EFFECTS OF ELEVATED TEMPERATURE ON THE FLEXURAL STRENGTH OF LATERIZED CONCRETE

EFFECTS OF ELEVATED TEMPERATURE ON THE FLEXURAL STRENGTH OF LATERIZED CONCRETE

ABSTRACT

Strength and durability of concrete are the most vital elements of structural design and specified for compliance purposes in construction industry. Concrete under service is possibly exposed to elevated temperature during fire accident or when subjected to furnaces and reactors; there are visible analytical observations that judge the effects of such concrete, they are: reduction in strength, loss of weight, colour variations and surface cracks they were significant during the exposur such concrete structure is in undesirable state. The use of the fine aggregate (sand) in normal concrete is increasing in an astronomical way as suggested the need for an alternative or partial replacement of the fine aggregate in concrete. This report research aimed at determines the effects of elevated temperature on the flexural strength of laterized concrete. The method employed includes the review of related relevant literature that covers published materials especially journals, past thesis and data based information from internet. A total number of 36 beams size 100mmx100mmx500mm were cast with ordinary Portland cement of laterite replacement at 0% (control), 10%, 20%, 30% respectively, the beams were cured in water at age 14days, 21days, 28days, heated at varying elevated temperatures 500⁰C, 600⁰C and 700⁰C. The flexural strength of laterized concrete was determine after subjected to elevated temperature which meet target strength 25N/mm² of water-cement ratio 0.70 and compared with the flexural strength of control beams. The analysis of the result obtained revealed that laterite reduces the durability of concrete at elevated temperature. The higher the percentage of laterite replacement, the lower the concrete withstands or resisting bending of concrete when subjected to load and temperature.

CHAPTER ONE

1.0       INTRODUCTION

1.1       Background of the Study

Concrete is a construction material obtained by mixing fine aggregate,cement, coarse aggregate and water in required proportions. The combination becomes hard like stone when cured. The hardening occurs as a result ofchemical action of cement that reacts with water makes concrete stronger as regard to age. Concrete characteristics such as strength, durability depend upon the property of the constituent, proportion of the mix, placing,method of compaction and curing of concrete (Krishnaswami, 2009).

            Concrete under service is feasibly exposed to elevated temperature and fire accident or when subjected to furnaces and reactors, the powered properties such as volume stability, modulus of elasticity and strength of concrete are notably reduced during the exposures such structure is in the state of unattractive conditions (Omer, 2007).

When concrete is subjected to elevated temperatures, the chemical and physical composition of concrete structure changes greatly. The dryness of the hydrated calcium silicate and the thermal growth of the aggregate amplify inner stresses from 300°C, micro cracks are induced through the material. The fire is generally extinguished by water and calcium oxide (Cao) turn into [Ca(0H)₂] causing fabulous and fragmentation of concrete. Therefore, the effects of elevated temperatures are generally detectable in the outward appearance of surface cracks, colours variation, loss of weight and reduction in strength.

The alteration produced by concrete subjected to elevated temperatures havemore palpable when the temperature surpasses 500°C. Most changes eligible by concrete at this concrete level are considered unalterable Calcium silicate           hydrate [CSH] gel, which is the strength giving compound of cement paste; putrefy further above 600°C. At 800°C, concrete usually crumbles. Due to severe micro-structural alter that are make concrete losses it strength and durability (Omer, 2007)

The behaviour and the load-bearing capacity of concrete element that exposed to blazeaccident is the main task in fire engineering design. Overview using temperature-dependent stress-strain curve proved to be accurate. When concrete exposed to elevated temperature, aesthetic damage and functional deteriorations of the structure occur.Aesthetics damage can be repair while functional mutilation are more profound which required unreasonable or total repair or replacement liable on their rigorousness (Omer, 2007).

1.2       Need for the Study

Khoury(1992) and Noumone etal (1994) had reported the effects of elevated temperature disclosure on the properties of concrete. Several ways have been disreputable for the descent of concrete due to elevated temperature. These include decomposition of the calcium hydroxide into lime and water, spreading out of lime on re-hydration, the development of micro crack due to thermal incongruity between cement paste matrix and aggregate segment. This research work have drawn attention in studying the alternative construction material  laterized concrete to ascertain convenient and reliable to judge the quality of the good concrete that withstand elevated temperature exposure and ascertain sustainability, safety assurance, serviceability consideration and low thermal conductivity. The fashionable concrete structures such as pavements, slabs, beams, runways and pre-stressed concrete can recommend laterized concrete without atom of doubt where bending is necessary in the structure, the design must obey the theory of flexural strength; key to propose Engineers to guide proper selection of materials. Maurice (2012) opined that the flexural strength property of concrete is predominantly when the concrete group is un-reinforced it is safely distribute resolute load over wide areas.

1.3       Aim and Objectives

1.3.1    Aim                                        

The aim of this research work is to verify the effects of elevated temperature on the flexural strength of laterized            concrete.

1.3.2    Objectives

Based on the aim, the following objectives were pursued:

1. To determine the properties of the aggregates.
2. To carry-out workability test on the laterized concrete.
3. To determine the flexural strength of laterized concrete after subjected to elevated temperature.
4. To compare the weight of flexural strength of control beams against the experiment and establish any difference in the concrete.

1.4       Scope ofthe Study

This research work covers the experimental and preliminary laboratory test to verify the effects of elevated temperatures on the laterized concrete. The study will be limited to Lateriteat0 % (control), 10%, 20% and 30% replacement of sand. The concrete is filled in the mould size 100mm x 100mm x 500mm and were de-moulded after 24hours and cured by submerging them in clean water for 14days, 21days and 28daysremoved, weighing, heated, re-weighing after impassioned and establish flexural strength on both control and experimental specimens. The preliminary tests for the research are:

1. Sieve analysis
2. Specific gravity
3. Moisture content
4. Bulk density
5. Consistency test
6. Slump test
7. Atterberg test
8. Flexural test

Table 1.1        Test for Concrete and Concrete Constituents

The grades obtained were subjected to statistical, graphical and mathematical analysis to produce reasonable, logical and scientific conclusion from which recommendation would be drawn.
1.5       Methodology

The methodology that was employed for this research work includes the review of related relevant literature that covers available materials especially journals and past thesis and data based information from interne that have bearing on this research work. Department of Environmental (DOE) method  of concrete mix design was employed, casting of un-reinforced concrete beams specimens in a mould size 100mmx100mm x 500mmwhich constitute material aggregate; laterite at 0% (control), 10%, 20%, and 30% surrogate of sand, de-moulded after 24 hours and curing age of the beams specimens at 14days, 21days and 28days respectively. The beams sample subjected to elevated temperature at varying temperatures to determine the effects at 500°C, 600°C, and 700°C. The maximum furnace temperature required is 100°C per 30minutes. The modifications fashioned by tall temperatures are more apparent when temperatures go beyond 500°C. Most alter that occur in concrete at this temperature level are regard as irrevocable. A total numbers of 36 beams were cast of mould size 100mm x 100mm x 500mm for this research work.

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