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External bonding of carbon-fibre-reinforced polymer composites has been proposed as an innovative technique to strengthen steel structures. This paper discusses an experimental study carried out to investigate the feasibility of using carbon-fibre-reinforced polymer composite strips for strengthening concrete-filled steel tubular columns. In this study, columns were strengthened using polymer composite strips 50 mm wide at two different spacings. They were then tested under compression until failure. The test results are discussed in terms of failure modes, stress–strain behaviour, load-carrying capacity and ductility. The results show that externally bonding composite polymer strips is an effective approach to restraining axial deformation and enhancing the ultimate capacity of columns under compression. By bonding the strips, the deformation of the columns was restricted to a maximum of 141·2% and 69·75% compared to the reference column when set at spacings of 20 mm and 40 mm, respectively. The capacity of the columns increased by about 30% for a 20 mm spacing, whereas no significant increase in capacity was observed for a 40 mm spacing. It is therefore recommended to apply this technique for strengthening and rehabilitating concrete-filled steel tubular columns and to use a 20 mm spacing.

The carbonation of concrete is one of the factors influencing the durability of reinforced concrete members or structures. Manual measurements can reportedly induce low reproducibility when measuring carbonation depths. This study presents a new image-processing algorithm for the automatic detection of carbonated regions of concrete sprayed with a phenolphthalein solution. The proposed image-processing algorithm consists of a primary detection process based on binarization and a morphology analysis and a secondary detection process based on a convex hull. A series of tests of images of carbonated concrete sprayed with the phenolphthalein solution is conducted to assess the validity of the proposed image-processing algorithm. The validation test results showed that the proposed image-processing algorithm is capable of the accurate detection of carbonated concrete regions compared to direct visual inspections.

A study to apply phase change material(PCM) to rapid hardening cement paste forming semi-rigid pavement was carried out. The characteristics fresh and hardened paste were evaluated through the experiment for a total of 6 mixtures according to the cement type and the substitution of phase change material for acrylate. The fluidity by substituting phase change material for acrylate satisfied the target flow time of 10 to 13 seconds. In case of setting time, it was possible to secure the performance of rapid hardening cement by substituting phase change material, and if the substitution ratio over 60%, the initial set occurred 1 to 2 minutes faster than other mixtures. In case of compressive strength and bond strength, it showed similar strength characteristics with the plain mixture, and it satisfied both the target compressive and bonding strength of 36MPa and 2MPa. The mixture substituting phase change material showed higher resistance to chloride ion penetration than the mixture only using acrylate and the OPC level was insufficient. From the results of physical and mechanical performances of semi-rigid pavement cement paste, the phase change material substitution rate of 20% was effective in the range of this study.

The pile-cap connection part which transfers foundation loads through pile body is critical element regarding flexural and shea r force because the change of area, stress, and stiffness occurs in the this region suddenly. The purpose of this study is to investigate the s tructural behavior of pile-cap connection dependent on fabrication methods using conventional PHC pile and composite PHC pile. A series of test under cyclic lateral load was performed and the connection behavior was discussed. From the test results, it was found that the initial rotational stiffness of pile-cap connection was affected by the length of pile-head inserted in footing and the location of longitudinal reinforcing bars. The types of pile an d location of longitudinal reinforcing bars governed the behavior of pile-cap connection regarding load-carrying capacity, ductility, and energy dissipati on.Keywords: Pile-cap connection, Cyclic lateral load, PHC pile, Composite PHC pile 1 정회원, 충남대학교 건설방재연구소 박사후 연구원

This article presents the test results of an investigation carried out on the reuse of coal bottom ash aggregate as a substitute material for coarse aggregate in porous concrete production for marine ranch applications. The experimental parameters were the rate of bottom ash aggregate substitution (30%, 50% and 100%) and the target void ratio (15%, 20% and 25%). The cement-coated granular fertiliser was substituted into a bottom ash aggregate concrete mixture to improve marine ranch applications. The results of leaching tests revealed that the bottom ash aggregate has only a negligible amount of the ten deleterious substances specified in the Ministry of Environment – Enforcement Regulation of the Waste Management Act of Republic Korea. The large amount of bubbles/air gaps in the bottom ash aggregate increased the voids of the concrete mixtures in all target void ratios, and decreased the compressive strength of the porous concrete mixture; however, the mixture substituted with 30% and 10% of bottom ash aggregate and granular fertiliser, respectively, showed an equal strength to the control mixture. The sea water resistibility of the bottom ash aggregate substituted mixture was relatively equal to that of the control mixture, and also showed a great deal of improvement in the degree of marine organism adhesion compared with the control mixture. No fatality of fish was observed in the fish toxicity test, which suggested that bottom ash aggregate was a harmless material and that the combination of bottom ash aggregate and granular fertiliser with substitution rates of 30% and 10%, respectively, can be effectively used in porous concrete production for marine ranch application.

