Heat transfer modelling and determination of material properties for sustainable masonry systems containing combustible materials in fire

A variety of innovative construction systems have been developed to promote sustainability. However, many of these systems contain biomass or recycled materials that are combustible, and this influences fire resistance and thermal properties. This paper presents a numerical investigation to determine the material parameters for (a) hempcrete, as well as masonry units containing (b) recycled plastic (RESIN8) and (c) crumb rubber, in fire. The latter masonry units studied have recycled synthetic contents ranging from 0 % to 50 % by volume. Complex heat and mass transfer phenomena are identified, and influence the temperature development under standard fire exposure conditions, making the accurate determination of conductivity and specific heat parameters difficult. During heating materials may melt, pyrolyse, combust, produce char, cause gas or moisture transport to adjacent areas, experience a change in density and develop an open matrix structure. The identification of these phenomena is important for understanding temperature development. Numerical models developed are validated against a series of furnace tests, with thermal parameters being determined in an iterative manner. In spite of the heat transfer complexities, it appears that the various phenomena counteract each other (e.g. decreasing density and conductivity being offset against increased porosity) resulting in constant parameters being able to sufficiently predict temperature development across the 2 h exposure with variation in experimental and numerical results being in the range of 0.4-22.7 %, although typically less than 9.6 % at 120 min. The determined thermal properties will assist with the development performance-based design models, with an application to insulation resistance ratings, heat release rates and smoke production being highlighted in this work.