04/05/2024
By Danielle Fretwell

The Francis College of Engineering, Department of Civil and Environmental Engineering, invites you to attend a Doctoral Dissertation defense by Dayou Luo on: "Nanoengineered Clay-based Internal Conditioning: Cement Hydration and Alkali-Silica Reaction Mitigation."

Candidate Name: Dayou Luo
Degree: Doctoral
Defense Date: Tuesday, April, 9, 2024
Time: 1 to 3 p.m.
Location: Perry Hall 315

Committee:

  • Advisor: Jianqiang Wei, Assistant Professor, Department of Civil and Environmental Engineering, University of Massachusetts Lowell
  • Tzuyang Yu, Professor, Department of Civil and Environmental Engineering, University of Massachusetts Lowell
  • Zhiyong Gu, Professor, Department of Chemical Engineering, University of Massachusetts Lowell
  • Arghavan Louhghalam, Associate Professor, Department of Civil and Environmental Engineering, University of Massachusetts Lowell

Brief Abstract:
Alkali-silica reaction (ASR) is a major deterioration mechanism of concrete that can cause volume expansion, cracking, and premature failure of structures. Concerns over durable concrete design and the high maintenance costs for ASR-impacted concrete structures have driven investigations into new strategies for ASR mitigation. However, a practical, robust, and cost-effective approach without deleterious effects on cement hydration and concrete properties is critically needed. Towards this end, this thesis investigates nanoengineered internal conditioning (NIC) for targeted ASR suppression without sacrificing the performance of concrete. In contrast to traditional studies, this study expands the application of natural pozzolans as functional mineral admixtures to improve the hydration of cement and the aging resistance of concrete. In pursuit of this goal, the following work has been performed:

(i) Functionalization of sodium montmorillonites (sMTs). In this study, two non-ionic surfactants, t-octyl phenoxy poly ethoxyethanol (TX100) and polyethylene glycol ether (PONPE9), were employed to upgrade sMT into an effective agent for internal conditioning. The results indicate that both TX100 and PONPE9 can be effectively intercalated into the interlayer space of sMT resulting in improved reactivity, hygroscopic swelling, water uptake, and dispersion of sMT particles.

(ii) Development of NIC based on the functionalized sMTs and its influence on the hydration of cement. In this thesis, the influence of NIC on the hydration kinetics and phase evolution of Portland cement was investigated. The results indicate that, in the presence of NIC, both silicate reaction and secondary aluminate reaction were enhanced with decreased apparent activation energy. Decreased calcium hydroxide content, improved degree of hydration, increased chemical shrinkage, and enhanced formation of calcium silicate hydrate (C-S-H) and aluminum-containing phases were obtained.

(iii) Development of metakaolin-based internal conditioning (MIC) and its role in cement hydration. In addition to sMT, calcined clay was investigated as an alternative NIC agent. The influence of MIC on the hydration kinetics, phase evolution, and development of microstructure and molecular structures of hydration products in the blended cement composite was investigated. A synergistic effect was found to exist between the saturated MK and lithium in enhancing the hydration of cement, interaction between metakaolin and cement, incorporation of Al in the silicate chains, and precipitations of Al-rich phases.

(iv) The efficacy of functionalized sMT in mitigating ASR. To understand the role of NIC in ASR mitigation, the expansion and cracking behavior of mortars containing reactive aggregates were investigated. Compared with the raw sMT, ASR-induced expansion and cracking can be more substantially mitigated in the presence of the functionalized sMT, which is supported by the improved consumption of portlandite, reduced formations of both crystalline and amorphous ASR gels, suppressed Q3 polymerization sites, and decreased [K + Na]/Si atomic ratio in ASR gels.

(v) The role of MIC in mitigating ASR. The developments of volume expansion, cracking, permeability, strength, and microstructure in mortars containing reactive aggregates with and without MIC were investigated to elucidate the role of MIC in ASR mitigation, as well as the mitigation mechanisms. Substantial decreases in ASR expansion and cracking density revealed the robust role of MIC in ASR suppression outperforming single uses of metakaolin or lithium. Multiple prerequisites of ASR from silica dissolution to water uptake and swelling of ASR gel were arrested.