Durability and microstructural properties of lightweight concrete manufactured with fly ash cenosphere and sintered fly ash aggregate

Abstract

This paper addresses the durability and microstructural characteristics of lightweight concrete prepared by using fly ash cenosphere (FAC) and sintered fly ash aggregate (SFA) as replacements of natural fine and coarse aggregate, respectively. To fulfil this objective, sixteen concrete mixes are produced by using FAC and SFA, in various combinations i.e. 0%, 50%, 75% and 100% for each. Properties of concrete, such as compressive strength, resistance to sulphate, acid and chloride attack of concrete are studied. Further, the scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses for these concrete mixes are performed in support of the above strength and durability behaviours. The results of the present study reveal that though the compressive strength decreases with incorporation of FAC/SFA/both of these, appreciable strength is achieved using high volume of FAC and SFA (50% FAC and 75% SFA), which is also comparable to the strength of concrete without FAC and SFA. Further, the above mix achieves the required target strength of M25 grade concrete for which design mix is made as per IS 10262 (2009). It is found from the durability results that on one hand, the strength loss in concrete caused by sulphate attack and acid attack increases with increase in percentages of individual and combined substitution of FAC and SFA and hence, the concrete comprising FAC and SFA is not suitable for the structures exposed to acidic environments. On the other hand, when FAC or SFA or both of these contents increases, the depth of chloride ingress decreases, exhibiting better performance in saline environments than the concrete mix without FAC and SFA. The XRD and SEM analyses confirm the strength and durability characteristics of these mixes.