RESIDUAL COMPRESSIVE STRENGTH
OF FLY ASH BASED GLASS FIBRE
REINFORCED HIGH PERFORMANCE
CONCRETE SUBJECTED TO ACID
ATTACK
Dr.H.Sudarsana Rao
Professor of Civil Engineering
JNTUA College of Engineering
Anantapur-515002
hanchate123@yahoo.co.in
Sri. H. M. Somasekharaiah
Research Scholar
J.N.T. University
Anantapur - 515002
ssskar07@gmail.com
Dr.Vaishali. G.Ghorpade
Associate Professor in Civil Engineering Dept.
JNTUA College of Engineering
Anantapur-515002
ghorpade_vaishali@yahoo.co.in
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
Keywords: Fly ash, High Performance Concrete, Glass fibres, Acid attack, Durability
1. 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
harmfuleffects 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. Smith [2001] presented the models to estimate the chloride ion ingress into the Portland cement concrete and silica fume enriched concrete under different exposure conditions.
Tixier and Mobasher [2003] modeled the damage in cement-based materials subjected to external sulphate attack. They reported that the parameters like w/b ratio and internal porosity are important in controlling the external sulphate attack. Aitcin [2003] presented a review on durability characteristics of high performance concrete and reported that HPC with its dense microstructure and very low permeability is more durable than ordinary concrete. Bakharev et al. [2003] presented the durability studies of alkali-activated slag concrete exposed to acid attack. They reported that alkali-activated slag concrete of grade 40 showed good resistance to acid attack and has superior durability when compared to OPC concrete of similar grade. Gillott and Quinn [2003] reported their studies on strength and sulphate resistance of concrete made with High Alumina cement, Type 10 Portland cement, Type 10 Portland cement plus fly ash and Type 50 Portland cement. They reported that the concrete made with High alumina cement showed good resistance to sulphate attack. Miller and Comway [2003] presented the use of ground granulated blast furnace slag in reducing the expansion due to delayed Ettringite formation.
Shannag and Shaia [2003] evaluated the deterioration and the relative Sulphate resistance of high performance concrete through visual observations and recommended the use of silica fume in combination with natural pozzolana for better performance in severe Sulphate environments. Tixer and Mobasher [2003] formulated a mathematical model to simulate the response of concrete exposed to external sulphate solutions. Schneider and Chen [2005] presented the deterioration of high performance concrete subjected to attack by the combination of ammonium nitrate solution and flexure stress. They concluded that the life-time of the concretes decrease with an increase in concentration of the ammonium nitrate solution, no matter with load or without load. Shazali et al. [2006] focused on modeling the impact of gypsum in predicting residual strength in unsaturated concrete exposed to sulphate attack and reported that the results for the case of initially unsaturated specimens before immersion in sulphate solution are not significantly different from the initially saturated condition.
mechanical strength of high performance concrete. Bhatty et al. [2006] presented utilization of discarded fly ash as a raw material in the production of Portland cement. Their studies revealed that using fly ash is beneficial in cement plants and power plants. Jerath and Hanson [2007] presented the effects of fly ash replacement of Portland cement and the use of dense aggregate gradation on the durability of concrete mixtures in terms of permeability. They found that, by the use of dense graded aggregate and increasing the fly ash content from 35 to 40% the durability of concrete mixtures increased. They also observed the reduction in the charge passed, when conducted rapid chloride ion permeability tests thus indicating increase in durability. Wang and Li [2007] presented the mechanical performance of engineered cementitious composites incorporating high volume fly ash. In view of these results, it is proposed to study the effect of fly ash as a partial replacement to cement on the durability of Glass Fibre Reinforced High Performance Concrete
2. Materials and Methods
Experimental program has been planned to consider the durability aspect by studying the “Resistance of Fly ash based GFRHPC to acid attack”. The details of various materials used in this investigation are given in the following sections.
Cement
Ordinary Portland cement of 53 grade of ACC brand conforming to IS: 12269 standards was used in this investigation. The specific gravity of the cement was 3.10. The initial and final setting times were found as 40 minutes and 360 minutes respectively
Fine Aggregate
The locally available Pandameru river sand conforming to grading zone-II of Table 4 of IS 383-1970 was used. The specific gravity of the sand is found to be 2.67.
Coarse-aggregate
Crushed granite aggregate available from local sources has been used. To obtain a reasonably good grading, 50% of the aggregate passing through 20mm I.S.sieve and retained on 12.5 mm I.S.sieve and 50% of the aggregate passing through 12.5 mm I.S.sieve and retained on 10 mm I.S.sieve was used in the production of HPC. In the production of M20 grade concrete, 20mm maximum size coarse aggregate has been used. The specific gravity of coarse aggregate is 2.75.
