The New Jersey Institute of Technology's
Electronic Theses & Dissertations Project

Title:	The impact of conversion on the durability of calcium aluminate cement concrete systems
Author:	Korayem, Marwa Mohsen
View Online:	njit-etd2020-096 (xv, 112 pages ~ 3.0 MB pdf)
Department:	Department of Civil and Environmental Engineering
Degree:	Doctor of Philosophy
Program:	Civil Engineering
Document Type:	Dissertation
Advisory Committee:	Adams, Matthew P. (Committee chair) Marhaba, Taha F. (Committee member) Wecharatana, Methi (Committee member) Bandelt, Matthew J. (Committee member) O'Neill, Megan E. (Committee member)
Date:	2020-05
Keywords:	Calcium aluminate cement Conversion Drying shrinkage Durability Electric resistivity Finely ground limestone
Availability:	Unrestricted
Abstract:	The deterioration of infrastructure in North America has resulted in a significant need for concrete repair materials that can be used to maintain service life of these structures. Hydraulic cement based rapid repair materials can be used to repair pavement and bridge deterioration with minimal impact on economic activities such as freight handling or public transportation. While there are many options for use in repair situations, calcium aluminate cements have become more popular recently, particularly in situations where repairs must be completed rapidly. Calcium aluminate cement (CAC) is a cement characterized by its rapid strength gain, even at low temperatures approaching 0°C. This key feature has made CACs extremely useful in certain concrete repair applications, particularly in cold regions. CAC systems undergo a unique process known as conversion, in which metastable hydrates convert to stable hydrates, resulting in an increase in porosity and strength loss. Understanding the time at which this conversion occurs, and the magnitude of strength loss is important for long-term design decisions involving repaired concrete systems. There has been significant previous research work on the kinetics of the conversion process in the CAC systems. However, there is very little information available on the impact of conversion on long-term concrete durability. This dissertation discusses the capability of using electric resistivity measurements in order to assess conversion in CAC systems in the field. A rapid procedure is recommended to detect when conversion occurs in different aspects. The validity of this approach is studied on CAC systems with various robustness factors including different cement formulations, different types of aggregates, different water to cement ratios, and different time to convert. This work also studies the relationship between converted and unconverted CAC concrete in terms of drying shrinkage; focusing on understanding the impact of conversion on CAC systems long term durability. A discussion is presented on various CAC systems using different water to cement ratios, different cement formulations, and different time to convert. This work shows a proof-of-concept that the electric resistivity measurement may be a promising tool to assess time to conversion in CAC systems. The presented data shows a significant reduction in electric resistivity correlating with a reduction in the compressive strength, which indicates that full conversion has occurred. This work also studies the impact of conversion on long term durability in CAC systems in terms of drying shrinkage. The presented data shows a much higher total shrinkage and mass loss in samples after conversion occurs than in unconverted ones. This work shows that it will be essential to ensure that the CAC system will gain enough strength and they should be prevented from converting at an early age, before it builds up stresses that occur due to drying shrinkage.