Analysis of shear rate inside a concrete truck mixer

In addition to the mixing energy applied to the fresh concrete (i.e. shearing during mixing), the shear history after mixing is also important. This applies especially to binder rich concretes like the different types of high performance concrete (HPC). With this in mind, the shear rate is analyzed inside a drum of a concrete truck mixer. The objective is to better understand the effect of transport of fresh concrete, from the ready mix plant to the building site. The analysis reveals the effect of different drum charge volume and drum rotational speed. Also, the effect of yield stress and plastic viscosity is investigated. The work shows that the shear rate decreases in an exponential manner with increasing drum charge volume. It is also shown that for a given drum speed, the shear rate decreases both with increasing plastic viscosity and yield stress.This work has been funded by the Icelandic Centre for Research - RANNIS [grant numbers 163382-051, 1006100202], Norcem AS (Heidelberg Cement Group) and ReadyMix Abu Dhabi."Peer Reviewed

Concrete mixing truck as a rheometer

Publisher's version (útgefin grein)An increasing interest has emerged in correlating the output of the concrete mixing truck to values obtained by rotational rheometers. The output of the former has usually been the hydraulic pressure needed to turn the drum. In such research, experimental errors can be higher than usual, which makes it harder to obtain confident relationships. To better understand the physical characteristics of the truck's Theological values, the above analysis is made by a series of computer simulations (i.e. with CFD). From this, it is evident that the slope H of the truck's pressure values depends both on the plastic viscosity mu as well as on the yield stress tau(0). However, for the intercept G of the truck's values, it is mostly dependent on the yield stress tau(0). In addition to this, both values H and G depend on volume of concrete in the truck as well as on density.The Icelandic Research Fund -RANNIS (grant numbers 163382-051,163382-052,163382-053) and Norcem AS (Heidelberg Cement Group)."Peer Reviewed

Low Carbon Concrete Possibilities: EPD and Regulations in Northern Periphery and Arctic

Concrete is one of the most common building materials in the Northern Periphery and Arctic, and therefore we should pay attention to its quality while reducing its carbon footprint. The concrete industry has established many measures to limit greenhouse gas emissions from concrete, as stated in the environmental product declaration (EPD). The most significant contributor is cement (common dose between 250 and 600 kg per 1 m3 of concrete) in a concrete binder. Aside from the use of alternative fuels for cement production, new alternative materials for cement replacement are being sought. Those materials are called supplementary cementitious materials and mainly originate from industrial waste streams. Some of the materials are already standard and limited by the maximum allowed replacement, and some are new and still under investigation. The benefits and limitations of low-carbon concrete regulations in Norway, Sweden, Iceland, and Finland are demonstrated on three different concrete mixes in this article. The sorting of a reference mix and two low-carbon concrete mixes according to 4 different systems showed the informative character of the Icelandic system and the underestimation of possibilities for the carbon footprint of concrete in the Swedish classification system