Shrinkage Cracking Of Concrete Research Articles

A simplified but improved numerical approach to determine moisture balance for plastic shrinkage cracking in concrete

This paper introduces an improved numerical approach for evaluating moisture balance on concrete surface which can initiate plastic shrinkage cracking on the surface of fresh concrete in concrete slab. Because plastic shrinkage cracks occur when the tensile stress induced from the surface drying of concrete exceeds the tensile strength in the freshly placed concrete, moisture balance calculated by the introduced approach can be used as the primary indicator for plastic shrinkage cracking. The numerical approach introduced in this paper therefore emphasized an exact evaluation of bleeding and evaporation on the concrete surface. In determining bleeding, the approach introduced in the previous study was improved through the consideration of additional influencing factors of the accelerator and steel fiber and the supplementation of additional experimental data. For reliable prediction of evaporation, an empirical relation was newly introduced. The reduction of evaporation rate with time was taken into consideration, and the use of the weighed characteristic velocity rather than the direct application of the wind velocity was recommended. Determination of an exact distribution for the weighed characteristic wind velocity on the surface of a concrete slab was based on computational fluid dynamic (CFD) analyses. In particular, the effect of installing a windscreen along the sides of the concrete slab was intensively examined. Upon verification of the introduced numerical approach through correlation studies between experimental data and numerical results, additional parametric studies were also performed to numerically examine the relative contribution of each influencing factor in plastic shrinkage cracking. Moreover, the introduced approach can effectively be used for the on-site prediction of surface drying time of a concrete slab and for the preparation of a proper curing strategy to mitigate plastic shrinkage cracking.

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.

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.

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.

Methods for Assessment of Early Age Shrinkage Cracks in Higher Strength Concrete: A Review

High-strength concrete is a type of concrete with compressive strength greater than 40 MPa (megapascals), which is much higher than the strength of normal concrete. High-strength concrete is often used in construction projects where greater strength is required, such as high-rise buildings, bridges, and other structures that need to withstand heavy loads or harsh environments. The high strength is achieved through the use of high-quality materials and careful proportioning and mixing of the concrete. Higher strength concrete experiences excessive early age cracking due to low water binder ratio. This early age shrinkage cracking directly affects the strength and durability of concrete. This paper discusses a review of methodologies used to assess the early age shrinkage cracks in concrete which will help in further high strength concrete shrinkage cracking study. In this review restrained shrinkage ring test, free shrinkage tests are discussed

Mechanism and control strategy of large-area concrete shrinkage cracks in the underground railway section

The cracks of the large-area concrete structure in the underground railway section directly affect the structural safety and service life. How to take effective measures to control concrete shrinkage cracks is a difficulty to be solved in the project.In view of the crack control demand of large-area concrete structure cracks in a vehicle section of Wuhan metro, based on the existing engineering cases of large-area concrete structure, shrinkage crack mechanism and control strategies, the corresponding measures are proposed to prevent crack production from two aspects of concrete raw materials and construction technology.The results show that through the regulation of concrete materials,maintenance,casting,post-pouring belt, temperature monitoring and other links, the reduction of shrinkage cracks of large-area concrete structure in the underground railway section is realized.These results can provide references for similar projects to lessen cracks, ensure structural safety and construction quality.

Effect of surface curing timing on plastic shrinkage cracking of concrete

Effect of surface curing timing on plastic shrinkage cracking of concrete

Effects of microfine aggregate in manufactured sand on bleeding and plastic shrinkage cracking of concrete

Effects of microfine aggregate in manufactured sand on bleeding and plastic shrinkage cracking of concrete

Experimental validation of a novel method for estimating the severity of plastic shrinkage cracking in concrete

Plastic shrinkage cracking in cementitious materials is caused mainly by rapid and excessive moisture loss during mixture’s early ages, before sufficient tensile strength is gained. A novel model has been previously developed by the authors to estimate the severity of plastic shrinkage cracking in concrete. This paper presents findings of a series of full-scale experiments carried out to validate the accuracy of the proposed model. The experiments included investigating the impact of cement type, water-cement ratio (w/c), and admixtures (i.e., accelerator, retarder, and superplasticizer). The tests were performed in three rounds under similar ambient conditions using 3 slabs (3 m × 2 m) and 3 ring test moulds at each round. The results confirm the accuracy of the model in anticipating/comparing the cracking severity of the tested concretes.

