• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.421-426
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• 2017

In this paper, the effect of freezing-thawing action on the dynamic modulus and porosity was examined by ultrasonic pulse velocity (UPV) measurement. UPV was measured every 30 cycles during the freezing-thawing test, and dynamic modulus and porosity of cement mortar were calculated by relationship among UPV, porosity and dynamic modulus. Porosity analysis was also performed to compare with calculated porosity by mercury intrusion porosimetry (MIP). From the test, it was found that dynamic modulus of cement mortar was decreased 13% after 300 cycles. The calculated porosity was increased about 30% compared with the initial porosity before freezing-thawing action. The calculated porosity showed similar increase tendency with the porosity measured by MIP. So, it can be concluded that the porosity change of cementitious materials by freezing-thawing action can be predicted by UPV measurement.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.2
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• pp.98-106
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• 2003

Nondestructive test (NDT) provides much information on concrete without damage of structural functions. Of NDT methods, elastic wave propagation methods, such as ultrasonic pulse velocity (UPV) method and impact-echo (IE) method, have been successfully used to estimate the strength, elastic modulus, and Poisson's ratio of concrete as well as to detect the internal microstructural change and defects. In this study, the concretes with water-binder ratio ranging from 0.27 to 0.50 and fly ash content of 20% were made and then their longitudinal wave velocities were measured by UPV and IE method, respectively. Test results showed that the UPV is greater than the longitudinal wave velocity measured by the If method, i.e., rod-wave velocity obtained from the same concrete cylinder. It was found that the difference between the two types of velocities decreased with increasing the ages of concrete and strength level. Moreover, for the empirical formula, the dynamic Poisson's ratio, static and dynamic moduli of elasticity, and velocity-strength relationship were determined. It was observed that the Poisson's ratio and the modulus of elasticity determined by the dynamic method are greater than those determined by the static test. Consequently, for the more accurate estimation of concrete properties using the elastic wave velocities, the characteristics of these velocities should be understood.

• Advances in concrete construction
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• v.5 no.4
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• pp.359-375
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• 2017

This paper presents a study of the properties and behavior of self-compacting concretes (SCC) in the hot climate. The effect of curing environment and the initial water curing period on the properties and behavior of SCC such as compressive strength, ultrasonic pulse velocity (UPV) and sorptivity of the SCC specimens were investigated. Three Water/Binder (W/B) ratios (0.32, 0.38 and 0.44) have been used to obtain three ranges of compressive strength. Five curing methods have been applied on the SCC by varying the duration and the conservation condition of SCC. The results obtained on the compressive strength show that the period of initial water curing of seven days followed by maturation in the hot climate is better in comparison with the four other curing methods. The coefficient of sorptivity is influenced by W/B ratio and the curing methods. It is also shown that the sorptivity coefficient of SCC specimens is very sensitive to the curing condition. The SCC specimens cured in water present a low coefficient of sorptivity regardless of the ratio W/B. Furthermore, the results show that there is a good correlation between ultrasonic pulse velocity and the compressive strength.

• Advances in concrete construction
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• v.5 no.5
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• pp.437-450
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• 2017

The present work investigates about the development of a novel construction material by utilizing Granulated Blast Furnace Slag (GBS), an industrial waste product, as substitution of natural fine aggregates. For this, experimental work has been carried out to determine the influence of GBS on the properties of concrete such as compressive strength (CS), modulus of elasticity, ultrasonic pulse velocity (UPV), chloride penetration, water absorption (WA) volume of voids (VV) and density. Concrete mixes of water/cement (w/c) ratios 0.45 and 0.5, and incorporating 20%, 40% and 60% of GBS as partial replacement of natural fine aggregate (sand) are designed for this study. The results of the experimental investigation depict that CS of concrete mixes increases with the increasing percentages of GBS. Moreover, the decrease in chloride penetration, WA and VV, and improvement in the modulus of elasticity, UPV, density of concrete is reported with the increasing percentage of GBS in concrete.

