Shrinkage Of Concrete Research Articles

Benchmarking Standard and Micromechanical Models for Creep and Shrinkage of Concrete Relevant for Nuclear Power Plants.

The creep and shrinkage of concrete play important roles for many nuclear power plant (NPP) and engineering structures. This paper benchmarks the standard and micromechanical models using a revamped and appended Northwestern University database of laboratory creep and shrinkage data with 4663 data sets. The benchmarking takes into account relevant concretes and conditions for NPPs using 781 plausible data sets and 1417 problematic data sets, which cover together 47% of the experimental data sets in the database. The B3, B4, and EC2 models were compared using the coefficient of variation of error (CoV) adjusted for the same significance for short-term and long-term measurements. The B4 model shows the lowest variations for autogenous shrinkage and basic and total creep, while the EC2 model performs slightly better for drying and total shrinkage. In addition, confidence levels at 5, 10, 90, and 95% are quantified in every decade. Two micromechanical models, Vi(CA)2T and SCK CEN, use continuum micromechanics for the mean field homogenization and thermodynamics of the water-pore structure interaction. Validations are carried out for the 28-day Young's modulus of concrete, basic creep compliance, and drying shrinkage of paste and concrete. The Vi(CA)2T model is the second best model for the 28-day Young's modulus and the basic creep problematic data sets. The SCK CEN micromechanical model provides good prediction for drying shrinkage.

Performance of concrete containing pristine graphene-treated recycled concrete aggregates

Upcycling recycled coarse aggregates (RCAs) in concrete is a promising way to decrease the environmental effect of construction and demolition waste and improve concrete sustainability. Pretreatment of RCAs helps to enhance the quality of the resulting concrete and results in an increased level of confidence for material suppliers to systematically use RCAs to replace virgin aggregates for concrete production. This study demonstrates the utilization of pristine graphene for pretreating RCAs with the aim of effectively alleviating the loss of mechanical and durability performance of concretes when compared to virgin aggregate concretes. The RCAs were presoaked in water solution containing graphene concentration ranging from 0 to 0.5 %. Then, 50 % of natural coarse aggregates were replaced with the RCAs for concrete production. Different properties of concrete including slump, axial compression, splitting tension, water absorption and drying shrinkage were measured. In addition, microanalysis of the aggregates was performed by x-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Based on results, treating the RCAs with 0.2 wt% pristine graphene results in increased workability (13 %), compressive strength (21 %) and tensile strength (12 %) and decreased water absorption (22 %) and drying shrinkage (20 %) of the RCA concrete. Increasing the concentration of the graphene beyond 0.2 wt% is found to decrease the workability and strength properties and increase the water absorption and drying shrinkage. This is attributed to the agglomeration of the graphene at high concentrations, leading to non-uniform filling effects and ineffective microcrack and void filling. It is also found that 0.2 wt% is the optimum pristine graphene concentration, which can lead to an RCA concrete with similar mechanical and durability properties to the conventional concrete.

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.

Shrinkage and thermo-mechanical properties of concretes incorporated with different substitutions of natural aggregates by cold bonded calcined attapulgite lightweight aggregates

Calcined attapulgite (CAT), a fibrous calcined clay represents a promising option for advancement as a relatively new cementitious material with strong pozzolanic activity. This study investigates the impact and potential use of CAT in producing cold-bonded lightweight aggregates and their utilization in microsilica (MS) and fly ash (FA) blended concretes by analyzing the shrinkage and thermo-mechanical behavior. Initially, attapulgite rocks were processed including crushing, grinding and calcination to produce pozzolanic material. Following this, a dry powder mix of 80% calcined attapulgite (CAT) and 20% Portland cement (PC) was pelletized into calcined attapulgite lightweight aggregates (CATLWAs) using cold bonding with moisture and cured for 28 days. Subsequently, twelve concrete mixtures were formulated considering different substitutions of normal aggregate with CATLWAs and various proportions of PC, MS and FA. Mechanical properties such as compressive, splitting, and flexural strengths as well as elastic moduli and impact resistance were evaluated. Drying shrinkage, weight loss and thermal conductivity were assessed for all mixtures. Likewise, scanning electron microscopy was employed to analyze microstructural changes. Experimental results indicated that the incorporation of fine and coarse CATLWAs reduced the concrete unit weight by approximately 22% compared to the control mixture. However, there was a declining trend in mechanical properties, especially for impact resistance with increasing CATLWA content. However, the use of binary and ternary blends of cementitious materials improved overall mechanical behavior. Regardless of CATLWA content, the utilization of CATLWA enhanced thermal conductivity up to 46.9%. These findings hold significance for using CATLWAs in sustainable lightweight concrete production, thus advancing lightweight concrete technology and offering valuable insights into their advantages and constraints.

