Early-age Shrinkage Research Articles

Early-age shrinkage behavior of cement mixtures regulated with metakaolin-based internal conditioning

Shrinkage occurs in concrete during its hardening and strength gain process leading to undesired deformation, cracking, and decreases in strength and durability. While metakaolin-based internal conditioning (MIC) has been validated as a promising technique for modifying cement and mitigating alkali-silica reactions in concrete, its impact on the early-age shrinkage behavior of cement remains unexplored. This study delves into the effects of MIC and its coupling with lithium on the chemical shrinkage, autogenous shrinkage, and drying shrinkage of portalnd cement incorporating 30 % metakaolin with varying degrees of saturation (50 %, 75 %, and 100 %). The results indicate that the hydration of cement can be substantially enhanced by MIC with 29.0 % more heat released and a 32.3 % decrease in calcium hydroxide content. As a result of the enhanced hydration, cement with MIC yielded increased chemical shrinkage. Compared with dry MK, the autogenous shrinkage and drying shrinkage of cement were decreased by 38.0 % and 11.0 %, respectively, in the presence of MIC. A synergistic effect between MIC and lithium was suggested by the higher efficacy in suppressing autogenous shrinkage.

Restraint effect of steel bar on early-age shrinkage of steel bar-mortar composites

Time-space-dependent stress and strain distribution within steel bar-mortar composites is key for shrinkage and cracking prediction of Reinforced-Concrete (RC) members. A novel system was designed to investigate the restraint of steel bars on the early-age shrinkage while digital image correlation was also employed to analyze spatial strain distribution. The measured restraint degree increases with the reinforcement ratio and maintains stable after about 36 h. Restraint effects is interfered by micro-cracks, because of which the calculated restraint degree matched the measured one better after being modified by a coefficient concerning reinforcement ratio. The overall restrained stress shows a three-stage process affected by the bonding evolution. The strain spatially undergoes a three-region distribution along the steel bar induced by the shear transfer and a two-region distribution on the cross-section aligning with the interface gradient. This study demonstrates a quantitative analysis on the steel bars restraint parameters and its evolution.

Effect of curing condition on mechanical properties and durability of alkali-activated slag mortar

While alkali-activated slag (AAS) has emerged as a promising alternative binder in construction engineering, a consensus on the optimal curing condition for this material has not been reached yet. It is well known that AAS can harden at ambient temperatures, but the influence of humidity on its properties remains poorly understood. Herein, we considered five curing conditions with different relative humidities (RH), including ambient/dry condition (RH=55 %), sealed condition (RH=80–95 %), fog condition (RH>95 %), water immersion condition (RH=100 %), and saturated limewater immersion condition (RH=100 %). Various properties have been examined, including flexural and compressive strengths, elastic modulus, shrinkage, pore structure, carbonation resistance, and freeze-thaw resistance of AAS mortars (AASM). Two types of activators, sodium hydroxide and sodium silicate (modulus at 1) solutions were used. The experimental results indicate that drying at early ages is detrimental to almost all the properties investigated. Sealed curing can deliver desirable mechanical properties and durability, but considerable shrinkage. Fog and water curings are highly effective at mitigating early shrinkage in AASM, but the problem of leaching adversely affects its long-term properties. Generally, limewater curing offers limited benefits compared to other high-humidity curing methods.

A data-enhanced approach for early-age drying induced moisture transport analysis on in-situ casted textile fibre reinforced concrete

