THE EFFECT OF SALINE WATER ON HIGH STRENGTH CONCRETE

THE EFFECT OF SALINE WATER ON HIGH STRENGTH CONCRETE

(A CASE STUDY OF THE WATER OF SALINE WATER (MOLUTEHIN VILLAGE) OF ILAJE LOCAL GOVERNMENT AREA OF ONDO STATE, NIGERIA)

ABSTRACT

The research aimed to investigate the effect the saline water (Molutehin water) could have on strength properties of High Performance Concrete. The investigation thus adopts laboratory controlled experimental approach, which induced the worst scenario concrete produced with Molutehin water can be, with regards to effects the water could cause to its compressive strength in compression and flexural strength in bending.Two sets of 100mm X 100mm X 100mm cubes and 100mm X 100mm X 500mm beams were cast using the same w/c ratio of 0.343 for the target strength of 60N/mm²for both sets of concrete. The first set which was cast and cured with portable water was taken as the control mix, and the other set cast and cure with Molutehin water as a variable. Superplasticizer (ConplastSp 430) was used in both mixes for better workability and self compaction. The results showed that both portable and Molutehin samples increased accordingly in both compressive and flexural strengths at the same rate. Their compressive strengths increased from49.13N/mm²and 49.07 N/mm² on the 7^th day to 54.82 N/mm²and 53.17 N/mm² on the 14^th day; to 57.5 N/mm²and 57.13N/mm²on the 21^st day; and to 60.7 N/mm²and 62.97 N/mm² on the 28^th day respectively.And their flexural strengths (determined using the 3^rd Point loading method) increased from 7.02 N/mm² and 7.74 N/mm² on the 7^thday to 8.82 N/mm² and 8.82 N/mm² on the 14^thday; but reduced to 8.1N/mm² and 8.46N/mm² (due to a constraint) and then increased to 10.42N/mm² and 10.8N/mm²respectively. The findings revealed that concrete samples cast and cured with Molutehin water gained strength appreciably alongside concrete samples cast and cured with portable water over 7, 14, 21 and 28 days period of curing. Therefore, the study recommends that High Performance Concrete should be used instead of conventional Normal Weight concrete in construction site under saline water attack. Concrete cover should also be increased to help protect against corrosion in case of Reinforced Cement Concrete. Non destructive test may also be carried out on formworks used under vertical loads like beams and slab before they are stripped.

CHAPTER ONE

1.0   INTRODUCTION

1.1 Background of the Study

Nawy, (1996), has it that the twenty-first century has been described as the millennium for the use of high performance concrete (defined in terms of both strength and durability performance under anticipated environmental condition). High performance concrete is designed for some particular applications for which conventional concrete is not suitable (Bhikshma, Nitturkar, and Venkatesham, 2009). It should have both high strength and high durability properties pertinent to an application (Vinayagam, 2012).

According to Khan, (2006), concrete is at present called upon to serve as a construction material for hostile environments such as seafloor tunnels, offshore piers and platforms, highway bridges, sewage pipes and confinement structures for solid and liquid wastes containing toxic chemicals and radioactive elements. Also due to the heavy cost of repairs or replacement, most of these structures are required to have a service life of hundreds of years instead of 40-50 years normally expected from ordinary cement concrete. High Performance Concrete (HPC) mixes are being developed to meet the challenge (Khan, 2006).

HPC is a concrete to fulfil specified purposes and no special mystery about it, no unusual ingredients or special equipment have to be used (Neville, 2000). However, it is now recognized that with the addition of different kinds of pozzolanic materials, mineral admixtures and chemical admixtures, low workability problem in concreting can be overcomed, further lowering of water-to-cement ratio is made possible but without its certain adverse effects on the properties of the material, and hence HPC will be achieved (Bhikshma, Nitturkar and Venkatesham 2009). Therefore, it is important to understand how concrete performance is linked to its microstructure and composition.

