SUITABILITY OF OYSTER SHELL AS LIGHT WEIGHT AGGREGATES FOR LIGHT WEIGHT CONCRETE PRODUCTION

SUITABILITY OF OYSTER SHELL AS LIGHT WEIGHT AGGREGATES FOR LIGHT WEIGHT CONCRETE PRODUCTION

ABSTRACT

The suitability of Oyster shell, a small water gastropod (mollusk), as lightweight aggregate, for the replacement of conventional granite concrete in the production of lightweight concrete was investigated in the Laboratory. Physical and mechanical properties of the shells and granite were determined and compared. The bulk density of the Oyster shells was found to be 3067 kg/m3 while that of Granite was 5000 kg/m3. The specific gravity for Oyster shells and Granite were 1.4 and 2.9 respectively. Concrete cubes and Cylinders were cast, by replacing granite (coarse aggregate) with 0%, 20%, 40%, and 60% of Oyster shells by weight, for compressive and splitting tensile strength tests respectively. At 28-days of curing after casting, the result for density, compressive strength and the splitting tensile strength test made from 60% replacement of oyster were found to be 1920 kg/m3, 24.61 N/mm2 and 7.39 N/mm2 while that of 0% replacement (control mix) was 2329 kg/m3, 30.67 N/mm2, 9.33 N/mm2 respectively. Hence, the density, compressive and splitting tensile strength test of Oyster shell concrete decreases, with a decreasing workability, in the range of 10-40mm, but the decrease in the properties still conforms to ASTM C 330 and C 567. From this study, it can be concluded that Oyster shells can be used, as it is suitable for partial replacement as lightweight aggregate in light weight concrete production, especially in places where granite is in short supply and Oyster shells are readily available, as this help to reduce the treat of the shells to the environment and people, from their decaying rate and odour.

CHAPTER ONE

1.0 INTRODUCTION

1.1       BACKGROUND OF STUDY

Concrete is a solid, rock-like mass formed from the mixture of sand, gravel/granite (aggregates), cement (binder) and of course water (to start hydration process), in a specified proportion to achieve a particular strength at the end of a particular day of curing.

Concrete has been the most useful material in the construction industries of the world (Aitcin, 2000; Mobasher, 2008) and right from the early Roman periods, the use of Light Weight Concrete (LWC) has been a prominent act in the construction industry as argued by Chandra (2002). Architects, Engineers, and Builders has so much recognized the unavoidable economies and advantages this product offers, such as providing: less dead load, improved seismic structural response (in earthquake and likes), longer spans, better fire ratings, thinner sections, decreased story height, smaller size structural members, less reinforcement and lower foundation costs. Lightweight concrete precast elements has solved weight and durability problems in buildings and exposed structures. It also offers reduced transportation and placement costs, as evidenced by the impressive lightweight concrete structuresfound throughout the world today.

Lightweight concrete is a mixture made with full or partial replacement of coarse aggregate (conventional Gravel or Granite) and in some cases, a portion or the entire fine aggregates may be a lightweight product conforming to ASTM C 330. Structural LWC has a unit weight of 1440 to 1840 kg/m³ compared to normal weight concrete of density ranging from 2240 to 2400 kg/m³ (about 25% to 35% lighter). The strength of a lightweight concrete for structural application should be comparable to that of a normal weight concrete, greater than 2500 psi (17.0 MPa) at 28 days of age when tested with the methods stated in ASTM C 330, and also has a dry air density not more than 1,840 kg/m3 as determined by ASTM C 567. Lightweight aggregates used in structural lightweight concrete are typically expanded shale, clay or slate materials (fired in a rotary kiln to develop a porous structure) and air-cooled blast furnace slag (Topcu and Boga, 2010; Bondar et al, 2011; Limbachiya et al, 2012). There are also non-structural LWC with lower density made with other aggregate materials and higher air voids in the cement paste matrix, such as in cellular concrete but the expectations of the performance have raised and now, there is an expectation of a consistent, reliable material with predictable characteristics and as a result of this, one of the promising use of oyster shells which is being used for this project, is in the construction industries, as substitutes for the normal dense aggregates ( Granite, Gravel, sand, etc) especially in the coastal areas where aggregates are found lacking but where the shells are available, to produce concretes with sustainable compressive strength, workability etc.

