Shrinkage Deformation Research Articles

Improvement of Ultra-High-Performance Concrete Matrix with Nanocellulose for Reduced Autogenous Shrinkage and Enhanced Mechanical Properties

Despite its numerous benefits and considerable potential, ultra-high-performance concrete (UHPC) faces challenges in wider application due to significant autogenous shrinkage deformation. Typically, efforts to inhibit UHPC autogenous shrinkage may compromise its mechanical properties through the utilization of various internal curing agents, presenting a contradictory situation. To overcome this situation, we explored the utilization of nanocellulose materials, which led to improvements in reducing autogenous shrinkage and enhancing mechanical properties. Experimental findings reveal that incorporating a cellulose nanofiber-2 suspension presents a significant improvement, even at minimal dosages. Specifically, relative to the control group, autogenous shrinkage diminishes by at least 62.2%, while mechanical properties at 28d are increased by nearly 10% in NC-3 group. The potential microscopic mechanisms were investigated, revealing that the cellulose nanofiber-2 suspension acts by decelerating the initial hydration rate (before the acceleration period) and subsequently enhancing the nucleation and growth of hydration products (after the acceleration period). In addition, capillary pressure can be effectively decreased by reducing the volume of nanopores and surface tension of the pore solution. Combined with the rigid support and bridging effects after water release, the incorporation of a cellulose nanofiber-2 suspension can significantly inhibit the development of autogenous shrinkage while improving mechanical properties. This novel nano-engineering strategy not only promotes wider industrial applications of UHPC but also holds considerable promise for future advancements.

Axial compressive and long-term shrinkage behaviors of self-compacting recycled concrete reinforced with recycled glass fiber

Self-compacting recycled concrete (SCC) has properties of significant shrinkage deformation and early cracking, which limits its wide application in civil engineering applications. Waste fiber addition offers an effective solution to these challenges. This research focuses on waste glass fiber and explored the impact of various parameters on the performance of recycled glass fiber-reinforced self-compacting recycled aggregate concrete (RGF-SCRC). Incorporating waste glass fiber effectively inhibits the long-term shrinkage rate of RGF-SCRC and improves its axial compressive strength, with the improvement of 2.2∼15.3 % in axial compressive strength and a reduction of 17.9∼66.5 % in the long-term shrinkage rate. However, excessive fiber addition shows an negatively effect on the performance of RGF-SCRC. The optimum addition was concluded as 7.5 kg/m³. On the other hand, the waste alkali-resistant glass fiber showed a higher improvement than waste glass fiber. Moreover, microstructure analysis reveals that the waste fibers could be uniformly dispersed within the investigated specimen, effectively bridging gaps and significantly enhancing the concrete’s strength and toughness. Furthermore, the number of large pores and overall porosity were reduced, resulting in greater compactness, improved axial compressive strength, and reduced long-term shrinkage of RGF-SCRC. After 180 days of curing, the porosity of the specimens significantly decreased when compared to the 28 day curing specimens. Based on experimental results, the axial compression stress-strain relationship and long-term shrinkage curves of RGF-SCRC were fitted and modified, and proposed an axial compression constitutive relationship and a long-term shrinkage theoretical analysis model which are applicable to RGF-SCRC. The models' correctness was verified by comparing them with experimental results. These research outcomes offer valuable insights for the future practical implementation of RGF-SCRC.

Bio-inspired widening concrete using cellulose nanofiber to enhance multiscale Fiber–Matrix interface

The cracking issue at the bonded interface due to the differing shrinkage performances of newly poured concrete and existing concrete poses a significant threat to the safe service of composite structures. Inspired by the musculoskeletal system, we propose the use of multiscale hybrid reinforced concrete materials, incorporating basalt fiber (BF), polypropylene (PP) fiber, and cellulose nanofiber (CNF), for bridge widening structures. Experimental investigations were carried out to assess the bond splitting tensile strength, diagonal shear strength, crack resistance, development of drying shrinkage deformation, and the propagation behavior of restrained shrinkage-induced cracks in both new and old concrete reinforced with single and hybrid combinations of BF, PP fiber, and CNF. The microstructure, phase composition, and pore structure evolution of BF, PP fiber, and CNF-reinforced concrete were observed and analyzed using scanning electron microscopy, thermogravimetric and derivative thermogravimetric analysis, nuclear magnetic resonance, and mercury intrusion porosimetry. The results indicate that the incorporation of BF, PP fiber, and CNF exhibits excellent synergistic effects, improving the bond and shrinkage performance of the concrete interface. As the CNF content increases, the macro fiber–matrix interface improves. This bio-inspired work will contribute to the development of strong, tough, and sustainable concrete for bridge widening structures.

