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An experimental study was conducted to examine the performance of self-sensing grout with a large amount of ultra-high powder fly ash. By substituting equal amounts of blast furnace slag fine powder and fly ash, which are representative industrial by-products, the flow properties of unhardened grout, compressive strength, length change rate, and electrical properties were evaluated. As a result, when replacing ultra-high powder fly ash, the plastic viscosity was significantly lowered and fluidity was improved. The compressive strength was also higher from the initial age than plain. Finally, the relationships between FCR-Stress and FCR-Strain were similar in electrical characteristics

Lee, Gun-Cheol

Kim, Jae-Yup

Kim, Young-Min

Im, Geon-Woo

CCC 2024 Proceedings of the Creative Construction Conference (2024)  
Edited by: Miroslaw J. Skibniewski & Miklós Hajdu  
https://doi.org/10.3311/CCC2024-112 
 
EFFECT OF FUNCTIONAL RECYCLED MATERIALS ON SELF-
SENSING GROUT MATERIAL 
Gun-Cheol Lee 1 Jae-Yup Kim 2 , Young-Min Kim 3, Geon-Woo Im 4 
1 Korea National University of Transportation, Chungju-Si, Republic of Korea, (gclee@ut.ac.kr) 
2 Korea National University of Transportation, Chungju-Si, Republic of Korea, (kimjy67@ut.ac.kr) 
3 Korea National University of Transportation, Chungju-Si, Republic of Korea, (imkym97@ut.ac.kr) 
4 Korea National University of Transportation, Chungju-Si, Republic of Korea, (lkw1284@naver.com) 
 
 
Abstract 
An experimental study was conducted to examine the performance of self-sensing grout with a large 
amount of ultra-high powder fly ash. By substituting equal amounts of blast furnace slag fine powder 
and fly ash, which are representative industrial by-products, the flow properties of unhardened grout, 
compressive strength, length change rate, and electrical properties were evaluated. As a result, when 
replacing ultra-high powder fly ash, the plastic viscosity was significantly lowered and fluidity was 
improved. The compressive strength was also higher from the initial age than plain. Finally, the 
relationships between FCR-Stress and FCR-Strain were similar in electrical characteristics. 
© 2024 The Authors. Published by Budapest University of Technology and Economics & Diamond Congress Ltd. 
Peer-review under responsibility of the scientific committee of the Creative Construction Conference 
2024. 
Keywords: grout, ultra high volume fly ash, self-sensing, carbon nano tube 
1. Introduction 
The section enlargement method is used to increase the internal forces of structural compression 
members. The section enlargement method places reinforcing bars around an existing column and then 
pours grout into the upper art after formwork construction, when the injection part is narrow, and the 
pouring height is deep. In these conditions, admixtures are generally added to ensure the fluidity of 
reinforcement materials for airtight placement. However, since an excessive use of admixtures results 
in problems with material segregation between grout components and delay in setting, it is necessary 
to minimize the use of admixtures and to then examine materials for fluidity improvement. In addition, 
because the load sharing of the enlarged section is limited to verification via structural calculation and 
modelling, health monitoring techniques are required for members after the section enlargement. 
Carbon nanotubes (CNTs) are used in research during real-time safety evaluations using electrical 
signals in structural members with a self-sensing capacity. However, when incorporated into 
cementitious composites, voids are created due to van der Waals forces, causing a decrease in 
mechanical performance [1]. Accordingly, the authors proposed S-CNT impregnated with porous 
material and CNT and applied it as a repair mortar to investigate mechanical performance due to 
improved CNT dispersion and to identify the self-sensing performance of a compression specimen with 
an enlarged section [2].  Therefore, this study seeks to examine the electrical properties of high flow 
self-sensing grout in which a large amount of cement is replaced with UFFA (Ultra High-Volume Fly Ash) 
and FA in self-sensing grout incorporated with S-CNT to reduce the use of admixtures under fluidity and 
compressive load conditions. 
2. Experiment plan and method 
2.1. Experiment plan 
The experiment plan to evaluate the performance of self-sensing grout is summarized in Table 1, and 
the mixture proportions of grout are shown in Table 2. As shown in Table 1, W/B was set to 34 %, and 
the ratio of powder binder(B): silica sand(S) was set to 1:1 in the mass ratio. Two types of by-products, 
FA and UFFA, were used as cement substitutes, and the replacement ratio was 40% of the total power 
mass. Regarding the flow characteristics, flow and outflow time were measured. For the mechanical 
performance, the compressive strength was measured at 3, 7, 28, and 91 days of age. With respect to 
electrical properties, electrical resistance and strain until compression failure were measured to analyse 
correlation. 
Table 1. Experiment plan. 
Factors Level 
Mixtures 
W/B (%) 1 34 
Binder type 3 OPC, FA, UFFA 
Binder compositions (%) 2 0, 40 
S-CNT/Sand composition (%) 1 3% 
Experiment 
Fresh grout 2 
Flow 
Outflow time 
Hardened grout 2 
Compressive strength 
Electrical resistance 
2.2. Materials used 
The binders used in this study were materials that fit KS, and the material properties of each binder are 
summarized in Table 3. Fig.1 shows the particle shape of each binder, where OPC has a square shape, 
and FA and UFFA have a spherical shape. As CNT mixed in grout, S-CNT with MWCNT (Multi walled 
CNT) bonded physically to a porous material was used. Fig.2-(a) shows the general shape of MWCNT, 
where agglomeration due to the Van der Waals force was observed. However, because the porous 
material of S-CNT is hydrophilic and allows for homogeneous dispersion in cement, the phenomenon of 
agglomeration is reduced further, and improved dispersibility is observed when compared to MWCNT 
used alone. 
Table 2. Mixture proportions of grout 
Spec 
W/B 
(%) 
Binder (%) Sand (%) 
Ad 
(%) OPC FA UFFA 
Silica sand S-CNT 
1.8 mm 0.9 mm 0.15 mm 0.15 mm 
Plain 
34 
100 0 0 50 40 10 0 
1.2 
S-OPC 100 0 0 50 40 7 3 
S-FA 60 40 0 50 40 7 3 
S-UFFA 60 0 40 50 40 7 3  
Table 3. Binder properties 
Spec 
Physical properties Chemical properties (%) 
Median particle size(㎛) Blain(㎠/g) Density(g/㎤) SiO₂ CaO Al₂O₃ Fe₂O₃ 
OPC 15.4 3 524 3.14 16.5 60.6 3.9 3.4 
FA 14.5 3 361 2.2 50.0 4.2 19.0 4.6 
UFFA 3.0 15 364 2.3 55.1 7.8 16.7. 4.9 
 