Oyster shells are obtained from oysters which are marine gastropods (mollusks) with thick round or elongated shells. They have a regular mathematical pattern of growth, i.e. they retain their forms as they increase in size. The increase in size is as a result of continual adding to the edge of the shell around an imaginary line or sphere and by so doing, the shell becomes a strong compacted home for the mollusk living in it.

The most common species of oysters found and harvested in the lagoon and mudflats, along the coast of Nigeria’s Niger Delta zones from Calabar in the east to Lagos in the west, are the small cupped oyster(Crassostrea spp) as identified by Li and Qi, (1994).Dahunsi (2003) relays it that over many years, large quantities of oyster shells have been accumulated in many parts of the country such as Bori, Western Ijaw, Burutu, Agoro, Ogalaga, Badagry and Lotugbene and used for purposes, such as the construction of roads, houses, slabs, soak ways, also for controlling floods which is more cheaper than that of granite chippings.

In the research of Yang et al;(2005), crushed oyster shells were substituted for fine aggregate in concrete and it was discovered that there wasn’t any reduction in the compressive strength of concrete at 28 days and that rate of increase of compressive strength was faster as substitution rate of oyster shell increased.

1.2       AIM AND OBJECTIVES OF THE STUDY

The aim of this research work is towards determining the suitability of oyster shells as light weight aggregates for light weight concrete production.

The main objectives of this work are as follows:

• To carry out laboratory test on the physical properties of oyster shells and other materials to be used for proper check on their suitability as aggregate materials.
• To calculate the proportion of the concrete constituents with a mix design and a trial mix to check for its workability before it is cast in cubes and cylinders.
• To test for the compressive strength and the splitting tensile strength of the concrete produced after curing for 3,14, 21 and 28days.
• To compare the alternative to normal weight concrete for strength, density, cost and other preferential advantages.

1.3       SCOPE OF THE STUDY

This research work is focused on how the wasting oyster shells in the coastal regions of Nigeria and other countries could be effectively and maximally utilized in the construction industries as light aggregates by-products for lightweight concrete production.It focuses onthe structural integrity of concrete made with the alternative oyster shells and the potential sustainability of the aggregate in the developing world. The structural integrity will be measured by determining the physical properties, compressive strength and splitting tensile strength of cast oyster shells. Cube moulds with nominal sizes of 100×100×100mm would be casted and cured for 3, 14, 21 and 28days,before it is crushed for compressive strength test while, cylindrical moulds of 150×150×150 sizes, would be cast and crushed, to test for the splitting tensile strength after 3 and 28days of curing. The concrete would becasted in different proportions of Oyster shells. A reference mix with 0% replacement of oyster shell (granite only) would be used as the control mix, before it is consequently replaced with 20%, 40%, and 60% of oyster shells as this help to determine the rate at which changes occur in the concrete mixture.

1.4       RESEARCH METHODOLOGY

The method that would be used to analyze this research is purely dependent on laboratory testing, due to cost and other constraints.The nature of the research is solely relying on the analysis and findings surrounding the LAC produced with oyster shells, which can be used in building construction.The mix would be designed using the absolute weight method of the DOE mix design method. Physical and mechanical properties of oyster shells and the crushed natural granite chippings would be investigated through the following tests: Specific gravity test, bulk density, slump and aggregate impact value tests. Sieve analysis would be carried out, using sieves arranged in decreasing size of opening, placed on a shaker in order to differentiate samples of the aggregate into sizes. The coefficients of uniformity, curvature and gradation will be determined. Cube crushing tests would be carried out to determine the compressive and the splitting tensile strengths of oyster-granite concretes. Also, a reliable qualitative approach is being put into consideration using secondary research data, from published resources such as journals, text books, scientific papers and the internet, as these provide validated information, for the qualitative analysis.

 1.5       JUSTIFICATION OF THE STUDY

The essence of carrying out this research work is to provide detailed technical awareness of the use of oyster shells as a good substitute for coarse aggregate in the production of light weight concrete in places where conventional gravel/granite is in short supply and where oyster shells are readily available, as it is economical, recyclable, durable and providing a high yield strengthwhich would be justified by carrying out a study on the compressive and splitting tensile strength of concrete produced from the material (Oyster shell)and these would help reduce the threat of the shells odour to our environment, since their decaying rate is insignificant.