Influence of MgO chemical activity on the drying shrinkage of the MgO-SiO2-H2O system

The magnesium silicate hydrate (MgO-SiO2-H2O) system is an innovative eco-friendly cementitious material. However, its poor volume stability and significant shrinkage have curtailed its widespread development and utilization. The primary component for preparing the MgO-SiO2-H2O system, MgO, has a substantial impact on the properties, particularly in relation to volume stability. This research examined the effects of MgO chemical activity on the volume stability of the system. The results suggested that reducing MgO chemical activity and increasing the Mg/Si ratio result in varying reductions in the water loss ratio and drying shrinkage, with the lowest drying shrinkage ratio being 0.913 %, representing a 14.1 % reduction compared to the sample with the highest drying shrinkage ratio. MgO chemical activity affected the shrinkage deformation of the system by influencing the generation rate and content of Mg(OH)2-induced volume expansion. Additionally, the increase in the Mg/Si ratio influenced the content of Mg(OH)2, ultimately reducing drying shrinkage. At an Mg/Si ratio of 1.25, the resulting M-S-H gel resembled a T:O structure, and promoted a higher degree of polymerization of the gel. In contrast, when the Mg/Si ratio is 1.00, the M-S-H gel exhibited characteristics more akin to a T:O:T structure, leading to an even higher degree of polymerization.

Superflexible Carbon Nanofibers for Multidimensional Complex Deformation Sensing in Soft Robots.

Soft robots can make complex motions or deformations due to their infinite freedom, which poses great challenges for monitoring their motion and position. While previous investigations of flexible sensing either focused on stretchable or compression deformations in one or two directions, the complex multidimensional deformations that occur on the surfaces of soft robots have been frequently overlooked. In this work, inspired by spider silk, superflexible carbon nanofibers with a bundled structure were biomimetically designed and fabricated using electrospinning technology and carbonization treatment. The fabricated fibers can be microscopically folded at 180° and can sustain multidimensional shrinkage deformation without microstructural damage during 200,000 times of repeated folding. In addition, the fibers process ultrasmall bending resistance that is two orders of magnitude lower than that of A4 paper and commercial conductive fibers, demonstrating excellent flexibility that is ideal for fabricating sensors in soft robots. Combining the study of origami techniques and mechanical simulations, the bending resistance of the fibers was found to have a step change in response to different deformation angles and radii. As a demonstration, a sensor based on this flexible carbon nanofiber successfully monitors the irregular shrinkage deformation of soft parts, showing great potential in applications of grasping, recognition, and perception. This work sheds light on the design of ultraflexible conductive carbon materials and provides an avenue for the extreme shape-morphing monitoring of soft robots.

Shrinkage and deformation of material extrusion 3D printed parts during sintering: Numerical simulation and experimental validation

Material extrusion 3D printing (ME3DP) combined with sintering is a low-cost additive manufacturing technique for fabricating components of difficult-to-print metals, such as copper, aluminum, and ceramics. However, the sintering process includes complex material science, such as volumetric shrinkage and free structural bending, to identify the relative density and deformation of a 3D printed sample. The prediction of the relative density and deformations during the sintering process provides information to the design engineer to optimize the design of the CAD model before sintering. In this study, a phenomenological model based on constitutive equations was developed to predict the density and structural deformation during the sintering process of pure copper components fabricated by ME3DP using metal injection molding feedstock. The densification rate was determined using shrinkage estimation with an isothermal stairway heating cycle in a vertical dilatometer. Furthermore, different sets of experiments were performed with a load on the probe with long isothermal heating cycles at 850, 900, 950, 1000, and 1050 °C in a vertical dilatometer to estimate the axial viscosity of the copper. The constitutive equations were solved using the solid mechanics module with user-defined creep in COMSOL Multiphysics by considering isotropic assumptions. Two types of geometries, cube and overhanging I section, were used to predict shrinkage and deformation during the sintering process. The developed model successfully predicted the relative density based on shrinkage and structural deformation owing to gravity during the sintering process.

