Magnitude Of Shrinkage Research Articles

High salinity prolongs water processes required for soil structure stability during drying–wetting cycles

AbstractClimate events, such as drought and rainfall, can lead to a cycle of drying and wetting that may cause changes in soil structure, leading to deteriorations in the health of saline soils. However, little is known about the extent and behavior of soil structure degradation under the combined influences of salinity and drying–wetting (D‐W) cycles. Thus, we systematically investigated the effects of salinity (0, 5, 30, and 100 g/L, labeled as CK, T5, T30, and T100) and D‐W cycles on soil structure by determining soil volume, shrinkage, and swelling potentials along with soil pore character obtained from soil shrinkage characteristics curve, intending to explore how D‐W cycles and salinity affect soil structure. The results showed that soil deformation behaviors in saline and non‐saline soils varied with the number of D‐W cycles. Irreversible deformation of the soil was observed during continual D‐W cycles. The soil volume increased by 3.75%–15.73% after three D‐W cycles. In vertical direction, the maximum expansion magnitude for each treatment was reached with the value of 29.03%, 23.42%, 34.23%, and 35.87% in CK, T5, T30, and T100, respectively. The magnitudes of shrinkage and expansion were equal in the horizontal direction since the soil samples consistently returned to their original dimensions. Furthermore, the decrease was observed in the micropores and capillary pores affected by salinity, with values of 50%, 58.6%, and 70.4% in CK, T5, T30, and T100, respectively. However, the D‐W cycles primarily affected large pores. High salinity levels enhanced swelling potential and inhabit shrinkage potential, prolonging the water processes required for the soil structure to achieve stability. The results of this study underscore the necessity of understanding the hysteresis of soil volume change and elucidate the mechanisms of soil structure deterioration driven by salinity and D‐W cycles. These findings provide a valuable reference for healthier soil management.

Sintering Behavior and Mechanical Properties of Dispersed-Reinforced Fe-TaC Composites Produced by High Energy Ball Milling

In this study, a high-melting point element, tantalum carbide (TaC) was added to improve the mechanical properties and the oxidation/corrosion resistance of Fe. The Fe-TaC composites were synthesized by high energy ball milling for the mechanical alloying of the non-equilibrium phase (Fe-Ta) and the homogeneous dispersion of TaC. Fe-TaC composite samples were fabricated using 5, 10, and 20 wt.% TaC. The ductile particles (Fe) got harden and the brittle particles (TaC) were uniformly dispersed, while facilitating short-range diffusion in the ductile matrix by the high energy ball milling method. Spark plasma sintering was performed at a sintering temperature of 850 oC and pressure of 60 MPa. As the TaC contents increased, the sintering exponential (m) increased. A higher ‘m’ value indicates a lower magnitude of shrinkage, by decreasing the lattice and grain boundary (G/B) diffusion path between the pores and particles. The hardness increased from 128.9±10.4 to 444.2±20.6 kg/mm<sup>2</sup> as the grain size decreased from 5.13 to 3.99 μm. This enhancement is attributed to the Hall-Petch relationship and dispersion strengthening effect. The mechanical properties of the sintered bodies were studied to evaluate how the different TaC content affect their characteristics. In addition, oxidation resistance increased with increasing TaC contents. It was considered that the local oxidation resistance based on the formation of an oxide layer of TaO and Fe<sub>2</sub>O<sub>3</sub>.

Luting laminate veneers: Do resin-composites produce less polymerization stress than resin cements?

ObjectivesRegular composites could produce less polymerization stress than resin cements when luting laminate veneers but there is no proper evidence to support this theory. The current study aimed to determine the degree of conversion, volumetric shrinkage, polymerization stress and the resultant elastic moduli of materials currently used for adhesive cementation and to determine possible correlations. MethodsThe study considered (i) regular resin composites (Admira Fusion, Gradia, Grandioso, Palfique, Sirius Z, Viscalor and Z100) at room and pre-warmed (PW) at 69ºC, (ii) flowable composites (Sigma Flow and Grandioso Flow); (iii) solely light-activated cements (AllCem Veneer, Variolink Esthetic and RelyX Veneer); and (iv) one dual-activated resin cement (SpeedCEM). Degree of conversion (DC, n = 3) was accessed with FTIR 1 h after irradiation. Bonded-disk and Bioman II instruments were used to access polymerization shrinkage strain and shrinkage stress, respectively, for 60 min at 23 ± 1◦C (n = 3). The elastic modulus was determined by 3-point bending flexural test (n = 6). The results were submitted to analyse s of variance, Tukey’s, and correlation tests. ResultsFor regular composites, the pre-warming did not affect DC, shrinkage and modulus but significantly increased the stress magnitude. Correlation tests indicated a significant relationship only between stress and polymerization shrinkage (r = 0.811343). SignificanceRegular composites can produce less polymerization stress than resin cements when luting laminate veneers. Polymerization stress was dependent on the shrinkage magnitude, but not on the degree of conversion nor the elastic modulus.

