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This work is focused on studying the time-dependent properties of recycled concrete, especially shrinkage and creep behaviour. For said purpose, two series of concretes (water to cement ratios of 0.50 and 0.65) were designed with ...
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This work is focused on studying the time-dependent properties of recycled concrete, especially shrinkage and creep behaviour. For said purpose, two series of concretes (water to cement ratios of 0.50 and 0.65) were designed with different replacement percentages of recycled coarse aggregate (0%, 20%, 50% and 100%).
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The present paper deals with the aging thermal creep of the reacting elastic con-crete. In Part I of the Paper, the theoretical formulation and significance of the proposedunified constitutive model have been presented. This Part ...
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The present paper deals with the aging thermal creep of the reacting elastic con-crete. In Part I of the Paper, the theoretical formulation and significance of the proposedunified constitutive model have been presented. This Part II of the Paper focuses on its em-pirical validation and practical relevance. Theoretical predictions for the creep, recovery andrelaxation of hydrating concrete, young cement paste and leaching concrete subjected to dif-ferent stress or strain histories have been found to be satisfactory. Different observed effectsof ambient constant temperature on creep of concrete have been accurately predicted. Ab-sence of any substantial effect of grade of concrete on creep coefficients has been confirmed.The proposed constitutive model is expected to be relevant for creep and durability designof concrete structures. Depending upon the environmental exposure conditions and ambienttemperatures, different creep coefficients have been suggested for concrete. Possible areasof future theoretical and experimental research in this field have been identified.
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Concrete creep and shrinkage at cold temperatures are less significant than those at room temperature. For the structures exposed to subarctic weather, in situ creep and shrinkage strains are important factors in design process, s...
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Concrete creep and shrinkage at cold temperatures are less significant than those at room temperature. For the structures exposed to subarctic weather, in situ creep and shrinkage strains are important factors in design process, such as estimating pre-stress losses, since ambient temperature and relative humidity change in a wide range. In the present study, the in situ creep and shrinkage strains were measured from high strength concrete specimens loaded in a concrete creep frame exposed to subarctic weather for 332 days. The measured creep strain was 23-30% of creep strain from specimens at room temperature. Also, the shrinkage strain was 67% of the shrinkage strain measured at room temperature. The comparison showed that the creep and shrinkage strains in real subarctic weather were larger than strains at a sustained cold temperature, but they were substantially smaller than strains at room temperature. The measured strains were compared with predicted values from widely used creep and shrinkage models. The AASHTO-LRFD model and the CEB MC90-99 model matched well with test results.
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The concrete shrinkage test results obtained in five research programs are compared with the results obtained through analysis according to two models (Eurocode 2 and B3). The comparisons show that the values obtained according to...
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The concrete shrinkage test results obtained in five research programs are compared with the results obtained through analysis according to two models (Eurocode 2 and B3). The comparisons show that the values obtained according to models greatly deviate from those obtained by testing. A coefficient is proposed as a means to increase accuracy of the EC 2 model, so that it can be used to anticipate shrinkage of the high-strength concrete. The model for anticipating the concrete creep coefficient is also analyzed.
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The creep-recovery behavior of both normal and high strength concrete (HSC) under various load conditions has not been studied thoroughly. Although the use of HSC is long-established, rational creep-recovery prediction of HSC is s...
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The creep-recovery behavior of both normal and high strength concrete (HSC) under various load conditions has not been studied thoroughly. Although the use of HSC is long-established, rational creep-recovery prediction of HSC is still unavailable since current study just regards recovery deformation as a secondary result of creep experiments. In this paper, a new prediction model for creep recovery of normal strength concrete (NSC) with considering the influence of stress level and load history was proposed at first. Then, a model for HSC creep-recovery was established according to creep-recovery data of NSC and HSC in literatures and the influence of compressive strength of concrete. To validate the HSC model, an experimental study of the creep behavior of C80 concrete was conducted. Creep and residual strain after unloading of specimens at various compression stress levels (30% and 50% of the compression strength) were compared with the HSC creep-recovery model. Although the HSC model tends to underestimate the first 7 days' creep-recovery value, the results show high overall prediction accuracy. Moreover, parametric analysis results indicate that the recoverable creep of HSC reduces significantly than that of NSC. The effect becomes stronger with the increase of loading age and weaker with a prolongation of load duration. (C) 2017 Elsevier Ltd. All rights reserved.
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Recent experiments on concrete have established that ongoing chemical reac-tions cause creep-like mechanical behaviour. Earlier, the present authors have proposeda Dissolution-Precipitation Mechanism and Theory capable of predicti...
