21-09-2013, 03:29 PM
RESIDUAL COMPRESSIVE STRENGTH OF FLY ASH BASED GLASS FIBRE REINFORCED HIGH PERFORMANCE CONCRETE SUBJECTED TO ACID ATTACK
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ABSTRACT
In recent years, improvements in concrete properties have been achieved by the invention of High-
Performance-Concrete (HPC). Improvements involving a combination of improved compaction, improved paste
characteristics and aggregate-matrix bond, and reduced porosity are achieved through HPC. The ductility of
HPC can be improved by altering its composition through the addition of glass fibers in the design mix. High-
Performance-Concrete made with glass fibers inside is regarded as Glass Fiber Reinforced High Performance
Concrete (GFRHPC). This paper presents the details of an experimental investigation planned to utilize fly ash
in the production of Glass fibre reinforced High-Performance-Concrete (GFRHPC). The investigation examines
the progressive deterioration of concrete mixtures containing various combinations of fly ash based GFRHPC
mixes exposed to sulphate and chloride solutions. Acid attack tests have been conducted to measure the
durability of GFRHPC. Cubes of 150X150X150 mm have been cast, cured and then kept immersed in 5%
concentrated solutions of HCl, H2SO4 and MgSO4 for 30, 60 and 90 days and then tested to record the residual
compressive strengths of GFRHPC produced with the fly ash mineral admixtures. The results have been
analyzed and useful conclusions have been drawn.
Introduction
Glass fibres are among the most versatile industrial materials known today. They are readily produced
from raw materials, which are available in virtually unlimited supply. The glass fibres are derived from
compositions containing silica. They exhibit useful bulk properties such as hardness, transparency, resistance to
chemical attack, stability, and inertness, as well as desirable fiber properties such as strength, flexibility, and
stiffness. When these glass fibres are added to HPC, it becomes Glass Fibre Reinforced High Performance
Concrete (GFRHPC).
Fly ash is the finely divided mineral residue resulting from the combustion of ground or powdered coal
in electric generating plant (ASTM C 618). Fly ash consists of inorganic matter present in the coal that has been
fused during coal combustion. Due to its pozzolanic nature, Fly ash is a beneficial mineral admixture for
concrete. It influences many properties of concrete in both fresh and hardened state. Moreover, utilization of
waste materials in cement and concrete industry reduces the environmental problems of power plants and
decreases electric costs. Utilization also reduces the amount of solid waste, greenhouse gas emissions associated
with Portland clinker production, and conserves existing natural resources. Hassan et al. [2000] presented the
influence of two mineral admixtures, silica fume and fly ash on the properties of super-plasticized high-
performance concrete. The results indicated that usage of the mineral admixtures improved the properties of
high performance concrete. Bentz [2000] developed a three-dimensional micro structural model for fiber-
reinforced concrete and applied it to examine the spalling phenomena of high-performance concrete and
suggested that 20 mm fibers showed superior performance when compared to that of 10 mm fibers. Day [2000]
presented performance tests for sulphate attack on cementitious systems. Chang et al. [2001] addressed the
harmful effects of marine climate on the durability of concrete structures built in coastal areas and reported that
it is important to know the methodology of achieving high strength and durable concrete in order to avoid
formation of cracks in the structural member.
Glass fibre
Glass fibre obtained from Saint-gobain Vetrotex company under the trade name Cem-FIl anti crack HD (High
Dispersion) glass fibres, was used in the present work. The glass fibre is of 12mm length and 14 micron
diameter. The details are presented in Table 2 (A & B).
Conclusions:
The present investigation establishes the superiority of GFRHPC produced with partial replacement of
cement by fly ash to stand well even in aggressive acidic environments. The important conclusions of the
present paper are summarized below.
Fly ash based GFRHPC mixes resisted acid attack in a better way as compared to conventional M20
concrete at all ages of exposure to HCl, Mg SO4 and H2SO4.
It is observed that the residual compressive strength of all GFRHPC mixes are considerably higher than
that of M20 grade reference mix at all ages of acid exposure for all the three acids tried in this
investigation.
The loss of compressive strength of GFRHPC mixes due to acid attack is least at 10% replacement of
cement by fly ash. Hence 10% replacement is considered as optimum dosage.
The loss of compressive strength is 22.5% for fly ash based GFRHPC mixes after 90 days immersion
in H2SO4 acid while similar exposure resulted in a loss of 38.8% for reference M20 concrete. This
confirms the superior performance of fly ash based GFGRHPC in resisting acid attack.
The residual compressive strength of GFRHPC decreases with increase in age of acid immersion.
Maximum loss of compressive strength has occurred at 90 days of acid immersion. This is true for all
the acids tried in the present investigation.
Maximum loss of compressive strength occurs in case of H2SO4 acid immersion as compared to HCl
and MgSO4 acids. Out of the three acids the least loss of compressive strength is recorded for HCl acid
immersion.