The prestressing force has not been managed after construction nevertheless it is one of the importrant factors that maintain the structural safety of PSC girder bridges. The prestressing force is just measured during construction using jacking device and after that, it can not be managed practically. For this reason, this study investigated the measurements of prestress using embedded sensors that can be available now with an ultimate goal to propose smart prestressed girders that can measure the prestress from the birth to the end of service life. 4 types of sensors were installed on the small prestressed girders, and the applicability and the accuracy of those sensors were tested while the prestress was applied to the girders. The results show that a center-hole type loadcell has a tendency to measure a prestressing force higher than a reference value, especially when it is loaded with an eccentricity. a EM sensor shows several advantages that has a good practical accuracy, that can be installed anyplace along the tendons.

Latex modified concrete (LMC) is used for a bridge deck pavement method that was introduced in Korea in the 2000s, and it is currently the concrete pavement method being used for most highway bridges. It has been recommended that mixing with latex approximately 15% in terms of polymer-cement ratio (P/C ratio) by weight showed no occurrence of cracks with sufficient tensile strength and bond strength of LMC. However, many cracks occur in the actual field mostly due to drying shrinkage of concrete, requiring frequent repair. Therefore, this study examined the feasibility of applying a shrinkage reducing agent(SRA) that could reduce plastic shrinkage cracks at early age as well as drying shrinkage cracks of LMC. Based on the test results, it was confirmed that adding a shrinkage reducing agent could secure the durability without affecting the fresh and hardened properties of LMC. The compression strength test results presented a 1.7–5.7% improvement in strength to the SRA mixture compared to the plain mixture. Length change test results indicated that SRA mix conditions presented more outstanding performance compared to mix conditions with the expansive admixture. The amount of shrinkage reducing agent suitable for achieving performance requirements in length change, crack resistance, chloride ions penetration resistance and scaling resistance, was evaluated as 3% by weight ratio of binding material under the limited condition of the present study.

This paper presents the results of an experimental study on the effect of limestone powder on the compressive strength, tensile behavior, and micromechanical parameters of a highly ductile cement composite incorporating limestone powder. Four mixtures were determined according to the replacement ratio of cement with limestone powder. A series of experiments including compressive strength, uniaxial tension, single fiber pullout, and matrix toughness tests were performed. Test results showed that the strength (compressive, initial cracking, and tensile strength) decreased, and that the tensile strain capacity increased, with an increase of the replacement ratio of cement with limestone powder. Micromechanical tests and analysis supported the uniaxial tension test result.

As new types of cement-based composites that require properties other than compressive strength have been developed, the properties of the matrix need to be tailored considering the targeted performance of the composites. This study examines the effect of fine aggregates in the matrix on mechanical behaviour in order to obtain fundamental information that can be used for matrix design. The mechanical properties of the mortar matrix according to the type and content of fine aggregates are investigated. The results reveal that the use of sand with a smaller diameter or a smaller sand–cement ratio can reduce the fracture toughness without significant reduction of the compressive strength and the elastic modulus.

In this study, to examine the use of sulfur polymer as a coating agent for concrete, durability and hazard evaluations were per formed. The result of the evaluation indicated that the chemical resistance of the coating agent for concrete was outstanding against acidi c, base, and alkaline solutions. The evaluation of the bond strength after an accelerated weathering test depending on the mixing condition indicated that the m ost outstanding strength characteristic was obtained when silica powder and fly ash were mixed at the same time. The bond strength exceeded 1 MPa in eve ry mixing condition even after the repeated hot and cold treatment of the coating agent specimen for concrete, and the SFS mix proportion showed th e highest bond strength. The examination of the accelerated carbonation and chloride ion penetration resistance of the concrete coated with the coating agent indicated that the specimen coated with the coating agent using silica powder as a filler showed the most outstanding durability. When a fish toxicity test was performed to examine the hazard of the use of the functional polymer as a coating agent for concrete, the functional polymer was found to have no effect on the organisms. When the chemical resistance, freezing and thawing resistance, carbonation, and chloride ion penetration resistance of the coating agent were considered, substituting silica powder and fly ash as the fillers of the functional polymer by 20%, respectively, was the optimal level in the range of this study.Keywords: Sulfur polymer, Concrete structures, Durability, Surface protecting agent, Bioassay

