Concrete Beam Specimens Research Articles

Smart construction material: Utilization of M−sand to mitigate environmental pollution and generalized mix design thereof

The insufficiency of conservative materials like cement, sand and aggregates becomes the main critical problem in civil engineering domain among the higher demand of best quality control infrastructure. This research paper is emphasized on fine aggregates (sand). Sand which is dredged from the river bank is unfavorable in favor of the environment due to the depletion of underground surface water table near the surface zone which included soil and rocks permanent saturation under the water. In this regard an experimental research has been conducted on M−Sand. The mix design procedure only with M−Sand has not been described in any design codes even for distinct value percentage of M−sand and grade of concrete. A generalized mix design procedure is developed here for 50% river sand and 50% M−sand to increase or decrease the quantity of M−sand in nearby future. A parametric study has been carried out for distinct value percentages of M−Sand. In this paper to show the impact of M−sand on river sand a mix design tests of M−25 grade concrete including river sand and replacement M−Sand as a fine aggregate in distinct values of i.e. 0.0%, 10%, 20%, 40%, 45%, 50%, 55%, 60%, 80% & 100% ratios have been conducted. It is observed that almost mechanical-chemical characteristics of river bank sand and crushed stone (manufactured) M−Sand are similar. Results are described here in graphical form to show the influence of M−sand and it is concluded that M−Sand can be utilized as a partial or completely replacement material in place of river sand with high compressive, tensile and flexural strengths of concrete cubes, cylindrical and beam specimens respectively. Results revels positive response to use M−sand to mitigate the environmental pollution.

Effect of concrete strength and tensile steel reinforcement on RC beams externally bonded with fiber reinforced polymer composites: A finite element study

Due to the continual deterioration of concrete infrastructures, the construction industry faces challenges in terms of their serviceability, structural strength, and durability. Therefore, efficient rehabilitation strategies are required to enhance their performance. Externally bonding fiber reinforced polymers (FRP) have evolved as a simple and convenient retrofit technique when compared to conventional techniques of strengthening. FRPs can be powerful toolsfor strengthening concrete structural members in shear and flexure because of their exceptional mechanical characteristics. Flexural strengthening is generally achieved by externally bonding FRP strips or laminates in the soffit side of beams, resulting in improved ultimate strength and bending capacity. This study aims to conduct a numerical parametric investigation on reinforced concrete (RC) beam specimens flexurally strengthened by externally bonding FRP. Three-dimensional finite element models of four RC beams strengthened with FRP and with different concrete compressive strength and flexural steel reinforcement were developed to predict their load capacity. Models were developed and simulated using finite element software called ABAQUS. The beam behavior was evaluated with the help of different material models available in the ABAQUS library. Study considerations included concrete damage plasticity, Hashin's damage in CFRP, and perfect bonding between CFRP and concrete interfaces. The parametric study included two groups of beams: one with varying concrete compressive strength (i.e., 25 MPa and 50 MPa) and the other with varying tensile steel reinforcement (5#14 mm diameter bars and 2# 22 mm diameter bars). The ABAQUS results were verified using experimental data from the previousliteratures.The computed numerical resultsand experimental results demonstrated reasonable accuracy for load–displacement curves and ultimate load capacity. It was found that the ultimate load increased significantly in high-strength (M50) beams with a higher number and smaller diameter (5#14 mm) tensile bars. In conclusion, RC beams with more compressive strength and tensile steel reinforcement boost the effectiveness of the external bonding technique.

