Using an Eirich Mixer, Leipzig University, the Institute for Structural Concrete and Building Materials in Germany, conducted a research project to determine the influence of mixing technology on the fresh concrete properties of HPFRCC.

High Performance Fibre-Reinforced Cementitious Composites (HPFRCC) serves as a more reliable transfer of production process from a laboratory environment into practice compared to conventional plants for ready-mixed concrete. An Eirich intensive mixer, renowned for ongoing homogenous mixing results and advanced mixing technology, was secured for the research project.

In a laboratory environment, the researchers studied the effect of the mixing period, intensity and order, including breaks, to determine how these parameters affect the HPFRCC fresh concrete properties. During the mixing process, the temperature of mixtures, engine speed, engine output and energy consumption, among others, were recorded and graphed constantly. Using the Eirich mixer it was shown that the HPFRCC mixtures could be produced methodically and homogenously, which is essential for the acceptance of these ‘high-tech’ materials in practice.

Mixing concrete is a complex procedure and can be divided into two parts. Within the first, the consistency of mix particles are changed by low shear velocities (distributive mixing), and in the second, agglomerations of mix particles are made more soluble by high shear velocities (dispersive mixing). In comparison to normal concrete, HPRFCC can be described as a six-material system consisting of cement, additives and additions, water, aggregates and fibres. Due to its concrete composition, the packing density of HPFRCC is higher than that of normal concrete. Mixing parameters such as particle size, distribution and shape, differences in density as well as their surface roughness is of primary importance. In order for mix particles to change their performance when mixing HPFRCC, kinetic energy must be supplied.

HPFRCC can be described as a group of fibre-reinforced cement-based composites which possess the unique ability to flex and self-strengthen before fracturing. It is a high performance material and its efficiency is attributable to its fresh and hardened properties. These can only be sufficiently utilised if the rheology of the fresh concrete offers optimal characteristics. Experiments with HPFRCC show that, for a usable concrete recipe, the desired properties in the fresh state are generated by frequent long mixing.

Performance of HPFRCC is influenced by its microstructure and the transition between matrix, aggregates and fibres. Research shows that besides composition and curing, mixing conditions during production affect the microstructure. In addition, the mixture performance is an indication of homogeneity and therefore a quality criteria. In addition, in a homogenous HPFRCC, only a few agglomerates of powder components and fibres remain. The achievable dispersion rate depends on the function of the mixer and the mixing regime, the mixing period and the mixing intensity. The Eirich intensive mixer was the ideal mixer for conducting these experiments.

With the Eirich intensive mixer different steps of mixing are possible. An advantage of the Eirich intensive mixer is constant data recording, which includes temperature of mix, control mode for mixer tools, engine speed, engine output, energy consumption, programmable mixing course, etc.

This recorded data from an Eirich intensive mixer enables traceability of the whole mixing process, and the data can be used to compare different concrete mixtures. The gained results indicate that the mixing processes have an emphatic influence on the obtainable HPFRCC properties in the fresh state.

“This is not the first time that Eirich mixers have been used by the scientific community for research purposes, and neither will it be the last,” says Louis Eksteen, Business Development Manager, Birkenmayer South Africa. “Eirich’s range of industrial mixers have always been at the forefront of technological developments. Their continued homogeneity capabilities, regardless of the environment within which they operate, make them ideal for practically any mixing application.”

Birkenmayer is a leader in industrial processing solutions and the exclusive South African representative and distributor for Eirich industrial mixers.