Shrinkage Cracking Research Articles

Prediction Model of Shrinkage Crack Propagation in Cross-Section of Timber Components

Shrinkage cracks severely affect the safety of wood structures. Therefore, the moisture stress distribution of shrinkage cracks should be analyzed, and the interface crack depth of wood components predicted. In this paper, the equilibrium conditions, physical conditions, geometric conditions, and coordination equations of the disk humidity stress under a moisture content gradient Δw are deduced by referring to the elastic analytical solution model of temperature stress. Moreover, the humidity stress distribution equation is established, which is verified via the finite element method. The critical water content and shrinkage crack depth prediction models are further deduced based on the humidity stress distribution. The usability of the model is further verified using the test data of actual engineered wood components. The results demonstrate that the moisture stress is not determined by the initial moisture content Wi, equilibrium moisture content We, or member size but by moisture content gradient Δw. The shrinkage crack prediction model of wood components in cross-section can be applied to actual engineering prediction to provide a theoretical basis for the reinforcement measures and safety evaluation of wood structures.

Use of fibre reinforced polymer (FRP) in new construction and in strengthening of existing structures

Concrete is the primary construction material for most building projects today owing to its versatility, moldability and superior strength in compression. Concrete however is an inherently brittle material with quite poor tensile strength and has very low resistance to cracks and their propagation throughout the medium. In this research paper, a thorough compilation of previous work on the development of FRPs, their performance under various conditions through traditional structural loading techniques such as 4-point loading and their implementation is provided. Fibre reinforced polymers (FRP) allow alterations in concrete’s structural behaviour under tensile loading as well as expansions during exposures to extreme temperatures and routine shrinkage cracks through addition of small fibres that act as anchors preventing the widening of cracks as well as behaving in a similar fashion to the conventional steel reinforcement. FRP not only comes from small hair like fibres but also in the form of wraps which provide confinement on beams and columns increasing the compressive strength of the element as well as reducing the tensile loads, similar to how prestressing tendons alter the behaviour of prestressed concrete.

Study on Development of M20 and M25 Grades of Self Curing Concrete Using Formaldehyde and Sodium Polyacrylate

Abstract: Self-curing concrete, a specialized solution, eliminates external curing for optimal performance in construction. It maintains internal moisture, reducing autogenous shrinkage and early-stage cracking. This innovative approach, promoting sustainable practices, is valuable for high-rise buildings and bridges. Self-Curing properties achieved in concrete through the incorporation of Sodium Polyacrylate and Formaldehyde. Extensive testing was conducted on diverse concrete samples to evaluate their properties, encompassing workability, compressive strength, tensile strength, and flexural strength. Sodium polyacrylate which is a super absorbent polymer is added to the concrete mix of M20 & M25 grade of concrete in variations (0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%) by weight of cement. Formaldehyde added to concrete mix used as shrinkage reducing agent is added 1% with water. Light weight aggregate like brick chips replaced 10% of coarse aggregate are used because bricks absorb and holds a large amount so water. So pre-saturated brick chips are also used to provide internal curing. Sand is replaced by wood powder by 5%, as it also absorbs water. The compressive strength tests were carried out on M20 and M25 grade concretes with different water-cement ratios (for M20 w/c ratio is 0.50 & for M25 w/c ratio is 0.40), adhering to BIS: 516 – 1959 standards. The results indicated that the addition of sodium polyacrylate by weight of cement up to 0.6% led to optimal compressive strength values, beyond which further additions resulted in a decline in strength. Similarly, the split tensile strength tests for M20 and M25 grade concretes showcased the highest values at 0.6% addition of sodium polyacrylate by weight of cement. Subsequent increases in the additive led to a decrease in split tensile strength. Finally, the flexural strength tests for both M20 and M25 grade concretes yielded their highest values at 0.6% sodium polyacrylate by weight of cement, with diminishing flexural strength observed with higher additive percentages. These findings offer valuable insights into enhancing the self-curing properties of concrete and optimizing its characteristics by utilizing sodium polyacrylate as an additive.

