Shrinkage Cracking Research Articles

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.

Application of low drying shrinkage ECC in the protection layer of thermal insulation wall

An innovative application of the fiber reinforced engineered cementitious composite (ECC) in thermal insulation wall is presented in this paper. Special focuses are paid for the purpose of eliminating bond failure between the structural layer, thermal insulation layer and surface protective layer, and enhancing cracking resistance of the surface protective layer. ECC with characteristics of low drying shrinkage (LSECC), strain-hardening and multiple cracking was used as surface protective material in the wall. The test results show that uniformly distributed steel wires crossing the thermal insulation layer at an inclination angle to the direction of horizontal direction of the wall and embedded in the structural concrete layer with certain length can provide sufficient bond strength of structural layer, thermal insulation layer and surface protective layer. Tensile test results on LSECC used in the surface protective layer of the wall show that LSECC can provide sufficient tensile strain capacity to adsorb the deformation induced by temperature change, material shrinkage and mechanical loads. Meanwhile, high crack opening control ability and fine crack opening is expected as well during service.

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

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

Mechanical Properties of Slag-Based Geopolymer Grouting Material for Homogenized Micro-Crack Crushing Technology

Homogenized micro-crack crushing can fully retain the bearing capacity of concrete pavement, but local weak road base needs to be reinforced before being directly overlaid with hot-mixed asphalt. Therefore, indoor tests were conducted to study the mechanical properties of slag-based geopolymer as a grouting material for weak road base, and the morphology and influence of polymerization reactants were observed. Concurrently, on-site grouting tests were conducted to study the grouting effect. The results show that the compressive strength, flexural strength and bonding strength of slag-based geopolymer all increase with age. The maximum compressive strength and flexural strength of the geopolymer at 28 d were 18.88 MPa and 6.50 MPa, respectively. The maximum flexural bonding strength at 14 d was 4.58 MPa. As the ratio between water and slag powder increased, the compressive strength and flexural strength gradually decreased, while the bonding strength first increased and then decreased. In the range of ratios of water to slag powder from 0.26 to 0.28, the above three strengths were relatively high, and the compressive shear bonding strength was the highest when the ratio of water to slag powder was 0.28. The shrinkage of the slag-based geopolymer increases with the increase in ratio of water to slag powder, and the porosity also increases, resulting in a decrease in compactness after consolidation. When the ratio of water to slag powder was 0.28, the reactant was mainly a gel-phase material, and the shrinkage crack of the consolidated geopolymer was relatively small. After grouting the weak road base of the concrete pavement, the voids at the bottom of the concrete pavement slab were effectively filled, and the deflection of the pavement slab was significantly reduced. The average deflections of monitoring line I, monitoring line II and monitoring line III decreased by 49%, 41% and 54%, respectively, after grouting. After solidification, the slag-based geopolymer was distributed in layers, which further compacted the road structure layer and improved the bearing capacity.

Implementing capillary pressure control measures to prevent plastic shrinkage cracking in concrete

Plastic shrinkage cracking occurs when fresh concrete is drying and restrained from deformation, which typically results in cracking. The tensile stresses causing cracking result from the negative capillary pressure that develops in the drying concrete. This study developed a model that uses live in-situ capillary pressure measurements in fresh concrete to control the capillary pressure response to prevent plastic shrinkage cracking at any reasonable evaporation rate, making it a valuable tool for preventing plastic shrinkage cracking.

Experimental Study on Mechanical Properties and Drying Shrinkage Compensation of Solidified Ultra-Fine Dredged Sand Blocks Made with GGBS-Based Geopolymer

As natural aggregates become increasingly scarce, attention has turned to ultra-fine dredged sand (UDS) generated in waterway regulation engineering. UDS is typically challenging to utilize due to its high clay content and high water demand. This article uses ground granulated blast-furnace slag (GGBS)-based geopolymer to solidify UDS, along with sodium silicate (SS) and sodium hydroxide (SH) as alkaline activators. This paper explores the effects of SS modulus (SiO2/Na2O molar ratio) and mass percentage content of Na2O on the fluidity, setting time, mechanical properties, and shrinkage behavior of hybrid UDS-GGBS geopolymer (HUGG) paste. According to the research findings, increased SS modulus and Na2O content lead to decreased fluidity and setting time. When the Na2O content reaches 6%, flash coagulation occurs in the slurry, leading to more internal shrinkage cracks and pores. This has been confirmed by scanning electron microscope (SEM) analysis. When Na2O content is 5%, and SS modulus is 1.0, the 90-day maximum compressive strength reaches 56.53 MPa, corresponding to a splitting tensile strength of 6.83 MPa, which can be considered the optimal formulation. Meanwhile, basalt and polypropylene fibers (BF and PPF) are chosen to compensate for the susceptibility to drying shrinkage. Both BF and PPF can significantly inhibit the linear drying shrinkage of the HUGG paste. The BF’s ability to enhance mechanical properties is more robust than PPF’s, which can make the paste more homogeneous. The research contributes an effective method for the resource utilization of UDS.

