The effects of nanosilica on the fresh and hardened properties of 3D printable mortars

This study presents the experimental results of an investigation on the effects of nanosilica NS on the material characteristics of printable mortars used for additive manufacturing. Printable cement mortars based on Ordinary Portland Cement, limestone filler and silica sand were modified with different dosages of nanosilica from 2 to 6 by weight of binder and its influence on their hydration, rheological, mechanical and transport properties was assessed. The study showed that NS accelerates significantly the setting and hardening of printable mortar, while reducing its open time. Moreover, an increment of yield stress, together with an increment in NS dosage, was found to have occurred. The incorporation of an optimal NS dosage results in a noticeable increase in the compressive strength and alteration of the pore structure as determined by the MIP measurements. Moreover, transport properties of the produced mortar are significantly improved due to incorporation of NS. In addition to the microstructure refinement, Micro CT and scanning electron microscopy SEM studies revealed that 3D printed mortars exhibit pore anisotropy in accordance with the printing direction. However, incorporation of NS in the mixture resulted in improved buildability, thus decreasing pore anisotrop

Shear-banding in a lyotropic lamellar phase, Part 2: Temporal fluctuations

We analyze the temporal fluctuations of the flow field associated to a shear-induced transition in a lyotropic lamellar phase: the layering transition of the onion texture. In the first part of this work [Salmon et al., submitted to Phys. Rev. E], we have evidenced banded flows at the onset of this shear-induced transition which are well accounted for by the classical picture of shear-banding. In the present paper, we focus on the temporal fluctuations of the flow field recorded in the coexistence domain. These striking dynamics are very slow (100--1000s) and cannot be due to external mechanical noise. Using velocimetry coupled to structural measurements, we show that these fluctuations are due to a motion of the interface separating the two differently sheared bands. Such a motion seems to be governed by the fluctuations of $\sigma^\star$, the local stress at the interface between the two bands. Our results thus provide more evidence for the relevance of the classical mechanical approach of shear-banding even if the mechanism leading to the fluctuations of $\sigma^\star$ remains unclear

Does Reviewing Lead to Better Learning and Decision Making? Answers from a Randomized Stock Market Experiment

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Escape rates for noisy maps with anomalous prefactors

The escape rate from a point attractor across an unstable fixed point is studied for a noisy map dynamics in 1 dimension. It is shown that for additive white noise ξ with a distribution proportional to $\exp[-|\xi|^\alpha]\,,\alpha>1$, the escape rate is dominated by an exponentially leading Arrhenius-like factor in the weak-noise limit. However, with the exception of Gaussian noise ($\alpha=2$), the pre-exponential contribution to the rate still depends more strongly than any power law on the noise strength

Gelation, Shear-Thinning and Shear-Thickening in Cement Slurries

The rheological behavior of cement slurries may be described in terms of a few elementary behaviors: - the rapid formation of a gel, at rest; - the collapse of this gel under a critical stress directly related to the strength of the interparticle forces; - the progressive destruction of the gel fragments under moderate shear rate, with an increasingly shear-thinning behavior as the elementary particles gets smaller; - the reconstruction, at high shear rate, of shear-resistant structures, probably as chains of grains at contact; - complete jamming, possibly. We analyze the transition mechanisms from one step to the next one. We show how the addition of a dispersing agent favors shear-thickening at the expense of shear-thinning and how the control of the particle surface state and of interparticle friction restricts shear-thickening and the risk of jamming