Shrinkage Of Concrete Research Articles

Experimental Study On Self-Compacting Concrete Mix Design By Using Yucca Zeolite

This report aims to present the experimental investigation on mix proportioning of normal concrete and self-compacting concrete with yucca zeolite. The study area comprises of ordinary portland cement of grade 53,mix proportioning of normal concrete for grade of concrete M40, M30 and M20 whereas mix proportioning for self-compacting concrete for grade of concrete M40, M30 ,M20.The parameters considered are cement content, Water cement ratio i.e. for normal concrete 0.4, 0.42, 0.45 and for self-compacting concrete 0.62, 0.44, 0.43 respectively. To reduce the risk of shrinkage, frost attack and corrosion of concrete, yucca zeolite as a mineral admixture and to increase the bond strength techno plast S 300 as a super plasticizer is added. The responses of material testing, normal concrete tests that includes slump flow test and compressive strength test recorded. Also, tests on self-compacting concrete recorded from slump flow test, J ring test, V funnel test, L box test, U box test, Rheological parameters, Compressive strength at 7 and 28 days. The various properties of SCC are ascertained with the IS code 1199:2018 [part 6] IS code 456:2000, IS code 10262:2019.

Effects of superabsorbent polymer and natural zeolite on shrinkage, mechanical properties, and porosity in ultra-high performance concretes

The low water-to-binder ratio of ultra-high performance concrete (UHPC) often causes shrinkage and cracking due to early-age self-desiccation. This leads to significant initial dimensional instability, which may compromise structural integrity. As a promising solution, internal curing agents such as superabsorbent polymers (SAP) and natural zeolite have the potential to mitigate shrinkage and achieve self-stressing properties. This research aims to provide a comprehensive comparison between SAP and zeolite's effects within a consistent UHPC formulation. Six UHPC mixtures (including the reference mixture) were designed: three with SAP dosages of 0.2%, 0.4%, and 0.6% by cement mass, and two with zeolite replacing silica fume at 25% and 50% by mass. Various testing methods, including autogenous and drying shrinkage assessment, heat of hydration and thermogravimetric analysis, compressive strength evaluation, mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), were employed to assess the mixtures at different stages of curing. The result reveals that the incorporation of SAP and zeolite in the mixtures significantly reduces UHPC's early-age autogenous shrinkage. Moreover, SAP and zeolite additions impact mechanical properties, demonstrating that a balance between shrinkage control and compressive strength can be reached, through an optimization of the additions to achieve the desired performance. Microstructural analysis through MIP and NMR reveals increased overall porosity of the UHPC with SAP and zeolite, suggesting that low-field NMR can be a valuable tool for complementing conventional test methods. The outcome of this study provided valuable insights into optimizing the balance between durability and mechanical performance, paving the way for more sustainable and cost-effective applications of UHPC in modern construction practices.

A Study on a New Method for Simultaneous Internal Curing and hydrophobic in Concrete

The high hydrophilicity and permeability of concrete caused by many pores and hydroxyl groups produced by cement hydration are the main factors leading to dry shrinkage, cracking, and poor corrosion resistance of concrete. Giving concrete internal curing and hydrophobicity is an effective measure to solve the above problems. In this paper, a new idea and preparation method for an organic combination of hydrophilic and hydrophobic materials are proposed to improve the service life of concrete structures. Furthermore, the combined effects of hydrophilic and hydrophobic amphoteric materials (HAM) on the mechanical properties, internal curing properties, and hydrophobic properties of concrete were comprehensively investigated. In addition, the physical and chemical action mechanisms were analyzed in conjunction with microscopic tests. The results indicated that HAM rapidly released water within 3-7 days before concrete curing, and then slowly released water accompanied by the release of hydrophobic materials, gradually from hydrophilic to hydrophobic properties; The addition of HAM did not reduce the mechanical properties of concrete, which solved the problem of low compressive strength of integral hydrophobic concrete; The addition of HAM reduced the drying shrinkage of concrete by 154.12%, increased the contact angle to 96°, and decreased the water absorption rate by 36%, allowing the concrete to achieve better internal curing and a hydrophobic effect. The preparation of this material can open up a new way to solve the hydrophilic and hydrophobic properties required by concrete at the same time, and fill the gap that concrete can not balance hydrophilic and hydrophobic properties.

