"Mechanisms and Mitigation of Plastic Shrinkage in Concrete" 

Halle Block, MSE PhD Candidate 

Advisor: Professor Kendra Erk

ABSTRACT

In modern infrastructure, durability is increasingly recognized as a priority-characteristic in concrete, rather than mechanical strength alone. Material resilience to external factors ensures that the structure is less vulnerable to deterioration over time. Durable concrete with enhanced service-life ensures more environmental and economic savings, as these structures require less frequent repair, replacement, and material input over time. Early-age shrinkage, and the cracks that form as a result, is widely recognized as a leading contributor to reduced durability and service-life, since exposure to environmental elements at early ages increases the likelihood of deterioration and material failure. Plastic shrinkage cracking is the earliest form of concrete shrinkage deformation and occurs at the material’s surface because of rapid moisture loss to the environment before setting. Superabsorbent polymer (SAP) hydrogels have been studied for and proven to mitigate autogenous shrinkage (shrinkage that begins after final set and occurs without external influence) by offering internal water reservoirs that release stored water back into the system to facilitate a more controlled hydration reaction. However, there is limited research that investigates SAP’s effectiveness in mitigating plastic shrinkage. This document discusses the mechanisms of plastic shrinkage cracking in concrete –including internal relative humidity, capillary pressure development, settlement, restraint, setting time, and environmental factors – and the behavior of polyelectrolyte SAP hydrogels within cementitious systems. The knowledge gained is then used to review published studies which investigate the effectiveness of SAP at mitigating plastic shrinkage cracking and related properties. Research critiques of these publications are then discussed and a conclusion is made regarding the need for further SAP research in the subject of plastic shrinkage cracking mitigation.