Journal of Environmental Science and Engineering A 1 (2012) 121-127

Formerly part of Journal of Environmental Science and Engineering, ISSN 1934-8932

D DAVID PUBLISHING

Feasibility of Using Sea Shells Ash as Admixtures for

Concrete

Benjamin R. Etuk1, Idongesit F. Etuk1 and Linus O. Asuquo2

1. Department of Chemical and Petroleum Engineering, University of Uyo, Uyo 52001, Nigeria
2. Department of Mechanical Engineering, University of Uyo, Uyo 52001, Nigeria

Received: June 24, 2011 / Accepted: August 2, 2011 / Published: January 20, 2012.

Abstract: This research aims at producing pozzolanic admixtures from waste shells of periwinkle, oyster and snail. The clean shells
were ashed at 800 °C and analysed for chemical composition. The results show that they are pozzolanic in nature. The effect of using
the shells ash as admixtures on the setting time and compressive strength of cement paste and mortar were investigated using varying
percentages of 0%, 5%, 10%, 15%, 20%, 25% and 30% by weight of each of the shell ashes. The results show that the water
consistency, initial, and final setting times of each of the cement blends were increasing with increase in percentage replacement of
cement with each of the shell ashes. The optimum compressive strength with percentage replacement level of 10% for periwinkle
shell ash (PSA), 15% for oyster shell ash (OSA), and 20% for snail shell ash (SSA) were obtained with ashes produced.

Key words: Sea shell ash, concrete, admixtures, waste utilization.

1. Introduction available and/or waste materials to partially or fully

replace the costly conventional materials.
Housing delivery in Nigeria in the rural, semi-urban
An admixture is a material other than cement, water
and urban areas is still a serious problem due partly to
and aggregates that is used as an ingredient of
the high cost of some essential materials, especially
concrete and is added to the batch immediately before
cement (a major material in the construction industry)
or during mixing [2]. According to Michael [3],
whose cost has increased over the years and may soon
admixtures in concrete can improve its workability,
be out of reach of the ordinary citizens. Recently, to
hardening, or strength characteristics and generally
arrest the escalating cost of cement, the Federal
result in a reduction in the cost of concrete
government directed local manufacturers to evolve
construction [4]. For instance, activated kaolin clay,
strategies to bring down the price of the commodity to
fly ash, silica fume, baryte powder and oil shale ash
avoid a review of the existing policy on cement which
had been used as components of blended binders for
gave 2013 as the deadline for the country to be
mortars with good results in terms of their pozzalinic
self-sufficient in cement production [1].
activity [5]. The use of cassava starch [6], rice husk
Concrete is an essential construction material
ash [7-10], rice straw ash [11], and wood waste ash
composed of cement, aggregate (gravel or granite and
[12] to partially replace different types of cement in
sand) and water. In order to reduce the construction,
concrete had also been reported. The use of these
researchers have been exploring the possibility of
agricultural materials helped to reduce waste as well
using pozzolanic admixtures produced from locally
as improve the strength properties of the concrete.
However, the strength reduced with time due to
Corresponding author: Benjamin R. Etuk, associate
professor, Ph.D., main research fields: separation processes, microbial activity.
particulate systems, food processing, waste control and In Nigeria, the intensity of fishing activities in the
utilization. E-mail: bretuk2001@yahoo.com.
122 Feasibility of Using Sea Shells Ash as Admixtures for Concrete

