Restrained Shrinkage Cracking Research Articles

Large Ring Test for Evaluation of Restrained Shrinkage Cracking: Calibration and Experimental Trial

The durability of shotcrete tunnel linings is significantly affected by restrained shrinkage cracking. Given the unique characteristics of shotcrete applied in tunnel linings, especially when dealing with accelerated shotcrete containing reinforcement fibres, it is necessary to upscale the ring test commonly used. This paper presents a comprehensive experiment using large ring tests with cast concrete to investigate the impact of upscaling ring test geometry. The two ring specimens demonstrated comparable cracking age (22 days) and strain measured in the steel ring, suggesting that consistent results can be obtained through the proposed instrumentation, calibration, and correction methods. Moreover, the estimated induced tensile stresses of the concrete rings (2.8 and 2.7 MPa) are slightly lower than the predicted tensile strength (3.3 MPa) at the age of cracking, which indicates that some driving forces contributing to restrained shrinkage cracking were not indicated in the strain gauge readings. Furthermore, the study identified multi-crack formation and additional potential causes for crack initiation, which include self-restraint due to the moisture gradient in the vertical direction, deflection of the concrete ring caused by its self-weight, and friction on the contact surface of the support. Therefore, optimising the geometry of the ring specimens and the apparatus is imperative to minimise additional driving forces and unmeasurable restraints for crack initiation, especially when employing the stress rate method to assess cracking potential.

Restrained Shrinkage of High-Performance Ready-Mix Concrete Reinforced with Low Volume Fraction of Hybrid Fibers.

Cracking due to restrained shrinkage is a recurring issue with concrete bridge decks, impacting durability and ultimately service life. Several scholars' research has proven that the incorporation of fibers in concrete mitigates restrained shrinkage cracking when utilizing high (0.5-3%) fiber volumes. This often presents a mixing and placement issue when used for ready-mixed concretes, which discourages their use in bridge decks. This study aims to optimize the incorporation of fibers for their benefits while producing concrete that is conducive to ready-mix, jobsite use. A series of tests were performed on a high-performance concrete (HPC) mix which incorporated blended, multiple fiber types (steel crimped, macro polypropylene, and micro polypropylene) while maintaining low total fiber (0.19-0.37%) volume. These "hybrid" fiber mixes were tested for multiple mechanical properties and durability aspects, with a focus on the AASHTO T334 ring test, to evaluate fiber efficiency under restrained conditions. Promising results indicate the use of a low-volume hybrid fiber addition, incorporating a macro and micro polypropylene fiber (0.35% by volume) blend, reduced the cracking area by 16.6% when compared to HPC incorporating a single fiber type, and 39% when compared to nonfibrous HPC control mixture.

Quantitative Analysis of Restrained Shrinkage Cracking in Oilwell Cement Using Digital Image Correlation

SummaryCracking of oilwell cement sheaths may lead to loss of reservoir isolation and uncontrolled hydrocarbon leakage to the environment. This paper presents a methodology to characterize the crack pattern and quantify individual cracks in cement sheaths formed due to the restrained shrinkage of the cement, focusing on the range of 5 to 200-µm crack widths. For this purpose, high-resolution cameras are used for image acquisition together with a digital image correlation (DIC) method, and a newly developed data analysis process is applied for crack detection and quantification. The methodology is applied in a case study where cracks formed in the top and perimeter surfaces of a cement ring are detected, quantified, and classified according to crack properties such as width and orientation. The obtained information on cracks with a resolution on the micrometer level proves the effectiveness of the methodology to quantify cracks in the target width range. In addition, crack characteristics such as position, length, and orientation are also quantified, and values including spacing between cracks and cracked areas are calculated. This methodology is demonstrated in this paper to detect cracking induced by restrained drying shrinkage deformations but can be applied generally to document cracking in cement sheaths under different loading and boundary conditions.

Sprayable engineered cementitious composites (ECC) using calcined clay limestone cement (LC3) and PP fiber

Sprayable engineered cementitious composites (ECC) has demonstrated in field applications as a promising repair material. However, the large cement dosage that leads to a high carbon footprint and potential restrained shrinkage cracking suggests needed improvements. In this study, a sprayable ECC was developed using calcined clay limestone cement (LC3), calcium sulfoaluminate (CSA) expansive additive and polypropylene (PP) fiber to increase the material greenness and durability. The sprayability and mechanical performance were examined by the flow table and uniaxial tension tests. The one-time build-up thickness achieved was 45 mm for vertical spraying and 35 mm for overhead spraying at 20–30 min rest-time, and up to 80 mm for vertical spraying at 50 min rest-time. The ECC had a comparable strength but higher tensile strain capacity (5.7%) and reduced crack width (30 μm at 1% tensile strain) when sprayed, in comparison to specimens prepared by casting. A spray-repaired layered ECC-concrete composite revealed multiple cracking and strain-hardening performance under flexural loading. The advantages of low carbon, low shrinkage, low cost, and ultra-high ductility of the developed sprayable ECC promote broader applications in infrastructure repair.

