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OLIS, JUSTINE V. CE133P/B1 21 JANUARY 2015CE/3/2011103603 HW # 1 ENGR. RONNIE J. DY HIANTO

COMPONENTS OF CONCRETE

Concrete is an engineering material that simulates the properties of rock and is acombination of particles closely bound together. It is composed of three basiccomponents: aggregates (rock, sand, or gravel), cement, and water. The ratio is typically1 part (by weight) of cement to 2 parts coarse aggregate to 2 parts fine aggregate.

 Aggregate

 Aggregates are inert granular materials such as sand, gravel or crushed stone thatare an end product in their own right. They are also the raw materials that are an essentialingredient in concrete. For a good concrete mix, aggregates need to be clean, hard,

strong particles free of absorbed chemicals or coatings of clay and other fine materialsthat could cause the deterioration of concrete.

Coarse Aggregates. Coarse aggregates are particles greater than 4.75mm, butgenerally range between 9.5mm to 37.5mm in diameter. They can either be from primary,secondary or recycled sources. Primary, or 'virgin', aggregates are either land- or marine-won. Gravel is a coarse marine-won aggregate; land-won coarse aggregates includegravel and crushed rock. Gravels constitute the majority of coarse aggregate used inconcrete with crushed stone making up most of the remainder.

Secondary aggregates are materials which are the by-products of extractiveoperations and are derived from a very wide range of materials

Recycled concrete is a viable source of aggregate and has been satisfactorily usedin granular sub-bases, soil-cement, and in new concrete. Recycled aggregates areclassified in one of two ways, as: recycled aggregate (RA), or as recycled concreteaggregate (RCA).

Fine Aggregate. Fine aggregates are basically sands won from the land or themarine environment. Fine aggregates generally consist of natural sand or crushed stonewith most particles passing through a 9.5mm sieve. As with coarse aggregates these canbe from primary, secondary or recycled sources.

Lightweight Aggregate. Lightweight aggregates are manufactured from naturalmaterials or from the manufacture or processing of industrial by-products. The requiredproperties of the lightweight concrete will have a bearing on the best type of lightweightaggregate to use.

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Cement

Cement, most commonly Portland cement, is a hydraulic binder, a finely groundinorganic material which, when mixed with water forms a paste which sets and hardensby means of hydration reactions and processes and which, after hardening, retains its

strength and stability even under water. Other cementitious materials such as fly ash andslag cement, are sometimes added to Portland cement and become a part of the binderfor the aggregate.

Water

Water is mixed with the dry composite, which produces a semi-liquid that workerscan shape, typically with the use of a form. The concrete solidifies and hardens throughhydration. The water reacts with the cement, which bonds the other components together,creating a robust stone-like material.

The amount of water in concrete controls many fresh and hardened properties ofconcrete including workability, compressive strengths, permeability and water-tightness,durability and weathering, drying shrinkage and potential for cracking. For these reasons,limiting and controlling the amount of water in concrete is important for bothconstructability and service life.

STRUCTURAL PROPERTIES OF CONCRETE

Water-Cement (W/C) Ratio

The single most important indicator of strength is the ratio of the water usedcompared to the amount of cement. Basically, the lower this ratio is, the higher the finalconcrete strength will be. A minimum w/c ratio of about 0.3 by weight is necessary toensure that the water comes into contact with all cement particles, thus assuring completehydration. Typical values range from 0.4 to 0.6.

 Advantages of low w/c ratio:o  Increased strengtho  Lower permeabilityo  Increased resistance to weatheringo  Better bond between concrete and reinforcemento  Reduced drying shrinkage and crackingo  Less volume change from wetting and drying

Curing

Curing is the maintenance of a satisfactory moisture content and temperature inconcrete for a suitable period of time immediately following placing and finishing so thatthe desired properties may develop. It is affected by time, temperature and moisture.

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Concrete strength gain versus time for concrete exposed to outdoor conditions.Concrete continues to gain strength for many years when moisture is provided by rainfalland other environmental sources.

Strength and Durability

Concrete is used in the majority of buildings, bridges, tunnels and dams for itsstrength. It gains strength over time and is not weakened by moisture, mold or pests.Concrete structures can withstand natural disasters such as earthquakes and hurricanes.