Low-carbon cementitious composite incorporated with biochar and recycled fines suitable for 3D printing applications: hydration, shrinkage and early-age performance

In recent years, the construction industry has witnessed significant advancements in concrete technology, particularly with the integration of 3D printing in cement-based materials. While this innovation offers promising opportunities for the sector, the high binder and fine particle content of 3D printing mixes presents a substantial environmental challenge due to their considerable carbon footprint. To mitigate this impact, strategies often involve substituting portions of the binder or aggregate with waste materials. This article presents a comparative analysis of two promising approaches to reducing the carbon footprint of 3D printing concrete mixes by partially replacing cement with biochar and recycled fines. The study examines the effects of these materials on the rheological properties and early-age hydration processes of the 3D printing mix. A reference mix (REF) was established, followed by the development of eight additional mixes, with four incorporating biochar and four incorporating recycled fines, each replacing 1.25%, 2.5%, 5%, and 10% of the cement volume. The findings indicate that recycled fines have a neutral effect on the spread flow diameter of the mixture but increase initial deformations in printed elements. Conversely, biochar, due to its water absorption capacity, reduces fluidity, enhancing buildability by enabling faster printing with minimal initial deformation. Additionally, replacing up to 2.5 vol.% of cement with either material accelerates the normalized heat flow, contributing to a quicker gain in mechanical properties. However, biochar increases shrinkage deformations within the first 12 hours, while recycled fines mitigate them. Importantly, replacing up to 10 vol.% of cement with these materials does not significantly compromise early compressive strength.

Development of sustainable self-compacting concrete: Replacement of sand with municipal solid waste incineration ash molten slag and recycled fine aggregate

The purpose of this study is to develop self-compacting concrete using MSWA and RA as fine aggregates, supplemented with fly ash and GGBS that can modify the workability of the concrete. To evaluate the performance of sustainable self-compacting concrete, its mechanical properties, workability, drying shrinkage, and pore structure were comprehensively analyzed. The results demonstrate the feasibility of producing self-compacting concrete by replacing 50–100 % of sand with MS and RA, as all mixes in this experiment achieved the target slump flow of 600 ± 20 mm. The compressive strength remained unaffected for MS contents below 25 %, but at 50 % MS, it was 10 % lower than that of normal concrete. The drying shrinkage deformation of all specimens was below 700 μ, meeting the requirements for practical engineering applications. Incorporating fly ash increases porosity but transforms micropores larger than 100 nm into those smaller than 100 nm. Incorporating GGBS not only reduces porosity but also converts pores of 10–100 nm into gel pores smaller than 10 nm. Additionally, the suitability of various formulas correlating compressive strength and static elasticity modulus, recommended by American Concrete Institute (ACI 363), European Practice (EN 1992), and the Architectural Institute of Japan (JASS 5), was evaluated, and appropriate formulas were determined through regression analysis.

Impact of typical environments in China's western mountainous areas on the durability of railway concrete: a review

PurposeThis study aims to analyze the impact mechanism of typical environments in China's western mountainous areas on the durability of railway concrete and propose measures to improve durability.Design/methodology/approachWith the continuous promotion of infrastructure construction, the focus of China's railway construction has gradually shifted to the western region. The four typical environments of large temperature differences, strong winds and dryness, high cold and low air pressure unique to the western mountainous areas of China have adverse effects on the durability of typical railway structure concrete (bridges, ballastless tracks and tunnels). This study identified the characteristics of four typical environments in the western mountainous areas of China through on-site research. The impact mechanism of the four typical environments on the durability of concrete in different structural parts of railways has been explored through theoretical analysis and experimental research; Finally, a strategy for improving the durability of railway concrete suitable for the western mountainous areas of China was proposed.FindingsThe daily temperature difference in the western mountainous areas of China is more than twice that of the plain region, which will lead to significant temperature deformation and stress in the multi-layered structure of railway ballastless tracks. It will result in cracking. The wind speed in the western plateau region is about 2.5 to 3 times that of the plain region, and the average annual rainfall is only 1/5 of that in the plain region. The drying effect on the surface of casting concrete will significantly accelerate its cracking process, leading to serious durability problems. The environmental temperature in the western mountainous areas of China is generally low, and there are more freeze-thaw cycles, which will increase the risk of freeze-thaw damage to railway concrete. The environmental air pressure in the western plateau region is only 60% of that in the plain region. The moisture inside the concrete is more likely to diffuse into the surrounding environment under the pressure difference, resulting in greater water loss and shrinkage deformation of the concrete in the plateau region. The above four issues will collectively lead to the rapid deterioration of concrete durability in the western plateau region. The corresponding durability improvement suggestions from theoretical research, new technology development and standard system was proposed in this paper.Originality/valueThe research can provide the mechanism of durability degradation of railway concrete in the western mountainous areas of China and corresponding improvement strategies.

