Effects of Using Cold Bonded Coarse and Fine Calcined Attapulgite Lightweight Aggregates on the Performance Properties of Microsilica and Fly Ash Blended Concretes

Recently, an incinerated fibrous clay in the form of calcined attapulgite (CAT) emerges as an encouraging avenue for progress in the realm of new cementitious materials, boasting good pozzolanic activity. This study aims to examine the strength and transport features of microsilica (MS) and fly ash (FA) blended concretes made of cold-bonded coarse and fine CAT lightweight aggregates. In this regard, attapulgite pure rocks were crushed, fined, and then calcined at a specific temperature to produce a pozzolanic material. Then, a dry powder composed of 80% CAT and 20% Portland cement (PC) by weight was transformed into calcined attapulgite lightweight aggregates (CATLWAs) by cold bonding pelletization process at room temperature. Then, they were cured for 28 days. Afterward, different concrete mixtures were designed in which normal aggregate was swapped out with cold-bonded coarse and fine aggregates in different percentages up to 100%. The binary and ternary cementitious blends of PC, MS, and FA were also taken into account at various contents. Concrete samples were tested at different ages to determine their transport-related performances based on the water permeability, gas penetration, and rapid chloride permeability. The strength and microstructural properties of the samples were also measured. The results revealed that with an increase in the volume friction of coarse CATLWA up to 100% and fine CATLWA up to 25% in the mixtures, a significant reduction in the strength up to 39% was observed. Additionally, transport properties especially for the sorptivity and rapid chloride permeability were deteriorating in case of 100% volume fraction of CATLWAs. However, it was observed that these adverse effects could be eliminated by introducing binary and ternary cementitious material systems in the mixtures.