Compressive Strength

Compressive strength is the measured maximum resistance of a concrete ormortar specimen to an axial load, usually expressed in psi (pounds per square inch) atan age of 28-days. During the first week to 10 days of curing it is important that theconcrete not be permitted to freeze or dry out. In practical terms, about 90% of its strength

is gained in the first 28 days. Concrete compressive strength depends upon the followingfactors:

  quality and proportions of the ingredients

  the curing environment

Density

The weight characteristic of concrete is also of primary requirement for theconcrete.

Fire Resistance

Being naturally fire-resistant, concrete forms a highly effective barrier to firespread.

Thermal Mass

Concrete walls and floors slow the passage of heat moving through, reducingtemperature swings. This reduces energy needs from heating or air-conditioning, offeringyear-round energy savings over the life-time of the building.

Consolidation

Consolidation is the mixing together of the components of concrete. Goodconsolidation is needed to achieve a dense and durable concrete. Poor consolidation, onthe other hand, can result in early corrosion of reinforcing steel and low compressivestrength.

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STRUCTURAL PROPERTIES OF STEEL

Hardness

Hardness is the resistance of a metal or steel to penetration.

Toughness

Steel has to contain imperfections which take the form of very small cracks. If thesteel is insufficiently tough, the 'crack' can propagate rapidly, without plastic deformationand result in a 'brittle fracture'. The risk of brittle fracture increases with thickness, tensilestress, and stress raisers and at colder temperatures. The toughness of steel and itsability to resist brittle fracture are dependent on a number of factors that should beconsidered at the specification stage.

Fatigue Resistance

Steel has to withstand a certain level of stress when it is subjected to an infinitelylarge number of repeated alternating stresses.

Ductility

Ductility is a measure of the degree to which a material can strain or elongatebetween the onset of yield and eventual fracture under tensile. The designer relies onductility for a number of aspects of design, including redistribution of stress at the ultimatelimit state, bolt group design, reduced risk of fatigue crack propagation and in thefabrication processes of welding, bending and straightening. Tensile strength is arequirement for steel in order to resist force that tends to pull it apart.

Yield Strength

Yield strength is the most common property that a designer will need as it is thebasis used for most of the rules given in design codes. For example, in EuropeanStandards for structural carbon steels, the primary designation relates to the yieldstrength, e.g. S355 steel is a structural steel with a specified minimum yield strength of355 N/mm².

Durability

Steel is a long lasting material which makes it ideal for buildings, rail lines andbridges. It is also resistant to wear.

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 ADVANTAGES AND DISADVANTAGES OF CONCRETE VS. STEEL INCONSTRUCTION

 Advantages of Concrete

Concrete buildings offer many safety advantages over steel skeleton structures.Compared to steel, concrete can endure very high temperatures for long periods andoffers excellent protection from explosions.

Reinforced concrete is resistant to explosion and impact. It resists hightemperature from fire for a long time without loss of structural integrity.

For concrete, the design possibilities are almost limitless. It can take on manyunique shapes and forms.

 Aside from their varied design possibilities, concrete construction gives more

rentable space because of lower floor-to-floor heights. Steel framing details typicallyinvolve decking that rests on joists, joists on beams, then beams on girders. This canmean a very thick floor. Concrete requires only 8 inches where utilities can run.

Building with concrete is also very fast. When time means money this makes it aparticularly attractive option.

Efficiency within concrete construction is being improved by the adoption of hybridsolutions and innovations in formwork such as self-climbing forms. Unlike steel, it is alsopossible for large sections to be pre-fabricated off site. This again speeds up constructionmeaning less time developing and more time using the structure.

Sacrificial probes can be integrated within concrete to provide strengthdetermination at an early age and this is likely to help further improve constructionmethodologies.

Companies also offer concrete repairs which tend to be a lot quicker, simpler andcheaper than other repairs on steel structures.

Concrete waste materials can also be included within the mix such as GGBS(Ground Granulated Blast-Furnace Slag) and PFA (Pulverized Fuel Ash).

Disadvantages of Concrete

Concrete, on its own, has one major downfall and that is that it is extremely strongin compression but has little to no strength when there is tension.

 A concrete superstructure may consume over three times as much energy as asteel one.

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  It may also consume up to six times as much natural resources, four times solidwastes and more produce more toxic wastes compared to a steel structure.

Concrete structures can pollute the air five times higher and water three times, andmay contribute to global warming seven times more than steel structures.

 Advantages of Steel

Steel, in terms of cost, is generally a cheaper option. It is also easier to recycleand can produce more useful secondary product.

Steel has a high strength/weight ratio. Thus, the dead weight of steel structuresis relatively small. This property makes steel a very attractive structural material fora. High-rise buildingsb. Long-span bridgesc. Structures located on soft ground

d. Structures located in highly seismic areas where forces acting on the structure due toan earthquake are in general proportional to the weight of the structure.