Water
Potable fresh water available from local sources was used for mixing and curing of both GFRHPC mixes and M20 grade concrete.
Super Plasticizer
To improve the workability of the GFRHPC mixes, a high range water-reducing agent COMPLAST SP-337 has been used in the present work.
Acids
The various acids used in the investigation are HCl, H2SO4 and MgSO4 each of 5% concentration.
Fly ash
Table 1. Properties of fly ash
A. Sieve analysis
Sieve size % Passing by weight
i) Dry sieve analysis
400m(40 Mesh) 100
250m(60 Mesh) 99.5
200m(80 Mesh) 98.5
150m(200 Mesh) 97.5
75m(100 Mesh) 89.50
ii) Wet sieve analysis
75m(200 Mesh) 92.0
53m(100 Mesh) 87.5
45m(325 Mesh) 85.5
37m(400 Mesh) 84.0
B. Chemical analysis
Constituent Test results (% by
weight)
IS 3812 Requirement
General Values
Silica as SiO2 59.16 35.0 min 49-67
Alumina as Al2O3 30.64 16-28
Iron oxide as Fe2O3 4.07 4-10
SiO2+ Al2O3+ Fe2O3 93.87 70.0 min -
Calcium oxide as CaO 2.85 0.7-3.6
Magnesium oxide as MgO 0.36 5.0 max 0.3-2.6
Sulphate as SO4 0.21 2.75 max -
Alkalies 1.38 1.50 max -
Loss on ignition 0.21 12.0 max 0.4-1.9
C. Physical properties
Property Test results IS 3812 Requirement
Grade 1 Grade 2
Fineness (Blaine) cm2 /gm 3989 3200 2500
Lime reactivity N/mm2 8.9 4.0 min 3.0 min
Drying shrinkage % 0.008 0.15 max 0.10 max
Autoclave expansion % 0.012 0.80 max 0.80 max
Specific gravity 2.18 - -
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).
Table 2. (A) Properties of Glass fibres
Table 2.(B) Technical characteristics
Strand Tex Filament Dia
(micron)
Standard Length(mm)
Moisture content (%)
Size content (%)
Filaments/ Kg (Millions)
ISO 1889:1987 ISO 3344:1977 ISO 1887:1980
306 14 12 < 0.3 1.0 212
3. Casting of test specimens
To evaluate the resistance of fly ash based Glass fibre reinforced high performance concretes to acid attack, a total of 4 GFRHPC mixes have been tried for Fly Ash mineral admixture and four plain GFRHPC mixes were
tried without any mineral admixture. One plain concrete mix of M20 grade has also been cast and tested in the
laboratory as reference mix. As there is no standard method for proportioning GFRHPC mixes, absolute volume method has been used for arriving at the mix proportions in this work.
S.No Property Value
1
2
3
4
5
Filament Diameter
Filament per stand
Length
Ultimate Elongation%
Specific Gravity
14 Micron
100
12 mm
2.4
All the materials were taken by weight as per the mix proportions and mixed thoroughly to obtain a uniform mix. The various parameters studied are given below.
Aggregate-Binder Ratio (A/B Ratio): 2.0
Water-Binder ratio (W/B ratio): 0.35
Percentage replacement of cement by fly ash: 0 & 10 Fibre Volume percentage: 0, 0.5, 1.0 & 1.5
For acid attack, for each mix 30 concrete cubes of size 150x150x150 mm are cast. Out of these, 3 cubes were tested for 28 days compressive strength and remaining 9 concrete cubes were tested for residual compressive strength after 30, 60 and 90 days of acid immersion. The test program consisted of finding out residual compressive strength test due to immersion in 5 % concentration of acid. The moulds were removed after 24 hours and the specimens were kept immersed in a clear water tank. After curing the specimens in water for a period of 28 days the specimens were removed out and allowed to dry under shade. Also 27 cubes were cast for each mix for durability studies. After water curing, the 27 cubes were kept in 5% concentration acid solution for 30, 60 and 90 days acid curing. The curing media was replaced with fresh solution at the end of every week to maintain the same concentration (i.e.5%) throughout the curing i.e. 30, 60 and 90 days of exposure.