Effect of aggregate micro fines in machine-made sand on bleeding, autogenous shrinkage and plastic shrinkage cracking of concrete

Effect of aggregate micro fines in machine-made sand on bleeding, autogenous shrinkage and plastic shrinkage cracking of concrete

ЭКСПЕРИМЕНТАЛЬНО-ТЕОРЕТИЧЕСКОЕ ОБОСНОВАНИЕ МЕТОДА ОЦЕНКИ ТРЕЩИНОСТОЙКОСТИ И РАССТОЯНИЯ МЕЖДУ УСАДОЧНЫМИ ШВАМИ БЕТОННЫХ ОБЛИЦОВОК ВОДОХОЗЯЙСТВЕННЫХ КАНАЛОВ

Assessment of the susceptibility of concrete to cracking with subsequent changes in the volume and nature of pores, as well as capillary passages, deformation and strength properties of the material (especially tensile deformations and tensile strength) are the main indicators by which the resistance and durability of linings of water channels can be predicted. By regulating technological factors, it is possible to signifi cantly reduce the intensity of moisture shrinkage, which in turn makes it possible to achieve an increase in the operational reliability and durability of concrete linings. The main reason for the manifestation of shrinkage cracks in concrete is the excess, at a certain point in time, of non-manifested shrinkage deformations, as a result of which tensile stresses are formed in the material with constrained shrinkage, the ultimate tensile strength of concrete. Qualitative prediction of the potential resistance and durability of linings of water channels is possible when assessing the predisposition of concrete to cracking with subsequent changes in the volume, nature of pores and capillary passages, deformation and strength properties of the lining material.

Utilising microCT scanning technology as a method for testing and analysing plastic shrinkage cracks in concrete

Plastic shrinkage cracking is tested by placing fresh concrete in a restrained mould and exposing it to high evaporation conditions. Plastic shrinkage cracking was studied using microCT scanning technology, which allowed the cracking and volume change to be studied below the surface of the concrete. The effect of the level of restraint on plastic shrinkage cracking was also analysed. The study showed that the shrinkage occurring in the concrete is isotropic, even with the formation of a crack. The settlement voids under reinforcing bars form almost immediately after casting the concrete and is mostly a problem in conditions with high evaporation.

The influence of solar radiation on plastic shrinkage cracking in concrete

Plastic shrinkage cracking (PSC) in concrete is related to the amount and rate of free pore water loss due to evaporation. This study investigates the influence of solar radiation on evaporation, the concrete temperature, plastic shrinkage and cracking. Literature suggests that exposure to solar radiation can either: increase the concrete temperature and, consequently, increase the rate of tensile strength gain resulting in less severe PSC or can increase the concrete temperature, resulting in a higher amount and rate of pore water loss to produce more severe PSC. The results of this study indicate that exposure to solar radiation significantly increases the amount and rate of pore water loss as well as plastic shrinkage and severity of PSC. To study PSC, many authors have estimated the evaporation rate from wind speed, air and concrete temperature and humidity which would result in significantly underestimating the actual evaporation rate if the concrete is exposed to moderate or high solar radiation. The accuracy of several radiation-related evaporation estimation models was evaluated by comparing the models to the actual rate of evaporation from specimens placed in the sun. A more accurate model was identified to estimate the evaporation in concrete specimens when exposed to solar radiation.

EFFECT POLYPROPYLENE OF FIBER ON DRYING SHRINKAGE CRACKING OF CONCRETE PAVEMENT USING RESPONSE SURFACE METHODOLOGY

In concrete when tensile stress surpasses the strength of the traction contributes to cracking, which is called shrinkage cracking. Shrinking allows for curling and folding of concrete. The principal goal of this research work is to develop optimal Eco-friendly concrete mixtures by using Response Surface Methodology (RSM), including different quantities of polypropylene fiber used in concrete pavement, identify the shrinkage factor (shrinkage cracking) in the concrete pavement. The testing program included using of thirty mixtures to investigate four parameters namely cement content (300,400 and 500) kg / m3, steel fiber (0, 0.075, and 0.15 vol. %), three separate amounts of polypropylene fiber (0, 0.35, and 0.7 vol. %), and (0, 5, and 10 %) silica fume by cement weight. The results indicated that the amount of cement is the higher factors affecting the shrinkage cracking of concrete. For the purpose of obtaining the best mixture for optimal components to design concrete mixtures used in the concrete pavement that give the compressive strength [> 30 MPa], flexural strength [> 4.1 MPa], minimum CO2 emissions, less cost, and fewer cracks width according to requirements and Iraqi specifications are cement [385.94] kg/m3, silica fume [0.000198Vol.%], steel fiber [0.0564 Vol.%], PP fibers [0.2926 Vol.%], Carbon dioxide emissions [379.59] kg CO2 -e / m3, total cost 99.96 USD / m3, and crack width [0.1]mm.

