Shrinkage Strain Of Concrete Research Articles

Performance of capsules in self-healing early-age concrete due to restrained shrinkage

Performance of capsules in concrete was evaluated numerically using a simulated ASTM C1581 restrained shrinkage test and experimentally measured concrete shrinkage strain data to determine their effectiveness in healing cracks in early-age concrete. The model accounts for the concrete’s time-dependent mechanical properties, and the capsule’s geometrical and mechanical properties, and depth. A finite element model was developed to simulate the concrete volume change due to autogenous and drying shrinkage and the corresponding state of stress, and fracture mechanics to trace crack initiation and propagation in a restrained shrinkage ring. The performance of capsules in self-healing early-age concrete was found to depend on the capsules’ geometry, the stiffness ratio of concrete-to-capsule, and bond strength-to-rupture strength ratio of concrete-to-capsule. Results reveal that corresponding ratios of concrete effective stiffness and bond strength at 28 days to the stiffness and rupture strength of the capsules provide a threshold limit after which capsules debond in self-healing early-age concrete.

<b>Prediction Equations for Shrinkage Strain of Concrete with Mixed Cement</b>

<b>Prediction Equations for Shrinkage Strain of Concrete with Mixed Cement</b>

Shrinkage model for concrete incorporating coal gangue coarse and fine aggregates

Our study aims to formulate a model for predicting the shrinkage behaviour of concrete incorporating coal gangue coarse and fine aggregates (CGCA and CGFA). In order to achieve this, the study conducted an experiment measuring the shrinkage of coal gangue aggregate concrete (CGAC) over a period of 126 days. The experiment involved varying replacement ratios of CGCA and CGFA, including 0%, 50%, and 100% of both types. Test results show that: (1) both CGCA and CGFA significantly increased concrete shrinkage strain, and the shrinkage strain increased by 145% when both CGCA and CGFA were 100% used, (2) the CGCA has a more pronounced influence on the shrinkage compared to CGFA, and (3) the incorporation of CGCA leads to a faster development of shrinkage in the concrete, whereas CGFA has no significant effect on the shrinkage development over time. A novel theoretical model was developed that can accommodates the coal gangue aggregate's effect on the development and ultimate value of shrinkage strain in CGAC. Benchmarking analysis was carried out using the study's test data and data from literature, which showed that the proposed model can well predict the CGAC shrinkage.

Concrete Shrinkage Analysis with Quicklime, Microfibers, and SRA Admixtures

This research explores the effect of various humidity conditions and the efficiency of shrinkage-reducing admixtures on the free shrinkage strain of ordinary Portland cement (OPC) concrete and its mechanical properties. An OPC concrete C30/37 mixture was replenished with 5% of quicklime and 2% of organic-compound-based liquid shrinkage-reducing agent (SRA). The investigation revealed that a combination of quicklime and SRA led to the highest reduction in concrete shrinkage strain. Polypropylene microfiber addition was not so effective in reducing the concrete shrinkage as the previous two additives did. The prediction of concrete shrinkage without quicklime additive was performed according to EC2 and B4 model methods, and the obtained results were compared with the experimental ones. The B4 model evaluates the parameters more than the EC2 model does and, therefore, was modified to calculate the concrete shrinkage for the case of variable humidity and to evaluate the effect of quicklime additive. The experimental shrinkage curve that best coincides with the theoretical one was that obtained by the modified B4 model.

