Development of Low-Carbon Lightweight Concrete Using Pumice as Aggregate and Cement Replacement

An experimental investigation was conducted to develop a low-carbon lightweight aggregate concrete (LWAC) using naturally occurring aggregates and evaluate its mechanical performance. Lightweight aggregates used in structural concrete are commonly manufactured from recycled pulverised fuel ash or expanded clay, which require high temperatures during production. Additionally, the availability of traditional supplementary cementitious materials used in concrete, such as Ground Granulated Blast Furnace Slag (GGBS), is diminishing. Therefore, more environmentally friendly alternatives are required. Pumice, a naturally occurring lightweight stone formed due to the rapid cooling of magma from volcanic eruptions, poses a promising candidate for using as lightweight aggregate, whilst it might also exhibit pozzolanic properties that make it suitable as a cement replacement material. Therefore, the present study is focused on examining the development of low-carbon LWAC mixes with pumice as coarse aggregate and ground pumice as cement replacement. In addition, a novel recycled waste known as Lytash was trialed as a filler. This is a by-product of the manufacture of fly-ash based lightweight aggregates (commonly known as Lytag, which is in itself is a recycled by-product from coal fired power plants). The fresh and hardened densities of concrete were evaluated as well as the compressive strength (targeting a strength class LC30/33). It was found that lightweight aggregate concrete with a density of less than 1800 kg/m3 was possible to achieve. Furthermore, the pozzolanic reactivity and X-Ray Diffraction (XRD) testing; as well as the 28 days compressive strength of samples tested revealed the potential of pumice powder to be used as a cement substitute. Embodied carbon calculations were also carried out accentuating the savings in carbon footprint that can be achieved with pumice aggregate and powder.