Self-sensing grout composition

Abstract

A self-sensing grout composition according to various embodiments of the present invention comprises a binder and an aggregate, wherein the binder includes cement and a polymer, and the polymer includes any one selected from the group consisting of blast furnace slag (BFS), fly ash (FA), and ultra fine fly ash (UFFA).

Description

Self-sensing grout composition

[0001] Various embodiments of the present invention relate to a self-sensing grout composition. Specifically, the present invention relates to a grout composition imparted with self-sensing properties by incorporating homogeneously dispersed carbon nanotubes.

[0002] The recent string of collapses of newly constructed buildings in Korea has led to growing public concern about safety. Building collapses are caused by a variety of factors, including material, construction, and structural issues. These incidents have also prompted a review of the safety of existing buildings. Building safety assessments are complex, diverse, and time-consuming. Therefore, active research is underway on equipping structures with magnetic sensing capabilities to enable immediate assessment. However, research on sensing technologies for reinforced structural members remains limited.

[0003] Carbon nanotubes (CNTs), a representative material used for magnetic sensing, have demonstrated their performance in numerous studies. However, they struggle to achieve uniform dispersion within cement composites, resulting in degraded mechanical performance. To address this issue, some research proposes CNT solutions using dispersants and ultrasound. However, these solutions have limited mass applicability and pose significant challenges for their application to reinforced dry cement mortars.

[0004] Furthermore, the construction industry is currently conducting extensive research to achieve carbon emission reduction goals, and efforts are being made to actively utilize cement substitutes to curb carbon emissions by reducing cement unit usage. Current target cement substitutes include blast furnace slag (BFS) and fly ash (FA). These two materials, byproducts of the steel and power generation industries, have the advantage of enhancing the long-term strength of cement composites. However, because the amount of cement substituted decreases proportionally to the amount of cement, only about 10-20% of the total powder is used due to the problem of reduced initial strength. Therefore, technology for mass utilization of binders is needed in the cement industry to reduce carbon emissions.

[0005] Meanwhile, for damage-sensitive grouts for precast concrete slab tracks (PST), typical ballasted tracks transmit train loads to the ground through sleepers and ballast beds. Ballasted tracks undergo plastic deformation due to crushing and wear of the ballast layer during repeated train passages, requiring periodic maintenance to ensure smooth operation.

[0006] Precast slab track (PST) has many advantages in terms of quality control and constructability, and its construction cases are increasing. However, the grout filled to integrate the PST and the base layer has the problem that cracks and brittle fractures occur due to vibration when a train passes after hardening.

[0007] In various embodiments of the present invention, it is intended to provide a magnetically sensitive grout composition having improved performance of a structural member and excellent magnetic sensing performance.

[0008] A self-sensing grout composition according to various embodiments of the present invention comprises a binder and an aggregate, wherein the binder comprises cement and a polymer, and the polymer comprises any one selected from the group consisting of blast furnace slag (BFS), fly ash (FA), and ultra fine fly ash (UFFA).

[0009] The self-sensing grout composition according to various embodiments of the present invention comprises a powder-type carbon nanomaterial, thereby preventing cracking due to long-term vibration and load applied from above, and simultaneously detecting and providing load and damage information to enhance maintenance performance. Furthermore, by utilizing a high-powder thermal power generation byproduct as part of the powder, fluidity, one of the key properties of the grout material, can be improved, while simultaneously securing compressive strength.

[0010] Figure 1 is a photograph showing the shape of a binder.

[0011] Figure 2 is a photograph showing the particle sizes of silica and S-CNT.

[0012] FIG. 3 is a schematic diagram illustrating a process for manufacturing carbon nanotubes impregnated in zeolite according to various embodiments of the present invention.

[0013] Figure 4 (a) is an SEM image of a carbon nanotube, and (b) is an SEM image of a carbon nanotube impregnated in zeolite.

[0014] Figure 5 is a photograph related to a test method for the flow time, flow, and rheology of uncured grout.

[0015] Figure 6 is a photograph related to a method for measuring the compressive and flexural strength of hardened grout and a method for measuring electrical properties.

