• Advances in concrete construction
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• v.9 no.2
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• pp.207-215
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• 2020

This paper describes the experimental studies carried out to determine the properties of fresh and hardened concrete with Recycled Plastic Waste (RPW) as a partial replacement material for fine aggregates. In the experimental study, RPW was used for replacing river sand and manufactured sand (M sand) aggregates in concrete. The replacement level of fine aggregates was ranging from 5% to 20% by volume with an increment of 5%. M40 grade of concrete with water cement ratio of 0.40 was used in this study. Two different types of RPW were used, and they are (i) un-activated RPW and (ii) activated RPW. The activated RPW was obtained by alkali activation of un-activated RPW using NaOH solution. The hardened properties of the concrete determined were dry density, compressive strength, split tensile strength, flexural strength and ultrasonic pulse velocity (UPV). The properties of the concrete with river sand, M sand, activated RPW and un-activated RPW were compared and inferences were drawn. The effect of activation using NaOH solution was investigated using FT-IR study. The micro structural examination of hardened concrete was carried out using Scanning Electron Microscopy (SEM). The test results show that the strength of concrete with activated RPW was more than that of un-activated RPW. From the results, it is evident that it is feasible to use 5% un-activated RPW and 15% activated RPW as fine aggregates for making concrete without affecting the strength properties.

• Geomechanics and Engineering
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• v.25 no.1
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• pp.41-48
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• 2021

In cold regions, the integrity of the infrastructures built on weak soils can be extensively damaged by weathering actions due to the cyclic freezing and thawing. This damage can be mitigated by exploiting soil stabilization techniques. Generally, ordinary Portland cement (OPC) is the most commonly used binding material for investigating the chemo-hydromechanical behavior. However, due to the environmental issue of OPC producing a significant amount of carbon dioxide emission, calcium sulfoaluminate (CSA) cement can be used as one of the eco-sustainable alternatives. Although recently several studies have examined the strength development of CSA treated sand, no research has been concerned about CSA cement-stabilized sand affected by cyclic freeze and thaw. This study aims to conduct a comprehensive laboratory work to assess the effect of the cyclic freeze-thaw action on strength and durability of CSA cement-treated sand. For this purpose, unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) tests were performed on the stabilized soil specimens cured for 7 and 14 days which are subjected to 0, 1, 3, 5, and 7 freeze-thaw cycles. The test results show that the strength and durability index of the samples decrease with the increase of the freeze-thaw cycles. The loss of the strength and durability considerably decreases for all soil samples subjected to the freeze-thaw cycles. Overall, the use of CSA as a stabilizer for sandy soils would be an eco-friendly option to achieve sufficient strength and durability against the freeze-thaw action in cold regions.

• Advances in concrete construction
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• v.13 no.6
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• pp.433-450
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• 2022

The conventional disposal methods of waste tires are harmful to the environment. Moreover, the recycling/reuse of waste tires in domestic and industrial applications is limited due to parent product's quality control and environmental concerns. Additionally, the recycling industry often prefers powdered rubber particles (<0.60 mm). However, the processing of waste tires yields both powdered and coarser (>0.60 mm) size fractions. Reprocessing of coarser rubber requires higher energy increasing the product cost. Therefore, the waste tire rubber (WTR) less favored by the recycling industry is encouraged for use in construction products as one of the environment-friendly disposal methods. In this study, WTR fiber >0.60 mm size fraction is collected from the industry and sorted into 0.60-1.18, 1.18-2.36-, and 2.36-4.75-mm sizes. The effects of different fiber size fractions are studied by incorporating it as fine aggregates at 10%, 20%, and 30% in the self-compacting rubberized concrete (SCRC). The experimental investigations are carried out by performing fresh and hardened state tests. As the fresh state tests, the slump-flow, T500, V-funnel, and L-box are performed. As the hardened state tests, the scanning electron microscope, compressive strength, flexural strength and split tensile strength tests are conducted. Also, the water absorption, porosity, and ultrasonic pulse velocity tests are performed to measure durability. Furthermore, SCRC's energy absorption capacity is evaluated using the falling weight impact test. The statistical significance of content and size fraction of WTR fiber on SCRC is evaluated using the analysis of variance (ANOVA). As the general conclusion, implementation of various size fraction WTR fiber as fine aggregate showed potential for producing concrete for construction applications. Thus, use of WTR fiber in concrete is suggested for safe, and feasible waste tire disposal.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.5
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• pp.31-38
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• 2009