Simplified shear equation of deep concrete beam considering orientation effect of opening and mechanical properties of fibre-concrete interface

In the present era of technology, the design of structural deep concrete beams is highly modernized through the use of computer-aided tools. However, theories for such design are the paramount aspects to be understood particularly when the beam has openings. To improve the mechanical properties of the deep beam with openings, recycled tyre steel fibres are required. To estimate the bond strength of the fibre-concrete interface, the concrete shrinkage strains for fibre lengths 30, 50 and 60 mm with a content of 0.5% were considered. To mitigate the conservativeness of some available shear models and improve the design of deep beams, the simplified shear equation model was developed. The model was established using a simplified compressive stress block, forces in steel reinforcement and shear stress at the fibre-concrete interface. The combined effect of opening height and length was also considered in the model. The results show that incorporating fibres in concrete increase the shear performance of deep concrete beams with openings due to high strains in the shear zone indicating high loads being transferred. For instance, beam BS2 had a strain of 0.0153 in the lower load path compared to 5.6 × 10−5 for beam BC2 There was a good correlation between measured and proposed shear capacities with t-test values of 0.46, 0.996 and 0.003 for beams without fibres, and with fibres and mesh respectively. Results also showed the model shear equation performed better compared to other equations with mean absolute error (MAE) and coefficient of variation (COV) of 9.3 and 18.9%, respectively for the control beams with openings. The model also showed a mean absolute error (MAE) and coefficient of variation (COV) of 11.6 and 7.4%, respectively for the beams with fibres. The COV and MAE for the proposed model were small than those in the database, therefore, the proposed model can provide the precise design of deep concrete beams with openings and fibres.

Early shrinkage experiment of concrete and the development law of its temperature and humidity field in natural environment

Concrete shrinkage is one of the main causes of structural deterioration, and clear understanding of the development law of temperature and humidity field is a key to accurately predict concrete shrinkage. To study the effect of temperature and humidity (T&H) difference of concrete caused by curing conditions on its shrinkage, this study designs a concrete shrinkage experiment with three different maintenance conditions of moisture-thermal exchange, moisture retention, and moisture-thermal retention. Subsequently, a data correlation algorithm combining maximum information coefficient (MIC) and random walk (RW) is proposed. The correlations between the environment T&H and the concrete T&H, concrete temperature and its humidity, as well as the concrete T&H and its shrinkage are quantitatively investigated. The experimental results indicate that the curing conditions of moisture retention and moisture-heat retention respectively reduce the concrete shrinkage strain by 30.7% and 11.3% compared with the moisture-heat exchange condition at the age of 125 days. The coupling effect between the change rate of temperature and the change rate of humidity needs to be considered in the analysis of the moisture and heat field of concrete, while the influence of the second derivative of temperature with respect to space on the humidity change rate (that is, the Soret effect) can be ignored. The conclusions obtained in this study can provide a basis for the selection of coupling terms in the moisture and heat transfer analysis of concrete and the establishment of shrinkage prediction models.

Nanocomposite Building Materials in Modern Architectural Design

Architecture is the precipitation of history, not only the embodiment of technical level but also the inheritance of history and culture. Excellent architecture contains high historical value and emotional factors, and it continues to deepen over time. Nanotechnology is a new technology that was born in the late 1980s and is emerging. It mainly refers to the study of the laws of motion and interactions of electrons, atoms, and molecules in the composition system of matter in the range of 0.1 to 100 nm. Nanomaterials have special properties and structures, and the composite materials made of them have the effect of strengthening and toughening the polymer by virtue of their high‐quality strength and toughness. Therefore, the aim of this text is to explore the application of nanocomposite building materials in modern architectural design and analyze the advantages and development trends of new building materials. The method in this paper is to use the method of experimental comparison to analyze the performance improvement effect of nanocomposite building materials on the current main building materials of concrete. By establishing a model to study the impact on the shrinkage and mechanical properties of cement‐based materials, it can also improve the environmental performance and comprehensive evaluation of building materials. Corresponding conclusions are drawn through data comparison. When the amount of nanocomposite building materials is 1.5%, the chemical shrinkage value of the cement paste will increase by 58.2%, and the shrinkage strain will increase by 15.3%. When the fly ash content is 20%, the chemical shrinkage value of cement paste is reduced by 30.5%, and the shrinkage strain of concrete is reduced by 8.8%. Therefore, adding nanocomposite building materials to cement‐based materials can promote cement hydration, optimize pore structure, and to a certain extent can make up for the shortcomings of mineral admixtures and achieve better improvement effects.

