Investigation of Some Technical Properties of Recycled Materials
The use of aggregates with different grades could have significant influence on workability and strength of concrete. A lower percentage of AIV indicates tougher and stronger aggregates. RA density is slightly lower than that of NA, probably because of the presence of impurities and old cement paste. Water absorption in RA ranges from 3-12% for coarse and fine fractions; this value is much higher than that of the natural aggregate for which the absorption is about 0.5- 1.0%. The substitution of PFA and RGD to partially replace cement improves and maintains, and at the very least did not adversely influence, the workability of RAC-SCC. Compressive strengths of RAC achieved higher strength with age reaching after 90 days. NAC and RAC concrete mixes with 30% PFA as a substitute for the cement exhibited substantial increase of strength at later, tensile and flexural strengths at 28 days of NAC-SCC-0.9SP (Mix 3) were relatively enhanced. The increased strengths were most likely due to the enhanced matrix of the concrete. The lower w/c ratio’s influence clearly appeared in SCC without cement substitution; the compressive of strengths, particularly the tensile strength, was observed when 30% of the cement was replaced by PFA compared to all other mixes, the 90 day compressive strengths were less than the target mean strength. Bleeding due to use of RA is generally similar to that of natural aggregates. An internal friction angle (φ) of 48.8˚ and an apparent cohesion (c) of 41.1 kPa were corresponded to the Mohr Coulomb failure envelope of crushed brick sample sourced from site 1. Similarly, an internal friction angle (φ ) of 44.6˚ and a n apparent cohesion (c) of 65.5 kPa were corresponded to the crushed brick sample sourced from site 2.