Prestressed concrete girder bridges are one of the most widely used bridges in the world because of their excellent construction feasibility, economic efficiency, serviceability, and safety. In certain situations, however, the prestressing tendon is supposed to be bent locally, and this leads to the loss of prestress force. This kind of prestress loss is not considered in the design and construction processes. This study shows that prestress loss occurs at the locally bent tendon, and that a 2% maximum of prestress loss occurs at the locally bent tendon, due to eccentricity.

For a long time, evaluation of soundness and strength in concrete has been performed through ultrasonic velocity(UV), which is essential work in field assessment. Porosity in concrete is a major parameter indicating durability and strength, and UV passing concrete depends on porosity variation. In this paper, a modeling on UV through concrete is carried out considering porosity and the results are verified with those from test. Additionally UV in concrete under compression/tension loading condition is measured and UV modeling with loading condition is performed. Up to 50% of loading ratio, UV slightly increases and greatly drops at peak load in compression region, however it fluctuates in tensile region due to micro cracking in matrix. The proposed model shows a reasonable agreement with test results in control and compression region, and needs modification for tensile region considering micro cracks and local aggregate interlocking.

Over the last several decades, various approaches to strengthening steel structures through the use of Carbon fibre reinforced polymer (CFRP) composites have been investigated; however, most of the studies have been focused on the steel tubes. This paper presents the feasibility analysis on the application of CFRP composite strips to strengthen the CFST column member under axial loading. CFRP strips having a width of 50 mm were used to confine the columns. The experimental parameters were the spacing between the CFRP strips (20 and 30 mm) and number of CFRP layers (one, two and three layers). All columns were tested under axial compression until failure. The experimental results revealed that bonding of CFRP composites effectively delayed the local buckling of the columns and also reduced the axial deformation by providing a confinement/restraining effect against the elastic deformation at both spacings. The confinement effect provided by CFRP composites was increased with the increase in the number of layers; however, the enhancement in buckling stress was not proportional. The load carrying capacity of the column increased with the application of CFRP strips, by up to 30% compared to the of un-strengthened column. From the test results it is suggested that the application of CFRP strips at a spacing of 20 mm or 30 mm is suitable for strengthening of a CFST circular column member; however, the application of strips at intervals of 30 mm recommended as an economical approach to strengthening compared to the 20 mm spacing. Finally, an analytical equation was proposed to predict the load carrying capacity of the CFRP strengthened CFST column, and the average difference between the calculated and experimental value was only ±5%.

The purpose of this study is to develop ecoefficient engineered cementitious composites (ECC) using supplementary cementitious materials (SCMs), including fly ash (FA) and blast furnace slag (SL) as a binder material. The cement content of the ECC mixtures was replaced by FA and SL with a replacement rate of 25%. In addition, the fine aggregate of the ECC was replaced by bottom ash aggregate (BA) with a substitution rate of 10%, 20%, and 30%. The influences of ecofriendly aggregates on fresh concrete properties and on mechanical properties were experimentally investigated. The test results revealed that the substitution of SCMs has an advantageous effect on fresh concrete’s properties; however, the increased water absorption and the irregular shape of the BA can potentially affect the fresh concrete’s properties. The substitution of FA and SL in ECC led to an increase in frictional bond at the interface between PVA fibers and matrix, improved the fiber dispersion, and showed a tensile strain capacity ranging from 3.3% to 3.5%. It is suggested that the combination of SCMs (12.5% FA and 12.5% SL) and the BA aggregate with the substitution rate of 10% can be effectively used in ECC preparation.

In this study, adiabatic temperature rise tests depending on binder type and adiabatic specimen volume were performed, and the maximum adiabatic temperature rises and the reaction factors for each mix proportion were analyzed and suggested. The results indicated that the early strength low heat blended cement mixture had the lowest maximum adiabatic temperature rise (Q(infinity)) and the ternary blended cement mixture had the lowest reaction factor (r). Also, Q and r varied depending on the adiabatic specimen volume even when the tests were conducted with a calorimeter, which satisfies the recommendations for adiabatic conditions. Test results show a correlation: the measurements from the 50 L specimens were consistently higher than those from the 6 L specimens. However, the Q(infinity) and r values of the 30 L specimen were similar to those of the 50 L specimen. Based on the above correlation, the adiabatic temperature rise of the 50 L specimen could be predicted using the results of the 6 L and 30 L specimens. Therefore, it is thought that this correlation can be used for on-site concrete quality control and basic research.