[0016] Figure 7 shows the flow measurement results and the flow time.

[0017] Figure 8 shows the relationship between shear stress and shear stress rate, and shows the yield value and plastic viscosity using the Bingham model.

[0018] Figure 9 shows the results of compressive strength measurement.

[0019] Figure 10 shows the results of bending strength measurement.

[0020] Figure 11 shows the SEM observation results at 3 and 28 days of age.

[0021] Figure 12 shows the mass reduction rate of calcium hydroxide relative to the total mass through TG / DSC analysis.

[0022] Figure 13 shows the XRD analysis results of a test piece manufactured at the paste level at ages of 3 and 28 days.

[0023] Figure 14 shows the change rate of electrical resistance according to the compressive load of the self-sensing grout.

[0024] Below, various embodiments of this document are described. The embodiments and terminology used herein are not intended to limit the technology described in this document to specific embodiments, but rather to encompass various modifications, equivalents, and / or alternatives of the embodiments.

[0025]

[0026] Hereinafter, the present invention will be described in detail as follows.

[0027] The self-sensing grout composition according to various embodiments of the present invention is a filling grout composition that detects load and damage information to prevent cracking and improve maintenance performance due to long-term vibration and load applied on the top of a concrete track. The grout composition according to various embodiments of the present invention can be used as a self-sensing repair material, which is a sensing material for monitoring structural members. That is, the stress burden situation of a cross-section that has been added can be estimated using the grout composition of the present invention.

[0028] Specifically, the grout composition according to various embodiments of the present invention includes a binder and an aggregate, and the binder includes cement and a polymer.

[0029] The cement may be at least one selected from the group consisting of portland cement, sulfuric acid-resistant cement, high-early strength cement, ultra-early strength cement, MDF cement, DSP cement, densitized cement, pyrite cement, calcium aluminate cement, plaster, silicate cement, gypsum cement, phosphate cement, high alumina cement, ultrafine cement, slag cement, magnesium oxychloride cement, rapid-hardening cement, alumina cement, and microcement.

[0030] The polymer is characterized in that it comprises any one selected from the group consisting of blast furnace slag (BFS), fly ash (FA), and ultra fine fly ash (UFFA). Preferably, the polymer may be ultra fine fly ash.

[0031] The medium particle size of the polymer may be from 1 μm to 20 μm. Preferably, the medium particle size of the polymer may be from 1 μm to 5 μm.

[0032] The polymer can be mixed in an amount of 30 to 40 mass% relative to the total mass of the binder. This mass ratio ensures the fluidity, compressive strength, and shrinkage-free performance of the grout composition.

[0033] Meanwhile, the binder is mixed with water, and the weight ratio of water / binder can be 10 to 40%.

[0034] The aggregate is characterized by including carbon nanotubes (CNTs). Here, the carbon nanotubes may be characterized by being impregnated into a porous material. At this time, the pore diameter of the porous material may be 0.3 to 2 nm, and the carbon nanotubes may have a diameter of 1 to 2 nm. The carbon nanotubes may be incorporated into the porous material in the form of a powder impregnated into the porous material. At this time, the powder diameter may be 0.1 mm to 0.3 mm. Specifically, the carbon nanotubes may be attached to the surface without being inserted into the nano-pores of the porous material. This allows the carbon nanotubes to be homogeneously dispersed within the grout.

[0035] The porous material may be characterized by at least one selected from the group consisting of zeolite, activated carbon, silica, bentonite, alumina, silicon carbide, zirconia, and fly ash. Preferably, the porous material may be zeolite.

[0036] The carbon nanotube may be a multi-walled carbon nanotube (multi-walled CNT, MWCNT).

[0037] Carbon nanotubes impregnated in a porous material can be manufactured as follows. First, the porous material and the MWCNT dispersion are stirred and then dried in a chamber maintained at a temperature of 50 to 70°C for 24 to 60 hours. The dried sample is then pulverized and passed through a 0.10 to 0.20 mm sieve. Through this, a material can be manufactured in which the carbon nanotubes are attached to the surface of the porous material rather than inserted into the pores. This is believed to be because the pore sizes of the porous material and the CNT particle sizes are not similarly inserted at the nanoscale. It is believed that even though the CNTs are attached to the porous material, the hydrophilic porous material is homogeneously dispersed within the grout, thereby ensuring the dispersibility of the CNTs.

