Improvement on durability of concrete by early age continuous loading treatment

This study investigated the effect of different pressure levels of continuous loading (2.5 MPa, 5.0 MPa, 7.5 MPa, and 10.0 MPa) on the enhancement of concrete durability and proposed the underlying mechanisms behind. To evaluate the efficiency of continuous loading, in addition to compressive strength, the durability, including chloride ion permeability, freeze-thaw resistance and carbonation resistance of the concree were determined, and the micro-scale investigation, including pore structure, microhardness, hydration product and microstructures were conducted. The results showed that, compared to reference (non-pressurized sample), the continuous loading process increased the 28d compressive strength of concrete by 10.3% to 27.4%, decreased chloride ion migration coefficient by 34% to 48.9%, increased freeze-thaw cycles by 20%, and reduced the carbonation depth by 12.3% to 36.2%. The improved performance was attributed to the enhancement of pore structure and reduction of ITZ width, which was a result of multiple factors such as increased compaction and improved movement of free water.