2593
Compressive Strength of Fiber-Reinforced Lightly-Cement Stabilized Sand
Résistance à la compression des sables renforcées par fibres et ciment
Sadek S., Najjar S., Abboud A.
Department of Civil and Environmental Engineering, American University of Beirut
ABSTRACT: The stabilization of soils using cementing agents has long gained acceptance and is well established in geotechnical
engineering practice. Furthermore, adding discrete fibers to the cement-treated soil has been shown to improve the soil’s response to
loading and its overall engineering behavior. Limited studies of the behavior of fiber-reinforced cemented sand in the laboratory
indicated that the addition of cement and fibers results in an increase in the strength of the composite, especially at high fiber contents
and lengths. Cemented sands were found to be brittle compared to un-cemented sands, with the brittleness decreasing with the
inclusion of fibers. The objective of this paper is to investigate the effect of randomly distributed fiber reinforcements and cement
addition on the response of sandy soils. To achieve this objective, the behavior of cement/fiber-reinforced sands was studied using
unconfined compression tests. The parameters that were varied are [1] the cement content (0.5% and 1%), [2] the fiber content (0%,
0.25%, 0.5%, and 1.0%), and [3] fiber lengths (6, 12 and 20 mm). The results of the tests were used to quantify the degree of
improvement in strength and stiffness due to the addition of fibers and cement to the cohesionless sand.
RÉSUMÉ: La stabilisation des sols en utilisant des agents de cimentation a longtemps été accepté et est bien établie dans la pratique
de la géotechnique. De plus, l'ajout de fibres discrètes au sol-ciment a été demontré effectif pour améliorer la réponse du sol au
chargement et son comportement mécanique global. Seules quelques études éxistent où le comportement des sols renforcés par des
fibres et ciment a été é tudie au laboratoire. Elles ont indiqué que l'addition de ciment et de fibres engendrent une augmentation de la
résistance du composite, en particulier à des teneurs en fibres et des longueurs élevées. Les sables cimentés ont été jugés fragiles par
rapport aux sables non cimentés; cette fragilité diminue avec l'inclusion de fibres. L'objectif de cet article est d'étudier l'effet de
renforts en fibres distribuées de façon aléatoire et l'ajout de ciment sur la réponse des sols sableux. Pour atteindre cet objectif, le
comportement de sables enforcés par ajout de ciment / fibres r a été étudiée par des essais de compression non confinée. Les
paramètres qui ont été variées sont [1] la teneur en ciment (0,5% et 1%), [2] la teneur en fibres (0%, 0,25%, 0,5%, et 1,0%), et la
longueur des fibres [3] (6, 12 et 20 mm). Les résultats des tests ont été utilisés pour quantifier le degré d'amélioration de la résistance
et de rigidité due à l'ajout de fibres et de ciment au sable pulvérulent.
KEYWORDS: fiber-reinforced sand, cement stabilized sands, fibers, cement, unconfined compressive strength.
1 INTRODUCTION
The geotechnical and materials/pavement engineering fields are
witnessing an increasing interest in exploring soil improvement
schemes that are based on the addition of stabilizing agents such
as synthetic or natural fibers and/or cementing agents for
various applications. The objective is to produce a composite
material with improved engineering properties that could be
used in lieu of good quality construction material that is
typically obtained through non-sustainable and environmentally
problematic activities such as quarrying. The composite
material with its improved engineering properties could be used
to replace conventional base and sub-base material under
pavements, or to support foundations of “light” structures or
infrastructure, which otherwise could not be adequately
supported by the natural soil. The improved material could also
be used as backfill behind earth retaining walls and reinforced
or stabilized slopes.
The experimental data that is available in the literature for
fiber/cement reinforced sands is relatively limited (Maher and
Ho 1993, Consoli et al. 1998, Kaniraj and Havanagi 2001,
Sobhan and Mashnad 2002, and Consoli et al. 2002). There is a
need for designing and implementing a comprehensive
experimental testing program that is aimed at investigating the
behavior of fiber/cement reinforced sands systematically. To
achieve this objective, the behavior of cement/fiber reinforced
sands was studied in the laboratory using unconfined
compression tests. The parameters that were varied in this study
are [1] the cement content (0.5% and 1%), [2] the fiber content
(0%, 0.25%, 0.5%, and 1.0%), and [3] fiber lengths (6, 12 and
20 mm). The results of the tests were used to quantify the
degree of improvement in strength, stiffness, and ductility due
to the addition of fibers and cement to the cohesionless sand.
2 EXPERIMENTAL PROGRAM
Twenty unconfined compression tests on fiber/cement
reinforced sands were conducted as part of this study.
2.1
Material Properties
The sand used in this study is Ottawa Sand with the properties
shown in Table 1. The sand classifies as a
poorly graded sand
(SP)
according to the Unified Soil Classification System.
The fibers (Fig. 1) chosen for the reinforcement are
polypropylene fibers, typically used as secondary reinforcement
of lightweight concrete and mortar mix designs. They were
adopted because they are available in several lengths, they can
be mixed with soil-cement mixtures and satisfy efficiently the
intended role of reinforcement. The fibers have a specific
gravity of 0.91 g/ml, a tensile strength of 0.38 kN/mm
2
and a
young modulus of 3.5 kN/mm
2
. Fiber lengths of 6 mm ±1, 12
mm ±1 and 20 mm ±1 were used in the testing program. The
nominal diameter of the fibers was determined in the lab under
an electronic microscope to be in the order of 0.1mm.
Table 1. Table caption (TNR 8), numbered consecutively. Tables placed
below caption. TNR 8 for text and numbers in Table.
Soil Property
Value
D
10
(mm)
0.22
D
30
(mm)
0.31
D
60
(mm)
0.42
Coefficient of uniformity (
D
60
/
D
10
)
1.95
Coefficient of curvature (
D
30
)
2
/(
D
60
*
D
10
)
1.04
Maximum and minimum void ratios (
e
max
,
e
min
)
(0.75,0.49)
Specific gravity
2.65
The cement used in this study is normal Portland cement type I.
The same sources of cement and sand were used for all the
specimens to eliminate all risk of material discrepancy.
2.2
Sample Preparation
