Plastic Shrinkage Cracking In Concrete Research Articles

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.

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.

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

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.

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.

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.

Combined effect of nano-silica, super absorbent polymers, and synthetic fibres on plastic shrinkage cracking in concrete

This research attempts to further add onto the existing knowledge-base of the utilisation of nano-silica in concrete by understanding its influence on plastic shrinkage in concrete, a subject with hardly any specific literature available. The results of extensive experimentation reveal that the adoption of nano-silica in concrete mixes should be cautiously undertaken, as it behaves in such a way to cause acceleration of the mechanisms of plastic shrinkage. This research has further been done in tandem with the combined plastic shrinkage crack mitigation methods, such as the use of synthetic fibres and super absorbent polymers (SAP) in concrete. The combined use of nano silica with SAP can be effective in alleviating the associated plastic shrinkage cracking. Synthetic micro-fibres too are useful in lessening plastic shrinkage cracking in nano silica mixes, but are not as effective as SAP. The mechanism of acceleration of plastic shrinkage cracking by nano silica is attributed to the finer particles of the material, causing reduced bleeding amounts in mixes in which it is incorporated.

A practical approach for reducing the risk of plastic shrinkage cracking of concrete

In this letter, a conventional method for mitigation of plastic shrinkage of fresh concrete based on comparing bleeding and evaporation rates (the former based on the commonly observed values of bleeding rate and the latter estimated by means of the commonly-used ACI nomograph) is critically assessed. It is shown that even if the initial bleeding rates are sufficiently high (i.e. higher than the evaporation rates), cracking may still occur if all the bleed water is lost by evaporation between the times of initial and final set, leading to the rise of capillary pressure. An alternative and more conservative method should be thus based on the total (accumulated) amount of bleed water compared to the total amount of evaporated water. The former should take into account the concrete’s properties and the geometry of the member, while the latter can be assumed based on the nomograph method.

Modelling the severity of plastic shrinkage cracking in concrete

Plastic shrinkage cracking (PShC) is one of the earliest forms of cracking in concrete as it occurs within the first few hours after the concrete has been cast. Concrete elements with large exposed surfaces are especially vulnerable to PShC. Many researchers have proposed models to simulate plastic shrinkage, bleeding and to predict the occurrence of PShC. In this paper a model to predict the degree of PShC is proposed. This model, the so called PShC Severity Model, is based on the volume of water that evaporates from the concrete between the placing and the initial setting time of the concrete. This model was verified using a large number of PShC test results. A further study was also done on the effect of the addition of low volumes of synthetic micro fibres on the degree of PShC. It was found that the addition of the fibres effectively reduces the PShC Severity value.

Plastic shrinkage cracking of concrete − roles of osmotic suction

Plastic shrinkage cracking of concrete occurs when the stresses arising in the concrete, due to a combination of suction and restraints of deformation such as reinforcement or formwork, equal its strength. However, three different types of suctions should be distinguished, namely total, matric and osmotic suctions. Although the total suction comprises matric and osmotic suctions, it is often used interchangeably with matric suction, with the underlying unconfirmed assumption that either the osmotic suction or its effect is negligible. In this paper, after a discussion of the pore moisture suctions and strength of unsaturated early-age concrete, experimental investigations of the suctions arising in, and the tensile strength and shear strength of, fly ash mixed with solutions of different osmotic suctions are described. It was found that osmotic suction has negligible effect on the shear and tensile strength, and hence, by inference, the inter-particle stresses in the fly ash mixture and early-age concrete. This strongly suggests that the role played by osmotic suction in the plastic shrinkage cracking of concrete is minimal and, accordingly, justifies the focus of earlier researchers on matric suction only.

Use of a New Approach (Design of Experiments Method) to Study Different Procedures to Avoid Plastic Shrinkage Cracking of Concrete in Hot Climates

Hot climate concreting requires specific procedures in order to reduce the undesirable effects caused principally by excessive water evaporation from concrete surfaces, which induce plastic shrinkage cracking and thereby reduce durability. This research highlights the effectiveness of some of these measures: plastic sheets, curing agent, cold water and polypropylene fiber. The design of experiments method was used to reduce the number of tests and allow study of the effects of factors (or measures) and the interactions between these factors and the response parameters, which include plastic shrinkage cracks, evaporation rate, and strength. The most efficient way to minimize plastic shrinkage is to use a curing compound followed by the application of a plastic sheet cover; and the most efficient measure to decrease evaporation is the application of a plastic sheet cover.

Plastic Shrinkage Cracking of Concrete

SummaryPlastic shrinkage cracking, which occurs during the first several hours after the casting of concrete, is of considerable economic significance in the concrete construction industry. In this paper, the mechanism of plastic shrinkage cracking and its related phenomena of evaporation and bleeding are first reviewed. Then, together with tensile strength of early-age concrete, the concept of matric suction, its effect on plastic shrinkage and an empirical relationship for its estimation are discussed. Practical implications of the discussion are also highlighted.

Influence of shrinkage-reducing admixtures on the reduction of plastic shrinkage cracking in concrete

Fresh concrete exposed to high evaporation rates is prone to plastic shrinkage cracking, especially in structures with large surface area/volume ratios. The present work shows that the reduction of the surface tension of the mixing water is an effective way for decreasing such cracking. In this study, conventional and high strength concretes with superplasticizers and shrinkage reducing admixtures (SRAs) were exposed to drying in the plastic state. Continuous monitoring of the surface displacement facilitated the identification of the different stages of plastic shrinkage cracking. Measurements of capillary pressure, settlement, internal temperature and evaporation rate were also made. The results show the effectiveness of SRAs in reducing plastic shrinkage cracking, even in high strength concrete. This is attributed to the reduction in the evaporation rate, delay of the peak capillary pressure due to the development of menisci in the pores and lower settlement.

Cracking Appraisal and Anti-Crack Measures Research of Cross Sea Bridge Concrete

Through the experiment, this paper carries on the appraisal to the cracking risk of cross-sea bridge concrete. Analyzed the influence of active admixture, sand ratio, cement content and water-cement ratio to the cracked degree of concrete. And proposed control measure of the plastic shrinkage cracking of concrete. Finally, through research to the concrete used in pile cap of the Shanghai Yangtze River Bridge, it obtains that all can be allowed to reduce the cracking risk of concrete by reducing active admixture, increasing to fly ash amount, reducing sand ratio, the slag powder has little effect the cracking risk of concrete, the silica fume can increase the cracking risk of concrete.

Use of flax fibres to reduce plastic shrinkage cracking in concrete

Abstract An experimental investigation was performed to measure the restrained and unrestrained plastic shrinkage properties of small mortar specimens containing short flax fibres (10–38 mm in length) in amounts ranging from 0.05% to 0.3% by volume. Based on the number of cracks, total crack area, and maximum crack widths produced within the first 24 h after casting and exposure to hot, dry, and windy conditions, flax fibres were found to be slightly more effective in controlling restrained plastic shrinkage cracking than commercially available polypropylene and glass fibres for the mortar mixture studied. At a flax fibre volume fraction of 0.3%, total crack areas were reduced by at least 99.5% relative to plain mortar specimens and maximum crack widths were reduced by at least 98.5% to less than 0.022 mm. Fibre length did not significantly influence cracking behaviour, nor did the presence of flax fibres significantly influence the free plastic shrinkage strains observed.