With the addition of textile fibres that alters pore structure, the novel Textile Fibre Reinforced Concrete (TFRC) exhibits great potential in reducing drying shrinkage and enhancing long-term durability. To advance material design, this study aims at developing a coupled experimental-numerical framework with a data-enhanced approach to identify the essential material properties that govern the moisture transportation in TFRC. The scope of analysis covers the TFRC manufactured with various fibre types and different fibre volumes, where the time-dependent effect associated with early age is investigated. An inverse analysis framework, coupling Particle Swarm Optimisation (PSO) and extended support vector regression (XSVR), is developed and validated against experimentation by monitoring moisture distribution. Results reveals that the incorporation of textile fibres leads to a substantial reduction in the moisture diffusivity of TFRC, as opposed to conventional concrete of identical w/b and aggregate content. Notably, TFRC mixtures with 0.4 % Nylon twist and PTT600 fibres showed a 95 % reduction in moisture diffusivity compared to the conventional concrete. This discovery illustrates the capability of textile fibres, when optimally introduced, to mitigate moisture loss from cementitious materials, reducing drying shrinkage of concrete building. The proposed approach is demonstrated to be able to robustly quantify the early-age moisture transportation in TFRC, which is of potential to guide future concrete design of using textile fibre reinforcement towards controlling early-age shrinkage in building industry.

Early-Age Shrinkage Stress of Alkali-Activated Cement-Free Mortar Using Shrinkage Reducing Agent and Expansive Additive

Cement-free concrete has a superior physical performance, such as in its strength and durability, compared to OPC concrete; however, it has the disadvantage of large shrinkage. Large shrinkage can cause cracks due to shrinkage stress in the long term. In this study, a shrinkage reducing agent (SRA) was used to reduce the shrinkage of cement-free mortar; its content was increased from 0.0 to 1.5%. For an SRA content of 1.0%, a calcium sulfoaluminate (CSA) expansive additive (EA) (2.5, 5.0, and 7.5%) was added. To calculate the shrinkage stress of cement-free mortar using the SRA and EA, the compressive strength, elastic modulus, and total and autogenous shrinkage were measured. The unit shrinkage stress of cement-free mortar was obtained by multiplying the elastic modulus by the length change and accumulated to obtain the shrinkage stress acting on the mortar according to the age. The shrinkage stress of cement-free mortar showed different tendencies as the age increased. At early ages, the shrinkage rate of the mortar occupied a large proportion of the shrinkage stress. In the long term, the shrinkage stress was significantly affected by the elastic modulus. As a result, SRA was found to be effective in reducing the shrinkage stress by decreasing both the elastic modulus and shrinkage. However, EA increased the shrinkage stress over the long term due to an increase in the elastic modulus even though it compensated for early-ages shrinkage.

Pore structure development of cementitious materials with manufactured sand from various lithologies and differential effect of CaO–MgO blend expansion agent

With intensifying the contradiction between the demand and supply of nature sand (NS), the extensive utilization of manufactured sand (MS) as a substitute has become prevalent in various projects. The pore structure development plays a crucial role in early-age shrinkage of concrete, but research on pore structure development of cementitious materials incorporating diverse lithologic MS is still lacking. This study examined the effects of MS powders and particles from diverse lithologies on pore structure, along with the differential impacts of CaO–MgO blend expansion agent (CMEA) on the pore structure of mortar containing MS from different lithologies. The results demonstrated a significant reduction in the peak value of pore size distribution and porosity in cement paste after incorporating MS powder, particularly with the most pronounced effect observed in tuff powder. In mortar, the incorporation of tuff manufactured sand (TMS) also led to a substantial decrease in both the peak value and peak area. However, the pore size distribution peak value and areas of limestone manufactured sand (LMS) mortar were slightly higher than those of NS mortar at 3 and 7 days. In comparison to cement pastes, the secondary peak proportion in mortars increased by approximately 4–5 percentage points at 28 days. Furthermore, the harmful pores and severely harmful exhibited varying degrees of increase in diverse lithologic MS mortar after incorporating CMEA, with the highest increase observed in NS mortar and the smallest increase observed in TMS mortar.

