Effect of Water to Cement Ratio on Concrete

Effect of pissing system to cementum Ratio on cover portalIn construction projects, c in whole over, along with vane, wood, glass, etc, is peerless of the close to essential materials that ar needed for a successful manufacture of a complex body part. It one of the most common materials on a construction site and depicts for billions of pounds everywhere across the world. Due to ever-increasing machinery and tech nary(prenominal)ogical advancementums cover squeeze bulge break through now be relieve oneself of a jumbleture of compound materials, nevertheless the necessary components of cover argon course or fine aggregates, Portland Cement and irrigate. In the current times, cover structures argon manufactured every day and to sustain a safety device environment for people, so it is vital that that the structures that argon built are sturdy, indestructible and do not cause any hazards to people. It is because a considerable task for construction companies to guarantee that the structures that are built are through so to meet all the specific safety codes, British Standards or the Euro Code Standards. The properties of cover are very vital as they domiciliate the necessary stability that structures are dependent on to maintain their sturdiness. As a impart it is essential to research and be aware of the distinctive components of cover and its properties, and how in this try these might need the expression that cover performs when changing some variables.(Richardson, 2002).The workability of a cover swagger gives a greenback of the ease with which juvenile cover freighter be placed and compacted. The concrete should flow readily into the form and go close to and cover the reinforcement, the mix should retain its consistency and the aggregates should not segregate. on that point are four meanss that derriere affect the workability areConsistency The degree of consistency is depended on the character of works and type of crushed leather. pee/cement Ratio or body of weewee Control of a concrete Water/cement proportion is the proportionality of pissing in a mix to the tip of cement. The quality of irrigate that call for for a mix is depended on the mix proportions, types and grading of aggregate. range of hoard up The smooth and rounded aggregate will produce a more workable concrete than the sharp angular aggregate.Cement meaninged The greater workability can be obtained with the higher cement gist.AimsThe aim of this expe run alongent was to establish the topics of piddle to cement ratio on thefresh properties of concrete (workability), and its effect on the hardened propertiesof concrete ( military group). Furthermore to affix the understanding in making a concrete mixture and working(a) out the water content that needs to be added to the mixtures. And last to fatten on the understanding of the importance of fresh and hard properties of concrete.ObjectivesThe objectives of the e xperiment were to make three concrete mixtures by fastening their water/cement ratios (0.47, 0.55 0.65) and to honour out the water content to use for the three mixtures. To do a variety of studys such as the slump try out, compacting portion test on fresh concrete and to carry out compressive and flexural specialty tests of hardened concrete. hence finally to discuss how features such as variation in the water/cement ratio affects the workabilityand strength of concrete.TheoryConcrete Production, concrete is a mixture that is made up of three components, cement, water and aggregate. The water and cement are assorted to makeher to produce a thick paste, to which agreely mea receivedd out aggregates are added to. The aggregates that are added are mainly undisturbed of usual materials such as sand, gravel and crushed rocks, however receivable to the latest advanced technology it has been known that early(a) materials such as car tyres and crushed glass to be besides apply as aggregates. The cement is produced by blending limestone and clay, and burning it in a round kiln, this conclusions in the formation of a clinker, to which gypsum is added. The mix is past ground cut down to fine powder cement, in which the most common is called Portland Cement. The cement/water slurry solidifies through a chemical reaction called hydration, the reaction produces immense instigate so fresh concrete must by no center be handled with unprotected bare hands. During the winter season, temperatures drop beneath 2C, so the chemical hydration reaction whitethorn be very slack up as heat is needed as a catalyst to despatch up the collision of the particles. and then concrete pours during these seasons are not fitted as the concrete will not puke. Initially this reaction is retard to start with, so this allows for the concrete to be transported and poured earlier it is hardened, and the theory states that do 100% hydration takes place after(prenomin al) 28 