Effect of Ca2+ on the sulfate multiple combined induced degradation of early aged mortar

Abstract

To investigate the influences of Ca2+ on the early degradation process and mechanism of cast-in-situ structures subjected to sulfate, chloride and combined attack, mortar specimens were prepared and immersed in different solutions for 28 days. Weight and size were measured to recorded the changes during immersion. Flexural and unconfined compression tests were conducted to study the mechanical development of specimens. XRD, SEM, EDS and TG/DTG analysis tests were performed to reveal the microstructural and mineral changes of mortar during the corrosion process. Porosity and sulfate concentration were determined by MIP test and chemical titration, respectively. Results show that internal aggressive corrosion sources negatively affect the strength development of cement mortar. Premixed chlorides clearly accelerate sulfate induced degradation process and speed up the damage process. Cement mortar with premixed Ca2+ shows relatively better strength development and better durability against corrosive conditions during the immersion, resulting in relatively high strength. Ca2+ helps to improve the durability performance against both sulfate and sulfate–chloride combined attack in the early corrosion stage, which could be considered as a potential way to improve the durability performance of cast-in-situ concrete in sulfate-rich environments.