Review on the mechanism and mitigation of cracks in concrete

Cracks and cavities belong to two basic forms of damage to the concrete structure, which may reduce the load-bearing capacity and tightness of the structure and lead to failures and catastrophes in construction structures. One of the most prevalent faults in concrete constructions is cracking, which, if left unchecked, can greatly diminish the longevity of the building. For the past few years, scientists have worked to understand the complex mechanics behind concrete cracking. It has been found that the primary initiators of plastic cracking include surface finishing, capillary action, bleeding, evaporation, and settlement of solid particles. A number of techniques and measurements have been developed to measure the influence of the various processes that result in concrete shrinkage and cracking. Cracking due to shrinkage and plastic segregation are now also referred to as plastic cracking. Numerous cracking prevention techniques have been suggested, such as fogging, using fewer particles, and using fibres. This cutting-edge study updates the significant growth of research on the subject to what is currently considered cutting-edge and state-of-the-art.

Bayesian-based prediction and real-time updating of axial deformation in high-rise buildings during construction

Estimating the axial deformation of concrete vertical members in a structure is challenging due to the shrinkage and creep characteristics of concrete together with the uncertainties involved in the construction process. To address the resulting inaccuracies, this paper presents a novel method that employs Bayesian theory to enhance the predicted results by incorporating measured strain from vertical members and equations for time-varying properties of concrete. The following five uncertain parameters are considered: environmental humidity, concrete strength, load transfer, concrete shrinkage calculation errors, and creep equation errors. The proposed method was experimentally evaluated on a twin tower high-rise building, with results showing that even with limited measured strain information, the uncertainty of the predicted results was significantly reduced and the predicted values were aligned closely with the measured values. The study also analyzed the impact of vertical deformation on the elevation deviation of adjacent wall-column members and the connected parts of the two towers.

Two-Way Time-Dependent Prestress Losses of Prestressed Concrete Containment with Bonded Prestressing Strands

Prestressing plays a pivotal role in ensuring the tightness and integrity of prestressed concrete containment in nuclear power plants. The prestress loss reduces the compressive stress in concrete resulting from the prestressing strands and increases the risk of containment leakage under severe accident conditions. Therefore, the accurate prediction of prestress loss is essential for the design and in-service management of prestressed concrete containment. Unlike one-way beams or girders in building structures and bridges, two-way prestressing systems are used in prestressed concrete containment. In the current simplified method for evaluating time-dependent prestress loss, the interaction of concrete creep in two directions resulting from the two-way prestressing strands and the influence of the steel liner and mild steel rebars in two directions are neglected. In this study, based on the principle of creep superposition, the age-adjusted effective method for the creep estimation of concrete, and considering concrete shrinkage, concrete creep, and the relaxation of prestressing strands, as well as the influence of the steel liner and mild steel rebars in two directions, a sectional analysis is performed for prestressed concrete containment with bonded prestressing strands, and equations for calculating the two-way time-dependent prestress losses are derived. The results of the two-way time-dependent prestress losses predicted by the derived equations are compared with those of tests in the literature, and great agreement is achieved. Finally, a case study is given to show the application of the proposed method for the prediction of prestress loss in prestressed concrete containment in the nuclear power plant.

Experimental evaluation of shrinkage deformations of concrete in tropical climates

Shrinkage of concrete is one of the main reasons affecting damage of structures. Shrinkage is the result of cement hydration, the evaporation of water during concrete hardens. It occurs mainly at the first stage of concrete hardening. Moreover, shrinkage is indirectly influenced by various factors such as environmental conditions, aggregate sizes, structure types, and water-cement ratio. Understanding the environmental factors is the key to accurately predicting shrinkage of concrete. Among environmental factors, wind is known as an important factor that significantly affects shrinkage of concrete. This study designs an experiment that considers the effects of tropical winds on shrinkage of concrete in Nghe An, Vietnam. Additionally, the result of this study is then analyzed and compared with that of published studies in Southeast Asia. Experimental results show that shrinkage in the tropical climate occurs according to existing rules. Moreover, the shrinkage strain develops rapidly at the early stage, and the value of shrinkage quickly reaches an asymptotic value.

The Application of Heat-Shrinkable Fibers and Internal Curing Aggregates in the Field of Crack Resistance of High-Strength Marine Structural Mass Concrete: A Review and Prospects.

