Shrinkage Strain Of Concrete Research Articles

Comparison of theoretical and experimental shrinkage in concrete

There are several models developed to predict shrinkage strains in concrete. These models are adopted by various codes or suggested by prominent researchers. The results of experimental measurements of shrinkage strains in plain concrete are compared to the theoretical shrinkage strains predicted using five available models which are: ACI 209, CEB-FIP, B3, Sakata, and GL2000. Measurements were taken on standard specimens (50×50×300mm) and plain prisms (80×150×500mm) subjected to moderate curing condition (28°C and 50% R.H.) and a harsh curing condition (50°C and 5% R.H.). ACI 209 and B3 models were found to have good prediction of experimental shrinkage strains in specimens cured in humidity room while GL2000 and Sakata models showed poor approximations. The best approximation of experimental shrinkage in standard specimens that are cured in temperature room are shown by GL2000 model while CEB-FIP model shows the best prediction in plain concrete prisms that are cured in temperature room. The effect of the considered specimen sizes on shrinkage strains is moderate when cured in humidity room while the effect is noticeable in specimens cured in temperature room. ACI 209 and Sakata models show good quantifications in specimens cured in humidity room and the predicted effect of specimen size in temperature room is far from the experimental effects for all models. All models assume constant and similar size effects on shrinkage for all type of drying conditions which cause inaccurate prediction.

A Simplified Concrete Creep and Shrinkage CEB-FIP90 Model in Long-Span Bridge Design

The concrete shrinkage strain and creep coefficient calculation method in CEB - FIP MC90 model is briefly introduced. For application convenience in bridge design, a simplified formula for calculation of the concrete shrinkage strain and creep coefficient is derived. Considering the varying range of every influence factor, a correlation analysis for the factor is carried out. And the weights of those factors related to concrete shrinkage and creep coefficient are discussed. Considering the climate characteristics and the bridge structure features in the Pearl River Delta area, the variation ranges of concrete nominal shrinkage strain and nominal creep coefficient are calculated respectively.

Concrete Shrinkage and Creep Effect Prediction Model and the Influence Factors Analysis

It is a complex problem that forecast and control the shrinkage and creep of concrete and influence on the performance of the structures.Through the conmparion of all kinds of common model,the article have also analysed the main influence factors about the concrete shrinkage and creep effect . The results showed that JTJ 85 model for shrinkage and creep effect tends to conservative calculation; the creep coefficient and shrinkage strain of JTG D62 model and the CEB-FIP model were basically consistent; and ACI 209 model underestimated the concrete shrinkage and creep effect. Theoretical depth of components was more sensitive to concrete shrinkage strain, and creep coefficient was smaller sensitivity; The effect of concrete creep increases with the decreasing of age at loading, when age of loading percentage increased from three to 28 days, the concrete creep effect of the terminal value reduced about 80%; The influence of environment average relative humidity on shrinkage and creep effect is more sensitive, when environment average relative humidity increased from 50% to 80%, creep coefficient nearly reduced about 30%,and shrinkage strain decreased 50%, in comparison, the influence of environment relative humidity chance on the concrete shrinkage effect is greater than that on creep effect.

Effects of specimen shape and size on water loss and drying shrinkage of cement-based materials

The effects of specimen size and shape on development of water loss and shrinkage of mortar and concrete respectively were investigated. The experimental results showed that the effects of specimen size and shape on water loss ratio were consistent with those on drying shrinkage strain. It is also indicated that drying shrinkage strain has obvious linear correlation with water loss ratios independent of specimen size and shape. The effects of specimen size and shape on the water loss ratio were embodied in established model of averaged relative humidity improved by considering effects of sequential hydration and calculated by finite difference method. Furthermore, the effects of specimen size and shape on drying shrinkage strain of concrete were experimentally deduced and applied to modify criterion EB-FIP1990. The comparison between experimental and calculated results shows that the modified EB-FIP1990 can be adopted to predict drying shrinkage strain of concrete with reasonable accuracy.

