PERFORMANCE OF CONCRETE BLENDED WITH STEEL FIBERSOBJECTIVETo increase the compressive strength, tensile strength and ductility of concrete byadding steel fibers to ordinary concrete
WORKABILITYAccording to IS:6461-1973 workability is defined as that property of freshly mixedconcrete or mortar which determine the ease and homogeneity with which concrete canbe mixed, placed, compacted and finished. Workability is broadly defined as the ease with which concrete can becompacted 100% having regard to made of compaction and place of deposition. Every job requires a particular workability. A concrete which is consideredworkable for mass concrete foundation is not at all workable for concrete to be used inroof construction. Similarly, a concrete considered workable for thick sections is notworkable required to be used in thin sections. Therefore, the word workability assumesfull significance of the type of work, thickness of sections, extent of reinforcement andmode of compaction.Factors affecting Workability Workable concrete is the one which exhibits very little internal friction betweenparticle and particle or which overcomes the frictional resistance offered by theformwork surface or reinforcement with just the amount of compacting efforts. Thefactors helping concrete to have more lubricating effect to reduce internal friction forhelping easy compaction are as follows:- 1. Water content 2. Mix proportions 3. Size of aggregates 4. Shape of aggregates 5. Surface texture of aggregates 6. Grading of aggregates 7. Use of admixturesWater content Water content in a given volume of concrete will have significant influence onworkability. The higher the water content per cubic meter of concrete, the higher will bethe fluidity of concrete, which is one of the most important factors affecting workability.The damaging effect of more water in concrete is reduction in compressive strength. In
case where all steps to improve workability fail, only as a loss recourse the addition ofmore water should be considered. More water can be added, provided acorrespondingly higher quantity of cement is also added to keep the w/c ratio content,so that the strength remains the same.Mix proportions Aggregate/cement ratio is an important factor influencing workability. The higherAggregate/cement ratio, the leaner is the concrete. In lean concrete, less quantity ofpaste is available for providing lubrication per unit surface area of aggregate and hencethe mobility of rounded aggregate of some volume. A reduction of inter particlesfrictional resistance offered by smooth aggregates also contributes to higher workability.Size of aggregates The bigger the Size of aggregates, the less is the surface area and hence lessamount of is required for wetting the surface and less matrix or paste is required forlubricating the surface to reduce internal friction. For a given quantity of water andpaste, bigger the Size of aggregates will give higher workability. The above, of coursewill be true within certain limits.Shape of aggregates Shape of aggregates influences workability in good measures. Angular,elongated or flaky aggregate makes the concrete very harsh when compared torounded aggregate or cubical shaped aggregates. Contribution to better workability ofrounded aggregate will come from the fact that for the given volume of concrete orweight it will have less surface area and less voids than angular or flaky aggregate. Thisexplains the reasons why river sand and gravel provide greater workability to concretethan crushed sand and aggregate.Surface texture The influence of surface texture on workability is again due to the fact that thetotal surface area of rough texture aggregate is more than the surface area of smoothrounded aggregate of same volume from the earlier discussion it can be inferred thatrough texture aggregate will show the poor workability and smooth or glassy textureaggregate will give better workability the reduction of inter particle frictional resistanceoffered by smooth resistance also contribute to the higher workability .Grading of aggregate This is one of the factors which will have maximum influence on workability. Awell aggregate is the one has least amount of voids in a given volume. Other factors
being constant, when the total voids are less, excess paste is available to givelubricating effect. Hence better the grading, less is the void content and higher theworkability.Slump test Slump test is the most commonly used method of measuring consistency ofconcrete which can be employed either in laboratory or at site of the work. It is not asuitable method for very wet or very dry concrete. It does not measure all factorscontributing to workability nor is it always representative of the placability of theconcrete. However it is used conveniently as a control test and gives or indication of theuniformity of concrete from batch to batch. Repeated batches of the same mix, broughtto the same slump, will the same water content and water cement ratio provided theweights of aggregate, cement and admixture or uniform and aggregate grading is wit inacceptable limit. Additional information of workability and quality of concrete can beobtained by observing the manner in which in concrete slumps. Quality of the concretecan also be further assessed by giving a few tamping or blows by tamping rod to thebase plate. The deformation shows the characteristics of the concrete with respect totendency for segregation. The apparatus for conducting the slump test essentially consist of a metallicmould in the form of frustum of a cone having the internal dimension as under. Bottom diameter : 20 cm Top diameter : 10 cm Height : 30 cTrue slump In this case mix subsides uniformly and cohesively. This type is obtained forrich mixtures which have proportion of fine aggregates.Shear slump In this half of the cone shear of along on inclined plane. This is so for leanermixtures such as 1:6 or 1:8 and where slump requirement is higher. The slump ismeasured from level of the cone to center of sheared plane.