[0038] Meanwhile, the aggregate may further include at least one of silica sand, colored sand, calcium carbonate, dolomite, and glass powder. The aggregate may include two or more types of aggregates having different particle sizes. For example, when the aggregate includes silica sand, the silica sand may include silica sand having different particle sizes. Specifically, the silica sand may include 5 to 9 wt% of particles having a particle size of 0.1 to 0.3 mm, 35 to 45 wt% of particles having a particle size of 0.8 to 1.7 mm, and 45 to 55 wt% of particles having a particle size of 1.7 to 1.9 mm, based on the total weight of the aggregate.

[0039] Carbon nanotubes may be included in an amount of 1 to 5 mass% of the total mass of the aggregate. Silica sand and carbon nanotubes may be mixed in a mass ratio of 96:4 to 98:2.

[0040] The binder and aggregate may be included in a mass ratio of 0.5:1 to 1:3. Preferably, the binder and aggregate may be included in a mass ratio of 1:1.

[0041] Meanwhile, the grout composition according to various embodiments of the present invention may further include a fluidizing agent. The fluidizing agent may be a polycarboxylic acid-based powder fluidizing agent used as an admixture to improve the fluidity of the repair mortar.

[0042]

[0043] The self-sensing grout composition according to various embodiments of the present invention comprises a powder-type carbon nanomaterial, thereby preventing cracking due to long-term vibration and load applied from above, and simultaneously detecting and providing load and damage information to enhance maintenance performance. Furthermore, by utilizing a high-powder thermal power generation byproduct as part of the powder, fluidity, one of the key properties of the grout material, can be improved, while simultaneously securing compressive strength.

[0044]

[0045] Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are intended only to illustrate the present invention and are not intended to limit the present invention.

[0046]

[0047] Example

[0048] The experimental plan for evaluating the performance of the self-sensing grout is as shown in Table 1 below, and the mixing specifications are as shown in Table 2. First, the weight ratio of water / binder (W / B) was set to 34%, and the ratio of binder (B) to aggregate (S) was set to 1:1 by mass. Three types of polymers were used for low-cement, BFS, FA, and UFFA, and 40% of the total binder mass was substituted.

[0049] To evaluate the flow characteristics of the uncured grout, the flow, flow time, and rheological properties were measured. For the cured grout, the flexural and compressive strengths were measured at 3, 7, and 28 days. For the microscopic characteristics, TG / DSC analysis was performed at 3, 7, and 28 days, and XRD and SEM analysis were performed at 3 and 28 days. For the electrical resistance characteristics, the electrical resistance and deformation until compressive failure were measured.

[0050]

[0051] Experimental factors Experimental level W / B (%) 134 B : S 11 : 1 Polymer type 3 BFS, FA, UFFA Polymer mixing ratio (%) 20, 40 Experimental details Uncured state 3 Flow time (sec) Flow experiment (mm) Rheology experiment Cured state 3 Mechanical properties Bending and compressive strength (3, 7, 28 days) Microscopic properties Thermogravimetric analysis (3, 7, 28 days) X-ray diffraction analysis (3, 28 days) Scanning electron microscope (3, 28 days) Electrical properties Under compressive load (28 days)

[0052]

[0053] SpecW / B(%)Binder(%)Sand(%)Ad(%)OPCBFSFAUFFASilicaSandS-CNTOPC3410000010001.2C-OPC100000973C-BFS604000973C-FA600400973C-UFFA600040973

[0054]

[0055] The cement used in the experiment was Ordinary Portland Cement (OPC) from domestic H Company, and the blast furnace slag powder used in the experiment was three types of blast furnace slag powder from domestic H Company that were suitable for KS F 2563 (concrete blast furnace slag powder), and the fly ash was two types of fly ash from domestic S Company that were suitable for KS L 5405 (fly ash). In addition, the fine fly ash was generated from the coal gasification combined cycle power plant of domestic S Power Company. The physical and chemical properties of the polymers are as shown in Table 3, and the particle shapes of each BFS, FA, and UFFA are as shown in Fig. 1.