Numerical 3D‐bifurcation analysis of star‐shaped crack patterns using the energy method

AbstractThe present research deals with a three‐dimensional (3D) Finite Element Method (FEM) bifurcation analysis based on the global mechanical potential that can be used to find the parameters at which a crack pattern changes. In our case we want to analyze at which point the star‐shaped shrinkage cracks in an aqueous colloidal suspension filled in a glass cylinder change from four to three or two cracks growing. The driving force for the crack growth is shrinkage caused by diffusion controlled drying. The 3D crack front geometry is described efficiently by using a Fourier series approach. Based on steady‐state crack growth, the Fourier coefficients are determined in a first step using an optimization algorithm. As a result, the time dependent crack growth can be determined. In a second step, the bifurcation point is determined by an eigenvalue analysis of the second order derivatives of the potential energy of the system. If the lowest eigenvalue reaches zero the fundamental solution becomes unstable and a transition will occur. Our analysis shows that the transition from four to two cracks is preferred over the transition from four to three cracks.

Long-term field monitoring of slabs-on-ground reinforced with GFRP bars

The current design of GFRP bar-reinforced slabs-on-ground, according to ACI 440.1R-15 is based on an empirical equation derived from the design of steel-reinforced concrete slabs-on-ground, developed based on the subgrade drag equation proposed in Portland Cement Association code (1990). ACI 440.1R-15 explicitly stipulates that field performance data from the application of FRP bar-reinforced slabs-on-ground is required to validate the equation. This paper reports the experimental outcomes of a comprehensive study on the long-term field monitoring of eight large-scale slab-on-ground specimens. Slabs of plan dimensions 6000 × 1100 mm2, resting on a lean concrete subbase over a compacted soil subgrade and exposed to harsh ambient environment, were monitored for 525 days to study rebar and concrete strain development and concrete cracking. The exposed ambient environment was characterized by averages of 41.7 ℃ with RH 12.8% in summer and 9.5 ℃ with RH 87.7% in winter. The major parameters of the study are reinforcement types (ribbed GFRP, sand-coated GFRP, and ribbed steel), reinforcement spacings (200 mm and 300 mm), slab thicknesses (100 mm and 200 mm), and the presence of a contraction joint. It was observed that all GFRP bar-reinforced slabs developed a transverse mid-panel shrinkage crack within the first 18 days of casting. The maximum average crack widths over the long-term were within the ACI 440.1R-15 and AASHTO LRFD code limit of 0.7 mm, and the maximum strains in rebars in the vicinity of the cracks did not exceed 12.4% of the ultimate strains of the bars. Decreasing the slab thickness from 200 mm to 100 mm did not affect the development of cracking or strain evolution. The presence of a saw-cut contraction was effective in localizing the cracking location.

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

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

Coupling Effect of Expansion Agent and Internal Curing Aggregate on Shrinkage of High-Modulus Ultra-High-Performance Concrete

In the realm of bridge structural engineering, it is customary to meticulously contemplate the material’s strength and rigidity attributes during the dimensioning phase. In recent years, there has been a burgeoning interest in employing Ultrahigh-Performance Concrete (abbreviated as UHPC) for the construction of bridge decks and wet joints. However, the large self-shrinkage of UHPC can easily lead to shrinkage cracking and affect its service life. This study delves into the utilization of a blend of basalt coarse aggregate and high-modulus aggregate (HMA) in the formulation of Ultrahigh-Performance Concrete (UHPC) with the objectives of achieving exceptional strength (>180 MPa), superior modulus of elasticity (>56 GPa), and synergistic effect of using prewetted internal curing aggregate (ICA), metallurgical ore sand (MOS), and calcium–magnesium composite-based expansion agent (EA) to reduce the shrinkage of UHPC. Furthermore, the mechanical properties, shrinkage, hydration process, and microstructure of UHPC prepared with EA and ICA were studied. The results show that UHPC prepared with both 3% EA and 20% ICA had the optimal volume stability (the shrinkage was only 273 με at 180 d). In contrast, the 180 d shrinkage of UHPC with 3% EA and 20% ICA separately was 287 με and 373 με, respectively. In addition, the incorporation of EA and ICA can effectively improve the flexural strength of UHPC, although it affects the compressive strength and modulus of elasticity of UHPC (small decrease).

Effect of cooling rate on microstructure and properties of SiCP/A359 composites

The microstructure and properties of stirred cast SiCP/A359 composites under different cooling rates were studied. The strengthening mechanism of the composite material under three cooling rates was analyzed, and the failure mechanism of the composite material was elucidated by means of in-situ tension and EBSD testing. The results showed that increasing the cooling rate simultaneously refined the grains, secondary dendrites, and eutectic silicon, resulting in improved distribution uniformity of SiC and the stacking fault density of eutectic silicon. Additionally, the relationship between the secondary dendrite arm spacing (SDAS) and cooling rate (v) of the SiCP/A359 composite was described using the equation SDAS = 56.02v^(-0.3). There was a positive correlation between cooling rate and yield strength, with particle strengthening being the main contributor to the strength of composites with high cooling rates, resulting in significantly higher strength than samples with low cooling rates. The geometrically necessary dislocations (GND) density at the eutectic Si-Al boundary was found to be higher than other positions after the material was loaded, and the main crack propagated mainly along the eutectic region. Secondary cracks, including SiC cracking, eutectic silicon cracking, interface separation, and shrinkage cracking, may become part of the main crack by bridging.