Acoustic and Fracture Energy Correlation in Mode I Fracture with Concrete Damage Plasticity Model and Three-Point Bend Experiment

The progressive damage monitoring and fracture evaluation of plain concrete beam specimens subjected to three-point bending (TPB) are reported in this paper. The objective of the present research is to systematically correlate the fracture behavior of a concrete beam with acoustic emission (AE) data recorded during the present set of experiments. The damage growth and failure mechanisms of the beam specimens are investigated with AE parametric analysis, b-value analysis, and digital image correlation method. Eventually, a reasonable correlation between AE energy and the released fracture energy is established at various stages of loading, which is confirmed with the set of TPB beam experiments and further validated with nonlinear numerical finite-element analysis. The energy released during the cracking processes at different loading stages in the experiment is quantified and systematically analyzed. Acoustic and fracture energies are dependent on active concrete cracking, and their correlation is helpful in determining the extent of damage in the concrete structures. Such a relationship can be used as an operational tool for structural health monitoring of structures as an early warning system supplemented with numerical analysis, a well-calibrated laboratory, and in situ AE experiments.

Experimental and Analytical Investigation on Flexural Behavior of High-Strength Steel-Concrete Composite Beams

This research investigated the flexural behavior of high-strength steel (HSS)—concrete composite beams. The effect of concrete strength on the load-deflection behavior, flexural capacity, and ductility of HSS—concrete composite beams was investigated. Four full-scale HSS—concrete composite beam specimens were tested under static load. The test results demonstrate that the failure mode of HSS—concrete composite beams is flexural failure of the steel member and compression fracture of concrete at mid-span. The HSS—concrete composite beam exhibits good mechanical performance and deformation behavior. The ultimate bending strength and ductility of HSS—concrete composite beams were improved with the increased concrete strength. The theoretical results demonstrate that the simplified plastic method overestimates the ultimate bending strength of HSS—concrete composite beams. The main reason is that only a small part of the steel beam bottom shows plastic strengthening, which is not enough to make up for the strength loss caused by the steel near the neutral axis failure to yield and the relative interface slip. The nonlinear method based on material constitutive model could predict the load-bearing capacity accurately. After analyzing the ultimate bending capacity of 192 sample beams, the simplified plastic method was modified, and the theoretical method for ultimate bearing capacity of HSS—concrete composite beams was proposed.

Concrete implantable bar enabled smart sensing technology for structural health monitoring

This work proposes a concrete implantable bar (CIB) enabled smart sensing technology for the detection of concrete beam damage. Instead of the conventional technique that posts the sensors on the host structure externally or embeds them inside the concrete before casting, this developed technology enables an implantable manner to install specially designed sensors with unique stable and replaceable functions. The CIB integrates a line array of tubular piezoceramic shells (TPSs) that can excite and receive probe signal in concrete. The working principle of this CIB was explained theoretically, and its basic performance regarding the conversion efficiency between the input and output signals was investigated numerically. To assess the structural state comprehensively, a singular value decomposition (SVD)-based wavelet packet algorithm was adopted. This algorithm relied on the classical wavelet packet analysis to construct an energy matrix at a certain frequency band, and then revealed the structural damage degree using the singular values of this matrix. The feasibility of the proposed methods was verified using a reinforced concrete (RC) beam specimen subjected to a four-point bending test, wherein a pair of CIBs, one as an actuator and another as a sensor, were implanted in the beam to sample data from different loading processes. The assessment results using the SVD-based algorithm well characterize the beam state throughout the loading process; and show higher accuracy than those using a convention method in this continuous monitoring case.

Shear capacity of reinforced concrete beams strengthened with web bonded steel bars or steel plates

This paper presents the report of two groups of experimental works to study the shear capacity and strain distribution of reinforced concrete beams strengthened on beam sides with the near-surface mounted (NSM) method. One group was strengthened with steel bars, and the other was strengthened with steel plates. Each group consisted of three control beams and six strengthened beams. Steel bars or plates were installed vertically or diagonally at an angle of 45°. The total number of reinforced concrete beam specimens tested in this study was 18. All beams tested were simply supported and monotonically loaded with two concentrated loads. The longitudinal reinforcement ratio was used as a test variable to attain differences in the required shear demand. An analytical study using the two-dimensional finite element method was carried out to observe the strain distribution along the length of the beams. In the finite element model strengthening on the beam side for either steel bars or plates was modeled with line segments as transversal reinforcement, and the bond between concrete and strengthening materials is assumed to be perfect. The complete flexural response of the cross-section due to bending was also analyzed using the fiber element method. The test results show that some of the specimens strengthened with steel bars or plates achieved flexural capacity, and others experienced a sudden failure due to shear. The analysis results using the finite element method predict well the test results for beams that fail in the flexural mode and on beams with shear failure mode before the failure occurs. The analysis results also show significant differences in the strain distribution between beams without and with strengthening. The orientation of the angle of installation of steel bars or plates and the ratio of longitudinal reinforcement also affect the strain distribution along the beam length. In addition, the fiber element method can satisfactorily predict the tested beams' flexural behavior.