Evaluation of interlocking moulded bricks with the effective usage of agro - waste fibres in construction industry

For a very long time, fibres have been employed in building materials. The use of natural and synthetic fibres in prior studies and investigations has yielded promising findings because their presence has proved considerable benefits for the composite material's overall mechanical and physical qualities. The major objectives of this work were the creation of manually crushed interlocking mud bricks and a study of their compressive strength. Mud bricks containing rice husk (1–6% by weight of soil) and wheat straw (1–6 % by weight of soil) were made to accomplish this. Straw husk, a soil additive that varied from 1 to 6 %by weight, was also made by mixing rice husk and wheat straw. Compressive strength analysis was utilized to look at the interlocking mud bricks strength and failure pattern. Bricks made of mud under control had shrinkage cracks, whereas bricks made of fibres did not exhibit any symptoms of shrinkage cracking (wheat straw, rice husk and straw husk). As the number of fibres in the mud brick samples increased, there was a corresponding drop in compressive strength. However, interlocking mud bricks with fibres in them met the minimal strength requirements of several mud brick standards. Therefore, interlocking mud bricks with fibres can be used in earthen building as a long-lasting, cost-effective, and eco-friendly material based on the findings of compressive strength tests.

Quantitative Study on Salinity Estimation of Salt-Affected Soils by Combining Different Types of Crack Characteristics Using Ground-Based Remote Sensing Observation

Soil salinity is one of the parameters used for determining the extent of soil salinization. During water evaporation, the surface of salt-affected soils in the Songnen Plain, China, exhibits obvious shrinkage and cracking phenomena due to the high salt content. The aim of this current study is to quantify the influence of the salt content on the surface shrinkage–cracking process and to achieve quantitative extraction of soil salinity parameters based on different crack parameter types. In order to achieve the above objectives, a controlled shrinkage–cracking experiment was conducted. Subsequently, three kinds of crack characteristics such as crack length, box-counting dimension, and 12 gray-level co-occurrence matrix (GLCM) texture features were quantitatively extracted from the standard binary crack patterns. In order to predict the soil physical–chemical properties of salt-affected soils in the Songnen Plain, three models such as multiple linear regression (MLR), multiple stepwise regression (MSR), and artificial neural network (ANN) were developed and compared based on the crack length, box-counting dimension, and the first two principal components of GLCM texture features. The results show that the extent of desiccation cracks was determined by soil salinity since the water film caused by exchangeable cations and the thickness of DDL determined by soil salinity can promote desiccation cracking. Although the three methods have high prediction accuracy for Na+, electrical conductivity (EC), and total soil salinity, the ANN-based method showed the best prediction with R2 values for Na+, EC, and soil salinity as high as 0.91, 0.91, and 0.89, and ratio of performance to deviation (RPD) values for Na+, EC, and soil salinity corresponding to 2.96, 3.47, and 2.95.

Potential utilization of oil shale as a stabilizing material for compressed Earth block

This research aims to produce a compressed Earth block (CEB) product locally from soil collected from North Jordan. The CEB mixture was further stabilized using oil shale (OS) and ordinary Portland cement (OPC). The CEB specimens were thoroughly characterized by studying their mechanical properties (compressive and flexural strength) and durability characteristics (erosion, absorption, and shrinkage tests). Eight mixtures were carried out for the CEB, one of which was the control mix. The other mixtures were carried out by replacing soil with OS, cement, and sand in different proportions. The results showed that higher compressive strength and flexural strength for CEB were obtained in the mixtures that contained 10% of OS and 10% of cement, resulting in an average compressive strength of 10.6 MPa and flexural strength of 0.25 MPa. The absorption increased when the OS increased in the soil. The consequent erosion test was related to the absorption test, where the higher the absorption, the more negative the results of the erosion test. Moreover, oil shale improved the shrinkage properties of the CEB, as the higher the proportion of oil shale in the CEB, the lower the shrinkage. Finally, using oil shale as a stabilizing agent in soil had a clear role in improving the mechanical properties, hiding the shrinkage cracks, and reducing the volume shrinkage value of the CEB.

