• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6A
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• pp.1033-1039
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• 2006

The purpose of this study are to evaluated bond, flexural properties and control of plastic shrinkage cracking of crimped type synthetic fiber with amplitude 6 mm and height 1.8 mm reinforced cement based composites. Bond and flexural test were conducted in accordance with the JCI-SF 8 and JCI SF-4 standard, respectively. The plastic shrinkage cracking test was conducted for evaluating the effect of fiber in reducing shrinkage cracking in cement based composites. Test results indicated that the crimped typel synthetic fibers performed significantly better than the straight type fiber in terms of interface toughness and pullout load and the crimped type synthetic fibers improved the flexural toughness of concrete. Also, the increasing the crimped type synthetic fiber volume fraction from 0.00% to 1.00% improved the plastic shrinkage cracking resistance. Specially, the effect of control of plastic shrinkage cracking is excellent at the more than 0.5% fibre volume fraction.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.265-268
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• 2004

Plastic shrinkage cracking is a major concern for concrete, especially for flat structures as highway pavement, bridge deck slabs, and bridge deck pavement. LMC(Latex Modified Concrete) be used mainly for bridge deck overlays, so occurrence possibility of plastic shrinkage cracking is very high. But LMC is form a close-packed layer of polymer particles in very early time from the time of adds the latex and water. So plastic shrinkage cracking compare with normal concrete is not occur at final setting time. Results indicates that LMC is advantage to prevent occurrence of plastic shrinkage crack and it's possible co construction for bridge deck overlay effectively.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.575-578
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• 2005

Recently, various concrete reinforcing fibers have been used to reduce the plastic shrinkage cracking which occurs before the concrete hardens. In this study, the physical properties of nylon fiber reinforced concrete such as slump, air content, compressive strength and tensile strength were investigated. In addition, the performance of nylon fiber in the plastic shrinkage cracking reduction of mortar has been estimated in comparison with polypropylene fiber and cellulose fiber. Nylon fiber showed considerable advantages in terms of the workability of concrete and the plastic shrinkage cracking reduction of mortar compared with polypropylene fiber and cellulose fiber.

• Journal of the Korea Concrete Institute
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• v.19 no.2
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• pp.233-239
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• 2007

The main objective of this study was to evaluate the effect of recycled PET fiber made from waste PET bottle on the control of plastic shrinkage cracking of cement based composites. PET is blown as a plastic material and used in a variety products such as a beverage bottle. However, waste PET bottles are thrown after the usage, raising huge problems in terms of the environment. Thus, the research on the method to recycle the PET bottles indicates important aspects in environment and economy. The method to recycle waste PET bottles as a reinforcing fiber for cement based composites is one of effective methods in terms of the recycle of waste PET bottles. In this research, the effect of recycled PET fiber geometry and length on the control of plastic shrinkage was examined through thin slab tests. A test program was carried out to understand the influence of fiber geometry, length and fiber volume fraction. Three type of recycled PET fibers including straight, twist crimped and embossed type. Three volume fraction and two fiber length were investigated for each of the three fiber geometry. Test results indicated that recycled PET fibers are effective in controlling plastic shrinkage cracking in cement based composites. In respect to effect of length of fiber, longer fiber was observed to have efficient cracking controlling with low volume fraction in same fiber geometry while shorter fiber controled plastic shrinkage cracking efficiently as addition rate increase. Also, embossed type fibers were more effective in controlling plastic shrinkage cracking than other geometry fiber at low volume fraction. But, for high volume fraction, straight type fibers were most effective in plastic shrinkage cracking controlling in cement based composites.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.795-808
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• 2006

In this paper, an analytical method which can predict the occurrence of plastic shrinkage cracking on concrete slabs with sequential placement is proposed on the basis of the numerical model introduced in the previous study. The influence of many design variables on plastic shrinkage cracking such as the number of layers and the time interval between layers is quantitatively analyzed through parametric studies using the analytical method. In advance, two equations are introduced to take into account the effect of sequential placement on the plastic shrinkage cracking of concrete slab; The first one is to calculate the time at which the surface of concrete slab begins to dry, and the second one is to determine the critical time interval to prevent the surface drying of previously placed concrete layers. The timing of curing and the sequence of concrete placement, which are important for the prevention of plastic shrinkage cracking, can be effectively planned using the introduced both equations without any rigorous analysis.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.319-323
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• 1998

