Non-destructive techniques (NDT) and statistical analysis for the characterization of bricks made with added glass

Abstract

The aim of this paper was to assess how adding crushed household glass to the clay mix affects the properties of handmade bricks. To this end, non-destructive techniques (NDT) were used to characterize solid bricks made with two mineralogically different clays with or without the glass additive. One of the clays (Jun) was rich in carbonates, while the other (Guadix) was richer in silicates and had no carbonates. The use of NDT combined with statistical analysis of the initial hypotheses proved to be a very useful method for evaluating whether these handmade bricks are suitable and efficient for use in heritage restoration and the construction industry in general. A second objective was to assess whether the firing temperature influenced the aesthetic (tested using videomicroscopy, colour measurement and radiography) and physical–mechanical (Leeb hardness test, ultrasonic pulse velocity and compressive strength) properties of the bricks. The addition of glass increased the vitrification and compressive strength of the bricks. The colour varied according to the raw materials used and the firing temperature. Radiography proved to be a very useful tool for observing the heterogeneous distribution of the density. In terms of physical–mechanical properties, the bricks from Jun performed better than those from Guadix, as confirmed by ANOVA analysis. However, the more pronounced variation in the colour of the bricks from Jun fired at 1100 °C made with added household glass could make them less suitable for heritage restoration work, where matching colours are a crucial factor.