Investigation on the Rheological Property of Engineered Fly Ash Micro-concrete

Abstract

Nowadays, flowing concrete such as self-consolidating concrete, shotcrete, pumpable concrete, etc. is gaining significance due to its advantages such as ease of placing and homogeneity. Flowability can be achieved by proper proportioning of suitable materials. Dilution effect, increased paste volume and reduced growth of hydration products make fly ash a potential material to enhance flowing property. Apart from these reasons, the spherical shape of fly ash particles facilitates the easy movement of neighbouring particles by ball bearing effect. A new class of concretes using smaller aggregate sizes is in practice for repair purposes. Self-compacting micro-concrete (SCMC) is one such concrete which is homogeneous and flowable mix characterized by the combination of materials such as binders and aggregates of size less than 100 μm. The aim of this study is to develop SCMC by replacing cement with 20 and 40% fly ash. Flowability is the essential quality required for the repair/grouting material; hence, in this study, the rheological property of the mixes is given the main focus. Due to its high filling ability, SCMC is used for grouting purposes; however, its usage is limited to few applications owing to its brittle nature. Hence, in order to impart ductility and to control multiple micro-cracks, polymeric or metallic fibres are often incorporated in SCMC at varying dosages. In this study, various types of fibres such as steel, glass, polypropylene and carbon nano-tube (CNT) are attempted in this study independently. V-funnel and horizontal flow tests are carried out for assessing the flowability. Compressive, split tensile and flexural strength tests are conducted for obtaining the mechanical properties. Among the various mixes attempted, the fresh and hardened properties shown by the mixes with quartz powder and CNT are better. The flexural strength of about 9.4 MPa at 28 days was obtained for the CNT incorporated mix made of 20% fly ash replacement.