DEVELOPMENT AND APPLICATION OF HIGH-FLUIDITY AND SUPER-LOW DRYING SHRINKAGE CONCRETES FOR FAIR-FACED CONCRETE WALLS USING A NEW HYBRID ADMIXTURE

New type admixtures were developed for High-fluidity and Super-low shrinkage concretes with water-cement ratio of 40-55%. Properties of fresh and hardened concretes using these admixtures were studied by laboratory test. Properties of these hardened concretes, such as strength and durability were investigated experimentally. Furthermore, effects of reducing and restraining cracks using these admixtures were verified by test on drying shrinkage cracking of restrained concrete. More than 10% drying-shrinkage reduction was obtained for super-low shrinkage concrete using one of these admixtures compared to ordinary concrete. This concrete was applied to a fair-faced wall of a building in Hyogo.

Dynamics of carbon dioxide emission during cracking in peanut shell biochar-amended soil

As a primary source of greenhouse gas emissions and a carbon sink, soil plays a key role in climate regulation. The development of cracks in soil strongly influences CO2 emissions, and soil amendment with biochar has been shown to reduce cracking. However, the impact of biochar on CO2 emissions during soil cracking is not well understood. This study investigates the release of CO2 flux during the cracking of peanut shell biochar-amended soil. The biochar-amended soil was incubated at a constant temperature of 35 °C for 160 h with periodic photography and analysis of CO2 concentration and soil moisture. To achieve continuous monitoring of incubation soil, a new coupled sensor was specially designed to measure CO2 concentration and soil moisture, based on the Arduino microcontroller. Measured results reveal that peanut shell biochar reduced the evaporation rate by 29 % compared to unamended soil, resulting in slower soil cracking caused by water loss. The biochar also decreased the shrinkage crack length by 20 % compared to unamended soil. In addition, the crack volume fraction was reduced by 16 % after the peanut shell biochar amendment. Due to the reduction of the soil crack channel openings during drying shrinkage when biochar was applied to the soil, cumulative CO2 fluxes were also reduced by 5 % compared to unamended soil. The presence of biochar induced more stable and larger compounds with the soil particles, which blocked the crack propagation path and inhibited further development of the crack.

3D deformation and strain fields in drying kaolinite obtained from tracking internal bubbles using X-ray CT and ANN

AbstractDrying fine-grained sediments experience shrinkage and desiccation cracking that may dramatically alter their mechanical and hydraulic properties. This study adopts X-ray computed tomography (CT) to monitor the three-dimensional (3D) internal deformation and strain fields, and their relationships with desiccation crack formation, for drying kaolinite samples contained in plastic containers. Two kaolinite samples, one dried at room temperature and the other oven-dried at 60 °C, were CT scanned at several intervals during the drying process. From sequential CT scans for the same sample, entrained gas bubbles were extracted and used as tracking markers for deformation and strain field measurements. Since the bubble morphology continuously changed during the drying process, an artificial neural network (ANN) model was developed to link bubbles in sequential scans for the same sample. The tracking algorithm was trained with manually linked bubbles and optimised by comparing different combinations of bubble information, e.g. bubble location, size and shape. The drying samples experienced primarily vertical displacement before the air-entry value, while horizontal displacement occurred during vertical crack formation. Internal vertical and horizontal strains were generally uniform, indicating a limited impact of non-uniform sample drying and substrate constraint.

Hot-air drying behavior of lignite and quantitative characterization for its surface damage

Cracking and fragmentation problems that occur during lignite drying limit its utilization value. In this study, the dehydration, surface damage, and pulverization behaviors of lignite were investigated under hot-air drying conditions, and the effect of the dewatering process on shrinkage cracking was analyzed. Cracks first appear at the edges of the lignite, then gradually extend inward until they spread over the entire surface of the lignite, before beginning to shrink, and eventually stabilize. The crack rate exhibited three stages: rapid development, shrinkage, and stabilization. The crack rate and shrinkage percentage increased significantly with increase in the drying temperature. The moisture content had a greater influence on the crack rate and shrinkage percentage of the samples than the surface temperature. A uniaxial compression test revealed that lignite with different degrees of dryness exhibited different degrees of breakage. The drying process drives the lignite toward finer grain sizes and, with moisture content below 0.8 g/g, the degree of breakage increases significantly. Thus, the main factor affecting the shrinkage and cracking of lignite was the moisture content. Cracks occurred when the tensile strain caused by shrinkage was greater than the tensile strength of the lignite.

State-of-the-Art Report: The Self-Healing Capability of Alkali-Activated Slag (AAS) Concrete.