Role of fiber dosages and lengths on the mechanical strength, shrinkage, and pore structure of CO2-cured amorphous metallic-fiber-reinforced belite-rich cement composites

The impact of varying dosages and lengths of amorphous metallic fiber (AMF) on the mechanical strength, shrinkage, and pore structure of fiber-reinforced cementitious composites cured in water and in a carbonation chamber were assessed. This study evaluated fourteen mortar mixes, i.e., seven mixes for traditional water curing and seven for CO2-curing (60% relative humidity, 20 °C, and 10% CO2 concentration). The outcomes reveal that the compressive and flexural strength are significantly augmented for the mixes reinforced with AMFs as compared to the control mix (fiber-free mix), and this behavior is more pronounced with increased dosages and lengths of the AMF. Furthermore, compared to the control mix, significant mitigation in the development and magnitude of shrinkage was recorded with increased dosages and lengths of the AMF. The porosity and voids were all increased in the samples with AMF as compared to the control mix. The carbonation-cured specimens exhibited significantly higher mechanical strength, fewer voids, and higher shrinkage than those cured in water. Based on the experimental findings, it is recommended to use 0.50% volume of AMF and a length of 20 mm to produce fiber-reinforced cement composites, as this combination provides outstanding performance among all mixes tested here.

New Experimental Evidence for Drying Shrinkage of Alkali-Activated Slag with Sodium Hydroxide.

Alkali-activated slag (AAS) is emerging as a possible and more sustainable alternative to Ordinary Portland Cement (OPC) in the construction industry, thanks to its good mechanical and chemical properties. Conversely, the effects of its high drying shrinkage are still a concern for its long-term durability. This study aims to investigate the drying shrinkage behaviour of six AAS/sodium hydroxide mortar compositions and the main phenomena affecting their drying shrinkage behaviour. Specifically, the molarity, solution-to-binder ratio (s/b), autogenous shrinkage, creep compliance, microcracking, and carbonation are considered as possible causes of the differences between AAS and OPC. The results show that it is not possible to correlate the shrinkage magnitude with the molarity of the activating solution, while an increase in the s/b increases the drying shrinkage. Concerning the other factors, autogenous deformation remains significant even after a period of 112 days, while the creep compliance is definitely affected by the drying process but does not seem to affect the shrinkage magnitude. Furthermore, the presence of microcracks caused by the drying process definitely influences the drying shrinkage. Finally, carbonation depends on the molarity of the activating solution, even though its effects on the material are still unclear.

Microstructure of TiAl Capsules Processed by Electron Beam Powder Bed Fusion Followed by Post-Hot Isostatic Pressing.