The potential for monitoring the construction of post-tensioned concrete beams and detecting damage to the beams under loading conditions was investigated through an experimental program. First, embedded sensors were investigated that could measure pre-stress from the fabrication process to a failure condition. Four types of sensors were installed on a steel frame, and the applicability and the accuracy of these sensors were tested while pre-stress was applied to a tendon in the steel frame. As a result, a tri-sensor loading plate and a Fiber Bragg Grating (FBG) sensor were selected as possible candidates. With those sensors, two pre-stressed concrete flexural beams were fabricated and tested. The pre-stress of the tendons was monitored during the construction and loading processes. Through the test, it was proven that the variation in thepre-stress had been successfully monitored throughout the construction process. The losses of pre-stress that occurred during a jacking and storage process, even those which occurred inside the concrete, were measured successfully. The results of the loading test showed that tendon stress and strain within the pure span significantly increased, while the stress in areas near the anchors was almost constant. These results prove that FBG sensors installed in a middle section can be used to monitor the strain within, and the damage to pre-stressed concrete beams.

The objectives of this study are to investigate the relationship between static and dynamic elastic moduli determined using shear-wave velocity measurements and to demonstrate the practical potential of the shear-wave velocity method for in situ dynamic modulus evaluation. Three hundred 150 by 300 mm concrete cylinders were prepared from three different mixtures with target compressive strengths of 30, 35, and 40 MPa. Static and dynamic tests were performed at 4, 7, 14, and 28 days to evaluate the compressive strength and the static and dynamic moduli of the cylinders. The results obtained from the shear-wave velocity measurements were compared with dynamic moduli obtained from standard test methods (P-wave velocity measurements according to ASTM C597/C597M-16 and fundamental longitudinal and transverse resonance tests according to ASTM C215-14). The shear-wave velocity measured from cylinders showed excellent repeatability with a coefficient of variation (COV) less than 1%, which is as good as that of the standard test methods. The relationship between the dynamic elastic modulus based on shear-wave velocity and the chord elastic modulus according to ASTM C469/C469M was established. Furthermore, the best-fit line for the shear-wave velocity was also demonstrated to be effective for estimating compressive strength using an empirical relationship between compressive strength and static elastic modulus.

Mechanical tests were carried out to evaluate the influence and effects of fluidity and compressive strength of cement grout on semirigid asphalt pavement. An open graded asphalt skeleton was designed in order to achieve target porosity in the range of 18~22%. In addition, four types of cement grout mixtures were produced with varying mix proportions with ultrarapid hardening cement and chemical admixtures, that is, accelerating and retarding agents. For the semirigid pavement specimens, mechanical experiments to measure properties such as porosity, flexural strength, Marshall stability, and wheel tracking resistance were carried out. The test results demonstrated that the flow time (fluidity) of cement grout is the most significant factor that determines the mechanical properties of semirigid asphalt specimens under constant condition of the open graded asphalt skeleton. For the semirigid pavement mixing proportion in the current study, it is recommended that the porosity of the open graded asphalt skeleton and flow time of cement grout should be 20% and within 12 seconds, respectively.

Concrete infill and reinforcement are one of the most well-known strengthening methods of structural elements. This study investigated flexural performance of concrete infill composite PHC pile (ICP pile) reinforced by infill concrete and longitudinal rebars in hollow PHC pile. A total four series of pile specimens were tested by four points bending method under simply supported conditions and investigated bending moment experimentally and analytically. From the test results, it was found that although reinforcement of infilled concrete on the pure bending moment of PHC pile was negligible, reinforcement of PHC pile using infilled concrete and longitudinal rebars increase the maximum bending moment with range from 1.95 to 2.31 times than that of conventional PHC pile. The error of bending moment between experimental results and predicted results by nonlinear sectional analysis on the basis of the conventional layered sectional approach was in the range of -2.54 % to 2.80 %. The axial compression and moment interaction analysis for ICP piles shows more significant strengthening effects of infilled concrete and longitudinal rebars.