Experimental study on mechanical behavior and countermeasures of mountain tunnels under strike-slip fault movement

In the seismic mountainous regions such as western China, it is usuallly inevitable to construct tunnels near active fault zones. Those fault-crossing tunnel structures can be extremely vulnerable during earthquakes. Extensive experimental studies have been conducted on the response of continuous mountain tunnels under reverse and normal fault movements, limited experimental investigations are available in the literatures on mountain tunnels with special structural measures crossing strike-slip faults. In this study, a new experimental facility for simulating the movement of strike-slip fault was developed, accounting for the spatial deformation characteristics of large active fault zones. Two groups of sandbox experiment were performed on the scaled tunnel models to investigate the evolution of ground deformation and surface rupture subjected to strike-slip fault motion and its impact on a water conveyance tunnel. The nonlinear response and damage mechanism of continuous tunnels and tunnels incorporated with specially designed articulated system were examined. The test results show that most of slip between stationary block and moving block occurred within the fault core, and significant surface ruptures are observed along the fault strike direction at the fault damage zone. The continuous tunnel undergoes significant shrinkage deformation and diagonal-shear failure near the slip surface and resulted in localized collapse of tunnel lining. The segments of articulated system tunnel suffer a significant horizontal deflection of about 5°, which results in opening and misalignment at the flexible joint. The width of the damaged zone of the articulated system tunnel is about 0.44 to 0.57 times that of the continuous tunnel. Compared to continuous tunnels, the articulated design significantly reduces the axial strain response of the tunnel lining, but increases the circumferential tensile strain at the tunnel crown and invert. It is concluded that articulated design provides an effective measure to reduce the extent of damage in mountain tunnel.

РОЛЬ САСО3 У ФОРМУВАННІ МІЦНІСНИХ І ДЕКОРАТИВНИХ ВЛАСТИВОСТЕЙ ПОРОШКОВОГО ЛУЖНО-АКТИВОВАНОГО ШЛАКОПОРТЛАНДЦЕМЕНТНОГО БЕТОНУ

The article discusses approaches to the formation of compositions of alkali-activated decorative Portland slag cements containing Portland cement type CEM1 5...45% with high performance and decorative properties. The optimization of the compositions of decorative alkali-activated Portland slag cements was carried out using statistical methods for designing experiments. Finely dispersed TiO2 and CaCO3 additives with a whiteness of 90% were used as bleaching components. The alkaline component is sodium metasilicate in the form of a non-hygroscopic powder. The research carried out made it possible to obtain decorative Portland slag cements with a whiteness of 45...77%, which allows them to be used to produce colored cements with a wide range of colors from white to black. It has been established that alkali-active decorative Portland slag cements have an activity of 37...59 MPa at the age of 28 days. All compositions have good hardening dynamics and, based on the strength at the age of 2 days  22...36.6 MPa, they can be classified as fast-hardening. Based on them, it is possible to produce dry construction mixtures. All mortar compositions based on alkali-active decorative Portland slag cements demonstrate fairly high frost resistance  F200. This allows them to be used for the manufacture of products and solutions both for indoor use and when exposed to atmospheric influences without loss of design characteristics and decorative appeal. The inherent shrinkage strains of decorative alkali-activated Portland slag cements are 0.51...0.61 mm/m, which eliminates cracking and premature destruction of products. The use of the CaCO3 additive is especially effective for controlling the shrinkage deformations. Thus, the CaCO3 additive performs the functions of not only a decorative component, but also a structure-forming component. Concrete and mortar mixtures can be used to produce decorative products using the traditional method, extrusion, 3D printing on construction printers, etc. And not too long setting times and a rapid increase in strength make it possible to produce products without thermal treatment or with minimal consumption of thermal energy.

