4158432
Influence of Selected Factors on the Relationship between the Dynamic Elastic Modulus and Compressive Strength of Concrete
In this paper, the relationship between the static and dynamic elastic modulus of concrete and the relationship between the static elastic modulus and compressive strength of concrete have been formulated. These relationships are based on investigations of different types of concrete and take into account the type and amount of aggregate and binder used. The dynamic elastic modulus of concrete was tested using impulse excitation of vibration and the modal analysis method. This method could be used as a non-destructive way of estimating the compressive strength of concrete.
136645252
The dynamic behavior and vibration monitoring of reinforced concrete beams
The dynamic behavior of a reinforced concrete beam was studied theoretically and experimentally. A relationship between the resonance frequency of the beam and the applied bending moment was established. A frequency criterion corresponding to the crack control criterion in the ACI Building Code was developed. It was found that resonance frequencies and damping will change rapidly when cracks are initialized and growing. The resonance frequency shift could be as large as 20 to 25% of the original value, and the decay rate could change by a factor of 4. The applied bending moment not only determines the number and the size of cracks but also determines the crack opening or closing condition that affects both resonance frequency and damping. To accurately estimate the frequency and damping of a cracked-reinforced concrete beam, empirical formulas are proposed based on a small number of experiments. The technique has promise for global nondestructive evaluation of reinforced concrete structures such as highway bridges.
135473679
Continuous monitoring of concrete E-modulus since casting based on modal identification : a case study for in-situ application
Abstract An in situ application of a recently developed technique for continuous measurement of concrete E -modulus since casting is addressed in this paper. Such technique is based on the continuous modal identification of a composite beam that contains the material under test. As concrete hardens, the flexural resonant frequency of the beam increases and the computation of E -modulus can be made with recourse to the beam’s equation of motion. Even though recent publications have shown the feasibility of this technique in laboratory environment, no actual in situ application has been tested so far. That is one of the topics of this paper, which also proposes improvements to the originally devised method and compares results with ultra-sound wave velocity measurements. The scope of the work is extended with the modal analysis of a prefabricated beam made of the same concrete under test, allowing insights to be made regarding the E -modulus of concrete.
136740530
A comprehensive investigation into the effect of aging and coarse aggregate size and volume on mechanical properties of self-compacting concrete
Abstract The popularity of self-compacting concrete (SCC), as an innovative construction materials in concrete industry, has increased all over the world in recent decades. SCC offers a safer construction process and durable concrete structure due to its typical fresh concrete behavior which is achieved by SCC’s significantly different mixture composition. This modification of mix composition may have significant effect on the hardened mechanical properties of SCC as compared to normal vibrated concrete (NVC). Therefore, it is necessary to know whether the use of all rules and relations that have been formulated for NVC in current design codes based on years of experience are also valid for SCC. Furthermore, this study represents an extensive evaluation and comparison between mechanical properties of SCC using current international codes and prediction equations proposed by other researchers. Thus, in this experimental study, major mechanical properties of SCC are investigated for twelve SCC mixes with wide spectrum of different variables i.e. maximum coarse aggregate size, coarse aggregate volume and aging. In the present study, an extensive body of data reported by many researchers for SCC and NVC has been used to validate the obtained results.
55816669
Effect of Type and Volume Fraction of Aggregate on the Fracture Properties of Concrete
Fine and coarse aggregates play a vital role in the fracture of concrete. There is however little quantitative information available in the literature on the effect of the volume fraction of the aggregates on the fracture properties of concrete. The main objective of this work is to gain a better understanding of this effect using appropriate experiment and a mesa-mechanical approach. For this, several control mixes ranging from hardened cement paste (hep) to normal concrete were prepared in which the aggregate grading, water to cement ratio, and the maximum particle size of aggregate were kept constant, but the volume fraction of aggregate was varied from 0.0 (hep) to 0.60 in steps of0.15. The critical stress intensity factor of the hardened cement paste, for which LEFM is valid, was determined from centrally notched disc specimens. The effective stress intensity factors of fine mortar, coarse mortar and concrete were then calculated from that of hep using the appropriate toughening mechanism in meso­ mechanical relations. The specific fracture energies, the macro-tensile strengths and the moduli of elasticity of fine mortar, coarse mortar, and concrete were also calculated from mesa-mechanical relationships. It is shown that the mesa-mechanical modelling approach gives a clear qualitative and quantitative picture of how a brittle matrix (i.e. hep) progressively transforms into a tougher, stiffer and more ductile composite as the volume fraction of fine and coarse aggregates is increased without altering their grading.
138978596
Investigation of performances of some empirical and composite models for predicting the modulus of elasticity of high strength concretes incorporating ground pumice and silica fume
Abstract In recent times, the importance of constructing different models to predict the elastic properties of concrete have become common. The objective of this study is to investigate the performances of some empirical and composite material models to predict the modulus of elasticity of high strength concrete (HSC) with ground pumice (GP) and silica fume (SF). The experimental compressive strengths and unit weights of these high strength concretes, are used in the calculations of the modulus of elasticity of concretes by common empirical models. Then, modulus of elasticity of same HSCs are also predicted using some common composite material models. Finally, all model predictions are compared to the experimental modulus of elasticity of high strength concretes. The performances of all models are discussed. Consequently, both empirical and composite material models can be employed to predict the modulus of elasticity for GP and SF concretes, using the assumptions in this study.
