Time-dependent tensile behavior of slag-based alkali activiated concrete

With the development and use of Alkali Activated Concretes (AACs), a more sustainable alternative to Portland Cement Concretes (PCCs), it is becoming ever more important to understand its mechanical behavior over time.Herein, tensile behavior of a slag-based AAC (S-AAC) was investigated on dog-bone shaped samples tested in direct tension and compared to a CEMIII/B-based concrete (S-PCC).Samples have been fog-cured for 28 days and successively exposed to 55% relative humidity and 20C until testing, at testing ages 28 days, 3 months, 6 months and 1 year.Stress-strain behavior of S-AAC was characterized by a significantly lower tensile strength and elastic modulus than S-PCC.From 28 days to 3 months, both concretes showed a reduction in tensile strength, which partially recovered at 6 months.Interestingly, after partial recovery, both concretes showed reduced tensile strength at the age of 1 year.Stress-crack opening curves and development of characteristic length over time showed that, unlike S-PCC, S-AAC softens under drying, which might be an effect of shrinkage-induced microcracking in S-AAC.