ANN-Powered Models for Predicting Shrinkage and Creep Properties of High-Performance Concrete Using Supplementary Cementitious Materials

ANN-Powered Models for Predicting Shrinkage and Creep Properties of High-Performance Concrete Using Supplementary Cementitious Materials

Optimization design of ultra-fine supplementary cementitious materials ultra-high performance concrete mix proportion based on orthogonal experiment

Traditional ultra-high performance concrete has problems such as high viscosity, high early-age autogenous shrinkage, and high heat release during early hydration. In recent years, with the development of ultra-fine grinding technology, ultra-fine supplementary cementitious materials (USCMs) have received widespread attention, which have higher pozzolanic activity than traditional supplementary cementitious materials. This study investigated the effects of water-binder ratio, silica fume content, and ultra-fine supplementary cementitious materials (USCMs) content on the workability, mechanical properties, and early-age autogenous shrinkage of ultra-high performance concrete (UHPC) based on orthogonal experiments. In orthogonal experiments, multiple factors and levels were introduced, and a combination of range analysis, variance analysis, and multi-factor interaction analysis were combined to determine the optimization level range of each factor. The results showed that the water-binder ratio had the greatest impact on the fluidity, compressive strength, and autogenous shrinkage of UHPC; The content of silica fume had the greatest impact on the flexural strength of UHPC. Compared with the control group, USCMs can significantly improve the workability and rheological properties of UHPC, reduce early hydration heat release, and inhibit the autogenous shrinkage of UHPC.

Research on humidity field and freezing resistance of green recycled ceramic internal cured concrete at early age

In cold and drought environment, concrete shrinkage cracking caused by water loss is serious, and thus the freezing resistance of concrete is deteriorated. The waste ceramic particles were used as internal curing materials to prepare concrete, based on this background. Then, the influence of internal curing with ceramic particles on humidity field and temperature of concrete is analyzed by using temperature and humidity sensor. Based on the change mechanism of the internal humidity of concrete, the relationship between the curvature radius of liquid surface and the relative humidity is revealed. Taking water loss and water loss rate as the index, the water transfer law of concrete surface under ceramic particle internal curing was defined. Through the drying shrinkage test, the mechanism of improving the drying shrinkage of concrete by internal curing in ceramic particles was mastered. Finally, the effects of ceramic internal curing on cement hydration, interfacial transition zone (ITZ) and freezing resistance of concrete were studied. The results show that the relative humidity, water loss and water loss rate of concrete increase with the increase of ceramic particle content, and the dry shrinkage value decreases with the increase of ceramic particle content. Compared with ordinary concrete, when the ceramic particle content is 10%, 15%, 20%, 25% and 30%, and the test period is 10 days, the internal relative humidity of concrete increases by 0.52%, 0.67%, 1.55%, 2.55% and 3.05%, respectively. The drying shrinkage values decreased by 3.42%, 7.69%, 10.26%, 15.17% and 30.13%, respectively. When the test period was 1032 hours, the water loss increased by 1.08%, 5.15%, 7.90%, 12.69% and 14.49%, respectively. Furthermore, when the ceramic particle content is 20%, the initial normalized heat flow of concrete increases by 2.74 mW/g, and the normalized heat flow minimum increases by 0.324 mW/g. The minimum ITZ microhardness increased by 2.64 MPa, the ITZ width decreased by 5 μm, and the maximum crack width at the contact between ITZ and aggregate decreased by 0.89 μm. At the same time, when the ceramic particle content is less than 20%, the effect of internal curing on the freezing resistance of concrete increases with an increase in ceramic particle content.

Analysis of the Impact and Mechanism of Polyacrylate-Based Composite Paste on the Performance of Recycled Aggregate.