The Relationship between Mechanical Properties and Shrinkage of the Concretes Used in Florida

This paper investigated the mechanical strength and shrinkage properties of the concrete mixtures frequently used in Florida. The concrete mixtures were proportioned with three different types of coarse aggregates, such as Miami Oolite limestone, Georgia granite and Stalite lightweight aggregate, and two mineral additives, including fly ash and slag. And fourteen concrete mixtures were evaluated on their characteristics of compressive strength, elastic modulus and shrinkage for 91 days. The empirical relationship between the mechanical properties of concretes and shrinkage strain was analyzed mathematically. The results indicate that the compressive strength and elastic modulus of concrete are exponentially related the shrinkage strain of concrete. The finding from this study is agreeable with that by Troxell et al [5]. Also, the effectiveness of ACI 209 and CEB-FIP models on predicting the shrinkage behavior of concretes used frequently in Florida was evaluated. The result indicates that CEB-FIP model gives more reliable prediction than ACI 209 model does.

Investigation on Cracks Creation and Propagation in Concrete Slab of Composite Beams

Analytical and experimental research have illustrated initiation of cracks in concrete deck immediately after its casting and placing on the upper flange of steel beams, especially prior to application of additional permanent load on composite element. Not only value of concrete shrinkage strain may influence creation and propagation of cracks in concrete. However ratio of deck reinforcement, cross-sectional area of reinforcement steel and strength of concrete can modify the process. Moreover, the ratio of steel beam flexural stiffness and flexural stiffness of concrete deck can be significant. Important shrinkage strains can occur at the lower concrete surface in the steel and concrete interface. Parametrical studies have provided the relationships illustrating impact of above parameters on crack aspect. The aim of the paper is to provide further details.

Numerical Simulation of The Drying Shrinkage Process of Concrete

Based on surface chemistry, the force status of capillary pores of concrete is analyzed and the mechanical model of a single capillary pore in concrete is built with use of ANSYS, a sort of software for analysis and calculation. Then drying shrinkage strain of concrete is simulated. With the continuous evaporation of water, when the radius of concave water surface drop to a certain value, the corresponding shrinkage strain of concrete can be approximately calculated out. Finally the curve of gradually increasing concrete volume-shrinkage strain versus the decreasing radius of concave water surface is described. The existed errors of this simulation are analyzed,and some suggestion for improvements is given.

Eliminating Shrinkage Effect from Moment Curvature and Tension Stiffening Relationships of Reinforced Concrete Members

Experimental results on cracking and deformation behavior of RC members subjected to short-term loading are frequently misinterpreted because shrinkage effect is not taken into account. Even at first loading, free shrinkage strain of concrete may well exceed the cracking strain. The shrinkage strain, restrained by reinforcement, significantly affects the cracking resistance and short-term deformations of RC members. Despite this, most known constitutive laws were derived by using the test data of shrunk RC members under the influence of tension stiffening coupled with shrinkage effect. In this paper, a numerical procedure has been proposed for eliminating shrinkage from moment-curvature and tension-stiffening relationships. The procedure is on the basis of the smeared crack approach and layer section model. It combines direct and inverse techniques of analysis of RC members. The inverse technique, earlier proposed by the first writer, aims at deriving tension-stiffening stress-strain relationships from experimental moment-curvature diagrams. The shrinkage effect was eliminated by assuming in the direct technique a positive (expansion) free shrinkage strain. On the basis of the proposed procedure, free-of-shrinkage tension-stiffening and moment-curvature relationships were derived by using test data of shrunk RC beams obtained by the writers and reported by other investigators. It was shown that negative portions of the tension-stiffening curves disappear after eliminating shrinkage.

