Shrinkage Behavior Research Articles

How to predict residual stresses of curing adhesives ab initio solely using extended rheometry

ABSTRACT Prediction of residual stresses in adhesively bonded joints is a major topic among practitioners, as they significantly contribute to failure. The experimental determination of relevant material properties, like shrinkage, modulus development, and relaxation behavior, is considered highly complex. Viscoelastic and numerical models are often simplified to suit specific applications. However, most of them do not consider all relevant parameters or limited portions of the curing process. This publication addresses the lack of experimental methods to determine cure-dependent properties of reactive adhesives to use them as input for FE modelling to predict cure-induced stresses. The authors focus on extended rotational rheometry (ExRheo), to determine shrinkage, shear modulus, and relaxation in dependency of curing time for three adhesives. The relationship between change of viscoelastic properties, shrinkage, and curing degree is determined through DSC and kinetic modelling. The experimental results are modelled to be implemented in a numerical analysis in order to predict cure-induced stresses in constrained rheological experiment in ExRheo. Numerical results show very good agreement with the experiments, which validate the methodology. For the first time, shrinkage induced residual stresses are modelled ab initio over the curing process, without any assumptions, solely based upon direct experimental data using a single device.

Suitability of Enset Fiber with Coffee Husk Ash as Soil Stabilizer

Expansive soil is a problematic soil due to swelling and shrinkage behavior during moisture variation. Damage to shallow foundations like pavement and footings of residential houses occurred due to these soils. Different scholars deal with stabilizing expansive soils using different mechanisms. This study also evaluated the suitability of Enset fiber with coffee husk ash materials to improve the expansive property of soils found in Jimma town. Different geotechnical parameters were determined for virgin soil and coffee husk ash with virgin soil. After treating the natural soil with varying percentages of coffee husk ash (5%, 10%, 15%, and 20%), the optimum levels of coffee husk ash were determined. Different laboratory tests such as CBR value, compaction test, and Atterberg limits were determined using the optimum coffee husk ash with varying percentages of enset fiber (0.3%, 0.6%, 0.9%, and 1.2%). The study reveals that the addition of coffee husk ash to enset fiber significantly increases the shear strength of expansive soils. With the addition of 15% of coffee husk ash and 0.9% of enset fiber, all tested geotechnical parameters improved the expansive soils to be used as subgrade materials. The soil changed from highly swelled material to poorly swelled material. Therefore, it can be concluded that the reuse of agricultural waste of coffee husk ash with enset fiber is applicable for expansive soil stabilization since it can improve the engineering strength of expansive soils and it is an economic and environmentally friendly material.

Drying shrinkage behavior of geopolymer mortar based on kaolinitic coal gangue

The coal industry generated tons of waste over the years of mineral extraction, and the waste disposal leads to soil and air pollution caused by acid mine drainage and spontaneous combustion. Seeking environmental sustainability, this paper investigated the valorization of coal tailings as a primary precursor in geopolymer mortar. The effect of Portland cement as a hardened admixture was evaluated on the mechanical and physical properties of geopolymer mortar, by replacing the coal tailings with a lower amount of Portland cement. Six mortars were characterized by several standard tests besides ultrasonic pulse velocity, mercury porosimetry (MIP), and drying shrinkage, the microstructure was evaluated by SEM/EDS analysis and X-Ray diffraction. The workability was slightly higher for geopolymer mortars with calcium by almost 5%, and the addition of sugarcane molasses and flue gas desulfurization increased the fluidity, reaching 220 mm. The Portland cement improved the early strength of geopolymer mortar by almost 10 MPa at 7 days, due to the acceleration of chemical reaction yielding a denser and heterogeneous matrix. The SEM/EDS analysis evidenced the co-existence of the polymeric matrix and C-A-S-H gel. The compressive strength at 28 days was higher than 20 MPa for all geopolymer mortars. A higher reaction rate provided by calcium addition leads to higher densification of the aluminosilicate matrix at early ages. The ultrasonic pulse velocity (UPV) confirmed denser matrix formation, and the geopolymer with 05 wt% of Portland cement presented UPV of 2700 m/s at 07 days, while the non-calcium geopolymer showed 2000 m/s. The denser matrix formed limited the water loss, decreased the open porosity, and improved the stiffness of geopolymer mortars, yielding a drying shrinkage almost 50% lower than for geopolymer without calcium addition. Finally, this paper established the lower replacement (5 wt%) of coal tailings for Portland cement produced efficient geopolymer mortar, with excellent physical and mechanical properties for in situ application without a thermal cure.