14586374
A Practical Equation for Elastic Modulus of Concrete
The mechanical properties of concrete are highly dependent on the types and proportions of binders and aggregates. Because existing equations for predicting the modulus of elasticity as a function of compressive strength are obtained from experiments performed on a restricted number of concrete specimens subjected to uniaxial compression, the existing equations cannot cover the entire experimental data. In this study, more than 3000 data sets obtained by many investigators using various materials have been collected and analyzed statistically in order to develop a reliable new equation for elastic modulus of concrete. The compressive strengths of the considered concretes range from 40 to 160 MPa (5.8 to 23.2 ksi). The new equation also takes into consideration the types of coarse aggregates and mineral admixtures. The proposed formula should be effective in the design of both normal strength concrete and high strength concrete structures.
43546828
Short-Term Mechanical Properties of High-Strength Concrete
A comprehensive experimental program was undertaken to determine the short-term mechanical properties of high-strength concrete (HSC). Modulus of rupture beams and two different sizes of concrete cylinders with three different target compressive strengths ranging from 10 to 18 ksi (69 to 124 MPa) were subjected to three different curing methods and durations. Test results were combined with data from the literature to improve predictive equations for the elastic modulus and modulus of rupture of HSC. Of the three different curing methods, cylinders moist-cured for 7 days exhibited the highest compressive strengths at ages of 28 and 56 days. In contrast, 1-day heat curing generally resulted in the lowest compressive strength. The study shows that a Poisson's ratio of 0.2 can be adequately used for HSC.
135920955
Verification of relationships between mechanical properties of concrete-like materials
It was proposed previously that a proper consideration of the concrete porosity can provide an improved method for the derivation of sound, reliable relationships between mechanical properties, such as strength and modulus of elasticity. The method of derivation is based on the differing effects of porosity in concrete on its mechanical properties. Several new formulas, such as equations 18) through 25) were derived from appropriate members of two groups of underlying equations: from equations 8) through 14), and equations 15) through 17). It is shown in figures 4 through 12 of this paper that the new formulas and, consequently, the outlined method of derivation are supported by experimental results despite the several simplifying assumptions applied. The fundamental advantage of the outlined method of derivation is that it is mathematical as compared to the empirical nature of the presently used methods.RésuméOn avait précédemment établi qu'une étude congrue de la porosité du béton pouvait fournir une métnode améliorée d'obtention de relations sûres entre des propriétés mécaniques telles que la résistance et le module d'élasticité. Cette méthode d'obtention repose sur les effets dissemblables de la porosité du béton et sur ses propriétés mécaniques. A partir de deux groupes d'équations de base, de (8) à (14), et de (15) à (17), on a obtenu plusieurs relations nouvelles telles que les équatiens (18) à (25). On montre dans les figures 4 à 12 de cet article que ces nouvelles relations et par consèment la méthode d'essai exposée, sont corroborées par les résultats, malgré les diverses hypothèses simplificatrees dent on s'est servi. L'avantage fondamental de cette méthode est son caractère mathématique si on la compare aux méthodes empiriques utilisées.
54211409
Effect of Cylinder Size on the Modulus of Elasticity and Compressive Strength of Concrete from Static and Dynamic Tests
The primary objective of this study is to investigate the effects of cylinder size (150 by 300 mm and 100 by 200 mm) on empirical equations that relate static elastic moduli and compressive strength and static and dynamic elastic moduli of concrete. For the purposes, two sets of one hundred and twenty concrete cylinders, 150 by 300 mm and 100 by 200 mm, were prepared from three different mixtures with target compressive strengths of 30, 35, and 40 MPa. Static and dynamic tests were performed at 4, 7, 14, and 28 days to evaluate compressive strength and static and dynamic moduli of cylinders. The effects of the two different cylinder sizes were investigated through experiments in this study and database collected from the literature. For normal strength concrete (≤40 MPa), the two different cylinder sizes do not result in significant differences in test results including experimental variability, compressive strength, and static and dynamic elastic moduli. However, it was observed that the size effect became substantial in high strength concrete greater than 40 MPa. Therefore, special care is still needed to compare the static and dynamic properties of high strength concrete from the two different cylinder sizes.
