6 research outputs found
Freeze-thaw durability of recycled concrete from construction and demolition wastes
Road engineering is one of the most accepted applications for concrete including
recycled aggregates from construction and demolition wastes as a partial replacement of the natural
coarse aggregates. Amongst the durability concerns of such application, the deterioration due to
freeze-thaw cycles is one of the most important causes decreasing the life span of concrete in
countries with a continental climate. Moreover, the use of de-icing salts, which is a common
practice to prevent ice formation on roadways and walkways, increases the superficial degradation
of concrete due to frost-salt scaling. Thus, this paper aims to assess the resistance to frost salt with
de-icing salts of two recycled concrete mixtures containing a 50% replacement of the conventional
gravel by recycled aggregates both of mixed and ceramic nature, i.e. containing ceramic percentages
of 34% and 100%, in comparison to a conventional concrete made with siliceous gravel. Therefore,
the surface scaling was evaluated based on EN 1339 (2004) on 28 days cured cylinders, exposed to
7, 14, 21 and 28 freeze-thaw cycles in the presence of sodium chloride solution. Given that no airentraining
admixture was used in any of the mixtures, the scaling of both conventional and recycled
concretes exceeded the 1 kg/m2 limit established by the European standard. Nonetheless, for the
casting surface, the recycled concrete with low ceramic content exhibited a similar behaviour to the
conventional concrete, whereas the performance of the recycled concrete with high ceramic content
was better. However, as expected, trowelled surfaces showed a worse performance and both
recycled concretes had a lower freeze-thaw durability than the conventional mixture. In any case,
the results suggested that the composition of the recycled aggregates could be used as a factor to
limit the differences in performance between recycled and conventional mixtures
Improving the quality of various types of recycled aggregates by biodesposition
Demand for construction materials has been rising in recent decades in many countries around the
world, placing a heavy burden on the environment in terms of both the natural resources consumed
and the enormous flow of waste generated. In order to obtain a more sustainable construction, it is
often suggested to reintroduce the industry’s own waste as input for the manufacture of new materials.
In this study, the use of construction and demolition waste of concrete or mixed concrete/ceramic
nature is investigated as a replacement of natural aggregates in concrete. The greater affinity of
recycled aggregates for water directly affects the workability and/or the concrete strength and
durability. One possible solution to reduce the aggregates water absorption is to apply a biogenic
treatment with calcium carbonate-precipitating bacteria that consolidate the aggregate surface or the
adhering mortar.
Experimental results show that the biodeposition treatment reduced the recycled aggregate water
absorption by generating precipitation in the pores and an impermeable outer layer, most effectively
on the roughest particle surfaces. The largest decrease happened in the aggregates with the highest
porosity. The biogenic layer had a good cohesion with the aggregates. The results of sonication
indicated that the most effective treatment was on recycled concrete aggregates (RCA) instead of
mixed aggregates (MA). Therefore, the treated RCA was used to make concrete for further
investigation. The concrete made with bio-treated RCA had a denser structure, a decreased water
absorption (around 1%) and an improved compressive strength (25%)