Effect of internal curing with super absorbent polymers on residual stress development and stress relaxation in restrained concrete ring specimens

• The cracking resistance of concrete with SAPs was investigated by ring test.
• The residual stress of concrete decreased with the increase of SAPs amount.
• The relaxed stress of concrete increased with the increase of SAP amount.
• The ratio of relaxed to elastic stress increased with the increase of SAPs amount.
• The time to cracking for concrete increased with the increase of SAPs amount.

The early age cracking of concrete is a persistent problem for structures. Internal curing was developed to mitigate the shrinkage of low w/c concrete in recent decades by introducing additional water into concrete. Although shrinkage development and the early age cracking resistance of internally cured concrete under restraint were investigated, result on stress relaxation of internally cured concrete with super absorbent polymers (SAPs) by ring test is still lacking. Tests on the cracking resistance of concrete with different amounts of SAPs (0%, 0.05%, 0.16%, and 0.26% by weight of cement) were conducted using restrained ring test in present study. Test results showed that: (1) the strain in the restrained steel ring decreased with the increase of amount of SAPs; (2) the residual stress of concrete ring decreased with the increase of amount of SAPs; (3) the stress rate decreased with the increase of amount of SAPs; (4) the relaxed stress increased with the increase of amount of SAPs after the initiation of drying; and (5) the time to cracking for concrete increased with the increase of amount of SAPs.