04/22/2021
By Sokny Long

The Francis College of Engineering, Department of Civil and Environmental Engineering, invites you to attend a master’s thesis defense by Madhab Adhikari on “Effects of Pre-Saturated Metakaolin and Lithium Nitrate on Cement Hydration and Alkali-Silica Reaction.”

MSE Candidate Name: Madhab Adhikari
Defense Date: Monday, April 26, 2021
Time : 2 to 4 p.m. EST
Location: This will be a virtual defense via Zoom. Those interested in attending should contact the student Madhab_Adhikari@student.uml.edu and committee advisor Jianqiang_Wei@uml.edu at least 24 hours prior to the defense to request access to the meeting.

Committee Chair (Advisor): Jianqiang Wei, Ph.D. Assistant Professor, Department of Civil and Environmental Engineering, UMass Lowell

Committee Members:

  • Susan Faraji, Ph.D. Professor, Department of Civil and Environmental Engineering, UMass Lowell
  • Alessandro Sabato, Ph.D. Assistant Professor, Department of Mechanical Engineering, UMass Lowell

Brief Abstract:
Alkali-silica reaction (ASR) is one of the most challenging degradation mechanisms in concrete causing volume expansion, cracking, and shortened service life of structures. In this study, a calcined clay, metakaolin, and a lithium-based admixture, lithium nitrate, were used to modify the cement matrix of concrete as a potential way to suppress ASR. Cement substitutions with 30 wt.% dry metakaolin, pre-saturated metakaolin, and dry metakaolin plus the same amount of extra water were investigated. Lithium nitrate with lithium to alkali molar mass ratio of 0.74 was mixed into cement. With these materials’ incorporations, their roles in both the hydration of cement and ASR mitigation were comprehensively studied. The results indicate that lithium can accelerate the early-age cement hydration but retards the hydration reaction after 24 hours. Comparing with lithium, metakaolin can modify the cement hydration behavior more significantly by consuming calcium hydroxide, producing additional calcium-silicate-hydrates, and forming a denser cement matrix with an improved degree of hydration and reduced autogenous shrinkage. The superior performance of pre-saturated MK, which can gradually release moisture to fuel long-term cement hydration, was observed. Although lithium-based admixtures have been proven an effective approach, the 30% cement replacement with metakaolin showed better performance in mitigating ASR in this study. In the presence of dry metakaolin, the ASR expansion was reduced to an innocuous level (< 0.1% after 16 days accelerated aging treatment), which is 95% lower than the control (plain cement) group. Due to the enhanced cement hydration and reactivity of metakaolin, the group containing pre-saturated metakaolin shows a lower long-term increasing rate of the ASR-induced expansion and fewer cracks than the group with dry metakaolin indicating the beneficial role of the metakaolin-based internal curing in suppression ASR.

All are invited to remote session.