Early-age Cracking Of Concrete Research Articles

Early-Age Cracking of Fly Ash and GGBFS Concrete Due to Shrinkage, Creep, and Thermal Effects: A Review.

Supplementary cementitious materials (SCMs) are eco-friendly cementitious materials that can partially replace ordinary Portland cement (OPC). The occurrence of early-age cracking in OPC-SCM blended cement is a significant factor impacting the mechanical properties and durability of the concrete. This article presents a comprehensive review of the existing research on cracking in OPC-SCM concrete mix at early ages. To assess the effects of SCMs on the early-age cracking of concrete, the properties of blended cement-based concrete, in terms of its viscoelastic behavior, evolution of mechanical performance, and factors that affect the risk of cracking in concrete at early ages, are reviewed. The use of SCMs in OPC-SCM concrete mix can be an effective method for mitigating early-age cracking while improving the properties and durability of concrete structures. Previous research showed that the shrinkage and creep of OPC-SCM concrete mix are lower than those of conventional concrete. Moreover, the lower cement content of OPC-SCM concrete mix resulted in a better resistance to thermal cracking. Proper selection, proportioning, and implementation of SCMs in concrete can help to optimize the performance and reduce the environmental impact of OPC-SCM concrete mix.

A simplified numerical model for the temperature profile of early-age concrete

The issue of early-age concrete cracking is challenging and relies on the state of concrete soon after it is placed in the formwork. The concrete state is a function of the strains associated with thermal and other dilatations and the level of in situ strength. Both strain and strength primarily require information on the temperature–time history of the concrete element. For larger elements, the thermal history varies significantly across the thickness and the concrete material itself acts as confinement for discrete elements. Due to complexity of this issue, designers currently rely on mock tests and/or finite-element (FE) modelling for structures that are deemed ‘important’. Both approaches are costly and time consuming. It is therefore important to have a robust yet simple model to estimate the temperature variation experienced by concrete elements. The proposed spreadsheet-based model presented in this paper aims to provide a rapid estimate of the temperature profiles within a hydrating concrete element. The model uses the concept of effective thickness and the revised heat compensation technique. It was validated based on the measured temperature development of a concrete block of rectangular section. The proposed model was also successfully compared with output from FE software (TNO Diana).

Cohesive element-based chemo-thermo-mechanical multi-field coupled cracking simulation of early-age concrete

Due to the intense exothermic hydration process, early-age concrete undergoes restrained shrinkage deformation, which can easily lead to cracks in concrete structures during construction. In order to accurately predict the adverse effects of early-age concrete cracking behavior, a cohesive element-based chemo-thermo-mechanical multi-field coupled cracking model of early-age concrete is proposed in this study. Parametric analysis shows that by selecting appropriate gap conductance, constitutive thickness, mesh size, and viscosity coefficient for the cohesive elements, the multi-field coupled cracking model can successfully simulate the entire cracking process of early-age concrete, and it has the ability to obtain crack development behavior based on the real displacement field jumps, coordinates, and damage of cohesive elements. The validation of the numerical examples reveals the competing mechanisms between thermal expansion and autogenous shrinkage in early-age concrete and accurately predicts the cracking strain, region, time, and width (within an order of magnitude) as reported in the literature.

Thermal Cracking in High Volume of Fly Ash and GGBFS Concrete

Supplementary cementitious materials (SCMs) such as fly ash and ground granulated blast furnace slag (GGBFS) are found to control the maximum temperature and the accompanying thermal gradients effectively. However, SCMs also lead to low early age strength development. Thus, it is crucial to understand the cracking behaviour of SCMs-based concrete affected by the mix design parameters. In this paper, the thermal cracking resistance was evaluated using a rigid cracking frame (RCF) with a computer-controlled temperature profile. The temperature profile was determined using the software ConcreteWorks by assuming the centre point of the mass concrete. The free shrinkage frame (FSF) and match-curing oven follow the same temperature profile as RCF to measure the free total deformation and time-dependent mechanical properties of concrete, respectively. An analytical model was proposed to calculate the autogenous shrinkage and the thermal stress separately. A time-dependent cracking risk coefficient allowing to estimate the risk of early age cracking of concrete was also proposed.

