• International Journal of Concrete Structures and Materials
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• v.7 no.1
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• pp.71-78
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• 2013

Prestressed concrete (PC) is the predominant material in highway bridge construction. The use of high-strength concrete has gained wide acceptance in the PC industry. The main target in the highway industry is to increase the durability and the life-span of bridges. Cracking of elements is one aspect which affects durability. Recently, nine 7.62 meter long PC I-beams made with different concrete strength were designed according to a simple, semi-empirical equation developed at the University of Houston (UH) (Laskar et al., ACI Journal 107(3): 330-339, 2010). The UH Method is a function of shear span-to-depth ratio (a/d), concrete strength $\sqrt{f^{\prime}_c}$, web area $b_wd$, and amount of transverse steel. Based on testing these girders, the shear cracking strength of girders with different concrete strength and different shear span-to-depth ratio was investigated and compared to the available approaches in current codes such as ACI 318-11 (2011) and AASHTO LRFD Specifications (2010).

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.537-542
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• 2001

Recently long-span bridges, such as Kwang-Ahn Grand bridge, Seo-Hae Grand Bridge, Young-Jong Grand Bridge, etc, have been designed and constructed near the shore. It needs to maintain the durability of marine concrete structures which are exposed to severe chloride environments. It is well known that corrosion of reinforcement steels in concrete structure is the most important cause for the durability of concrete structure which can be controlled by systematic preparatory corrosion protection works for economic and safe infrastructures. Various corrosion protection systems have been used for the corrosion protection of reinforcement steels from detrimental chemical components such as chloride, sulphate and etc. Since chloride can be penetrated into concrete in a variety way, an effective method has to be adopted by taking into full economical aspects and technical data of each protection system. The objective of this experimental study is to investigate the corrosion behavior of reinforcing steel in laboratory concrete specimens which are exposed to cyclic wet and dry saltwater, and then to develop pertinent corrosion protection system, such as corrosion inhibitors and cathodic protection for reinforced concrete bridges exposed to chloride environment. Resistance of various corrosion inhibitors and impressed current system have been experimentally evaluated under severe environmental conditions, and thus effective corrosion protection systems could have been Practically developed for future concrete construction.

• Structural Engineering and Mechanics
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• v.63 no.1
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• pp.55-64
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• 2017

The paper concerns concrete carbonation, the phenomena that occurs in every type of climate, especially in urban-industrial areas. In European Standards, including Eurocode (EC) for concrete structures the demanded durability of construction located in the conditions of the carbonation threat is mainly assured by the selection of suitable thickness of reinforcement cover. According to EC0 and EC2, the thickness of the cover in the particular class of exposure depends on the structural class/category and concrete compressive strength class which is determined by cement content and water-cement ratio (thus the quantitative composition) but it is not differentiated for various cements, nor additives (i.e., qualitative composition), nor technological types of concrete. As a consequence the selected thickness of concrete cover is in fact a far estimation - sometimes too exaggerated (too safe or too risky). The paper presents the elaborated "self-terminated carbonation model" that includes abovementioned factors and enables to indicate the maximal possible depth of carbonation. This is possible because presented model is a hyperbolic function of carbonation depth in time (the other models published in the literature use the parabolic function that theoretically assume the infinite increase of carbonation depth value). The paper discusses the presented model in comparison to other models published in the literature, moreover it contains the algorithm of concrete cover design with use of the model as well as an example of calculation of the cover thickness.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.549-554
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• 2001

The authors have proposed that waste glass, which is crushed to pieces, can be used as a concrete aggregate. At the present time, recycled-glass concrete is used for sidewalk concrete blocks and pavement as glass is ornamental. However, in cases where recycled-glass concrete is used for structural concrete, strength and durability are required as structural concrete is exposed to the weather. Glass that is used generally is a mixture of SiO$_2$, Na$_2$O and CaO. SiO$_2$is the most likely cause of alkali-aggregate reaction when waste glass was used for concrete aggregate. In this study, an alkali-aggregate reaction test that is one of the important tests related to durability of aggregate was carried out far discussion of utilization of waste glass for concrete aggregate. From the results of the tests, it is found that glass is a reactive aggregate. The pessimum proportion of glass is about 75%. Then the cases of using fly ash, blast furnace slag and artificial zeolite for admixture materials were also examined for the purpose of prevention of alkali-aggregate reaction. from the results of the test, it was found that using them is an effective way to prevent alkali-aggregate reaction. The compressive strength in the cases of using admixture materials is larger than that without admixture materials.

