Alkali-activated based concrete - Eco-efficient Concrete - page 463

Table 17.4 Results for monoblock railway sleepers made with Portland cement-
free, alkali-activated fly ash concretes (Palomo et al., 2007b; Fernández-Jiménez
and Palomo, 2009)

3 H-FA-W sleeper
(kN)

Minimum load (kN)

1 RENFE 2 UIC

Static test* 1st crack 127.53 147.15 417.62

Failure 280.56 323.73 583.40

Dynamic test 1st crack > 0.05 mm 195 228 350

Failure 286 334 390

1 RENFE: Red Nacional de Ferrocarriles Españoles (Spanish national railway system).
2 UIC: International Union of Railways.
3 H-FA-W: sleeper made with fly ash alkali-activated with NaOH + Na 2 SiO 3 .
*Further to European standard EN 13230 (parts 1 and 2).

age strength in cement and concrete). many researchers have shown that the
addition of alkaline activators could enhance the potential pozzolanicity of
such supplementary materials and improve the properties of the respective
cementitious systems, especially at early ages.
dilution of the Pc content reduces the effectiveness of the activation of
these materials unless an alkaline activator can be added, however. This is the
solution adopted in hybrid Portland cement - alkali activated aluminosilicate
systems (Fernández-Jiménez et al., 2011; macphee and García-Lodeiro, 2011).
These systems are complex cementitious blends in which the type of product
formed depends largely on the reaction conditions, including the chemical
composition of the prime materials, alkaline activator type and concentration
and curing temperature. in the systems containing portland clinker (clinker
+ blast furnace, phosphorous or steel mill slag, clinker + fly ash, clinker +
slag + fly ash), C-S-H gel normally prevails as the main reaction product in
slightly alkaline media (i.e., 2 m naoH), whereas n-a-S-H gel prevails in
highly basic environments (10 m naoH) (alonso and Palomo, 2001).
consequently, the compatibility of the two cementitious gels, c-S-H (the
main reaction product of ordinary Portland cement hydration) and n-a-S-H
(the main product of the alkali activation of aluminosilicate materials), may
have important technological implications for future cementitious systems
in which both products might be expected to precipitate (alonso and
Palomo, 2001; Yip et al., 2005; Palomo et al., 2007a; García-Lodeiro et al.,
2012b).
The hybrid cementitious systems most frequently studied include:
∑ Portland cement-blast furnace slag blends;
∑ Portland cement-phosphorus slag blends;
∑ Portland cement-fly ash blends;
∑

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Portland cement-steel mill and blast furnace slag blends;