Development of three-dimensional characteristic values for the classification of aggregates - Part 2: Correlation between three-dimensional particle shape and fresh and hardened mortar properties

• Applicant: Professor Dr.-Ing. Wolfgang Breit
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: from 2018 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 413140723

Aggregates represent the largest volume fraction of concrete and mortar and their shape properties influence the properties in fresh as well as hardened state. Unlike standard laboratory procedures like the determination of flakiness or shape index computed tomography enables the determination of a wide range of three-dimensional shape parameters for every particle within an aggregate sample. Within the previous project a procedure was developed to scan aggregate samples as loose bulks and to automatically perform the necessary image processing steps. This includes the identification of bor-ders between touching particles which was performed manually so far. Characterization of particle shape of a representative sample of fine or coarse aggregates becomes now possible. In literature, first experimental results of the influence of three-dimensional particle shape parameters on certain fresh and hardened mortar properties are reported. However, detailed analysis of optimal distribution of shape parameters within the aggregate fraction to precisely influence fresh or hardened mortar properties is still missing. Main focus of the further course of the project is the analysis of the relation between three-dimensional particle shape determined using computed tomography and fresh and hardened mortar properties. Correlation between this shape characterization of four fine materials and the fresh mortar properties water demand, packing density, flowability, mini slump, dynamic viscosity and yield as well as the hardened mortar properties bending strength, compressive strength and Young’s modulus is investigated. For mortar tests aggregates with different values of flakiness, elongation, angularity or surface irregularity are used. Optimal distribution of shape parameters within the aggregate fraction is derived based on an analysis of covariance. First aim is to compose the aggregate fraction for mortar in dependence of the aspired field of application based on the optimal shape parameter distribution and to control fresh and hardened mortar properties by means of aggregate shape. Second aim is to find optimization approaches for crushed aggregate production.

• DFG Programme: Research Grants