# Automated Control of the Fresh State of Industrial Concrete Behaviour by Rheometer Test Adjustment
###### Abstract  
This study aimed to develop a rheometer prototype and define a procedure for adjusting the automated control of the fresh state of concrete. Sixteen batches were produced, and their fresh behaviour was measured at different testing times by applying the Abrams cone and flow curve test (FCT) as the rheological protocol. During this test, the yield stress and plastic viscosity of the concrete were measured in relative units. The rheometer prototype was used to define a new protocol to select the most suitable rheometer impeller arrangement and optimal FCT configuration. This protocol considers the torque at the end of the breakdown period, torque reduction during the breakdown period, segregation, and negative values of the yield stress in relative units. This protocol also enabled an iterative adjustment procedure, facilitating the use of a rheometer for the automated control of the homogeneity and behaviour of fresh concrete, as well as real-time decision making. fresh behaviour; flow chart; yield stress; plastic viscosity; concrete characterisation Article  
[PERSON], [PERSON], [PERSON], [PERSON], F. Automated Control of the Fresh State of Industrial Concrete Behaviour by Rheometer Test Adjustment  
[PERSON], G.  
shear stress are directly proportional to the impeller's rotational velocity and the torque, respectively [6]. This method permits the analysis of concrete flow at different shear rates; however, it does not permit the assessment of the viscosity and yield stress in fundamental units. The \"Two-Point\" device was modified and computerised by [PERSON] and [PERSON] [7]. Other apparatus employed to measure the rheology of concrete in fresh state are BTRHEOM, which uses parallel plates, IBB and ICAR rheometers, which employ an impeller, and BML and CEMAGREF-IMG, which are coaxial cylinder rheometers [8; 9; 10]. In the BML and CEMAGREF-IMG apparatus, one cylinder (outer for BML and inner for CEMAGREF-IMG) is rotated at various speeds. When the fresh concrete occupies the space between the inner and outer cylinders, the torque on the inner cylinder is measured. The amount of the concrete sample is the most noticeable distinction between these two rheometers, which is only 17 L for the BML, whereas it is 500 L for the CEMAGREFIMG tests [11]. The BTRHEOM rheometer is a parallel-plate apparatus. A cylindrical container with a fixed bottom plate is filled with a sample of concrete. The torque on a top plate inserted into the concrete is measured while it rotates at different speeds [11]. The ICAR, IBB and two-point rheometers have a rotating impeller which is introduced into fresh concrete in a cylinder-shaped container. The impeller of the two-point rheometer shows a helical pattern, but the IBB employs an H-shaped impeller. A four-blade vane is the impeller used in the ICAR device [10]. These are axial rheometers because the impeller rotates at the centre of the sample container, and the torque produced is recorded as a function of the rotation velocity. Although there is an apparent relationship between measurements for different rheometers, the absolute values determined for a specific mix are not the same. The measurement of the rheological parameters in absolute units is not possible in all rheometers. Rheometers with cone-plate, parallel-plate or concentric cylinders measure rheological values that are independent of the geometry. However, when measuring concrete rheology, due to the aggregate size, these geometries are not possible and relative measuring geometries must be employed (such us rotational devices). A relative measuring geometry provides values in relative units (rotational velocity, rps or rad/s, and torque, N m) as opposed to absolute units (shear rate, rps, and shear stress, Pa). The conversion of relative units into absolute measurements depends on the geometry of the device, on the fluid boundary conditions, etc., and sometimes a direct conversion is not possible [12; 13].