Effect of early‐strengthening of RC beams using UHPC layers on their performance against reinforcement corrosion

AbstractIn the present work, the effect of early‐strengthening of reinforced concrete (RC) beam specimens using layers of ultra‐high performance concrete (UHPC) on their performance against reinforcement corrosion was examined. A number of fifteen RC beam specimens were prepared, one beam specimen uncorroded and unstrengthened was considered as a control beam, two beams were corroded and unstrengthened, and twelve corroded and strengthened beam specimens that were divided into two groups. RC beam specimens of the first group were corroded continuously to cause total theoretically targeted mass losses of the steel rebars and then strengthened using UHPC layers. RC beams of the second group were also corroded to the same degrees but in two steps. In the first step, the beams were corroded to cause a portion of targeted theoretical mass losses. Then the beams were strengthened in the same way as the beams of the first group and then subjected to second‐step accelerated reinforcement corrosion to achieve finally the same degrees of total theoretical mass losses as that of the first group. The corroded and strengthened beam specimens were exposed to flexural testing, and then the corroded rebars extracted from the beams were used to conduct gravimetric tests to determine the actual values of the mass losses due to accelerated corrosion. The gravimetric and flexural tests' results were used mainly to observe the influence of early‐strengthening on the actual mass loss and the flexural behavior of the tested beam specimens. Results showed a significant reduction in the values of the actual mass loss and better flexural behavior due to the early‐strengthening of the corroded beams. An analytical model, developed and validated using the data collected from the experimental tests, can be utilized to predict the ultimate load‐carrying capacities of the corroded strengthened RC beam specimens.

Evaluation of flexural strengthening methods for beams with simulated deterioration using spike-anchored FRP externally bonded sheets and near-surface-mounted strips

• 20 beams were tested to evaluate FRP flexural strengthening techniques. • Specimens were detailed to mimic the common deterioration of bridge beams. • The effect of FRP spike anchor arrangements were evaluated. • Results show that more FRP spike anchors may not translate to superior performance. • Unsymmetrical steel and NSM reinforcement layouts were considered. In consideration of past research on both externally bonded and near-surface-mounted (NSM) fiber-reinforced polymer (FRP) reinforcement for the strengthening of deteriorated reinforced concrete elements, additional work is needed to investigate the application of FRP for flexural strengthening in specific scenarios and for specific member types. Furthermore, the need exists for guidance regarding reliable anchorage of externally bonded sheets for flexural strengthening. An experimental investigation was conducted on 20 reinforced concrete beam specimens with details and simulated deterioration patterns representative of the beams of in-service adjacent box beam bridges. Special focus was placed on the effective arrangement of FRP spike anchors for externally bonded FRP, unsymmetrical deterioration of steel reinforcement, and the eccentric placement of NSM strips. The results show that spike anchors located only at the ends of the externally bonded FRP sheets provided superior performance compared to anchors placed at multiple locations along the sheets. Moreover, the eccentricity of reinforcement did not play a significant role in the effectiveness of the strengthening systems. The test results also highlight the importance of bond on the performance of members strengthened with NSM reinforcement. Overall, the findings extend beyond adjacent box beam bridges and have a wide applicability to other flexural members.