Considering ductility, steel can undergo large plastic deformation before failure,thus providing a large reserve strength. Properly designed steel structures can have highductility, which is an important characteristic for resisting shock loading such as blasts orearthquakes. A ductile structure has energy-absorbing capacity and will not incur suddenfailure. It usually shows large visible deflections before failure or collapse. Moreover, steelstructures have good fatigue strength

Properties of steel can be predicted with a high degree of certainty. Steel in factshows elastic behavior up to a relatively high and usually well-defined stress level. Also,in contrast to reinforced concrete, steel properties do not change considerably with time.

Steel, while having a high lead time, is known for its fast erection on site.Prefabrication of steel can allow thin film intumescent coatings to be applied offsite. Steelstructures can also be built with high-quality workmanship and narrow tolerances. Steelstructures in general can be repaired quickly and easily.

Steel buildings can be easily expanded by adding new bays or wings. Steel bridgesmay be widened.

Steel offers architects a far greater array of options when it comes to buildingdesign. The strength-to-weight ratio of steel is higher than any other (affordable)construction material. Steel offers aesthetics that concrete may never be able to.

Steel, being fast to erect, can allow the building to be occupied sooner. In addition,reduced labor costs are possible through dryness of form in comparison with concrete.

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The construction of a steel framework is comparatively lightweight, as much assixty percent lighter than a comparable reinforced concrete frame solution which mightallow for a less expensive foundation system. In addition, modification to the building cansometimes be facilitated by simple removal of a structural steel member.

Disadvantages of Steel

Steel, as mentioned has a high lead time.

Steel needs fire protection whereas within concrete, this is inherent. The strengthof steel is reduced substantially when heated at temperatures commonly observed inbuilding fires. Also, steel conducts and transmits heat from a burning portion of thebuilding quite fast. Consequently, steel frames in buildings must have adequatefireproofing.

Steel structures exposed to air and water, such as bridges, are susceptible to

corrosion and should be painted regularly. Application of weathering and corrosion-resistant steels may eliminate this problem.

Due to high strength/weight ratio, steel compression members are in general moreslender and consequently more susceptible to buckling than, say, reinforced concretecompression members. As a result, considerable materials may have to be used just toimprove the buckling resistance of slender steel compression members.

In terms of production, steel structures are likely to produce non-fatal injuries andillnesses higher than concrete structures.

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REFERENCES

(31 July 2014). Concrete vs steel . Designing Buildings Wiki. Retrieved fromhttp://www.designingbuildings.co.uk/wiki/Concrete_vs._steel

2010. Concrete credentials: sustainability. MPA, The Concrete Centre.

Basham, K. (23 April 2014). Water in concrete. For Construction Pros.com. Retrievedfrom http://www.forconstructionpros.com/article/11359846/water-in-concrete

De Jesus, A. (11 January 2013). Concrete or steel? Philippine Daily Inquirer

Hughes, S. (2 February 2014). Concrete vs steel construction. OnSite SpecialistMaintenance. Retrieved from http://www.onsite-sm.co.uk/blog/index.php/concrete-vs-steel-construction/

(n.d.). Properties of concrete. Cement Sustainability Initiative. Retrieved fromhttp://www.wbcsdcement.org/index.php/key-issues/sustainability-with-concrete/properties-of-concrete#2

(n.d.). What is concrete?  Hanson Heidelberg Cement Group. Retrieved fromhttp://hansonready-mixconcrete.co.uk/technical-information/what-is-concrete/

(n.d.). Introduction to concrete. Helff College of Engineering, The Universtiy of Memphis.Retrieved from http://www.ce.memphis.edu/1101/notes/concrete/concrete_properties_slides.pdf

(n.d.). Proportioning concrete. Helff College of Engineering, The Universtiy of Memphis.Retrieved from http://www.ce.memphis.edu/1101/notes/concrete/cylinder_concrete_mix_proportations.pdf

(n.d.). Properties of steel . BlueScope Steel. Retrieved fromhttps://www.bluescopesteel.com/media/10530/Properties%20of%20Steel.pdf

(n.d.). Steel material properties. SteelConstruction.info. Retrieved fromhttp://www.steelconstruction.info/Steel_material_properties#Strength

(n.d.). Steel vs concrete. MIT East Campus. Retrieved fromhttp://www.archinode.com/lcasteel.html