This paper presents the results of experiments carried out to evaluate the utilization of foundry sand (FS) as a substitute material for fine aggregate in concrete production. The physical and chemical characteristics of the FS were also addressed. FS obtained from the aluminium casting industry was used as a substitute for fine aggregate in five different substitution rates (10%, 20%, 30%, 40% and 50%). Several tests, including density, slump cone, split tensile strength, flexural strength; ultrasonic pulse velocity (UPV) and compressive strength tests were performed to understand the effects of FS on the behavior of concrete. The grain size distribution analysis of FS revealed that 8% of FS were less than 75 μm, and the water absorption of FS was about 1.13%. The test results revealed that the strength properties of the concrete mixtures containing FS up to 20% was relatively close to the strength value of the CM, and the average decrease in strength was only 2.1%. The decrease in the strength is attributed to the fineness of the FS and the presence of dust, clay and wood flour in the FS. From the test results obtained it was concluded that a substitution rate of up to 20% can be effectively used in good concrete production without affecting the concrete standards, and a substitution rate beyond 20% is not beneficial.

Prestressed concrete girder bridge has been one of the most widely used bridges in the world because of its excellent construction feasibility, economic efficiency, serviceability, and safety. In certain situations, the prestressing tendon is supposed to be bent by the construction error and the radius of curvature at the continuous joint of PSC girders, and this leads to the loss of prestressing force. However, this kind of prestress loss is not considered in the design and construction processes. This study proves that the prestress loss occurs at the continuous joint due to the local bending of tendon by the construction error or the radius of curvature. Also, a method that can reduce this type of prestress loss is proposed, and proved by the experiment. The result shows that maximum 10% of prestress loss occurs at the continuous joint and the proposed block-out method can reduce the prestress loss ratio by maximum 5%, approximately. This means that the block-out method can enhance the prestressing efficiency of continuous PSC girder bridges.

The conventional PHC pile-footing connection is the weak part because the surface area and stiffness are sharply changed. The Composite PHC pile reinforced with the transverse shear reinforcing bars and infilled-concrete, hereafter ICP pile, has been developed for improving the flexural and shear performance. This paper investigates the cyclic behavior and performance of the ICP pile-footing connection. To investigate the behavior of the connection, one PHC and two ICP specimens were manufactured and then a series of cyclic loading tests were performed. From the test results, it was found that the ICP pile-footing connection exhibited higher cyclic behavior and connection performance compared to the conventional PHC pile-footing connection in terms of ductility ratio, stiffness degradation and energy dissipation capacity.

Prediction of concrete cracking due to hydration heat in mass concrete such as reactor containment building (RCB) in nuclear power plant is a crucial issue in construction site. In this study, the numerical analysis for heat transfer and stress development is performed for the containment wall in RCB by considering the severe weather conditions. Finally, concrete cracking risk in hot and cold weather is discussed based on analysis results. In analyses considering severe weather conditions, it is found that the through-wall cracking risk in cold weather is high due to the abrupt temperature difference between inside concrete and the ambient air in cold region. In hot weather, temperature differences between inner and outer face is relatively small, and accordingly the relevant cracking risk is relatively low in contrast with cold weather.

Half cell potential is a widely adopted Non-Destructive Technique in field to evaluate the corrosion of steel in concrete structures qualitatively. If the concrete is exposed to chloride attack, the cracks on concrete surface will rapidly accelerate the steel corrosion due to the intrusion of chloride ions and water permeation. This paper presented the test results of half cell potential evaluation in cracked concrete exposed to chloride attack. The test parameters taken were cover depth (30 mm and 60 mm), w/c ratio (0.35, 0.55, and 0.70), and crack widths (0.0–1.5 mm). To accelerate corrosion cyclic salt spraying test was performed on reinforced concrete beams for the duration of 35 days. Half cell potential (HCP) and corrosion state of rebar were evaluated. From the test results, HCP evaluation technique was proposed considering the effects of w/c ratios, crack width, and cover depth. Furthermore required cover depths for anticorrosive condition were obtained through chloride penetration analysis and the results were compared with previous study.

Bending of a prestressing tendon by construction error or the radius of curvature at the continuous joint of PSC girders cannot be avoided. However, this kind of prestress loss is not considered in design and construction processes. This study proves that prestress loss occurs at the continuous joint due to local bending of the tendon which is induced by construction error or the radius of curvature. The result shows that a maximum 3 % of prestress loss occurs at the continuous joint for a single tendon.

