Avoiding inaccurate interpretations of rheological measurements for cement-based materials Olafur H. Wallevik a,b , Dimitri Feys c , Jon E. Wallevik a, ⁎, Kamal H. Khayat c a ICI Rheocenter, Innovation Center Iceland, Arleynir 2-8, 112 Reykjavik, Iceland b Reykjavik University, Menntavegur 1, 101 Reykjavik, Iceland c Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, Rolla, MO, United States abstract article info Article history: Received 13 April 2015 Received in revised form 4 May 2015 Accepted 5 May 2015 Available online xxxx Keywords: Rheology (A) Experimental error Modeling (E) Kinetics (A) Dispersion (A) Rheology is a high quality tool to evaluate the effect of variations in constituent materials and mixture proportions on fresh properties of cement-based materials. However, interpreting rheological measurements is relatively complicated, and some pitfalls can lead to wrong conclusions. This paper offers a review of measuring devices and transformation equations used to express rheological parameters in fundamental units. The paper also discusses some of the major issues that can lead to errors during the interpretation of rheological measure- ments. Although the Bingham model is mostly used for cement-based materials, some non-linearity has been observed, necessitating the selection of an alternative rheological model, which could influence the rheological parameters. Other measurement errors related to thixotropic and structural breakdown, plug flow and particle migration are also demonstrated. The paper also discusses the challenges of using numerical simulations to derive rheological parameters for complicated rheometers or industrial devices, such as a concrete truck. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Research on cement-based materials has expanded rapidly over the last decades, focusing on multiple aspects and materials that influence the behavior in fresh, hardening and hardened state. In the last decade, many initiatives have been made to render concrete a more sustainable material and increase the service life of concrete structures. Advances in concrete science have led to new greater use of alternative materials, including supplementary cementitious materials (SCMs) [1–4] and SCMs from alternative sources [5,6]. Several efforts dealing with the development of novel construction materials have necessitated better understanding of aggregate packing [7–10] and the implementation of a variety of chemical and mineral admixtures to enhance concrete performance [11–13]. In addition, large efforts have been made by the cement industry to create more sustainable products and reduce energy needed in cement production. In parallel, many advances have been made in the last few years regarding the use of rheology to optimize the behavior of novel construction materials, such as self-consolidating concrete (SCC) and evaluate material science aspects of the suspension, including binder–admixture interaction and hydration kinetics. Under- standing the rheological properties is key in automation and special material processing, such as 3-D printing with cement-based materials. The consequences of the developments in research and implemen- tation of new cement-based construction materials are being studied in the fresh, the hardening and the hardened state of the material. New advances are also made in the characterizing equipment, adding specifications on concrete properties, beyond the 28-day required com- pressive strength. Similarly, to characterize fresh properties, rheology is introduced as an alternative to the nearly 100-year old slump test [14–16]. The advantage of rheology is the scientific description of the flow properties of cement-based materials and the more complete information gathered. In general, the resulting rheological properties are highly dependent on how the measurements are executed and on data interpretation [15,17]. Rheological measurements enable the determination of yield stress, plastic viscosity as well as thixotropic build-up at rest, thixotropic- and structural breakdown, and their variations with time. Slump testing offers an indication of yield stress of cement-based materials [18,19]. Further workability-oriented tests are necessary to evaluate other important rheological parameters, such as plastic viscosity and structural build-up at rest. The more complete characterization of fresh cement-based materials by means of rheology is a helpful tool in the development of specific chemical admixtures that alter the fresh properties [11,20,21] (see Fig. 1). Furthermore, even the cement properties, which show some variation slightly alter due to the complexity of the production process, can in some cases significantly affect the fresh properties of cement-based materials [22–27]. Examples are known of variations in yield stress and plastic viscosity, and their evolution in time, with Cement and Concrete Research xxx (2015) xxx–xxx ⁎ Corresponding author. Tel.: +354 522 9000; fax: +354 522 9111. E-mail address: jon.wallevik@vvpf.net (J.E. Wallevik). CEMCON-04960; No of Pages 10 http://dx.doi.org/10.1016/j.cemconres.2015.05.003 0008-8846/© 2015 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Cement and Concrete Research journal homepage: http://ees.elsevier.com/CEMCON/default.asp Please cite this article as: O.H. Wallevik, et al., Avoiding inaccurate interpretations of rheological measurements for cement-based materials, Cem. Concr. Res. (2015), http://dx.doi.org/10.1016/j.cemconres.2015.05.003