Collapse slump In this type of slump the concrete just collapse and spread over a large area.This occurs in very wet mixes.Lamination of slump test The slump test has no relation to the useful internal work. For very low degreeworkability the mix gives zero slumps and the text is in effective. It is also ineffective forlow mixes. For low workability concrete compaction factor test is useful.Compaction factor test The compaction factor test was developed by the road research laboratoryUK; the test was works on the principle of determining the degreeof the compaction achieved by standard amount of work done by following the concreteto fall through a standard height. The degree of compaction is measured by density ratiothat i.e. radio of actual density achieved in test to density of some concrete fullycompacted. The compaction factor test apparatus consist of to hopper vessels providedwith hinged doors at bottom. A cylindrical vessel is placed below the hopper. In anexperimental procedure the concrete after mixing is placed in an upper hopper than itshinged bottom door is opened to allow the concrete to fall in to second hopper. Thesecond hopper is opened next and concrete falls in to the cylinder. Excess concrete incylinder is struck of and cylinder is then weighted. The cylinder is then emptied andrefilled in three layers of concrete. Each layer being compacted by giving 25 blows. Theexcess concrete is then struck of and cylinder is weighted again. The radio of uncompacted concrete and hand compacted concrete gives the compaction factor.Workability of different condition Workability is dependent on the proportions of the ingredient materials aswell as on their individual characteristics. The degree of workability required for properplacement and consolidation of concrete is governed by dimension and shape of thestructure and by spacing and size of reinforcement. Small complicated section withmuch reinforcement steel or either embedded parts require concrete of high.
Si.no. Type of construction Slump Max(cm) Min(cm)1 Reinforced foundation walls and footings 10.0 5.02 Unreinforced footings caissons & substructure 7.5 2.5 walls3 Reinforced slabs beams and columns 12.5 7.54 Building columns 12.5 5.05 Bridge decks 7.5 5.06 Pavements 5.0 2.57 Side walls drive ways & slabs on ground 10.0 5.08 Heavy mass construction 5.0 5.0 Table 4.3.1Significance of compressive strength Test to determine are undoubtedly the most common type made to evaluate the properties of hardened concrete. The reasons are mainly 1. The strength of concrete in compression has in most cases a direct influence on the load carrying capacity of both plain and reinforced concrete structure 2. Of all the properties of hardened concrete, those concerning strength can usually by determine early. 3. By means of correlation with other more complicated test, the result of the strength can be used as qualitative indication of other important properties of hardened concrete.Factor affecting compressive strength The factors affecting the compressive strength of the hardened concrete areas follows 1. The ratio of cement to mixing water 2. The ratio of cement to aggregate 3. Grading, surface structure, shape, strength and stiffness of aggregate particles 4. Degree of compaction 5. Maximum size of aggregate In the above factors it can be further inferred that water cement ratio primarilyaffect the strength directly, where as other factor indirectly affect the strength byaffecting the water cement ratio.