Great bodies of water cover about five-seventh of the earths’ surface, about 71% reaching in some places to depth more than ten kilometres (10km). Sea water has a total salinity of about 3-5 percent, with quantity of chlorides in the water (e.g. sea water) which tend to cause persistent dampness, efflorescence and corrosion to reinforcement (Osei, 2000 and Water encyclopaedia, 2012). Deterioration of concrete is rarely due to one isolated cause, (i.e. no one cause could be described as a factor causing degradation of concrete). It then readily follows that, concrete can often be satisfactory despite some undesirable feature (Physical features) but in the addition of further adverse factor, damage will be completely done. Therefore, the quality of concrete in a broad sense is considered as a cause or factor that could be responsible for the deterioration of concrete and not any isolated factor (Emmanuel, Oladipo and Olabode, 2012). But, in tackling deterioration of concrete, the salinity effect must never be left out, as it usually comes into the scene most especially when water of its constituent is used or when concrete is being worked upon in region of its (salt) reach (ccsenet.org, 2012).

According to Khan, (2006), the mineral admixtures are generally industrial by products and their use can provide a major economic and environmental benefits. Thus the combined use of chemical and mineral admixtures can help to develop high performance concrete with high durability. When the efficiency factor is known then the cement content can be reduced according to the equivalent cement content of each mineral admixture. Therefore, it is necessary to know the effectiveness of different admixtures towards the development of strength and also their optimum replacement (Malathy and Subramanian, 2007).

The main purpose of using superplasticizers is to produce flowing concrete with very high slump in the range of 7-9 inches (175-225 mm) to be used in heavily reinforced structures and in placements where adequate consolidation by vibration cannot be readily achieved. The other major application is the production of high-strength concrete at w/c’s ranging from 0.3 to 0.4 (Ramachandran and Malhotra, 1984).

1.2 Statement of Problem

There has been a problem with moderate use of concrete in environment due to the unavailabity of trusted (portable) water for producing concrete as the water of the village (Molutehin) is a replica of sea water which is generally believed to be of some negative side effects to concrete strength properties.

1.3 Need for the Study

It is a pain to see some environments in the country, which are so blessed with some valuable natural resources (e.g crude oil exploration in Molutehin, Ilaje Local Government Area of Ondo State, whose residents are as a result of this enriched), being unable to have good looking concrete constructed structures in their land, which is as a result of the ever-stable salty water they interact with, in their several environments.

For any nation to excel technologically in her construction industry, there is a need for a double-paced improvement in the quality of concrete produced in such a country. The use of concrete in Nigeria mostly has been of the routinely Ordinary Portland Cement (OPC), i.e the conventional concrete which is shown no favouritism by some conditions of some of our environments.

According to Shetty (2006), the use of and superplasticizer was not popular in India until recently (1985), due to the non acceptance of wider use of admixtures . This was as a result of the fact that 90% of concreting activities were in the hands of the common builders and Government Departments. This problem is still wallowing in our construction industries in Nigeria, and yet they desire and agitate for technological growth in their concrete production. With the look of things as a researcher in the building construction field, this may be due to the fact that the common builders do not think beyond their conventional methods of producing concrete, which may be as a result of unawareness and lack of education on the benefits accrued by the use of superplasticizers.

Grade 25 to 30 (regarded as a low strength concrete), always produced by the technology aspiring nation, which do not really need the use of plasticizers (Shetty, 2006), are delimiting factors affecting our production of high performance concrete, hence our growth in technology.

In the test of Bhiskshma, Nitturkar and Venkalensham (2009), exceeding partial replacement of cement by silica fume to a certain percentage, results to drop or fall in compressive strength of the concrete in question. The test confirms that as gradual replacement levels of cement with silica fume increases from 0%, 3%, 6%, to 12%, there is a great contribution to the increase in strength of the sample concrete, but at 15% replacement level, there is a consequent decrease in strength. Thus, this research then tends to see, if the addition of this superplasticizer (conplast SP 430), is subsequently increased, if it will further lead to more increase in the strength of the concrete.

1.3 Aim and Objectives

The aim of this project is to study the effects of Molutehin water on the strength of High Performance Concrete containing superplasticizer (conplast SP430).

The Objectives are:

• To analyse the chemical composition of (saline water) Molutehin Water
• To check the degree of workability had a concrete mix, produced with a substantial quantity of superplasticizer (conplast Sp430).
• To determine both the compressive and flexural strengths of concrete produced with Portable water, and that produced with (saline water) Molutehin water (salty).
• To compare the strength properties of the concrete cast and cured with Molutehin water, and that cast and cured with portable water; both with the application of the chemical superplasticizing admixture (conplast Sp430) to enhance their strength and workability.
• To check the effects of density on the compressive and flexural strengths of concrete.

