Crushed rubber waste impact of concrete basic properties

Cement CEM I 42.5 N was used for the investigation. Waste tire crumb rubber classified into fractions 2/4 and 4/6 was used for the tests. Sand in concrete mixes was replaced by crumb rubber at the proportion from 5% to 20%. Compressive strength, water absorption, ultrasonic pulse velocity in concrete modified with crumb rubber were measured in the tests. Structural performance indicators of concrete specimens were calculated. The tests results revealed that compressive strength dropped 68-61.3%. The calculation of structural performance indicators showed that higher content of crumb rubber in the mix reduces the relative pore and capillary wall thickness and the spare pore space. With higher content of crumb rubber in the specimens the spatial inhomogeneity indicator gradually increases because the bigger amount of coarser rubber granule causes uneven distribution of pores and capillaries by their length. When up to 20% of fine aggregate in concrete mixes is replaced by crumb rubber the predicted freeze-thaw resistance increases.