31482384
The Ratio between Static and Dynamic Modulusof Elasticity in Normal and High Strength Concrete
There is a simple linear relationship between the static and dynamic elastic module, this lead to hope that using dynamic elastic modulus may remove the problems in measuring the static elastic modulus of concrete. Normal strength concrete (mix (1)) exhibited lower dynamic modulus of elasticity than that of high strength concrete (mix (2)). The reason for that was the difference in the quality of past, due to the difference in the water content of these mixes. Type (HB) the quartz is higher in static modulus of elasticity of concrete for cylinder specimens than types HA (dolomite), HD (dolomite content organic), HF (round gravel), HE (rough gravel) and HC (calcite) by (9%), (19%), (20%), (21%) and (25%) respectively in 91 days. Type (HB) the quartz is higher in dynamic modulus of elasticity of concrete for cylinder specimens than types HA (dolomite), HC (calcite), HD (dolomite content organic), HF (round gravel), and HE (rough gravel) by (4%), (22%), (23%), (23%) and (25%) respectively in 91 days. The ratio of static modulus of elasticity of concrete to the dynamic modulus of elasticity of concrete (Ec/Ed) for the normal strength concrete (mix (1)) is between (36 to 55%). While for high strength concrete (mix (2)) the ratio is between (15 to 27%). خلا ـ صلا ـــــــ ة ةذنورملا لذماعم اادختذسا سذلى دوذوي ااذهو ةطيسب ةيطخ ةقلاع يكيمانيدلا و يكيتاتسلا ةنورملا لماعم نيبام ةقلاعلا اذقر ةذطلخلا ليكيتاتذسلا ةذنورملا لذماعم ماذيق لكاذشم نم صلختلل يكيمانيدلا 1 رذ تر ةذيدايتعنا طاطذغننا ةذمواوم ) تنراوم لقا يكيمانيد ةنورم لماعم اذقر ةطلخلاب ه 2 ةذني ع ةذيعون لاتذخا سذلى دوذعي وبذسلاو ةذيلاعلا طاطذغننا ةذمواوم ) نمسلإا ل اطلخلا هاه يف ءاملا ىوتحم لاتخا وبسب د ) تياملودذذلا ر (اوذذن ا نذذم ةناوطذذسنا نااذذمنل ةناذذسرخلل يكيتاتذذس ةذذنورم لذذماعم يذذلعا لتراوذذكلا )و (وذذنلا ) ةيوذغع داوذم سذلع وذتحي تياماود ) ياذسلكلا ن )رذسكم داذيتعا ااذكر )رذسكم رذير داذيتعا ااذكر رادذذومب 9 )% 19 )% 22 )% 21 و )% 22 رذذمع دذذنع نباذذتتلاب )% 91 ةذذنورملا لذذماعم نيذذب اذذم ةبذذسنلا لاوذذي ) ةطلخ ةيدايتعنا طاطغننا ةمواوم اا ةيناسرخلا ةطلخلل يكيمانيدلا ةنورملا لماعم و يكيتاتسلا 1 ت ) نيباذم وارذت 33 سلى 22 ةطلخ ءاد ا ةيلاع ةيناسرخلا ةطلخلل امنيب )% 2 نيب ام وارتت ) 12 يلر 22 ل)%
53481213
Comparison of Two Experimental Techniques for Determination of Young ’ s Modulus of Concrete Specimens
Two different experimental techniques, namely impulse excitation method and standard compression test, were used to determine the Young’s moduli of concrete specimens. Using impulse excitation method, the dynamic Young’s moduli were calculated based on measured resonant frequencies of longitudinal vibration of concrete specimens. The major advantage of this method is its nondestructive character. Therefore, the standard destructive compression test could be done on the same specimens. From the results of the second method, the static Young’s moduli were evaluated. At the end of the paper, the methods and also the static and dynamic Young’s moduli are compared. Key-Words: Dynamic Young’s modulus, Impulse excitation, Resonant frequency, Nondestructive testing, Concrete
137235179
Effect of nonlinear response of concrete on its elastic modulus and strength
Abstract The purpose of this paper is to investigate the effect of nonlinear response of concrete on the relationship between modulus of elasticity at static and dynamic loading as well as on its strength. The obtained relationships are based on the thermofluctuation strength theory coupled with a nonlinear stress–strain material model. From the corresponding equations it was found that the ratio of the static to the dynamic modulus of elasticity depends on the strength of concrete, its temperature, rate of loading. Also it was confirmed that the dynamic modulus is greater than static modulus of elasticity. These equations explain the influence of the value of applied stress on the value of the static or dynamic modulus of elasticity. Comparative study shows substantial agreement with existing experimental results and the general equations given in standard BS 8110, Part 2:1985, and ACI documents. Based on the obtained relationships new methods for evaluating the static modulus of concrete and its strength from the results of dynamic tests are described subsequently.
137517298
A fundamental study on compressive strength, static and dynamic elastic moduli of young concrete
Abstract This study investigates the influence of volume content of aggregates, maximum size and type of coarse aggregates, water-to-cement ratio and curing temperature on mechanical properties, i.e. prismatic compressive strength (fc), static modulus of elasticity (Ec) and dynamic modulus of elasticity (Ed) of concrete at early age. A new equation is proposed to correlate prismatic compressive strength and elastic moduli of concrete. Based on the experimental data and the analysis results, the Ec–Ed relationship is also proposed. It is found that the relationship between Ec and Ed is linear, and the coefficients of linear relationship are analyzed by multiple regression analysis, considering aggregate content, maximum size of the coarse aggregate, water-to-cement ratio and curing temperature. It is found that the volume content of aggregates is the most significant factor that influences the Ec–Ed relationship.