Effect of methyl cellulose on cement hydration and pore creation in high-strength mixes at elevated temperatures

Abstract

Concrete is known for its inherent fire resistance in addition to several other desirable properties, making it a highly used construction material. Newer scenarios have given rise to enhanced use of high-strength concrete (HSC). However, HSC possesses a dense microstructure because of the lower water-to-binder ratio and finer filler materials. HSC thus has a tendency of explosive spalling when subjected to a rapid increase in temperature. Fibers such as steel and polypropylene (PP) increase the tensile strength and create microchannels in HSC to mitigate explosive spalling, respectively. However, these fibers possess the challenge of lower workability and fiber agglomeration during the mixing of fresh HSC mixes. Water-soluble polymers have been shown to reduce spalling in high-strength mixes at elevated temperatures without compromising on workability. The present work investigates the effect of methyl cellulose (MC) polymer on the hydration of cement and its potential to create additional pores in high-strength mortar mixes at elevated temperatures. The addition of 0.5% MC increased the initial and final setting time of ordinary portland cement by 16% and 10%, respectively. Bound water calculations showed retardation in the initial hydration rate after 1 day of hydration. However, thermal characterization and Fourier transform infrared spectroscopy (FTIR) results demonstrated that the addition of MC polymer did not alter the rate and degree of hydration of cement pastes in the long term. MC polymer showed high pore creation ability when subjected to elevated temperatures. Higher mass loss and water absorption capacity of MC-mixed mortar samples indicate the formation of interconnected pores that can effectively mitigate explosive spalling. The formation of pores was also confirmed through ultrasonic pulse velocity measurement. The present work is expected to form the basis, and future adoption of MC as a cost-effective water-soluble polymer as admixtures in HSC to reduce the susceptibility to spalling at high temperatures.