|M.Sc Student||Daniele Kulisch|
|Subject||Recycled Aggregate as a Replacement for Fine Aggregate in|
|Department||Department of Civil and Environmental Engineering||Supervisor||Full Professor Katz Amnon|
|Full Thesis text|
The interest of the construction industry to find suitable alternatives to replace natural sand as fine aggregate in concrete production is increasing by the shortage of good quality natural sand and the environmental pressure to minimize natural sand extraction. Considering the use of fine aggregate from recycled concrete as a replacement for natural sand, the advantages are economic aspects, reduction of environmental impacts and saving resources.
Recycled material from two recycling plants in Israel was obtained and used as fine aggregate in mortar specimens. From the first recycling plant, three types of aggregate were obtained: fine (RA-1) and coarse (RA-2) aggregate after beneficiation and aggregate before beneficiation (RA-3). One type of aggregate was obtained from the second recycling plant, before beneficiation (RA-4). Mortar specimens were produced with cement, water and sand (four types of recycled sand and crushed sand for reference). Two water/cement (w/c) ratios (0.4 and 0.6) and two replacement rates (30% and 100%) were tested and compared.
The filler portion of recycled aggregates (<75 μm) was tested as fine aggregate in mortar specimens and compared with CaCO3 filler. Also, artificial recycled fine aggregate was obtained by crushing concrete produced in laboratory and by crushing cement paste produced in laboratory, which represents the cleanest and purest possible construction waste, without impurities. These artificial materials were used as fine aggregate in mortar specimens and compared with recycled aggregates from recycling plants and crushed sand.
Properties of the recycled aggregate show that beneficiation reduces the content of fines, organic matter, absorption capacity and increases the specific gravity of the material. Also, the presence of old cement paste attached to natural and crushed aggregate is clear.
The effect of recycled aggregates in mortar is also significant, with lower density, higher air content and longer setting times. For the same w/c, compressive strength is reduced for all recycled aggregates (from 3% using 30% RA-1 up to 53% using 100% RA-4). About durability properties, there is an increase in capillary absorption (total replacement), air permeability and carbonation depth, which are related to the old cement paste attached to the aggregates.
The effect of the filler portion as fine aggregate in mortar is also expressed by a reduction in compressive strength, especially for RA-4. It seems that the composition of the filler portion and the beneficiation process of the recycling plant have an influence on strength parameters.
Artificial recycled aggregate from crushed concrete (RFA-C) presents lower content of fines, higher absorption capacity and lower specific gravity, compared to reference. Artificial recycled aggregate from crushed cement paste (RFA-P) presents lower content of fines, higher absorption capacity (almost 10 times the reference) and significantly lower specific gravity, compared to reference. The granulometry of both artificial materials is similar to the reference.
As a result, compressive strength presents a reduction from the reference, but, similar values as RA-1 (low w/c) and to RA-2 (high w/c). The use of artificial recycled aggregate may not represent the real composition and components of recycled aggregates from a real recycling plant.