[0056] SpecPhysical propertiesChemical propertiesMedian particle size(㎛)Blain(cm) 2 / g)SiO2(%)CaO(%)Al2O3(%)Fe2O3(%)BFS12.34,14430.941.414.00.4FA14.53,36150.04.219.04.6UFFA3.015,36555.17.816.74.9

[0057]

[0058] The silica sand used in the experiment as aggregate was silica sand from domestic company K, and the particle size is as shown in Table 4. The CNT used in the experiment to provide magnetic sensing performance was Multi-Walled CNT (MWCNT) from Russian company O. To ensure homogeneous dispersion of CNT in the repair mortar, a dispersion liquid was used to impregnate the porous powder with CNT.

[0059] Silica sand (%)S-CNT (%)1.8 mm0.9 mm0.15 mm0.15 mm504073

[0060]

[0061] Specifically, in order to secure homogeneous dispersion of CNTs within the grout, CNTs were inserted into the nano-pores of the zeolite porous material. The insertion process was as shown in Fig. 3, in which the zeolite and MWCNT dispersions were stirred and dried in a chamber maintained at a temperature of 60°C for 48 hours. The dried sample was then pulverized and passed through a 0.15 mm sieve to produce a sample. Fig. 4 a) is an SEM image of MWCNTs, showing that the CNTs were clumped together like threads by van der Waals forces. However, referring to Fig. 4 b), the CNTs (S-CNTs) impregnated into the porous material zeolite were not inserted into the pores of the zeolite, but were attached to the surface. This is believed to be because the pore sizes of the porous material and the CNT particle sizes are both nano-sized and not inserted in a similar size. However, it is believed that the hydrophilic porous material is homogeneously dispersed within the grout even though CNTs are attached to the porous material, thereby ensuring the dispersibility of the CNTs.

[0062]

[0063] Experimental Method 1: Unhardened Grout

[0064] The flow time of the self-sensing grout was measured by filling a funnel-shaped tester with uncured grout as shown in a) of Fig. 5 in accordance with KS F 4044 (hydraulic cement non-shrinkage grout) and measuring the time from the time when the uncured grout was discharged from the outlet until the first break in the flowing grout.

[0065] The flow test was conducted in accordance with KS F 2476 (Testing method for polymer cement mortar) using a flow cone as shown in Fig. 5 b) and vertically lifting the flow cone without compaction or dropping motion, and the diameter of the grout spread was measured in the maximum direction and in the direction perpendicular thereto. The rheology test was conducted using a Brookiled R / S solids type rheometer as shown in Fig. 5 c) to measure the rheological constant.

[0066]

[0067] Experimental Method 2: Hardened Grout

[0068] To evaluate the mechanical properties of the self-sensing grout, the bending and compressive strength were measured in accordance with KS F 2476 (Test method for polymer cement mortar), and the grout was manufactured in a size of (40×40×160) mm as shown in a) of Fig. 6. After demolding, curing under water was performed in a water tank maintained at (20±2) ℃, and the bending strength was measured at a specified age, and the compressive strength was measured using a split specimen.

[0069] In order to analyze the relationship between electrical resistance and deformation under compressive load conditions, a circular test specimen of (Φ50±100) mm was manufactured as shown in b) of Fig. 6, and then removed from the mold and cured underwater in a water tank maintained at (20±2) ℃ for 28 days. After drying for 24 hours at a temperature of (50±2) ℃, electrodes and strain gauges were attached to the test specimen and the electrical resistance and deformation were measured. At this time, the rate of change in electrical resistance was calculated based on the following equation.

