Elastic Modulus Of Concrete Research Articles

Comparison of the Values of Compressive Strength and Elasticity Modulus of Concrete of Frozen and Unfrozen Specimens

In term of practical applications, it is important to know how to change the modulus of elasticity of concrete, which is in wintertime exposed to low temperatures. The partial results of research are presented and oriented on monitoring the changes of the values of modulus of elasticity in time of frozen and unfrozen concrete specimens.

Fuzzy Neural Network-Based Damage Assessment of Bridge under Temperature Effect

Vibration-based method has been widely applied for damage identification of bridge. Natural frequency, mode shape, and their derivatives are sensitive parameters to damage. However, these parameters can be affected not only by the health of structure, but also by the changing temperature. It is essential to eliminate the influence of temperature in practice. Therefore, a fuzzy neural network-based damage assessment method is proposed in this paper. Uniform load surface curvature is used as damage indicator. Elasticity modulus of concrete is assumed to be temperature dependent in the numerical simulation of bridge model. Through selecting temperature and uniform load surface curvature as input variables of fuzzy neural network, the algorithm can distinguish the damage from temperature effect. Comparative analysis between fuzzy neural network and BP network illustrates the superiority of the proposed method.

Analysis of Factors Influence on Void Underneath at Concrete Pavement Joints

Three-dimensional finite element analysis was made on the transverse joint stress state of the concrete pavement slab with void underneath using ANSYS. The transfer effect of dowel bar was discussed with aircraft loaded in the joints. The influence rule of load transfer effect under different dowel bar spacing and dowel bar cross section dimension was compared. Based on the results of finite element analysis, this paper had carried on the experimental study on stress-transferring effect on concrete pavement joints with different location of the dowel bar. The influencing factors of pavement slab transverse joint with void underneath and the resistance of pavement damage on the joint was analyzed. Theoretical analysis showed that in order to reinforce the resistance capacity of local cavity on concrete pavement joint, the largest spacing of transverse dowel bar set shall not be more than 45cm, and the main factors influencing the resistance void ability on the joint are top reaction modulus, coefficient of cavity, the concrete elastic modulus and coefficient of transverse reinforcement.

Comparing Tests on the Durability of Concrete after Long-Term Immersion in Different Salt Solution

The western region of Jilin province is one of the areas with the most serious saline soil, which is the type of inland soda salt. In order to study the damage law of concrete under the condition of long-term erosion by the soluble salts in saline soil or groundwater or saturated salt water, three groups of salt solution, Na2SO4, NaCl, NaHCO3 solution, were made according to the content of soluble salts in saline soil of Daan city in spring, and water was as a comparison. The comparing tests of long-term immersion were conducted on the normal concrete specimens with the size of 40mm×40mm×160mm. The results show that there is little change on the appearance, mass and dynamic elastic modulus of concrete soaked in water. But for the concrete soaked in salt solution, the loss rate of mass changes from reduction to growth, the relative dynamic elastic modulus of concrete grows at first and declines later. Through analysis of electron microscope scanning, energy spectrum and chemical composition of concrete samples, concrete damage caused by salts includes chemical erosion and salt crystallization damage. Na2SO4 mainly influences the dynamic elastic modulus of concrete, NaCl mainly influences the mass of concrete due to its strong penetration, while NaHCO3, ranking between the two salts above, largely influences not only the mass of concrete, but also the dynamic elastic modulus of concrete.

Measuring specific parameters in pretensioned concrete members using a single testing technique

Pretensioned concrete members are designed and manufactured by using at least two materials: concrete and prestressing reinforcement. Also, two main stages must be considered: prestress transfer and member loading. Hence, the behavior of these members depends strongly on the reinforcement-to-concrete bond performance and prestress losses. In this paper, a testing technique to measure the specific parameters related with the involved phenomena is presented. The testing technique is based on the analysis of series of specimens varying in embedment length to simulate several cross sections at only one end of a pretensioned concrete member. Each specimen is characterized by means of the sequential release of the prestress transfer (detensioning) and the pull-out (loading) operation. The test provides data on prestressing force, transmission length (initial and long-term), anchorage length (without and with slip), reinforcement slips, bond stresses, longitudinal concrete strains, concrete modulus of elasticity, and prestress losses (instantaneous and time-dependent).