Alkali-activated slag (AAS) has emerged as a potentially sustainable alternative to ordinary Portland cement (OPC) in various applications since OPC production contributed about 12% of global CO2 emissions in 2020. AAS offers great ecological advantages over OPC at some levels such as the utilization of industrial by-products and overcoming the issue of disposal, low energy consumption, and low greenhouse gas emission. Apart from these environmental benefits, the novel binder has shown enhanced resistance to high temperatures and chemical attacks. However, many studies have mentioned the risk of its considerably higher drying shrinkage and early-age cracking compared to OPC concrete. Despite the abundant research on the self-healing mechanism of OPC, limited work has been devoted to studying the self-healing behavior of AAS. Self-healing AAS is a revolutionary product that provides the solution for these drawbacks. This study is a critical review of the self-healing ability of AAS and its effect on the mechanical properties of AAS mortars. Several self-healing approaches, applications, and challenges of each mechanism are taken into account and compared regarding their impacts.

Long-term phase composition and microstructure characteristics of phosphoric acid modified magnesium oxychloride cement exposed to natural environment

Magnesium oxychloride cement (MOC) is widely used as fireproof materials, decorative materials, and adsorption materials, etc. However, its poor water resistance limits the engineering application as a building material. The existing researches mainly focus on improving the short-term durability and water resistance, but few focus on long-term durability of MOC. In this paper, phosphoric acid-modified MOC samples with an age of 2–16 years from China and the Netherlands were collected. Their phase composition and microstructure characteristics were studied, which is of practical engineering significance for the modification of MOC. The results indicate that MOC modified by phosphoric acid would be decomposed and carbonated, and water in the ambient where MOC exposed to is the main factor. MOC exposed to humid environment presents a loose and porous morphology, but shows dense matrix with drying shrinkage cracks in dry air condition. MOC exposed to the air shows good carbon capture ability. The carbonated wood-MOC shows lower porosity than fresh wood-MOC paste. Carbonation phase on the surface of MOC products is beneficial to the internal structure and stability of MOC matrix. Besides, MOC is an environmentally friendly material. The manufacture of MOC requires less energy compared to ordinary Portland cement and shows good carbon neutralization potential under service life.

Effect of Curing Methods on Plastic Shrinkage Cracking

Early-age cracking during the plastic stage is unsightly and a cause of future durability problems. This paper investigates the effects of various simple curing methods used in practice to enhance early-age concrete cracking performance, including covering concrete with a plastic sheet and wet hessian fabric, surface power floating and use of cold water in the mix. The benefits offered by the use of three standard curing admixtures (Safecure Super concrete, Safecure Super 90W-10%, and superplasticizer), as well as recycled tire steel fibres at 40 kg/m3, are also examined. A digital image processing (DIP) technique is used to measure the crack widths, whilst the temperature in the concrete is measured via a thermocouple. The results show that all the concrete curing methods are successful in restraining micro and plastic shrinkage cracks, although the use of recycled tire steel fibre (RTSFC40) is most effective in eliminating micro and plastic shrinkage surface cracks. All of the examined methods are compared in terms of the speed and cost of application, quality of the surface finish and environmental credentials. This study will inform best practice on enhancing the durability and sustainability of concrete structures, particularly for slab-on-grade applications.

Field trials of unbound granular pavements treated with an insoluble dry powdered polymer

Unbound granular pavement materials deteriorate with traffic, time and water ingress. In-situ recycling of fatigued pavement layers can be cost-effective, provided that appropriate additives are chosen. The polymer additive used in this study is suitable for aggregates with clay-rich fines. It is an insoluble dry powdered polymer (DPP) and is a proprietary product. According to Australian Road Research Board’s certificate, DPP is a granular powder comprising a cationic polymer thermally bonded to fine ground limestone. Long-term field trials of two in-situ recycled road sections on semi-rural roads were established to support an ongoing laboratory investigation. The polymer was suitable for these trials due to poor site drainage and risk of flooding. Field data from the La Croix deflectograph indicated good performance of the treated sections compared to the adjacent control sections. At the first site, the average central deflection under wheel loading over five years of monitoring was 0.3 mm compared with 0.6 mm over the control section. The second site initially showed similar level of improvement (0.5 mm compared with 1.1 mm), but deterioration of the treated pavement became evident with average deflections increasing to 0.8 mm by spring of 2020. Central deflection information can be supported by deflection ratio data. Visual inspections of road conditions highlighted the need for caution with shrinkage of the material treated with DPP. Transverse shrinkage cracks between 1 and 2 mm wide were observed. Laboratory testing of one of the granular materials confirmed high levels of shrinkage.