Time-Dependent Shrinkage Model for Recycled Fine Aggregate Thermal Insulation Concrete.

In this study, the shrinkage performance of recycled aggregate thermal insulation concrete (RATIC) with added glazed hollow beads (GHB) was investigated and a time-dependent shrinkage model was proposed. Two types of recycled fine aggregate (RFA) were used to replace natural fine aggregate in RATIC: RFA from waste concrete (RFA1) and waste clay brick (RFA2). Besides, the mechanical properties and thermal insulation performance of RATIC were also studied. Results showed that the pozzolanic reaction caused by RFA2 effectively improved the mechanical properties of RATIC; 75% was the optimal replacement ratio of RATIC prepared by RFA2. Added RFA decreased the thermal conductivity of thermal insulation concrete (TIC). The total shrinkage strain of RATIC increased with the increase of the replacement ratio of RFA. The 150d total shrinkage of RATIC prepared by RFA1 was 1.46 times that of TIC and the 150d total shrinkage of RATIC prepared by RFA2 was 1.23 times. The addition of GHBs led to the increase of early total shrinkage strain of concrete. Under the combined action of the higher elastic modulus of RFA2 and the pozzolanic components contained in RFA2, the total shrinkage strain of RATIC prepared by RFA2 with the same replacement ratio was smaller than that of RATIC prepared by RFA1. For example, the final total shrinkage strain of RATIC prepared by RFA2 at 100% replacement ratio was about 18.6% less than that of RATIC prepared by RFA1. A time-dependent shrinkage model considering the influence of the elastic modulus of RFA and the addition of GHB on the total shrinkage of RATIC was proposed and validated by the experimental results.

Shrinkage behavior of concrete containing bottom ash granules as partial replacement of natural sands

This study aims to provide databank and comprehensible design equations for the shrinkage strain curve of concrete using bottom ash granules to replace conventional natural sands. We prepared 27 concrete mixtures with various parameters, including the substitution level of natural sand for fine bottom ash aggregates, unit water content, and fine aggregate-to-total aggregate volume ratios. To derive reliable design models to predict the drying shrinkage of concrete using fine bottom ash aggregates, the time function specified in fib 2010 was modified by introducing the parameter of equivalent porosity of aggregates. Moreover, the shrinkage strain values at an age of 91 days were formulated by conducting a regression analysis using test data as a specified reference to determine the ultimate shrinkage strain. The test results showed that the shrinkage strain of concrete is marginally affected by the bottom ash aggregate content but significantly affected by the volume fraction of aggregates and their equivalent porosity. The proposed models are promising for estimating the shrinkage strain response of concrete using fine bottom ash aggregates by considering the restraining action of aggregates.

Application of HCSA expansive agent in crack control of mass concrete

The open section of the west artificial island of the Hong Kong-Zhuhai-Macao Bridge is a mass concrete structure. The concrete was poured in two times in the vertical direction, that is, the whole bottom plate was poured in the first time, and the middle wall and two side walls were poured in the second time. The side wall and middle wall are easy to crack due to the long time interval between two concrete castings. In order to study the function and effect of HCSA expansion agent in the crack control of mass concrete, the applicable condition of compensating shrinkage in the crack control of mass concrete is analyzed first. Then the effect of HCSA expansion agent was studied in laboratory and field. The experimental results show that HCSA expander has a good expansion effect under laboratory conditions, but it has no expansion effect on the middle side of the mass concrete test block in the engineering site, instead, it will further increase the internal temperature rise of concrete and increase the shrinkage strain of concrete. HCSA expander is helpless for crack control of mass concrete.