Two-Dimensional Shear Stress on Bonding Interface of FRP Plate Reinforced Hydraulic Concrete

The bonded interface between FRP plate and the hydraulic concrete is a key part while reinforcing the hydraulic concrete structure with FRP plate. The bond property of the interface directly decides the results of structural reinforcement. In most of the external loading conditions, this interface is under the shear stress state. Therefore, accurate measurement and analysis of interfacial shear stress distribution is the guarantee of FRP reinforced hydraulic concrete structure the premise of success. Focusing on the shear-resisting bonding strength of FRP-concrete interface, this paper improved the ASTM D905 standard shear sample and carried out numerical simulation of shear test to the bonded interface of FRP-reinforced hydraulic concrete structure by adopting the bi-dimensional finite element method, and conducted parameter analysis of the influence factors (elasticity modulus of FRP and concrete, shear modulus and thickness, etc) of shear stress on the FRP-concrete bonded interface and finally the distribution characteristics of shear stress on the bonded interface were obtained. This paper mainly discussed the influence rules of stress concentration to the distribution of shear stress on the bonded interface, which provides theoretical guidance and direction to the shear-resisting bonding strength test in the next step as well as technical support to the processing of FRP-strengthened hydraulic concrete bonded interface.

The Test of Dynamic Characteristics of Concrete under Biaxial Compression State

Concrete structure in reality mostly in complicated stress state, dynamic characteristics and static characteristics under earthquakes and other dynamic loads are very different. For a further understanding of the dynamic characteristics of the concrete, true triaxial testing machine system was used to the C30 concrete at different strain rates and different side of the cube concrete specimens stress biaxial dynamic compression tests. Biaxial stress state concrete elasticity modulus, peak stress, peak strain, was obtained by the experimental study, and carries on the comparative analysis. Results show that: the dynamic characteristics of concrete under biaxial compression state of concrete and uniaxial condition are very different.

Study on the Effect of Cellulose Fiber on the Crack Resistance of High Performance Concrete

Combining the South-to-North Water Diversion Middle Route Project, the effect of cellulose fiber on the mechanical property, ultimate tensile value, compressive elasticity modulus, durability and crack resistance property of high performance concrete was studied. The test results show that mixing with the cellulose fiber in concrete has less effect on the compressive strength, but can improve the splitting tensile strength, the axial tensile strength and ultimate tensile value of concrete, extend the cracking time of concrete, reduce the crack width and the cracking area of concrete and improve the crack resistance of concrete.

Elastic Modulus of Concrete Cast with Recycled Aggregates

In view of the importance of recycled aggregates concrete with primary aim to minimise environmental impacts from construction waste, this study was conducted in order to investigate the effects of recycled aggregates on concrete elastic modulus. The outcomes indicate that type of recycled aggregates influences the development of concrete elastic modulus. In general, the use of recycled aggregates posts significant reductions in concrete elastic modulus.

Effect of a Time Dependent Concrete Modulus of Elasticity on Prestress Losses in Bridge Girders

Prestress losses assumed for bridge girder design and deflection analyses are dependent on the concrete modulus of elasticity (MOE). Most design specifications, such as the American Association of State Highways and Transportation Officials (AASHTO) bridge specifications, contain a constant value for the MOE based on the unit weight of concrete and the concrete compressive strength at 28 days. It has been shown in the past that that the concrete MOE varies with the age of concrete. The purpose of this study was to evaluate the effect of a time-dependent and variable MOE on the prestress losses assumed for bridge girder design. For this purpose, three different variable MOE models from the literature were investigated: Dischinger (Der Bauingenieur 47/48(20):563–572, 1939a; Der Bauingenieur 5/6(20):53–63, 1939b; Der Bauingenieur, 21/22(20):286–437, 1939c), American Concrete Institute (ACI) 209 (Tech. Rep. ACI 209R-92, 1992) and CEB-FIP (CEB-FIP Model Code, 2010). A typical bridge layout for the Dallas, Texas, USA, area was assumed herein. A prestressed concrete beam design and analysis program from the Texas Department of Transportation (TxDOT) was utilized to determine the prestress losses. The values of the time dependent MOE and also specific prestress losses from each model were compared. The MOE predictions based on the ACI and the CEB-FIP models were close to each other; in long-term, they approach the constant AASHTO value. Dischinger’s model provides for higher MOE values. The elastic shortening and the long term losses from the variable MOE models are lower than that using a constant MOE up to deck casting time. In long term, the variable MOE-based losses approach that from the constant MOE predictions. The Dischinger model would result in more conservative girder design while the ACI and the CEB-FIP models would result in designs more consistent with the AASHTO approach.

