• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.683-686
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• 2004

In recent years, some attention was particularly given to cracking sensitivity of high performance concrete. It has been argued and demonstrated experimentally that such concrete undergoes autogenous shrinkage due to self-desiccation at early age, and, as a result, internal tensile stress may develop, leading to micro cracking and macro cracking. One possible method to reduce cracking due to autogenous shrinkage is the addition of expansive additive. Tests conducted by many researches have shown the beneficial effects of addition of expansive additive for reducing the risk of shrinkage-introduced cracking. However, the research on hydration model of expansion additive has been hardly researched up to now. This paper presents a study of the hydration model of Ettringite-Gypsum type expansive additive. Result of comparing forecast values with experiment value, proposed model is shown to expressible of hydration of expansive additive.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.631-637
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• 2002

This paper deals with hydration properties of the OPC with CSA-system expansive materials. In OPC using CSA, that was formed monosulfate for the main part. but In OPCs using CSA and gypsum, using CSA and gypsum and lime, that were formed ettringite for the main part. On the shrinkage ratio, the former is larger than the latter And CSA-system with gypsum and lime is smallest of all systems. According to dimension of shrinkage ratios are as follows; OPC using CSA only＞ OPC only＞ OPC using CSA and gypsum＞ OPC using CSA, gypsum and lime. And "R"s are 0.32, 0.37, 0.8, 0.8, 0.8 each others. In OPC with CSA-system expansive materials, we know that expansive properties were depend upon the value of "R". "R" means supplying quantities about demanding quantities for ettringite. In the case of expansive materials with CSA-system and lime, it is to be rich Ca(OH)$_2$ in the solution. so, it is formed small ettringite as the needle shapes. they are contribute to expansive.

• International Journal of Concrete Structures and Materials
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• v.9 no.4
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• pp.391-399
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• 2015

This study modeled the compressive strength and elastic modulus of hardened cement that had been treated with an expansive additive to reduce shrinkage, in order to determine the mechanical properties of the material. In hardened cement paste with an expansive additive, hydrates are generated as a result of the hydration between the cement and expansive additive. These hydrates then fill up the pores in the hardened cement. Consequently, a dense, compact structure is formed through the contact between the particles of the expansive additive and the cement, which leads to the manifestation of the strength and elastic modulus. Hence, in this study, the compressive strength and elastic modulus were modeled based on the concept of the mutual contact area of the particles, taking into consideration the extent of the cohesion between particles and the structure formation by the particles. The compressive strength of the material was modeled by considering the relationship between the porosity and the distributional probability of the weakest points, i.e., points that could lead to fracture, in the continuum. The approach used for modeling the elastic modulus considered the pore structure between the particles, which are responsible for transmitting the tensile force, along with the state of compaction of the hydration products, as described by the coefficient of the effective radius. The results of an experimental verification of the model showed that the values predicted by the model correlated closely with the experimental values.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.393-398
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• 2000

To use concrete box culverts effectively, precast goods are manufactured at a factory, then linked and anchored with prestressing tendon at a field. However, the corrosion of rebar and prestressing tendon in the box culverts utilizing portland cement concrete is issued when the cracks occur at a underground water level. It has been reported that reported that expansive concrete, compared with portland cement concrete, has many structural advantages such as increasing capacity of watertight, controling initial crack and improving durability due to its property of expansion. During flexure test with RC beam made from expansive concrete, in the case of a constant section of concrete element, the lower steel ratio is, and in the case of a constant steel ratio, the more incremental the section of concrete element, the more incremental the amount of chemical prestress by expansive concrete is. At the segment of the box culverts using expansive concrete, the numbers of crack and its gap is reduced, and ultimate load and initial crack load is much larger than the segment at which expansive concrete is nor used. Also lay-out of tendon with a curvature generate upward force so that deflection is reduced. Through the whole procedure, it could be confirmed that performance precast box culvert by means of using expansive concrete is improved.

• Journal of the Korea Concrete Institute
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• v.27 no.5
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• pp.569-577
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• 2015

The aim of this study is to qualitatively evaluate the cracking control effects of expansive concrete used in reinforced concrete building. The result of experiments in laboratory shows that autogenous shrinkage and drying shrinkage are suppressed by using expansive additive. The tensile stress-strength ratio is lower in expansive concrete than normal concrete under fully restrained condition. Compression stress could be effectively generated in early age in the walls in buildings by the use of expansive additive, and tensile stress due to drying shrinkage at later age eventually decreased. Additionally, visual observation at long-term ages shows that the cracking area of expansive concrete was approximately 35% of normal concrete, which confirms that the use of expansive additive reduces concrete cracking in reinforced concrete buildings.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.75-83
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• 2014