Mechanical Properties and Shrinkage Behavior of Concrete-Containing Graphene-Oxide Nanosheets

Graphene oxide (GO) has been widely used as an additive due to its numerous unique properties. In this study, the compressive strength, flexural strength and elasticity modulus of concrete containing 0.02 wt%, 0.05 wt % and 0.08 wt % GO, and its dry shrinkage performance have been experimentally investigated. After the sample preparation, apparatus for compression test and flexural test were used to test the relevant properties of concrete containing GO. The dial indicators were used to measure the shrinkage of samples. The results indicate that GO can considerably improve the compressive strength, flexural strength, and elasticity modulus of concrete at the concrete age of 28 days by 4.04–12.65%, 3.8–7.38%, and 3.92–10.97%, respectively, which are substantially smaller than the increment at the age of 3 d by 5.02–21.51%, 4.25–13.06%, and 6.07–27.45% under a water-cement ratio of 0.35. It was also found that GO can increase the shrinkage strain of concrete. For example, at the age of 60 days, 0.02 wt%, 0.05 wt% and 0.08 wt% GO can increase the shrinkage strain of ordinary concrete by 1.99%, 5.79% and 7.45% respectively under a water-cement ratio of 0.49. The study has advanced our understanding on mechanical and shrinkage behavior of concrete containing GO.

Relationship between Drying Shrinkage Strain of Concrete and Quality of Coarse Aggregate

コンクリートの乾燥収縮は，使用材料，配合，施工条件，環境条件，形状などの様々な要因の影響を受ける。近年では，JIS規格に適合する粗骨材を用いたコンクリートでも過大な乾燥収縮ひずみを生じたことで大きな注目を集めた。コンクリートの乾燥収縮に対して，従来から指摘されている単位水量の影響よりも，使用する粗骨材種類の影響の方が卓越することが報告されている。そこで筆者らは，粗骨材の乾燥収縮特性に着目した検討を通じて，ひずみゲージによる粗骨材の乾燥収縮率の測定法の確立や，コンクリートの乾燥収縮率と粗骨材の各種品質指標との関係性を明らかにしてきた。本稿ではこれまでに得たデータを再整理した結果について報告する。

Impact of Selected Environment Conditions on the Shrinkage Strains in Respect to Standard Recommendations

The article discusses the issues related to concrete shrinkage. The basic information on the phenomenon is presented as well as the factors that determine the shrinkage are described. Under laboratory conditions, these factors can be imposed and controlled, but in the field, it is not possible to maintain stable environmental conditions. The paper describes the experimental research that allows determining the effect of changes of humidity and ambient temperature on the values of shrinkage strains in concrete samples and verify the obtained results based on the theoretical model included in the Eurocode 2 standard. The shrinkage strains were measured on samples with dimensions 150x150x600 mm, made of C30/37 concrete with Portland cement and limestone aggregate and with water/cement ratio of 0.43. The samples were divided into two groups - the first group of samples was stored in a chamber with set and controlled values of temperature and humidity, and the second group was left in the laboratory hall with freely changing environmental conditions. The shrinkage strains were measured on samples in accordance with the ITB 194/98 for 175 days. A 20 cm base extensometer was used for the strain measurements. The studies of experimental results of the concrete shrinkage strain are presented with a comparative analysis of the results estimated by the guidelines of the standard according to PN-EN 1992-1-1:2008. The obtained results confirmed that the unstable humidity as well as temperature have a significant impact on the course of shrinkage strains in concrete and they both should be taken into consideration during performing concrete elements.