Experimental and Numerical Study of the Influence of Solar Radiation on the Surface Temperature Field of Low-Heat Concrete in a Pouring Block

With the influence of intense solar radiation heat and the greater temperature difference between day and night, surface concrete with a drastic temperature change can easily experience a great nonlinear temperature difference, which increases the risk of early-age concrete cracking. In this study, a distributed optical fiber temperature sensing (DTS) system is used to monitor the surface temperature gradient of concrete in real time, and a solar radiation heat monitoring test is also carried out based on the Baihetan project. Based on this, a solar radiation loading model and a finite element model of a typical pouring block considering solar radiation are established. Combined with the measured temperature data and different calculation conditions, the surface temperature changes of medium-heat and low-heat concrete experiencing solar radiation are analyzed, and the temperature control effect of surface concrete with different surface insulation measures is further analyzed. The results show that the temperature variation of medium-heat concrete at the same depth is more obvious than that of low-heat concrete. Additionally, the temperature variation of low-heat concrete is noticeable within 20 cm of the top surface. In addition, in an intense solar radiation environment, covering the concrete with a 4- or 5-centimeter-thick polyethylene coil can effectively control the surface temperature gradient and maximum daily amplitude of low-heat concrete, and surface concrete cured by running water has a significant temperature control effect. Therefore, it is suggested that 22–24 °C water temperatures be used for water curing during periods of intense solar radiation during the day and a 4-centimeter-thick polyethylene coil be used for coverage at night. These study results have been employed in the Baihetan project to optimize the temperature control scheme of the pouring blocks.

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.

Influence of Discrete Basalt Fibres on Shrinkage Cracking of Self-Compacting Ambient-Cured Geopolymer Concrete

Short basalt fibres (BFs) have recently gained significant interest in the building materials sector due to their superior mechanical characteristics and cheaper manufacturing cost than other fibre types. Drying shrinkage and the early-age cracking of concrete are the root cause of many durability issues in the long run. Including small dosages of fibres within concrete composites has been shown as an effective technique to minimise drying shrinkage rates and reduce the crack widths developed due to plastic shrinkage cracking. Nevertheless, limited research studies have investigated the influence of short and long BFs with different dosages on the drying shrinkage rates and early-age cracking of geopolymer composites. In the present study, self-compacting geopolymer concrete (SCGC) using fly ash and slag as the binder is mixed with anhydrous sodium metasilicate powder as an alkali-activator. The study aims to investigate the influence of short (12 mm), long (30 mm) and hybrid-length (1:3 (short/long)) BFs with 1%, 1.5% and 2% dosages on the drying shrinkage properties and plastic shrinkage cracking of SCGC. The study results showed that adding BFs to SCGC reduces the drying shrinkage rates compared to plain SCGC, and SCGC reinforced with a 2% dosage of hybrid-length BFs recorded the lowest drying shrinkage rate. Two methods were used to measure crack widths: manual measurement (crack width gauge) and image analysis. No plastic shrinkage cracks were identified in mixes reinforced with 12 mm (1.5% and 2% dosages), 30 mm and hybrid-length BFs.

The practical application of a self-developed temperature stress testing machine in development of expansive concrete blended with calcium sulfoaluminate additives

Early-age cracking of concrete is a complex problem related to temperature, restraint and curing conditions. Cracking sensitivity is hard to evaluate quantitatively and the use of expansive additives to mitigate cracking remains empirical in-situ. This study developed a Temperature Stress Testing Machine (TSTM) to evaluate early-age properties of concretes under varied engineering conditions. The general design of TSTM and the mathematical derivation of its working principle are provided. With the developed TSTM, early-age properties (free deformation, restrained stress, elastic modulus and early-age creep effect) of Calcium Sulfoaluminate (CSA) expansive concrete are tested comprehensively. Experimental results indicate that under high temperature condition, CSA concrete is not effective to compensate shrinkage, while the combination of CSA and lightweight aggregate resolves the problem. It offers us valuable insights on potential application of TSTM into mix design of crack-resistant concretes under complex engineering conditions.

Understanding the role of rheology in the plastic settlement and shrinkage cracking of early age concrete

Understanding the plastic (settlement/shrinkage) cracking phenomena of early-age concrete is important in-order to establish a holistic approach to minimise its occurrence. One of the factors associated with early-age concrete is the rheo-related behaviour which occur simultaneously within the timeframe known for plastic cracking. It is therefore useful to establish their links to broaden the knowledge of plastic cracking. This study is a novel evaluation of the influence of rheo-physical and rheo-viscoelastic behaviour on the plastic cracking behaviour by systematically altering these behaviours of formulated concrete mixes and extensively characterising them. The theory and frameworks for linking the behaviours were presented and established via statistical and analytical approaches. Significant rheo-related parameters found to influence plastic cracking phenomena include yield stress, structuration, creep and stress relaxation. The rheo-mechanics modelling suggests that the plastic cracking initiation tends to be a ductile failure that is pressure insensitive and sufficiently represented by von Mises criteria. This study opens up a consciousness to start evaluating mitigation strategies directed towards the materials optimisation of concrete mixtures to minimise the occurrence of plastic cracking in early-age concrete.

