Concrete mix design with crushed aggregate

Purpose and goal

The purpose with the project was to increase the knowledge, among aggregate- and concrete producers, how to use crushed aggregates in concrete production. The goal was to suggest simple test methods to evaluate the aggregate propperties that are important for concrete mix design. The Project has reached the goal by suggesting a test procedure that will give relevant information if the aggregate is suitable for concrete production and how it will affect the concrete mix design. A mix design philosophy has been presented but it has not been verified in this project.

Expected results and effects

The result of the project is that sieve curve, particle shape and water demand are the properties that must be tested first to evaluate crushed aggregates for use in concrete. The properties are achieved by wet sieving, loose packing/flow time and mortar spread flow. Crushed sand can be improved by VSI crushing and air classification but the benefit in concrete composition must be compared with the cost for the improvements. The water demand of the sand has the largest impact on the concrete mix design regarding cement paste volume, admixture dosage and stone content. .

Planned approach and implementation

The project consist of several parts that were carried out differently. A litterature study based on previous crushed aggregate studies was made to find how aggregate properties influence the concrete composition. Concerning test methods, both a litterature study and method development in the laboratory were performed. The evaluation of different processes to improve crushed sand was based on concrete trials in the laboratory. The concrete mix design philosophy was mainly based on practical experience from concrete production by interviews with several concrete technicians.