Efficient modified concrete for irrigation and drainage facilities construction

The paper describes scientific and technical prerequisites for the development of composition of and production method for hydrophobic complex modifier based on the industrial wastes, including technical lignosulfonates (TLS) as a plasticizing ingredient; oil and fat tar as hydrophobic ingredient; and saponified wood pitch (SWP) as air entraining ingredient. The purpose of the presented studies was the development of an efficient modified concrete composition for construction of irrigation and drainage facilities construction by using a complex hydrophobic modifier. Experimental studies were carried out on concrete samples made of reference and test compositions in the laboratory of the “Building Materials” Department of the National Research Moscow State University of Civil Engineering. Comprehensive studies showed that the use of hydrophobic modifier allows obtaining concrete with water bleeding ratio reduced by 35–40%; reducing the concrete capillary suction and water absorption by 3 times; and increasing water penetration pressure (W8 and more), in comparison with concrete without additives. The developed complex hydrophobic modifier increases the strength by 12-18% and reduces shrinkage strain of concrete by 7.5% in comparison with the control composition without the modifier.

An Experimental Study on Shrinkage Strains of Normal-and High-Strength Concrete-Filled Frp Tubes

It is now well established that concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs) are an attractive construction technique for new columns, however studies examining concrete shrinkage in CFFTs remain limited. Concrete shrinkage may pose a concern for CFFTs, as in these members the curing of concrete takes place inside the FRP tube. This paper reports the findings from an experimental study on concrete shrinkage strain measurements for CFFTs manufactured with normal- and high-strength concrete (NSC and HSC). A total of 6 aramid FRP (AFRP)-confined concrete specimens with circular cross-sections were manufactured, with 3 specimens each manufactured using NSC and HSC. The specimens were instrumented with surface and embedded strain gauges to monitor shrinkage development of exposed concrete and concrete sealed inside the CFFTs, respectively. All specimens were cylinders with a 152 mm diameter and 305 mm height, and their unconfined concrete strengths were 44.8 or 83.2 MPa. Analysis of the shrinkage measurements from concrete sealed inside the CFFTs revealed that embedment depth and concrete compressive strength only had minor influences on recorded shrinkage strains. However, an analysis of shrinkage measurements from the exposed concrete surface revealed that higher amounts of shrinkage can occur in HSC. Finally, it was observed that shrinkage strains are significantly higher for concrete exposed at the surface compared to concrete sealed inside the CFFTs.

Testing specimen effect on shrinkage of lightweight concrete

The shape and size of the testing specimen influence the measured shrinkage strain of concrete at different ages. This study compares the shrinkage strain of lightweight concrete containing treated expanded polystyrene beads measured by prism (285 × 75 × 75 mm) and cylindrical (150 × 300 mm) specimens for 225 d after 7 and 14 d of moist-curing, respectively. The shape of the specimen had a distinct effect on the shrinkage, especially immediately before and after the age of 60 d. The increasing trend of the shrinkage strain in the prism and cylinder specimens was different. Considering the specimen shape, a relationship is proposed and verified by the existing models and experimental data to predict the shrinkage strain of lightweight concrete.

