• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.104-112
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• 2019

The material properties of the 3D printing cement composite mortar were evaluated, and the performance range in which printing was possible was calculated using the void ratio in a fresh state as a single index. As a results of the tests, as the water-binder ratio (W/B) increased, the mortar flow value increased and the density and strength decreased. As the sand-binder ratio (SS/B) increased, the mortar flow value decreased. However, strength and density increased and decreased up to a certain SS/B. As admixture-binder ratio (Ad/B) increased, mortar flow value, density, and strength decreased. These trends make it difficult to mix-design to meet the target performances of 3D printing mortars, represented by extrudability and buildability. The value of mortar flow increased proportionally with the void ratio, while the density and strength apparently decreased as the void ratio increased. This indicates that void ratio can be utilized as a single index for controlling the material properties in the design of mortar mixtures. It was found that mortar mixture could be printed by a 3D printer when the void ratio was in the range from 0.6 to 0.7. This was verified by printing a mortar which has the void ratio of 0.634. The mortar was produced with the mixture design of W/B 35.0%, SS/B 60.0%, and Ad/B 0.1%. Further research applying diverse admixtures is needed to improve the quality of 3D printing output mortars.

• Steel and Composite Structures
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• v.47 no.1
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• pp.91-102
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• 2023

To study the evaluation standard and control limit of mortar filling layer void length, in this paper, the train sub-model was developed by MATLAB and the track-bridge sub-model considering the mortar filling layer void was established by ANSYS. The two sub-models were assembled into a train-track-bridge coupling dynamic model through the wheel-rail contact relationship, and the validity was corroborated by the coupling dynamic model with the literature model. Considering the randomness of fastening stiffness, mortar elastic modulus, length of mortar filling layer void, and pier settlement, the test points were designed by the Box-Behnken method based on Design-Expert software. The coupled dynamic model was calculated, and the support vector regression (SVR) nonlinear mapping model of the wheel-rail system was established. The learning, prediction, and verification were carried out. Finally, the reliable probability of the amplification coefficient distribution of the response index of the train and structure in different ranges was obtained based on the SVR nonlinear mapping model and Latin hypercube sampling method. The limit of the length of the mortar filling layer void was, thus, obtained. The results show that the SVR nonlinear mapping model developed in this paper has a high fitting accuracy of 0.993, and the computational efficiency is significantly improved by 99.86%. It can be used to calculate the dynamic response of the wheel-rail system. The length of the mortar filling layer void significantly affects the wheel-rail vertical force, wheel weight load reduction ratio, rail vertical displacement, and track plate vertical displacement. The dynamic response of the track structure has a more significant effect on the limit value of the length of the mortar filling layer void than the dynamic response of the vehicle, and the rail vertical displacement is the most obvious. At 250 km/h - 350 km/h train running speed, the limit values of grade I, II, and III of the lengths of the mortar filling layer void are 3.932 m, 4.337 m, and 4.766 m, respectively. The results can provide some reference for the long-term service performance reliability of the ballastless track-bridge system of HRS.

• Computers and Concrete
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• v.21 no.4
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• pp.367-376
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• 2018

This study reports the results of nondestructive monitoring of macro void developments in mortars manufactured with both ordinary Portland cement and sulfate resistant cement. Two types of curing were utilized; tap water curing and another curing environment that contains 5% $Na_2(SO_4)$ solution. Being the primary objective of this study, macro void developments of the mortar specimens were monitored by X-ray Medical Computerized Tomography. Compressive strength tests and water absorption tests were conducted on specimens that were kept in both curing environments for a duration of 560 days. Data analyses yielded consistent results among the three tests used in this experimental study. Macro void ratios of mortars decreased at the beginning of experiments for a certain period; afterwards, macro void ratios increased. The objective of this study was accomplished as anticipated since X-CT image analysis was able to nondestructively monitor macro void development process in cement mortars.

• Computers and Concrete
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• v.4 no.6
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• pp.425-436
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• 2007

This study is mainly focused on applying Fuller's ideal gradation curve to theoretically design blended ratio of all solid materials of a reactive powder mortar (RPM), also known as reactive powder concrete (RPC), with the aid of error function, and then to study the effect of fly ash/slag on the performance of RPM. The solid particle is assumed to be spherical particles. Then, the void volume of paste ($V_{\nu}$) and the paste content with specific quality can be obtained. As conclusion, under Fuller's ideal grading curve, the amount of fly ash/slag mixture is higher than that with silica fume along due to it better filled the void within solid particle and obtains higher packing density.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.05a
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• pp.91-92
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• 2016

Structural integrity of reinforced concrete structures including nuclear power plants needs to be evaluated on a regular basis. Deterioration inside the concrete structures can be represented by voids. In this study, the varied volume fraction of voids inside mortar specimens was studied as a parameter using ultrasonic testing equipments. Both direct and indirect measurement methods were employed. The results show that there is a clear distinction between the specimens with different void volume fractions.

