Effects of Diethanolamine (DEA) and Glass Fibre Reinforced polymer (GFRP) on setting time and mechanical properties of shotcrete
Introduction
Nowadays, concrete and shotcrete play a key role in the mining and civil construction industries [[1], [2], [3], [4], [5]]. The application of shotcrete with 50 mm–500 mm thickness in tunneling can be temporary or can be as the final lining depends on the tunnel requirement. Shotcrete provides early structural support when it is used as a temporary support system. The second layer of support can be applied to create permanent support system However, the fibre-reinforced shotcrete or final lining is used as a form of a Single Pass Tunnel Lining (SPTL) which is a combination of rock bolts, cable bolts [6], fibre reinforced shotcrete, and steel arches (in terms of requirement for additional support) [1].
Since the early 70s, the use of fibre in shotcrete was started to create secure tunnel vaults [7]. Drawn steel wire, slit steel sheet, or polypropylene (monofilament or fibrillated) are the most common types of fibre to be used in shotcrete; however, nylon, glass, aramide and carbon are also used as less regular types [[7], [8], [9], [10]]. The steel fibres have been the mostly common types of fibre to be used in shotcrete [11], although there is a risk of corrosion in steel fibres [12]. The use of synthetic fibres has been reported problematic due to their long term behavior and post-crack creep [13]. However, the advantages of macro-synthetic fibre reinforced shotcrete in mines and temporary works have been reported due to larger deformations for ground control purpose [14]. The use of polyolefin-based plastic fibres in shotcrete could be disadvantageous due to a low modulus of elasticity which affects the mechanical properties of shotcrete negatively. However, the mechanical properties of shotcrete due to the use of polymer fibres can be maintained if appropriate additives be added to increase the degree of crystallization and achieve higher stretch levels [15].
In order to improve the long-term properties of concrete such as strength and durability in different environments, various admixtures are widely used which may have a beneficial or adverse effect on concrete properties. Many studies have been conducted to evaluate the effects of various admixtures on concrete properties [[16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36]]. Amine is a concrete admixture that affects the mechanical properties of concrete by changing the concrete chemical structure. Heren and Ölmez [37] studied the effects of monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA) on the setting time and tensile and flexural strengths of concrete in three cement replacement levels (0.1%, 0.5% and 1%) and a constant w/c ratio of 0.4. The results showed that the low concentration of amines has a minor impact on the concrete setting time. Despite relatively constant tensile and flexural strengths at a certain MEA level, concrete strength decreased by adding DEA and TEA [37]. The effects of MEA, DEA and TEA on tensile strength of 28-day-old concrete were investigated at three cement replacement percentages (1%, 2% and 3%) and a constant w/c ratio of 0.53 by Saraswathy and Song [27]. The results indicated a decrease in the tensile strength by adding 1 wt% (percent weight) of all alcohol types. The tensile strength decreased by adding 2 wt% of DEA and TEA, while it increased by adding 2 wt% of MEA. The tensile strength of the concrete further decreased by adding 3 wt% of all alcohol types as compared with 1 wt% of ethanolamines [17]. Different additives have been used for reduction of setting time. Although calcium chloride is used as an accelerator, this additive leads to the corrosion of steel parts and metal meshes. Dodson presented an overview on various non-chloride accelerators [38]. Aggoun et al. [39] studied the effect of different accelerators such as calcium nitrate, TEA, TIPA on setting time and strength evolution of two types of cement containing various amounts of iron oxide. It was concluded that calcium nitrates as an accelerator has positive effects on setting time and negligible effects on the long-term development of mechanical resistances. Moreover, regardless of the type of cement, both alkanol amines (TEA, TIPA) work as an accelerator at any age. However, the final setting time of cement containing less iron oxide increased while the setting time of the cement containing more iron oxide decreased by 30%. It caused an increase in the strength of 1, 3, 7 and 28-day-old of both cements with a further increase in the strength of the cement containing less iron oxide [39]. Heren and Olmez conducted a study on the effect of three different amines (MEA, DEA and TEA) on the hydration and mechanical strength of Portland white cement. It was reported that TEA and MEA had high and low effect on hydration respectively [37].
