PSI - Issue 64

Niloofar Heirani et al. / Procedia Structural Integrity 64 (2024) 6–13 Author name / Structural Integrity Procedia 00 (2019) 000–000

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D’Alessandro et al., 2016b; Du et al., 2013; Han et al., 2015, 2020; Qin et al., 2024; Sun et al., 2015; Tian et al., 2019). They are, therefore, extremely compatible with the host structure. These multifunctional composites have shown promise in monitoring strain, corrosion, cracks, and many other conditions (Qin et al., 2024). However, the diversity in mix design and fabrication procedures adopted by each research project makes comparisons of sensing properties, such as sensitivity and repeatability, inherently inconsistent. Figure 1 serves as an example illustration of this diversity by displaying of how the volume fraction ( ) of the conductive phase can influence strain sensitivity by comparing gauge factors reported by a representative set of publications (Azhari and Banthia, 2012; Baeza et al., 2013; Belli et al., 2018; Camacho-Ballesta et al., 2016; D’Alessandro et al., 2021, 2016a; Dehghani and Aslani, 2021; Demircilioglu et al., 2020; Dong et al., 2022, 2019; Fan et al., 2011; Fu and Chung, 1997; García-Macías et al., 2017a, 2017b; Guo et al., 2022; Han et al., 2009, 2007; Han and Ou, 2007; Lee et al., 2018; Luo et al., 2018; Monteiro et al., 2017, 2022; Teomete and Kocyigit, 2013; Wang et al., 1999; Wen and Chung, 2006, 2008, 2003, 1999; Xiao et al., 2010; Xu et al., 2021; Yoo et al., 2019, 2017; You et al., 2017). To advance the state of research and the implementation of cementitious sensors, it is essential to establish consensus on best fabrication practices. This paper presents our preliminary methodology and findings aimed at optimizing the mix proportions and fabrication procedures, specifically for carbon fiber reinforced cement paste (CFCP) composites. CFCP sensors are piezoresistive, allowing them to measure applied stress and strain through monitoring changes in their electrical resistivity.

Fig. 1. The diversity in the conductive phase content and resulting sensitivity reported in publications on cementitious sensors (citation in text). *CF: Carbon fiber; CNT: Carbon nanotube; SF: Steel fiber; CB: Carbon black 2. Materials and methods 2.1. Materials and fabrication We used the Taguchi design of experiments method (Roy, 2010) to evaluate the effect of five fabrication parameters on sensing properties: CF content, cementitious material, mixer type, mixing speed, and mixing order (Table 1). Coal tar pitch-based CF with specifications given in Table 2 were used in all mixes along with methylcellulose (MC) and defoamer (DF) to help with their dispersion. One of three mixing procedures presented in Figure 2 were then followed.

Table 1. CFCP fabrication factors and their corresponding levels

Levels

of CF

Factors

1

2

3

4

5

6

A B

0%

0.5%

1%

5%

10%

15%

General Use Cement (GU)

GU + 20% Silica Fume

GU + 10% slag

Cementitious Material

Centrifugal (KK-1000W)

C

Mixer type

Hobart (HU3841)

Mixing speed Hobart (RPM) Centrifugal (RPM)*

Low 139 230

Medium 285 590 Method B

High 691 950

D

E

Mixing order

Method A

Method C

* For the centrifugal mixer, rotation and revolution speeds were kept the same