Research on concrete early shrinkage characteristics based on machine learning algorithms for multi-objective optimization

Cracking phenomena in tunnel side wall structures (TSWS) increasingly jeopardize their longevity due to water leakage, reinforcement corrosion, and eventual collapse. The primary contributor, early-age shrinkage (EAS) induced by hydration reactions, significantly undermines structural stability and durability. The integration of expansion agents (EA) and fibers presents a low-cost, efficient strategy to counteract EAS-induced cracking. Despite its promise, limited research on the influencing factors constrains its broader application. This study delves into the impacts of EA content, the CaO–MgO ratio, and fiber reinforcement on flexural strength (FS), compressive strength (CS), and EAS, revealing a complex interplay where EA and CaO content detrimentally affect mechanical properties yet beneficially influence EAS. Results showed that EA and CaO content had negative effects on the mechanical properties, but had positive effect on EAS. Additionally, Random Forest (RF) was developed with hyperparameters refined via the firefly algorithm (FA) based on the experimental data. The validity of the built RF-FA models was verified by substantial correlation coefficients and low root-mean-square errors. Subsequently, a coFA-based firefly algorithm (MOFA) was proposed to optimize tri-objectives of mechanical properties, EAS, and cost simultaneously. The Pareto fronts were obtained effectively for the optimal mixture design. This study contributes to its practical implications, offering a scientifically grounded approach to enhancing TSWS concrete design for improved performance and durability.

Novel multi-scale experimental approach and deep learning model to optimize capillary pressure evolution in early age concrete

Early-age shrinkage of concrete can initiate pre-mature cracking, which can compromise the durability of concrete structures. Monitoring capillary pressure, the leading cause of concrete shrinkage, and understanding its evolution is crucial for the performance-based design of concrete, particularly at early-stages when it is more prone to cracking. This study deploys an innovative multi-scale experimental program using high-capacity tensiometers to monitor the capillary pressure up to 2000 kPa. This allowed investigating the effects of key design parameters, including the water-to-cement ratio, GGBS, SRA, and measurement depth, on the capillary pressure evolution in concrete. A new robust deep neural network model was developed to conduct extensive numerical experiments to predict the capillary pressure evolution of diverse mixtures. The net effect of multi-parameters on the capillary pressure can be investigated with this model, providing insights into the optimum design of more durable concrete mixtures with the lowest capillary pressure evolution, and guiding the implementation of appropriate cost-effective shrinkage-mitigating strategies.

Early-age inhomogeneous deformation of 3D printed concrete: Characteristics and influences of superplasticizer and water-binder ratio

3D printed concrete (3DPC) commonly experiences significant shrinkage along the printing direction (x-direction) at the early-age for its high cementitious material content, low water-binder ratio and formwork-free manufacturing process. This shrinkage with gradient along the vertical direction (z-direction) can cause interlayer slippage and further deformation within each filament. To investigate these early-age deformations and their dependence on materials, digital image correlation (DIC) was used to monitor the inhomogeneous deformation of 3DPC at the age of 0.5–6.5 h. It was found x-direction inhomogeneous shrinkage pattern is correlated with early-age hydration process and elastic modulus. After conducting mechanic analysis, it was found that an individual filament could be treated as a Winkler foundation beam with frictional moment, which can provide a semi-quantitative explanation of the phenomenon that the bottom filament shows significant downward deflection, while other layers show minimal upward deflection or almost no deflection. Additionally, the influence of superplasticizer and water-binder ratio on early-age inhomogeneous deformation was monitored. There exists an optimal dosage range for superplasticizer that ensures both better printing quality and lower x-direction shrinkage, shrinkage gradient as well as bottom layer deflection. With the same printing quality, early-age shrinkage, shrinkage gradient and the bottom layer deflection were reduced by adopting higher water-binder ratio. The influence of materials on the moisture evaporation rate and early-age strength was also measured and correlated with early-age x-direction shrinkage, shrinkage gradient of 3DPC and the extent of early-age bottom layer deflection.