Plastic shrinkage cracking is a major concern for concrete, especially for flat structures as highway pavement, slabs for parking garages, and walls. One of the methods to reduce the adverse effect of plastic shrinkage cracking is to reinforced concrete with short randomly distributed fibers. The contribution of cellulose fiber to the plastic shrinkage crack reduction potential of cement composites and its evaluation are presented in this paper. The effects of differing amounts of fibers(0.9kg/㎥, 1.3kg/㎥, 1.5kg/㎥) were studied. The results of tests of the cellulose fiber reinforced concrete were compared with plain concrete and polypropylene fiber reinforced concrete. Results indicated that cellulose fiber reinforcement showed an ability to reduce the total area and maximum crack width significantly(as compared to plain concreted to plain concrete and polypropylene fiber concrete).

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2003.10a
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• pp.375-378
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• 2003

Plastic shrinkage cracking occurs at the exposed surfaces of freshly placed concrete due to consolidation of the concrete mass and rapid evaporation of water from the surface. This so-called shrinkage cracking is a major concern for concrete, especially for flat structural such as pavement, slabs for industrial factories and walls. This study has been performed to obtain the plastic shrinkage properties of hydrophilic fiber reinforced mortar and concrete. The results of tests of the hydrophilic fibers were compared with plain and polypropylene fibers. Test results indicated that hydrophilic poly vinylalcohol fiber reinforcement showed an ability to reduce the total crack area and maximum crack width significantly (as compared to plain and polypropylene fiber reinforcement).

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.661-664
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• 2006

Recently, various concrete reinforcing fibers have been used to reduce the plastic shrinkage cracking which occurs before the concrete hardens. In this study, the physical properties of nylon fiber reinforced concrete such as slump, air content, compressive strength and tensile strength were investigated. In addition, the performance of nylon fiber in the plastic shrinkage cracking reduction of concrete has been estimated in comparison with polypropylene, poly vinyl alcohol fiber and cellulose fiber. Nylon fiber showed considerable advantages in terms of the workability of concrete and the plastic shrinkage cracking reduction of concrete compared with polypropylene fiber and cellulose fiber.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.448-455
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• 2005

In this paper, an analytical model for estimation of the time at which the concrete surface begins to dry is introduced to predict whether or not plastic shrinkage cracks occur. First of all, the validity of a consolidation model for bleeding of cement paste proposed by Tan et al. is verified by comparing the analytical results with the experimental results, and used to evaluate the rate and amount of bleed water of concrete. Also an analytical model for evaporation of bleed water which considers the effect of the temperature variation of concrete surface due to hydration heat on the evaporation rate is proposed, and the experimental and analytical results are then compared to verify the validity of the introduced model. In advance, the time at which the concrete surface begins to dry is estimated using above two analytical models, and compared with the experimental results about the time at which plastic shrinkage cracks occur. From the comparison, it is verified that the proposed model can predict the occurrence of plastic shrinkage cracking with comparative precision.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.785-788
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• 2005

In this paper, the influence of many factors related to the concrete mixture and the weather condition on plastic shrinkage cracking are analyzed through parametric studies using the numerical models introduced in the companion paper. First of all, through a systematic calculation of bleeding, the relationship between the bleeding constants and concrete mixture is proposed on the basis of the experimental data obtained by many researchers. Moreover, an equation, which can directly determine a critical point at which the evaporation and bleeding is balanced, is introduced, and the efficiency of the introduced equation is verified through the correlation study between the obtained results by the introduced equation and those by the rigorous analyses. The introduced equation can effectively be used to predict and to prevent plastic shrinkage cracking without any rigorous analysis and, in advance, to cope with the sudden changes in the concrete mixture and/or weather condition.