This study developed three composite slurries for coating recycled aggregate by incorporating polyacrylate emulsion, fly ash, and gypsum into a cement-based mixture. The filling and pozzolanic effects of fly ash help to improve microcracks in the recycled aggregates. The polyacrylate emulsion forms a strong bonding layer between the cement matrix and the aggregates, enhancing the interfacial bond strength. Based on relevant studies, the following mix designs were developed: Slurry 1 consists of pure cement paste; Slurry 2 contains 15% fly ash and 3% gypsum added to the cement paste; Slurry 3 adds 22% polyacrylate emulsion to the slurry. The study first compared the effects of the three composite slurries on the crushing value and water absorption of recycled aggregates, and then analyzed their impact on the mechanical properties, permeability, and drying shrinkage of concrete. Finally, the mechanisms behind the enhancement were investigated using the Vickers Hardness Test (HV), Mercury Intrusion Porosimetry (MIP), and scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS). The results showed that the polyacrylate emulsion composite slurry had the most significant improvement effect. For recycled aggregate AL, the crushing value decreased from 28.8% to 22.5% and the saturated surface-dry water absorption decreased from 15.1% to 13.8% after cement slurry modification. After coating with the composite slurry, the crushing value further dropped to 18.2% and the water absorption to 9.5%. Two aspects of the performance of recycled aggregates are enhanced with the polymer composite slurry: first, fly ash provides nucleation sites for CH, reducing the tendency for directional CH alignment. Second, the long chains of PAE (polyacrylic ester) encapsulate cementitious particles, effectively filling surface defects on the recycled aggregates, improving the bonding strength at the new-to-old interface, and significantly enhancing the performance of both recycled aggregates and recycled concrete.

Effects of thermal cycles and time-dependent behavior of the deck on steel network arch bridges

Network arches are a type of arch bridges with inclined hangers, in which some hangers cross each other at least twice. This paper aims to evaluate the effects of thermal fluctuations and volumetric changes of the concrete deck on steel network arches. Fifty-nine variants of a reference network arch bridge were developed, assuming identical arch geometries but varying hanger arrangements. Each bridge was modeled using the finite element method and subjected to heat flux due to solar radiation and changes in ambient temperature in addition to heat transfer via conduction, convection, and radiation. The time-dependent deformations of the concrete deck were implemented using a rate-type formulation. Results obtained during a one-year period after the assumed end of construction showed that stress changes in the arch bridge due to ambient and time-dependent effects were not very sensitive to the hanger layout. Neglecting concrete creep and shrinkage was found to cause a 15-20% underestimation of maximum stresses in the concrete deck, whereas a 40-60% error was observed in both the deck and rib when thermal effects were ignored. The radial arrangement of hangers, already known to perform favorably under live loads, was also found to provide the smallest bending moments and the fewest number of relaxed hangers due to thermal and time-dependent effects.

Compensating for Concrete Shrinkage with High-Calcium Fly Ash

Shrinkage of concrete during hardening is a serious problem in attempts to maintain the integrity of concrete structures. One of the methods of combating shrinkage is compensating for it using an expansive agent. The purpose of this work is to develop and study an expanding agent to concrete, including high-calcium fly ash and calcium nitrate as an expansion activator. The content of Ca(NO3)2 can be used to regulate the degree of expansion of the additive itself during hydration and, accordingly, to control shrinkage, thus obtaining shrinkage-free or expanding concrete. Shrinkage–expansion deformations of concrete can also be regulated by the amount of expanding additive replacing part of the cement. With the Ca(NO3)2 content of fly ash being 10% or more, concrete experiences expansion in the initial stages of hardening. The transition of deformation through 0 to the shrinkage region occurs depending on the composition and content of the additive after 8–15 days of hardening. It has been established that replacing cement with pure fly ash with a curing period of 90 days or more has virtually no effect on the strength of concrete, either in bending or in compression. The use of an expanding additive containing 5–15% Ca(NO3)2 reduces the strength of concrete by an average of 9%, despite the fact that calcium nitrate is a hardening accelerator.