Influence of fly ash and granulated blast furnace slag on autogenous shrinkage and drying shrinkage of cement-based materials mixed with alkali accelerator and alkali-free accelerator

Shotcrete shrinkage and cracking are getting more threatening due to its high content of cementitious materials, small aggregate particle size and a large amount of accelerator, which poses a great threat to the construction safety of engineering structures. This paper studies the volume stability of cement mortar with different contents of fly ash (FA) and granulated blast furnace slag (GBFS) (10%/20%/30%) under the condition that the dosage of alkali liquid accelerator is 4% and that of the alkali-free liquid accelerator is 7%. This work is designed to provide a guidance for the basic research and practical application. By comparing the autogenous shrinkage, drying shrinkage, mass loss caused by drying condition, and internal humidity change of drying condition of cement mortar within 180 days of age. Combined with MIP analysis, XRD hydration product analysis, and SEM hydration product morphology analysis, the results show that both fly ash and granulated blast furnace slag can reduce the autogenous shrinkage and drying shrinkage of cement mortar mixed with accelerator to a certain extent, and the shrinkage reduction effect of FA is more prominent. The reduction effect of GBFS is more obvious at high dosages. Adding FA and high content of GBFS can increase the mass loss of cement mortar under drying shrinkage conditions. The high content of mineral admixtures will exacerbate the rate of decrease in the internal humidity of the cement mortar. The reasons for the reduction of autogenous shrinkage and drying shrinkage of cement mortar mixed with accelerators due to the addition of FA and GBFS are: the early activity of the two mineral admixtures is low, and the hydration process is slow. And the reduction of pore size with the range of 5-50nm leads to the reduction of capillary tensile stress and the weakening of the driving force for shrinkage deformation. Among them, the shrinkage reduction effect of fly ash is more pronounced. Therefore, mineral admixture can be used to replace a certain amount of cement in actual shotcrete construction, so as to increase the volume stability of shotcrete.

On increasing the crack resistance of reinforced concrete structures by introducing fiberglass nets into the protective layer of concrete

Under operating conditions, the protective layer of concrete undergoes significant internal and external influences that lead to the formation of cracks. To increase the reliability and durability of reinforced concrete structures, it is proposed to install fiberglass nets in the protective layer of concrete, which is most susceptible to various aggressive influences during the operation of structures. The purpose of this work was to study the effect of fiberglass nets on increasing the crack resistance of the protective layer of concrete. The forces in the stretched concrete and in the rods of the fiberglass mesh located in the protective layer of concrete are calculated theoretically and using the software package «LIRA-CAD 2016» for a strip of concrete reinforced with a fiberglass mesh. The relative movements of the nodes in concrete and in the grid are determined and the obtained values are compared. As a result of the study, it was found that with a short-term effect of the load, fiberglass nets in the protective layer of concrete do not significantly affect the formation of cracks, with a long-term effect of the load, the presence of fiberglass nets reduces the formation of cracks by up to 2%. After the formation of microcracks in concrete, including from shrinkage deformations, fiberglass nets significantly hinder their further development.

Mechanical properties, hydration behavior and shrinkage deformation of ultra-high performance concrete (UHPC) incorporating MgO expansive agent

To reduce the extremely high autogenous shrinkage deformation of ultra-high performance concrete (UHPC) caused by low water-to-binder ratio and high binder materials content, this work aimed to designed and prepared low shrinkage UHPC containing MgO-based expansive agents (MEA). The effects of UHPC with different reactivity of MEA (R-MEA and S-MEA) were compared in terms of fluidity, mechanical properties, hydration characteristics, shrinkage deformation, pore structure and microstructure. The results indicated that the incorporated of MEA decreased the fluidity and mechanical properties of UHPC, while the autogenous shrinkage deformation was compensated significantly. When 6 % R-MEA was incorporated, the flow and compressive strength decreased by 16 % and 7.9 %, respectively, but the autogenous shrinkage at 7 days also decreased by 70.1 % at the same time. The same amount of S-MEA showed lower compensation for the autogenous shrinkage of UHPC than R-MEA, but with the same reduction in compressive strength loss. This was due to the highly reactive R-MEA showed higher hydration degree and larger swell increment, which caused more compensation for shrinkage in UHPC, while it had slight adverse effect on the strength development. It is worth noting that the compensation effect of autogenous shrinkage is very limited when the doping is higher than 6 % for either MEA, but the loss of mechanical properties is serious. In addition, the microstructure showed that the crystal growth pressure of brucite forced the pastes to expand and thus resulted in increase on the porosity for UHPC. This study provides a feasible and effective way for mitigating the autogenous shrinkage of UHPC.

