EFFECT OF SALT WATER ON CONCRETE USING BIDA NATURAL STONES AS COARSE AGGREGATE

ABSTRACT

Concrete is a combination of cement, fine and coarse aggregates and water, which are mixed in a particular proportion to arrive at a particular strength. The cement and water react together chemically to form a paste together with the aggregate particles. The mixture sets into a rock-like solid mass, which has considerable compressive strength but little resistance in tension. In this research, concrete was properly mixed using salt water at 35g/l and water only respectively with Bida natural stones as coarse aggregate in the production of concrete. The physical and mechanical properties of the aggregates were determined and the compressive strength of hardened concrete were determined at 7, 14, 21 and 28 days curing. A total of 144 cubes were cast and cured for 7, 14, 21 and 28 days. The mix ratio of 1: 2: 4 and w/c 0f 0.5 were used. The concrete developed in this work has slump ranging from 0 – 135 mm, compressive strength ranging from 8.94 N/mm² – 27.11 N/mm² and density ranging from 1757.04kg/m3 to 2198.52kg/m3 respectively. The use of salt water should be welcome and not feared for casting and curing of concrete during construction most especially in coastal environment if a mix ratio of 1:1.5:3 grade M20 is applied.

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background to the Study

Concrete  is  a  mixture  of  cement,  water  and  aggregates  in  a  given  proportions. Aggregates represent some 60-80% of the concrete volume. They are inert grains bound together by means of a binder which is cement. Although inert, they introduce an important contribution to these major characteristics which make concrete the most favoured building material. Aggregates help to reduce shrinkage and heat dissipation during hardening and also contribute to the increase in the mechanical strength of concrete. Depending on the mix, cement generally represents about 12-14% of concrete weight. It plays an active part in the mixture by ensuring cohesion between aggregate grains and, in doing so, it introduces a decisive contribution to concrete mechanical strengths. During the hardening process, due to it heat dissipation it could lead to shrinkage and cracking (Malhotra, 1988). Water occupies 6-8% of the composition of fresh concrete also depending on the mix. It provides for cement hydration and for the workability of the fresh  concrete mixture. When in excess, it determinately affects concrete porosity and mechanical strengths (Mbadike and Elinwa,2011).

On average, seawater in the world’s oceans has a salinity of about 3.5% (35 g/L). This means that every kilogram (roughly one litre by volume) of seawater has approximately

35 grams of dissolved salts (predominantly sodium (Na+) and chloride (Cl−) ions). It was reported that the use of sea water for mixing concrete does not reduce the strength of concrete although it may lead to corrosion of reinforcement in certain cases. Research workers are unanimous in their opinion, that sea water can be used in un-reinforced concrete or mass concrete, sea water slightly accelerates the early strength of concrete (Fred, 2020).

Granite, limestone, sand stone, or basaltic rock re crushed for use principally as concrete aggregate or road stone. Thus, this research intends to determine the effect of ‘salt water’ on hardened concrete using Bida natural stones (BNS) as coarse aggregate.

1.2 Statement of the Research Problem

About 75 percent of the surface of the earth is covered by oceans; therefore, a large number of structures are exposed to Salt water with high salinity either directly, or indirectly. As a result, several coastal and offshore sea structures are exposed to the continuous action of physical and chemical deterioration processes (Modupeola and Olutoge,2014).

The planet earth is experiencing noticeable shortage of pure clean water sources for future  construction  work  and  the  use  of  water  containing  salt  to  develop  durable concrete of lasting performance will be greatly beneficial if looked into properly (Falah, 2010).

Only 2.5 Percent of the world’s water bodies is said to be fresh water, the remaining constitute  seawater  (Adebakin,  2003).  This  challenge  of  building  and  maintaining durable concrete structures in coastal environs have long become a serious issue to the people living in this areas and this provides an excellent opportunity to understand the complexity of concrete durability problems in these areas.

1.3 Aim and Objectives of the Study

The aim of this research is to determine the effect of salt water on concrete made using Bida Natural Stones as coarse Aggregates.

The objectives of the research are to;

i.    Determine the physical and mechanical properties of the Aggregates. ii.   Determine the effect of salt water at 35g/L on concrete

iii.  Determine the workability of fresh concrete using fresh water and salt water for casting.

iv.  Determine  the  Compressive  strength  of  concrete  produced  using  Bida  Natural Stones, at 7, 14, 21 and 28 days of curing using salt water at 35g/L.

1.4 Justification of the Study

Crushed stones are available in some parts of Nigeria, like Abuja and are transported to other places like Bida and its environs. This increases haulage distance. Bida natural stones  are  abundantly  available  in  Bida  areas.  These  aggregates  are  cheaper  than crushed granite and have been proved with laboratory evidence that the aggregate is suitable (Alhaji, 2016).

The planet earth is experiencing noticeable shortage of pure clean water sources for future  construction  work  and  the  use  of  water  containing  salt  to  develop  durable concrete of lasting performance will be greatly beneficial if looked into properly (Falah, 2010). Hence this research work seeks to determine the effect of salt water on concrete as substitute for ordinary water.

1.5 Scope of the study

The scope of this research covers the collection of materials, determination of physical and mechanical properties of the aggregate which includes, determination of Moisture content, Bulk density, Specific gravity, Sieve analysis, Aggregates Impact Value (AIV), Aggregates  Crushing Value (ACV);  mixing salt  and  water to  form  salt  water (sea water)in the production of concrete specimen using 150mm x 150mm x 150mm cube. It also includes the determination of workability of fresh concrete and lastly, the determination of compressive strength of the concrete cubes after 7, 14, 21 and 28 days curing using salt water at 35g/L and ordinary water.

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