Effects of Sabalan Tuff as a Natural Pozzolan on
Properties of Plastic Concrete
R. Sadeghi Doodaran and M. Pasbani Khiavi
*
Abstract. One of the most common methods for watertighting in dams is to use
cutoff or watertight walls. These types of walls should have high plasticity and
low permeability [1]. Developing these walls with such qualities requires using
plastic concrete with paneling method. In most cases, adding these materials to
concrete improves some of its qualities such as consistency, viscosity of fresh
concrete, decrease in permeability, increase in plasticity, long term increase in
compressive strength, durability against sulphats and decrease in price. The main
purpose of this project is using Sabalan natural tuff in plastic concrete for an access to a desirable modulus of elasticity without a decrease in compressive
strength. In this paper, in addition to the impact of Sabalan natural pozzolan tuff
on plastic concrete qualities, the impacts of pozzolan cement made of this kind of
tuff (Ardebil pozzolan cement) on it has been considered. The results showed improvement on the qualities of plastic concrete such as decrease in permeability,
decrease in modulus of elasticity and increase in durability against destructive factors with retaining compressive strength.
1 Introduction
Pozzolan is a substance that shows cement properties in the vicinity of lime. A
standard definition for pozzolan is a siliceous or aluminates siliceous material that
bears no cementation value in itself, however, in the form of tiny particles and in
the vicinity of moisture with ordinary temperature it shows chemical redaction
with calcium hydroxide and creates combinations that bear cementation properties
[1]. Plastic concrete is a type of concrete which comes from the combination of
water, cement, bentonite, gravel, sand and in some cases clay. For this purpose
one can use admixture in cases where required. Since Sabalan tuff is well available in Ardabil region, and taking account of the economic considerations of pozzolan applications in concrete industry and the need to understand its effect on
plastic concrete properties, pozzolanic cement of Ardabil cement plant and also
R. Sadeghi Doodaran
Islamic Azad University, Astara Branch, Islamic Republic of Iran
M. Pasbani Khiavi
University of Mohaghegh Ardabili, Ardabil, Islamic Republic of Iran
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R.S. Doodaran and M.P. Khiavi
different percents for pozzolan (10, 20, 30) have been selected and studied as
weight substitute for Soofian cement (control cement).
2 Material Characteristics
Water used in this project was fresh water of Sahand University of Technology in
Iran. Cement used in this project can be classified into two kinds: Portland cement
of Soofian cement plant with the relative density of 3.15 and Portland-pozzolan
cement of Ardabil cement plant with the relative density of 3.1. The relevant abbreviations for five types of cement materials are as follows:
1.
2.
3.
4.
5.
Scc for Sufian Portland cement
Apsc for Ardabil Portland-pozzolan cement
Scc+ 10% P for Soofian cement + 10 percent of pozzolan of Sabalan tuff
Scc + 20% P for Soofian cement + 20 percent of pozzolan of Sabalan tuff
Scc + 30% P for Soofian cement + 30 percent of pozzolan of Sabalan tuff
Added pozzolans are as weight substations for the consumed cement.
Washed river pea gravel, production of sand screwing plant of zafar Imamiyeh
in Tabriz was selected and used. In this project washed river sand of Seram mine
in Tabriz was used. Since the grading curve of the used sand was not within the
recommended range by ASTM, the used sand was screened by NO.4 sieve. Bentonite used in this project was that of Afra Company (35km to Zanjan, Shahid Bahonar Industrial Town). Sabalan tuff used in Ardabil cement plant, whose mine is
located at 5 kilometers to Namin, has been used in this project, then this pozzolan
was ground and screened using NO.100 sieve in Azar Dash industry plant. According to the recommendation made by ASTM–C618 standard the sum of the
three main oxides (SiO2, Al2O3, and Fe2O3) must exceed 70% and the maximum
shortage of ignition loss is limited to 10 percent. The fall of the used tuff ignition
loss was 3.85 percent and the sum of the three main oxides (61, 17, 3.5) was 81.5
percent and this ranges within the ASTM–C618 standard limitations.
3 Mix Design
3
In this research 45 mix design with cement materials (C= 200kg/m ), water to ce3
ment ratio (W/C= 1.5, 2, 2.5), Bentonite (B= 30 , 40 , 50 kg/m ) and coarse aggregate to fine aggregate ratio equal to 1, were provided and curing in ordinary as
well as sulfated environment (containing 10% sodium sulfate).