The application of sulfur polymer emulsion (SPE) as an acrylate substitute for semi-rigid pavement grout was evaluated, and the performance improvement by employing PVA fibers were also evaluated. The result indicated that the filling ratio of semi-rigid pavement material decreased as the fiber content increased, but it was measured to be 92~94% in every mixing condition, which satisfies the target performance, 90%. The maximum Marshall stability value of semi-rigid pavement material was measured to be 25.4 kN, which is about 4.7 times higher than the Korean Standard required for semi-rigid pavement material, 5.0 kN. The dynamic stability evaluation of semi-rigid pavement material indicated that the resistance to deformation from the wheel tracking test was improved by an SPE substitution, and in every mixing condition, the deformation converged to a constant value after 45 minutes with the same dynamic stability of 31,500 times/mm. The strain at the flexural failure was about 0.53%, which shows superior rigidity to asphalt pavements. The examination of abrasion resistance and impact resistance showed that the loss ratio was 9.8~6.0% in every mixing condition, which indicates a good abrasion resistance. Also, when fiber content ratio was 0.3%, the impact resistance was 2.82 times higher compared to plain (i.e., when fibers were not added). In the limited range of this study, an SPE substitution ratio of 30% was found to be an optimal level considering the mechanical and durability performance. In addition, it is thought that semi-rigid pavement material with superior performance could be manufactured if fiber content ratio up to 0.3% is applied depending on the purpose of use.

The cracking and strength improvement in beams are one of main issues in the area of architecture and civil engineering. This paper presents the experimental and numerically predictive studies on the flexural performance of reinforced concrete (RC) beams strengthened with a strain-hardening cementitious composite (SHCC) and high strength reinforcing steel bar (HSRS bar) as a new strengthening method for beams. In order to investigate the effects of SHCC and HSRS bar on the control of cracking and load bearing capacity, four types of beam specimens were manufactured and a series of flexural bending tests were performed. The test results showed that the crack width can be controlled by applying SHCC and the load-bearing capacity of beams improved by applying the SHCC and HSRS bar.

Steel corrosion in reinforced concrete (RC) structure is such a critical problem to structural safety that many researches have been performed for maintaining required performance during intended service life. This paper is for a numerical technique for obtaining optimum concrete mix proportions through genetic algorithm (GA) for RC structures under carbonation which is considered as a serious deterioration in underground sites and big cities. For this study, mix proportions and CO2diffusion coefficients are analyzed through the previous studies, and then the fitness function of CO2diffusion coefficient is derived through regression analysis. The fitness function from 69 test results includes 5 variables of mix proportions such as w/c (water to cement) ratio, cement content, sand content percentage, coarse aggregate content, and R.H. (relative humidity). Through GA technique, simulated mix proportions are obtained for 12 cases of verification and they show reasonable results with average relative error of 4.6%. Assuming intended service life and design parameters, intended CO2diffusion coefficients and cement contents are determined and then related mix proportions are simulated. The proposed technique can provide initial concrete mix proportions which satisfy service life under carbonation.

Water is often added to concrete placing for easy workability and finishability in construction site. The additional mixing water can help easy mixing and workability but causes increased porosity, which yields degradation of durability and structural performances. In this paper, cement mortar samples with 0.45 of W/C (water to cement) ratio are prepared for control case and durability performances are evaluated with additional water from 0.45 to 0.60 of W/C. Several durability tests including strength, chloride diffusion, air permeability, saturation, and moisture diffusion are performed, and they are analyzed with changed porosity. The changing ratios and patterns of durability performance are evaluated considering pore size distribution, total porosity, and additional water content.

In this study, the chloride resistant properties of concrete with MBC (marine blended cement) were evaluated by an accelerated corrosion test of reinforced concrete. The half-cell potential measurements indicated that the chloride resistance of MBC concrete is approximately 32% larger than that of TBC (ternary blended cement) concrete. As for the reinforcement corrosion area, while the TBC specimens exhibited 5.32-6.11% corrosion at the final 40th cycle, the MBC specimens did not show any sign of steel corrosion. The chloride penetration depth of the MBC specimens was approximately 41-79% smaller than that of the MBC specimens.