  
                             Fig. 1. Shape of binder (SEM)                                                   Fig. 2. Shape of CNT(SEM) 
2.3. Experiment method 
2.3.1. Flow characteristics of fresh grout 
The outflow time of self-sensing grout was measured based on KS F 4044, as shown in Fig. 3-(a). The 
flow test was performed in accordance with KS F 2476, as shown in Fig. 3-(b). 
2.3.2. Hardened grout 
The specimen to evaluate the strength characteristics of self-sensing grout was measured in accordance 
with KS F 2476, and the specimen to evaluate the electrical properties was fabricated in a size of 
(Φ50×100) mm. For the electrical resistance test, a specimen of 28 days was dried for 24 hours in a 
drying chamber with a temperature maintained at (50±2) ℃ to prevent errors in measuring resistance 
values due to internal moisture. A strain gauge and copper electrode were then attached to the center 
of the specimen, and electrical resistance and deformation due to loading were measured using 
BenchVue.  
 
Fig. 3. Fresh grout test view                                                Fig. 4. Hardened grout test view 
3. Experiment results and analysis 
3.1. Fresh grout 
The flow characteristics of self-sensing grout are shown in Figure. 5. The outflow time of grout met all 
of the flow time standards of 60 seconds or less specified in KS F 4044, and the flow also met the KS 
standard of 225mm or more. However, in the case of S-FA, the fluidity was reduced as compared to 
plain. In general, FA is spherically shaped, and its fluidity is improved by the action of ball bearings. The 
optimal replacement ratio is 20% (Cho et al. 2021) [3]. However, in this study, the replacement ratio of 
industrial by-products was 40%. Rather than improving the fluidity due to the effects of ball bearings, 
the low density of the FA led to an increase in the total volume of powder and the adsorption of mixing 
water, resulting in a decrease in fluidity due to the W/B reduction effects. However, the outflow time of 
S-UFFA was improved by more than 50%. This suggests that although it has a high degree of fineness, 
it has a relatively uniform particle size compared to other binders used in this study and spherical 
particles, leading to a significant improvement in fluidity due to the action of the ball bearing.   
3.2. Hardened grout 
3.2.1. Compressive strength properties 
For the S-OPC mixed with S-CNT, the compressive strength was about 10% higher than that of plain at 
all ages. The specimen substituted with industrial by-products showed a lower strength than S-OPC at 
3-days. This is because the cement content was reduced by the substitution amount of the industrial by-
product. In the case of S-UFFA, the strength was higher than that of S-OPC after 7 days. This results 
from the acceleration of tissue density and pozzolanic reaction due to the high fineness of UFFA. 
 
        Figure. 5. Outflow and flow                                        Figure. 6. Compressive strength 
3.2.2. Self-sensing properties 
The electrical properties of self-sensing grout mixed with S-CNT are shown in Figure. 7. When a 
compressive load was applied, the electrical resistance values tended to decrease in all specimens. 
Meanwhile, changes in electrical resistance were found in the range of –1.8 % for S-OPC, –4 % for S-
FA, and –22 % for S-UFFA. The reason why the range of electrical resistance change rate varies for 
each specimen is that although the electrical performance is determined by CNT, the change of 
resistance value occurs depending on the size and distribution of internal pores. Accordingly, it is 
thought that the specimen structure is tightly filled in UFFA with high fineness, resulting in a broad 
detection range of electrical resistance values. The relationships between FCR-Stress and FCR-Strain 
were similar in all specimens, and the correlation (R2) values were all more than 0.9. Therefore, it is 
believed that the fractional change in resistance (FCR) can be used to assess the self-sensing capability 
of the material to estimate the deformation and stress of the specimen. 
 
Figure. 7. Electrical performance 
4. Conclusion 
The main objective of this study was to evaluate the performance of self-sensing grout substituted with 
large amounts of industrial by-products. When replaced with UFFA, the mechanical and physical 
properties were improved, and electrical properties for self-sensing were identified. In addition, it was 
confirmed that due to the UFFA replacement, fluidity was improved, and compressive strength increased 
compared to S-OPC after 7 days of age. For self-sensing properties, the specimen incorporating UFFA 
showed the highest electrical resistance change detection ratio at 22%, and the relationships between 
FCR-Stress, and FCR-Strain were similar. Therefore, it is expected that the fractional change in 
resistance can be used as basic data for the health evaluation of the specimen. 
Acknowledgements 
This research was supported by the Basic Science Research Program through the National Research Foundation 
of Korea (NRF), funded by the Ministry of Education (No. 2021R1A4A2001964 and 2023R1A2C2006400). 
 
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