Investigation of functionalized graphene oxide incorporated superabsorbent polymers for enhanced durability, hydration, microstructure and mechanical strength of modified concrete

ABSTRACT This study focuses on enhancing cementitious materials by incorporating silanized graphene oxide (SGO) and superabsorbent polymers (SAPs), aiming to improve their mechanical and durability properties. The primary goal is to evaluate the effects of SGO/SAP composites on the hydration, absorption, shrinkage, and overall performance of concrete. The composites were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) to understand their microstructure. Mechanical and durability tests revealed that adding SGO/SAP composites significantly increased the mechanical strength and water absorption capabilities of the concrete. The compressive strength, split tensile strength, and flexural strength of the SGO/SAP-modified concrete were measured at 57 MPa, 4.90 MPa, and 8.25 MPa, respectively. Shrinkage tests demonstrated the composite hydrogel’s excellent water-holding capacity at 0.3 wt.% SGO/SAP, facilitating internal curing in concrete structures. FE-SEM analysis indicated a reduction in microcracks due to the presence of SGO/SAP. The improvements are attributed to the synergistic effects of SGO and SAP, which enhance water retention, dispersion, and interfacial bonding within the cementitious matrix. The microstructural studies confirmed the exceptional stability of the SGO/SAP-modified mix, emphasizing its potential as an additive to improve concrete properties. This research underscores the significant potential of SGO and SAP in advancing the performance of cement-based materials, highlighting their applicability in infrastructure development and construction for creating more durable and high-performing concrete structures.

Mechanical and autogenous shrinkage properties of coarse aggregate ultra-high performance concrete (CA-UHPC): The effect of mineral admixtures

To reduce the shrinkage and explore the best content of mineral admixtures of coarse aggregate ultra-high performance concrete (CA-UHPC), this study conducted 12 groups of autogenous shrinkage, basic material properties (compressive strength, tensile strength, and flowability), and X-ray diffraction experiments on CA-UHPC with coarse aggregate and different amounts of mineral admixtures (slag powder, limestone powder). The effects of coarse aggregate and mineral admixtures on the autogenous shrinkage and basic material properties of CA-UHPC were analyzed, and the measured values of CA-UHPC autogenous shrinkage strain were compared with the theoretical values calculated by six commonly used concrete shrinkage prediction models. The experimental results show that under the condition of 15 % coarse aggregate content and no steam curing, a CA-UHPC with a compressive strength greater than 110 MPa, a tensile strength greater than 11 MPa, a flowability greater than 290 mm, and an autogenous shrinkage of less than 700 after 120d can be obtained. The mineral admixture has a significant impact on the fundamental properties of CA-UHPC. The compressive strength, tensile strength, and flowability of CA-UHPC with 15 % limestone powder and 15 % S95 slag powder increased by 6.6 %, 5.4 %, and 27.6 % compared to UHPC with only coarse aggregate added, and the autogenous shrinkage after 120 days decreased by 10.5 %. However, when the dosage of limestone powder and S95 slag powder exceeds 30 %, the tensile and compressive strength of CA-UHPC will rapidly decrease. This study also revised the GL 2000 shrinkage prediction model based on the CA-UHPC autogenous shrinkage test results, introduced the influence coefficient of mineral admixture content on autogenous shrinkage strain, and established a theoretical calculation model suitable for CA-UHPC autogenous shrinkage strain.