Study on Compressive Stress-Strain Relationship of Polymer-Modified Concrete

The axial compressive stress-strain relationship of concrete reflects its basic mechanical performance, which is important in analyzing the performance of materials, especially in the analyzing of the elastic modulus, ductility and carrying capacity. In order to study the mechanical properties of polymer-modified concrete and steel fiber reinforced polymer concrete, a comparative study of the compressive stress-strain relationship of polymer-modified concrete and steel fiber reinforced polymer concrete was carried out, the complete compressive stress-strain curves were obtained, and the influence of polymer and steel fiber on concrete elastic modulus and compressive ductility was also studied. It is demonstrated that the compressive ductility index of steel fiber reinforced polymer concrete can reach 7.39 which is greater than that of polymer-modified concrete with the same ingredients. The results also show that steel fiber reinforced polymer concrete is better than both polymer-modified concrete and steel fiber reinforced concrete.

Prediction of the Elastic Modulus of Self-Compacting Concrete Based on SVM

With the powerful regression and fitting of support vector machines in uncertainty and the non-linear,based on the determination of the content of the coarse aggregate and characteristic parameters, this paper established a predictive model of self-compacting concrete elastic modulus based on support vector machine.Through analysis and comparison with experimental results, it proves the accuracy and effectiveness of the model.

Compressive Strength Properties of Fly Ash-Based Geopolymer Concrete

This study intends to investigate experimentally the mechanical characteristics of the compressive strength and elastic modulus of concrete using 3 types of binder that are ordinary Portland cement, fly ash and physically milled fly ash. The test results show that the compressive strength and elastic modulus of the cement-zero concrete reached respectively 30.0 MPa and 19.1 GPa, and indicated that more than 90% of the strength was developed at early age. In addition, a comparison of the geopolymer concrete with ordinary concrete enabled to derive and suggest formulaeexpressing the elastic modulus in function of the compressive strength.

Influence of Water Content on Dynamic Elastic Modulus of Concrete

Water content is one of key effect factors on the dynamic elastic modulus, which is an important damage assessment index of concrete structures induced by freeze-thaw cycles, fire and chemical attacks. Through the ultrasonic and bending vibration test, the regularity of dynamic elastic modulus changed with the water content of concrete specimens was analyzed in this paper. The results show that the ultrasonic velocity has a low sensitivity to water content when it is below 1.5%. The bending vibration method can better reflect the effect of water content change on dynamic elastic modulus. The regression equation of dynamic elastic modulus and water content was set up by introducing the index function. The research results offer technical reference for the predicting of actual concrete dynamic elastic modulus in different humidity environment.

Dynamic compressive behavior of ceramic fiber reinforced concrete under impact load

Dynamic properties of ceramic fiber reinforced concrete (CRFRC) are investigated using a 100-mm-diameter split Hopkinson pressure bar (SHPB) system. Different ways of choosing strain rate were adopted to express the strain rate effects on dynamic compressive stress, elastic modulus and impact toughness of CRFRC. The results show that the dynamic compressive strength and impact toughness increase with strain rate, while the elastic modulus decrease with strain rate. The addition of ceramic fiber can significantly improve the dynamic strength and elastic modulus of concrete. 0.1% and 0.2% volume fraction of ceramic fiber improve the impact toughness at higher strain rate. And the optimum volume fraction of ceramic fiber is 0.2%. The dynamic damage model was established based on the improved parallel bar system (IPBS) model. The result reveals that the model can well describe the relation between stress and strain of CRFRC.