riverine areas has resulted in the production and used were UNICEM® Ordinary Portland Cement
accumulation of large quantities of sea shells as (OPCEM), water and sand.
wastes along the coastal regions, market areas and The periwinkle, snail and oyster shells were
dump sites. Usually, the fleshes of the species are obtained from Akpan Andem market in Uyo, a dump
processed for consumption while the inedible hard site at Okpoedu, Itu, and Issiet in Itu and Uruan Local
shells are dumped at open sites thereby causing Government Areas respectively, all in Akwa Ibom
environmental pollution. State, Nigeria.
Periwinkle, snail, oyster and all marine animals
2.1 Production of Pozzolanic Admixture
belonging to phylum mollusca and class gastropoda
[13]. They belong to the group of exoskeleton animals. The three different shell samples were each washed
The exoskeletons contain rigid and resistant thoroughly to remove dirt and mud and then sun-dried
components that fulfill a set of functional roles for three days. The samples were then placed in a
including protection, excretion, support, feeding, furnace and ashed at temperatures of 800 °C for a
acting, etc.. They contain chitin and when calcium period of four hours. The ash samples were then
carbonate is added, the exoskeleton grows in strength ground into a powdered form using metallic mortar
and hardness [14]. and pestle, sieved through a sieve mesh size of 63
An exploratory study on the suitability of sea shells, microns, and kept in tight containers for analyses.
such as periwinkle shells, as partial or full
2.2 Chemical Analyses
replacement for granite in concrete work had been
reported with satisfactory compressive test results at The shell ashes were analysed to determine their
appropriate concrete mix ratios [15]. Using the ash of composition at the Quality Control Laboratory of
the sea shell, investigation had shown that up to 50% Ashakacem, Gombe, State, in accordance with
replacement of cement in sandcrete blocks and 5% Nigerian Industrial Standard (NIS) method [18]. In the
replacement in laterite blocks were possible with good method, stearic acid (0.4 g) and 20.0 g of each of the
results in terms of compressive strength [16, 17]. three different shell ashes obtained at temperatures of
In this paper, the utilization of the ash of waste 800 °C were measured and were put in a grinding pot
shells of periwinkle (PSA), snail (SSA) and oyster and ground for 60 seconds using the Herzog grinding
(OSA) as partial replacement for cement in the machine. The aluminum cup was filled half way with
construction industry is reported. The concentrations stearic acid and then filled up with the samples. The
of the ash from the different shells in finely divided cup was carefully inserted into the pellet making
form are evaluated to determine the optimum needed machine (Herzog pressing machine). The pellet
that will not compromise the workability, hardening produced was then placed in the cement X-ray
and strength properties of the concrete produced. The spectrophotometer and the programme to which the
effective utilization of these sea shell wastes which are samples were analysed was selected, that is, the
available almost free of cost and in abundance will not program OPCEM (ordinary Portland cement), and the
only reduce their pollution tendency but will help in start key was clicked so that within 2-3 minutes the
reducing the amount of cement used in concrete work. results were obtained [19].

2. Materials and Methods 2.3 Determination of Specific Gravity

The materials used in carrying out the research were The specific gravity of the ash samples was
periwinkle, snail and oyster shells. Other materials determined in accordance with BS method [20]. The
 Feasibility of Using Sea Shells Ash as Admixtures for Concrete 123