Методы прогнозирования долгосрочного поведения преднапряженных железобетонных мостов

Purpose: to analyze the causes of long-term deformations of prestressed concrete bridge spans and the problems associated with their prediction. To provide a brief overview of existing methods for predicting the long-term behavior of prestressed concrete bridges. The relevance of the problem is due to the need to ensure the reliability and durability of these structures, which are widely used in modern bridge construction. The objective of this paper is to identify factors that influence the development of long-term deformations and to develop approaches for their accurate prediction. Methods: the study examines the long-term deformations of prestressed concrete bridge spans and the problems associated with their prediction using existing bridge structures as examples. Existing methods for predicting long-term deformations in prestressed concrete are evaluated. In particular, the effects of high-strength reinforcement relaxation and the effects of concrete creep and shrinkage are analyzed. Results: accurate prediction of long-term deformations is a complex task that requires consideration of many factors, such as prestress losses, environmental conditions, material properties, and structural characteristics of bridges. The methods discussed in this paper, including the multiplier method and the approximate time interval method, demonstrate their effectiveness in evaluating long-term deformations. However, further research is needed to improve the prediction methods and increase the efficiency of prestressed concrete bridge design. Practical significance: provides design engineers with specific methods and approaches for evaluating the long-term behavior of prestressed concrete bridges. Application of these methods can reduce the risk of excessive deformations and deflections, ultimately ensuring the safety and reliability of bridge structures.

Mesoscopic simulation of concrete drying shrinkage with hydration kinetics

Shrinkage-induced cracking significantly impacts the durability of mass concrete structures. Quantitatively evaluating drying shrinkage of concrete proves challenging due to the time-consuming experiments and overlooked microstructure changes during the hydration process. To address this concern, this study initially characterized the long-term hydration products and microstructure of low-heat Portland cement (LHPC) through microstructural experiments. Subsequently, a novel high-resolution mesoscale framework is developed to investigate the drying shrinkage with hydration kinetics. High-resolution models consist of realistic-shaped aggregates are validated by the aggregate morphology and gradation parameters of core sample from mass concrete. Concurrently, the quantitative effects of internal and external factors on LHPC drying shrinkage are explored. Results indicated that LHPC possesses a denser microstructure, lower porosity, higher carbonation resistance, and 20% lower drying shrinkage compared to moderate-heat Portland cement, suggesting promising applications. Furthermore, experimental and computational findings suggested that increasing aggregate volume, controlling aggregate morphology, and adjusting curing time and humidity could be employed to reduce and manage drying shrinkage, ensuring concrete structure durability.

New insights into the evolution mechanism of mechanical and shrinkage properties of UHPC under sustained sub-elevated temperatures

In this paper, the mechanical properties, damage pattern, mass loss, and drying shrinkage of ultra-high performance concrete (UHPC) under sustained sub-elevated temperatures (60 ℃-200 ℃) are studied. The effect of UHPC mixture, temperature levels and durations are analyzed. The performance evolution mechanism is revealed based on the analysis of hydration products and microstructures. Results show that at 150 ℃, the water loss of C-S-H gel is continuous (>90d). After sustained action at 100 ℃-200 ℃ for 3d or 7d, UHPC shows obvious expansion, which is attributed to the interlayer water evaporation of gel phase causing spacing between the gel sheets. At 60 ℃ and 100 ℃, the strength incresear and the mean chain length (MCL) decrease are associated with the increase in the SiO4 tetrahedron production in the C-S-H gel phase. At 150 °C and 200 °C, the increase of C-S-H gel’s MCL, gel phase stiffening, and pore structure refinement are important reasons for the increase in compressive strength of UHPC.

A time-series deep learning model for predicting concrete shrinkage and creep verified with in-situ and laboratory test data

This paper proposed a time series prediction method for concrete shrinkage and creep based on deep learning and the accuracy of the method was verified by field tests. Based on the experiment data in the Northwestern University (NU database), a deep learning model considering the material, environment, and history was constructed by integrating Gated Recurrent Units and Self-Attention mechanism (GSA model). To validated the model, short-term indoor and outdoor field tests of concrete shrinkage and creep were conducted. The proposed GSA model outperformed the LSTM model for both creep and shrinkage predictions. Moreover, the comparison between the GSA model prediction and the outdoor test data indicated that the model can accurately capture the real-time outdoor temperature and humidity variation through historical data. To predict the ten-year shrinkage and creep of concrete, a recursive multi-step method was proposed to extrapolate the short-term predictions of the GSA model. The effectiveness of the recursive multi-step method was validated against the long-term test data in the NU database. Overall, the proposed GSA model demonstrated high accuracy in both short-term and long-term predictions.