1.4 Methodology

The experimental programme was designed to compare the mechanical properties i.e, the 28days, 21days, 14days and 7days compressive stresses and flexural strengths of two different concrete sets of specimens. Both sets intended for concrete grade C60 i.e of crushing strength 60N/mm².

The first set of the specimen mixed and cured with the water from the Molutehin village (salty water), and the other set of concrete produced with portable water. Both set with the application of the super-plasticizer (conplast SP430). The workabilities of the two different sets of concrete were checked and their results recorded.

Then the programme comprised casting and testing trials of 6 specimens. The specimens of standard cube (100mm _* 100mm _*100mm) were cast, 3specimens cast using the salty water from the village (Molutehin); and the other 3specimens cast with portable water. Both with the application of the superplasticizing chemical admixture (conplast SP430). All the above mentioned program was repeated three(3) times, intended for determining their 7days strengths, 14days strengths, 21days strengths and 28days strengths. All targeted at 60N/mm².

Both sets of cubes contain the same proportion of ordinary Portland cement, aggregates’ quantities and the same quantity of mixing water. The cement has the soundness value of 1.17mm, specific gravity of 3.0, initial setting time of 2hours:13minutes, 30 seconds, and final setting time of 2hours: 20minutes. The fine aggregate used was clean river sand, free of deleterious substances with finess modulus of 2.72, specific gravity (S.D.D) of 2.53, and moisture content of 4.01%. The coarse aggregate (granite), was obtained from a local supplier with a maximum size of 40mm, specific gravity (S.D.D) of 2.81.

The method of mix design used in target of the desired compressive strength 60N/mm² is DoE (Department of Environment) method- also known as the British method.

Both sets of cubes were cured by total immersion in the different waters in separate curing tanks for 7days, 14days, 21 days and 28days. Universal Testing Machine was then used in crushing them, and their results recorded respectively.

For the test for the Modulus of Rupture (i.e the flexural strength), six (6) beams of equal dimensions (100mm _* 100mm _*500mm) were cast, three (3) with the Molutehin water, and the other three(3) of the beams cast with portable water. Both consisted of the application of the superplasticizing chemical admixture (conplast SP430). Both sets of beams also had equal aggregate quantities and water/cement ratio. This was repeated three other times, and they were intended for curing age of 7days, 14days, 21days and 28days respectively. The concrete cube moulds were lubricated with oil before the mixed concrete was placed inside them to reduce friction between the concrete and the surfaces of the moulds.

The tests for flexural strength of these beams were then carried out, their results were recorded, comparisms were made and conclusions were drawn.

1.5 Scope and Limitation of the Study

The investigation covers the determination of the compressive and the flexural strengths of Grade C60 superplasticized concrete, prepared at 0.343w/c mixed and cured with the salty water of Molutehin Village for 7, 14, 21 and 28 days respectively, and comparing their compressive and flexural strengths with another concrete of the same grade C60, but produced with portable water, cured for 7, 14, 21and 28 days and crushed respectively.

The laboratory tests employed in this project were limited to soundness test, consistency test (and determination of the initial and final setting times), and the specific gravity of the cement. Sieve analysis for particle size distribution, specific gravity and bulk density tests for the aggregates were carried out. Laboratory tests on water and the super-plasticizer used were done as well. Slump test was done for the concretes to check their workability. Crushing on the cubes and beams were conducted.

The research is limited to producing High-Performance-Concrete using only the conventional materials for concrete i.e 40mm and below crushed coarse aggregate, sharp sand as the fine aggregate and Dangote Ordinary Portland Cement as the binding agent, with conplast Sp430 as the superplasticizer for the mix specimens.

The major problem encountered that limited the scope of this project work, was the unavailability of some laboratory equipment which made the tests processes tedious and even a few undone. Example was unavailability of standard sieves set for coarse aggregate, Tare scale with wire basket in water (for specific gravity of coarse aggregate). Past researchers recommended using rounded uncrushed coarse aggregate particles, but due to its uneasy availability in the city, where project was carried out, crushed granite stones were used instead.

Instability in power supply constituted some damages to some tests procedures, whose results were discarded and tests re-done.

The project is therefore limited for applications in areas where their everyday water for mortar or concrete production is salty (or with other related questionable characteristics).

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