Water distribution and transport-kinetics model in fresh cement-based mixtures containing superabsorbent polymers based on 1H low-field NMR

Superabsorbent polymer (SAP) can be used as a curing agent in cement-based materials. Due to the replenish of humidity decline caused by the continuous consumption of water, the SAPs will contribute substantially to mitigating the shrinkage and obtaining the expected curing efficiency. Many studies have described the characteristics of water immigration in SAP-modified cement-based mixtures, but the travelled distance, volume, and transport-kinetics model of the water released from the SAP in cement-based materials still need to be investigated in detail. The paper focuses on the sustained water distribution of SAP at early-age cement-based mixtures. The swelling characteristics of SAP in different liquids and the water transport kinetics in hydrating cement-based mixtures were studied based on the ion concentration test and low-field Nuclear Magnetic Resonance (NMR) measurement. The results show that when SAP is in contact with water or cement filtrate, the exchangeable cations on the SAP structure will move freely to the solution and rapidly exchange with the metal cations in the solution within a few minutes (about 5 min). The most predominant form of water in fresh cement-based mixtures was the absorbed water (adsorbed on the surface of particles or in pores). Part of the adsorbed water or small capillary water on the surface of cement particles was consumed for hydration. The incorporation of SAP can prevent bleeding and segregation and promote the 28-day compressive strength of cement-based materials under the same total w/c ratio. Finally, the water-transport model in fresh cement-based mixtures was established and verified.

Automated summary

This paper investigates the curing effect and water transport characteristics of SAP in cement-based materials. When SAP is in contact with water or cement filtrate, exchangeable cations will quickly move to the solution and exchange with metal cations. The primary form of water in cement-based mixtures is absorbed water.