• Computers and Concrete
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• v.24 no.3
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• pp.193-206
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• 2019

Although concrete is the most widely used construction material, its deficiency in shrinkage and low tensile resistance is undeniable. However, the aforementioned defects can be partially modified by addition of fibers. On the other hand, possibility of adding waste materials in concrete has provided a new ground for use of recycled concrete aggregates in the construction industry. In this study, a constant combination of recyclable coarse and fine concrete aggregates was used to replace the corresponding aggregates at 50% substitution percentage. Moreover, in order to investigate the effects of fibers on mechanical and durability properties of recycled aggregate concrete, the amounts of 0.5%, 1%, and 1.5% steel fibers (ST) and 0.05%, 0.1% and 0.15% polypropylene (PP) fibers by volumes were used individually and in hybrid forms. Compressive strength, tensile strength, flexural strength, ultrasonic pulse velocity (UPV), water absorption, toughness, elastic modulus and shrinkage of samples were investigated. The results of mechanical properties showed that PP fibers reduced the compressive strength while positive impact of steel fibers was evident both in single and hybrid forms. Tensile and flexural strength of samples were improved and the energy absorption of samples containing fibers increased substantially before and after crack presence. Growth in toughness especially in hybrid fiber-reinforced specimens retarded the propagation of cracks. Modulus of elasticity was decreased by the addition of PP fibers while the contrary trend was observed with the addition of steel fibers. PP fibers decreased the ultrasonic pulse velocity slightly and had undesirable effect on water absorption. However, steel fiber caused negligible decline in UPV and a small impact on water absorption. Steel fibers reduce the drying shrinkage by up to 35% when was applied solely. Using fibers also resulted in increasing the ductility of samples in failure. In addition, mechanical properties changes were also evaluated by statistical analysis of MATLAB software and smoothing spline interpolation on compressive, flexural, and indirect tensile strength. Using shell interpolation, the optimization process in areas without laboratory results led to determining optimal theoretical points in a two-parameter system including steel fibers and polypropylene.

• Structural Engineering and Mechanics
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• v.90 no.5
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• pp.493-504
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• 2024

This paper presents the methodology and results for the investigation of the structural safety of 40 aged underground water tanks to support the weight of photovoltaic (PV) systems that were supposed to be placed on their roof reinforced concrete (RC) slabs. The investigation procedure included (1) review of available documents; (2) visual inspection of the roof RC slabs; (3) carrying out a series of nondestructive (ND) tests; and (4) analysis of results. Out of the 40 tanks, eleven failed the visual inspection phase and were discarded from further investigation. The roof RC slabs of the tanks that passed the visual inspection were subjected to a series of ND tests that included infrared thermography, impact echo, ultrasonic pulse velocity (UPV), Schmidt hammer, concrete core compressive strength, and water-soluble chloride content. The NDT results proved that eight more tanks were not suitable to support the PV systems. Based on the results of the visual inspection and testing, a probabilistic decision-making criterion was established to reach a decision regarding the structural integrity of the roof slabs. The study concluded that the condition of the drainage filter was essential in protecting the tanks and its intact presence can be used as a strong indication of the structural integrity of the roof RC slabs.

• Journal of the Korea Concrete Institute
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• v.29 no.1
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• pp.11-21
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• 2017

The paper presents experimental results of self-healing effects of OPC-GGBFS paste with cracked and uncracked specimens. The self-healing of cracked specimens is processes of crack closing with re-hydration of unhydrated in crack surface. The OPC paste with GGBFS replacement ratios of 0%, 10%, 20% and 30% were prepared having a constant water-binder ratios of 0.5. The OPC-GGBFS paste specimens immersed in tap-water and sea-water. The temperature of tap and sea-water was $5^{\circ}C$, $15^{\circ}C$ and $25^{\circ}C$. The cracked specimens after deterioration were immersed for 60 days. The relationship between self-healing effect and age-effect was calculate based upon the experimental results. The self-healing effect was measured in ultrasonic pulse velocity (UPV) before and after loading. When the relative change rate of UPV is increases with the increase in GGBFS replacement ratios. Moreover, the self-healing effect is increased with the temperature of tap-water is increase. But the cracked specimens immersed in sea-water was unclear effects of different temperature. Furemore, most of the healing for OPC-GGBFS specimens immersed in tap-water and sea-water occurred during the first 30 days. The self-healing effect until 30 days is higher than that the age-effect. After 30 days, self-effect and age-effect was largely decreases. SEM/EDS analysis of crack on the surface of the specimens in tap-water were covered with aragonite, and sea-water were covered with brucite.