Investigation of the effect of using geogrid, short glass, and steel fiber on the flexural failure of concrete beams

This research studies the flexural behavior of concrete beams reinforced with biaxial geogrids, distributed short glass and steel fibers. No longitudinal steel reinforcement bars were used. Therefore, an amount of short glass and steel fibers was used to improve the concrete beam behavior against flexural failure. Eleven specimens of single reinforced (flexural reinforcement) concrete beams and double reinforced (compression and flexural reinforced) concrete beams using two biaxial geogrids sheet layers, with randomly distributed short glass and steel fibers were cast. The samples were tested using two points of load along the beam specimen span with an increment of loading by 5 KN to evaluate several parameters. The studied parameters are using geogrids as a main flexural reinforcement, using geogrid sheet layers as a flexural and compression reinforcement, using short glass and steel fibers as an additional reinforcement of concrete with various ratios 0.25 %, and 0.75 %. The test results indicated that the use of geogrid layers as the main flexural reinforcement improved the behavior of the concrete beam specimens at failure. As well as; more enhancement of beam specimens at failure was observed when using short glass and steel fibers with geogrid reinforcement in concrete beams. The tested beam specimens which were reinforced by geogrids in the flexural and compression zone using 0.75 % of steel fibers gave better results due to modes of failure, toughness, failure load capacity, crack width, and post cracking stiffness.

Shear strengthening of RC beams using FRCM system made with industrial wastes

In the present study, industrial wastes were used as a partial replacement for cement to form cement-based repair mortars, and the feasibility of using these mortars as the matrix in fiber reinforced cementitious matrix (FRCM) system for shear strengthening of reinforced concrete (RC) beam specimens was investigated. Accordingly, an experimental program comprising two parts was carried out. Firstly, the properties of the mortars were examined through compressive strength, tensile strength, sulfuric acid resistivity, and electrical resistivity tests. Finally, 6 shear-critical RC beam specimens were manufactured, two of which remained un-strengthened acting as control specimens. Two specimens were strengthened in shear by carbon fiber reinforced polymer (CFRP) strips and two specimens were strengthened by fiber reinforced cementitious matrix (FRCM) layers made with prepared mortars. The shear capacity of the specimens was measured through 3-point bending test. The parameters investigated in the beam specimens included the effect of shear strengthening system (FRP/FRCM) and shear span/depth ratio. It was shown that the specimens strengthened by the FRCM system made with waste materials had similar or slightly better performance compared to the FRP strengthened specimens.

Recycled concrete beams subjected to combined reinforcement corrosion and static pre-loading

To investigate the flexural behavioural characteristics of recycled concrete beams under the combined action of steel corrosion and static pre-loading, 12 recycled concrete beam specimens, encompassing a combination of three recycled coarse aggregate (RCA) replacement ratios (0, 50 and 100%) and four static pre-load levels expressed as ratio of the ultimate moment capacity (0, 0.2, 0.4 and 0.6), were prepared for accelerated corrosion test and four-point bending test. The test results indicated that under a given RCA replacement ratio of the beams, the maximum width of corrosion-induced longitudinal cracks exhibited a linear relationship with the corresponding corrosion depth of longitudinal tension reinforcement. For the beams with 50% RCA replacement ratio, when the applied static pre-load level increased from 0 to 0.6, the ultimate load and ultimate deflection reduced by 10.4% and 21.2%, respectively, whereas for the beams with 100% RCA replacement ratio, the corresponding reduction in ultimate load and ultimate deflection were respectively 8.9% and 35.5%. Theoretical degradation models for the ultimate moment capacity and yield moment capacity of corroded beams were proposed, whereby the analytical values were in good agreement with the experimental values. This study provides useful reference for practical analysis of recycled concrete beams, which promote sustainable concrete construction.

