Light Transmitting Lightweight Concrete with Transparent Plastic Bar

2.1. Overview

This study applied the problem-solving method proposed by TRIZ (theory of solving inventive problem) to resolve the problems of the existing light-transmitting, transparent concrete: costly materials and low constructability [1]. For the first problem, this study substituted existing materials with low-cost transparent materials, and improved the old labor-intensive production process, which involves laying thousands or tens of thousands of optical fibers into concrete, by changing it into a labor-saving production process capable of mass production. To find a creative solution by reducing the gap between the current and desired targets, this study applied ENV (element, name of feature, value of feature), one of the problem-solving models proposed by TRIZ. The ENV model consists of the elements, name of feature, value of feature (the current target, and the desired target) as shown in Table 1. First, the elements were divided into the material property, material type, manufacturing method and economy. The names of feature were light transparent, working hours, arrangement and production method. The existing costly optical fiber transparent material can be replaced with low-cost transparent and straight type of materials such as plastic fiber, glass, or acrylic. The existing connecting materials were replaced with an external multi-porous mold to improve the construction process from a labor-intensive process to a labor-saving one. The production system was also improved into a system capable of mass production, where an integral production system produces a long shape with an even thickness, which can be divided into the desired sizes.

2.2. Materials Used

For the experiment, the ordinary Portland cement (type 1) was used. The physical properties of the cement satisfy the KS L 5201 specifications. The specific gravity of the fine aggregates is 2.58 g/cm³, the absorption rate is 1.5%. Coarse aggregates were not used to fill the inside of the transparent materials due to construction issues. 10 mm steel fibers were applied to 0.5% of the overall volume. Acrylic pipes and rods were applied as shown in Fig. (1) to secure transparency for the cement concrete block matrix and to greatly improve the constructability using their straight shapes. The existing optical fiber offers superb light transmission but involves a serious amount of labor and cost increase for arranging thousands or tens of thousands of bent fibers in one direction within the cement or concrete matrix. Light-transmitting and straight plastic materials, however, can be arranged in a matrix with a smaller workforce in a shorter time. The diameter of the materials that were used varied from 3 to 10 mm, and the types that were applied included hollow pipes.

2.3. Experiment Design

In the experiment, the design of the mix proportion was done by excluding coarse aggregates to prevent the fiber balling phenomenon and problems in construction due to the narrow gap of the transparent materials in the process of pouring high-fluidity concrete inside the block. The concrete mix design is summarized in the Table 2 below. The materials that are used are made by mixing cement, ground granulated blast slag (GGBS), fine aggregates (FA), steel fiber (10 mm), super-plasticizer and transparent materials (acrylic). With a mix of 38% W/C, 3% air, 0.5% steel fiber, and up to 2% super-plasticizer (SP), high-fluidity concrete was produced and poured.

2.4. Production Process

The production process of light-transmitting concrete block is shown in the following Fig. (2). First, low-cost acrylic rod or pipe for securing transparency is prepared, with 110 mm lengths. The outside of the mold is drilled to make various-sized holes (3, 5, and 10 mm) in stainless steel. The distance between the holes is the same as the size of the hole. The size and number of holes are important factors that determine the constructability and economic efficiency of the project, and the degree of light transmission is determined depending on the number of holes. The advantages of the external-type mold are that it can be reused as it is prefabricated by the outside partner and requires no intricate operations for the arrangement of the optical fibers in a line after adjusting each fiber and connecting it to the holes. In addition, there is no need to widen the surface area by heating the end of the optical fiber, as in the case of optical fiber [7]. In the prepared mold as shown in Fig. (3), cement, water, fine aggregates, steel fiber and super-plasticizer were mixed with high fluidity (about 70 cm as a result of the flow test) and were placed inside the mold, into which a transparent material was inserted, and then the mold was hammered lightly with a rubber mallet so that the mold would be filled with the concrete. The prototype was completed by cutting it with the desired thickness after proceeding with underwater curing for 28 days by removing the mold after room curing for at least 24 hours in the mixing process.