The relationship between capillary pressure and tensile strength of fresh cementitious materials under water evaporation

Tensile strength is a crucial parameter for understanding the plastic shrinkage cracking of concrete. It is difficult to characterize tensile strength at early age due to its very small value. In this study, the tensile strength of the cementitious paste was measured using a horizontal direct tensile device, and corresponding capillary pressure was simultaneously tested under a high evaporation rate (>1.0 kg/m2/h). Thereafter, the relationship between capillary pressure and tensile strength was studied when the negative capillary pressure of the paste was 0–70 kPa. The results indicate that when the negative capillary pressure is lower than a specific value (approximately 14.0 kPa), the tensile strength rapidly increases and is higher than the corresponding value of the negative capillary pressure. Subsequently, the growth of tensile strength slows down, and the tensile strength is less than the value of the negative capillary pressure. At 70 kPa, the tensile strength is about 30 kPa. Meanwhile, the tensile strength evolution for pastes with various mix proportions was consistent when tensile strength was plotted as a function of the negative capillary pressure. Furthermore, a fitting model based on capillary pressure was created to predict the tensile strength. Consequently, due to the simplicity of capillary pressure measurement, the model proposed in this paper can predict the tensile strength of cementitious materials in the plastic stage without conducting tensile testing.

Maceral evolution of lacustrine shale and its effects on the development of organic pores during low mature to high mature stage: A case study from the Qingshankou Formation in northern Songliao Basin, northeast China

Organic matter (OM) hosted pores are crucial for the storage and migration of petroleum in shale reservoirs. Thermal maturity and macerals type are important factors controlling the development of pores therein. In this study, six lacustrine shale samples with different thermal maturities from the first member of the Qingshankou Formation in the Songliao Basin, of which vitrinite reflectance (Ro) ranging from 0.58% to 1.43%, were selected for a comparative analysis. Scanning electron microscopy (SEM) and reflected light microscopy were combined to investigate the development of organic pores in different macerals during thermal maturation. The results show that alginite and liptodetrinite are the dominant primary macerals, followed by bituminite. Only a few primary organic pores developed in the alginite at the lowest maturity (Ro = 0.58%). As a result of petroleum generation, oil-prone macerals began to transform to initial-oil solid bitumen at the early oil window (Ro = 0.73%) and shrinkage cracks were observed. Initial-oil solid bitumen cracked to oil, gas and post-oil bitumen by primary cracking (Ro = 0.98%). Moreover, solid bitumen (SB) was found to be the dominant OM when Ro > 0.98%, which indicates that SB is the product of oil-prone macerals transformation. Many secondary bubble pores were observed on SB, which formed by gas release, while devolatilization cracks developed on migrated SB. Additionally, at the late oil window (Ro = 1.16%), migrated SB filled the interparticle pore spaces. With further increase in temperature, the liquid oil underwent secondary cracking into pyrobitumen and gas, and spongy pores developed on the pyrobitumen at higher levels of maturity (Ro = 1.43%), which formed when pyrobitumen cracked into gas. Vitrinite and inertinite are stable without any visible pores over the range of maturities, verifying their low petroleum generation potential. In addition, it was concluded that clay minerals could have a catalytic effect on the petroleum generation, which may explain why organic-clay mixtures had more abundant pores than single OM particles. However, after Ro > 0.98%, authigenic minerals occupied the organic pore spaces on the organic-clay mixtures, resulting in fewer pores compared to those observed in samples at the early to peak oil window.