Compressive and shrinkage behaviors of recycled aggregate concrete containing recycled sand from weathered residual soil of granite and MgO expansion agent

The simultaneous use of recycled coarse aggregate and recycled sand from weathered residual soil of granite to prepare recycled aggregate concrete can further promote the recycling of construction and demolition waste. However, the shrinkage performance of concrete containing both recycled coarse aggregate and recycled sand remains unknown. In this study, compressive and shrinkage tests were conducted on recycled aggregate concrete with recycled coarse aggregate, recycled sand and MgO expansion agent (MEA). The compressive and shrinkage behaviors suggest an optimum MEA dosage of 6%. The results showed that: (a) increasing recycled sand replacement ratio (30–70%) has little effect on compressive behaviors of concrete, but including 50% recycled coarse aggregate decreases the compressive strength, as does increasing MEA dosage (4–8%); (b) the autogenous shrinkage of concrete decreases with the addition of 50% recycled coarse aggregate, but it increases with increased recycled sand replacement ratio, this can be significantly compensated by incorporating MEA; (c) the drying shrinkage of concrete increases with the adoption of 50% recycled coarse aggregate and increased recycled sand replacement ratio. Adding MEA compensates, with the compensation increasing with its dosage. Finally, models for predicting autogenous and drying shrinkage of recycled aggregate concrete with recycled coarse aggregate, recycled sand and MEA are proposed.

Tail void grouting material: A parametric study on the role of hydro-mechanical characteristics in mechanized tunneling

This paper investigates the influence of the hydro-mechanical properties of the tail void grouting material on short and long-term behavior of the tunnel. These characteristics are of high importance affecting the deformations and pore pressure regime around the tunnel as well as forces and deformations in the linings. Various properties of the tail void grouting material including thickness of grouting layer, permeability, stiffness, hardening ratio, shrinkage, and creep behavior are investigated using 3D Finite Element Method. The effect of each parameter variation on the representative surface settlements as well as deformations and excess pore pressures around the tunnel along with the axial forces and radial displacement of the linings has been thoroughly investigated. According to the results, a high hardening ratio corresponding to a fast-hardening grout could lead to 75% lower surface settlement. Utilization of a low permeable grout results in excess pore pressure remaining in the system which is 4.5 times higher than using a high permeable grout. The magnitude axial forces of the lining will depend on the direction of dissipation, when the permeability of the grout is concerned.

Creep Deformation and Its Effect on Mechanical Properties and Microstructure of Magnesium Phosphate Cement Concrete

Creep deformation is an important aspect of magnesium phosphate cement (MPC) used as a structural material. In this study, the shrinkage and creep deformation behaviors of three different MPC concretes were observed for 550 days. The mechanical properties, phase composition, pore structure, and microstructure of MPC concretes after shrinkage and creep tests were investigated. The results showed that the shrinkage and creep strains of MPC concretes stabilized in the ranges of -140 to -170 με and -200 to -240 με, respectively. The low water-to-binder ratio and the formation of crystalline struvite were responsible for such low deformation. The creep strain had almost no effect on the phase composition; however, it increased the crystal size of struvite and reduced the porosity, especially the volume of pores with diameters <20 nm and >200 nm. The modification of struvite and densification of microstructure led to an improvement in both compressive strength and splitting tensile strength.

Numerical simulation of shrinkage porosity defect in billet continuous casting

Abstract Shrinkage porosity is a typical internal defect in the continuous casting billet, which occurs frequently and is difficult to solve. To explore the influence factors of central shrinkage porosity, a novel unsteady thermomechanical coupling analysis algorithm is developed based on the billet solidification characteristics, and the central shrinkage behavior during the ending solidification process is simulated. Results show that when the casting speed increases from 1.6 to 2.8 m·min−1 and the center outward displacement is reduced from 9.20 × 10−2 mm to 5.8 × 10−2 mm, it means casting speed has a significant effect on the formation of shrinkage porosity, and for this caster, the higher casting speed is more suitable for the secondary cooling zone. Without the changes in the solidification structure, when the superheat degree of molten steel increases from 10 to 40°C, the center outward displacement value decreases from 7.12 × 10−2 mm to 6.91 × 10−2 mm. In that case, the superheat degree has no obvious effect on the center displacement value.

Mechanical properties, durability performance and interlayer adhesion of 3DPC mixtures: A state‐of‐the‐art review

AbstractIn this study, the strength and durability performance of 3D printing concrete mixtures (3DPC) were examined in terms of the materials used in their production and printing process parameters (interlayer interval time, printing speed, and nozzle shape). Due to the anisotropic nature of 3DPC, it was understood that the compressive strength depends on the loading direction. It was emphasized that it is necessary to control the shrinkage behavior of 3DPC mixtures due to the lack of formwork and the high dosage of binders. It was reported that the interlayer adhesion of 3DPC is highly dependent on the interlayer interval time and printing speed parameters. It was understood that nozzle shape and standoff distance affect the mechanical properties and surface roughness of 3DPC specimens, and this effect is more pronounced in mixtures with high static yield stress values.