empty density bottle with stopper was weighed as W1 making the needle penetrate the paste of standard
and then filled with shell ash to about three quarter of consistency was repeated at intervals of 5 minutes,
the bottle. This was measured as W2. The bottle until the paste was stiffed enough for the initial set
containing the shell ash was then filled up with water needle to penetrate only to a point 10 mm to 20 mm
and a stopper used to cover it. This was measured as from the bottom of the mould. The initial setting time
W3. The content of the density bottle were then poured was recorded as the time that elapsed from when the
out and the bottle rinsed with water. The bottle was paste was made to when it set [21].
thereafter filled with water and the stopper inserted. The initial set needle was then replaced with the
This was measured as W4. The specific gravity for final set needle with a 1 mm square needle having a
each of the shell ashes was determined, using the circular cutting edge of 5mm in diameter. The final set
formula: needle was made to penetrate the paste in the mould,
W2 – W1 so that it left a circular cutting edge of 5 mm in
Sp gr = (1)
diameter and set 0.5 mm behind the tip of the needle.
(W2 – W1) – (W3 – W4)
The process of allowing the needle penetrate the paste
2.4 Determination of Consistency of Cement Pastes was repeated at intervals of 5 minutes, and the final
Four hundred and ninety grams of the OPCEM was set was said to have taken place when the needle
weighed and placed on a non-absorbent metallic tray. which was gently lowered to the surface of the paste
By trial mixtures, the required water content which made an impression on it but the circular cutting edge
produced the cement paste of desired standard failed to penetrate [6].
consistency of between 26 and 33 (expressed as a 2.6 Production of the Mortar Cubes
percentage by mass of the dry cement) was chosen.
The measured water was then added to the weighed The moulds of size 50 × 50 × 50 mm were used for
cement, thoroughly mixed and finely ground together all the casting of the mortar cubes. The moulds were
with a hand-trowel for four to five minutes to form a cleaned and oiled to enhance easy removal of the
neat cement paste. The neat cement paste was then cubes after setting and prevent damage of the test
placed in a special metallic mould and the consistency cubes. A mixture of 0.27 kg of cement, 0.81 kg of
of the neat cement paste was then determined by sand, and 0.135 kg of water, all in a mix ratio of
lowering the plunger which is attached to the Vicat® (1:3:0.5) was measured. The mixture was mixed
apparatus and allowed to make contact with the top thoroughly by means of a trowel on a non-absorbent
surface of the paste before it was finally released. metallic tray to obtain a homogenous mixture. This
Under the action of its weight, the plunger was was used as a reference sample (i.e 0% replacement).
allowed to penetrate the paste and the depth of The mix was then transferred into the mould of 50 ×
penetration for a standard and consistent cement 50 × 50 mm and filled in three equal layers. Each of
paste was to a point 5 mm to 7 mm from the bottom of the layers was compacted 25 times using a rod of three
the mould. This test meets the requirement stated in quarter diameter and allowed for twenty four (24)
BS [21]. hours before removing it and then cured in water for
7 days.
2.5 Determination of Initial and Final Setting Times
This process was repeated with cement replaced by
The plunger used for consistency test was replaced each of the shell ashes by weight at varied
with a round needle with a cross-sectional area of 1 concentrations of 5, 10, 15, 20, 25 and 30 percent.
mm2 used as the initial set needle. The process of The cubes were put into a curing tank containing
124 Feasibility of Using Sea Shells Ash as Admixtures for Concrete

water. This was done to maintain satisfactory moisture cement used. Nevertheless, they are in accordance
content as that hydration of the cementious material with BS [20].
continues long enough to achieve the required strength,
3.3 Consistency/Setting Time Test
durability and reduce shrinkage induced cracking in
the cube [22]. Fig. 1 shows the results of water consistency of
cement paste blended with PSA, OSA and SSA
2.7 Compressive Strength Test
produced at temperature of 800 °C. The water
This test was done in accordance with BS EN consistency of the blended cement paste increases
method [23] and used by Oymael [24]. The cubes were with increase in percentage replacement in the
removed from the curing tank at the end of the curing following trend of PSA > OSA > SSA. The reason for
period (7 days) and then weighed, before compressive this trend may be attributed to the high silica contents
strength was conducted. Three cubes each for the in PSA compared to OSA and SSA. For SSA the
different replacement levels were crushed at 7 days lowest water consistency could also be as a result of
using a manual compressive machine, with capacity of high lime content.
1000 kN. The test was carried out in the Building The results of initial and final setting times of
Department Laboratory, University of Uyo, Uyo. cement paste blended with PSA, OSA and SSA
obtained at 800 oC are presented in Figs. 2 and 3. The
3. Results and Discussion
results show that the initial and final setting times
3.1 Chemical Analyses increase with increase in the percentage replacement
of each of the shell ash. This may be due to the
The chemical composition of the OPCEM used and
increase in the required mix water, as well as retarded
the shell ashes are shown in Table 1. The results show
hydration caused by having more of the shell ashes
the cement to have the four major compounds, namely,
than cement in the mix.
CaO, SiO2, Al2O3, and Fe2O3, with high percentages
Table 1 Chemical composition of OPCEM and the sea
of CaO and SiO2 which accounts for its strength. shells ash obtained at 800 °C.
Also the results for each of the shell ashes show that Composition (wt %)
Component
they contain the main chemical compounds of cement OPCEM PSA SSA OSA
namely, CaO, SiO2, Al2O3, and Fe2O3, and the SiO2 20.06 26.26 10.20 13.41
similarity in most of the chemical composition in the Al2O3 5.85 8.79 4.81 4.95
Fe2O3 3.05 4.82 3.15 3.80
OPCEM and the latter make the partial replacement of
CaO 61.44 55.53 61.95 57.95
cement by each of the shell ashes to be feasible. From MgO 0.93 0.4 0.18 0.19
the data presented, the amount of sulphur trioxide SO3 2.71 0.18 0.03 0.12
(SO3) present in each of the shell ashes lies within the K2O 0.97 0.20 0.05 0.02
Na2O 0.14 0.25 0.04 0.22
optimum range of not more than 3.0% recommended
P2O5 0.17 0.05 0.01 0.01
by ASTM [25]. However, the results show that PSA MnO3 0.20 0.07 0.01 0.01
contains more SO3 followed by OSA and SSA. TiO2 0.28 0.05 0.01 0.01