Experimental and theoretical study of the restrained shrinkage cracking of early age well cement

The shrinkage cracking occurring in oil & gas well cement material is a major factor that reduces the cement sheath integrity and impairs the durability of an underground well. Shrinkage mainly takes place in the early hydration period of the cement, and the resulting restrained shrinkage cracking can form a leaking network for oil & gas or carbon dioxide stored in an underground reservoir. It is thus important to understand the early age behavior of well cement and the leaking pathway formation in the well. This study describes the application of the digital image correlation (DIC) method as a tool to measure the strain development and crack distributions of well cement in the lab during early phase changes. A theoretical model is presented to calculate the stress distribution built up in the cement sheath during early ages of well cement hydration, which helps to interpret the experimental observations and determine the major factors influencing the cracking sequences. This study presents the whole hydration – drying shrinkage – and cracking mechanism of early age well cement under restrained ring conditions experimentally and theoretically. The results offer useful insights on the key material and geometric parameters which control the fracture of a well cementing structure.

Fracture Properties and Restrained Shrinkage Cracking Resistance of Cement Mortar Reinforced by Recycled Steel Fiber from Scrap Tires

Thanks to better processing technology, quality recycled steel fiber (RSF) is routinely extracted from scrap tires, offering opportunities to reinforce cementitious materials in a more economical and sustainable manner. In this study, a detailed experimental program on cement mortar reinforced by up to 2 vol. % RSF was carried out. The work involved conventional tests to characterize cement mortar mechanical properties including compressive strength, elastic modulus, and splitting tensile strength. It also featured an innovative semi-circular bending (SCB) fracture test to characterize fracture-related properties, and a customized ring test to study the cracking resistance under restrained drying shrinkage of the studied mortars. The combined use of the fracture and ring tests is believed to lead to a better assessment of concrete structure behaviors in the field. Based on the test results, the addition of up to 2% RSF shows noticeable improvement on the splitting tensile strength, but it has marginal effects on the cement mortar compressive strength and elastic modulus. The improved fracture properties of the cement mortar reinforced by 2% RSF from the SCB fracture test demonstrate that the RSF-reinforced mortar not only has a better resistance to the initiation of major cracks but also exhibits an enhanced post-cracking performance. Based on the ring test results, the longer cracking time and higher residual strain level of the 2% RSF mortar samples clearly reveal that the RSF could effectively delay and bridge cracks.

Finite element simulation of restrained shrinkage cracking of cementitious materials: Considering moisture diffusion, aging viscoelasticity, aleatory uncertainty, and the effects of soft/stiff inclusions

Simulation of restrained ring shrinkage and cracking of cementitious materials in a multiphysics simulation framework (MOOSE) is discussed in this paper. The 3D numerical model analyzes residual stress development and crack initiation/propagation in cement pastes by applying an eigenstrain which varies over the depth of the specimen based on the relative humidity of the pores as moisture diffuses from the drying surface. The numerical modeling framework explicitly considers: (i) moisture diffusion that generates differential shrinkage along the depth of the specimen (ii) viscoelastic response of aging cementitious materials through a rate-type creep law based on generalized Maxwell model, (iii) isotropic damage model with Rankine′s criterion determining the failure initiation, and (iv) aleatory uncertainty-based distribution of tensile strengths of individual finite elements to account for statistical variability and associated microstructural size effects. The model is implemented for cement pastes containing compliant/stiff inclusions subjected to variable drying conditions. The numerical model can be used to compare the cracking propensity of different cementitious mixtures.

The Influence of Curing Time on Restrained Shrinkage Cracking of Concrete with Shrinkage Reducing Admixture

AbstractThe positive effect of increased duration of curing in enhancing strength and durability of concrete is well established. However, there have been reports suggesting that longer curing times can result in increased drying shrinkage and can affect restrained shrinkage cracking. Although shrinkage reducing admixtures (SRAs) were introduced to the concrete industry about 25 years ago, the effect of curing time on their restrained shrinkage performance has not been previously investigated. In this study, the effects of three curing times of 1, 3, and 7 days on drying shrinkage performance of the control mix (mix without SRA) and the mix containing SRA were investigated. The results indicate that the restrained shrinkage cracking potential of the control mix increased with increased duration of curing. However, for the mix containing SRA, an opposite effect was observed and longer curing reduced both the free drying shrinkage and potential for restrained shrinkage cracking. The results also indicate that by increasing the curing time, the crack width for the control mix increased, whereas there was no significant effect on the crack width of the mix containing SRA.

