Page 336 - New Trends in Eco efficient and Recycled Concrete

Equivalent functional unit in 11

recycled aggregate concrete

1
2
Jorge de Brito , Luı´s Evangelista and Jose ´ D. Silvestre 1
1
CERIS-ICIST, Instituto Superior Te ´cnico, Universidade de Lisboa, Lisboa, Portugal,
2
CERIS-ICIST; ISEL, Instituto Superior de Engenharia de Lisboa, Lisboa, Portugal

11.1 Introduction

The use of recycled aggregate (RA) concrete strongly relies on its potential eco-
nomic and environmental advantages. Under equal circumstances (same composi-
tion except for the aggregates themselves) RA concrete is expected to have a
similar or worse performance than the corresponding natural aggregate (NA) con-
crete. In other words, the use of RAs in concrete production can only be justified if
these potential economic and environmental advantages can be demonstrated.
This chapter will focus on the environmental impacts issue, but also takes into
account the performance of comparative economic analyses of recycled and NA
concrete (NAC) mixes. In fact, and since the technical performance of these mixes
is not the same, as will be demonstrated in this chapter, by analysing the various
fundamental properties of concrete, the direct comparison of concrete elements
with the same size/volume but made with concrete mixes with different types of
aggregates is not correct (actually this issue should also be raised when comparing
concrete mixes made with different types of NAs, e.g., limestone, basalt, granite or
sandstone).
Therefore, a methodology must be devised in order to define the size of concrete
elements that can guarantee the same performance according to the various limit
states (ultimate and serviceability) defined in the structural codes (in this case,
Eurocode 2 was used as the reference code). Bearing in mind the fact that RA con-
crete is a new material and that structural designers need to become confident about
their safe use in structures, a conservative approach was used. A NA reinforced
concrete element is used as a reference and all limit states are checked and com-
plied with, thus, defining the element’s geometric characteristics, as well as the
steel reinforcement area and location. Then adjustments to these various character-
istics are made in the compared RA reinforced concrete element to guarantee that
all limit states are also complied with. The conservative nature of this approach
results from the fact that the margin of safety of the various limits states of the RA
reinforced concrete element will be equal to or larger than for NA reinforced con-
crete element. The resulting elements can then be compared, since they correspond
to effectively equivalent functional units (EFUs).

New Trends in Eco-efficient and Recycled Concrete. DOI: https://doi.org/10.1016/B978-0-08-102480-5.00011-7
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