The Civil Engineering Contractor February 2018 | Page 23

TECHNOLOGY
“Recycled concrete aggregate made from crushed concrete has proven viable and makes economic
and ecological sense.” Daniel van der Merwe – PPC
the mix actually performs better
than concrete made with virgin
materials, and can be used as a
high-performance concrete for
the construction of bridges and
structural building elements.
Key innovative procedures
and insights have shown that
there will always be unhydrated
cement available in recycled
concrete aggregate to form
cementation pastes for a new
mix. By using the fine fraction
of the recycled material and
reclaimed water, nucleation sites
for cement crystal are created
that are already hydrated and
therefore supports additional
hydration.”  
Furthermore, the recycled
aggregates
having
some
cementitious
mater ial,
encourage crystal growth and a
better microstructure, making
a reduced total cementitious
content possible. Recycled
aggregate has made it possible
to use more supplementary
cementitious
materials,
producing a denser concrete
that requires little or no
waterproofing.  
Van der Merwe says that the
recycled concrete aggregate
mix can use up to 95% recycled
content with only 2% added
Portland cement. “Tests have
shown that using the recycled
materials leads to an 80% CO 2
reduction when compared
to new concrete mixes, with
a 75% embodied energy
reduction,” he says.
Transport costs for aggregate
continue to increase, and
finding good sources of virgin
material close to urban areas are
increasingly difficult. Recycled
aggregate is closer and more
readily available. It is stronger,
has a longer life cycle, and saves
money in replacement costs. nn
The Tate Modern — a converted
power station — is one of the most
visited art galleries in the UK, and,
in Johannesburg, the conversions
of derelict buildings in the CBD
and surrounds have created vibrant
cultural and economically active
nodes.” Also, in Cape Town, he says
that the reuse of the Old Biscuit
Mill has been a catalyst that has
regenerated the Woodstock area. 
Van der Merwe contends that
when considering buildings that
have reached the end of its first life,
the order of decision-making should
be: reuse of the building, reuse of
the components, and then — only
as a last resort — demolition, with
the recycling of materials. 
“The large volumes of potentially
reusable components and ‘building
waste’ that are land-filled —only to
be replaced with similar components
— have become unacceptable,” he
attests, adding that “Conservation
and performance-based legislation,
and the cost of demolition and
new construction, are driving the
design for deconstruction, reuse,
and recycling as key facets.  
“Recycled concrete aggregate
made from crushed concrete has
proven viable and makes economic
and ecological sense. As a coarse
aggregate, it is used in the same
way as a natural aggregate and is
particularly appropriate for use as
bedding material, concrete roads
and pavements, floors, reinforced
concrete, precast and masonry
elements, and foundations.”
Recently, a new concrete mix
that combines recycled materials
with a tiny amount of Portland
cement, was awarded a US award
for innovation.
Van der Merwe explains: “The
mix uses only 2% cement with the
rest of the mix consisting of fly ash,
slag, crushed recycled concrete,
recycled water, and admixtures.
Developed by Cemstone Products,
Daniel van der Merwe, architect at PPC, is the chief curator of the PPC
Imaginarium, one of South Africa’s largest art and design support platforms.
He co-initiated the national ArchitectureZA initiative in 2010 and has
participated as convener of the annual architectural conferences ever since.
He served on the SAIA (South African Institute of Architects) board and
its MANCO as convener: marketing. Van der Merwe is the immediate past
president of GIfA and currently serves as secretary on its MANCO.
CEC February 2018 - 21