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Recent experiments on concrete have established that ongoing chemical reac-tions cause creep-like mechanical behaviour. Earlier, the present authors have proposeda Dissolution-Precipitation Mechanism and Theory capable of predicting such chemo-mechanical response. However, this theory is incapable of predicting observed aging basiccreep of concrete in absence of reactions. For this purpose, another physical mechanism—Modified Adaptive Link Mechanism—has been proposed in this Paper. Two expressions forthe material viscosity tensor and a unified constitutive equation for the aging thermochemo-viscoelasticity of concrete have been derived. Ambient temperature has been assumed toaffect the pace of reactions and of the bond breakage and restoration process. In this Part Iof this Paper, theoretical foundations of the proposed constitutive' model have been pre-sented. The theoretical significance of the work done has been discussed. In Part II of thepaper, the empirical validation and practical relevance of the proposed constitutive model have been presented.
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The present study aims to characterize the creep behaviour of Polystyrene Aggregate Concrete (PAC). The creep and creep recovery of PAC were determined experimentally and compared with normal weight concrete. The parameters studie...
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The present study aims to characterize the creep behaviour of Polystyrene Aggregate Concrete (PAC). The creep and creep recovery of PAC were determined experimentally and compared with normal weight concrete. The parameters studied include polystyrene aggregate (PA) content, curing and storage conditions. The ultimate creep strains for the polystyrene aggregate concrete were estimated using a hyperbolic expression and compared to the other common prediction models for normal weight concrete. The experimental results showed that creep of polystyrene aggregate concrete increased with the increase of PA content in the mix. The ratios of creep recovery to creep strains decreased slightly with an increase in PA content. The curing and storage conditions showed remarkable influences on the creep of PAC, but not for its creep recovery. Besides, the creep prediction results were compared against the prediction models given by ACI and CEB-FIP.
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The response of cementitious materials is highly dependent. On the hand, it can lead to delayed collapse of structures fabricated of such materials. On the other hand, the time dependence is associated with the relaxation of peak ...
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The response of cementitious materials is highly dependent. On the hand, it can lead to delayed collapse of structures fabricated of such materials. On the other hand, the time dependence is associated with the relaxation of peak stresses, which avoids, or postpones damage. A finite element formulation is presented for the analysis of the time-dependent cracking of cementitious materials. The constitutive law incorporates continuum plasticity and linear visco-elasticity.
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In a radioactive waste disposal, concrete containment structures must be studied over extended periods during which it is necessary to account for a possible degradation by calcium leaching due to on-site water. An experimental in...
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In a radioactive waste disposal, concrete containment structures must be studied over extended periods during which it is necessary to account for a possible degradation by calcium leaching due to on-site water. An experimental investigation is described where the effects of an accelerated calcium leaching process of concrete on creep of concrete are highlighted. The comparison with a creep test where the sample is immersed in water shows that leaching generates tertiary creep and rupture of the specimen. A Dirichlet series coupled to a mechanical damage are used to model the coupled tertiary creep. With this method we can evaluate the lifetime of concrete structures subjected to chemical and mechanical loading.
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Concrete structures develop high levels of transient creep strain when exposed to fire, especially when temperatures in a member exceed 500 degrees C. This high-temperature creep strain can dominate the deformation response under ...
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Concrete structures develop high levels of transient creep strain when exposed to fire, especially when temperatures in a member exceed 500 degrees C. This high-temperature creep strain can dominate the deformation response under severe fire scenarios and needs to be properly accounted for in the fire resistance analysis. Most of the current approaches for fire resistance calculations, including advanced analysis methods, do not consider the transient creep strain to the full extent. This paper presents design recommendations for the treatment of creep in the fire resistance analysis of concrete structures. Three design alternatives are proposed for incorporating creep in fire resistance analysis depending on the conditions encountered during fire exposure. The first solution is'creep-not critical'scenario where the temperature-induced creep strain can be neglected in a structural member subjected to low stress level and experiencing low sectional temperatures. In the second scenario ('creep-implicit'), where temperature-induced creep strain is moderate, creep can be incorporated implicitly in the analysis. Finally, in situations where creep is significant (as in the case of high stress level and sectional temperatures), it needs to be incorporated explicitly in the fire resistance analysis ('creep-explicit'scenario). The practicality of the proposed solution in accounting for creep in the fire resistance analysis of concrete members at different levels is demonstrated using three case studies.
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