Non‐isometric deformation in double curvature and symmetric composite laminates due to shrinkage

AbstractApplication of the global Gauss–Bonnet theorem for the prediction of changes in Gaussian curvature for double curvature laminate geometries due to shrinkage is developed for non‐isometric deformation states where in surface area change accompanies changes in curvature. The transition between isometric and non‐isometric deformation is strongly influenced by the ratio of the principal radii of curvature of the double curved surface and a relationship is proposed by the authors to accommodate the transition. Examples for the radii of curvature ratios of 2, 3, and 4 are compared to results from finite‐element simulations and the developed relationship is shown to be accurate within 0.55%. Furthermore, these results demonstrate that isometric deformation state can be taken as an adequate representation for double curvature toroidal laminate geometries of >10 and the class of materials studied in this work.Highlights Shrinkage induced deformation in multi‐curvature composite laminates is a recurring issue in polymer composite manufacturing. Thermal, crystallization and cure shrinkage are the dominant sources of shrinkage deformation in polymer composite systems. Isometric deformation of multi‐curvature, symmetric laminates composite is defined by the absence of membrane strain. The Gauss–Bonnet theorem provides a platform for determining radii of curvature changes in multi‐curvature symmetric laminates, Non‐isometric deformation of symmetric laminates can be treated by the Gauss–Bonnet theorem for radii of curvature ratios that correspond to geometric self‐constraint. The above highlights yield insight into the anticipated geometric distortions due to shrinkage in polymer composites.

Two-step approach to manufacture sustainable artificial steel slag aggregate used in alkali-activated concrete

This study utilized 3 mol/L hydrochloric acid to activate steel slag powder in combination with carbonation and produced the artificial steel slag aggregate (ASSA) for the use in alkali-activated concrete. The composition, microstructure, and properties of the ASSA were investigated. The results indicated that acid activation enhanced the compressive strength of the ASSA by 26.7 %, reduced the total porosity by 5.2 %, and facilitated the formation of portlandite, C-S-H gel, and monocarbonate in the hydration products. Carbonation enhanced the compressive strength of the ASSA by 28.5 %, reduced the total porosity by 14.5 %, and led to the formation of calcite and aragonite. The effect of acid activation coupled with carbonation on the ASSA manifested in a 43.6 % enhancement in compressive strength, a 17.9 % reduction in porosity, and an expansion rate reduction to 1.2 %. The alkali-activated concrete produced with the modified ASSA exhibited enhanced compressive strength by up to 21 % compared with the control group, facilitated internal curing to balance internal humidity, and mitigated drying shrinkage deformation. This study provides a viable and secure approach to the reutilization of steel slag.

Multi-objective optimization, shrinkage and fracture properties of unsaturated polyester resin modified concrete for bridge deck pavement based on system theory

For the purpose of fabricating unsaturated polyester modified concrete (UPMC) with excellent shrinkage and fracture properties for bridge deck pavement, the optimization design of mix proportion and enhancement mechanism analysis were implemented based on system theory. Firstly, for unsaturated polyester resin (UPR) subsystem, the viscosity, mechanical properties and droplet-size distribution were analyzed to determine the types and dosage of auxiliary additives after emulsification treatment; Next, for UPMC mortar slave-system, the optimization design was implemented through the combination of experimental analysis and hybrid multi-attribute ellipsoidal decision of grey-target (HMEDG) model; Subsequently, for UPMC main-system, the optimal proportion was determined utilizing orthogonal design test. Finally, the variation law and enhancement mechanism on fracture properties and shrinkage characteristics of UPMC was analyzed by combining macroscopic test, thermogravimetry (TG) and X-ray diffraction (XRD). The results demonstrated that 2.0 wt%BPO+1.0 wt%DMA and meta-benzene types UPR were utilized as auxiliary additives for UPMC based on the results of HMEDG models. The demulsified and cured WUP might supplement the interior moisture losses based on humidity compensation, and substantially constrain the evaporation loss inside the matrix, upgrading the hydration degree and facilitating the generation of hydration products. The introduction of 3 %-6 % waterborne-UPR (WUP) would improve 28d-fracture toughness within approximately 23.33 %-49.32 %, and reduce the shrinkage deformation by roughly 28–43 % through inducing the crack tip stress redistribution against the initiation and propagation of interior microcracks and enhancing the homogenization and densification.

