Nigerian Journal of TechnologyVol. 40, No. 1, January, 2021, pp. 13–18.
www.nijotech.com
Print ISSN: 0331-8443Electronic ISSN: 2467-8821
http://dx.doi.org/10.4314/njt.v40i1.3
Performance of Sand-Crushed Oyster Shells BlendedFine Aggregates in Concrete: Waste Management
Perspective in Nigeria
O. A. Ubachukwua,∗, F. O. Okaforb, K. B. Nwokoukwua, K. P. EsochaghiaaDepartment of Civil Engineering, Michael Okpara University of Agriculture, Umudike, P.M. B. 7267, Abia
State, NIGERIA.bDepartment of Civil Engineering, University of Nigeria, Nsukka, Enugu State, NIGERIA.
AbstractPollution of our environment with wastes and the associated harm to our ecosystem and health is of great concernglobally. In addition, the unabated mining of sharp sand for concrete with environmental degradation arisingtherefrom is worrisome. In the Niger Delta region of Nigeria, enormous quantities of oyster shells are being litteredalong the streets, riverbanks and landfills, after eating the fleshy part as meat. As a means of managing the wasteand conserving sand, this study examines the properties of concrete made, using crushed oyster shells (COS) aspartial replacement of sand. Sand was partially replaced in concrete with COS at the rate of 0, 5, 10, 15, 20 and25%. The concrete matrix was cast in a metal cube mold of 150mm3 and cured for 3, 7, 14 and 28 days. A total of 72cubes were cast in three replicates for each replacement level and each curing period, using a standard mix of 1:2:4and water-cement ratio of 0.5. The results reveal that the addition of COS reduces the slump of the fresh concretefrom 27 mm at 0% to 20 mm at 25%. The addition of COS up to 25% reduced the density of the concrete by 4.05%.The compressive strength slightly reduced as the percentage replacement increased from 0 to 25%. The findingsrecommend replacement not exceeding 15% that has true slump of 23.5 mm, lighter density of 25.17 kg/m−3 andcompressive strength of 26.2 Nmm−2 which are good for concrete works. When sand is partially replaced with COSin concrete, we can confront the environmental degradation arising from indiscriminate disposal of oyster shells,as well as the depletion of sand as non-renewable component of concrete.
1. INTRODUCTIONIn Nigeria, the disposal of waste materials from
agricultural and industrial operations like palmbunches, coconut shells, palm kernel shells, usedtyres, snail shells, animal bones, wastepapers,seashells, and so on has been a source of worry[1]. The search for alternative cheaper materi-als and utilization of industrial wastes and by-product materials in infrastructure developmentis proven economically viable when environmen-tal factors are considered and these materialsmeet appropriate performance specifications andstandards [2]. The availability of sand for con-struction works is becoming rare due to the ex-cessive mining as a result of increasing demandfor shelter and other infrastructural facilities, es-pecially in the developing countries, like Nigeria.This has resulted in high cost of sand for con-
struction works [3]. The over-exploitation of non-renewable natural materials has caused sharp in-crease in its cost [4]. Oyster aquaculture is oneof the key businesses in island nations [5]. Mol-luscs aquaculture is advocated as a highly sus-tainable food source. One of the regularly over-looked aspect of aquaculture is its waste genera-tion, which is regarded as nuisance to our environ-ment [6]. Between 2008 and 2012, Taiwan gen-erated 300,000 tons of oyster shells, which callsfor environmental concerns [7]. In South Korea,there were excess oysters; hence, can be utilizedin the construction industry [8]. Approximatelythree hundred thousand tons of oyster shells oc-cur in South Korean seas annually. Only a verysmall percentage is re-used. Hence, there existsthe problem of disposing the remnant of the wasteoyster shells. This results in illegal disposal in thesurrounding area.