The primary objective of this study was to estimate the deterioration degree of jointed concrete pavement which was major concrete pavement type in Korea. First of all, visual survey of concrete pavement was performed to observe deterioration types. In the result of visual survey, the majority of concrete pavement deterioration was investigated in joint area. It is appeared that most of the distresses are durability cracking and joint distress. Second, concrete core specimens were taken from eight locations including good section (4 locations) and bad section (4 locations) based on visual survey. The deterioration reasons of concrete pavement were analyzed with ultrasonic pulse velocity test, splitting tensile strength test, and image analysis for concrete core specimens. Among the image analysis test result for 21 concrete core specimens, only two specimens satisfied the Kansas DOT criteria of spacing factor, $250\;{\mu}m$, and the remains of 19 specimens were estimated to be above $250\;{\mu}m$. The durability factor of concrete was estimated very low. As a result, it was analyzed that the main deterioration reason of the deteriorated jointed concrete pavement was to be freezing and thawing damages.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.389-397
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• 2010

Concrete has excellent mechanical properties, high durability, and economical advantages over other construction materials. Nevertheless, it is not an easy task to apply concrete to long span bridges. That's because concrete has a low strength to weight ratio. Ultra high performance concrete (UHPC) has a very high strength and hence it allows use of relatively small section for the same design load. Thus UHPC is a promising material to be utilized in the construction of long span bridges. However, there is a possibility of crack generation during the curing process due to the high binder ratio of UHPC and a consequent large amount of hydration heat. In this study, adiabatic temperature rise and mechanical properties were modeled for the stress analysis due to hydration heat. Adiabatic temperature rise curve of UHPC was modeled superposing 2-parameter model and S-shaped function, and the Arrhenius constant was determined using the concept of equivalent time. The results are verified by the mock-up test measuring the temperature development due to the hydration of UHPC. In addition, models for mechanical properties such as elastic modulus, tensile strength and compressive strength were developed based on the test results from conventional load test and ultrasonic pulse velocity measurement.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.593-600
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• 2016

The paper presented investigates the effects of kaolinite on strength properties of alkali-activated multi-component cement. The binders of this study was blended of ground granulated blast furnace slag (GGBFS), fly ash (FA), silica fume (SF) and kaolinite (KA). In this study, the specimens of combination of 20%~70% GGBFS, 10%~60% FA, 10% SF (constant ratio) and 10%~50% KA binder were used for strength properties tests. The water/binder ratio was 0.5. The binders (GGBFS + FA + SF + KA) was activated by sodium hydroxide (NaOH) and sodium silicate ($Na_2SiO_3$) was 10% by total binder weight (10% NaOH + 10% $Na_2SiO_3$). The research carried out is on the compressive strength, water absorption, ultrasonic pulse velocity (UPV) and X-ray diffraction (XRD). The compressive strength decreased as the contents of KA increase. One of the major reason for this is the low reactivity of KA compared with other raw materials used as precursors such as GGBFS or FA. The presence of remaining KA indicates that the initially used quantity has not fully reacted during hydration. Moreover, the results have indicated that increased of KA contents decreased UPV under all experimental conditions. The drying shrinkage and water absorption increased as the content of KA increase. Test result clearly showed that the strength development of multi-component blended cement were significantly dependent on the content of KA and GGBFS.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.205-212
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• 2016

This research investigates the influence of ground granulated blast furnace slag (GGBFS) composition on the alkali-activated slag cement (AASC). Aluminum oxide ($Al_2O_3$) was added to GGBFS binder between 2% and 16% by weight. The alkaline activators KOH (potassium hydroxide) was used and the water to binder ratio of 0.50. The strength development results indicate that increasing the amount of $Al_2O_3$ enhanced hydration. The 2M KOH + 16% $Al_2O_3$ and 4M KOH + 16% $Al_2O_3$ specimens had the highest strength, with an average of 30.8 MPa and 45.2 MPa, after curing for 28days. The strength at 28days of 2M KOH + 16% $Al_2O_3$ was 46% higher than that of 2M KOH (without $Al_2O_3$). Also, the strength at 28days of 4M KOH + 16% $Al_2O_3$ was 44% higher than that of 4M KOH (without $Al_2O_3$). Increase the $Al_2O_3$ contents of the binder results in the strength development at all curing ages. The incorporation of AASC tended to increases the ultrasonic pulse velocity (UPV) due to the similar effects of strength, but increasing the amount of $Al_2O_3$ adversely decreases the water absorption and porosity. Higher addition of $Al_2O_3$ in the specimens increases the Al/Ca and Al/Si in the hydrated products. SEM and EDX analyses show that the formation of much denser microstructures with $Al_2O_3$ addition.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.2
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• pp.63-69
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• 2012

Recently, the cement industries brought very severe environment problems such as resource depletion and global warming with massive carbon dioxide during its production. The number of cases using industrial by-products such as the ground granulated blast furnace slag (GGBFS) in concrete mixtures is increasing to resolve the environmental issue. GGBFS is mainly used in the range between 20 to 50% to replace cement, but nowadays lots of researches are carried out to develop the alkali-activated slag (AAS) concrete with no cement. In this study, the early age properties of alkali activated slag (AAS) mortar are investigated to obtain the fundamental data for AAS concrete application to structural members. The experimental variables were the water-binder ratios of 0.3, 0.4, and 0.5 and NaOH as the alkali activator of 4%, 8%, and 12% by the mass of GGBFS, and compressive strength, flow, setting time, and ultrasonic pulse velocity of AAS mortars were measured and analyzed. It is found from the test results that as the normal concrete the lower W/B, the higher compressive strength. However, superplasticizer has to be used for producing high strength AAS concrete because the workability of AAS mortar are significantly lowered.