Early-age shrinkage and hydration of concrete incorporating a mutually reinforcing systems of super absorbent polymers and MgO expansive agent under low humidity conditions

This study centers on evaluating the mechanical properties, autogenous and drying shrinkage kinetics, and crack propagation behavior in concrete samples internally cured with SAP and integrated with MgO-based expansive agents. A comprehensive material characterization was performed using state-of-the-art analytical methods such as Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Mercury Intrusion Porosimetry (MIP), aiming to shed light on the microstructural transformations, phase composition shifts, and evolution of the pore network. Our findings reveal that SAP's moisture-release mechanism effectively mitigates water competition between the MgO expansive agents and the cement hydration process. Moreover, MgO's delayed expansive behavior serves as a beneficial factor in curtailing localized high-porosity zones in internally cured concrete. The knowledge gleaned from this investigation offers a robust framework for the design of concrete structures that need to withstand challenging environmental conditions marked by low ambient humidity and significant temperature fluctuations.

Evaluation of tensile properties and cracking potential evolution of fly ash-cement mortar at early age based on digital image correlation method

The early-age tensile properties and shrinkage behaviors of mortar are important to investigate its early-age cracking potential. This study employs the digital image correlation method to quantify the tensile properties and shrinkage behaviors of fly ash-cement mortars at early age, aiming to reveal the effect of fly ash on the mortar's cracking potential evolution. Fresh mortars with varying fly ash (FA) contents (0%, 10%, 20%, 30%) undergo comprehensive tests, encompassing tensile strength, ultimate tensile strain, plastic shrinkage, mass loss, and damage assessment within 90–180 mins after casting. The results show that FA could enhance early-age ultimate tensile strain and extend the time for the mortar to maintain plasticity while reducing early-age shrinkage strain and mass loss. The mortar's cracking risk is potentially linked to its setting time. The rheological state of mortar gradually changed from plastic to non-plastic after initial setting, and the ultimate tensile strain stabilized, but the shrinkage strain increased rapidly, which resulted in a greater risk of shrinkage-induced cracking. Furthermore, after 180 mins of curing, the damage index of the fly ash-cement mortar (10% FA) was 1.6 times that of pure Portland cement mortar, whereas the damage indexes of the fly ash-cement mortars with 20% and 30% FA contents are approximately equivalent to 82% of the pure Portland cement mortar's damage index. This indicates that incorporating more than 20% fly ash is beneficial in reducing the risk of plastic shrinkage-induced cracking in mortar.

Early-age properties of cement paste with mechanically ground Yellow River sediment

Yellow River sediment(YRS) is a rich, low-activity silica-aluminum dredged sediment resource, which can provide a new source of supplementary cementitious materials(SCMS). This study investigated the influence of mechanically ground Yellow River sediments (MGYRS) on the hydration kinetics and early-age shrinkage of cement paste. Hydration kinetics revealed that MGYRS could significantly accelerate the hydration process, proceeding directly from the nucleation and crystal growth stage (NG) to the diffusion stage (D). In the plastic stage of cement paste, the early-age shrinkage of MGYRS at 40 min and 70 min increased by 250 µm/m and 99 µm/m, respectively. Microscopic analysis showed that MGYRS could promote the generation of Ca(OH)2, and the nucleation, micro-aggregate filling effect of MGYRS could refine the pore structure. This study can provide theoretical support for realizing the gelatinization of YRS.

Early-age shrinkage characteristic of UHPC in strengthening stone masonry arch: Influence of restraint from arch structure

Ultra-high performance concrete (UHPC) is frequently employed in strengthening existing bridges, due to its extremely high mechanical qualities and exceptional durability. Nevertheless, the early shrinkage of UHPC layer restrained by the arch structure may result in the risk of cracking, when used for strengthening masonry arch bridges. This paper aimed to investigate the shrinkage and cracking potential of ultra-high-performance concrete (UHPC) at early age under restraint from masonry arch structure. For that, different types of masonry model arches were respectively strengthened by using UHPC and then the shrinkage behaviors of UHPC layer were tested. The effects of four different strengthening modes, i.e., F-hoop (wrapping for four sides), T-hoop (wrapping for three sides), Intrados and Extrados, three different rise-span ratios, i.e., 1/5, 1/4, 1/2 and two different arch ring widths, i.e., 0.42 and 0.15 m, were considered. Results indicate that the shrinkage strain time-varying curve of UHPC layer was not only related to the material characteristics, but also negatively related to the change in external environment temperature. For different strengthening methods, the final shrinkage strain of UHPC layer follows: F-hoop < T-hoop < Intrados < Extrados. The shrinkage strain was unaffected by different strengthening modes along the thickness and arch axis directions. The shrinkage effect of UHPC generates the maximum tensile stress value (1.0–2.0 MPa) at the arch top of the strengthening layer, which was significantly less than the tensile strength of UHPC during the same risk period. The arch foot is the most complex area under stress and should be taken seriously.