コンクリートの乾燥収縮ひずみの推定と収縮ひび割れ対策の選定─ASCoT「コンクリートの収縮ひび割れ研究委員会」の成果報告─

NPO法人コンクリート技術支援機構（ASCoT）に組織された「コンクリートの収縮ひび割れ研究委員会」は，コンクリートの乾燥収縮ひずみの推定方法の提案と，収縮ひび割れ対策の整理の2つの課題に取り組んだ。1つ目の課題に関しては，委員会で共通実験を行ったうえで，骨材の影響の考慮に主眼を置いた推定方法を提案した。この方法は，骨材の気乾含水率，比表面積，または粗骨材からの乾燥収縮ひずみの直接的な測定値から骨材の乾燥収縮ひずみを推定し，その値を基に，複合理論によりコンクリートの乾燥収縮ひずみを計算するものである。また，2つ目の課題に関しては，各種ひび割れ対策の有効性を，効果，コストメリットおよび汎用性の面から評価した。

Drying Shrinkage of Concrete Affected by Content of Stone Powder in Proto-Machine-Made Sand

To improve the application of the new proto-machine-made sand in structural engineering, tests are carried out to study the drying shrinkage of concrete affected by stone powder in proto- machine-made sand. The target cubic compressive strength of concrete is 55 MPa, the main factor varied in mix proportion of concrete is the contents of stone powder by mass of proto-machine-made sand from 3 % to 16 %. The drying shrinkage strains of concrete are measured by the standard method at the ages of 1 d, 3 d, 7 d, 14 d, 28 d, 60 d, 90 d, 120 d, 150 d and 180 d. Based on test results, the drying shrinkage of concrete affected by the contents of stone powder in proto-machine-made sand is analyzed and compared with that of similar test of concrete with traditional machine-made sand, which shows that there is the optimum content of stone powder resulting in the lower drying shrinkage of concrete. The formula for predicting drying shrinkage strain of concrete is proposed.

Shrinkage of High Strength Concrete

This paper presents the results of an experimental investigation carried out to evaluate the shrinkage of High Strength Concrete. High Strength Concrete is made by partial replacement of cement by flyash and silica fume. The shrinkage of High Strength Concrete has been studied using the different types of coarse and fine aggregates i.e. Sandstone and Granite of 12.5 mm size and Yamuna and Badarpur Sand. From the test results of the above investigation it can be concluded that the shrinkage strain of High Strength Concrete increases with age. The shrinkage strain of concrete with replacement of cement by 10% of Flyash and Silica fume respectively at various ages are more (6 to 10%) than the shrinkage strain of concrete without Flyash and Silica fume. The shrinkage strain of High Strength Concrete is also compared with that of normal strength concrete. Test results show that the shrinkage strain of high strength concrete is less than that of normal strength concrete.

国内の実験データに基づいたコンクリートの時間依存性ひずみの予測式に関する研究 : 乾燥収縮ひずみの予測式

In the performance-based design for shrinkage cracking in building, the reliable mathematical model for predicting shrinkage and creep strain of concrete is required. It is desirable that the mathematical model is simple and accurate, and every engineer can use it without any difficulties. Then, in this paper, the prediction formula of shrinkage strain of concrete with a normal to high strength concrete was discussed using the test data published in the annual meeting of Architectural Institute of Japan. The proposed model was expressed as the product of two terms; one is the ultimate shrinkage strain that is expressed in terms of the product of three coefficients taking into account of mix proportions, age at drying and relative humidity, the other the time-effect function (the hyperbolic-power type) in which the effect of specimen size is concerned. Moreover, the effects of the kinds of cement, aggregate and admixture were introduced as the correction factors of ultimate shrinkage strain. It was found that the proposed prediction formula can estimate the shrinkage strain more accurately than the other formulas such as JSCE, CEB-FIP1990 and ACI209.