On the Feasibility of Using Industrial Urea to Mitigate Thermal and Shrinkage Cracking in Concrete

Industrial urea is an organic compound that is widely used for various physiological processes and for producing nitrogen fertilizers. This study hypothesized that mixing urea with concrete would decrease the temperature and expansion of the cement microstructure abruptly due to the reaction with water and a cement hydration product. This study tested the hypothesis by experiments. The performance of concrete was evaluated after setting the mixing ratio of industrial urea was to 0%, 5%, 10%, and 15%. The results showed that temperature decreased drastically immediately after mixing and the decrease in temperature increased with a higher mixing ratio. Consequently, condensation was delayed, and heat of hydration decreased. It was found that when considering workability and compressive strength development performance, the proper mixing ratio of urea was around 10%. This study proposed the mixing design technique of concrete mixed with urea. Additionally, this study reported better carbonation resistance and mitigated shrinkage strain of concrete mixed with urea compared to existing low-heat mixing ratios.

The severity of plastic shrinkage cracking in concrete: a new model

Plastic shrinkage cracking in concrete is mainly a physical process, in which chemical reactions between cement and water do not play a decisive role. It is commonly believed that rapid and excessive moisture loss due to evaporation is the primary cause of the phenomenon. This paper presents a new model to estimate the severity of plastic shrinkage cracking, based on the initial setting time and the amount of water evaporating from within the concrete bulk. A number of experiments were performed under controlled ambient conditions, during which the water/cement ratio, cement type and dosage of superplasticiser were altered. The results, alongside those reported by other researchers, were utilised to check the validity of the proposed model. According to the outcomes, the model could predict the cracking severity of the tested concretes with good precision.

Experimental Validation of a Novel Method for Estimating the Severity of Plastic Shrinkage Cracking in Concrete

Experimental Validation of a Novel Method for Estimating the Severity of Plastic Shrinkage Cracking in Concrete

The effect of superabsorbent polymers on the mitigation of plastic shrinkage cracking of conventional concrete, results of an inter-laboratory test by RILEM TC 260-RSC

This article presents the results of an inter-laboratory study performed by six international research groups in the framework of RILEM Technical Committee 260 RSC “Recommendations for use of superabsorbent polymers in concrete construction”. Two commercially available superabsorbent polymer (SAP) samples with different chemical compositions were tested in terms of their ability to mitigate plastic shrinkage cracking of concrete. The SAP mixtures showed a clear reduction of plastic shrinkage cracking in conventional concrete. On the contrary, if only additional water is added and no SAP, the area of plastic shrinkage cracks increases. This suggest the ability of SAP to mitigate plastic shrinkage cracking. Upon addition of the predetermined amount of SAP and additional water, the compressive strength decreased on average by 3% for the mixtures with 0.15% SAP (by mass of cement) and by 10% for the mixtures with 0.30% SAP.

Longitudinal restraining devices for the evaluation of structural behaviour of cement‐based materials: The past, present and prospective trends

AbstractThe problem of thermal and shrinkage cracking in concrete has been long recognised by researchers and engineers as it can jeopardise the intended serviceability of a concrete structure. This has led researchers to develop testing devices which aim to simulate the behaviour of concrete under restrained deformations. Such devices are discerned in passive and active, depending on how concrete's movement is restrained, whilst a new type of devices has been developed to account for the combined effects of intrinsic restrained deformations and externally imposed actions. This paper presents a detailed and critical literature review on the developed restraining devices and an analysis of the capabilities, complexities and peculiarities associated with their use. Further to this, the challenges the developers of testing devices are faced with, the gaps and uncertainties with the methods found in the literature and recommendations for potential improvements in the field are discussed.

Utilising super absorbent polymers as alternative method to test plastic shrinkage cracks in concrete

Plastic shrinkage cracking in concrete is due to evaporation, which is aggravated by harsh environmental conditions. By controlling the conditions in a laboratory to cause high evaporation rates, plastic shrinkage cracks can be induced and then tested. However, in order to control these conditions (wind, temperature, humidity) a large and expensive climate controlled chamber is required. Super absorbent polymers (SAP) are designed to absorb water and could possibly be used to mimic evaporation and thus induce plastic shrinkage cracks. In this study, by testing varying amounts and types of SAP, as well as different concrete mixes, the validity of using SAP as a novel method for testing plastic shrinkage cracking is investigated. The test results indicated that by using the method proposed and placing SAP on the surface of the concrete, plastic settlement and shrinkage occurs in the concrete. The results showed that higher amounts of SAP placed on the surface of the concrete resulted in more plastic shrinkage and ultimately larger plastic shrinkage cracks. Larger plastic shrinkage cracks also formed when SAP with a higher and faster absorption was used. Based on the results of the tested proposition, the proposed method of placing SAP on the surface of the concrete can be utilised to induce plastic shrinkage cracks in concrete. If the same SAP is used internationally for this purpose, all tests could be compared using the same test procedure.