Methodology for Quantifying Features of Early-Age Concrete Cracking from Laser Scanned 3D Data

AbstractQuantifying the features of concrete cracking is of significance for assessing the bearing capacity and durability of concrete structures. However, there is a lack of efficient and reliable...

Early Age Shrinkage Behavior of Triple Blend Concrete

The early age shrinkage is responsible for the early age cracking of concrete. It is very critical for durability of concrete. The change in volume of concrete due to evaporation of water or dehydration process is known as shrinkage. To reduce the early age shrinkage utilized the supplementary cementitious material (SCM) in concrete. In present research industrial and agricultural waste byproduct like fly ash (FA) and rice husk ash (RHA) along with cement were used as SCM. The triple blend concrete was prepared by the combination of 20%, 30% and 40% partial cement replacement with FA and RHA for 0.30, 0.35 and 0.40 water-cement ratio. The concrete samples were tested by advanced instrument as shrinkage cone meter were used for measure the shrinkage. The result shows that the early age shrinkage reduced with increasing the SCM content. The microstructure characteristics enhanced with raising the content of FA and RHA up to 30% replacement; that was due to the dense particle packing.

Shear rheo-viscoelasticity approach to the plastic cracking of early-age concrete

The self-settlement phase of plastic cracking is majorly shear dominated and can be characterised by shear rheometry. This phase is susceptible to microstructural damage/cracking that can be rapidly propagated by the later occurring plastic shrinkage. This study experimentally determined the material properties and behaviour of rheologically modified concrete mixes using shear rheometry and measured their plastic cracking. Von-Mises and Hencky, and Bresler-Pister theories were then used as failure criteria with hypothetically fully restrained plastic strain/stress analyses to model the occurrence of plastic cracking. The incorporated rheology modifiers influenced the shear properties, viscoelastic abilities and plastic cracking of the concrete. The predictions of the model revealed that the plastic settlement is indeed mainly shear-related, the viscoelastic behaviour influences plastic cracking, and microcracking can occur before the initial setting time. It was also concluded that plastic concrete damage tends to be strain-oriented with pressure-insensitive form of ductile failure.

Effect of Various Supplementary Cementitious Materials on Early-Age Concrete Cracking

AbstractThis paper focuses on the effect of supplementary cementitious materials on early-age mechanical and viscoelastic properties of concrete, restrained shrinkage-induced cracking, and time to ...

Effect of crystalline admixture, fly ash, and PVA fiber on self-healing capacity of concrete

The ability of concrete admixtures to self-heal is an important way to improve concrete durability. The influence of crystalline admixture (CA), fly ash (FA) and PVA fiber on the self-healing capacity of early-age cracks in concrete was studied. The compressive strength recovery, electrical resistivity recovery, and morphology of crack surfaces were used to evaluate of early-age cracking in concrete. In this research four mixes are cast, control mix (M1), 0.1% of PVA fiber by volume mix (M2), 20% partial replacement of cement with fly ash mix (M3) and 2% of CA by mass of cement mix (M4). The cracks were formed by applying the compressive load for early-age cracks after 3 days of curing. Self-healing products are studied using scanning electron microscopy (SEM). It was observed that all admixtures show self-healing capacity to some extent. The results showed that the recovery of compressive strength and electrical resistivity of the cracked CA concrete samples has the highest self-healing capability due to the presence of calcium carbonate and C-S-H gel which were confirmed by SEM analysis.

A multiscale prediction model and simulation for autogenous shrinkage deformation of early-age cementitious materials

Abstract Autogenous shrinkage of cementitious materials is a key factor leading to early-age cracking of concrete. Based on the micromechanics, the underlying multiscale framework and capillary pressure theory, a multiscale model of autogenous shrinkage is presented for cementitious materials with a homogenization method. By comparing the predictive values from models with the experimental data in the literature, the HYMOSTRUC relative humidity model and Shimomura and Maekawa pore size distribution model are recommended for use in the proposed autogenous shrinkage multiscale model. Combined with the HYMOSTRUC chemical shrinkage model, the simulated results of the autogenous shrinkage multiscale model proposed in this paper match well with the experimental data in the literature and the predictive capability is successfully validated.

Early-Age Cracking in Concrete: Causes, Consequences, Remedial Measures, and Recommendations

Cracking is a common problem in concrete structures in real-life service conditions. In fact, crack-free concrete structures are very rare to find in real world. Concrete can undergo early-age cracking depending on the mix composition, exposure environment, hydration rate, and curing conditions. Understanding the causes and consequences of cracking thoroughly is essential for selecting proper measures to resolve the early-age cracking problem in concrete. This paper will help to identify the major causes and consequences of the early-age cracking in concrete. Also, this paper will be useful to adopt effective remedial measures for reducing or eliminating the early-age cracking problem in concrete. Different types of early-age crack, the factors affecting the initiation and growth of early-age cracks, the causes of early-age cracking, and the modeling of early-age cracking are discussed in this paper. A number of examples for various early-age cracking problems of concrete found in different structural elements are also shown. Above all, some recommendations are given for minimizing the early-age cracking in concrete. It is hoped that the information conveyed in this paper will be beneficial to improve the service life of concrete structures. Concrete researchers and practitioners may benefit from the contents of this paper.