4 Results of the Experiments
Substituting the pozzolan for cement with high percentages (30%) leads to considerable compressive strength reduction (7 day, 32.22% and 150 day, 27.21%). This
reduction in compressive strength, particularly in law water cement is more observable. This is so, perhaps because additional pozzolan does not take part in
Effects of Sabalan Tuff as a Natural Pozzolan on Properties of Plastic Concrete
421
pozzolanic reactions and remains as filler in the mixture of plastic concrete. In
other words, some part of substituted pozzolan cannot take part in pozzolanic reaction with cement hydration products and remains inactivated in the mixture and
reduces its resistance. So, from the point of view of compressive strength and regarding the Fig1, it can be concluded that the 10% substitution is an optimized one
and any additional one to it will cause considerable reduction in compressive
strength.
Fig. 1 Comparison of compressive strength for cements and variable percents of pozzolan
with increasing measures of bentonite
Some part of the combination of Ardabil cement has been formed of natural
pozzolan. As it is evident in the section about the compressive strength of specimen, this pozzolan in its early ages can not completely take part in giving resistant
to the cement paste and it operates as filler, and accordingly bears weaker function
than that of Soofian cement. As diagrams show, addition of pozzolan to Soofian
cement reduces the elasticity module of the specimen. It should be noted that this
reduction brings reduction in compressive strength and the more the percent of
subsistent pozzolan, the more the reduction in specimens with low measures of
bentonite and high water to cement ratio (Fig 2).
Fig. 2 Comparison of modulus of elasticity for cements and variable percents of pozzolan
with increasing measures of bentonite
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R.S. Doodaran and M.P. Khiavi
One of the objectives that are followed in plastic concrete production is increasing or retaining the compressive strength while reducing the elasticity
module. In other words, ductile and flexible plastic concrete with good relative
compressive strength will have better function. As Fig3 show, the lines representing the communication of compressive strength with elasticity module of specimen prepared by Ardabil pozzolanic concrete are lower than those representing
the Soofian cement ones. In other words, for a case of fixed compressive strength,
the elasticity module of plastic concretes prepared with pozzolanic cement of
Ardabil is lower than those specimens relating to Soofian cement, and this is especially true in case of mixtures with less bentonite. By studying the lines representing the communication of compressive strength and elasticity module of plastic
concretes prepared with different percentages of substitution of Soofian cement
with natural pozzolan of Sabalan tuff, it can be seen that the more the rate of pozzolan increases, the better the functions of plastic concretes prepared for retaining
the compressive strength -while decreasing the elasticity module- will be.
Fig. 3 Comparison of modulus of elasticity with compressive strength
Considering Fig. 4 and comparing the amounts of permeability for the three selective plans (Soofian cement (Scc1), Ardabil cement (Apsc 10 ), and substituting
10 percent of Soofian cement with Sabalan tuff (scc+p1 19)), we can say that
ready – made plastic using the pozzolanic cement of Ardabil shows lower permeability coefficient in both ordinary and sulfated curing environments. Also, the
concrete made of Soofian cement 10 percent of natural pozzolan of Sabalan tuff in
sulfated environment showed better function. Studying Fig. 5, we can also see that
in sulfated environment, the more the percent of substitution of Soofian cement
with natural pozzolan of Sabalan tuff increases, the more the compressive strength
of curing specimen in sulfate, increases. This is so, perhaps because, the molecular
volume of CH (calcium hydroxide) is about 33.2 ccm, while in case of hydrated
sodium sulfate it is 74.3 ccm [2], and with the presence of pozzolan and its reaction with CH and forming CHS the pores in concrete will be filled and the result
will be a relative solid material that prevents the penetration of materials that increase sulfates, and it also adds to the compressive strength of the plastic cement.
Effects of Sabalan Tuff as a Natural Pozzolan on Properties of Plastic Concrete
423
Fig. 4 Permeability of plastic concrete
and comparison of them in sulphated
environment
Fig. 5 Effect of sulphated curing on
compressive strength of plastic concrete
5 Discussions
• Replacing 10% pozzolan of Sabalan tuff in the form of weight replacement is
optimal and the replacement exceeding the afore-mentioned amount will cause
more reduction in compressive strength.
• In case of adding pozzolan to Soofian cement, the elasticity module of mixtures
will be decreased.
• For fixed compressive strength, elasticity module of plastic concretes prepared
from pozzolanic Ardabil cement is lower than that of specimens pertaining
Soofian cement.
• The more the rate of pozzolan, the better function of prepared plastic concretes, regarding the retention of compressive strength as well as the reduction
in elasticity module will be.
• Plastic concrete made from Ardabil pozzolanic cement shows lower permeability coefficient in both normal and sulfated environments.
• In sulfated environment, the more the percent of replacement of soofian cement
with natural pozollan of Sabalan tuff, the more the compressive strength of fostered specimens in sulfate will be.
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References
1. ICOLD BULLETIN, Filling materials for waterting cut off walls. 51 (1985)
2. Janotka, I., Stevula, L.: Effect of bentonite and zeolite on durability of cement suspension under sulfate attack. ACI Mater. J. 95, 710–715 (1998)