• Journal of The Korean Society of Agricultural Engineers
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• v.49 no.3
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• pp.51-60
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• 2007

This study was performed to evaluate void ratio, compressive and flexural strengths, and pH properties according to the content ratio of rice husk ash, aggregate size, and neutral treatment time of porous concrete with content of rice husk ash produced as an agricultural by-product. The SEM results for cement mortar with a 5% rice husk ash for the weight of cement formed more C-S-H hydrates due to the $SiO_2$ of rice husk ash. In the XRD test, cement mortar with a 5% rice husk ash for the weight of cement registered a higher peak point of approximately $2{\theta}=20{\sim}25^{\circ}$ compared to cement mortar without rice husk ash. According to the results of the XRD and SEM tests, the $SiO_2$ that was a major chemical element of rice husk ash generated a large amount of calcium hydroxide in the early stage of the hydration process of cement leading to the formation of ettringite. The void ratio of porous concrete with rice husk ash decreased with increasing content ratio of rice husk ash. In addition, the void ratio of porous concrete with rice husk ash decreased compared to porous concrete without rice husk ash. The compressive and flexural strength of porous concrete with a 5% and 10% content ratio of rice husk ash slightly increased compared to concrete without rice husk ash. The pH value of porous concrete rapidly decreased immediately after neutral treatment. Then, it gradually increased and decreased again after 14 days. However, the pH value was nearly the same regardless of neutral treatment time in 28 curing days. Also, for neutral treatment, the pH value of porous concrete showed appropriate pH levels (less than 9.5) in all mixtures for planting at 28 curing days.

• Journal of Industrial Technology
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• v.33 no.A
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• pp.93-99
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• 2013

Shotcrete has been referred to as gunite, pneumatically applied mortar or concrete, sprayed concrete or mortar. There are sound reasons why sprayed mortar is one of the best portland cement based material for repairing old concrete structures. However, it is difficult to find the research results on the latex-modified mortar nevertheless on the impact of air onto the fresh and hardened properties of latex-modified mortar. So, the main experimental program included strength test, slump test, rapid chloride permeability test, image analysis for air void system, and chemical attacks with the main experimental variables of latex content, fine aggregate content, water-cement ratio, and air foamer content.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.620-623
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• 2004

Waste concrete powder(WCP) has been estimated with a great value-added material as by-product of waste concrete manufactured to fine and coarse aggregate for concrete, because it is able to utilized for cement clinker and concrete admixture. In the experimental results for this study, chemical composition of WCP was similar to that of cement, and specific gravity of WCPs were 2.46 and 2.48 due to internal micro-void of WCP. Final setting of paste with WCP was delayed, and flow value of mortar with WCP was tendency to reduced in comparison with that of paste and mortar with only ordinary portland cement as replacement ratio of WCP increased. Furthermore, sorptivity of mortar with WCP was increased as replacement ratio of WCP increased. Compressive strength of mortar with $15\%$ WCP was developed about 27MPa at 28days.

• Journal of Industrial Technology
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• v.33 no.A
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• pp.101-107
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• 2013

The purpose of this study was to investigate bond strength between substrate and HES-LMS mortar, durability of HES-LMS mortar with latex content(0%, 5%, 10%). To measure the bond strength, the direct tensile test based on uniaxial tensile test was used, which was proposed by Kuhlman(1990). Also, Resistance for water permeability, water absorption and image analysis for air void system were conducted to estimating durability of HES-LMS mortar.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.05a
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• pp.103.2-108
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• 2003

The purpose of this study is to understand the Physical characteristics of cement mortar about humidity control on indoors and wall crack restraint. Experiments were conducted on the strength, water absorption coefficient, drying-shrinking crack, length change, cracks of mortar plaster bases according to mixture rate by mixing cellulose fiber and diatomite into cement mortar. The excellent tensile & bending reinforcement efficiency of cellulose fiber and void filling ability of diatomite proved to be suppressing cracks of cement. And diatomite seems to improve moisture-protection efficiency of cement mortar because of its high water absorption ratio and slow drying speed.