Geoscience Reference
In-Depth Information
7.8 CONVENTIONAL ADDITIVES AND/OR FIBRE
REINFORCEMENT IN ORGANIC SOILS AND PEAT
Conventional additives are cement, blast furnace slag, silica fume, lime, fly ash and
bituminous materials. These additives enhance the properties of soil. Cementation
and pozzolanic reactions have been investigated in detail by Taylor (1997) and Hwan
Lee and Lee (2002). When water comes in contact with cement, three phenomena
take place: (1) cement reacts with water (called hydration), (2) pozzolanic reactions
between Ca(OH)
2
from burnt cement and pozzolanic minerals in the soil, and (3) ion
exchange between calcium ions (from cement and additives) with ions present in the
clay, which leads to an improvement in the strength of the treated soil (Kazemian,
2011).
7.8.1 Ground granulated blast furnace slag (BFS)
Ground granulated blast furnace slag is the granular pozzolanic material formed when
molten iron blast furnace slag is rapidly chilled (quenched) by immersion in water.
It is a granular product with very limited crystal formation, is highly cementitious in
nature and, ground to cement fineness, hydrates like Portland cement with a specific
surface around 450m
2
g
−
1
, specific gravity of 2.9 and bulk density of 1150 kgm
−
3
(Fernandez and Puertaz 1997; YTL cement 2008). Axelsson
et al.
(2002) reported
that ground blast slag used as stabilizer has latent hydraulic properties. This means
that, like pozzolanic materials, the slag can form strength-enhancing products with
calcium hydroxide (Ca(OH)
2
).
Blast furnace slag, being a latent hydraulic material, needs an activator such as
calcium hydroxide to react. Its reactivity also depends on the CaO/SiO
2
ratio. As this
ratio is increased, the more hydraulic the material will be. The CaO/SiO
2
ratio for
blast furnace slag is about 1, while it is up to 3 for ordinary Portland cement (OPC).
Hydraulic materials such as OPC react spontaneously with water. Since the reaction
produced by blast furnace slag is slower than that of OPC, it results in slower strength
gain and lower heat evaporation than with cement. However, the long-term strength
of the slag admixture can be higher (Axelsson
et al.
2002; Janz and Johansson 2002).
The effects of BFS as an additive on stabilized fibrous peat with OPC have been
examined by Kalantari
et al.
(2011) using unconfined compressive stress (UCS) tests.
Various trial mixtures of OPC treated with and without BFS were tested for their UCS
values. Undisturbed samples and samples made of only 5, 15 and 30% OPC were
tested as control measure samples. The stabilized samples were mixed initially with
the fibrous peats (FPt) with natural moisture content
w
=
200% and air cured for three
months.
The results of various trial mixtures for UCS stabilized samples are shown in
Figure 7.14.
Four types of mixtures chosen for compaction test were fibrous peat with;
(a)
3.75% OPC and 1.25% BFS
(b)
11.25% OPC and 3.75% BFS
(c)
22.5% OPC and 7.5% BFS
(d)
22.5% OPC and 22.5% BFS