Mechanical properties and flexural behaviour of reinforced concrete beams containing recycled concrete aggregate

Increasing waste recycling has become an essential process in the construction industry due to the environmental and economic advantages, such as minimizing waste in landfills, saving natural resources, and decreasing pollution. Crushing and sieving waste from standard compression test cubes is used to produce the recycled concrete aggregate (RCA). A set of standard concrete cylinders, cubes, and beam specimens were made by utilizing coarse aggregate replacement ratios of 0%, 30%, 50% and 70%. At the day 28 stage, the specimens were tested to determine compressive strength, stress–strain relationship, splitting tensile strength, and flexural strength. In addition, four reinforced concrete (RC) beams were cast and tested under a four-point load to evaluate the flexural behaviour of RC beams with partial replacement of the natural aggregate with RCA. One was a natural aggregate (NA) control beam, while the others had varying RCA ratios (30%, 50% and 70%). The results show that the compressive strength of RCA concrete with the replacement by 30%, 50% and 70% decreased by 9.10%, 18.88% and 22.57% respectively, in comparison to the compressive strength of normal concrete (NC). The RCA concrete showed a high strain capacity, which indicated high ductility. The maximum RCA type strains ranged from 0.0056 to 0.0072. Concrete flexural strength showed a slight decrease in comparison to NC (18.83% decrease), where the tensile strength showed a 10.61% decrease in comparison to NC. As for RC beams, the load-carrying capacity decreased by 10.5% with increases in the replacement ratio.

Structural Behavior of Prestressed RC Dapped Beam with Openings Strengthened Using CFRP Sheets

This research examines the strengthening efficiency of prestressed concrete dapped end beam with opening under monotonic point load. The study concerns with the position of the opening relative to the dapped end, the shape of opening, as circle or square, in addition, the effect of CFRP strengthening around the opening. The experimental program consisted of testing nine scaled down prestressed concrete dapped end beam specimens with single opening near the dapped end. Beam specimens consisted of one control beam and the remaining eight beams classified into two groups. The first group contained four unstrengthened specimens, whereas the second group included beams with opening strengthened using CFRP sheets. A full wrapping configuration for the opening region was adopted in this research. The results presented the detrimental influence of the openings on the shear strength of the dapped beam and the additional strength achieved from strengthening. This study concludes that the shear strength of the prestressed dapped beam decreased by the presence of openings in the web with maximum reduction about 20% when the opening was located close the dapped end. Based on the test results, the strengthened beams recovered significant part of their original load carrying capacity. Generally, prestressed dapped beams regain a maximum of 92% of their strength when openings with different configurations and locations were strengthened with full CFRP wrap.

Experimental study on the influence of polypropylene and steel fiber on flexural behaviours of high strength concrete beams

Many properties of plain concrete are readily enhanced by adding various fibers. Different types of fibers were added to improve its tensile and bending behaviours. In the present experimental study, four different fiber dosages of polypropylene (0.025, 0.050, 0.075, and 0.10%) and steel fiber (0.25, 0.50, 0.75, and 1.00%) considered to determine the optimized content of 0.05% of polypropylene and 0.75% (both by volume of concrete) of steel fiber based on the workability and strength test results. These fiber content were added in controlled concrete of 60 MPa compressive strength to observe the improvements in flexural behaviour. Set of three reinforced concrete beam specimens of dimension 200 × 300 × 2100 mm were casted for considered series: controlled concrete (CC), polypropylene fiber reinforced concrete (PFRC) and steel fiber reinforced concrete (SFRC). Four-point bending test was conducted on all specimens by continuously recording the mid span deflection using liner variable differential transformer (LVDT). Primarily, load vs deflection response was plotted to analyze the improvements in, energy absorption capacity, flexural toughness, ductility and post-peak energy dissipation. The cracking pattern was studied in terms of crack width, spacing and number. Results indicated, increased average load sustaining capacity of CC specimen from 58.4 kN to 70.5 kN and 110.6 kN in PFRC and SFRC respectively at yield point. The magnitude of ultimate load enhanced by 12.1 kN in PFRC and 50.1 kN in SFRC specimens. Normalized flexural toughness values increased by 14.86% and 23.51% in PFRC and SFRC. The total energy absorption capacity of CC samples improved by 689.57 kN-mm due to polypropylene fiber and 2271.89 kN-mm because of steel fiber addition. The CC, PFRC and SFRC series displayed 1892.96 kN-mm, 2184.19 kN-mm and 2956.15 kN-mm of energy dissipation in the post-peak region. Steel fiber inclusion indicated the branching of cracks from the primary cracks.

