2633
Fiber Reinforced Cement Treated Clay
Fibro-ciment renforcé argile traitée
Xiao H.W., Lee F.H., Zhang M.H., Yeoh S.Y.
National University of Singapore, Singapore
ABSTRACT: Cement-treated soil has been used widely in ground improvement for several decades. However, its behavior, especially
at high cement content, is highly brittle. Previous studies have shown that addition of both fibers and cement in soil improvement
seems to be more efficient and attractive than adding fibers or cement alone. This paper presents an experimental study on fiber-
reinforced cement-treated marine clay. Two different types of fibers and fiber lengths as well as different fiber contents (0.0%-0.32%)
will be investigated with cement content ranging from 20%-50% and water content ranging from 100%-167%. The experiment results
indicate that the strength and ductility of cement-admixed marine clay improve significantly with increasing fiber content until an
optimum fiber content is reached. It was found that the factors affecting the behavior of fiber-reinforced cement-treated marine clay,
such as fiber content, type and cut length and cement soil mix ratio, are not independent. In general, for water content not higher than
100% and cement content higher than 20%, using 12-mm polyvinyl alcohol fiber was found to give higher strength and better
ductility than polypropylene or shorter fibers.
RÉSUMÉ : Des études précédentes ont démontré que l’incorporation de fibres et du ciment dans l'amélioration de sol semble être plus
efficace et attrayante qu'en ajoutant seulement les fibres ou le ciment. Cet écrit présente une étude expérimentale de l'argile marine
traitée au ciment et renforcée avec fibres. Deux différents types et longueurs de fibres de même que des teneurs en fibre différentes
(0.0%-0.32%) seront examinés avec une teneur en ciment qui s’étend de 20%-50% et d’eau qui s’étend de 100%-167%. Les résultats
de l’expérience indiquent que la résistance et la ductilité du ciment-sol sont améliorées de manière significative avec le contenu
croissant de fibres jusqu'à ce qu'une teneur en fibre optimale soit atteinte. Il a été trouvé que les facteurs qui affectent le comportement
de l'argile marine traitée au ciment et renforcée avec fibres, tel que la teneur en fibres, la longueur et le type de fibre et la proportion
du mélange du sol-ciment, ne sont pas indépendants. En général, pour une teneur en eau ne dépassant pas les 100% et une teneur en
ciment de plus de 20%, il a été constaté que l’utilisation de la fibre d'alcool de polyvinyl de 12mm offre une plus haute résistance et
une meilleure ductilité que le polypropylène ou des fibres plus courtes.
KEYWORDS: fiber reinforcement, cement treated soil, brittleness index, compressive strength
1 INTRODUCTION
Cement-treated soil has been used widely in ground
improvement during the past forty years and is becoming more
attractive and efficient method for soil treatment due to its
economy, availability and feasibility. However, cement-treated
soil, especially at high cement content, tends to be brittle.
Previous studies have shown that fiber-reinforcement increases
the strength and ductility while decreasing the stiffness of the
soil (e.g., Gray & Ohashi 1983). Recent studies have also
shown that incorporation of both fibers and cement in soil
improvement seems to be more efficient than fibers or cement
alone (e.g., Maher and Ho 1993, Consoli et al. 1998). Maher
and Ho’s work presented a basic study of the mechanical
behavior of artificially cemented sand reinforced with randomly
distributed glass fibers.
The use of randomly distributed fiber as a new reinforcement
material for cement-treated soil has been receiving increasing
attention in recent years (e.g., Consoli et al. 2003, Khattak and
Alarshidi 2006, Tang et al. 2007, Park 2009; Consoli et al 2011;
Ud-din et al. 2011). Previous research works, however, have
focused mainly on low cement content (
10%), sand or sandy
soil and particular fiber. In this paper, different fiber types (PP
& PVA), fiber lengths (6 & 12mm) and fiber contents (0.0%-
0.32% by volume of mixture) will be investigated with different
cement and water contents for Singapore marine clay treatment.
The specimens were made in laboratory and tested with
unconfined compression loading. The strength and ductility of
the FRCT marine clay specimens were then analyzed based on
the experiment results.
2 EXPERIMENT INVESTIGATIONS
The materials used in the study are Singapore upper marine
clay, type I Ordinary Portland cement, and fibers. The
constituents of the clay are 24.13% of colloid, 21.77% of clay,
47.71% of silt and 6.39% of very fine to medium sand. Two
different fibers were used, namely polypropylene (PP) and
polyvinyl alcohol (PVA) fibers. PVA fibers are commonly used
in concrete reinforcement to improve the tensile and flexural
strength of concrete. The properties of the fibers are given in
Table 1. A naphthalene-based superplasticizer (Rheobuilder
1000) was used in some mixtures for workability purpose.
Table 1 Physical and mechanical properties of fibers
The cement soil mix ratio will be expressed in the form of
S:C:W wherein S is mass of soil solid, C the mass of cement
and W the mass of water at the point of mixing. The cement
content A
w
is defined as the ratio of mass of cement to the mass
of soil solid. The water content C
w
is defined as the ratio of
mass of water to the total mass of soil solid and cement. In this
study, the cement content ranges from 20 to 50% by weight of
soil solid while the water content ranges from 100 to 167% by
weight of cement and soil solid. The fiber content is defined as
the ratio of volume of fiber to the total volume of the mixture at
the point of mixing, and ranges from 0 to 0.32%. The ductility
of the fiber-reinforced cement-treated (FRCT) soil is designated
herein by the brittleness index (BI), which is defined as the ratio
of the peak strength to the strength at a prescribed post-peak
strain.
Fiber
Type
Length
(mm)
Diameter
(micron)
Aspect
ratio
Tensile
strength
(MPa)
Elastic
modulus
(GPa)
Density
(kg/m
3
)
PP6
6
26
231
540
7
910
PP12
12
26
462
540
7
910
PVA6
6
26
231
1600
40
1300
PVA12
12
38
316
1500
40
1300