High-strength large-volume marine concrete is a critical material required for the construction of large-span sea-crossing bridges. However, the widespread issue of cracking in this concrete type significantly impacts the durability and load-bearing capacity of concrete structures. Dealing with these cracks not only delays construction schedules but also increases project costs. Addressing these pressing technical issues, this project proposes the use of newly developed high-modulus heat-shrinkable fibers (polyethylene terephthalate fiber, also known as PET fiber) from the textile industry. These fibers utilize the heat generated during the hydration of large-volume concrete to trigger its contraction, applying three-dimensional micro-prestressing stress to enhance its crack resistance, while simultaneously incorporating prewetted aggregates with high-performance micro-porous structures and utilizing their internal curing effect to reduce concrete shrinkage. This helps to minimize the loss of micro-prestressing stress caused by concrete shrinkage and creep. This synergistic approach aims to improve the crack resistance of high-strength large-volume marine concrete. By employing modern testing and simulation analysis techniques, this study aims to uncover the mechanism by which the heat-shrinkable fibers exert micro-prestressing stress on concrete and the water release mechanism of internal curing aggregates during the temperature rise and fall stages of large-volume concrete. It seeks to elucidate the cooperative regulation of the microstructure and performance enhancement mechanisms of high-strength large-volume marine concrete by the heat-shrinkable fibers and internal curing aggregates. This research will lead to the development of novel methods for the design and crack control of high-strength large-volume marine concrete, which will be validated through engineering demonstrations. The outcomes of this study will provide theoretical foundations and technical support for the preparation of the crack-resistant large-volume marine concrete used in large-span bridges.

Moisture Diffusion Coefficient of Concrete under Different Conditions

Humidity change in concrete is the leading cause of concrete shrinkage. Moreover, the moisture diffusion coefficient of concrete is an essential parameter for assessing and predicting the internal moisture content of concrete. However, there is a lack of theoretical construction and experimental studies on the effect of different conditions, especially different constraints, on the moisture diffusion coefficient of concrete. Therefore, the internal humidity, pore structure parameters, and basic mechanical properties of concrete under different strength grades C30, C40, C50, and C60 (C stands for concrete and numbers indicate the strength class of the concrete), curing environments (dry and sealed curing conditions), and constraints were tested in this study. In addition, a calculation model of concrete’s internal humidity and humidity diffusion coefficient was established. The research findings show that the internal humidity of concrete decreased with age due to hydration and drying. External humidity had a significant effect on the moisture change of concrete, and the lower the external humidity, the larger the humidity diffusion coefficient and the faster the internal humidity of concrete decreases. Reinforcement (confinement) changes the pore structure parameters of the concrete, which in turn affects the transport of moisture within the concrete. The higher the reinforcement rate, the larger the pore structure parameters of the concrete, the larger the humidity diffusion coefficient, and the faster the concrete humidity decreases. The method proposed in the study can accurately predict the internal humidity of concrete using the humidity diffusion coefficient. The research results are a reference for preventing concrete shrinkage and cracking in construction.

Effect of different expansive agents on the early age structural build-up process of cement paste

CaO-based expansive agent (CEA) and MgO-based expansive agent (MEA) are commonly used expansive agents to control the shrinkage of concrete. Understanding the effect of CEA and MEA on the structural build-up of cement paste is of significance to their application in 3D printing concrete. This study investigates the effect of CEA and MEA on the structural build-up process of cement paste within 120 min. The calorimetric, 1H low-field nuclear magnetic resonance and ion concentration tests were carried out to explore the intrinsic mechanism. The findings suggest that CEA significantly accelerates structural build-up rate by elevating the ionic strength in solution and facilitating cement hydration. The addition of 1%, 3% and 5% CEA increases the 120-min static yield stress of cement paste by 40.6%, 66.8% and 132.9%, respectively. MEA increases the initial static yield stress by decreasing the interparticle distance through its great specific surface area and intensifying interparticle interactions, and the addition of 1%, 3% and 5% MEA increases the initial static yield stress of cement paste by 22.5%, 35.3% and 66.5%, respectively. However, the delaying impact of MEA on hydration offsets its improvement of interparticle interaction, leading to an insignificant impact on the static yield stress evolution. The combination of CEA and MEA takes advantage of their respective benefits in promoting hydration and flocculation, which increases the structural build-up rate while increasing the initial static yield stress of the paste. This study can provide guidance for the rheological controlling of 3D printing concrete containing expansive agent.

