Abstract
Rheological curves of cement–fly ash (C–FA) paste incorporating nanomaterials including nano-SiO2 (NS), nano-CaCO3 (NC) and nano-Al2O3 (NA) at different resting times (hydration time of 5 min, 60 min, and 120 min) were tested with a rheometer. The rheological behaviors were described by the Herschel–Bulkley (H–B) model, and the influences of these nanomaterials on rheological properties of C–FA paste were compared. Results show that the types, content of nanomaterials and resting time have great influences on the rheological properties of C–FA paste. Incorporating NS and NA increases yield stress and plastic viscosity, and decreases the rheological index of C–FA paste. When the content of NS and NA were 2 wt%, the rheological index of C–FA paste was less than 1, indicating rheological behavior changes from shear thickening to shear thinning. Meanwhile, with rising resting time, yield stress and plastic viscosity increased significantly, but the rheological index decreased evidently, showing paste takes on shear thinning due to the rise of resting time. However, incorporating 3 wt% NC and the rising of resting time did not change the rheological properties of C–FA paste. These differences are mainly that the specific surface area (SSA) of NS (150 m2/g) and NA (120 m2/g) are much larger than that of NC (40 m2/g). The huge SSA of NS and NA consume lots of free water and these tiny particles accelerate the hydration process during resting time.
Highlights
As the main by-product generated from coal-firing power stations, fly ash (FA), which mainly consists of active SiO2 and Al2 O3, has gradually become an essential component for modern concrete products [1]
(b) η0 of cement–fly ash (C–FA) paste with 0% and(c)1% NS almost increased with shear rate, but η0 of C–FA paste with 2% decreased with the rising shear rate
Kof C–FA paste was on the decline, but K of C–FA paste incorporating NS was onpaste incorporating incorporating NS
Summary
As the main by-product generated from coal-firing power stations, fly ash (FA), which mainly consists of active SiO2 and Al2 O3 , has gradually become an essential component for modern concrete products [1]. Replacing cement by a certain amount of FA can significantly improve workability in the fresh stage and the long-term properties in the hardening stage [5,6,7,8,9]. Fresh cementitious material (FCM) is a complex multiphase dispersion system, which consists of different particles with complex chemical constituents, resulting in different rheological behaviors. The incorporation of FA leads to the decrease of yield stress, plastic viscosity and thixotropy [10], which makes cementitious materials easy pour and cast. As a result of this, the workability of FCM incorporating FA has improved obviously. The decrease in plastic viscosity results in instability of FCM, including segregation, bleeding, and coarse aggregate sinking in the fresh stage, which affect the performance of hardened concrete. The improvement of stability of fresh cement–fly ash (C–FA) paste is important
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