In a particular year in Taiwan, the yield of oys-ter shells was 34,000 megatons. After shelling,the total quantity of oyster shells produced glob-ally was approximately 200,000 megatons. How-ever, only a very small portion is recovered and
14 O.A. Ubachukwu, F.O. Okafor, K.B. Nwokoukwu and K.P. Esochaghi
Figure 1: Drying of washed oyster shells under the sun.
reused, according to Department of FisheriesAdministration, Yuan, Taiwan [9]. In Nigeria,oyster shells are found in the Niger Delta re-gion located at latitude 5.3261°N and longitude6.4708°E. Niger Delta is the delta of the NigerRiver at the Gulf of Guinea on the Atlantic Oceanin Nigeria. The region has a tropical climate withtwo distinct wet and dry seasons. The mean an-nual rainfall usually exceeds 3500 mm along thecoast. It has annual mean temperature of be-tween 18 to 35 ℃[10]. These make the NigerDelta region a good habitat for oysters; hence,enough waste shells. The nine Nigerian statescomprising Niger Delta region are found in theswamp/fresh water forest ecological zone. World-wide, between 8 and 10 billion tons of concreteis produced annually. Such amount of concreterequires higher amounts of natural resources foraggregates [11]. Time will soon come when allsources of natural aggregates will decrease [12].Consequently, alternative fine aggregates for con-crete has become imperative. Oyster shell is asea food which result to waste after consumption,causing environmental hazard due to pollution.If crushed oyster shells is used as substitute forfine aggregates, charges for disposal of waste willbe avoided. Oyster shells are composed of cal-cium carbonate, CaCO3 (approximately 96%) andother minerals in trace amounts [13–15]. As a re-sult of this predominant chemical composition ofoyster shells with CaCO3, some researchers, [16–19] have crushed and used its powder to partiallyreplace cement in either mortar or concrete dueto its resemblance in chemical composition withlimestone used in the production of ordinary Port-land cement. When crushed oyster shell (COS)powder is used in partial replacement of cement,the chaff has resemblance with sand. Hence, canpartially or fully replace sand in concrete. Thisresearch therefore explores the properties of con-crete produced with COS as partial replacementof sand in concrete, having waste management ofwaste oyster shells in Nigeria in focus.
2. MATERIALS AND METHODS2.1. MaterialsThe cement used in this work was Dangote
brand and it conformed to the requirements of[20]. The sharp river sand was sourced fromOvimRiver in Isuikwuato Local Government Area ofAbia State, Nigeria. The well graded sharp sandwas free from deleterious substances and it con-formed to the requirements of [21]. It was thor-oughly flushed with water to reduce the levelof impurities and organic matter. The graniteof 20 mm maximum size was sourced from thequarry belonging to Setraco Construction Com-pany, Amasiri, Ebonyi State, Nigeria and it con-formed to the requirements of [22]. The waterused for the study was obtained from boreholesunk in the College of Engineering and Engineer-ing Technology, Michael Okpara University ofAgriculture, Umudike, Abia State, Nigeria. Thewater was clean and free from any visible impu-rities. It conformed to the requirements of [23].Oyster shells used for this research were collectedfrom where they were obtained from Waterfrontand Creek Road where they were discarded PortHarcourt, Rivers State, Nigeria, where they werediscarded, having taken by the fleshy part of theoyster as food.2.2. MethodsIn order to remove the little flesh attached to
the oyster shells, the oyster shells were soaked inwater for about 48 hours and thoroughly washed.The shells were sun-dried and crushed mechani-cally with the aid of the Hammer Mill Machine ofbrand TFR400. Figure 1 shows where the washedoyster shells were undergoing drying under thesun, while Fig. 2 shows the crushed oyster shellsawaiting sieving.Having confirmed that the sand, granite, ce-
ment, crushed oyster shells conformed to the rel-evant British Standards, we used standard mixof 1:2:4 of binder: sand/COS: granite at water-cement ratio of 0.5 with target strength of 25N/mm2. Sand was partially replaced with COS at
Nigerian Journal of Technology (NIJOTECH) Vol. 40, No. 1, January 2021.
Performance of Sand-Crushed Oyster Shells Blended Fine Aggregates in Concrete 15
Figure 2: Crushed oyster shells while awaiting sieving in the laboratory.
Table 1: Mix proportions for partial replacement of sand with crushed oyster shells.