4. Discussion of test results
4.1 Effect of percentage replacement of glass fibre on residual compressive strength of GFRHPC:
The variation of Residual compressive strength (after 30, 60 and 90 days immersion in acids) with varying percentage of glass fibre are presented in Fig. 1-3
0.00 0.25 0.50 0.75 1.00 1.25 1.50
66 68 70 72 74 76 78 80 82 84 86
0% Fly ash 10% Fly ash
Resi
dual Compressi
ve
str
ength (MP
a)
% of Glass fibre Acid immersion for 30 Days
Hl MgSO
4
H2SO4
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
66 68 70 72 74 76 78 80 82 84 86 88
10% Fly ash 10% Fly ash
Residual Compr essive St rengt h (MP a)
% of Glass fibre Acid immersion for 60 Days
HCl MgSO
4
H2SO4
Fig.2 Variation of Residual Compressive strength with % of Glass fibre (For 0% and 10% Fly ash, Acid immersion for 60 Days)
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
60 62 64 66 68 70 72 74 76 78 80 82 84
10% Fly ash
0% Fly ash
Residual Compressi ve S tr eng th ( M P a )
% of Glass fibre Acid immersion for 90 Days
HCl MgSO
4 H2SO4
Fig.3 Variation of Residual Compressive strength with % of Glass fibre. (For 0% and 10% Fly ash, Acid immersion for 90 Days)
It can be observed from these Figures that the residual compressive strength increases with percentage of glass fibres 0, 0.5 and 1%. The addition of glass fibres enhances the load carrying capacity of the mix. It is observed that the maximum residual compressive strength attained is at 1% of glass fibre ratio in the present investigation. Further increase in percentage of glass fibre ie, 1.5% decreases the value of residual compressive
strength.The maximum residual compressive strength of GFRHPC at 1% glass fibre is 91.6 MPa for GF C 10
mix, for 30 days and 87.6 MPa, 80.6 MPa for 60 day and 90 days respectively in HCl acid immersion. The maximum residual compressive strength of GFRHPC at 1% glass fibre is 91.3 Mpa for GF C 10 mix, for 30
days and 87.2 MPa, 79.8 MPa for 60 day and 90 days respectively in MgSO4 acid immersion. The maximum
residual compressive strength of GFRHPC at 1% glass fibre is 90.2 MPa for GF C 10 mix, for 30 days and 85.8
4.2. Effect of age of acid immersion on residual compressive strength:
The effect of age of acid immersion on residual compressive strength for fly ash based GFRHPC mixes
for three different acids HCl, MgSO4 and H2SO4 is presented in Fig. 4
30 40 50 60 70 80 90
60 62 64 66 68 70 72 74 76 78
0% Fly Ash 10% Fly Ash
Resi
dual
Compressi
ve S
tr
ength
(MPa)
Age of Acid Immersion in HCl, MgSO4 and H2SO4 HCl
MgSO4 H
2SO4
Fig. 4 Effect of Age of acid immersion in HCl, MgSO4 and H2SO4 on Residual Compressive strength (For 0% and 10% Fly ash)
From this figure, it can be observed that the residual compressive strength decreases with increase in age of acid immersion. This is true for all the acids tried in the present investigation. Maximum loss of compressive strength is noticed at 90 days of acid immersion. For e.g. For mix GF C 10 there is a decrease of 11 MPa as the age of HCl acid immersion increased from 30 to 90 days. And for the same mix with MgSO4 acid immersion there is a decrease of 11.5 MPa in residual compressive strength from 30 to 90 days immersion,
similarly for H2SO4 acid immersion there is a decrease of 13.05 MPa in residual compressive strength from 30
to 90 days immersion. The decrease in residual compressive strength is expected because of formation of more and more ettringite with increase in age of acid immersion.
4.3. Effect of type of acid on residual compressive strength:
In the present investigation GFRHPC mixes have been subjected to 5% concentration of solutions of
HCl, MgSO4 and H2SO4. The influence of these acids on residual compressive strength of different GFRHPC
-5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98
1% Glass fibre
H 2SO4 MgSO
4
H2SO4 MgSO 4 HCl HCl Re sidu al com pre ssive stren gth (M P a )
% of Fly ash
HCl,MgSO4 and H2SO4 Acid immersion
30 Days 60 Days 90 Days
Fig. 5 Variation of Residual compressive strength with % of fly ash in acid immersion for 30, 60 and 90 Days (For 1% Glass fibre)
From this figure it can be observed that maximum loss of compressive strength occurred in case of
H2SO4 acid immersion when compared to HCl and MgSO4. This is true for all the three mineral admixtures tried
in the present investigation. Out of the three acids the least loss of compressive strength is recorded for HCl acid immersion. This is true at all replacement levels of cement by mineral admixtures. For example for GM C 10
mix the residual compressive strength after 90 days on HCl acid immersion is 80.60 MPa and that with H2SO4
acid immersion is 76.8 MPa indicating the severity of H2SO4. Similar trends can be observed for other mixes as
well. From the results of the present investigation it can be concluded that the attack of H2SO4 is most severe on
GFRHPC and HCl is the mildest one in the ranges tested.
5. 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.
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