Keleş, Ömer Faruk

Roller compacted concrete (RCC) pavements, which stand out as an alternative to conventional concrete and asphalt pavements, are increasingly preferred because of their high strength, fast construction, and low cost advantages. The properties of aggregates directly affect the performance in roller compacted concrete mixtures. In particular, the maximum aggregate particle size (Dmax) and gradation play a determining influence on the mixture's density, compressibility, and mechanical strength. This study aimed to investigate the effects of maximum aggregate particle size and gradation on the mechanical performance of roller compacted concrete pavement mixtures. Within this scope, roller compacted concrete pavement mixtures were produced using three Dmax (12.5, 19, and 25 mm) and three different cement dosages (300, 350, and 400 kg). Tests for physical properties on mixtures were conducted using unit weight and ultrasonic pulse velocity (UPV) tests, while tests for mechanical properties were conducted using compressive strength, flexural strength, and splitting tensile strength tests. Increasing the Dmax to 25 mm significantly improved the compressive and flexural strength of the mixtures. However, the splitting tensile strength increased up to 19 mm and showed a slight decrease when reaching 25 mm. The increase in cement content consistently improved all mechanical properties. Overall, the use of well-graded coarse aggregates with Dmax in the range of 19–25 mm was found to improve the mechanical properties and compressibility of roller compacted concrete mixtures.

Bulut, H. Alperen

This study was carried out to present a different approach to green concrete production by utilizing electronic waste (e-waste) and waste rubber powders in order to provide a solution to both the cost and carbon footprint problems arising from the rapid consumption of aggregate resources and cement. For this purpose, 0%, 5% and 10% of ewaste was utilized instead of aggregate and 0%, 2.5% and 5% of waste rubber powder was utilized instead of cement. In addition, mixtures in which both wastes were combined in concrete were also prepared and comparisons were conducted. Capillary water absorption, acid and sulfate attack tests were carried out on the concretes with different wastes at the end of 28 and 90 days. The capillary water absorption of concrete produced with 5% waste rubber powder at the end of 28 days (P5E0/28) was 80% less than the control concrete (C/28) (these values were 0.46, 2.36 respectively). It was determined that the utilization of waste rubber powder had a decreasing effect on the compressive strength losses of the concretes after acid attack compared to the control concrete, while e-waste had an increasing effect. It was determined that the compressive strength losses of the concretes in which waste rubber powder and e-waste were combined against sulfate attack were positively differentiated from both control concrete and concretes produced with single waste type. In parallel with the weight and compressive strength losses obtained after acid and sulfate attack, the results of the visual analyses of the concretes were similar. The use of 5% waste rubber powder in the concrete produced the greatest results. In addition, the ideal ratio between concretes in which e-waste and waste rubber powder used together was determined as 5% waste rubber powder and 5% e-waste. The results verified that e-waste and waste rubber powder can be considered for the production of green concrete.