An eco-efficient approach to concrete carbonation - Eco-efficient Concrete - page 375

Table 15.3 Types of surface improving agents (Tsujino et al. 2007)

Type Oil (O) Silane (S)

Application Release agent used in wooden

form

Water-repellent agent with
permeability to the concrete
surface

Main
constituent

Mineral oil (paraffin) 85-95% Silicon analogue 28-32%

Emulsifying agent 1-5% Emulsifying agent Minute quantity

Lanolin fatty acid salt 1-5% Water 68-72%

State Emulsion Emulsion

sodium silicate solution, designated n42 solution; 1(b) diluted (50%) n42
solution; 2 diluted n42 solution and lime; 3 diluted n42 solution and silica
fume; and 4 diluted n42 solution, silica fume and lime. These treatments
were initially applied to coarse rca for the assessment of their effect on
the rca surface features.
They mentioned that the mixes with no chemical treatment had lower
carbonation depths. They also mentioned that since carbonation depth is a
function of the amount of water in concrete, lower carbonation depths could
result from high humidity or wet concrete. Tsujino et al. (2007) used an oil
and silane-type surface improving agents (Table 15.3) that increases the
resistance to carbonation both for W/b = 0.4 and 0.6. otsuki et al. (2003)
suggested a double mixing method to improve carbonation resistance. in the
double mixing method, the addition of water is divided into two stages. The
first portion of water is added into the mixer for 30 s after fine and coarse
aggregates have been mixed for 30 s. The mixing is then stopped while the
cement is being added into the mixer. This is followed by 60 s of mixing by
machine and 60 s of mixing by hand. After that, the final portion of water
is added for 30 s and the mixing continues for the last 90 s. This method is
devised to coat rca with mortar of a lower W/b ratio than the rest of mortar
matrix. Xiao et al. (2010) suggested the use of a maximum volume of coarse
recycled aggregates and the use of recycled aggregates from concrete with
minimum strength class as a way to increase resistance to carbonation.

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15.5 References
abbas, a.; Fathifazl, g.; isgor, o.; razaqpur, a.; Fournier, b.; Foo, S. (2009) durability
of recycled aggregate concrete designed with equivalent mortar volume method.
Cement and Concrete Composites 31 , 555-563.
assie, S.; escadeillas, g.; Waller, V. (2007) estimates of self-compacting concrete
'potential' durability. Construction and Building Materials 21 , 1909-1917.
Atis, C. (2003) Accelerated carbonation and testing of concrete made with fly ash.
Construction and Building Materials 17 , 147-152.
bai, J.; Wild, S.; Sabir, b. (2002) Sorptivity and strength of air-cured and water-cured