Restrained Shrinkage Mechanism of Ultra High Performance Concrete

The understanding and controlling of the restrained shrinkage is critical for the application of ultra high performance concrete (UHPC). This study made an analysis of restrained shrinkage mechanism of four kinds of UHPCs based on the direct tensile test accompanied with acoustic emission (AE) source location, free shrinkage test and restrained shrinkage test. The effects of UHPC tensile properties (strain softening or strain hardening) and high performance calcium sulphoaluminate (HCSA, a new kind of expansion agent) dosages (0%, 3% and 6% by mass of total binder) were investigated. The restrained shrinkage cracking mechanism of strain hardening UHPC and strain softening UHPC was analyzed based on AE analysis method under direct tensile loading. The results indicates that strain hardening UHPC shows multiple micro-defects to relax the restrained tensile stress marginally while strain softening UHPC shows several hairline cracks to relax the restrained tensile stress evidently. In ASTM C1581-04 ring test, the restrained shrinkage of strain hardening UHPC with HCSA dosage of 0%, 3% and 6% at 80d is 141 μe, 96 μe and 16 μe, respectively. The HCSA expansion agent can effectively reduce the restrained shrinkage of UHPC and the influence on the structure.

Study of Drying Shrinkage Mitigating Concrete Using Scaled Bridge Bays

Cracks reduce the durability and service life of bridge decks and they usually form as a result of tension induced from restrained shrinkage of concrete. There are several mixture design technologies that can be used to reduce concrete shrinkage and subsequent cracking. The main focus of this study is to evaluate the effectiveness of three such technologies to limit restrained shrinkage cracking in a scaled laboratory bridge deck. The first mixture evaluated shrinkage compensating cement (Type-K) as a partial replacement of Portland cement, the second mixture evaluated pre-wetted lightweight fine aggregate as a partial replacement of fine aggregate to promote internal curing (IC), and finally, the third evaluated a mixture incorporating shrinkage reducing admixture (SRA). Strain of the deck reinforcement was monitored during and after placement of the concrete for a period of 6 months. All of the data was compared with similar measurements from a control deck containing a standard concrete mixture used by the Illinois Department of Transportation. The results showed that, the experimental deck containing Type-K cement exhibited around 100% higher expansion compared to control mixture during the curing period. The IC mixture showed approximately 50% less expansion at 7 days but exhibited 10% less shrinkage at the end of drying period compared to the control mixture. The initial expansion of SRA mixture showed similar peak value compared to control mixture but at the end of the drying period, the shrinkage of SRA mixture was around 75% less than the deck cast with control mixture.

Prediction of Restrained Shrinkage Cracking of Shotcrete Rings Using Fracture Mechanics–Based Approach

AbstractA fracture mechanics–based approach is developed to predict the shrinkage cracking age of shotcrete ring specimens under various curing regimes. Prolonged water curing and curing compound a...

Early-age cracking resistance of ground granulated blast furnace slag concrete

High-performance concrete (HPC) generally experiences rather high autogenous shrinkage. If restrained, residual tensile stress will be induced which may be sufficient to cause cracking. Ground granulated blast furnace slag (GGBFS) has been utilized as a mineral admixture to reduce shrinkage cracking in HPC. The restrained shrinkage cracking of concrete containing GGBFS appears to be less than that of concrete without slag. However, the data is limited, and the effect of the GGBFS on the restrained cracking resistance needs to be further investigated. Restrained ring tests on cracking resistance of HPC using GGBFS as 0%, 20%, 35%, and 50% by weight replacements of cement were performed. Four concrete mixtures with the same w/b ratio of 0.32 were placed in a 23 ± 1 °C, 60 ± 5% RH environment, and covered with vinyl and aluminum adhesive tape. The outer rings were removed at 24 h after casting to allow water evaporation through the height of the specimen. Test results showed that: (1) the residual tensile stress at the age of 14.25 days after casting decreased by 18.6%, 33.2%, and 40.9% when the amount of GGBFS increased from 0% to 20%, 35%, and 50%, respectively; (2) the stress rate decreased by 58.9%, 62.5%, and 66.8% when the amount of GGBFS increased from 0% to 20%, 35%, and 50%, respectively, indicating that the cracking resistance based on stress rate increased with increasing GGBFS replacement.