The microstructures of intermetallic γ-titanium aluminide (TiAl) alloys are subjected to a certain degree of Al evaporation when processed by electron beam powder bed fusion (EB-PBF). The magnitude of the Al-loss is mainly correlated with the process parameters, and highly energetic parameters produce significant Al evaporation. The Al-loss leads to different microstructures, including the formation of inhomogeneous banded structures, thus negatively affecting its mechanical performance. For this reason, the current work deals with creating EB-PBFed TiAl capsules with the inner part produced using only the pre-heating step and melting parameters with low energetic parameters applying high beam speed from 5000 to 3000 mm/s. This approach is investigated to reduce the Al-loss and microstructure inhomogeneity after hot isostatic pressing (HIP). The results showed that the HIP treatment effectively densified the capsules obtaining a relative density of around 100%. After HIP, the capsules produced with the inner part melted at 3000 mm/s presented a lower area shrinkage (around 6.6%) compared to the capsules produced using only the pre-heating step in the core part (around 20.7%). The different magnitudes of shrinkage derived from different levels of residual porosity consolidated during the HIP process. The HIPed capsules exhibited the presence of previous particle boundaries (PPBs), covered by α2 phases. Notably, applying low energetic parameters to melt the core partially eliminates the particles' surface, thus reducing the PPBs formation. In this case, the capsules melted with low energetic parameters (3000 mm/s) exhibited α2 concentration of 3.5% and an average size of 13 µm compared to the capsules produced with the pre-heating step in the inner part with an α2 around 5.7% and an average size around 23 µm. Moreover, the Al-loss of the capsules was drastically limited, as determined by X-ray fluorescence (XRF) analysis. More in detail, the capsules produced with the pre-heating step reported an atomic percentage of Al of 48.75, while using low energetic melting parameters led to 48.36. This result was interesting, considering that the massive samples produced with standard parameters (so more energetic ones) revealed atomic Al percentage from 48.04 to 47.70. Finally, the recycled small particles showed a higher fraction of α2 phases with respect to the coarse particles, as determined by X-ray diffraction (XRD).

Experimental and numerical study on the mitigation of autogenous shrinkage of cementitious material

This study experimentally investigated the effects of surfactants and water-repelling agents on the hydration process, relative humidity, and mechanical properties of Portland cement pastes. Based on the measurement results, the degree of hydration, degree of saturation, capillary tension of autogenous shrinkage, and magnitude of autogenous shrinkage were simulated using a numerical model. In the numerical model, the elastic and creep components of autogenous shrinkage were calculated separately, and the creep component was simulated based on the solidification theory. The simulation results indicated that adding admixtures led to lower degrees of hydration and saturation. The capillary tension of the pure Portland cement was larger than that of the other mixtures. This can be attributed to several factors, including the smaller surface tension of mixtures with surfactants, larger contact angle of mixtures with water-repelling agents, and a lower degree of hydration of mixtures with both admixtures. Analyses of the simulated and measured results for different mixtures also show that creep plays an indispensable role in autogenous shrinkage. Adding a surfactant and a water-repelling agent can effectively mitigate autogenous shrinkage. However, when an excessive amount of water-repelling agent was added, its influence on the mitigation of autogenous shrinkage was insignificant.

Quantification of plastic shrinkage and plastic shrinkage cracking of the 3D printable concretes using 2D digital image correlation

There is great potential for 3D concrete printing to considerably transform the construction industry. An important step toward the transfer of this new technology into practical application is to gain the ability to control and mitigate plastic shrinkage of printed elements as well as related cracking. These phenomena occur at a very early age after the deposition of concrete due to the absence of formwork in the first place. The cracks can negatively influence durability, serviceability, and aesthetics of the printed structures. In this context, it is an important task to quantify plastic shrinkage of printed concrete and to capture the formation and propagation of cracks. The research at hand presents an easy-to-use, inexpensive experimental setup for quantifying the magnitude of plastic shrinkage and an accurate method for assessing plastic shrinkage cracking by means of 2D digital image correlation.

Cyclic swell shrink behaviour of lime and lignosulphonate amended expansive soil—An experimental quantification and comparison

The behaviour of expansive soils is majorly influenced by the mineralogy and the environmental conditions contributed by the seasonal moisture changes. Many structures found on the expansive soil depict severe distress due to the volume change behaviour of the soil. The volume changes correspond to moisture fluctuations which occur with the wetting–drying cycles associated with climatic variations. The wetting–drying​ cycles also impact the chemical treatment methods adopted to curtail swelling and shrinkage. The present study evaluates and compares the magnitude of swelling and shrinkage depicted by Lime and Lignosulphonate amended soils under wetting and drying cycles imposed under laboratory conditions. A specially modified oedometer apparatus was adopted to simulate the field drying conditions. The untreated soil exhibits higher swelling strain than the shrinkage strains with cycles of wetting and drying. There is a decrease of nearly 9% in swelling and 5% in shrinkage from the first cycle to steady state cycle. The swelling strain followed a decline to the steady state, however lime and LS amended soil depicted an initial decrease and then an increase in swelling strains before steady state. The treated and untreated soils also attain equilibrium characterized by different bandwidths and also exhibit difference in swelling and shrinkage rates, with untreated soil exhibiting a longer time to complete the swell-shrink cycles. The study further quantifies these variations for treated and untreated soil and the respective rates of primary and secondary swelling and shrinkage. The results are also justified with a physicochemical analysis of the leachate collected during the wetting–drying cycles.

