Internal bonding microstructures characterisation between plant nanocellulose and concrete mortar mixtures for indoor Radon-222 gas emanation reduction

Abstract

• CNF crystallinity index fosters by high frequency ultrasonication. • Great CNF dissemination enhances mechanical strength of the composite brick. • CNF significantly impact internal porosity nanonization of the composite brick. • Tiniest internal porosity observed on 40 mL kenaf CNF composite brick. • Lowest 222 Rn concentration emanated from 40 mL oil palm CNF composite brick. Radon-222 ( 222 Rn) is a natural radioactive gas produced by the radium-226 ( 226 Ra) decay process, which is part of the uranium-238 ( 238 U) decay series. 222 Rn gas can penetrate into the respiratory system during the inhalation process and have an indirect effect on lung tissues due to energetic alpha particles. Brick is a common building material that consists of rock, water, and sand. It is the most prevalent source of 222 Rn gas emanation to humans in an indoor building environment. To reduce indoor 222 Rn gas emanation, kenaf and oil palm cellulose nanofibrils (CNF) were mixed into bricks in certain ratios and acted as liquid fillers. CNFs were produced by using chemical pulping, bleaching, and ultrasonic techniques. Ten composite bricks with different ratios of CNF and one control brick were fabricated by following Malaysia Standard (MS 7.6:1972). The characterization of CNF was done using Fourier Transformed Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). The Brunauer-Emmett-Teller (BET) was used to analyse the internal porosity and surface area of the fabricated bricks. 222 Rn concentrations in the bricks and humidity inside the prototype Perspex box were recorded using the Radon Sentinel Monitor Model 1030. The surface areas for control brick, 40 mL kenaf, and oil palm CNF composite bricks are 3.4473 m 2 /g, 4.449 m 2 /g, and 4.9025 m 2 /g, respectively. Meanwhile, pore sizes for control brick, 40 mL kenaf and oil palm CNF composite bricks are 2.92 nm, 0.347 nm and 2.27 nm, respectively. The highest 222 Rn concentration was measured in control brick, which is 3.77 pCi/L, followed by 40 mL kenaf CNF brick and 40 mL oil palm CNF brick, with readings of 1.4 pCi/L and 0.93 pCi/L. The incorporation of CNFs has the ability to reduce 222 Rn emissions while increasing the physical strength of the bricks.