Influence of the mix parameters on shrinkage properties of environment-friendly mortar

ABSTRACT Cracks in concrete structures are generally initiated due to the shrinkage i.e. the volume change characteristics of the concrete structures. In this experimental study, effects of the mix parameters related to alkaline liquid (AL) and recycled fine aggregate (RFA) on the shrinkage behaviour of environment-friendly mortar mixes produced with fly ash (FA)-based geopolymer binder and RFA were investigated and reported. To find out the effects of AL, concentration of liquid sodium hydroxide (LSH) was varied from 6M to 16M, ratio of liquid sodium silicate (LSS) to LSH in AL was varied from 1.0 to 2.5 and AL/FA ratio was considered as 0.4 and 0.6. Different fly ash-based geopolymer mortar mix were produced depending on above-said combinations of mix parameters along with the RFA content (by weight) of 10%, 20%, 30%, 40% and 50% in lieu of natural fine aggregate. Prismatic specimens (25 mm × 25 mm × 285 mm) were cast and cured at ambient air temperature to determine the shrinkage behaviour. Higher RFA content in mix, higher LSS/LSH ratio in AL and higher AL/FA ratio resulted in higher shrinkage value. But, lesser shrinkage value was noticed for those specimens of mortar mix with the consideration of higher concentration of LSH in AL with varying RFA content.

Curing-dependent thermo-viscoelastic and shrinkage behaviour of photopolymers

This study investigates the influence of curing on the thermo-viscoelastic properties and chemical shrinkage of a commercially available photopolymer resin used in SLA and DLP 3D printing and presents a modelling approach for predicting material properties. UV rheometer and DMA measurements were performed to investigate the viscoelastic properties of the photopolymer material as a function of temperature, degree of cure, and frequency. Time–temperature and time-cure superposition principles were applied to the experimental results. In addition, the chemical shrinkage behaviour was studied by the UV rheometer as a function of the degree of cure and temperature, and a model equation was proposed based on these parameters. Our experimental findings have led to the development of constitutive equations for the complete material behaviour.

Prediction of Shrinkage Behavior of Stretch Fabrics Using Machine-Learning Based Artificial Neural Network

Stretch fabric provides good formability and does not restrict the movement of the body for increased tension levels. The major expectations of a wearer in an apparel fabric are a high level of mechanical comfort and good aesthetics. The prediction of shrinkage in stretch fabric is a very complex and unexplored topic. There are no existing formulas that can effectively predict the shrinkage of stretch fabrics. The purpose of this paper is to develop a novel model based on an artificial neural network to predict the shrinkage of stretch fabrics. Different stretch fabrics (core-spun lycra yarn) with stretch in the weft direction were manufactured in the industry using a miniature weaving machine. A model was built using an artificial neural network method, including training of the data set, followed by testing of the model on the test data set. The correlation of factors, such as warp count, weft count, greige PPI, greige EPI, and greige width, was established with respect to boil-off width.

Finite Element Analysis of High-Strength Concrete Pavement Made With The Addition Of Fibres

This paper provides an analytical Solutions and software-based analysis on the determination of Stress-Strain behaviour of High strength concrete pavement slab by applying number of axle load parameters given in the guideline of IRC-58 in the construction of Rigid pavement. The effect of the use of hybrid fibres, such as steel fibres and polypropylene fibres, on the behaviour of stress distribution is also studied. Shrinkage in HSC due to the incorporation of Hybrid fibres in different proportions at four Curing Temperatures is also analysed. FEA has been used to analyse the Shrinkage behaviour of High Strength Concrete Pavements with different geometry and thermal curing temperatures as (5°C, 20°C, 35°C, and 50°C). In the present research, the shrinkage analysis, Stress distribution behaviour in High Strength concrete pavement will be studied using Hybrid fibre of steel and polypropylene with a dosage of 1%, 1.5% and 0.1%, 0.2% respectively and by applying axle loadings of single, dual, tri and tandem axle as per IRC 58. Axle load is applied at the centre, edge and corner of the pavement slab and the stress distribution results are obtained. The Analytical solutions are obtained from Westergaard’s equations and software-based results are compared with the analytical solutions and there are very less dissimilarities between both the results.

