Recycling Excavated Clay to Produce ‘Sand-Like’ Material Through Sintering: Static Furnace Versus Rotary Kiln

Abstract

Traditionally, sand is used as infilling material in land reclamation projects in Singapore. One-third of Singapore area is underlaid with marine clay deposits; hence, marine clay generated from underground excavation works for building and infrastructure developments is a significant source of excavated material in Singapore. Marine clay is not a suitable material for land reclamation due to its low permeability and high compressibility, which results in excessive settlements and low bearing capacity problems. Given the availability of excavated marine clay in Singapore, this study focuses on transforming marine clay into a “sand-like” reclamation fill material using a heat-treatment process called “Sintering”. Sintering is a thermal process where the clay is subjected to high temperature (850 °C), in which the weak mineral in clayey soil is transformed into a stronger mineral, i.e. transformation of kaolin to metakaolin. The end product of sintered clay product can be designed to process ‘sand-like’ properties. In order to achieve this high temperature, either a static furnace or a rotary kiln could be used. This paper focuses on the comparison of these two methods for this sintering process. The main objective of the study is to find the optimum operating conditions of the rotary kiln so that less heating energy is used to produce a ‘good’ quality sintered clay product. The test results indicate a positive mineral change when the temperature is maintained at 850 °C for 10 min in the kiln. The sintered clay products had a friction angle of about 39° and hydraulic conductivity around 1 × 10^–3 m/s. Finally, the properties of sintered clay products produced from the rotary kiln and produced from the static furnace are compared.