Durability and rheological characteristics of high-volume ground-granulated blast-furnace slag concrete containing CaCO3/anhydrate-based alkali activator

In this paper, durability and rheological characteristics of binary blended mixtures incorporating high-volume ground-granulated blast-furnace slag (GGBFS) were assessed based on a series of laboratory tests. Various durability characteristics such as restrained shrinkage cracking, freeze-thaw resistance, carbonation resistance, and chloride ion diffusion resistance were comprehensively investigated. The experimental results verified that the high-volume GGBFS replacements with a CaCO3/anhydrate-based alkali activator effectively improved the overall durability performance, especially when a replacement level of 70% was used. The promoted durability was mainly attributed to the formation of dense microstructure and low capillary porosity resulting from the enhanced degree of latent hydraulic and pozzolanic reactivity of GGBFS in the presence of alkali activator, which transformed a number of weak phases in cement hydrates (Ca(OH)2) into dense calcium silicate hydrate (CSH) phases. It was also found that the flow behavior was largely affected by the GGBFS replacement level, use of alkali activator, and elapsed time after mixing. Based on the findings of the present study, the high-volume GGBFS replacement, up to 70–80 wt%, appears to be a substantial strategy for enhancing the durability and sustainability of concrete.

Prediction of restrained shrinkage crack width of slag mortar composites using data mining techniques

The purpose of this study is to develop data mining models to predict restrained shrinkage crack widths of slag mortar cementitious composites. A database published by BILIR et al. [1] was used to develop these models. As a modelling tool R environment was used to apply these data mining (DM) techniques. Several algorithms were tested and analyzed using all the combinations of the input parameters. It was concluded that using one or three input parameters the artificial neural networks (ANN) models have the best performance. Nevertheless, the best forecasting capacity was obtained with the support vector machines (SVM) model using only two input parameters. Furthermore, this model has better predictive capacity than adaptativenetwork- based fuzzy inference system (ANFIS) model developed by BILIR et al. [1] that uses three input parameters. Keywords: mortar; data mining; prediction; restrained shrinkage cracking.

Dimensional stability of deflection‐hardening hybrid fiber reinforced concretes with coarse aggregate: Suppressing restrained shrinkage cracking

High Performance Fiber Reinforced Concretes (HPFRCs) with deflection‐hardening capability are relatively novel materials with high damage tolerance. However, mixture proportions of such materials are mostly designed with fine aggregates for easier/homogenous fiber distribution and low matrix fracture toughness which increases the amount of cementitious materials as the main binder and related risk for dimensional instability, high cost, and environmental unfriendliness. Here, with the idea of developing concrete that is free of shrinkage‐related cracking at a more reasonable price, deflection‐hardening HPFRC mixtures incorporating different amounts of coarse aggregates (with maximum size of 12 mm) were developed with different mixture parameters (fiber types/dosages and fly ash contents) and tested for their dimensional stability by focusing mainly on the drying and restrained shrinkage measurements. Experimental results reveal that the combined effectiveness of utilizing hybrid fiber reinforcement and high amounts of coarse aggregates by properly adjusting the matrix properties without compromising high ductility (deflection‐hardening behavior) can help the realization of possible producibility of HPFRC mixtures that are completely free of restrained shrinkage‐related cracking. The findings of this study are believed to make a significant impact on the wide‐spread usage of deflection‐hardening HPFRC mixtures with similar ingredients to that of conventional concrete in actual field conditions.

Internal Curing to Mitigate Cracking in Rapid Set Repair Media

Abstract Rapid hydration and high early strength portland cement and calcium sulfoaluminate (CSA) concretes are commonly used as pavement repair media. Field trials reveal a tendency to crack along the longitudinal axis of the repair. The authors hypothesized that internal curing with saturated lightweight aggregate would prevent or delay restrained shrinkage cracking in the rapid repair media. The fresh properties (slump, setting time), mechanical properties (elastic modulus, compressive and tensile strength), and volume stability (autogenous shrinkage, drying shrinkage, restrained ring shrinkage, creep) of the rapid repair media were evaluated with and without internal curing with saturated lightweight aggregate. Despite delayed hydration and reduced early-age strength, internally cured concretes could retain the requisite minimum 4-hour compressive strength of 4,000 psi. Significant improvements in volume stability were also noted. Drying and autogenous shrinkage were reduced by factors up to 20 % and 50 %. However, detrimentally, creep shrinkage was increased by factors up to 45 %, respectively. The time to cracking in restrained ring shrinkage tests was increased by factors up to 60 %. These results indicate that internal curing can successfully improve volume stability and mitigate restrained shrinkage cracking in rapid repair media without compromising fresh properties or ultimate mechanical strength.

