Influence of SAP particle size on the thermal properties of cement-based materials at cryogenic temperatures

Abstract

Thermal properties can significantly affect the engineering properties of cement-based materials (CBMs) containing superabsorbent polymers (SAP) at cryogenic temperatures. This paper studied the pore structure of SAP-modified CBMs with a mercury intrusion porosimeter. The distribution and freezing behavior of free water were analyzed with a nuclear magnetic spectrometer and a differential scanning calorimeter. Moreover, the effect of SAP on the thermal diffusivity (α), specific heat capacity (C_p), and thermal conductivity (λ) of CBMs at cryogenic temperatures (−20 °C to −80 °C) was investigated using a laser thermal conduction instrument. The results show that the addition of SAP and the rise of SAP size can increase the cumulative pore volume. Raising SAP size will enlarge the pore size of gel pores and capillary pores. Moreover, adding SAP and the rise of the water-binder (w/b) ratio can raise the height of heat flow peaks and the accumulated ice content. The rise of SAP size promotes the growth of heat flow peak and its corresponding temperature. At 25 °C, the addition of SAP and the rise of the w/b ratio can reduce the α value, C_p value, and λ value of the matrix. When the temperature decreases from 25 °C to −80 °C, the α value gradually increases, while the C_p value and λ value both reduce. Adding SAP and raising SAP size and w/b ratio will enlarge the change amplitude of α value and C_p value, and reduce the change amplitude of λ value.