Rapid self-sealing of cracks in cementitious materials incorporating superabsorbent polymers

•Rapid self-sealing of cracks by SAPs in cementitious materials was investigated.•Rapid swelling of SAPs effectively sealed the cracks within five minutes.•Most SAPs were split in the cracks while remaining bonded to the surrounding matrix.•Intact SAPs swelled across voids formed by swelling of SAPs including the cracks.•Split SAPs swelled only as much as the volume of voids by SAPs not including crack. The effect of superabsorbent polymers (SAPs) on rapid self-sealing of cracks in cementitious materials was investigated experimentally. Rapid swelling of SAPs effectively sealed cracks in materials within five minutes, resulting in the reduction ratio of water runoff per unit time in ranges of 34–52% and 52–72% for SAP dosages of 0.5% and 1.0%, respectively. X-ray computed tomography (CT) analysis showed that the swelling ratio of SAPs in the specimens was less than that in the filtered cement pore and synthetic solutions. Analyses of images obtained using X-ray CT, cryofracture scanning electron microscopy, and optical microscopy indicated that when a crack occurred, most SAPs, which were split because of the crack while remaining bonded to the surrounding cement matrix, swelled only as much as the volume of voids formed by swelling of SAPs, not including the crack. However, a part of the SAPs that remained intact swelled across voids, including the crack.