A Parametric Study on Behavior of Elliptical Cantilever Deep Beams

This parametric study used finite element method (ETABS 2019), on 20 elliptical reinforced concrete cantilever deep beam specimens that have rectangular sections. Five parameters were taken into consideration: beam height, beam width, concrete compressive strength, load position and load type. Results showed that when the beam height was increased by 12%–66.5%, the negative and torsional moments and load capacity increased by about 11.23%–76.33%, 11.2%–77% and 11.1%–78%, respectively, whereas deflection decreased by about 15%–39%. The negative and torsional moments and load capacity increased by 26.13%–166.53%, 27%–172.5% and 28%–180%, respectively, and a decrease in deflection of about 1.73%–2.3% took place when beam width increased by about 14.3%–81%. In addition, increasing the compressive strength of concrete by 7.5%–36% led to an increase in the negative moments, torsional moments, load capacity, and deflection by about 8.22%–19.2%, 8.7%–20.4%, 9.4%–22% and 4.7%–7.1%, respectively. When changing the load type from concentrated to uniformly distributed over a third of the span’s length, two-thirds of the span’s length and then over the full span’s length, the negative moments increased by 5.23%, 8.47% and 52.67%, whereas torsional moments decreased by 1.1%, 1.12% and 16%, respectively. Finally, placing the concentrated load at a distance of 0.75, 0.5 and 0.25 of the span lengths led the negative moments to increase by 56.9%, 102.3% and 110%, respectively, whereas torsional moments decreased by 8.64%, 25%, and 58.3%, respectively. The load capacity increased by 87.5%, 243.75% and 556.25%, respectively, accompanied by a decrease in the deflection of the free end by 3.24%, 17.65% and 49.8%, respectively.

Influence of Micro-Crack Healing on Viscoelastic Properties of Moisture Damaged Asphalt Concrete

One of major asphalt pavement distresses is the moisture damage which influences the degradation of the viscoelastic properties of the mixture. The present work assesses the impact of practicing micro-crack healing on the viscoelastic properties of moisture damaged asphalt concrete. Roller compacted slab samples of asphalt concrete were prepared at optimum binder content. Beam specimens were obtained from the slab samples and subjected to moisture damage. Part of the asphalt concrete beam specimens were then tested under dynamic flexural stresses, while another part of the asphalt concrete beams was subjected to micro-cracks healing process using external heating at 60° C for 120 minutes, then tested under the dynamic flexural stresses. The viscoelastic properties of asphalt concrete in terms of permanent deformation, flexural stiffness, phase angle, and cumulative dissipated energy were monitored and compared among both testing conditions. It was observed that a significant increase in the flexural stiffness could be observed after healing. The increase in the phase angle after healing is significant at the early stages of loading. Higher cumulative dissipated energy could be observed for mixture which had practiced micro-crack healing. It was concluded that healing process does not exhibit positive influence on permanent deformation of moisture damaged asphalt concrete. A significant increase of 41.6 % in the flexural stiffness could be observed after healing after the first load repetition as compared with the mixture before healing. The permanent deformation after healing is higher by 22 % at failure as compared with that of mixture before healing.