Multiscale Hierarchical Fiber Gradations in Concrete to Reduce Early-Age Shrinkage Cracking Potential

Multiscale Hierarchical Fiber Gradations in Concrete to Reduce Early-Age Shrinkage Cracking Potential

Early-age shrinkage assessment of cementitious materials: A critical review

With the advent of formwork-free construction technologies like 3D concrete printing, evaluating early-age shrinkage in cementitious materials has become more critical. This paper reviews different test methods for assessing early-age shrinkage. These methods are classified as contact-based, which includes measurement systems that must remain in physical contact with the test specimen or embedded sensors placed inside the fresh concrete, and non-contact-based, which includes optical-based approaches either using white light (digital image correlation) or laser beams. The working principles, advantages, and challenges of the techniques, particularly while handling fresh concrete are discussed. The different mechanisms contributing to early-age shrinkage are reviewed and the common shrinkage mitigation strategies are also pointed out.

Design-oriented method for concrete pavements with volumetric stability admixtures: An integrated experimental and analytical approach

The high-performance demands on industrial floors, both in terms of larger slab dimensions and increased durability under harsh operating conditions, have led to the growing use of expansive admixtures. These generate a controlled expansive reaction within the concrete and compensate the early-age shrinkage. Despite their increasing use, calculation methods that permit to consider the expansive agents during the pavement design phase with a certain level of reliability are still unexistent. This study presents a straightforward cross-sectional model to assess both the stress-strain state and joint-opening of concrete pavements with volumetric stability admixtures by considering the slab dimensions, concrete composition, exposure conditions, and base friction characteristics. For that, a novel experimental device is designed and implemented in this work to characterize the dimensional variations associated with expansive agents since casting. A Type-G commercial volumetric stability admixture is considered as the expansive admixture. A full-scale validation of the proposed model is performed on a jointless concrete panel constructed by RCR Industrial Flooring in Spain. This validation proves the feasibility of the combined approach of laboratory calibration of the expansive addition and the cross-sectional model presented to accurately estimate both the slab deformations and joint opening developed over the 77-day test period.

The early-age shrinkage cracking and late-age fracture properties of fiber-reinforced cementitious composites

In this research, the shrinkage cracking and fracture properties of fiber-reinforced cementitious composites (FRCC) are investigated using eccentric ring test and three-point bending test. In the eccentric ring test, the concept of the equivalent crack width (weq) is proposed based on the morphology and number of cracks of FRCC. A function considering curing time and fiber volume fraction is established to calculate the equivalent crack width of FRCC. The initial and complete-through cracking times of FRCC were measured to explain the effect of the fibers. In the three-point bending test, the crack initiation in FRCC is determined based on the average transverse force. The initial and unstable fracture toughnesses, as well as the fracture energy, have been calculated. The experimental results indicate that an increase in polyvinyl alcohol (PVA) fiber content can reduce the crack width and prolong the initial and complete-through cracking times induced by shrinkage. The unstable fracture toughness and fracture energy increase with the increase in the PVA fiber content. The results of the eccentric ring test and three-point bending test demonstrate that the primary role of PVA fibers is to extend the intermediate stage of cementitious materials from initial cracking to unstable cracking. Additionally, PVA fibers delay the energy release rate during the failure process.

