Enhancing the properties of lightweight aggregates using volcanic rock additive materials

Abstract

The aim of the research was to investigate the applicability of different volcanic rocks as additives materials in lightweight aggregates (LWA) production. This study explains how the high amorphous content can improve the bloating properties of expandable clays and the properties of the LWAs produced. Ten different expandable clays, suitable for lightweight aggregate production, were collected and tested from clay deposits in Egypt and Hungary. Perlite and rhyolite tuff were used as volcanic rock aggregates. The composition of the samples was investigated by X-ray fluorescence spectroscopy (XRF) and X-ray powder diffraction (XRD, Rietveld method), while their expandability was characterized by heating microscopy (HM). The ideal amount of volcanic rock additives (10 wt%) and the required firing temperatures (1225 °C for the Hungarian clays and 1275 °C for the Egyptian clays) were determined and the LWAs were then produced. The LWAs produced (by hand rolling) by mixing of 90 wt% of expandable clay with 10 wt% of the additive materials (10 wt% perlite or 10 wt% rhyolite tuff) as green pellets then fired for different temperature. The LWAs made by mixing 10 wt% perlite or 10 wt% rhyolite tuff were characterized by their density, compressive strength, mineral composition, and pore structure. All samples had a density of less than 1.2 g/cm3, so they can be used as LWA. The results show that the additives helped some clay samples produce LWA with higher strength but lower density than the reference sample which was used, enabling the construction of lighter but stronger structures. Compositional analysis of the LWAs showed that there is a strong correlation between the amorphous content of the samples and their density, with higher amorphous content resulting in lower density.