Effect of 60 °C sustained temperature conditions on the mechanical properties and microstructure of alkali-activated fly ash-slag pastes and mortars

The temperature effect has been proven to affect the mechanical properties and microstructure of alkali-activated materials greatly. The research on the long-term complex high-temperature environment for alkali-activated materials remains blank. In this paper, the actual working temperature is selected to study the effects of long-term exposure at 60 °C on the mechanical properties of static/impact load, quality, shrinkage deformation, hydration products, pore structure, and microscopic morphology of alkali-activated fly ash-slag (AAFS). The results show that the mass loss rate of AAFS tends to be stable, the shrinkage deformation rate decreases, and the compressive strength decreases after 28d of sustained high-temperature action. The sustained high temperature causes changes in the hydration product phase, mean chain length (MCL) of the gel phase, pore structure, and micro-morphology. When the duration for 7d and 28d at 60 °C temperature, the compressive strength under static and impact loads increases, which is related to the increase of diffraction peak and MCL of the gel phase; when the duration is 60d and 90d, the compressive strength under static/impact loads decreases, which is related to the increase of cumulative pore volume and the decrease of MCL. Sustained high temperature refines the pore diameter of AAFS samples.

The influence of nano-silica composite superabsorbent polymer on the autogenous shrinkage of mortar

To address the diminished shrinkage reduction capacity due to high ion sensitivity of superabsorbent polymers (SAP) within cement-based materials, this study employs solution polymerization where acrylic acid and acrylamide are copolymerized with nano-silica at varying concentrations to synthesize innovative SAPs. The investigation encompasses the structural groups, microscopic morphology, liquid absorption characteristics of these SAPs, and their effect on mortar's autogenous shrinkage. The results indicate that nano-silica can be encapsulated within polyacrylate-acrylamide network via physical adsorption and chemical grafting. The incorporation of nano-silica enhances the water absorption and retention capacities of SAPs in alkaline environments. Nano-silica composite SAPs absorb sufficient internal curing water and prolong the subsequent moisture gradient-driven water release process, continuously releasing water within matrix to maintain internal humidity, thereby further enhancing the shrinkage reduction effect on mortar. Based on Scanning Electron Microscopy (SEM) observations of SAPs morphologies within mortar and X-ray Computed Tomography (X-CT) monitoring of internal curing water distribution, it is revealed that nano-silica undergoes pozzolanic reactions, forming a tightly connected domain with matrix. This facilitates continuous water release to the surrounding through capillary action, thus maintaining capillary pore liquid levels. Consequently, it effectively mitigating shrinkage stress and deformation, leading to an enhancement in shrinkage reduction effects.

Aramid Honeycomb Cores under Constant Pressure: Unveiling the Out-of-Plane Compression Deformation.

The primary challenge during the secondary bonding process of full-height honeycomb sandwich structures is the aramid honeycomb core's height shrinkage. This paper systematically investigated the height evolution behavior of the honeycomb core by using a creep testing machine. The results showed that the out-of-plane compression deformation curve of aramid honeycomb cores is mainly divided into three stages: the dehumidification stage, the pressurization stage and the creep stage. Under conditions of high temperature and pressure, height shrinkage was attributed to the dehydration caused by moisture infiltration, and the compression creep resulted from the slippage of polymer molecular chains. Dehydration shrinkage is stable, whereas compression creep reflects typical viscoelastic polymer characteristics. By employing the viscoelastic Burgers mechanical model and applying the nonlinear surface fitting method, the total height shrinkage deformation behavior of the aramid honeycomb core during the curing process can be accurately predicted by summing the above three stages. This research contributes valuable insights for the manufacturing process of honeycomb sandwich structures.