The memory of thin polymer films generated by spin coating

We present results from isothermal and temperature-sweep creep experiments adapted to filaments which were derived from spin coated and subsequently crumpled thin polystyrene films. Due to the existence of residual stresses induced by preparation, the filaments showed significant shrinkage which we followed as a function of time at various temperatures. In addition, the influence of preparation conditions and subsequent annealing of supported thin polymer films on shrinkage and relaxation behavior was investigated. The temporal evolution of shrinkage revealed a sequence of relaxation regimes. We explored the temperature dependence of this relaxation and compared our observations with published results on drawn melt-spun fibers. This comparison revealed intriguing similarities between both systems prepared along different pathways. For instance, the magnitudes of shrinkage of melt-spun fibers and of filaments from crumpled spin coated polymer films are similar. Thus, our results suggest the existence of generic mechanisms of “forgetting”, i.e., how non-equilibrated polymers lose their memory of past processing events.Graphical abstract

A plastic shrinkage cracking risk model for 3D printed concrete exposed to different environments

The absence of formwork leaves early age 3D printed concrete vulnerable to excessive pore water evaporation. This study investigates the fundamental behaviour of the resulting plastic shrinkage cracking by exposing printed specimens to six drying conditions at concrete ages of 0, 1, 2 and 4 h (delay times). The results show that the rate of concrete mass loss is equal to the drying condition’s free water evaporation rate for the first few hours, causing significant desiccation and plastic shrinkage. A moderate evaporation rate removed 24% of the total mixing water from the specimen in only 2 h. The minimal surface moisture and low bleeding rate provide limited protection against pore water evaporation. Therefore, increasing the evaporation rate results in an immediate and direct shrinkage response in the concrete. Delaying the evaporation to the initial setting time decreases the shrinkage magnitude by 56%. A model for cracking risk is proposed based on the evaporation rate, surface to volume ratio, delay time and stiffening rate. Experimental results are used as validation.

Dimensional stability of cement paste and concrete subject to early-age carbonation curing

Early-age carbonation curing of concrete is receiving more interest in terms of performance improvement and emission reduction. However, the volume change of cement-based products subject to carbonation curing may become a concern because of the potential carbonation shrinkage and its related shrinkage cracking. The purpose of this study was to investigate the dimensional stability of cement paste and concrete subject to the early-age carbonation curing. It was found that the carbonation curing introduced first an initial shrinkage due to water evaporation upon gas injection and then generated an expansion due to CO2 uptake and carbonate precipitation. As carbonation proceeded, the deformation was switched to a secondary shrinkage after expansion. The residual deformation due to carbonation curing was shrinkage in cement paste samples and expansion in concrete samples. This was because the relative expansion due to carbonate precipitation in paste was not large enough to compensate for the shrinkage caused by water loss. However, for concrete samples, the introduction of aggregates reduced the pore spaces in concrete, leading to an expansion owing to the limited precipitation. The results of carbon dioxide uptake, XRD, and SEM analysis confirmed that calcium carbonate formation played a critical role in the relative expansion. The study also showed that cement-based products were more resistant to weathering carbonation after the early-age carbonation curing. After 61-day weathering carbonation exposure, both paste and concrete samples exhibited carbonation shrinkage as a result of carbonation of hydration products. However, the magnitude of shrinkage was much smaller in carbonation curing than in weathering carbonation because of the short period of exposure. Both carbonations did not significantly affect the compressive strength of carbonated products. Carbonation curing likely makes concrete products more dimensionally stable in the long-term service.

Drying shrinkage of one-part alkali-activated slag concrete

The aim of this study was to evaluate the drying shrinkage of one-part alkali-activated slag concrete (AASC) for up to 180 days that is influenced by mix design parameters. A total of 24 mix designs for AASC and one for OPC concrete were made and cured in two different environments. The impacts of mix design parameters including water to binder ratio, silica fume to binder ratio, alkaline activator to slag ratio, and two curing regimes, in water and sealed plastic bag, on drying shrinkage were investigated, using experimental tests and SEM analysis. The results showed nearly 75% of the 180-day shrinkage was reached within 20 days. The results also revealed that the addition of silica fume considerably reduced drying shrinkage magnitude. AASC samples cured in sealed plastic bags resulted in at least a 5.9% increase in drying shrinkage. The maximum drying shrinkage was observed in a mix design containing the highest water to binder ratio and zero silica fume content regardless of curing type. The results indicated that the application of silica fume as a co-binder led to a considerable reduction in the drying shrinkage.

