Effect of mineral admixtures on fluidity and stability of self-consolidating mortar subjected to prolonged mixing time

► Prolonged agitation time can increase the risk of instability of the mixture. ► Fly ash increases the fluidity, but mixture is more prone to instability. ► MK provides stability retention particularly when prolonged mixing is into consideration. ► Effect of MK to stabilize mixtures is more noticeable at higher w/b ratio. ► Mixtures containing MK and FA have higher fluid capacity without any signs of segregation. During continuous mixing of concrete in a truck mixer for its hauling to a construction site, concrete should remain workable without any signs of instability. Good workability at construction site is essential for high quality concrete since concretes of bad workability are prone to yield low strength and poor durability properties. This paper presents the effects of water to binder ratio, binary and ternary blends use of fly ash (FA) and metakaolin (MK) on fluidity, viscosity, and stability of self-consolidating mortars (SCMs) subjected to prolonged mixing time. The obtained results indicate that, by prolonged mixing time, flocculated cement particles are dispersed and as a result, fluidity is increased and so, the risk of instability increases. In addition, increasing FA content from 0 in the reference mixture to 20% and 50% of total binder mass increased the segregation index by about 48% and 160%, respectively. Furthermore, mixtures containing MK and FA have higher fluid capacity without any signs of instability. The addition of 7.5% MK has significantly improved the overall performance of the mixture, including the segregation stability.