The influence of mix composition, w/b ratio and curing on restrained shrinkage cracking of cementitious mortars

Cracking due to restrained shrinkage deformations affects the durability and structural performance of concrete structures negatively. This paper initially reviews the outcome of previous studies, in which several crack-influencing parameters were investigated. A simplified analytical model for predicting the age at cracking based on elastic modulus, tensile relaxation, shrinkage strain and tensile strength is also presented. The experimental investigations confirm that the analytical model can predict the age at cracking with good accuracy. Results from the studies presented indicate that, against common belief, an increase in overlay strength decreases the age at cracking. To investigate this phenomenon further, many mortar mixes with different strength and mix characteristics were tested against cracking performance. An inverse relationship between mortar strength and age at cracking was identified. For the particular application of patch repair mortars, the outcome of this study is used to critique common performance requirements in the European Standards.

Evaluation of early age cracking in rendering mortars with polypropylene fibers

Abstract The incorporation of fibers in concrete produces an improvement in the characteristics of the material as observed in different studies. In order to obtain the same good results, fibers are added to rendering mortars to reduce some of their drawbacks. However, this type of mortar has some specific characteristics, such as hydrated-lime utilization or higher air, which is not usual in concrete. Thus, this study aims to evaluate the potential of polypropylene fibers to reduce early age cracking caused by restrained shrinkage in rendering mortars. Two types of mortars were used to verify possible differences in the way they responded to the introduction of fiber. The influence of the fiber content was also investigated. Mortars were evaluated in fresh state, and mechanical behaviors were measured at several ages. The restrained shrinkage cracking was followed for 21 days using the ring test method. The use of polypropylene fibers leads a smaller value of total crack width and a delay of the first crack. Also, the elastic modulus shows a higher correlation with the mortars crack width. Both parameters were successfully used to predict the mortars crack width. The ring test method may be a suitable test method to evaluate the capacity of fibers to control the crack formation in rendering mortars.

Restrained Shrinkage Cracking of Fiber-Reinforced High-Strength Concrete

Concrete shrinkage and volume reduction happens due to the loss of moisture, which eventually results in cracks and more concrete deformation. In this study, the effect of polypropylene (PP), steel, glass, basalt, and polyolefin fibers on compressive and flexural strength, drying shrinkage, and cracking potential, using the ring test at early ages of high-strength concrete mixtures, was investigated. The restrained shrinkage test was performed on concrete ring specimens according to the ASTM C1581 standard. The crack width and age of restrained shrinkage cracking were the main parameters studied in this research. The results indicated that the addition of fiber increases the compressive strength by 16%, 20%, and 3% at the age of 3, 7, and 28 days, respectively, and increases the flexural toughness index up to 7.7 times. Steel and glass fibers had a better performance in flexural strength, but relatively poor action in the velocity reduction and cracking time of the restrained shrinkage. Additionally, cracks in all concrete ring specimens except for the polypropylene-containing mixture, was developed to a full depth crack. The mixture with polypropylene fiber indicated a reduction in crack width up to 62% and an increasing age cracking up to 84%.

Restrained shrinkage cracking of self-consolidating concrete roads

Abstract The present study is dedicated to investigate the liability of continuously reinforced concrete pavement (CRCP) cast with self-consolidating concrete (SCC) to restrained shrinkage cracking and the values of restraint stresses in these pavements. SCC, which is becoming increasingly popular due to its several superiorities over conventionally vibrated concrete (CVC), has higher amounts and rates of shrinkage compared to CVC. The higher risk of restrained shrinkage cracking of SCC is a great cause of concern in pavement construction as the penetration of water, chemicals, and salts increases the risk of corrosion of reinforcement. In the present study, an analytical restraint stress expression was developed for typical CRC pavements by modifying the restraint stress equation developed previously for RC beams. Using this equation, the restraint stresses induced to the longitudinal reinforcement by the rigid pavement, cast with CVC or SCC, were calculated for eight different example sections. These restraint stress values were found to reach up to 50% of the limit stresses of bars, allowed by the design guidelines, when the pavement is cast with SCC. The amounts of longitudinal reinforcement used in typical CRCP roads were found to be more critical when the pavement is cast with SCC.