The review of previous studies shows that significant studies have been conducted to determine the effect of MEA, DEA and TEA on the setting time and mechanical properties of concrete. The results showed that using these additives could affect the setting time and mechanical properties of concrete and cement. Based on previous studies, DEA decreases the hardened properties of concrete. The aim of current study is to investigate the effects of both DEA, to increase the setting time of shotcrete, and the GFRP, to improve the mechanical properties of shotcrete including tensile and flexural strength. To achieve this aim, at w/c ratio of 0.30, 0.35 and 0.4, nine mixes including a control sample without GFRP and DEA and eight mixes with 0.1, 0.3, 0.5 and 1 wt% DEA and 0.5 and 1 wt% GFRP in replacement of cement were prepared and tested to evaluate the effects of DEA and GFRP on shotcrete setting time. Seven mixes were designed at w/c ratios of 0.40, 0.50 and 0.55 with 0.5% and 1% DEA and GFRP to evaluate the effects of DEA and GFRP on tensile and flexural strength of shotcrete.
Section snippets
Materials
The mechanical properties of concrete materials can be influenced by the amount and type of water [[40], [41], [42], [43], [44], [45], [46], [47], [48]]; therefore, in the current study, three w/c ratios of 0.3, 0.35 and 0.40 were used to determine the initial setting time of the cement. In order to have enough time for measuring the setting time, various setting time was considered. The w/c ratios in the specimens used for tensile and flexural strength were 0.40, 0.50 and 0.55. Portland Cement
Setting time
Setting time experiment was carried out based on ASTM C 191–04 [54]. Three different w/c ratios of 0.30, 0.35 and 0.4 were used for this purpose. Eight mixes were prepared for each w/c ratio in which 0.1 to 1 wt% DEA and 0.5 and 1 wt% GFRP were used in replacement of cement. Fig. 3, Fig. 4, Fig. 5 show the setting time for w/c ratio of 0.30, 0.35 and 0.40, respectively. The initial setting time of the control shotcretes prepared with a w/c ratio of 0.30, 0.35 and 0.40 without DEA and GFRP was
Conclusions
The impact of incorporating Diethanolamine and GFRP on the initial setting time tests and mechanical behavior of the shotcrete was investigated. Nine mixes with w/c ratios of 0.30, 0.35 and 0.40, 0.1, 0.3, 0.5 and 1.0 wt% DEA and 0.5 and 1.0 wt% GFRP in replacement of cement and seven mixes cured for 28 days with w/c ratios of 0.40, 0.50 and 0.55 with 0.5% and 1.0% DEA and GFRP were prepared to evaluate the shotcrete setting time and the tensile and flexural strengths, respectively. The
Funding
This study was supported by the Laboratory of Soil and Concrete of Abadgaran Negin Jonoobshargh Company (ANG Co.) in Iran (Grant number 121B). The authors would like to thank them for their valuable supports.
CRediT authorship contribution statement
Mohammad Rezania: Methodology, Validation, Formal analysis, Investigation, Writing - review & editing, Visualization. Hamed Moradnezhad: Conceptualization, Methodology, Validation, Formal analysis, Visualization. Mohsen Panahandeh: Formal analysis, Investigation, Resources, Data curation, Writing - original draft. Mohammad Javad Rahimpoor Kami: Validation, Formal analysis, Investigation, Resources. Aida Rahmani: Writing - original draft, Writing - review & editing, Visualization, Supervision.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The authors would like to thank the valuable assistance from the Laboratory of Soil and Concrete of Abadgaran Negin Jonoobshargh Company (ANG Co.). Also, the authors sincerely thank Dr. Haleh Rasekh and Mr. Soheil Jahandari for their constructive supports in improving the manuscript.
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