Strength of the concrete primarily depends upon on the strength of the cementpaste. The strength of the paste increases with cement content and decreases with aircontent. The relation between water cement ratio and strength of the concrete shown infig It can be seen from the graph that low water cement ratio could be used whenthe concrete is vibrated to achieve higher strength, where as comparatively higher watercement ratio is required when concrete is hand compacted or un compacted. INDIAN STANDARD SPECIFICATIONSCOMPRESSION TEST SPECIMENSMaking and curing of specimens IS : 516-1959 “Indian standard methods of tests for strength of concrete”specifies the procedure for making and curing compression test specimens of concreteof the quantities of materials making and curing of specimens and test conditions arepossible. The method is specially suitable mix proportions.Preparations of materials
All materials shall be brought to room temperature, preferably 27degree Celsius+3 degree Celsius before the tests. Samples of aggregate and cement, on arrival at the laboratory shall wethoroughly mixed dry either by hand or n a suitable mixture in such a manner as toensure the greatest possible blending and uniformity in the material care being taken toavoid the intrusion of foreign matter .Proportioning The proportion of the materials including water in concrete mixes used fordetermining the suitability of the material available shall be similar in all respects tothose to be employed in the work where the proportions of the ingredients of theconcrete as used on the site to be specified by volume. they shall be calculated from theproportions be weight used in the test specimens and the unit weights of the materials.Weighing The quantities of cement size of aggregates and water for each batch shall bedetermined by weight to an accuracy of 0.1% for the total weight of the batch.Mixing of concrete The concrete shall be mixed by hand, or preferably in laboratory batch mixer, insuch a manner as to avoid loss of water or other materials. Each batch of concrete shallbe such a size as to leave about 10% excess after molding the desired number of testspecimens.Workability Each batch of concrete shall be tested for workability, immediately after making,by one of the methods described in IS 1199-1950. Sufficient care to ensure that nowater or any other materials is lost. The concrete used for the workability tests may beremixed with the remainder of the batch before the test specimens.Compacting The test specimens SHALL be made as soon as possible after mixing , and insuch a way as to produce full compaction of the concrete with neither segregation norexcessive laitance. The concrete shall be filled into the mould in layers approximately 5cm deep. Each layer shall be compacted either by hand or by vibration. After the toplayer has been compacted the surface of the concrete shall be finished level with thetop of the mould, using a trowel, and covered with a glass of metal to preventevaporation.
Curing The test specimen shall be stored in a place away from vibration, in moist air or90% relative humidity and a at a temperature of 27+ or – ½ hours from the time ofaddition of water to try ingredients. After this period, the specimen shall be marked andremoved from the moulds and unless required for test within 24 hours, immediatelysubmerged in clean, fresh water of saturated lime. The solution in which the specimensare submerged in clean water.TESTING IS 516-1959-“methods of tests for strength of concrete” specifies the procedureas follows for determining compressive strength of concrete.ApparatusTesting machine The testing machine may be of any reliable type, of sufficient capacity for thetests and capable of applying the load at specified rate of 140kg/cm/min without shock.The permissible error shall be not greater than +or -2% of the maximum load.Age at test Tests shall be made at recognized ages of the test specimens, the most usualbeing 7, 14 and 28 days. Where it may be necessary in obtain the strengths, tests may be made at theages of 24 + or -1/2 hrs & 72 + or - 2 hrs. the ages shall be calculated from the theaddition of water to the dry ingredients.Number of specimens At least 3 specimens, preferably from different batches, shall be made for testingat each selected age.Procedure Specimens stored in water shall be tested immediately on removal from thewater and while they are still in wet conditions. Surface water and grit shall be wiped ofthe specimens and any projecting fins removed. Specimens when received dry shall bekept in water for 24 hours before they are taken for testing.
Placing the specimens in the testing machines The cube specimens shall be placed in the machine in such a manner that theloads shall be applied to the opposite sides of the cubes as cast, that is not top andbottom. The maximum load applied to specimens shall be recorded and the appearanceof the concrete and any features in type of failure shall be noted. MIX DESIGNScope of investigations This investigation consists of studies of slump variation, compaction factor variation and strength variations of concrete mixes with normal coarse aggregate concrete and recycles coarse aggregate concrete. For this investigation the following materials are used. 1. Cement (53grade) 2. Sand 3. Water 4. Coarse aggregate 5. Recycle coarse aggregate
To calculate the value of ingredients Size of cube = 15 cm Volume of cube = 15*15*15 = 3375 cc Density of concrete = 2400 kg/m Density = mass/volume Mass = 2400*3.375*10 =8.1 kgMixed proportionCement : sand : coarse aggregate = 1:11/2 :3Weight of cement required for one cube = 8.1/5.5 = 1.472 kgsWeight of sand require for one cube = (1.5/5.5)*8.1 = 2.209 kgsWeight of coarse aggregate for one cube = (3/5.5)*8.1 = 4.418 kgsHence for 9 cubesWeight of cement = 1.472*9 = 13.248 kgsWeight of sand = 2.209*9 = 19.881Weight of coarse aggregate = 4.418*9 = 39.672 kgsWater/cement ratio = 0.45Weight of water = 0.45*9 = 4.05 lts= 4050 cc.Steel fibers =0.3%, 0.4%, 0.5%
TEST PROCEDURESTest procedures for slump testApparatus Slump cone with measuring scale, tamping rod , concrete constituents.Procedure Mould are prepared with water cement ratio (by weight)0.5 for concrete of 1:11/:3 1. mix the dry constituents thoroughly to get a uniform colour and then add water , mix thoroughly. 2. Concrete is filled in the standard slump cone which consists of vessel which is frustum shaped . it is compacted with in 3 layers.after laying each layer it is compacted with 25 strokes using a tamping rod of 16 mm diameter 60 cm long whose striking end is bullet pointed. 3. Level the top surface of the mould with a trowel. 4. remove the top cone immediately raising it slowly and carefully in the vertical direction. 5. As soon as the concrete settlement comes to shop measure the vertical settlement of the body of concrete which is called as the slump of concrete.