• Journal of the Korea Institute of Building Construction
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• v.11 no.4
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• pp.379-386
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• 2011

Durability of concrete is an important issue, and one of the most critical aspects affecting durability is chloride diffusivity. Factors such as water.cement ratio, degree of hydration, volume of the aggregates and their particle size distribution have a significant effect on chloride diffusivity in concrete. The use of polypropylene fibers(particularly very fine and well dispersed micro fibers) or mineral additives has been shown to cause a reduction in concrete's permeability. The main objective of this study is to evaluate the manner in which the inclusion of fiber(in terms of volume and size) and blast furnace slag(BFS) (in terms of volume replacement of cement) influence the chloride diffusivity in concrete by applying 3D computer modeling for the composite structure and performing a simulation of the chloride penetration. The modeled parameters, i.e. chloride diffusivity in concrete, are compared to the experimental data obtained in a parallel chloride migration test experiment with the same concrete mixtures. A good agreement of the same order is found between multi.scale microstructure model, and through this chloride diffusivity in concrete was predicted with results similar to those experimentally measured.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.429-432
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• 2008

Large area members such as foundation concrete of underground structures in power plants have an effect on structural stability and durability of the structure due to danger of crack occurrence and shrinkage crack that occur owing to the difference of temperature by heat of hydration between inside and outside of the members at initial age. And a construction for waterproofness is performed additionally to protect marine structures from osmosis of seawater because the structures adjoin below the surface of sea. So, if a rise of the heat of hydration, crack, and corrosion of bars are controled effectively using a composite such as fluosilicate salt in concrete production process of a initial construction, expenses are cut down and construction hours are reduced by securing durability through improvement of watertightness. The property tests of adiabatic temperature by hydration are carried out at initial age about standard concrete and test concrete using a fluosilicate salt composite to evaluate an effect on improvement of watertightness for concrete structures in this study. And the experiments such as a permeability test of hardened concrete, a water absorption test, a compression strength test and a elongation test are carried out and the results from these are described.

• Journal of the Korean Society of Safety
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• v.29 no.4
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• pp.103-109
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• 2014

In this study, two types of water-soluble sulfur, LSA and LSB, were developed and the influence of the water-soluble sulfur on the mechanical properties and durability of concrete were experimentally evaluated. In order to evaluate mechanical properties and carbonation resistance of concrete with water-soluble sulfur, compressive strength test, flexural strength test, bonding strength test, and carbonation resistance test were performed. Compressive strength of only concrete with 1% LSA was increased while that of concrete with LSB was proportionally increased with the higher LSB dosage. On the other hand, flexural strength of concrete with LSA and LSB was increased by 12-41% and 36-74%, respectively. Carbonation resistance of concrete with water-soluble sulfur were increased by 25-66%. As a result, it should be noted that the water-soluble sulfur can not only solve the demerit of sulfur concrete but also offer the durability of sulfur concrete.

• Advances in concrete construction
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• v.11 no.2
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• pp.151-161
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• 2021

The major shortcoming of concrete in most of the applications is its high self-weight and thermal conductivity. The emerging trend to overcome these shortcomings is the use of foam-concrete, which is a lightweight concrete consisting of cement, filler, water and a foaming agent. This study aims at the development of a cost-effective high-volume fly-ash foam-concrete insulation wall cladding for existing buildings using natural fiber like rice straw in different proportions. The paper reports the results of systematic studies on various mechanical, acoustic, thermal and durability properties of foam-concrete with and without replacement of cement by fly-ash. Fly-ash replaces 60 percent by weight of cement in foam-concrete. The water-solid ratio of 0.3, the filler ratio of 1:1 by weight, and the density of 1100 kg/㎥ (approx.) are fixed for all the mixes. Rice straw at 1%, 3% and 5% by weight of cement was added to improve the thermal and acoustic efficiency. From the investigations, it was inferred that the strength properties were increased with fly-ash replacement up to 1% rice straw addition. In furtherance, addition of rice straw and fly-ash resulted in improved acoustic and thermal properties.

• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.385-392
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• 2005

The object of this study is to prove the quality and reliability of recycled aggregate concrete by finding a way to improve the durability of the material through the experiment on the accelerated carbonation, freezing and thaw, and drying shrinkage, analysing the influence on the durability to Promote more active use of recycled aggregate concrete. The result of study as follows. (1) Resistibility to the freeze and thaw of the recycled aggregate concrete showed relative dynamic modulus of elasticity over $90\%$ which is very good, and all cycles show $99.2{\~}91.0\%$ dynamic modulus of elasticity which is improved compared with the $97.5{\~}90.6\%$ relative dynamic modulus of elasticity of ordinary concrete made of broken stone. (2) Carbonated thickness of the recycled aggregate concrete and the normal concrete was similar or it appeared with the tendency which it diminishes more or less. (3) Length change rate in drying contraction of the recycled aggregate concrete made of the recycled aggregate was lower than the ordinary concrete made of the broken stone by $18.5{\~}3.9\%$ in all blending.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.393-399
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• 2007

Concrete bridge decks are directly exposed to the severe environmental conditions such as rain water and deicing chemicals resulting in the freeze-thaw action and the rebar corrosion during their service lift. These deteriorations of bridge decks shorten the service lift and consequently they are the major concerns of the maintenance. The high performance concrete (HPC) deck is proposed as the alternative to minimize the deterioration problems. To develop more durable concrete deck, the performance characteristic tests of HPC mixtures were carried out. In this study, 4 different concrete mixtures were used varying the mineral admixtures as the cement replacement; ordinary portland cement (OPC), 20% fly ash (FA),20% fly ash with 4% silica fume (FS), and 40% ground granulated blast-furnace slag (BS). The design compressive strengths of HPC specimens were 27 MPa and 35 MPa, respectively. The results showed that the compressive strength of concrete did not much affect the durability of concrete. HPC with fly ash and silica lune (FS) were turned out to have the good durability and crack resistance.