複合則理論を用いたコンクリートの乾燥収縮ひずみの予測式 : 終局乾燥収縮ひずみの評価方法

Drying shrinkage of concrete exerts a serious influence toward the long-term reliability such as the durability of the structure. The estimation formula of drying shrinkage of concrete is necessary by using examine this behavior of properties. In this paper, the prediction estimation formula of drying shrinkage strain of concrete is obtained with two-phase composite material model as cement paste and aggregate. The results of the this study are summarized as follows: 1) The elastic modulus of cement paste can be explained as a function of the cement-water ratio and age at drying, as well as drying shrinkage strain. 2) Drying shrinkage of aggregate can be explained as a function of its absorption. 3) Drying shrinkage of concrete can be calculated using five parameters of water-cement ratio, age at drying, the absorption of aggregate, the volume of aggregate and volume-surface ratio of member. The calculated results agreed well with the experimental data.

Effect of water-to-cementitious materials ratio and silica fume on the autogenous shrinkage of concrete

This paper presents an experimental study on the autogenous shrinkage of Portland cement concrete (OPC) and concrete incorporating silica fume (SF). The results were compared with that of the total shrinkage (including drying shrinkage and part of the autogenous shrinkage) of the concrete specimens dried in 65% relative humidity after an initial moist curing of 7 days. The water-to-cementitious materials (w/c) ratio of the concrete studied was in the range of 0.26 to 0.35 and the SF content was in the range of 0% to 10% by weight of cement. The results confirmed that the autogenous shrinkage increased with decreasing w/c ratio, and with increasing SF content. The results showed that the autogenous shrinkage strains of the concrete with low w/c ratio and SF developed rapidly even at early ages. At the w/c ratio of 0.26, the autogenous shrinkage strains of the SF concrete were more than 100 micro strains at 2 days. For all the concretes studied, 60% or more of the autogenous shrinkage strain up to 98 days occurred in the first 2 weeks after concrete casting. The results indicated that most of the total shrinkage of the concrete specimens with very low w/c ratio and SF exposed to 65% relative humidity after an initial moist curing of 7 days did not seem to be due to the drying shrinkage but due to the autogenous shrinkage.

Stress‐Induced Thermal and Shrinkage Strains in Concrete

A previous material model for the increase of creep of concrete caused by simultaneous drying is extended to describe the effect of both drying and wetting, as well as the increase of creep caused by temperature changes, both heating and cooling. By theoretical arguments and comparisons with numerous existing test data, it is shown that the creep increase due to temperature changes, sometimes called the transitional thermal creep, is physically the same phenomenon as the increase of creep due to humidity changes, known as the Pickett effect (or the drying creep effect). In accord with the previous model for drying creep alone, the present extended model explains the increase of creep due to humidity or temperature changes as a consequence of principally two effects: (1) Stress-induced shrinkage (or swelling) or stress-induced thermal expansion (or contraction); and (2) the distributed tensile cracking (or strain-softening) of concrete. The former effect is explained by the previously advanced hypothesis that the creep viscosity depends on the pore humidity rate. The latter effect reduces measured overall deformations, and thus results in the true thermal expansion or shrinkage of uncracked material being considerably larger than observed on load-free companion specimens when significant nonuniformly distributed self-equilibrated stresses are produced by the temperature or humidity change. The proposed material model is suitable for finite-element programs.

Variation of stress resultants in concrete structures due to time-dependent creep and shrinkage strains of concrete

A general procedure for calculating the variation with time of the internal stress resultants and hence the stresses, in concrete structures is discussed. In particular, a study is made of the changes in the stress resultants due to time-dependent creep and shrinkage strains of concrete. A general procedure of calculating the variation in the stress resultants due to differential creep strains in concrete structures has been proposed by the author[1]. A similar procedure is followed in this paper to study these variations when creep and shrinkage strains take place simultaneously. The method leads to a system of n-linear differential equations of the form: X = AXt + B the solution of which is performed by a computer using Runge-Kutta numerical procedures. A reinforced concrete portal frame exhibiting creep and shrinkage strains is solved by the proposed method and the results are given in tabular and graphical form.