[0070] △R= (R1-R0) / R0x 100

[0071] Here, △R: electrical resistance change rate (FCR(%))

[0072] R1: Resistance measured when loading

[0073] R0: Resistance before loading

[0074]

[0075] Experimental Method 3: Microanalysis

[0076] Microscopic analysis of self-sensing grout was performed by manufacturing a paste with a W / B of 34% into a size of (20×20) mm, crushing it at a predetermined age, and passing the powder through a 0.15 mm sieve, drying it at a temperature of (50±2) ℃ for 24 hours, and then performing XRD, TG / DSC, and SEM analyses. For TG / DSC analysis, the crushed sample was placed in an aluminum pan and heated to 1000 ℃ at a heating rate of 5 ℃ / min, and then the hydrate content was analyzed.

[0077]

[0078] Experimental Results 1: Characteristics of Unhardened Grout

[0079] Figure 7 shows the flow time and flow measurement results. The flow time measurement results were 23.5 seconds for OPC, 22.2 seconds for C-OPC, 33.5 seconds for C-BFS, 38.1 seconds for C-FA, and 10.7 seconds for C-UFFA. This is the 15,000 cm of UFFA. 2 It is judged that the fluidity increased due to the high powderiness of over / g and the spherical particle shape. The time to reach 300 mm of flow showed a similar trend to the flow time, with UFFA being the fastest at 1.6 seconds and FA being the slowest at 9.8 seconds. Figure 8 shows the relationship between shear stress and shear stress rate, and shows the yield value and plastic viscosity using the Bingham model. OPC and C-OPC showed a large yield stress of over 20 Pa, whereas BFS showed 2.0 Pa, FA showed 1.2 Pa, and UFFA's yield stress value converged to 0 depending on the polymer mixing. In addition, the plastic viscosity showed a value of 7~8 Pa·s, but UFFA showed a value of 4.8 Pa·s. It is judged that this showed excellent fluidity even when the same amount of Ad agent (superplasticizer as a plasticizer) was added due to the fineness.

[0080]

[0081] Experimental Results 2: Properties of Hardened Grout

[0082] 1) Strength characteristics

[0083] The strength characteristics of the self-sensing grout are shown in Figs. 9 and 10. First, the specimens containing S-CNT exhibited slightly higher compressive strengths than OPC throughout the curing period, similar to previous research results. At 3 days, BFS, FA, and UFFA were measured to be 31.1 MPa, 20.7 MPa, and 29.7 MPa, respectively, which were lower than OPC's 34.8 MPa. However, C-BFS and C-UFFA exhibited higher strengths than OPC from 7 days onward, and in particular, UFFA showed a 52% increase over OPC, reaching 53.5 MPa. Meanwhile, the flexural strength results showed a different trend from the compressive strength. At 3 days, C-UFFA, not C-OPC, showed the highest strength of 6.5 MPa. In addition, at 7 days, OPC showed the highest strength at 7.9 MPa, and at 28 days, C-UFFA showed the greatest strength at 10.2 MPa in the mixture containing UFFA. This is due to the filling effect and improved reactivity of the high-powder UFFA, and it is believed that the strength was increased by filling the pores of the test specimen due to UFFA, which will be able to solve the problem of low initial strength of existing binders.

[0084] 2) Scanning electron microscope (SEM) observation

[0085] Figure 11 shows the SEM observation results at 3 and 28 days of curing. In the case of 3 days of curing, as in Figures 11 a) and 11 c), in the case of the test specimens containing BFS and FA, a large amount of polymer was observed on the upper part of the hardened cement, but as shown in Figure 11 e), in the case of UFFA, a large amount of hydration products were observed around it. In the case of 28 days of curing, as in Figure 11 d), in the case of the test specimen containing FA, a large amount of pores were observed, but in the case of Figure 11 f), due to the high fineness of UFFA, the pores were filled and the polymer was observed to be homogeneously dispersed in the cement layer.

