reinforcing bars were tested under a four-point bending load with different reinforcement ratios, bar diameters and clear span lengths to evaluate their cracking behavior. The test results showed that using steel fiber-reinforced lightweight aggregate concrete (SFLWC) and increasing the clear span length mitigated the maximum crack width at low load levels, while increasing the reinforcement ratio tended to decrease the maximum crack width during the entire loading period. At service load, all CFRP-reinforced beams satisfied the crack width criteria of 0.7 mm, while more than half of the GFRP-reinforced specimens exhibited unconservative crack widths. Crack width prediction equations in the current design codes in the US, China, and Canada were compared based on the experimental results. The original average crack spacing equation recommended by GB 50608 was modified considering the effect of bar position. Furthermore, using the method of probability and statistics, the relationships between the maximum crack width and the average crack width for the tested beams were investigated. Accordingly, a rational alternative crack width model was proposed for CFRP- and GFRP-reinforced beams incorporating the effects of lightweight aggregates and steel fibers.

Size effect in shear failure of lightweight concrete beams wrapped with CFRP without stirrups: Influence of fiber ratio

Lightweight aggregate concrete (LWAC) is a superior material due to its light weight and high strength. There however remain significant lacunae in engineering knowledge with regards to shear failure of LWAC beams. Focusing on exploring the shear resistance and the corresponding size effect in shear failure of LWAC beams wrapped with CFRP sheets, we propose a 3D meso-scale simulation method to evaluate the structural behavior of both LAWC and NWC (normal weight concrete) beams wrapped with CFRP sheets. The concrete material is viewed as a complex heterogeneous material consisting of mortar matrix in which are dispersed various aggregates with interface transition zone between them. It is hypothesized here the CFRP and the concrete beams are perfectly bonded and we investigate the effects of structural size, of CFRP ratio and of aggregate type on the shear failure of a CFRP-strengthened concrete beam. Besides, we analyze also the shear contribution by CFRP on the LWAC beams having different structural sizes (i.e. beam-depth) and the size effect on the nominal shear strength of CFRP-strengthened LWAC beams. Based on the numerical results via 3D mesoscale simulation, we propose a novel size effect law that can quantitatively describe the influence of CFRP fiber ratio on shear strength of the CFRP-strengthened concrete beam, and the newly proposed law is verified by experimental data and simulation results.

Shear behaviour and diagonal crack checking of shale ceramsite lightweight aggregate concrete beams with high-strength steel bars

Fifteen specimens with different shear span ratio, concrete strength and transverse stirrup ratio were tested to investigate the feasibility of 500 MPa steel bars used in shale ceramsite lightweight aggregate concrete structure. Shear failure modes, shear force-stirrup strain curves and load-deflection curves were all analysed. The results show that suitably detailed 500 MPa steel bars can be reinforced as transverse reinforcement and longitudinal reinforcement. Reduced stirrup spacing can obtain better ductility and cracking behaviour. Based on our own study results and reference data, the equations for calculating the diagonal cracking load and diagonal crack width of shale ceramsite lightweight aggregate concrete beams with 500 MPa steel bars were all regressed, and the equations offer good agreement with the test data. When the design value of the tensile strength of 500 MPa stirrups is 360 MPa, the maximum diagonal crack width corresponding to the serviceability limit state is calculated by the regressed equations, and the calculated crack width of the test beams is no more than 0.2 mm, which meets the requirements of the current codes in China for the maximum crack width limit.

Numerical Analysis on Flexural Behavior of Steel Fiber-Reinforced LWAC Beams Reinforced with GFRP Bars

Three-dimensional nonlinear finite-element (FE) models using an explicit algorithm were established to simulate the behavior of beams reinforced with glass fiber-reinforced polymer (GFRP) bars cast using lightweight aggregate concrete (LWAC) with and without steel fibers, and the progressive damage model was employed to simulate the rupture of GFRP. The developed FE model was evaluated by test results, and it exhibited good agreement with the test results in terms of moment–deflection response, serviceability performance, ultimate capacity, and failure mode. Influencing factors, including the section height, reinforcement ratio, and span length were discussed according to the established FE model. It was revealed that the reinforcement ratio corresponding to balanced failure was higher than that given by code ACI 440.1R, which confirmed the necessity of the amplification factor of a balanced reinforcement ratio to ensure concrete crushing of the beam. For specimens that failed due to concrete crushing, the increase in fiber-reinforced polymer (FRP) reinforcement ratio did not significantly improve the ultimate capacity, but it did have an obvious effect on the reduction of deflection at service load. Moreover, a greater reinforcement ratio was needed for beams when the span length increased.