Composite slab floors made of cross laminated timber and ultra high-performance concrete: Early-age deflection, stripping time, and its implication on the structural performances

Timber-Concrete Composite floors made of Cross-Laminated Timber (CLT) and Ultra-High-Performance Concrete (UHPC) boast remarkable efficiency in lightweight and slenderness. While the rapid UHPC hardening facilitates swift construction, the optimal shoring time depends on the effect of the UHPC autogenous shrinkage on the floor deflection. This study aims to investigate the experimental deflection of CLT-UHPC floors at an early age without shoring and to develop a simplified model for predicting the optimal shoring time for TCC floors.An eco-friendly UHPC with recycled glass waste is considered in this study. Firstly, the evolution of its modulus of elasticity and compressive strength as well as the early-age shrinkage were experimentally characterized. Furthermore, the shear behavior of the notch connection was evaluated after 28 days, and it was estimated to be proportional to the stiffness of the concrete at an early age. Then, two TCC floors made of CLT-UHPC with a span of 3.6 m were cast and their deflection under the self-weight of fresh concrete was measured over the initial 28-day period in a simple supported configuration without the use of shoring. A simplified analytical model was developed to predict the TCC deflection at an early age by coupling an existing solution with the concept of Age-Adjusted Effective Modulus (AAEM). The model effectively predicted the experimental early-age deflection of the CLT-UHPC floor without the use of shoring. Finally, after 3 months, the TCC floors were tested under bending, showing a reduced structural stiffness of about 35 %, caused by concrete cracking due to restrained shrinkage. The parametric analysis with the developed analytical tool allowed for estimating the maximum span of CLT-UHPC floors without shoring or, for longer spans, the optimal time of shoring removal. This study offers valuable insights into the behavior of CLT-UHPC along, along with a robust analytical tool to optimize their design and construction of TCC floors.

Early-age shrinkage behavior of cement-fly ash paste under wind speeds: A study using BSE-IA and MIP techniques

While laboratory studies have shown that fly ash (FA) can reduce shrinkage in cement-based materials in the absence of wind, its impact on cement-based materials under wind speed conditions has not been extensively studied. This research investigates the influence of FA on the early-age shrinkage of cement paste under various wind speeds. The corresponding changes in pore structure were tested using mercury intrusion porosimetry (MIP) and backscattered electron image analysis (BSE-IA). The results show that under wind speed conditions, FA is not effective in reducing early-age shrinkage of cement paste. In fact, high levels of FA content can increase shrinkage values under wind speed conditions. Both wind speed and FA increase water evaporation, but they have different impact times. Although both wind speed and FA decrease mesopore content below 50 nm and increase water evaporation, they have opposite effects on early-age shrinkage. This suggests that mesopore content and water evaporation alone cannot fully characterize the change trend of early drying shrinkage. The two-factor parameter rs, which combines water evaporation and MIP-based pore size distribution, can effectively characterize drying shrinkage trends under the combined effects of wind speed and FA. BSE-IA can intuitively characterize pore size distribution above 200 nm, while the results of MIP underestimate the distribution of large capillary pores. Therefore, the current rs obtained based on MIP may be smaller than the actual value. With the advancement of testing technology in the future, rs can be further optimized.

Influence of Stone Powder Content from Manufactured Sand Concrete on Shrinkage, Cracking, Compressive Strength, and Penetration

The market demand for manufactured sand has grown rapidly, and the solution to the problem of optimum stone powder content from manufactured sand concrete is imminent. The workability, early age shrinkage strain and cracking, strength, chloride ion penetration, and pore structures of concrete with different stone powder contents were tested to study the influence of stone powder content from manufactured sand concrete. The test results show that the addition of stone powder is beneficial in improving the working performance of manufactured sand concrete. But at the same time, it will increase the amount of concrete water reducer and the total shrinkage strain at an early age. The workability and durability of manufactured sand concrete can be significantly improved by adding an appropriate stone powder. However, excessive stone powder will lead to a reduction in the strength and durability of manufactured sand concrete. It is suggested that the best stone powder content of concrete with a water/cement ratio of 0.32 is 10%, and that of concrete with a water/cement ratio of 0.45 should be less than 20%.