Hole layout calculation method of reinforced concrete beam demolition with soundless chemical demolition agents: Experimental investigation

Nowadays, urban renewal is accompanied by the demolition of a large number of obsolete buildings. The pollutions caused by blasting demolition have a serious adverse impact on the environment. Soundless chemical demolition agents (SCDAs) are put forward as a green and environment–friendly demolition method and have the potential to solve the pollution problems in the blasting demolition of concrete buildings. To this end, this paper aims to investigate the key problems in reinforced concrete beam demolition with SCDAs. The tests on 18 reinforced concrete beam specimens were carried out. The fracture phenomenon and failure mechanism were analysed. The expansive rate of SCDAs was proposed as the crushing effect index to investigate the impacts of hole diameter, hole spacing, concrete strength, stirrup spacing, and stirrup diameter. Besides, the influence mechanism of the stirrups was explored in depth, in which SCDAs in the hole were considered to be constrained by the surrounding concrete, and the stirrups were considered as the enhancement to the constraint of concrete. Eventually, a new hole layout calculation method was proposed, which accorded well with the experimental results.

WATER-REPELLANT EFFECT OF REINFORCED CONCRETE (RC) BEAM COATED WITH A SURFACE-PENETRANT

Concrete coated with surface-penetrant is an efficient method to improve durability because it can decrease the ingress of deterioration factors such as water and chloride ions. Our previous study had focused on a silane-based penetrant having high water-repellant effect and examined the freeze-thaw (F-T) durability of the concrete coated with the penetrant. As well as F-T action, the water-repellant effect must decrease the possibility of deterioration related to water and chloride ions ingress. It is well known that water in pore of concrete is a compromising factor to decrease the fatigue durability of RC structures. The effect of surface-penetrant may be significantly varied by microscopic pore structures in concrete. Hence, the study prepared concrete cylinders and RC beam specimens made by wide range of water-cement ratios (w/c) from 0.55 to 1.0. Noting that the low-strength concrete made by the w/c = 1.0 is very unusual for structural concrete. However, such low strength properties are occasionally observed in short-span RC bridges constructed in 1960s or earlier. Hence, the study examined the effect of the surface-penetrant by using various w/c concretes. The paper reports the fundamental investigations of penetration depth and fatigue durability of the coated RC beams.

Influence of Additives on the Viscoelastic Behavior of Asphalt Concrete

Implication of mineral additives into the asphalt concrete mixture can influence the viscoelastic behavior; change the density, gradation, and strength properties. In the present investigation, fly ash and silica fumes were added to the asphalt concrete mixture. Slab samples were compacted with the aid of laboratory roller, and then beam specimens were sawed from the slab samples. The asphalt concrete beam specimens were subjected to repeated flexural stresses through the four-points bending test at 20℃ and under 400 micro-strain level until failure. The influence of the additives was monitored and compared. It was concluded that the phase angle, flexural stiffness, and the fatigue life declines while the cumulative dissipated energy increases after implication of the additives. However, the silica fumes additives exhibit a significant impact on the viscoelastic properties as compared with the control or the fly ash treated mixtures.

The Role of Fiber-Type Reinforcement in the Torsional Behavior of Solid and Hollow Reinforced Concrete Beams

In order to improve the strength of concrete structures, the fiber reinforcement of concrete has become an essential factor. This study was conducted as an experimental program to gain a better understanding of how the variance of fiber shape and type affect the structural performance of solid and hollow reinforced concrete beams using four types of fiber (hooked-end, straight, corrugated steel fiber, and polyolefin fiber) under torsion. For this purpose, ten fiber-reinforced concrete beam specimens, five solid and five hollow, with square cross sections were fabricated using the adopted types of fiber. The role of fiber type in the improvement of the mechanical properties of hardened concrete was also investigated. The results revealed that the mechanical properties of the hardened concrete mix was enhanced by using the existing fiber in concrete, and the higher improvement was shown in the splitting tensile strength test and modulus of rapture in specimens with corrugated steel fiber. The torsional behavior of solid and hollow beams was improved significantly, and the capacity of torsional strength was especially improved for the beams strengthened with corrugated steel fiber. Straight and polyolefin fiber showed a slight improvement in the concrete mechanical properties and less enhancement in the torsional capacity of the tested beams. However, the tested beams reinforced by polyolefin fiber provide better ductility under torsion compared with the use of other types of fiber.