The mechanical properties of water-permeable concrete after mixing with coated recycled aggregates, silica fume, and PVA fiber were investigated in this study. Recycled aggregate was coated double-layer and then mixed as the coarse aggregate of water-permeable concrete. As a result, the void ratio, water-permeability coefficient and strength decreased, as compared to concrete with mixed crushed aggregates. When both silica fume and PVA fiber was added, the strength of the water-permeable concrete increased (compressive strength : by 4.3%, flexural strength : by 2.1 times). Also, the freeze and thaw resistance of the water-permeable concrete increased by approximately 44.15% compared to the plain concrete with no added reinforcing element.

Semi-rigid pavement, which mitigates the drawbacks of cement concrete and asphalt concrete pavements, is being widely used, but the body of research on enhancing the performance of cement grout remains limited. This paper discusses basic research on the development of a rapid hardening cement grout for semi-rigid pavement that meets chloride resistance, rheological property, and strength requirements. Evaluation results indicate that with up to 10% addition of expansive additive, in terms of the weight fraction of cement particles, the rheological property and strength requirements were satisfied. Examination of the chlorine ion penetration resistance revealed that an increase of expansive additive content yielded lower numbers of charged chlorine ions, resulting in 75.5 times higher resistance over a plain mix designed without expansive additive. In contrast, it was found that excessive addition of expansive additive, that is, beyond 10% in terms of the weight fraction of cement particles, was detrimental to achieving the desired rheological property.

A basic study is performed on the application of highly ductile SHCC(Strain Hardening Cementitious Composites) to precast method. A special focus was placed on applying class C fly ash with a high CaO content to secure early-age strength of the steam cured SHCC. The flexural strength of the SHCC panels dependent on fly ash type and varied curing methods were evaluated. The results showed that class C fly ash could enhance the flexural strength of 1 day-old steam cured SHCC panels. Additionally, 1 day-old steam cured specimens produced with class C fly ash exhibited up to 58% of the flexural strength of 28 day-old wet cured specimens produced with class F fly ash.

Recently, in order to reduce a damage of chloride attack and hydration heat in marine concrete structures, blended cement in mixing the marine concrete is widely used. Long term strength development is distinct in concrete with blended cement and it also has excellent resistance to chloride attack and reduction of hydration heat. However, blended cement has a characteristic of relatively low compressive strength in early age of 28 days. On the other hand, a high level of compressive strength is required in the Standard Specification for marine concrete mix design. Such concrete mix design satisfying Standard Specification is effective to chloride attack but disadvantageous for hydration heat reduction due to large quantity of binder. In this study, the material properties of marine concrete considering water-binder ratio and binder type are experimentally investigated. Through the research results, compressive strength in blended cement at the age of 56 days is similar although it has smaller compressive strength at the age of 28 days compared with result of OPC (ordinary portland cement). Even though blended cement has a large water-binder ratio and small unit of binder content, chloride ion diffusion coefficient is still small and hydration heat is also found to be reduced. For meeting the required compressive strength in Standard Specification for marine concrete at 28 days, the increased unit content of binder is needed but the increased hydration heat is also expected.

The development of the oil refining industry has resulted in an annual 120 million tons of sulphur, which is a by-product of the desulphurization process. To exploit this abundance, the applications of sulphur must be expanded. as excellent durability of reuse of leftover sulphur which has high potential for utilization in construction materials, the study is actively in progress. Meanwhile, there has been active research on semi-rigid pavements that draw on the strengths and overcome the weaknesses of asphalt and concrete pavements. Acrylate is used to prevent cracking but involves a high cost, thus, an alternative material is required. As such, this study presents methods on the reuse of leftover sulphur and examines the engineering performance of grout containing sulfur polymer emulsion (SPE) for use in semi-rigid pavements. Our analysis shows that grout in which 30% of acrylate is replaced with SPE has superior properties in terms of time of flow and strength compared to regular grout. However, performance declined when more than 50% of acrylate was replaced by SPE, indicating that the optimum replacement level is 30%. Through SEM analysis, we found that grout with utra harding cement in this study at three hours had similar hydration properties to that of Type 1 Ordinary Portland Cement (OPC) at seven days, and maintained the properties regardless of grout containing SPE. OPC and grout with a replacement level of 30% displayed similar levels of chloride invasion resistance, whereas grout without SPE was far less resistant. Within the scope of this paper, the optimum replacement level of acrylate with SPE was found to be 30% in consideration of various properties such as time of flow, strength, and chloride invasion resistance.