The combined effect of steel fiber and MgO on the deformation and mechanical properties of high-strength concrete

Shrinkage cracking of concrete is one of the main problems affecting the durability of high-strength concrete. One of the main measures to solve this problem is to use expansion agents to compensate for the shrinkage of concrete. But on the other hand, excess expansion, while compensating for shrinkage, is likely to have a detrimental effect on mechanical properties of concrete. Especially for bridge decks and airport pavement with high requirements for impact resistance, toughness, and crack resistance, the use of expansion agents alone cannot meet the performance requirements. In this study, the mechanical properties and autogenous shrinkage of concrete were studied when MgO expansion agent (MEA) and steel fiber were used simultaneously. The results showed that the expansion produced by MEA increased the porosity while compensating for the shrinkage of concrete. Compared with plain concrete, the porosity increased by 4.4% when MEA was incorporated alone. After MEA and steel fiber were used simultaneously, the steel fiber constrained the expansion of MEA through the adhesive friction between fiber and matrix, which made the interface transition zone (ITZ) between cement paste and fiber densified. In this way, the shrinkage of concrete was avoided without reducing the mechanical properties. Especially when 8% MEA and 1% steel fiber were used simultaneously, the compressive strength and splitting tensile strength of concrete were increased by 20.6% and 65.0% respectively, and the porosity was decreased by 20.9%. The expansion of concrete at 410d when used simultaneously was 371 × 10−6, which was 20.7% lower than that of MEA alone, avoiding the possible adverse effects of excessive expansion of MEA. The research results have guiding significance for improving the crack resistance and impact resistance of concrete.

Shrinkage Characteristics and Microstructure Evolution of Yili Loess under Different Wetting and Drying Cycles

The loess in Yili Valley is prone to landslides in the rainy season. We studied the influence law of shrinkage and the microstructure of the loess in Yili Valley under different wetting and drying cycles. Considering the climatic conditions and sampling depth of the study area, shrinkage tests were carried out under six kinds of dry and wet cycling paths. The fracture changes and shrinkage characteristics of the loess under different dry–wet cycling times were analyzed, and the deformation characteristics of the loess during the process of water-loss shrinkage under the dry–wet cycling conditions were discussed. The results show that (1) there is an exponential relationship between the number of dry and wet cycles and the final shrinkage rate. The influence of dry and wet cycles on the final shrinkage rate is significant in the early stage. (2) With the increase in the number of dry and wet cycles, the decline in the final shrinkage rate decreases, and the final shrinkage rate and shrinkage coefficient of soil also show a decreasing trend, while the soil sample area first increases and then gradually decreases, and the surface shrinkage cracking is gradually stable. The surface porosity tends to increase. (3) Under the action of repeated wet expansion and dry contraction, irregular cracks are produced inside the soil body, which leads to the increase in soil permeability, reduces the strength of the soil body, reflects the phenomenon of strength deterioration, and thus indicates the stability of loess slopes. The research results of this paper can provide an important parameter basis for the prevention and control of loess landslide geological disasters in Yili Valley.

Long-Term Performance and Forensic Evaluation of an Asphalt Pavement with Cold Central Plant Recycled Asphalt

In 2012 Virginia Department of Transportation constructed two test sections at the National Center for Asphalt Technology Test Track containing asphalt processed via cold central plant recycling (CCPR) with identical asphalt overlays. One section contained a stabilized base beneath the CCPR layer (Section S12), similar to a full-depth reclamation layer; the other included an unstabilized aggregate base beneath the CCPR layer (Section N4). Both sections were subjected to trafficking by loaded trucks for a total of 30 million equivalent single axle loads. Minor cracking was observed at the surface of the section with the unstabilized base; the section with the stabilized foundation exhibited no surface cracking. Furthermore, strain, pressure, and deflection measurements showed better performance for the section with the stabilized foundation than the section with the unstabilized base. Because of the relatively unchanged performance of Section S12, it was taken out of service to conduct a forensic investigation. This paper presents the analysis of the instrumentation results, coring, trenching, and mechanistic testing and modeling, to better understand and compare the performance between sections. The stabilized base was found to greatly reduce bending action in the section, exhibited no substantial rutting, but also contained what appeared to be some shrinkage cracks. However, these cracks did not propagate to the surface, indicating that the CCPR layer may be an effective crack mitigator. Further, it was found that mechanistic modeling using AASHTOWare Pavement ME design software overestimated the rutting but predicted similar international roughness index and cracking to that observed in the field.