• Geomechanics and Engineering
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• v.15 no.1
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• pp.615-620
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• 2018

In order to analyze the healing effectiveness of rock salt cracks affected by the applied stresses and time, we used the ultrasonic technology to monitor the ultrasonic pulse velocity (UPV) variations for different initial stress-damaged rock salts during self-healing experiments. The self-healing experiments were to create different conditions to improve the microcracks closure or recrystallized, which the self-healing effect of damaged salt specimens were analyzed during the recovery period about 30 days. We found that: The ultrasonic pulse velocity of the damaged rock salts increases rapidly during the first 9 days recovery, and the values gradually increase to reach constant values after 30 days. The damaged value and the healed value were identified based on the variation of the wave velocity. The damaged values of the specimens that are subject to higher initial damage stress are still keeping in large after 30 days recovery under the same recovery condition It is interesting that the damage and the healing were not in the linear relationship, and there also existed a damage threshold for salt cracks healing ability. When the damage degree is less than the threshold, the self-healing ratio of rock salt is increased with the increase in damage degree. However, while the damage degree exceeds the threshold, the self-healing ratio is decreased with the increase in damage.

• Journal of the Korean Society of Safety
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• v.32 no.2
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• pp.98-104
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• 2017

The ultrasonic pulse velocities of pressure, shear, and Rayleigh waves ( P-, S-, and R- waves) have been used for the condition evaluation of various concrete structures, but the statistical distribution according to the wave type has not been studied clearly in view of data reliability and validity. Therefore, this study analyzed the statistical distribution of P-, S-, R-wave velocities in concrete wide beams of $800{\times}3100mm$ (width ${\times}$ length) with a thickness of 300 mm. In addition, we investigated an experimental consistency by the Kolmogorov-Smirnov goodness-of-fit test. The experimental data showed that the R-, S- and P- wave velocities in order have better statistical stability and reliability for in situ evaluation because R- and S-waves are less sensitive to confinement and boundary conditions. Also, good correlations between wave velocities and strength and modulus of elasticity were found, which indicate them as appropriate techniques for estimating the mechanical properties.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.66-74
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• 2016

The aim of this research work is to investigate the mix proportion of multi-component cement incorporating ground granulated blast furnace(GGBFS), fly ash(FA) and silica fume(SF) as an addition to cement in ternary and quaternary combinations. The water-binder ratio was 0.45. In this study, 50% and 60% replacement ratios of mineral admixture to OPC was used, while series of combination of 20~40% GGBFS, 5~35% FA and 0~15% SF binder were used for fundamental characteristics tests. This study concern the GGBFS/FA ratio and SF contents of multi-component cement including the compressive strength, water absorptions, ultrasonic pulse velocity(UPV), drying shrinkage and X-ray diffraction(XRD) analysises. The results show that the addition of SF can reduce the water absorption and increase the compressive strength, UPV and drying shrinkage. These developments in the compressive strength, UPV and water absorption can be attributed to the fact that increase in the SF content tends basically to consume the calcium hydroxide crystals released from the hydration process leading to the formation of further CSH(calcium silicate hydrate). The strength, water absorption and UPV increases with an increase in GGBFS/FA ratios for a each SF contents. The relationship between GGBFS/FA ratios and compressive strength, water absorption, UPV is close to linear. It was found that the GGBFS/FA ratio and SF contents is the key factor governing the fundamental properties of multi-component cement.