3.2 Specific Gravity Test Table 2 Specific gravity.

Material Specific gravity
Table 2 shows the results of the specific gravity for Cement 3.10
cement, periwinkle shell ash, snail shell ash and oyster Periwinkle shell ash 2.50
shell ash obtained. From the data, it is clear that the Oyster shell ash 2.33
Snail shell ash 2.44
specific gravity of the ashes are all lower than that of
 Feasibility of Using Sea Shells Ash as Admixtures for Concrete 125

Fig. 1 Water consistency with percentage replacement of cement with sea shell ash in concrete.

Fig. 2 Initial setting time with percentage replacement of cement with sea shell ash.

Fig. 3 Final setting time with percentage replacement of cement with sea shell ash.
126 Feasibility of Using Sea Shells Ash as Admixtures for Concrete

Fig. 4 Compressive strength with varying percentage replacement of cement with sea shell ash.

3.4 Compressive Strength (3) The initial and final setting times of the blended
cement pastes were found to increase with increasing
The results of the compressive strength of the
percentage replacement of each of the shell ashes;
mortar cubes produced from cement blended with
(4) The compressive strength of the mortar cubes
each of the shell ashes are shown in Fig. 4. The figure
decreases with increase in the amount of the shell ash
shows the plots of the 7 days compressive strength
in the cement paste;
against percentage replacement of PSA, OSA and
(5) The cement can be replaced partially by up to
SSA obtained at temperatures of 800 °C. The results
10% by weight of periwinkle shell ash (PSA), 15% by
show that at first the compressive strength of each of
weight of oyster shell ash (OSA), and 20% by weight
the mixes is low compared to that of the control mix.
of snail shell ash (SSA) in making of mortar cubes
This is so, because the pozzolanic activity is slow as it without the strength being affected.
allows for the hydration of cement, but later increases
with increases in percentage replacement up to 10% Acknowledgments
by weight of PSA, 15% for OSA and 20% for SSA, The authors are deeply thankful to Ashaka Cement
and then decreases as the percentage for each of the Company, Gombe State for their help in the chemical
shell ash increases. analyses of the ash samples.
4. Conclusions References
Based on the results of this study, the following [1] R. Badmus, Cement: Manufacturers fine-tune strategies
conclusions are drawn: to meet ultimatum, The Punch Newspaper (Nigeria), May
20, 2011, p. 32.
(1) Periwinkle shell ash (PSA), oyster shell ash
[2] M.S. Shetty, Concrete Technology, Theory and Practice,
(OSA) and snail shell ash (SSA) are pozzolanic in revised ed., S. Chand and Company Ltd., Ram Nagar,
nature and satisfies the requirements of ASTM [25]. New Delhi, 2005, pp. 124-217.
Therefore, it can be used as a cement replacement [3] R.L. Michael, Civil Engineering Reference Manual, 6th
ed., Professional Publications, Inc., Belmont, CA, USA,
material;
1992, pp. 142-144.
(2) The water consistency increases with increase in [4] C. Piper, Why Use an Admixture with Concrete?
the percentage replacement of each of the shell ashes; [Online],
 Feasibility of Using Sea Shells Ash as Admixtures for Concrete 127

http://www.ehow.com/info_8761265_use-admixture-con 43 (2003) 166-177.

