Tension Stiffening and Cracking Behavior of Axially Loaded Alkali-Activated Concrete

Hamdi Abdulrahman; Rahimah Muhamad; Ahmad Azim Shukri; Amin Al-Fakih; Gamal Alqaifi; Ayad Mutafi; Husam S Al-Duais; Abdulnaser M Al-Sabaeei

doi:10.3390/ma16114120

Tension Stiffening and Cracking Behavior of Axially Loaded Alkali-Activated Concrete

Materials (Basel). 2023 May 31;16(11):4120. doi: 10.3390/ma16114120.

Authors

Hamdi Abdulrahman¹, Rahimah Muhamad¹, Ahmad Azim Shukri², Amin Al-Fakih³, Gamal Alqaifi⁴, Ayad Mutafi⁵, Husam S Al-Duais⁶, Abdulnaser M Al-Sabaeei⁷

Affiliations

¹ Razak Faculty of Technology and Informatics, Universiti Teknologi Malaysia, Kuala Lumpur 54100, Malaysia.
² Faculty of Civil Engineering, Universiti Teknologi Malaysia, Johor Bahru 81310, Malaysia.
³ Interdisciplinary Research Center for Construction and Building Materials, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia.
⁴ School of Built Environment, Faculty of Design, Architecture & Building, University of Technology Sydney, Ultimo, NSW 2007, Australia.
⁵ Jamilus Research Centre for Sustainable Construction (JRC-SC), Faculty of Civil Engineering and Built Environment, Universiti Tun Hussein Onn Malaysia, Parit Raja 86400, Malaysia.
⁶ Department of Architecture, Faculty of Built Environment, Universiti Malaya, Kuala Lumpur 50603, Malaysia.
⁷ Department of Civil Engineering, Faculty of Engineering, Thamar University, Dhamar 87246, Yemen.

Abstract

Alkali-activated concrete is an eco-friendly construction material that is used to preserve natural resources and promote sustainability in the construction industry. This emerging concrete consists of fine and coarse aggregates and fly ash that constitute the binder when mixed with alkaline activators, such as sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃). However, understanding its tension stiffening and crack spacing and width is of critical importance in fulfilling serviceability requirements. Therefore, this research aims to evaluate the tension stiffening and cracking performance of alkali-activated (AA) concrete. The variables considered in this study were compressive strength (f_c) and concrete cover-to-bar diameter (C_c/d_b) ratios. After casting the specimen, they were cured before testing at ambient curing conditions for 180 days to reduce the effects of concrete shrinkage and obtain more realistic cracking results. The results showed that both AA and OPC concrete prisms develop slightly similar axial cracking force and corresponding cracking strain, but OPC concrete prisms exhibited a brittle behavior, resulting in a sudden drop in the load-strain curves at the crack location. In contrast, AA concrete prisms developed more than one crack simultaneously, suggesting a more uniform tensile strength compared to OPC specimens. The tension-stiffening factor (β) of AA concrete exhibited better ductile behavior than OPC concrete due to the strain compatibility between concrete and steel even after crack ignition. It was also observed that increasing the confinement (C_c/d_b ratio) around the steel bar delays internal crack formation and enhances tension stiffening in AAC. Comparing the experimental crack spacing and width with the values predicted using OPC codes of practice, such as EC2 and ACI 224R, revealed that EC2 tends to underestimate the maximum crack width, while ACI 224R provided better predictions. Thus, models to predict crack spacing and width have been proposed accordingly.

Keywords: OPC codes of practice; alkali-activated concrete; compressive strengths; concrete cracking; tension stiffening.

Grants and funding

Q.K130000.2556.21H60/University of Technology Malaysia