Numerical simulation of fracture mechanisms due to directional shrinkage in natural composites

The use of natural composites in modern engineering applications has numerous benefits owing to their excellent sustainable attributes and negligible environmental impacts. The full commercialization of natural composites as alternative materials to conventional ones is undermined by environmental factors such as moisture content leading to varied shrinkage and swelling behaviors. Uncontrolled shrinkage behavior can often lead to premature split in natural composites. The aim of this study is to investigate the fracture mechanisms due to directional shrinkage in natural composite material through numerical simulation by considering the finite element modelling software of LS-DYNA. From numerical results, directional shrinkage could be seen to clearly affect the fracture patterns in natural composites as compared to the control one. The fracture patterns, which indicated a narrowed region of stress concentration in the material, is assumed to emanate from internally induced forces in the material, namely tensile and compressive forces. This specific pattern is associated to longitudinal split failure typically observed in orthotropic materials. Results of this study can be useful to further investigate the complex fracture behavior in natural composite materials to better understand their durability limitations.

Comparison of Direct Ink Writing and Binder Jetting for additive manufacturing of Pt/Al2O3 catalysts for the dehydrogenation of perhydro-dibenzyltoluene

Two additive manufacturing (AM) techniques, namely extrusion-based Direct Ink Writing (DIW) and powder-based Binder Jetting (BJ), were thoroughly compared to assess their respective advantages and drawbacks for catalyst shaping. The 3D printed monolithic Al2O3 supports were wet impregnated with H3Pt(SO3)2(OH) and tested for the dehydrogenation of perhydro-dibenzyltoluene (18H-DBT), a liquid organic hydrogen carrier (LOHC). The supports were analyzed regarding their specific surface area, compression strength, shrinkage behavior and pore size distribution with calcination temperatures ranging from 600 - 1200°C as well as 3D print specific characteristics. Benefiting the liquid phase reaction, pore diameters below 26nm were diminished above Tcalc = 1050°C, revealing a BET surface area of 26m2/g for BJ and 11m2/g for DIW printed supports. Furthermore, increasing the impregnation duration from 0.5h to 12h showed increased Pt loading, larger metal particles, and a deeper penetration into the support. Most notably, for BJ the Pt loading is generally higher due to higher meso- and macroporosity of the support. Catalytic 18H-DBT dehydrogenation with powder and monolithic catalysts showed equal dehydrogenation rates with both 3D printing methods, respectively. The achieved Pt productivity was about 4.3gH2gPt−1min−1 for powder tests and 2.7gH2gPt−1min−1 for monolithic pellets.

Utilisation of Plastic Waste as Synthetic Fiber and Aggregate in Concrete –A Review

Plastic waste materials are non-biodegradable and therefore require safe and economic disposal to have a green environment. The use of plastic waste in the construction industry holds a big potential in minimizing the global environmental burden. For this purpose a comprehensive review of published research works was done which disclosed the use of plastic waste materials like polypropylene (PP), high-density polypropylene (HDPE) and polyethylene terephthalate (PET) in concrete as partial or full replacements for cement and aggregates. This paper reviewed various properties like workability, compressive strength, split tensile strength, flexural strength, temperature effect, elastic modulus, drying shrinkage, carbonation and structural behavior of concrete with stated plastic waste materials. The review revealed that the strength, durability and structural characteristics of such concrete improved while the workability was reduced. The review gave information that the footpath panels with HDPE, PP and PET fibre can be used as a substitute for steel-reinforced panels. The review also indicated that further detailed investigations on various strength and durability properties are required on concrete made using plastic wastes like HDPE, PP and PET with various aspect ratios.

Swelling–shrinkage mechanisms of diatomaceous soil and its geohazard implication

Current understanding of soil behaviors from classic soil mechanics is constantly challenged by a variety of unusual soils, one of which is diatomaceous soils (DSs). It is well understood that this biological-origin soil has fundamentally different geotechnical features from that of common fine-grained soils because of the presence of diatom fossils. Recently, increasing geohazards and engineering disasters associated with DS swelling–shrinkage are reported but the exact role of diatoms in determining soil swelling–shrinkage, the underlying mechanisms, and the geohazard implications, have not yet been revealed. This study systematically investigates the swelling–shrinkage behavior of natural DS as well as artificial mixture of diatoms and clay minerals (kaolinite and montmorillonite). The swelling–shrinkage behaviors are explained from the perspectives of mineralogy and microstructure as revealed through X-ray diffraction, scanning electronic microscopy, and transmission electron microscopy. Diatoms have a special microstructure with inter-frustule pores, and the intra-skeletal and skeletal pores in DS make the soil characterized by a high void ratio and water content. In addition, the presence of diatoms curbs the swelling–shrinkage of DS but this may be overwhelmed by the high stress generated due to the swelling of montmorillonite. The wetting–drying cycles subjected to DS result in fissure development, a higher level of swelling–shrinkage behavior, and ultimately in related geohazards such as landslides. The distinct swelling–shrinkage behavior of DS makes the previous classification inapplicable; thus, more rational classification methods are adopted. This study enhances the understanding of the swelling–shrinkage behavior of DS and the control of related geohazards.