Experimental Research on the Mechanical Properties of PVA Fiber Reinforced Concrete

This study reports an experimental study on mechanical properties of concrete prepared by polyvinyl alcohol (PVA) fibers. Concrete mixtures are prepared under the same proportions, but by addition of different fibers content. Compressive, splitting tensile and directly tensile tests are carried out for concrete. Primary test results show that, the unit water consumption of mixture was increased with the dosage of PVA fibers, but the slump of concrete mixture was decreased. Experimental results show that, the compressive strength and splitting tensile strength are increased very quickly at the early ages (before the age of 28 days). The compressive strength of concrete is decreased with the increasing of fibers content, but the splitting tensile strength of concrete is increased with the increasing of fibers content. The elastic modulus of concrete was decreased with the dosage of PVA fiber, but the limit tensile strain was increased with the dosage of PVA fiber.

Integral Abutment Bridge behavior under uncertain thermal and time-dependent load

Prediction of prestressed concrete girder integral abutment bridge (IAB) load effect requires understanding of the inherent uncertainties as it relates to thermal loading, time-dependent effects, bridge material properties and soil properties. In addition, complex inelastic and hysteretic behavior must be considered over an extended, 75-year bridge life. The present study establishes IAB displacement and internal force statistics based on available material property and soil property statistical models and Monte Carlo simulations. Numerical models within the simulation were developed to evaluate the 75-year bridge displacements and internal forces based on 2D numerical models that were calibrated against four field monitored IABs. The considered input uncertainties include both resistance and load variables. Material variables are: (1) concrete elastic modulus; (2) backfill stiffness; and (3) lateral pile soil stiffness. Thermal, time dependent, and soil loading variables are: (1) superstructure temperature fluctuation; (2) superstructure concrete thermal expansion coefficient; (3) superstructure temperature gradient; (4) concrete creep and shrinkage; (5) bridge construction timeline; and (6) backfill pressure on backwall and abutment. IAB displacement and internal force statistics were established for: (1) bridge axial force; (2) bridge bending moment; (3) pile lateral force; (4) pile moment; (5) pile head/abutment displacement; (6) compressive stress at the top fiber at the mid-span of the exterior span; and (7) tensile stress at the bottom fiber at the mid-span of the exterior span. These established IAB displacement and internal force statistics provide a basis for future reliability-based design criteria development.

Experimental Research on Mechanical Properties of Recycled Aggregate Concrete under Uniaxial Loading

The complete stress-strain curves of recycled aggregate concrete with different recycled coarse aggregate replacement percentages were tested and investigated. An analysis was made of the influence of varying recycled coarse aggregate contents on the complete stress-strain curve, peak stress, peak strain and elastic modulus etc. The elastic modulus of RC is lower than natural concrete (NC), and with the recycled coarse aggregate contents increase, it reduces. While with the increase of water-cement ratio (W/C), recycled concrete compressive strength and elastic modulus improve significantly. In addition, put forward a new equation on the relationship between Ec and fcu of the RC.

Longitudinal cracking at transverse joints caused by dowel bars in Jointed Concrete Pavements

Longitudinal cracking at transverse joints in the Jointed Concrete Pavement (JCP) was investigated and causes were discovered by performing field observation and numerical analyses. Finite element models of JCP were developed considering very detailed modeling of dowel bars and their contact characteristic to concrete. Using the models, transverse stresses at joints that could induce longitudinal cracking were comprehensively analyzed. The results showed that primary causes of longitudinal cracks at joints were found to be related to the vertical translation of dowel bar and the curling of the JCP slab due to environmental loading. Other factors affecting those cracks included concrete elastic modulus, concrete thermal expansion coefficient, foundation stiffness, vertical temperature gradient, and bond characteristic between concrete and dowel bar. To mitigate longitudinal cracking at joints, dowel bars should be installed at the mid-depth of the slab and cares must be taken when installing dowel bars to prevent their vertical translation.

Experimental Research on Elastic Modulus and Compressive Strength of High-Strength Concrete after Fire

The bottom surface of the bridge beam, which is made of C50 high-strength concrete, is heated to 800°C in fire-resistant experiment. Then the elastic modulus and strength of the concrete are measured by the rebound method and core sampling method, and the test results are used to validate the theoretical methods. The study shows that the strength and elastic modulus of concrete decrease with the increasing of temperature. The strength from the current theoretical analysis agrees well with that from the experiment. But for the elastic modulus, there is a great difference between the theoretical and experimental analysis. The strength of the concrete after fire gotten from the rebound method has a bigger error than that from the core sampling method, so that the core sampling method should be used in preference.