Shrinkage prediction model of high strength lightweight aggregate concrete based on relative humidity

Concrete shrinkage affects the overall stability and long-term service performance of the structures. Lightweight aggregates (LWAs) with a porous structure are an ideal internal curing material to mitigate concrete shrinkage. Nevertheless, the low elastic modulus of LWAs has a negative impact on concrete shrinkage. In order to clarify the influences of LWAs in the high strength lightweight aggregate concrete (HSLC) on its shrinkage performance, the compressive strength, internal relative humidity (IRH), elastic modulus, and autogenous shrinkage (AS) of HSLC were analyzed experimentally in this study. The correlation of these parameters was investigated. As indicated by the results, compressive strength and elastic modulus were negatively related to the content of LWAs. The 28-day AS and IRH of HSLC and the critical moment of IRH increased by 3.9%, 20.2% and 36 h, respectively, when the content of LWAs increased from 0% to 100%. A linear relationship between AS and compressive strength and an exponential relationship between AS and IRH were established. Additionally, a shrinkage prediction model considering IRH of concrete and water absorption by LWAs was proposed for HSLC.

Structural Assessment of a Post‐Tensioned Box Girder Bridge affected by Concrete Creep

AbstractThe behavior of post‐tensioned concrete bridges is often influenced by time‐dependent phenomena, such as relaxation of prestressing steel, creep and shrinkage of concrete. For bridges built using the balanced cantilever method, the evolution of time‐dependent phenomena during the construction phase must be carefully considered. In common practice, the assessment of the structural safety of this bridge typology is a complex task due to the numerous factors and uncertainties involved in the evaluation process. Numerical models can be adopted to perform structural analyses at successive phases over bridges' lifetime, while destructive and non‐destructive evaluation methods are used to gather information to ensure that the numerical model matches the actual behavior of the bridge. In this context, this paper presents the structural behavior assessment of a multi‐span post‐tensioned box girder bridge with vertically prestressed internal joints. A numerical model was constructed to investigate on the effect of creep and construction phases on the actual stress/strain conditions of the bridge. To reduce model‐based uncertainties, compression tests were carried out on concrete cores extracted from the structure and the results of static load tests were used for model validation purposes.

Long-Term Creep and Shrinkage of Alkali-Activated Concrete Incorporating Fly Ash and Rice Husk Ash

Long-Term Creep and Shrinkage of Alkali-Activated Concrete Incorporating Fly Ash and Rice Husk Ash

A Simplified Mesoscale Approach for the Prediction of Drying Shrinkage of Concrete

A Simplified Mesoscale Approach for the Prediction of Drying Shrinkage of Concrete

Shear transfer at the steel‐concrete interface using different mechanical connectors

AbstractThe present article is dealing with an assessment of the longitudinal shear at the steel‐concrete interface using several types of mechanical connections. Experimental and numerical tests have been performed to understand better the short and long‐term effects of the influence of the newly defined connectors.Experimental tests consisted of 12‐column push‐out tests (CoPOT). In the test campaign, four types of surface finishing have been tested: i) reference tests (0v2) without any mechanical shear connectors, (ii) angled, V‐shaped, variant of the novel flat shear connector (Av2), (iii) transversal variant of the novel flat shear connector (Bv2) and (iv) multiple ribs on the flanges having a height of 0.7mm (Cv2). Three specimens for each configuration were tested in short‐term loading. The loading procedure defined in EN1994‐1‐1:2004 Annex B was applied for all the tests. Also, one of each specimen was tested in long‐term loading to observe the effect of concrete shrinkage on the quality of bond performance. No significant differences in behavior were observed between both load sequences and the test results after shrinkage is within the short‐term tests’ margin of variation. Numerical simulations performed using FE software Abaqus®, while applying a simplified definition of the bond, supported the results of the previous investigation.

Early Shrinkage Modeling of Complex Internally Confined Concrete Based on Capillary Tension Theory

This paper evaluates the shrinkage performance of concrete under complex internal constraint environments comprising steel plates, studs, and reinforcement to investigate their respective influence laws on the shrinkage performance of concrete. An early shrinkage model of concrete under complex internal constraints was established based on the theory of capillary tension, and the effects of steel plate, nails, and steel reinforcement on the shrinkage performance of concrete were theoretically analyzed. Six sets of concrete-constrained shrinkage tests and pore structure tests were then performed under different internal constraint conditions with the steel plate thickness, reinforcement diameter, and stud-related parameters (stud diameter, height, and spacing) as research variables. The test results demonstrate that the pore structure of concrete increases with the increase in the constraint coefficient, and that the increase in the pore structure will cause a decrease in the capillary pore stress, which is the driving force of concrete shrinkage. Its decrease will inevitably lead to a decrease in concrete shrinkage. By comparing the calculated values of the shrinkage model with the measured values, it is found that the average value of the prediction error is less than 15%, which reveals that the predicted values of shrinkage are in good agreement with the measured values and proves that the model can effectively predict the shrinkage of concrete that is restrained by steel plates, pins, and reinforcing bars.

