Portable and instant sensor for fresh concrete mix ratio measurement

Abstract

The civil construction market, specifically in Brazil, shows great potential for growth and improvement, as well as innovation and control. Observing the evolution of cement sales, which has surpassed 60 million yearly tonnes, our team has identified an opportunity to contribute through the usage of technologies originally developed for the monitoring of industrial flows. There is currently no commercially available tool capable of instantly measuring the mix ratio of concrete (mixture proportions of cement, water and total aggregate) during its hydrated precure stage, whether it is freshly mixed onsite or purchased from a professional concrete delivery company, and this is the blank on which we want to act. Based on the Wire-Mesh Tomography (TWM) technique, studied by researchers in LEMI (Industrial Multiphase Flow Laboratory - São Carlos School of Engineering, University of São Paulo) since 2008, this proposal aims at developing equipment capable of determining the mix ratio of fresh concrete through the measurement of its electrical properties. The TWM measurement principle has already been proven capable of identifying the spatial distribution and volumetric proportions of three-phase mixtures in industrial flows composed of water, oil and gas, with high spatial and temporal resolution. This research aims to use this technology principle (electrical impedance measurement) for homogeneous concrete mixtures measurement with variable component proportions, demanding additional studies for which the researchers at LEMI have the necessary qualifications. In a given construction site, multiple types of mix ratio can be used, based on the required application. Compliance to the specified mix ratio has a direct impact on construction safety, quality and costs. Even though these ratios are easily specified, guaranteeing this compliance is not an easy task both when mixing onsite and when buying premixed concrete from third parties. This tool will be a competitive advantage for professionals that have real concerns about mix ratio compliance and who will often oversize their structures to compensate for this limitation. This will also be advantageous to concrete companies who want to deliver a guaranteed mix ratio as added value to their customers, considering the competitive and tamper prone market to which they are exposed. To achieve this goal, diverse samples of fresh hydrated concrete mix will be prepared and submitted to electrical impedance measurements. The component proportions used will be based on commonly used mix ratios from civil engineering applications, varied in a controlled and predetermined manner. A theoretical and practical study on different types of impedance probe will be also performed as a means to determine the optimal geometries, materials and insulations as a function of their usage practicality and measurement accuracy. In possession of data from these measurements, with the spectrum of impedance values, the best excitation wave frequency will be determined and employed in mathematical models to correlate the mix ratio from the read impedance value. (AU)