Specimen Mass of water Mass of cement Mass of sand Mass of granite Mass of crushed oyster(kg) (kg) (kg) (kg) shell (kg)
the rate of 0, 5, 10, 15, 20 and 25%. The homog-enized mixture was cast in concrete cube moldsof 150 × 150 × 150mm, in layers of 50mm andcompacted with the tamping rod at 25 strokes perlayer and the top finish with the trowel and la-bel accurately conforming to [24]. The concretecubes were released from themetal molds after 24hours and immersed for 3, 7 ,14, and 28 days in acuring tank. A total of 72 cubes of concrete werecast. After the test for setting times of cement andgrading of aggregates were done to ascertain thesuitability of the materials, the workability, den-sity and compressive strength of the concrete werealso examined. Each sample was replicated thricefor each curing period and for each replacementlevel. Density is calculated from Eq. (1):
Density = Mass of concrete cube in kgVolume of concrete cube in m3
= Mass0.15×0.15×0.15
(1)
After obtaining the crushing load (load at frac-ture) from the universal testing machine of brandOKH-200, where load of uniform pace of 5.25KN/Sec was applied and maintained, the com-pressive strength is calculated using Eq. (2);
Fcu = Crushing Load in NArea of concrete in mm2 (2)
The mix proportions are as given in Table 1.
3. RESULTS AND DISCUSSION
3.1. Workability of Sand-COS ConcreteThe workability of the fresh sand-COS concrete
as the percentage replacement increased from 0to 25% is shown in Fig. 3.It can be seen that concrete became less work-
able as the percentage of COS increased from 0%to 25%. The slump decreased from 27 mm at 0%to 20 mm at 25% replacement levels. This is sim-ilar to the results of [7, 25]. This is attributableto sharper and irregularly shaped particles of theCOS, resulting in lowered fluidity and higher fric-tion. However, the concrete is still of good work-ability and has ease of placement, despite the re-duced slump.
3.2. Density of Sand-COS ConcreteThe variation in average densities of standard
and COS-sand concrete after each curing periodare shown in Table 2.As the percentage replacement of sand with
COS increases, the density of concrete continuesto decrease, leading to concrete of lighter weight.This is as a result of lower specific gravity of COSthan sand. Consequently, there is reduced deadload of the structure. This is advantageous asthe ability of the structure to resist loads is en-hanced. For instance, the density reduced from2619 kg/m3 at 0% to 2515 kg/m3 at 25% replace-ment. Thus, partial replacement of sand withCOS up to 25% produces concrete that is 4.05%lighter than the standard concrete. This is be-cause the specific gravity of COS is less than thatof river sand.
3.3. Compressive Strength of Sand-COS Con-crete
Figure 4 shows that there was a general in-crease in compressive strength as the curing ageincreases from 3 to 28 days. The compressivestrength of concrete of COS-sand concrete con-tinued to decreases slightly as the percentage re-placement increases. Figure 4 shows that the 28-day compressive strength of COS-sand concretemet the target strength of 25 N/mm2. The com-pressive strengths for 5, 10, and 15% are respec-tively 29.2, 27.4, and 26.2 N/mm2. This agreeswith the results of [7, 23]. This is as a result ofporous structure and lower absorption rate thatleads to slower hydration of cement. Hence, lowercompressive strength. When concrete of slightlylower strength is needed, higher percentage re-placement is advised.
4. CONCLUSIONThe present study focused on investigating the
rheological and hardened properties of concreteproduced using the readily available crushed oys-ter shells as partial replacement of sand, with em-phasis on managing the environment of the NigerDelta region of Nigeria. From the foregoing re-sults and discussion, the following conclusions arehereby drawn:
(a) The addition of COS to partially replace sandfrom 0 to 25% reduces the workability (slump)of concrete. However, the concrete is still ofgood slump. Hence, workable.
Nigerian Journal of Technology (NIJOTECH) Vol. 40, No. 1, January 2021.
Performance of Sand-Crushed Oyster Shells Blended Fine Aggregates in Concrete 17
Figure 4: Variation of compressive strength of sand-COS concrete at with curing age.
(b) Sand-COS blended concrete is slightly lessdense than the normal concrete. This willlead to reduced dead load of the structure.Hence, sand-COS concrete produces lighterweight concrete.
(c) As the percentage replacement of sand withCOS increases, compressive strength slightlyreduces. However, the compressive strengthis generally good.
(d) The compressive strength of sand-COS in-creases as the curing age increases.
(e) Replacement level not exceeding 15% for re-inforced concrete is recommended for sand-COS fine aggregates as a waste managementapproach in the Niger Delta region of Nige-ria for healthier environment and reducedassociated health hazards is hereby recom-mended.
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Nigerian Journal of Technology (NIJOTECH) Vol. 40, No. 1, January 2021.
