•The moisture transfer mechanism of SAP in cement slurry is revealed.•The method of shrinkage control and anti-fracture based on humidity compensation is proposed.•The rule of shrinkage development and fracture properties of SAP concrete is studied.•The enhancement mechanism for the hydration of concrete is discussed. In this work, we studied the moisture transfer mechanism of a superabsorbent polymer (SAP) in cement slurry, analyzed the influence of the SAP parameter on the mechanical property of concrete, and continuously monitored the internal relative humidity (IRH) of SAP curing pavement concrete using sensors. The method of shrinkage control and anti-fracture was proposed based on the principle of humidity compensation. Finally, scanning electron microscopy (SEM) was used to reveal the enhancement mechanism for concrete hydration. The results show that the SAP can reach a swell-equilibrium state in 30 min, and the larger the particle size is, the greater the absorptance is. Moreover, water retention of 88% can be maintained in the early period of the real hydration process. With the incorporation of SAP, the humidity saturation period of C40 pavement concrete is prolonged, and the IRH within the 28 d can be maintained above 90%. The increase in additional water can significantly relieve the total shrinkage strain of C40 pavement concrete within 28 d. The rupture process of SAP concrete is similar to that of the benchmark concrete, and the occurrence of cracking can be postponed, thereby significantly reducing the deterioration rate of the concrete after fracture instability. In summary, concrete with 0.134% of SAP2 (180–380 μm) shows the best shrinkage control and anti-fracture characteristics, where its compressive strength, IRH, peak load and fracture energy can be improved by 3.62%, 15.17%, 41.87% and 54.25%, respectively, and total shrinkage strain can be effectively reduced by 45.56%. Combined with the SEM method, the SAP concrete can generate a C-S-H gel cluster, thereby increasing the degree of concrete hydration. The number of primary cracks in early hydration was reduced, and the strength of the cement matrix was increased such that the concrete could effectively resist the moisture gradient and load deformation.