In order to prevent brittle failure of concrete, steel fiber reinforcement is effective composite material. However ductility of steel fiber reinforced concrete may be limited due to shrinkage caused by large content of cement binder. Chemical prestressing for steel fiber reinforcement in cement matrix can be induced through expansive admixture and this can increase reinforcing effect of steel fiber. In this study, mechanical performances in concrete with CSA (Calcium sulfoaluminate) expansive admixture and steel fiber reinforcement are evaluated. For this work, steel fiber reinforcement of 1 and 2% of volume ratio and CSA expansive admixture of 10% weight ratio of cement are added in concrete. Mechanical and fracture properties are evaluated in concrete with steel fiber reinforcement and CSA expansive admixture. CSA concrete with steel fiber reinforcement shows increase in tensile strength, initial cracking load, and ductility performance like enlarged fracture energy after cracking. With appropriate using expansive admixture and optimum ratio of steel fiber reinforcement, their interactive action can effectively improve brittle behavior in concrete.

• Geomechanics and Engineering
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• v.19 no.1
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• pp.1-9
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• 2019

Shallow failures occur frequently in both engineered and natural slopes in expansive soils. Rainfall infiltration is the most predominant triggering factor that contributes to slope failures in both expansive soils and clayey soils. However, slope failures in expansive soils have some distinct characteristics in comparison to slopes in conventional clayey soils. They typically undergo shallow failures with gentle sliding retrogression characteristics. The shallow sliding mass near the slope surface is typically in a state of unsaturated condition and will exhibit significant volume changes with increasing water content during rainfall periods. Many other properties or characteristics change such as the shear strength, matric suction including stress distribution change with respect to depth and time. All these parameters have a significant contribution to the expansive soil slopes instability and are difficult to take into consideration in slope stability analysis using traditional slope stability analysis methods based on principles of saturated soil mechanics. In this paper, commercial software VADOSE/W that can account for climatic factors is used to predict variation of matric suction with respect to time for an expansive soil cut slope in China, which is reported in the literature. The variation of factor of safety with respect to time for this slope is computed using SLOPE/W by taking account of shear strength reduction associated with loss of matric suction extending state-of-the art understanding of the mechanics of unsaturated soils.

• Geomechanics and Engineering
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• v.30 no.2
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• pp.139-151
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• 2022

The mechanical properties of expansive soil are very unstable, highly sensitive to water, and thus easy to cause major engineering accidents. In this paper, the expansive soil foundation pit project of the East Huada Square in the eastern suburb of Chengdu was studied, the moisture content of the expansive soil was considered as an important factor that affecting the mechanics properties of expansive soil and the stability of the non-equal-length double-row piles in the foundation pit support. Three groups of direct shear tests were carried out and the quantitative relationships between the moisture content and shear strength τ, cohesion c, internal friction angle φ were obtained. The effect of cohesion and internal friction angle on the maximum displacement and the maximum bending moment of piles were analyzed by the finite element software MIDAS/GTS (Geotechnical and Tunnel Analysis System). Results show that the higher the moisture content, the smaller the matrix suction, and the smaller the shear strength; the cohesion and the internal friction angle are exponentially related to the moisture content, and both are negatively correlated. The maximum displacement and the maximum bending moment of the non-equal length double-row piles decrease with the increase of the cohesion and the internal friction angle. When the cohesion is greater than 33 kPa or the internal friction angle is greater than 25.5°, the maximum displacement and maximum bending moment of the piles are relatively small, however, once crossing the points (the corresponding moisture content value is 24.4%), the maximum displacement and the maximum bending moment will increase significantly. Therefore, in order to ensure the stability and safety of the foundation pit support structure of the East Huada Square, the moisture content of the expansive soil should not exceed 24.4%.

• Proceedings of the Korean Geotechical Society Conference
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• 1996.10a
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• pp.165-172
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• 1996

• Journal of the Korea Concrete Institute
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• v.16 no.5 s.83
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• pp.605-612
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• 2004

This study investigated the fundamental properties and shrinkage properties of high performance concrete with water/binder ratio of 0, 30 and with combination of expansive additive and shrinkage reducing agent. According to the results, the fluidity of high performance concrete showed lower the using method in combination with expansive additive and shrinkage reducing agent than the separately using method of that, so the amount of superplasticizer increased when the adding ratio of expansive additive and shrinkage reducing agent increased. However the air content of concrete increased when used in combination with expansive additive and shrinkage reducing agent, so the amount of AR agent decreased. The compressive strength showed the highest at $5\%$ of expansive additive, and decreased with an increase of the amount of shrinkage reducing agent. Furthermore, in order to reduce the shrinkage of high performance concrete, it was found that the using method in combination with expansive additive and shrinkage reducing agent was more effective than separately using method of that. Therefore, it analyzed that the combination of expansive additive of $5\%$ and shrinkage reduction agent of $1\%$ was the most suitable mixture, considering to the fluidity, strength and shrinkage under the condition of this experiment.