Compaction factor testApparatus Compaction factor test, trowels, graduated cylinder of 100 ml capacity, balancedto weight up to 30 kg, tamping rod and iron buckets.Procedure 1. Keep the compaction factor apparatus on a level ground and Greece all inner surface of hopper and cylinder. 2. Fastened the hopper door. 3. Weight the empty cylinder accurately and note down the weight as w1 kg. 4. Fix the cylinder on the base with the fly net and bolt in such a way that the central point of happens and cylinder lie on one line. Cover the cylinder with a plate. 5. Mixes or to be prepared for water cement ratio 0.4 for each mix take 9 kg aggregate, 4.5 kg of sand 2.25 kg of cement the mix proceed is as follows. 6. Fill the freshly mixed concrete in upper hopper gently and carefully with hand scoop without compacting. 7. After two minutes release the trap doors to that the concrete may fall in to the lower hopper bringing the concrete in to standard compaction. 8. Immediately after the concrete as come to rest open the trap door of lower hopper and allow the concrete to fall in to the cylinder bringing the concrete in to standard compaction. 9. Remove the extra concrete above the top of the cylinder by a pair of trowels, one in each hand, with horizontally sliding from the opposite edges of the mould, inwards to the center with a sawing motion.
Compressive strength of concreteApparatus I.S. mou77lds tampering rod balance, constituents of concrete ,compressiontesting machine.Procedure 1. For preparing concrete of proportion 1:11/2:3 by weight by weight ,find the weight of the concrete and volume of test mould. Thus calculate the weight of each constituent required. 2. After knowing the weights of individual constituents, take constituents and m ix it with water to cement ratio 0.5. mix it through to have uniform colour . 3. Oil the inner surface of the moulds and fill it with concrete in three layers. Tamping each layer 25 times by tamping rod. 4. Level the top surface of the mould by using trowel 5. After 24 hrs the specimen removed from the mould and kept in water for curing. 6. The character compressive strength is noted after the testing of mould and under compressive strength is noted after the testing of mould under compressive testing machine after 7,14 & 28 days.
TEST RESULTSSLUMP CONE TESTshows the results for slump cone test. SPECIMEN SLUMP VALUE (CM)PCC 11.10.3% STEEL FIBERS 9.10.4% STEEL FIBERS 7.60.5% STEEL FIBERS 6.8Figure 8.1.1 shows the comparison between slump values of concrete with differentproportion of steel fibers
12 11.1 SLUMP (cm) 10 9.1 7.6 8 6.8 6 4 SLUMP VALUE 2 0 PCC (0 0.30% 0.40% 0.50% %) PERCENTAGE OF STEEL COMPACTION FACTOR TESTshows compaction factor test results for different proportion of steel fibers. SPECIMEN COMPACTION FACTOR (%)PCC 0.890.3% STEEL FIBERS 0.920.4% STEEL FIBERS 0.930.5% STEEL FIBERS 0.95shows the comparison between compaction factor for different proportions of steel fibers inconcrete.
RESULT RESULT • Thus optimum compressive strength is obtained when 0.3% of steel fiber is added to PCC. • Compressive strength is been hiked by more than 45% by introduction of 0.3% steel fiber. CONCLUSIONCONCLUSION • The experimental program conducted indicated that adding steel fiber with PCC is an effective measure to enhance the compressive strength. • Improves bonding strength between materials. • The experiment indicates with increase in steel fiber content workability decreases. However the problem can be overcome by adding admixtures like plasticizers.