Study on the Relevance of the Carbonated Fly ash in Concrete and its Performance Assessment with respect to Control Concrete and Fly ash Concrete

Abstract

Substantial amount of research has been undertaken towards finding a suitable substitute of cement as total or partial replacement in concrete, owing to concerns related to economy and ecology. Industrial wastes, which demonstrate pozzolanic activities, are preferred choices in this regard. Fly ash is a waste from coal based industries and a popular choice as partial replacement of cement, in regions where it is generated in large quantity. Fly ash concretes have displayed improved strength and durability. Capability of fly ash as a suitable reagent to sequester atmospheric carbon dioxide is an established research finding. Fly ash after carbonation is referred to as carbonated fly ash, whose application areas are limited to few fields such as mines and agriculture. Use of carbonated fly ash in concrete has not yet been reported in literatures. In the present research feasibility of using carbonated fly ash as a part substitute of cement in concrete has been investigated. newlineIn the present research, experiments are done to determine compressive strength, flexural strength, split tensile strength of carbonated fly ash concrete over a wide range of water curing age. Durability aspects considering strength loss and weight loss subject to chemical exposure have also been investigated. In order to draw inference regarding relative performance, similar set of experiments have been carried out on control concrete and fly ash concrete. Pore structure characterization, X-Ray diffraction and Thermogravimetric analysis have also been done to study the concrete performance. Two replacement levels for fly ash and carbonated fly ash have been considered through the experiments. Strength of carbonated fly ash concrete is observed to be more than that of control concrete when water curing period exceeds 180 days. The strength gain rate of carbonated fly ash concrete is seen to be higher than both control concrete and fly ash concrete at later curing age. Durability of carbonated fly ash concrete is observed superior to control concrete and fly ash concrete against exposure to chloride solution, sulphate solution and acid solution. To obtain information on pore structure, Mercury intrusion porosimetry has been conducted. The results reveal higher distribution of pores in narrow diameter range. The TGA indicates higher weight loss in carbonated fly ash concrete. XRD study indicates presence of crystallites favouring strength gain and durability. From the studies performed, carbonated fly ash can be recommended as a partial replacement of cement in concrete. Such use will be an economical and ecologically benign strategy. newline newline