Evolution and mechanism on shrinkage of high-performance concrete with full aeolian sand cured by superabsorbent polymer

Preparing high-performance concrete with full aeolian sand (FA-HPC) can address the shortage of high-quality aggregates. Its low water-binder ratio (w/b) and high content of cementitious material content endow this concrete with great strength and durability but a high risk of shrinkage cracking. Herein, the effect of superabsorbent polymer (SAP) on the separate shrinkage of FA-HPC, and the mechanism of internal curing (IC) were investigated from various macro–micro perspectives. IC water migration was monitored via nuclear magnetic resonance (1H NMR). The results showed that autogenous shrinkage dominated the total shrinkage of the FA-HPC, accounting for 70%–80%. The SAP with medium particles effectively reduced the total shrinkage in the plastic and hardening stages, with nearly zero autogenous shrinkage at 0.3% content. From the characterization of mechanism, capillary pressure build-up of FA-HPC containing SAP was delayed with significant suppression in internal relative humidity (IRH) drop and moisture loss especially due to self-desiccation. The coupling effect of self-desiccation and evaporation triggered the nonlinear correlation between moisture loss and total shrinkage, whereas SAP amplified the proportion of drying shrinkage. Microscopically, the incorporation of SAP with IC water hindered the early hydration process but resulted in a higher final hydration degree within 72 h bringing a refined pore structure. Moreover, the adaptive release of IC water was used for hydration mainly within 72 h, and it continuously compensated for IRH drop over 28 d based on the supply–demand mechanism in FA-HPC. This study proposes a promising strategy for shrinkage resistance of FA-HPC and promotes the application of aeolian sand-based concrete.

Early-Age Cracking Behavior of Concrete Slabs with GFRP Reinforcement.

This paper reports on a combined experimental and numerical modeling investigation of cracking of concrete slabs with GFRP reinforcement. At this stage of the project, attention is given to early-age cracking driven by plastic shrinkage, preceding longer term considerations of cracking resistance over the service life of field applications. Of interest is the effectiveness of GFRP reinforcement in restricting plastic shrinkage cracking. Nine small-scale slab specimens were subjected to controlled evaporation rates. Images of crack development were acquired periodically, from which crack width estimations were made. Comparisons were made between slabs reinforced with conventional steel and those reinforced with GFRP, along with control specimens lacking reinforcement. During the period of plastic shrinkage, the time of crack initiation and subsequent crack openings do not appear to be influenced by the presence of the reinforcing bars. To understand this behavior, six early-age bond tests were conducted for both types of the bars after 1, 2, and 3 h exposure to the controlled evaporation rate. In addition, concrete strength development and time of settings were measured using penetration resistance tests on a representative mortar. The numerical modeling component of this research is based on a Voronoi cell lattice model; in this approach, the relative humidity, temperature, and displacement fields are discretized in three-dimensions, allowing for a comprehensive investigation of material behavior within the controlled environment. Based on the measured bond properties, our simulations confirm that the reinforcing bars restrict crack development, though they do not prevent it entirely.

Utilization of rubber aggregates in cement-treated bases: A review

Cement-treated bases are commonly used in high-classified road pavements due to their stable strength and improved durability. However, this type of pavement base is sensitive to shrinkage caused by early water loss or temperature change after construction, resulting in shrinkage cracks and subsequent reflective cracking in semi-rigid pavements. To address this issue, various waste or by-products, such as oil, steel slag, end-of-life tires etc., have been investigated for use as an additive or a replacement for aggregates in cement-treated base. This review focuses specifically on the impact of rubber aggregates on the properties of rubberized cement-stabilized aggregates. In general, rubber aggregates are detrimental to the mechanical properties of cement-treated aggregates. However, the rubberized cement-stabilized aggregates exhibited reduced shrinkage and improved shrinkage cracking resistance, as confirmed through actual field applications. Furthermore, internal microstructure analyses indicate that rubberized cement-stabilized aggregates possess excellent anti-cracking capacity, particularly when subjected to compressive loadings. The review ends with recommendations and future studies to promote the applicability of rubberised cement-stabilized bases in semi-rigid pavements.

Creep Behavior of Fiber Reinforced Mortars and Its Effect to Reduce the Differential Shrinkage Stress