[0086] 3) Thermogravimetric analysis (TG / DSC)

[0087] Figure 12 shows the mass reduction rate of calcium hydroxide relative to the total mass through TG / DSC analysis. In the case of 7 days, C-UFFA and C-BFS showed a decrease in calcium hydroxide compared to 3 days, which is believed to be due to the latent hydraulicity of BFS and the pozzolanic reaction of UFFA. Compared to UFFA, FA showed a slower pozzolanic reaction, and it was confirmed that calcium hydroxide decreased after 7 days, which can be confirmed that the pozzolanic reaction was promoted by the high-powder UFFA, so that calcium hydroxide consumption progressed faster than that of FA.

[0088] 4) X-ray diffraction analysis (XRD)

[0089] Figure 13 shows the XRD analysis results of the test pieces manufactured at the paste level at 3 and 28 days. Portlandite (CH), a hydration product, was detected, and a decrease in portlandite was observed at 28 days for C-BFS, C-FA, and C-UFFA. In the case of C-BFS, the decrease in portlandite is thought to be due to latent hydraulicity, and in the cases of FA and UFFA, the decrease in portlandite is thought to be due to the pozzolanic reaction. In the case of C-UFFA, it was confirmed that portlandite was reduced more than in C-FA, and this is thought to be because the pozzolanic reaction was promoted at 3 days due to the higher fineness of UFFA than FA.

[0090] 5) Electrical characteristics

[0091] Figure 14 shows the electrical resistance change rate according to the compressive load of the self-sensing grout. In the case of C-OPC, deformation increased with the compressive load, and the electrical resistance change rate showed a tendency to decrease. This is believed to be due to the narrowing of the distance between the CNT networks within the specimen under the compressive load, which actively occurs electrical conduction and changes the electrical resistance. In contrast, the polymer-substituted specimen showed no significant change in the electrical resistance change rate.

[0092]

[0093] The features, structures, effects, etc. described in the above-described embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to just one embodiment. Furthermore, the features, structures, effects, etc. exemplified in each embodiment can be combined or modified in other embodiments by those skilled in the art to which the embodiments pertain. Therefore, the contents related to such combinations and modifications should be construed as falling within the scope of the present invention.

[0094] In addition, although the above description focuses on embodiments, these are merely examples and do not limit the present invention. Those skilled in the art to which the present invention pertains will appreciate that various modifications and applications not exemplified above are possible without departing from the essential characteristics of the present embodiments. For example, each component specifically shown in the embodiments can be modified and implemented. In addition, differences related to such modifications and applications should be interpreted as being included within the scope of the present invention defined in the appended claims.

Claims

1. Contains binders and aggregates, The above binder comprises cement and polymer, A grout composition, characterized in that the polymer comprises any one selected from the group consisting of blast furnace slag (BFS), fly ash (FA), and ultra fine fly ash (UFFA).

2. In paragraph 1, A grout composition, characterized in that the polymer is contained in an amount of 30 to 50 wt% based on the total weight of the binder.

3. In paragraph 1, A grout composition, characterized in that the medium particle size of the polymer is 1 μm to 20 μm.

4. In paragraph 1, A grout composition, characterized in that the aggregate comprises carbon nanotubes (CNT) impregnated in a porous powder.

5. In paragraph 4, A grout composition, characterized in that the porous powder is at least one selected from the group consisting of zeolite, activated carbon, silica, bentonite, alumina, silicon carbide, zirconia, and fly ash.

6. In paragraph 4, A grout composition, characterized in that the carbon nanotube is a multi-walled carbon nanotube (multi-walled CNT, MWCNT).

7. In paragraph 4, A grout composition, characterized in that the carbon nanotubes are contained in an amount of 1 to 5% of the total mass of the aggregate.

8. In paragraph 1, A grout composition, characterized in that the above binder and aggregate are included in a mass ratio of 0.5:1 to 1:

3.

9. In paragraph 1, A grout composition, characterized in that the aggregate further contains silica sand.

10. In paragraph 9, The above silica is, with respect to the total weight % of the above aggregate, Containing 5 to 9 wt% of particles having a particle size of 0.1 to 0.3 mm, Containing 35 to 45 wt% of particles having a particle size of 0.8 to 1.7 mm, A grout composition characterized by containing 45 to 55 wt% of particles having a particle size of 1.7 to 1.9 mm.

Images