Effect of GGBFS on the mechanical properties of metakaolin-based self-compacting geopolymer concrete

The focus of this study is the production and testing of a new self-compacting geopolymer concrete（SCGC）. The concrete has excellent self-compacting properties, mechanical properties and environmental advantages, showing great potential for engineering applications. Due to the high specific surface area of metakaolin (MK), it is challenging to produce a self-compacting geopolymer concrete using metakaolin as the main material. A self-compacting geopolymer concrete with excellent properties was produced by partially replacing metakaolin with ground granulated blast furnace slag (GGBFS). This innovation enriches the diversity of powder material choices for self-compacting geopolymer concrete. The experimental results showed that the addition of ground granulated blast furnace slag significantly enhanced the filling capacity and interstitial passage capacity and wet packing density of ground granulated self-compacting concrete. The best working performance of the concrete was achieved at 40 % GGBFS replacement. The test data were slump extension of 749 mm, T50 time of 3.23 s, V-funnel test time of 8.2 s, L-box test result of 0.96, and wet packing density of 1.946 g/cm3. With the increase in the replacement rate of the ground granulated blast furnace slag, the compressive strength of self-compacting ground polymer concrete and the split tensile strength showed a trend of increasing and then decreasing. The maximum compressive strength of 55.2 MPa and splitting tensile strength of 4.11 MPa were obtained when the substitution rate of ground granulated blast furnace slag was 20 %. The drying shrinkage of self-compacted geopolymer concrete was significantly increased by the addition of excess ground granulated blast furnace slag. The drying shrinkage was increased by 147 % at 40 % substitution rate compared to 0 % substitution rate. Scanning electron microscope (SEM) tests and thermogravimetric analysis were performed on all samples. At ground granulated blast furnace slag substitution rate of 20 %, a uniform and dense gel structure was formed inside. At 40 % ground granulated blast furnace slag substitution rate, the weight loss of the specimens reached 13.4 %, which was 4.22 % more than the control group with 0 % substitution rate. The results showed that GGBFS effectively promoted the generation of internal cementitious structures in SCGC. This study provides the necessary information for the development of metakaolin-based self-compacting geopolymer concrete and contributes to the popularization of metakaolin-based self-compacting geopolymer concrete. It will also broaden the scope of use of metakaolin in self-compacting geopolymer concrete, which will contribute to the diversification of building materials and the development of the construction industry towards a low-carbon and sustainable future.

Numerical investigation into the influence of interfacial transition zone on elastic modulus, creep, shrinkage of concrete

Interfacial transition zone (ITZ) is a weak part around aggregate in concrete, which could threaten the macroscopic properties of concrete such as strength, stiffness, deformation, and durability. However, it is difficult to quantify the ITZ effect on the macroscopic behavior of concrete only by experimental methods due to the tiny thickness of ITZ. This study employed finite element (FE) method to investigate the ITZ effect on the elastic modulus, creep, and shrinkage. A mesoscale three-phase FE model consisting of homogeneous matrix phase, aggregates and ITZ around them was developed for concrete in this study. The influences of the FE model dimension and the meshing size on the calculated results were first discussed. Then the influence of the thickness, viscoelasticity and shrinkage of ITZ on the macroscopic properties of concrete were evaluated based on the FE calculation and grey relation analysis. Finally, the measured elastic modulus, creep and shrinkage of concrete with different contents of clay on coarse aggregates were used to validate the FE model. It is found that the calculated results of the two-dimensional (2D) FE model are in good agreement with those of the three-dimensional (3D) FE model under the linear viscoelastic assumption. The meshing size has a minor effect on the calculated results when it is 0.2–2 times of the ITZ thickness. The influence of ITZ properties on the macroscopic properties of concrete will become more significant as the ITZ thickness increases. Moreover, the elastic modulus of ITZ has a greater impact on the effective properties of concrete than the thickness, creep, and shrinkage of ITZ. The findings in study can contribute to a better understanding of ITZ effect on the macroscopic properties of concrete and provide references to the reasonable consideration of ITZ in numerical studies.