Drying shrinkage properties of expanded polystyrene (EPS) lightweight aggregate concrete: A review

Expanded polystyrene (EPS) is currently being utilized in sustainable materials owing to its ultra-low density and superior thermal performance. It can be incorporated in concrete mixtures to replace coarse aggregate to produce lightweight aggregate concrete (LWAC). Concerning the high shrinkage development in LWAC, the present study reviews the available published articles regarding the drying shrinkage of lightweight concretes containing expanded polystyrene. According to the previous studies, the drying shrinkage development in expanded polystyrene concrete (EPSC) has been reported to be greater than that in conventional concrete, which must be considered for its application in the construction industry. It is mainly attributed to the low elastic modulus and mechanical properties of the EPS. However, incorporating additives and fibers can improve its shrinkage resistance properties. A comprehensive comparison of drying shrinkage magnitude between various LWAC showed that the drying shrinkage strain of EPSC is not generally higher than other types of LWAC; however, the density of EPSC was measured lower than that in other types of lightweight aggregate concretes.

Mango Stem Response under Different Irrigation Regimes

ABSTRACT Mexico has dominated the international mango trade having high yields and excellent fruit quality. The use of soil, plant and environmental sensors can monitor plant hydric status and optimize water application. Linear resistance dendrometers were developed and installed in a high-density 8-year old commercial mango orchard during two seasons; 10 in 2019 and 40 in 2020. Stem diameter fluctuations were acquired every 10 minutes to obtain maximum diameter (MXD), minimum diameter (MND), morning slope (MS) and afternoon slope (AS). Mango stem response during flowering, fruit-fall and fruit-growth was analyzed after applying daily irrigation (DI) or reduced deficit irrigation (RDI). Yield was similar for both treatments, but water use efficiency was higher with deficit irrigation. A new variable known as negative integral (NI) was obtained from the dendrometer signature after adding all the values between 8:00 and 18:00. NI provided a stem shrinkage magnitude, peaks attributed to transpiration and slopes showing flow transport to and from the trunk. NI presented a high correlation of 0.85 against T7 during the flowering stage for RDI-1. If NI crossed zero, a severe stress was present; a high AS present in the evening, indicates nutrient solution provided to fruits. Fruit yield depends on panicle number and fruit-drop during the first production stages, being RDI-1 more efficient in retaining fruits.

Drying shrinkage behavior of hybrid alkali activated cement (HAAC) mortars

Shrinkage is a vital factor for hybrid alkali activated cement (HAAC) related to durability. In this work, the drying shrinkage behavior of HAAC mortars with various precursors, curing regimes and activator states was investigated. Portland cement mortar and alkali activated cement (AAC) mortar were used as control groups. Results showed that the drying shrinkage magnitude of HAAC mortar is lower than that of AAC mortar but higher than that of Portland cement mortar. Slag-based HAAC mortar shows the largest shrinkage value and the introduction of fly ash could temper shrinkage slightly. The steam curing and solid activation could mitigate the magnitude of drying shrinkage for HAAC mortar. The drying shrinkage is irrespective of the water loss in this study. MIP, SEM, and XRD analyses were undertaken to gain more insights into the mechanisms of drying shrinkage of HAAC. More crystalline phase and higher Ca/Si gel of HAAC paste tempers the drying shrinkage of HAAC mortar. The larger capillary pores size is likely to explain the lower shrinkage of fly ash-based HAAC mortar.

