3231
Application of a Method to Accelerate Granulated Blast Furnace Slag Solidification
Une méthode de solidification accélérée des granulats issus de laitier de haut fourneau
Kikuchi Y.
Department of Civil Engineering, Tokyo University of Science, Noda, Japan
Mizutani T.
Geotechnical Engineering Field, Port & Airport Research Institute, Yokosuka, Japan
ABSTRACT: On-site observations indicate that granulated blast furnace slag (GBFS) solidifies over time, but the entire mass
solidifies quite slowly. This means that if GBFS is to be relied upon to be solid, it must be treated in order to accelerate the
solidification process. Adding blast furnace slag in micro powder form to GBFS effectively speeds GBFS solidification in seawater.
To improve the material’s resistance to separation, we recommend Prior Homogeneous Mixing Treatment (PHMT), which reduces
the amount of separation of the material during pouring but does not interfere with the speed of the mixture’s accelerated
solidification. PHMT-treated GBFS tends to solidify better when inundated in seawater than in fresh water. It is strong enough to
protect against liquefaction if it remains in seawater for about two months.
RÉSUMÉ : les observations in-situ indiquent que les granulats issus de laitier de haut fourneau (GLHF) se solidifient dans le temps,
avec néanmoins une vitesse de prise assez lente. L'utilisation de GLHF solidifiés implique donc que ces derniers fassent l'objet d'un
traitement afin d'accélérer ce processus de prise. L'ajout sous forme de poudre fine issue de laitiers accélère de manière efficace cette
solidification sous l'eau. Afin de limiter la ségrégation, il est recommandé d'effectuer au préalable un mélange homogène avec la
poudre. Cela réduit la ségrégation entre les matériaux durant le déversement du mélange tout en n'influençant pas l'augmentation de la
vitesse de prise. Les GLHF traités avec de la poudre de laitier tendent après un mélange homogène à se solidifier de manière plus
efficace lorsqu'il sont plongés dans de l'eau de mer plutôt que dans de l'eau douce. Ce mélange a alors assez de résistance pour résister
à la liquéfaction si celui-ci reste immergé dans l'eau de mer plus d'une année et demi.
KEYWORDS: granulated blast furnace slag, solidification, backfill, quay wall
1
INTRODUCTION
Granulated blast furnace slag (GBFS) solidifies when it reacts
with water. This property is known as latent hydraulicity.
However, this characteristic of GBFS was ignored in the
Japanese handbook for port construction engineers published in
1989 (CDIT, 1989) due to the lack of adequate information on
the solidification of GBFS used in port construction. If used as a
self-solidifying material, GBFS holds great promise for use in
protecting against liquefaction and for earth pressure reduction.
Most GBFS used to backfill quay walls does solidify, but a
post-construction follow-up survey showed that GBFS
solidification is a lengthy process, it never solidifies uniformly,
and some may remain unsolidified (Kikuchi et al. 2005). As a
result, some treatment is necessary before GBFS can be used as
a self-hardening material.
In this study, we examine a method to accelerate the
solidification of GBFS and propose a practical way to apply that
method.
2
PREVIOUS RESEARCH
GBFS is vitreous, and the silicate SiO
4
it contains is in an
unstable condition compared with crystalline material (NSA
1980). GBFS has high chemical reactivity and therefore
solidifies in the presence of water and under high pH conditions
where the pH exceeds 11.
Nishi et al. (1982) concluded that the latent hydraulicity of
GBFS is high in highly alkaline water but low in seawater,
which has a pH of about 8.
0
500
1000
1500
2000
2500
0
50
100
150
Pure water + cement 10%
Sea water + cement 10%
Pure water + PBFS10%
Sea water + PBFS 10%
Sea water
Unconfined compression strength q
u
(kN/m
2
)
Curing time (days)
Granulated blast furnace slag
Dr=50%
Figure 1. Acceleration of solidification achieved by mixing cement or
PBFS with GBFS and by varying pore water type.
These facts suggest that solidifying GBFS in seawater is
difficult because seawater acts as buffer solution with a very
high buffering capacity (Christian 1986), and adjusting the pH
of seawater is impractical.
A site investigation of GBFS placed as backfill 6-12 years
previously showed that most of the GBFS had solidified, but its
strength varied greatly (Kikuchi et al. 2006).
Kikuchi et al. (2011) tested various combinations of pore
water and additives, attempting to speed GBFS solidification.
