Properties of concrete with thermal treated recycled concrete aggregates and cement
Examensarbete för masterexamen
The cement and concrete industries are accountable for 7% of global CO2 emission and 2530% of all waste generated; in the form of construction and demolition waste (C&DW). It is therefore imperative to find methods to reduce the impact from these industies. In This study both the cement and aggregate part of concrete are investigated. About 70 kg of concrete were recycled, where 3 kg was cement and the remaining part was aggregates. The concrete was crushed to appropriate size and then heat-treated for 4-7 hours in 650C. After cooling the crushed material was grinded in a ball mill for 1 hour. The material was then sieved into the following fractions, 0-0.075 mm, 0.075-0.125 mm, 0.125-2 mm, 2-4 mm, 4-16 mm. Were 00.075 mm and 0.075-0.125 mm are considered as the cement fractions and 4-16 mm are the aggregates. The fractions 0.125-2 mm and 2-4 mm were not used in this study. The recycled material was mixed in different compositions with new cement and aggregates. For the recycled cement six different cement mixtures were made, including a reference. The ratio of recycled to new cement was 0/100 (reference), 10/90, 25/75 with 3 different cement fractions, and 50/50. The compressive strength was measured after 1, 7 and 28 days. After 28 days the reference showed a compressive strength at 61.7 MPa while the recycled material had results from 57,6 MPa for the 10/90 mix, down to 28.7 MPa for the 50/50. For the aggregates five mixtures were blended with the following ratios: 0/100 (reference) 25/75, 50/50 and 100/0 with heat-treated and non-heat-treated aggregates. The compressive strength for the concrete samples were determined after 1, 7 and 28 days. After 28 days the compressive strength for the reference sample was 61.7 MPa and the strength of the casted heat-treated mixtures were all around 56 MPa after 28 days, whilst the non-heat-treated had a somewhat higher compressive strength at 61.5 MPa.