The effect of restrained early age shrinkage on the interlayer bond and durability of 3D printed concrete

3D printed concrete exhibits a high magnitude and rate of plastic shrinkage (early age drying-induced shrinkage) compared to conventional cast concrete. This study investigated if restraining this shrinkage adversely affects the long-term durability and mechanical performance. Shrinkage was restrained by inserting reinforcement-like rods into the fresh concrete and exposing the specimen to a moderate evaporation rate. The interlayer bond strength, permeability and ion penetration of the unrestrained and restrained specimens were then compared. The results show that shrinkage causes shear strain concentrations at the interlayers due to a lack of particle interlocking and non-uniform pore water evaporation from the undulated evaporation face. Consequently, discrepancies in the transfer of shrinkage between layers occur, a phenomenon coined as interlayer slip. Evidence is presented of a 12% reduction in interlayer bond strength, a 70% higher permeability and 17% higher chloride ion penetration. These adverse consequences were due to interlayer slip and microcracking. Nonetheless, the durability of uncracked printed concrete is satisfactory, even with localised interlayer slip and microcracking.

Geospatial Analysis of Wetland Dynamics on Lake Abaya-Chamo, The Main Rift Valley of Ethiopia

Wetlands worldwide and in Ethiopia have long been subject to severe degradation due to anthropogenic factors. This study was aimed at analyzing the impact of land use/land cover dynamics on Lake Abaya-Chamo wetland from 1990–2019. Data were acquired via Landsat TM of 1990, ETM+ of 2000, and OLI of 2010 and 2019 images plus using interview. Supervised classifications (via ERDAS14 and ArcGIS10.5) were applied to detect land use/land cover classes. Change matrix model and Kappa coefficients were used for analysis of the land use/land cover dynamics in the lake-wetland. It was found that forest; water body, shrub land, agricultural land, settlement and swamp area were the main land use/land cover classes. Wetland/swamp area has continuously declined throughout 1990–2000, 2000–2010 and 2010–2019 where its magnitude of shrinkage in the respective periods was 11.4 % (700 ha), 16 % (867 ha) and 31.3 % (1,424 ha). While ‘settlement’ and ‘water body’ of the lake-wetland increased at progressively increasing magnitudes of changes in three periods within 1990–2019, ‘shrub land’ and wetland/‘swamp’ declined at progressively increasing magnitudes of loss in the same periods. Siltation, rapid population growth-led expansion of settlement and irrigation-based farming were the main drivers of the land use/land cover dynamics and degradation of the lake-wetland. Thus, consistent mapping and integrated actions should be taken to curb the threats on the sustainability of the lake-wetland in Southern Ethiopia. To reduce the impact of LULC dynamics on wetlands, the regime should: advance a clear political, institutional and legal framework for wetland management.

24 hour polymerization shrinkage of resin composite core materials.

The study's purpose was to evaluate the 24-hour polymerization shrinkage of resin composite core materials. Eleven resin composite core material samples (n= 12) were evaluated using a non-contact imaging device with measurements obtained over 24 h. Shrinkage values were determined corresponding to proposed times involved with CAD/CAM same-day treatment and at 24 h. Shrinkage data was statistically compared using Friedman/Dunn's test for intragroup analysis and Kruskal Wallis/Dunn's test for intergroup analysis, all at a 95% level of confidence (α=0.05). Mean results identified a wide volumetric shrinkage range with considerable similarity overlap. Inconsistent shrinkage behavior was evident and all materials reached maximum values before 24 h. No significant difference was observed during proposed digital same day all ceramic crown procedures, but some differences were noted at 24 h. Under this study's conditions results were material specific, at times inconsistent, with wide variation. Shrinkage consistently increased for all products and it is not known if the continued shrinkage magnitude may compromise the stability and fit of all-ceramic crowns at 24 h.

SIZE EFFECT ON THE ULTIMATE DRYING SHRINKAGE OF CEMENT MORTAR: 1-YEAR EXPERIMENT AND NUMERICAL MODELING

The magnitude and time evolution of shrinkage are influenced by numerous factors which are implemented in the design codes often in a different way. The time-dependent behavior of concrete in structures sensitive to creep and shrinkage should be verified by means of short-term laboratory measurements. Extrapolation of drying shrinkage from short-term measurements is an illposed problem. The process is extremely slow but can be accelerated by reducing the specimen size. The knowledge of the size-effect on drying shrinkage is a necessity to establish the transition from the laboratory to the structural size. In the literature, the experimental data on such size-effect are insufficient. For this reason a new experiment was developed to study this phenomenon on small-scale specimens made of cement mortar and the results from the first year are summarized in this paper. The measured data are validated by coupled FEM hygro-mechanical simulations.