Ceramics-Silikáty 65, (4) 354 - 362 (2021)

In an attempt to solve the uncontrollable water absorption of a superabsorbent polymer (SAP), microcapsules (MPCP), with calcium alginate and paraffin powder as the main raw materials, were prepared. The structure and water absorption properties of the MPCP was characterised and its influence on the shrinkage performance of a cement mortar was studied. The shrinkage-reducing mechanism of the MPCP was analysed through the heat of cement hydration, pore structure and relative humidity (RH) of the cement mortar. The results show that the MPCP particles are based on a calcium alginate network skeleton structure with a paraffin wax filling the round particles in the skeleton cracks, where its content determines the water absorption of the MPCP. The MPCP exhibited a good internal curing effect. The internal RH of the mortar containing the pre-absorbed MPCP basically changed as much as that containing the pre-absorbed SAP. The shrinkage of the MPCP-containing mortar reduced by more than 8% compared with the SAP-containing mortar after 7 days. The reason was that the MPCP absorbed the heat of the cement hydration and reduced the shrinkage caused by the excessive heat of the early cement hydration. In addition, because the water absorption of the MPCP is controllable, the MPCP exhibits little effect on the pore structure of cement-based materials. Therefore, the compressive strength of the cement mortar with the pre-absorbed MPCP content is 39 times that of the pre-absorbed SAP, which was only 2.3 MPa lower than that of the corresponding SAP-containing cement mortar.