Model for Early-Age Rate of Evaporation of Cement-Based Materials

Published on Nov 1, 2012in Journal of Engineering Mechanics-asce2.62
· DOI :10.1061/(ASCE)EM.1943-7889.0000435
Mehdi Bakhshi9
Estimated H-index: 9
(AECOM),
Barzin Mobasher56
Estimated H-index: 56
,
Mansour Zenouzi4
Estimated H-index: 4
(Wentworth Institute of Technology)
Sources
Abstract
AbstractEarly-age cracking affects the structural integrity of concrete structures and, if not inhibited, would lead to a reduction in service life. Plastic cracks are observed in the first few hours after placing the concrete, a time period well within the initial stages when the drying process is controlled by the rate of evaporation of concrete surfaces, which is roughly constant and similar to the rate of evaporation from water surfaces. In the absence of a theoretical method, this rate is commonly estimated using a nomograph based on Dalton’s law. In this paper, a fluid mechanics–based approach for water evaporation based on the boundary-layer theory, mass transfer, diffusion, and convection is described. A parametric study is conducted on the effect of boundary-layer temperature, wind speed, relative humidity, and evaporation characteristic length on the calculated evaporation rates. Predicted evaporation rates are verified by recent experiments. Results show that given appropriate environmental par...
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References39
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#1Mehdi Bakhshi (ASU: Arizona State University)H-Index: 9
#2Barzin Mobasher (ASU: Arizona State University)H-Index: 56
Last. Chote SoranakomH-Index: 12
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Moisture flow through hydrating cement-based materials under early-age drying and shrinkage conditions is studied. The mechanism of drying of cementitious materials as a porous media is described. A dual-stage methodology for modeling the drying is presented based on surface moisture transfer and internal moisture transport characteristics. The proposed model for the internal moisture transfer simulates initial constant drying rate period (stage I) as a funicular liquid water transport stage, su...
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#1Mehdi Bakhshi (ASU: Arizona State University)H-Index: 9
#2Barzin Mobasher (ASU: Arizona State University)H-Index: 56
Plastic shrinkage cracking of concrete surfaces directly affects the long-term durability of structures. It can be attributed to the rapid rate of surface moisture evaporation while the microstructure is undergoing the early phases of hydration. A test method for characterizing evaporation parameters and simulating the sequential formation of shrinkage cracks in two-dimensional cement paste samples under low-pressure condition was developed. Effects of sample size, w/c ratio, initial curing and ...
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In this paper, the tensile properties of concrete at very early ages and their measurements are reviewed, and the need for further study is clearly highlighted, A newly developed apparatus and procedures for uniaxial direct tensile testing of concrete specimens at ages of 1.5 hours or more after mixing, together with the experimental results obtained, are reported. An improved knowledge of various important early-age properties is presented. The tensile strength, Young's modulus, and fracture en...
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#1T. Aly (RMIT: RMIT University)H-Index: 9
#2Jay Sanjayan (Monash University)H-Index: 71
Moist curing improves the properties of concrete. However, shrinkages at early ages are found to increase with increased curing. The reason for this phenomenon is studied with four binders and two types of curing. The binders are comprised of Portland cement/slag blends with 0, 35, 50 and 65% of slag. Initial moist curing times of 1 and 7 days were studied. The samples were then exposed to standard drying conditions (23°C and 50% RH). During drying, the moisture losses in 7-day cured concretes w...
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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 displaceme...
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Plastic shrinkage in fresh cement-based materials is caused by capillary pressure in the pore system. Within the first few hours after casting, evaporation results in the loss of water and possibly in the formation of menisci in the water surface between the superficial solid particles. With decreasing radius of the menisci the capillary water pressure rises. At a certain pressure, the system becomes unstable and air penetrates into the system. This event is called air entry and assumed to be th...
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#1Oskar Esping (Chalmers University of Technology)H-Index: 6
This paper presents a study on the use of limestone fillers with different specific surface area and their effect on the fresh and hardened properties of self-compacting concrete (SCC). The surface area was determined by a simplified BET method using water vapour as adsorbate. A rheometer and a slump flow test were used to measure the flowability of fresh concrete. A concrete dilatometer was used to measure the autogenous shrinkage, and a ring-test for the plastic cracking tendency. The compress...
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#2Sanford KleinH-Index: 61
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#1C A MenzelH-Index: 1
The author of this paper begins with a clear mission “… cracking can be practically eliminated if appropriate measures to minimize the causes are taken at the right time.” This paper discusses many of the factors that can cause cracking at early ages before focusing on the cracking that occurs before the concrete sets (that is, when it is in the plastic state). The paper describes how plastic shrinkage cracking is greatly dependent on the relationship between the rate of evaporation and the rate...
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Abstract null null 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 temperat...
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Abstract null null Using the designed test device, the water loss and surface humidity of three strength grades of concrete with curing time under the condition of environmental wind speed of 0, 5, 10 and 15 m/s were quantitatively measured, and the surface factor test values of each strength grade of concrete under different wind speed conditions were further obtained. Based on the surface diffusion theory, the theoretical calculation model of concrete surface factor considering the influence o...
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