Forensic investigation of ettringite formation in hardened mass concrete structures

• Main Author: Chng, Sebastian Wee Tat
• Other Authors: Fan Sau Cheong
• Format: Final Year Project
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/67368
• Institution: Nanyang Technological University

Ettringite as known as 3CaO•Al2O3•3CaSO4•32H2O( in chemistry abbreviation) which are found in concretes/cement mixtures are classified into two different groups; (Primary Ettringite as known as Type 1) or (Secondary Ettringite as know as Type 2 or Delayed Ettringite Formation {DEF}). Studies have shown that a certain type of Ettringite to be detrimental and affecting the overall concrete strength in a long period. However, the true identification of the root cause of the development of the Ettringite still remains as a doubt to most researchers. Primary Ettringites that are developed during hydration process have a positive effect as it regulates the settling process during the initial stage of concrete mixing. Hence, the presence of the Primary Ettringite does not create any significant stress to the concrete. In turn, Delayed Ettringite Formation (DEF) which are formed, at the later stage (28 days and beyond) in the concrete are shown to create damage and affecting the strength of the concrete. Hence, the strength of the concrete is unable to be maximise in accordance to its maturity as it projects to be. The formation of Delayed Ettringite Formation (DEFs) in the air voids of the Interface Transition Zone (ITZ) between the aggregates and cement paste is the main factor that harms the concrete strength from enveloping to its eventual stage. Various factor such as temperature, the hydration process and the amount of sulphur content presence in the concrete/cement mixture are some of the debatable root causes of the development of Delayed Ettringite Formation. In the investigation, the objective is to identify if high temperature coring and a certain percentage of sulphur content is the key elements that causes the development of Delayed Ettringite Formation and how its presence affect the compressive strength