• Advances in nano research
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• v.12 no.5
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• pp.501-514
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• 2022

This study aimed to investigate the effects and potential mechanisms of Chikusetsusaponin V (CsV) on endothelial nitric oxide synthase (eNOS) and vascular endothelial cell functions. Different concentrations of CsV were added to animal models, bovine aorta endothelial cells (BAECs) and human umbilical vein endothelial cells (HUVECs) cultured in vitro. qPCR, Western blotting (WB), and B ultrasound were performed to explore the effects of CsV on mouse endothelial cell functions, vascular stiffness and cellular eNOS mRNA, protein expression and NO release. Bioinformatics analysis, network pharmacology, molecular docking and protein mass spectrometry analysis were conducted to jointly predict the upstream transcription factors of eNOS. Furthermore, pulldown and ChIP and dual luciferase assays were employed for subsequent verification. At the presence or absence of CsV stimulation, either overexpression or knockdown of purine rich element binding protein A (PURA) was conducted, and PCR assay was employed to detect PURA and eNOS mRNA expressions, Western blot was used to detect PURA and eNOS protein expressions, cell NO release and serum NO levels. Tube formation experiment was conducted to detect the tube forming capability of HUVECs cells. The animal vasodilation function test detected the vasodilation functions. Ultrasonic detection was performed to determine the mouse aortic arch pulse wave velocity to identify aortic stiffness. CsV stimulus on bovine aortic cells revealed that CsV could upregulate eNOS protein levels in vascular endothelial cells in a concentration and time dependent manner. The expression levels of eNOS mRNA and phosphorylation sites Ser1177, Ser633 and Thr495 increased significantly after CsV stimulation. Meanwhile, CsV could also enhance the tube forming capability of HUVECs cells. Following the mice were gavaged using CsV, the eNOS protein level of mouse aortic endothelial cells was upregulated in a concentration- and time-dependent manner, and serum NO release and vasodilation ability were simultaneously elevated whereas arterial stiffness was alleviated. The pulldown, ChIP and dual luciferase assays demonstrated that PURA could bind to the eNOS promoter and facilitate the transcription of eNOS. Under the conditions of presence or absence of CsV stimulation, overexpression or knockdown of PURA indicated that the effect of CsV on vascular endothelial function and eNOS was weakened following PURA gene silence, whereas overexpression of PURA gene could enhance the effect of CsV upregulating eNOS expression. CsV could promote NO release from endothelial cells by upregulating the expression of PURA/eNOS pathway, improve endothelial cell functions, enhance vasodilation capability, and alleviate vessel stiffness. The present study plays a role in offering a theoretical basis for the development and application of CsV in vascular function improvement, and it also provides a more comprehensive understanding of the pharmacodynamics of CsV.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.5
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• pp.104-111
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• 2015

This study shows the mechanical properties of alkali-activated slag cement (AASC) synthesized using sulfate with NaOH solution. The used sulfates were calcium sulfate ($CaSO_4$, denoted CS) and sodium sulfate ($Na_2SO_4$, denoted SS). The replacement ratio of sulfates was 2.5, 5.0, 7.5 and 10.0% by weight of slag. NaOH solution of 2M and 4M concentration was used. A sample was activated with sulfate and activated with blended activator (blending NaOH solution with sulfate) respectively. 24 mix ratios were used and the water-binder weight ratio for the test was set 0.5. This research carried out the compressive strength, flexural strength, ultrasonic pulse velocity (UPV), absorption and X-ray diffraction (XRD). In the case of samples with CS, sample with 7.5% CS, sample with 2M NaOH+5.0% CS and sample with 4M NaOH+5.0% CS showed the good performance in the strength development. In the case of samples with SS, sample with 10.0% SS, sample with 2M NaOH+7.5% SS and sample with 4M NaOH+2.5% SS obtained good performance in strength. The results of UPV and water absorption showed a similar tendency to the strength properties. The XRD analysis of samples indicated that the hydration products formed in samples were ettringite, CSH and silicate phases. In this study, it is indicated that when compared to the use of sulfate only, the use of both sulfate and NaOH solution makes mechanical properties of AASC better.