Production of Lightweight Concretes from Pumice/Bentonite Mix

Abstract

This study deals with the replacement of pumice by bentonite in the production of lightweight concretes. Pumice Aggregate is highly recommended in lightweight concrete blocks either blended or as an all in a pumice mix. Expanded clay aggregate has been pelletized and fired in a rotary kiln. During firing, the organic compounds in the clay burn off, forcing the pellets to expand. The resulting pellets are lightweight, porous and have a high crushing resistance and they can use as replacement for pumice aggregates. Lightweight concretes were prepared from clay materials under investigation by firing the activated bentonitic materials with Na2CO3 (5%) up to 1150 °C using a rate of heating 20 °C/min. The results showed that the Egyptian expandable clay can be substituted for pumice in the building block and concrete applications. Lightweight concrete pastes from different percentages of palletized bentonite and pumice aggregates showing that the compressive strength, density and bulk density are affected by the shape, percentage and grain size of the aggregates and interfacial zone between the aggregates. Most of the hydration process and strength gain take place within the first month of the concrete life cycle, but the hydration continues at a slower rate for many years. Some needles like shape of calcium silicate hydrate crystals can be observed forming skeleton shape morphology. Strength minerals formed which increase the concrete strength and are represented by calcium silicate-hydrate and calcium aluminate-hydrate.