Effect of Carbonation Curing on Efflorescence Formation in Concrete Paver Blocks

Abstract

Efflorescence is a staining salt deposit that usually forms on or near the surface of portland concrete products. It is not an indication of internal damage, but rather an aesthetic blemish that affects a product’s appearance, leading to higher replacement and rejection rates. The primary goal of this work was to investigate whether early-age carbonation curing helps reduce or eliminate efflorescence formation in concrete paver blocks. The devised carbonation technique involved curing concrete pavers in a chamber filled with either pure-gas (99.5% carbon dioxide concentration) or flue-gas (20% carbon dioxide concentration) under a pressure of 5 bar. Efflorescence formation in hydrated and carbonated pavers was evaluated using a modified wicking test. A MATLAB-assisted image-analysis technique was used to quantify efflorescence severity. Results clearly show that pure-gas carbonation successfully eliminated surface efflorescence compared to paver batches that underwent flue-gas carbonation and conventional hydration curing. This improved performance was attributed mainly to a reduction in permeability, which in turn was a result of the densifying precipitation of calcium carbonate crystals during pure-gas carbonation. Results from X-ray diffraction (XRD) and scanning electron microscope (SEM)—coupled with energy-dispersive X-ray spectroscopy (EDX)—identified efflorescence as crystalline potassium-sulfate-based salt deposits.