Construction and Building Materials 322 (2022) 126338 Available online 18 January 2022 0950-0618/© 2022 Published by Elsevier Ltd. Rheological, fresh, and mechanical properties of mechanochemically activated geopolymer grout: A comparative study with conventionally activated geopolymer grout Mukhtar Hamid Abed a, b , Israa Sabbar Abbas a , Majid Hamed c , Hanif Canakci d, * a Department of Civil Engineering, Gaziantep University, Gaziantep, Turkey b Department of Civil Engineering, University of Anbar, Anbar, Iraq c Department of Civil Engineering, Kirkuk University, Kirkuk, Iraq d Department of Civil Engineering, Hasan Kalyoncu University, Gaziantep, Turkey A R T I C L E INFO Keywords: Grouting Mechanochemical activation Geopolymer Rheological Setting time Strength Slag Fly ash ABSTRACT In this research, a mechanochemically activated geopolymer (MG) grout is adopted to activate slag, fy ash, sodium hydroxide, and sodium silicate by dry grinding in a ball mill for 2 h, after which water is the only additive required to initiate the geopolymerization reaction. A conventionally activated geopolymer (CG) grout was also evaluated for comparison purposes. Twenty-four different slag and fy ash mixtures have been prepared at different slag/fy ash ratios (0S100F, 50S50F, 75S25F, and 100S0F) at three different molarities of sodium hy- droxide (1.25, 2.5, and 3.75) to assess the behavior of both MG grout and CG grout. A series of tests were examined, such as rheological characteristics, setting time, bleeding, unconfned compressive strength (UCS), ultrasonic pulse velocity (UPV), and scanning electron microscopy (SEM). The experimental results showed that the mechanochemical activation technique reduced the rheological characteristics and fresh properties (setting time and bleeding) of geopolymer grout compared to the conventional activation process. Considering me- chanical properties, both UCS and UPV of MG grout were higher than that of CG grout. Furthermore, slag content and sodium hydroxide concentration signifcantly affected the rheological, fresh, and mechanical properties of all geopolymer grouts regardless of the activation method. Both the rheological characteristics and mechanical properties were increased considerably with the increase in molar concentration and slag content. Whereas the bleeding capacity and setting time dramatically reduced with the increase of molar concentration and slag content. 1. Introduction Grouting is one of the effective methods for ground improvement in the construction sector (e.g., tunnels, anchors, dam barriers, pre-stressed coating cables, building foundations, etc.) [1-3]. The construction in- dustry is considered a higher consumer of Portland cement, and many grouting applications rely on cement for ground improvement in con- ventional practice. However, the previous studies stated that the over- dependence on Portland cement has led to ecological issues such as large CO 2 emissions, resource depletion, dust generation, etc. [4-6]. Furthermore, the utilization of Portland cement has been found to have side effects like high bleeding, high plastic shrinkage, and some strength problems owing to the loss of water and incomplete hydration at early ages [7,8]. To eliminate these issues, many researchers paid considerable attention to replacing cement with pozzolanic materials or some admixtures by considering better grout performance with some eco-friendly materials [9-12]. In the last two decades, a new type of material called geopolymer has been successfully adapted in construc- tion works, and it could be a good alternative material for grouting applications instead of cement [13-15]. The geopolymer binder consists of alumina-silica sources such as metakaolin, slag, rice husk ash, and fy ash activated with an alkali activator solution like sodium or potassium hydroxide and sodium sili- cate [4,5,7,16]. Geopolymer materials are environmentally friendly, durable, highly resistant to chemical attack, resistant to alkali-aggregate reaction, possessing good mechanical performance, and viscoplastic behavior similar to conventional cement, etc. [6,17-24]. Despite the remarkable greenness potential of geopolymer, which promotes its * Corresponding author. E-mail addresses: majid79@uokirkuk.edu.iq (M. Hamed), hanif.canakci@hku.edu.tr (H. Canakci). Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat https://doi.org/10.1016/j.conbuildmat.2022.126338 Received 11 October 2021; Received in revised form 12 December 2021; Accepted 3 January 2022