Resistance of alkali-activated binders against organic acid attacks
How resistant are mortars and concretes based on alkali-activated binders against organic acids? This was investigated by German researchers at the Institute for Mineralogy of the University of Leipzig.
The acids used were acetic acid, propionic acid and lactic acid (pH ≈ 3).
Acid resistance decreases with increasing CaO content
The development of residual strength, degradation depth and mass loss over time were recorded after six, twelve and 18 weeks of storage. Additionally, the damage mechanisms were examined by micro X-ray computer tomography and microscopy, including spatially resolved porosity as well as phase analyses. The degree of degradation, especially in the pre-damaged zone, decreases with a decreasing Ca-content of the binder. No damage zones, an increased residual strength and a densification (detected as a reduction in porosity) at the acid-exposed fringe zone was observed for so-called geopolymer binders (low-Ca alkali-activated binders) the longer the exposure to acid was. A lower degree of degradation was detected for high-Ca alkali-activated binders compared to cementitious reference mortars/concretes.
The study was published in: Construction and Building Materials, Volume 151, October 1, 2017, pages 405-413.
