Superhydrophobic foamed concrete based on response surface method: Mix design and its potential application in roofing systems

Abstract

This study employs the response surface method to optimize the mixture design of superhydrophobic foamed concrete. The study investigates the influence of calcium stearate (CS, dosage 1 %∼5 %), polydimethylsiloxane (PDMS, dosage 2 %∼8 %), and hydroxypropyl methylcellulose (HPMC, dosage 0.05 %∼0.2 %) on various properties of foamed concrete, including density, compressive strength, contact angle, and water absorption. Additionally, the research explores the application of superhydrophobic foamed concrete in integrated roofing systems and assesses its thermal and structural performance through finite element analysis. Results reveal that foamed concrete achieves a contact angle greater than 150° when formulated with a mix ratio of CS (3 %), PDMS (8 %), and HPMC (0.05 %), or CS (3 %), PDMS (5 %), and HPMC (0.125 %). A negative linear correlation between the heat transfer coefficient and the thickness of foamed concrete is found. Furthermore, the heat transfer coefficient is inversely related to the spacing between the concave and convex drainage boards. Specifically, for a toe spacing of 50 mm and foamed concrete thickness exceeding 70 mm, the heat transfer coefficient of the roof measures 0.788 W/(m²·K). When the roof thickness increases from 70 mm to 100 mm, the roof heat transfer coefficient drops to 0.69 W/(m2∙K). When the toe spacing is increased from 50 mm to 60 mm, the heat transfer coefficient of the roof drops sharply to about 0.66 W/(m2∙K) at the thickness of 50 mm. The insulation requirements for the roof are satisfactorily met to 0.8 W/(m²·K). Under applied roof loads, the maximum von Mises stress experienced by the integrated roof is 0.6 MPa at a toe spacing of 50 mm. With the increase of the roof thickness, the maximum value of the DAMAGEC damage coefficient gradually decreases from 0.3 to 0.17. The maximum damage position has always been at the weak position of the four corners, which is consistent with the actual use status. The research findings on superhydrophobic foamed concrete have significant theoretical and engineering application value. Moreover, the construction of an "insulation/hydrophobic integrated" roof system demonstrates the feasibility of an integrated roof system and the potential for insulation/hydrophobic integration in roof system construction.