crete.html. [15] A.P. Adewuyi, T. Adegoke, Exploratory study of
[5] A. Shvarzman, K. Kovler, I. Schamban, G. Grader, G. periwinkle shells as coarse aggregates in concrete works,
Shter, Influence of chemical and phase composition of Journal of Applied Sciences Research 4 (2008)
mineral admixtures on their pozzolanic activity, 1678-1681.
Advances in Cement Research 13 (2001) 1-7. [16] A.A. Umoh, I.A. Odesola, The effects of periwinkle shell
[6] O.E. Alutu, T.O. Ehondor, The setting time of portland filler on the compressive strength developments of
cement pastes dosed with cassava starch admixtures, lateritic blocks, Intern. J. Eng. 2 (2008) 1-11.
Nigerian Journal of Industrial & Systems Studies 4 (2005) [17] O.F. Job, A.A. Umoh, S.C. Nsikak, Engineering
24-31. properties of sandcrete blocks containing periwinkle shell
[7] D.C. Okpala, Rice husk ash (rha) as partial replacement ash and ordinary Portland cement, Inter. J. Envir. Sci. 1
of cement in concrete, in: Proceeding of the Annual (2009) 18-24.
Conference of the Nigerian Society of Engineers, Port [18] Nigeria Industrial Standard, NIS 412, Standards for
Harcourt, Nigeria, 1987, pp. 20-25. Cement, Standard Organization of Nigeria, Abuja,
[8] J.I.C. Mbachu, J.O. Kolawole, Shrinkage and elastic Nigeria, 2009, pp. 9-15.
moduli of ordinary portland cement (opc) and rice husk [19] M. Abdulfattah, Determination of chemical analysis
ash (rha) concrete made with different coarse aggregate using pellets, in: A laboratory Manual of Quality Control,
types, J. Envir. Sci. 1 (1998) 35-40. Ashakacem Plc., Gombe State, 2001, pp. 1-12.
[9] K. Sakr, Effects of silica fume and rice husk ash on the [20] Methods for Sampling and Testing of Mineral Aggregates,
properties of heavy weight concrete, J. Mater. Civ. Eng. Sands and Fillers, British Standard Institution, London,
18 (2006) 367-376. 1975.
[10] E.B. Oyetola, M. Abdullahi, The use of rice husk ash in [21] Specification for Ordinary and Rapid Hardening of
low-cost sandcrete block production, Leornardo Electronic Portland Cement, British Standard Institution, London,
Journal of Practices and Technologies 5 (2006) 58-70. 2000.
[11] M.A. El-Sayed, T.M. El-Samni, Physical and chemical [22] A.M. Neville, Properties of Concrete, 5th eds., Ritman
properties of rice straw ash and its effect on the cement Limited, New York, 2000, p. 900.
paste produced from different cement types, J. King Saud. [23] Cement, Composition, Specifications and Conformity
Univ. Eng. Sci. 19 (2006) 21-30. criteria for Common Cements, British Standards
[12] F.F. Udoeyo, H. Inyang, D.T. Young, E.E. Paradu, Institution, London, 1997.
Potential of wood waste ash as an additive in concrete, J. [24] S. Oymael, Suitability of oil shale ash as a constituent of
Mater. Civ. Eng. 18 (2004) 605-611. cement, Oil Shale Journal 24 (2007) 45-58.
[13] C. Peter, E. Michael, Marine Biology, 15th ed., Mc [25] Specification for Fly Ash and Raw or Calcined Natural
Graw-Hill Companies, New York, 2005, pp. 167-225. Pozzolanas for Use as Mineral Admixture in Portland
[14] B. Nicholas, Exceptional fossil preservation and the Cement Concrete, American Society for Testing and
combian explosion, Integrative and Comparative Biology Materials Standards, Philadelphia, USA, 2008.