Enhancing the mechanical and thermal properties of foam concrete by incorporating glass lightweight microspheres

The inferior mechanical strength and thermal resistance of foam concrete limited its application in thermal insulation engineering. This study focused on enhancing the mechanical strength and thermal resistance of foam concrete by incorporating glass lightweight microspheres (GLM) to partially replace foam. The roles of GLM in foam concrete were investigated through physical, mechanical, and thermal properties tests. The improvement mechanism behind the mechanical strength and thermal resistance was further revealed. Results indicated that the addition of GLM enhanced mechanical strength of foam concrete by promoting hydration reaction, optimizing pore structure, and improving GLM-paste interfaces. The mechanical strength of foam concrete with 20 % GLM increased by about 40 %. Moreover, GLM improved the residual compressive strength after exposure to 800°C, with an enhancement of 39.8 %. The inclusion of GLM reduced the risks of crack formation, densified the paste, and strengthened the foam wall due to its hollow structure, pozzolanic reactivity, melting and filling effects, and the phase transformation of additional C-S-H into well-packed wollastonite. Additionally, GLM with closed and isolated pores reduced the drying shrinkage and water absorption rate of foam concrete. The finding suggests that incorporating an appropriate amount of GLM can produce high-strength, low-density, and thermal-resistant foam concrete.

Shrinkage evolution and mechanism of self-curing concrete cooperatively cured with superabsorbent polymers and waterborne epoxy coatings

Shrinkage-induced cracking is a common phenomenon in concrete structures. To reduce concrete shrinkage, herein, a novel curing approach involving the concurrent application of internal superabsorbent polymers (SAPs) and external waterborne epoxy coatings (WECs) was adopted. Subsequently, the combined effects of the SAPs and WECs on the internal temperature, water retention behavior, relative humidity, and shrinkage performance of concrete were investigated. Furthermore, their underlying shrinkage-mitigation mechanisms were clarified and verified through mercury intrusion porosimetry tests. Results revealed that increasing the WEC application rates and number of spraying turns increased the relative humidities and reduced the shrinkage strains of the concrete specimens. The combined use of SAPs and WECs led to considerable reductions in the specimens’ humidity drop, water loss, and shrinkage values. The water losses of the concrete specimens exerted more considerable impacts on their relative humidity and shrinkage compared to their cumulative temperatures. Furthermore, the combination effects of the SAPs and WECs reduced the median pore diameters and increased the fractal dimensions of gel pores, thus triggered a reduce in capillary tension, and further mitigated the development of shrinkage strains. Overall, this study underscores the critical roles of evaporation, temperature, relative humidity, and pore-structure parameters on the shrinkage behavior of concrete. Additionally, it highlights the effectiveness of the combined application of SAP-based internal curing and WEC-based external curing, offering a feasible approach and technical support for reducing shrinkage in concrete structures.

Numerical model for time-dependent cracking and deflection of large-span concrete bridge structures

A new computational framework is proposed to analyse the simultaneous occurrence of multiple physical processes affecting the long-term behavior of large-scale concrete structures. Relying on the additivity of small strain, the framework comprehensively takes the nonlinearity of concrete creep, cyclic creep induced by traffic load, concrete shrinkage, concrete cracking, normal-strength steel rebars and prestressing strands relaxation into account, and other physical processes are further imagined. The algorithm is implemented with Abaqus/Standard with the aid of several user-supplied subroutines. The implicit time integration scheme is deemed appropriate for large-scale structures. The framework is systematically validated by several classical experimental results. Finally, a three-dimensional study of a three-span continuous rigid frame bridge with 270 m main span is performed. Comparison between the experimental and numerical results further reveals the contributions of various potential influencing factors. The proposed model shows promise for predicting the time-dependent performance of large-scale reinforcement concrete (RC) structures.