2.5. Results

The results of the observation of the changes in the color of luminous concrete due to the emission of light are shown in Fig. (4). The space was filled using the concrete after the arrangement of the transparent materials in one direction. The transmission of light was found to be superior in all the materials and diameters. In particular, the smaller the diameter of the transparent material is, the more excellent the permeation degree of the object caused by the transmission of light, due to the dense array of small light sources. In addition, it was found that although as the diameter becomes larger a huge amount of light can be transmitted due to the greater light source, the accuracy of the object tends to be lower. Fig. (5) shows the transmission effects caused by the external object. When held up before the light prior to processing the concrete, the shape of the person was clearly shown behind the concrete block, which indicates that the object blocked the external light, thereby preventing the transmission of light, and the outline of the object appeared. Fig. (5) also shows that the results of the observation of the transmission of light after the concrete were cut into 50mm pieces using a concrete saw cutting machine. After processing, the light transmission effect was further enhanced, and the effect of seeing through the external object was significantly improved as well.

2.6. Problem

As concrete structures become larger and higher, the heavy dead load of the structure becomes one of the defects. Accordingly, there is a need to reduce the weight of the structure while maintaining the mechanical performance to decrease the dead load and to improve the constructability when applied to the structure. The light-transmitting concrete block with enhanced constructability and economic efficiency was produced by utilizing materials that transmit light, but critical problems were found in the process of transmitting light using the prototype. It is expected that if ordinary concrete materials are used, difficulties will arise in the materials preparation, transportation, and processing processes. In particular, as the labor force and time required after the production of large concrete locks is expected to increase in the transporting and processing processes, these problems need to be solved before the field application in the future. To solve the problems that occur in the relatively complicated manufacturing and processing steps, and to secure more practical technologies, this study sought to further investigate methods of ensuring the mass production and ease of production through lightweight concrete placement by applying lightweight aggregates and a lightweight foaming agent in ordinary concrete with a large unit weight [12].

3.1. Materials Used

In the experiment, ordinary Portland cement (type 1) as before mentioned was used. The physical properties of the used cement meet the KS L 5201 specifications. The specific gravity of the fine aggregates is 2.58 g/cm³, the absorption rate is 1.5%. The steel fiber with a 10 mm length was used to enhance the crack resistance in the transverse direction by applying 0.5% of the total volume. Fly ash artificial lightweight aggregates were purchased from S Company and were used in the experiment. The maximum aggregate size was 10 mm, and the physical properties of the aggregates that were used in the experiment are summarized in Table 3. To secure transparency in the matrix of the cement-concrete block, acrylic pipes and rods were also applied.

3.2. Experiment Design

In the experiment, the design of the mix proportion was done by limiting the maximum dimension of the coarse aggregates to 10 mm to prevent problems in construction due to the narrow gap of the transparent materials in the process of pouring high-fluidity, artificial, light weight aggregate concrete inside the block. The concrete mix design is summarized in the following Table 4. The materials that were used are made by mixing cement, fine aggregates, artificial lightweight aggregates (LWA), steel fiber (10 mm), super-plasticizer, and transparent materials (acrylic rods and pipes with 5 mm size). With a mix of 33% W/B, 4.5% air, 0.5% steel fiber, and up to 2% super-plasticizer (SP), fluidity lightweight aggregate concrete was produced for placement.

3.3. Mixture and Production

The production process of light-transmitting concrete block is shown in the following Fig. (6). First, low-cost acrylic rods and pipes for securing transparency are prepared. In the artificial lightweight aggregate concrete, a mold (size-200×300×500 mm, distance between holes-20mm) made of stainless steel is prepared to fabricate several specimens with different thicknesses using a cutter. The outer side of the mold is fixed with the use of strong adhesive tape after connecting rods or pipes made of various materials to prevent the rod from shaking. The advantage of the external-type mold is that it can be reused several times as it is prefabricated by the outside partner.