The Effects of Insulation Thickness on Temperature Field and Evaluating Cracking in the Mass Concrete

This paper is mainly to study the effects of insulation thickness (0 - 3) cm on temperature field and evaluating cracking in the mass concrete by using Finite Element Midas Civil 2011. The finite element method is developed for simulation analysis of the temperature field in the concrete in early age mass concrete. From the results temperature field and evaluating cracking for the mass concrete it is concluded that insulation with adequate thickness at the face of massive concrete should be used to reduce the temperature differentials and control cracking of early-age concrete. Finally, the results are applied to provide some references for the constructions in the mass concrete such as dams, bridges beams, bridge piers, foundations of bridges and buildings.

Early-age thermal analysis and strain monitoringof massive concrete structures

Hydration heat and thermal induced cracking have always been a fatal problem for massive concrete structures. In order to study a massive reinforced concrete wall of a storage tank for liquefied natural gas (LNG) during its construction, two mock-ups of 0.8 mx0.8 mx0.8 m without and with metal corrugated pipes were designed based on the actual wall construction plan. Temperature distribution and strain development of both mock-ups were measured and compared inside and on the surface of them. Meanwhile, time-dependent thermal and mechanical properties of the concrete were tested standardly and introduced into the finite-element (FE) software with a proposed hydration degree model. According to the comparison results, the FE simulation of temperature field agreed well with the measured data. Besides, the maximum temperature rise was slightly higher and the shrinkage was generally larger in the mock-up without pipes, indicating that corrugated pipes could reduce concrete temperature and decrease shrinkage of surrounding concrete. In addition, the cooling rate decreased approximately linearly with the reduction of heat transfer coefficient h, implying that a target cooling curve can be achieved by calculating a desired coefficient h. Moreover, the maximum cooling rate did not necessarily decrease with the extension of demoulding time. It is better to remove the formwork at least after 116 hours after concrete casting, which promises lower risk of thermal cracking of early-age concrete.

Thermo-mechanical simulations of early-age concrete cracking with durability predictions

Concrete performance is strongly affected by mix design, thermal boundary conditions, its evolving mechanical properties, and internal/external restraints with consequences to possible cracking with impaired durability. Thermo-mechanical simulations are able to capture those relevant phenomena and boundary conditions for predicting temperature, strains, stresses or cracking in reinforced concrete structures. In this paper, we propose a weakly coupled thermo-mechanical model for early age concrete with an affinity-based hydration model for thermal part, taking into account concrete mix design, cement type and thermal boundary conditions. The mechanical part uses B3/B4 model for concrete creep and shrinkage with isotropic damage model for cracking, able to predict a crack width. All models have been implemented in an open-source OOFEM software package. Validations of thermo-mechanical simulations will be presented on several massive concrete structures, showing excellent temperature predictions. Likewise, strain validation demonstrates good predictions on a restrained reinforced concrete wall and concrete beam. Durability predictions stem from induction time of reinforcement corrosion, caused by carbonation and/or chloride ingress influenced by crack width. Reinforcement corrosion in concrete struts of a bridge will serve for validation.

Mechanical properties of early-age concrete reinforced with multi-walled carbon nanotubes

The results of mechanical property tests on early-age concrete reinforced with industrial-grade carbon nanotubes (CNTs) are reported. The objective of the study was to validate the effectiveness of CNTs and establish the development of concrete properties with CNT dosage and concrete age. Ultrasonication, ultraviolet–visible spectrophotometry and scanning electron microscopy were employed to inspect or improve the dispersion quality. The test programme considered four CNT dosages and seven concrete ages, with three replicates. The results indicated that industrial-grade CNTs can lead to increases in cubic compressive strength, tensile splitting strength, prismatic compressive strength and ultimate strain of concrete (up to 34·2, 11·1, 19·4 and 8·3%, respectively) comparable to those obtained with the use of fine nanotube particles; no significant influence was found for the other tested concrete properties. The results of this study also indicated that increases in strengths and strain were most significant during the first 7 d, the period when concrete is most prone to cracking due to shrinkage and hydration heat. This implies that industrial-grade CNTs may have a great potential in reducing early-age concrete cracking with much less health risk and lower testing requirements compared with the use of fine nanotube powders.