This research aims to develop durable repair materials that can resist shrinkage cracking by exploring the role of creep in reducing shrinkage stress. In this regard, the creep effect can only be quantified if an accurate creep prediction model and theoretical analysis of the shrinkage stress in the patch repair system exist. For this purpose, the research was carried out in the following sequences: first, the research investigated the short-term creep of the patch repair materials containing accelerator and micro-synthetic fibers in the 0.00–0.12% volume fraction range. This short-term creep was measured on five-cylinder specimens (having a diameter of 75 mm and a height of 275 mm). Three specimens were used to determine the deformation of the repair material under unloading conditions, while those remaining were used to determine the total deformation under loading conditions. The amount of creep deformation was determined by taking away the unloaded (shrinkage) and instantaneous (elastic) deformations from the total deformation of the loaded specimens. Secondly, a modified prediction model of ACI 209R-08 is introduced to accurately capture the rate and magnitude of the observed creep of the repair materials. Finally, a formulated theoretical analysis of shrinkage stress in the patch repair system was proposed to examine how creep potentially reduces the repair material's cracking tendency. The results show that the asymptotic value of the creep curve is attained at an earlier age and that its magnitude is greater than that of most concrete. The modified ACI 209R-08 prediction model can closely estimate the repair materials' creep behavior. The best-fit line, residual values, and coefficient of error analyses confirm the modified model's prediction accuracy. The analysis of tensile stress development in the repair layer suggests that creep can reduce stress by up to 50%. With such a reduction, the repair material is expected to be durable in resisting shrinkage and cracking tendency. Doi: 10.28991/CEJ-2023-09-08-014 Full Text: PDF

Development of a Laboratory Microcracking Procedure for Full-Depth Recycled Cement Stabilized Materials

Microcracking of full-depth recycled cement stabilized layers can be an effective method to mitigate the effect of reflective drying shrinkage cracks. To date, no effective method of performing microcracking in the laboratory has been developed. This is needed to determine appropriate levels of microcracking in the field, and to understand how the material will perform after microcracking. This paper covers the development and validation of a nondestructive laboratory procedure that can induce microcracking in specimens to controlled levels. The test setup used in this work was identical to that for the resilient modulus test, which facilitates stiffness measurement before and after microcracking. The use of on-specimen linear variable differential transducers is recommended to exclude end effects that can affect the stiffness result. The results indicate that: stiffness loss is a function of applied energy, and independent of the stress sequence; stiffness should only be calculated at low stress sequences, when the backbone of the stress–strain curve is linear, to accurately represent the stiffness of the material; microcracking effectively reduces the stiffness of the material; the microcracking test is a repeatable and nondestructive test; the stiffness reduction level is controllable; and the test can replicate microcracking effectively in the laboratory to represent microcracking in the field.

Experimental and numerical study of the influence of inclusion size on the drying shrinkage cracking in cementitious composites

AbstractThis study investigates the effect of inclusion size on drying shrinkage cracking in cementitious materials. A series of laboratory desiccation tests on concrete with different size of inclusions are conducted. Nondestructive X‐ray micro‐tomography images were used to reconstruct the drying‐induced shrinkage cracks of samples in desiccation tests. To better understand the mechanism of shrinkage cracking, a fully coupled hydro‐mechanical bond‐based Peridynamic model was developed that takes into account the interactions among deformation, cracking, and permeability evolution. The efficiency of the proposed model was verified through two benchmark problems. The influence of inclusion size on shrinkage cracks was numerically analyzed by reproducing experimental results and conducting a parametric study. The results indicate that, as the size of the inclusion increases, the quantity of drying induced cracks increases while the length of the cracks decreases and the average width of the cracks increases. However, the distribution of cracks appears to be unaffected by the size of the inclusion.

Axial compression testing and constitutive model of a novel BF-reinforced ambient-cured LEGC

Ambient-cured lightweight expanded polystyrene geopolymer concrete (LEGC) currently undergoes early shrinkage cracking, and the low density of EPS causes segregation during the mixing process, resulting in a significant decrease in the strength of LEGC. To solve the above problems to obtain higher strength LEGC and promote its wide application, uniaxial compression tests and constitutive modeling studies of LEGC with different basalt fiber (BF) lengths (3 mm, 6 mm, 9 mm, 12 mm and 15 mm) reinforced with different expanded polystyrene (EPS) volume contents (10%, 20%, 30% and 40%) were conducted in this study. First, the damage pattern of the specimen was analyzed, and the crack development morphology was analyzed based on the Digital Image Correlation-3D (DIC-3D) technique. Additionally, the mechanism of BF-reinforced of LEGC was analyzed comprehensively at three levels: micromechanical theory, microscopic (scanning electron microscopy, SEM) and mesoscale (computerized tomography, CT). Empirical formulas for peak stress, peak strain, threshold stress, threshold strain and elastic modulus were established based on the stress‒strain curves of the specimens. In addition, the specific form of the damage evolution equation considering the energy dissipation of the specimen was derived from the energy balance principle and basic laws of irreversible thermodynamics based on composite damage theory. Finally, elastic‒plastic damage constitutive models established previously and in this study were compared, and the results showed that the method proposed in this study can better reflect the damage evolution of BF- reinforced LEGC.