Influence of compaction on the soil shrinkage and swelling curves

The behaviour of soils undergoing deformation due to changes in water content can be described using Soil Shrinkage Curves (SSCs). The SSCs are normally influenced by several factors as the soil’s fabric, different compaction levels, residual void ratio, and the shrinkage limit. In this study, shrinkage curves at different compaction levels were obtained using both wax coating and image analysis as volumetric quantification methods. Both techniques returned consistent results. To fit the obtained experimental data, a single equation is proposed with fitting parameters pertaining to the physical characteristics of the soil samples used. The use of Mercury Intrusion Porosimetry (MIP) is also incorporated to further analyse the structure of the soils being studied. The effect of the drying path on the structure was more apparent in the size range of 100-2000 nm. The effects of compaction on soil structure and shrinkage behaviour were also discussed in the study. The presented work provides valuable insights on the effect of different compaction levels on the soil shrinkage behaviour.

Effect of using alternate elastic and non-elastic yarns in warp on shrinkage and stretch behavior of bi-stretch woven fabrics

Stretch woven fabrics are known for their elastic and recovery properties. To date, they found many interesting applications from simple jeans to complex fabric structures with functional properties for example bi-stretch auxetic woven fabrics, compressions garments and stretchable textile carriers for healthcare applications. Many studies have been carried out on the physical, mechanical and comfort properties of stretchable knitted and woven fabrics. However, to identify combination of yarns with different stretch properties and other design parameters required to meet multiple objectives in the production and usage of bi-stretch woven fabrics is an area that has been taken up by fabric scientists recently. This study compared the effect of using elastic yarns and alternate elastic and non-elastic yarns in warp on the properties of bi-stretch woven fabrics while using elastic yarns in weft direction. It was found that shrinkage of the fabrics made of elastic yarns was higher along the warp direction as compared to that in weft direction due to shrinkage balancing effect; however, in case of fabrics made of alternate elastic and non-elastic yarns in warp the shrinkage behavior was exact opposite. The comparison of shrinkage for different weave patterns revealed that satin had the highest shrinkage followed by twill and plain, due to least number of interlacements in satin among these three patterns.

Um novo método para a determinação da retração de argamassas nas primeiras 24 horas de hidratação

abstract: The shrinkage of cementitious materials is a complex phenomenon of volume reduction that can result in cracking, affecting the durability of these materials. The Brazilian standard ABNT NBR 15261 addresses long-term shrinkage without emphasis on the initial phase (&lt; 24h) of hydration, which contains the plastic state of the cementitious material. Therefore, a method was proposed to measure the shrinkage in the first 24h of mortar hydration, on a laboratory scale, from prismatic samples, using molds from the Brazilian standard ABNT NBR 15261 (285x25x25mm) and rigid elements that transmit horizontal displacements of the sample to dial gauges. Cement mortar specimens were studied with the water/dry materials ratio fixed at 0.168 and varying the binder/aggregates ratio linearly: 33% (1:3); 25% (1:4); and 17% (1:6). Different exposures to the environment (sealed, open and wind) were applied. The analysis indicated that the proposed method was sensitive enough to indicate statistically significant relationships between the maximum initial shrinkages and the variation in the concentration of the binders, as well as indicating variations in the behavior of the initial shrinkage. The increase in cement concentration caused an increase in the average initial shrinkage of 76% in the samples exposed to air, 54% in those exposed to 5 m/s wind, and 22% in the sealed samples.

Seismic Behavior and Failure Mechanism of Pile-Group in Mildly Sloping Liquefiable Soils with Crusts: Large-Scale Shaking Table Experiment

ABSTRACT A one-g shake table experiment was performed to reveal the failure mechanism of the pile group in sloping liquefiable soils with crusts. The results show that the shallow saturated sand exhibits the alternate behavior of dilatancy and shrinkage, which induces high-frequency peak acceleration. In addition, larger PGA tends to transfer vulnerable positions of the pile in the liquefiable layer from the shallow layer to the interface. Moreover, the pile group effect mainly manifested in piles at the bottom of saturated sand and pile-head during strong earthquakes.