乾燥収縮するコンクリート壁面の拘束度マップ

The free shrinkage deformation occurring in concrete members is generally restrained by members around one with different stiffness and shrinkage rate, and a restraining ratio which expresses degree of restraining has a major influence on state of shrinkage cracking. Therefore, in order to predict the shrinkage cracking, it is important to get the restraining ratio of concrete members in addition to free shrinkage strain of concrete. With this background, in order to prepare eventually a design material for controlling shrinkage cracking with the organized distribution of restraining ratio, an experimental and analytical study to find out the regularity of distribution of restraining ratio in concrete walls was previously performed by authors. Additionally, it was noted that the restraining ratio in a wall with drying shrinkage should be reasonably considered by dividing it into the following two areas. (1) Non edge area: the area whose restraining direction is horizontal and distribution of vertical direction of restraining ratio is linear because bending deformation is dominant and Bernoulli-Euler's hypothesis holds. The distribution of restraining ratio in this area can be calculated by replacing a concrete wall with a uniaxial model. (2) Edge area: the area whose restraining direction is turbulent and distribution of vertical direction of restraining ratio is non-linear because shear deformation is dominant and Bernoulli-Euler's hypothesis does not hold. This signifies that the distribution of restraining ratio in concrete walls can be potentially predicted by the following policy: (1) First, the distribution of restraining ratio in a concrete wall is calculated by the uniaxial model, (2) Next, the position of areas to which the value calculated at above (1) can be not applied (i.e. edge area) and the value of restraining ratio in those areas is obtained from the design material prepared previously, considering various conditions of concrete walls. In this study, the map of distribution of restraining ratio in concrete walls, which is the design material in line with above policy, was created. In particular, the distribution of restraining ratio in concrete walls with various conditions was calculated by FEM analysis. Moreover, the areas to which the value calculated by the uniaxial model can be not applied (peculiar areas) were shown by organizing that result, and restraining ratio and restraining direction in those areas were shown. The distribution of restraining ratio shown in the map has the following characteristics. (1) The peculiar areas occur at the upper and lower parts of both ends of a wall. (2) The position and largeness of peculiar area at lower part of both ends of a wall hardly changes depending on stiffness balance between members. Additionally, the area extends vertically as the shape of a wall is horizontally long. Furthermore, though the area is decoupled by columns and beams with increased number of layer and span, the position of that entire area hardly changes. (3) The average restraining ratio at the peculiar area at lower part of both ends of a wall is obtained by adding a constant value (approximately 0.4) to the restraining ratio calculated by the uniaxial model, and the average restraining direction at the area is 30° to 35° in any wall.

Long-Term Deflection Prediction and Correction of Creep and Shrinkage Model of High-Strength Concrete Based on Short-Term Measured Data for Bridge

To investigate the laws of creep and shrinkage in high-strength, concrete for long-span prestressed continuous box-girder bridge and predict long-term deflection, strain sensors were embedded in the midspan of a box-girder bridge. The shrinkage strain of concrete was then directly measured, and the creep strain was obtained using the incremental algorithm of measured data. The measured data show that if the creep and shrinkage model in the existing specification is used, then the shrinkage effect is underestimated as a whole and the creep effect is overrated for the C55 high-strength concrete of the bridge. The long-term deflection is predicted using the modified prediction models of creep and shrinkage that are based on short-term measured data when the bridge is under dead load. The deflection prediction values of two modified prediction models were compared with the measured deflection. Results of the comparison indicate that the integrality of the short-term measured strain data in concrete, measurement accuracy, and modified prediction model that is based on the measured data influence the prediction accuracy of the modified prediction models.

Experimental Verification of the Concrete Shrinkage Strains Course According to En 1992-2 Standard

Abstract The article provides basic information about the shrinkage of concrete and discusses the major impact on the size and course of the shrinkage. There are the guidelines to estimate the shrinkage strain of concrete bridge structures for the high tensile strength-SCI in accordance with PN-EN 1992-2. The article presents the results of experimental studies which aim was to analyze the course of shrinkage in two types of specimens made of different composition mixes. The studies have also made possible to verify the actual size of the shrinkage strain and designated ones on the basis of the PN-EN 1992-2.

Evaluation of the influence of shrinkage strain on the fatigue strength of the connection in steel–concrete composite beams

The paper presents the author's proposal for calculation of shear stresses (disintegrating) induced by concrete shrinkage at the interface of steel and concrete. The proposal also presents expressions to calculate the fatigue strength of a connection in steel–concrete composite girders. The expressions to calculate fatigue strength are based on the results of experiments performed by the author. Based on the results of analyses it can be stated that the load bearing capacity of a connection with flexible shear connectors is strongly affected by a concrete slab adhesion to a steel girder. This effect depends on the stiffness ratio of the girder to concrete deck (coefficient δ), concrete strength and diameter of shear studs d, as well as the value of shrinkage strain of concrete. Fatigue strength of a connection with strip connectors is affected by the geometry of the composite girder and its components, concrete strength and concrete shrinkage strain. At low values of δ, low concrete grades and large diameters of shear connectors or holes, the fatigue strength of the composite connection is likely to be exhausted.