In the mold with which acrylic rods and pipes are connected, cement, water, fine aggregates, artificial lightweight aggregates, steel fiber, and super-plasticizer are mixed with high fluidity (about 60 cm as a result of the flow test) and are placed inside the mold into which a transparent material is inserted, and then the mold is hammered lightly with a rubber mallet so that the mold would be filled with the concrete. The prototype was completed by cutting it with the desired thickness after proceeding with underwater curing for 28 days by removing the mold after room curing for at least 24 hours in the mixing process.

4.1. Materials Used

As a foaming agent, Alcohol Ethoxy Sulfate (AES) consisting of anionic surfactants widely used in South Korea was applied (Table 5). To secure transparency in the matrix of the cement-concrete block, acrylic pipes and rods were applied. In the prototype that was produced earlier, transparent materials that ensure higher applicability in the field were applied considering the constructability and economic efficiency. Acrylic rod and pipe with 5 mm size were applied.

4.2. Experiment Design

The lightweight foamed concrete mixture design is summarized in Table 6. The level of volume equal to the amount of the powder was applied to the foaming agent. The materials that were used were made by mixing cement, fine aggregates, a foaming agent, and transparent materials (acrylic rods and pipes). The foaming agent was applied to the concrete using a pre-foaming method. The foam was made using a foaming machine after pouring foaming agent diluting fluid with the use of a method for extruding air. The status of the foam (spherical type) was checked prior to being put into the concrete sludge.

4.3. Mixture Production

The production process of lightweight foamed concrete block following almost same procedure is shown in the following Fig. (7). In the mold with which acrylic rods and pipes are connected, high-fluidity foamed concrete as shown in Fig. (7) is placed inside the mold into which a transparent material is inserted, and then the mold is lightly hammered with a rubber mallet so that the mold would be filled with the concrete. The prototype was completed by cutting it with same procedure mentioned above lightweight aggregate applied specimen.

5.1. Unit Weight

The results of the comparison of the unit weights of the fresh-concrete statuses in Fig. (8) revealed that the unit weights of the lightweight aggregates and of the lightweight foamed concrete were much lower than that of ordinary concrete, and especially, the unit weight of lightweight foamed concrete was about half that of lightweight aggregate concrete. This suggests that due to the effects of the foaming agent and lightweight aggregates, a lighter unit weight contributes to easier production in the commercialization phase, and to superior constructability in the field.

5.2. Compressive Strength

The compressive strength test results are summarized in the following Fig. (9). In the case of the lightweight aggregate concrete specimen, the distribution statuses of the aggregates and of steel fiber were confirmed after surface grinding, and the compressive strength was found to be 18.2 MPa, which is significantly lower than that of the specimen to which ordinary concrete was applied. The formation of numerous foams was found on the surface of the lightweight foamed concrete specimen, and the compressive strength was 4.6 MPa.

5.3. Effects of the Light-Transmitting Lightweight Concrete

The following Fig. (10) shows the transmission of light by cutting the 300x500mm specimen into a 50-mm-thick piece after applying lightweight aggregates and foaming agent. The light transmission is clearly identified, as shown in the figure. There are any no differences between products except for materials used for reducing unit weight. The effect of light transmission is the same due to the same transparent materials used. In particular, as the diameter of the transparent rod or pipe becomes larger, the surface area of the entire concrete becomes greater, and the light transmission becomes higher. As the light source becomes larger, however, the representation of the object may not be as detailed as it should be.

5.4. Various Visual Effects of the Light Emotion Friendly Concrete

The light emotion friendly concrete (LEFC) named by author can have a variety of aesthetic effects by being applied to inorganic concrete with the use of transparent plastic-based rods or pipes. LEFC is the name of the technology applied in this study, an abbreviated form of “light-transmitting, emotion-friendly concrete.” In addition, it is possible to deliver a strong message by mixing transparent materials of various sizes and representing letters as shown in Fig. (11).