Cellular sprayed concrete for simple and economic remixing

The development of various supplementary cementitious materials (SCMs) and chemical admixtures, makes the manufacturing of high-performance shotcrete possible. The most important SCM in high-performance shotcrete is silica fume because of its effect on pumpability, high-strength and durability which lies in its Pozzolanic reaction. Furthermore, the very small particle size of silica fume reacts more quickly than other SCMs and acts as a filler which contributes to the nano-sized porosity occurring in the interfacial transition zone. On the other hand, because of the extremely small particle size of silica fume, it is used as a pre-blended type with a Portland cement for a better distribution of silica fume in concrete. This results in a high cost material. If it is possible to distribute the very fine silica fume in a ready-mixed concrete, this would results in a very simple and an economic way. A very innovative method, which was named as Cellular sprayed concrete, was developed. Cellular sprayed concrete is a process to produce a High-Performance Concrete (HPC) by adding cellular and silica fume in ready-mixed concrete. This method enable to distribute the very fine silica fume in a ready-mixed concrete. This paper describe on the very new and innovative concept and procedures of cellular sprayed concrete

Application examples of a very economic way of cellular sprayed concrete on retaining wall and artificial rock

An economic slope structure construction method for landscape was developed, which utilized the cellular sprayed concrete for high performance shotcrete. This can improve the performance of shotcrete material, maximize the construction advantages of shotcrete and further harmonize with the surrounding environment. This may solve various problems such as efficient slope stabilization of large-scale slopes from natural disasters that occur annually due to climate change, the necessity of disaster prevention and restoration technologies, existing slope maintenance and reinforcement construction methods for weathering. This construction method maximizes the economic feasibility by manufacturing a high-performance cellular shotcrete using an ordinary ready mixed concrete and concrete pump car. Cellular shotcrete is produced by incorporating cellular and mineral admixtures in the process of remixing and dispersing the mineral admixture in an ordinary ready mixed concrete at a job site. High strength and high durability are secured by using high-performance cellular shotcrete without using accelerators. Speed and safety are improved by adopting a concrete pump car reaching a far way on the slope without formwork in the top-down and bottom-up method. In addition, this technique can highlight nature-friendly scenery since it is a construction method that comprehends natural rock shapes and colors, by carving various natural rock patterns on the placed high-performance shotcrete before the thickness is adjusted and before it hardens. After curing for a certain period of time, a coloring agent like stain is sprayed on the surface to develop color by neutralization reaction

Mechanical and Pore Properties of Concrete Using Basalt-Based Recycled Aggregates According to Mixture Conditions

This study investigated recycled aggregates of Jeju Island—where porous basalt exists as a natural aggregate—and is a study aimed at verifying the applicability of the basalt-based recycled aggregate in the field. To this end, the application properties of concrete were analyzed using the quality improvement of the recycled aggregate (PRA), the type of fine aggregate received in the region, and the cement content as variables. In an experiment using concrete in which 50% of the PRA was replaced with basalt (BA), the air content of the fresh concrete decreased due to the increasing solid content of the aggregate when PRA and fine aggregates (with an even particle size distribution) were used. Regarding the properties of the hardened concrete, when the PRA and fine aggregate (with a high fineness modulus) were used, the compressive strength was 33.6 MPa and the modulus of elasticity was 23.1 GPa, which are higher than those of the BA specimen. The resistance to carbonation increased due to the improved quality of the PRA specimen. Pores that are 0.3 mm in size or larger decreased when the PRA and fine aggregates of even particle sizes were used. This form of pore reduction was found to have a direct correlation with the improvement of mechanical properties

Structural Topic Model Analysis of Mask-Wearing Issue Using International News Big Data

Media plays an important role in the acquisition of health information worldwide. This was particularly evident in the face of the COVID-19 epidemic. Relatedly, it is practical and desirable for people to wear masks for health, fashion, and religious regions. However, depending on cultural differences, people naturally accept wearing a mask, or they look upon it negatively. In 2020, the COVID-19 pandemic led to widespread mask-wearing mandates worldwide. In the case of COVID-19, wearing a mask is strongly recommended, so by analyzing the news data before and after the spread of the epidemic, it is possible to see how the direction of crisis management is being structured. In particular, by utilizing big data analysis of international news data, discourses around the world can be analyzed more deeply. This study collected and analyzed 58,061 international news items related to mask-wearing from 1 January 2019 to 31 December 2020. The collected dataset was compared before and after the World Health Organization’s pandemic declaration by applying structural topic model analysis. The results revealed that prior to the declaration, issues related to the COVID-19 outbreak were emphasized, but afterward, issues related to movement restrictions, quarantine management, and local economic impacts emerged

Mechanical Properties of Basalt-Based Recycled Aggregate Concrete for Jeju Island

Recycled aggregate is essential to protect Jeju Island’s natural environment, but waste concrete, including porous basalt, is a factor that lowers the quality of recycled aggregate. Therefore, an experiment was conducted to analyze the properties of concrete application of basalt-based recycled aggregate (B-RA) through quality improvement. The absorption of the B-RA ranged from 3–5%; restricting its absorption to less than 3% was challenging owing to its porosity and irregular shape. However, the increase in the solid volume percentage of the concrete when replacing 25 or 50% of fresh basalt aggregate with recycled basalt aggregate improved the mechanical performance of the concrete, especially at 25%, for which a compressive strength of 55.9 MPa and modulus of elasticity of 25.9 GPa exceeded those of concrete with fresh basalt aggregate. Moreover, increasing the replacement ratio of the fresh basalt with recycled aggregate reduced the slump and decreased the air content, consequently increasing the concrete drying shrinkage. However, the replacement of fresh basalt aggregate with recycled basalt aggregate unaltered the mechanical performance of the concrete. The results indicate that efficient use of recycled aggregates can yield superior performance to that of fresh basalt, irrespective of aggregate quality

Rehabilitation of Marine Concrete Structure with Under-Water Hydrodemolition and Sprayed Concrete

Hydrodemolition is a method of surface preparation using high-pressure water jets. Hydrodemolition cutting depth is dependent on the length of time that the water jet is directed at the concrete surface that determines the depth of removal, and contact time is controlled at the robotic cutter. During hydrodemolition concrete removal, the cement matrix is removed from the aggregate. This paper describe on the test results of under-water hydrodemolition which was done on a prefabricated concrete basin. A very simple and economic method for repairing the damaged concrete structures is a using a sprayed concrete, which is some times called as shotcrete. This paper, also, describe on the test results of sprayed concrete for the rehabilitation of marine concrete structure

Rehabilitation of Marine Concrete Structure with Under-Water Hydrodemolition and Sprayed Concrete

Hydrodemolition is a method of surface preparation using high-pressure water jets. Hydrodemolition cutting depth is dependent on the length of time that the water jet is directed at the concrete surface that determines the depth of removal, and contact time is controlled at the robotic cutter. During hydrodemolition concrete removal, the cement matrix is removed from the aggregate. This paper describe on the test results of under-water hydrodemolition which was done on a prefabricated concrete basin. A very simple and economic method for repairing the damaged concrete structures is a using a sprayed concrete, which is some times called as shotcrete. This paper, also, describe on the test results of sprayed concrete for the rehabilitation of marine concrete structure