Compressive behaviour of circular steel tube confined reinforced concrete (STCRC) columns considering shrinkage and creep

Thin-walled steel tube confined reinforced concrete (STCRC) columns are increasingly used in high-rise and heavily loaded structures. One concern is whether concrete shrinkage affects the load resistance of STCRC columns, as the confinement to the concrete may become less effective when the concrete shrinks. This paper presents ultimate tests on STCRC columns after subjected to 490-day-sustained-loading or 490-day-shrinkage. The compression tests are conducted on specimens with different steel ratios, reinforcement ratios, concrete strengths and steel-concrete interfacial bonding conditions, or with long-term load first applied at different concrete ages. The sustained load history and the shrinkage effects on the short-term axial stiffness, ultimate strength, and peak strain of STCRC columns are investigated. The development of confinement effects and the tube's axial stiffness contribution after shrinkage and creep history are compared against those test results without experiencing shrinkage or long-term load history. A non-linear finite element model is finally developed for the ultimate response prediction of STCRC columns with the consideration of the creep and shrinkage history, and its accuracy is compared against the test data. The results show that concrete shrinkage and creep significantly affect the occurrence and development of the confinement effects, but not the confining pressure at the peak load. The axial stiffness and peak strain of STCRC columns are sensitive to time effects, while the ultimate strength is not. Under service loading, the tube's contribution to the axial stiffness of STCRC columns is negligible due to concrete shrinkage, while at the ultimate strength limit state condition, the column compression resistance is barely influenced by shrinkage and creep effects. The proposed FE model achieves reasonable accuracy in evaluating the ultimate responses of STCRC columns considering the shrinkage and creep effects.

The combined effect of steel fiber and MgO on the deformation and mechanical properties of high-strength concrete

Shrinkage cracking of concrete is one of the main problems affecting the durability of high-strength concrete. One of the main measures to solve this problem is to use expansion agents to compensate for the shrinkage of concrete. But on the other hand, excess expansion, while compensating for shrinkage, is likely to have a detrimental effect on mechanical properties of concrete. Especially for bridge decks and airport pavement with high requirements for impact resistance, toughness, and crack resistance, the use of expansion agents alone cannot meet the performance requirements. In this study, the mechanical properties and autogenous shrinkage of concrete were studied when MgO expansion agent (MEA) and steel fiber were used simultaneously. The results showed that the expansion produced by MEA increased the porosity while compensating for the shrinkage of concrete. Compared with plain concrete, the porosity increased by 4.4% when MEA was incorporated alone. After MEA and steel fiber were used simultaneously, the steel fiber constrained the expansion of MEA through the adhesive friction between fiber and matrix, which made the interface transition zone (ITZ) between cement paste and fiber densified. In this way, the shrinkage of concrete was avoided without reducing the mechanical properties. Especially when 8% MEA and 1% steel fiber were used simultaneously, the compressive strength and splitting tensile strength of concrete were increased by 20.6% and 65.0% respectively, and the porosity was decreased by 20.9%. The expansion of concrete at 410d when used simultaneously was 371 × 10−6, which was 20.7% lower than that of MEA alone, avoiding the possible adverse effects of excessive expansion of MEA. The research results have guiding significance for improving the crack resistance and impact resistance of concrete.

Effect of fly ash on early-age properties and viscoelastic behaviors of supersulfated cement concrete under different degrees of restraint

This paper aimed to study the early-age properties and viscoelastic behaviors of supersulfated cement (SSC) concrete with different replacement ratios (15%, 30%, and 50%) of fly ash (FA). Ordinary Portland cement (OPC) concrete was also designed for reference. Mechanical properties and free shrinkage were tested. Stress relaxation and creep as the significant viscoelastic behaviors were investigated in restrained ring test with different degrees of restraint. The results showed that later mechanical properties of SSC concrete approached or exceeded that of OPC concrete while replacement of FA caused a significant reduction. The workability of SSC concrete was improved with FA replacement. Free shrinkage was mitigated by FA due to the significant reduction on autogenous shrinkage of SSC concrete. At a high degree of restraint, SSC concrete with a FA replacement ratio of 50% exhibited a high cracking resistance. At a relatively low degree of restraint, cracking potential was reduced by FA replacement due to its significant mitigation on shrinkages. Relaxed stress of SSC concrete decreased with an increase on FA replacement ratio. The nonlinear relationship between relaxation and creep coefficients of SSC concrete was established regardless of FA replacement ratios and degrees of restraint, which was different from OPC concrete. The results obtained in this paper might promote the reliable applications of SSC concrete in the future.