Shrinkage and thermo-mechanical properties of concretes incorporated with different substitutions of natural aggregates by cold bonded calcined attapulgite lightweight aggregates

Abstract

Calcined attapulgite (CAT), a fibrous calcined clay represents a promising option for advancement as a relatively new cementitious material with strong pozzolanic activity. This study investigates the impact and potential use of CAT in producing cold-bonded lightweight aggregates and their utilization in microsilica (MS) and fly ash (FA) blended concretes by analyzing the shrinkage and thermo-mechanical behavior. Initially, attapulgite rocks were processed including crushing, grinding and calcination to produce pozzolanic material. Following this, a dry powder mix of 80% calcined attapulgite (CAT) and 20% Portland cement (PC) was pelletized into calcined attapulgite lightweight aggregates (CATLWAs) using cold bonding with moisture and cured for 28 days. Subsequently, twelve concrete mixtures were formulated considering different substitutions of normal aggregate with CATLWAs and various proportions of PC, MS and FA. Mechanical properties such as compressive, splitting, and flexural strengths as well as elastic moduli and impact resistance were evaluated. Drying shrinkage, weight loss and thermal conductivity were assessed for all mixtures. Likewise, scanning electron microscopy was employed to analyze microstructural changes. Experimental results indicated that the incorporation of fine and coarse CATLWAs reduced the concrete unit weight by approximately 22% compared to the control mixture. However, there was a declining trend in mechanical properties, especially for impact resistance with increasing CATLWA content. However, the use of binary and ternary blends of cementitious materials improved overall mechanical behavior. Regardless of CATLWA content, the utilization of CATLWA enhanced thermal conductivity up to 46.9%. These findings hold significance for using CATLWAs in sustainable lightweight concrete production, thus advancing lightweight concrete technology and offering valuable insights into their advantages and constraints.