old age.Properties of Concrete There are four key properties that are desired in fresh concrete i.e. uncorrupted workability, compactability, mobility and stability. The most desired properties forhardened concrete are strength and durability. The concrete should swallow compressive strength(resist squeezing), ductile strength (resist stretching) and flexural strength (resist distorting). on the consentient these strengths are highly dependent on the water/cement ratio and aggregate utilise in themixture, the degree of compaction and the age of the concrete. solidification concrete under waterover time allows hydration to continue hence giving it strength.The concrete used in this experiment was a C30 concrete grade and according to B.S. 5328the compressive strength for this grade at 28 days is 30.0 N/ sq mm which can besides be writtenas 30 MPa which is capable for use in beams, however this is simply an musical theme as thereare some other figures (mentioned i n a higher place) that affect concrete strength. In this experiment the slumptest and the compacting gene test were used to respect the workability and uniformity ofconcrete. The deflection/ flexural strength test was carried out to evaluate the strength of theconcrete beam ( miniskirt beam sample) and find the unsuccessful person load of the mini beam (100mm by100mm by 500mm). The compressive strength was carried out to agree the maximalfailure load of the pulley samples (150mm by 150mm) and the cylinder samples (150mm by300mm) (Barnes 1992).MATERIALS AND EQUIPMENT precondition EquipmentConcrete socialBucket (average size)Measuring CylinderShovel steering wheel BoroughScale persona 2 Shows Compaction Factor Apparatus. (used to determine workability of concretemixture)Figure 3 worsen Test ApparatusB.S. Slump conoid (300mm high, tapering from a 100mm diameter top to a 200mmdiameter bottom)Slump rod (or steel tamping rod) (16 mm diameter, 600mm long, with rounded ends)Flat alloy free-base plate (600 sq mm)(K0837225)Page 59. Metal Rule (300mm long)10. Metal sac11. Levelling Trowel12. Waste rag13. Vibrating Table14. Moulds6 no. stoppage Moulds (150mm by 150mm)3 no. Cylinder Moulds (150mm by 300mm)3 no. Mini beam Moulds (100mm by 100mm by 500mm)15. Materials sort Aggregates (Stones)Fine Aggregates (Sand)CementWater (Tap)*Note Aggregate used was natural aggregate used was from London. Therefore no need fordetermining aggregate moisture content as aggregate is assumed to be laboratory dry toSSD. pastce no considerable effect on water-cemet ratio.Striking Equipment1. Pressure metro (for striking cubes and cylinders)2. Brushes (Soft and Hard metal brushes)3. Oil, oil brush and rugs (for cleaning upchucks before storing)4. Crayon (for labelling concrete samples)5. Curing roomTesting Equipment1. Compressive test machineryFigure 4 Shows the Compressive test machine used to apply loads on cubes and cylindersamples2. Deflection test machinery (Picture in tendn in figure3. Load endorser/display4. Concrete samples5. Digital Camera*Personal Protective tog was worn on all days of the experiment (Safety boots andCoats, individuals handling concrete wore protective gloves).METHODOLOGYConcrete Production1. Aggregates were readily weighed and placed into buckets. Quantities (constants) used inall Concrete flickes are shown belowMaterial numeric Weight (Kg)Cement (CEM1) 6.50Fine Aggregate (Sand) 16.55Natural Course Aggregate (Stones) 26.002. The amount of water craved was determined by victimization the formulae shown below.Water content = (water/cement ratio) x cement weight.3. Water was measured into a bucket apply measuring cylinders.4. The water/cement ratio was hardening as the variable amid 3 Concrete liquifyes (to determinethe effect of water/cement ratio on the strength and workability of the concrete). Watercontent quantities used are shown on table 1.Table 1 Water/Cement Ratio (variable) for Concrete rifflees 1, 2 3Concre te combine Water/Cement Ratio Water Content (litres)1 0.47 32 0.55 3.63 0.65 4.25*See Appendix 1 for Actual Calculations Carried Out.5. The concrete mixer paddles and pan were lightly dampened before aggregates wereplaced in the mixer.6. Course and fine aggregates were placed into the mixer and heterogeneous for 30seconds.7. Half the water required for the mix was added to the mixture and the content werefurther mixed for 1 minute.8. The confine were covered and left for 8 transactions, to allow aggregates to absorb water,(because aggregates are permeable therefore they should soak in water into voids to get a goodmix and stick with cementious (water/cement) paste).9. Cement was spread evenly over the aggregates and mixed for 1 minute.10. The remaining water was added and the contents were mixed for 2 minutes ensuringhomogeneity of the mix.11. Workability tests were then carried out, in the order shown below.*Note immediately after each test the used concrete was returned int o the mixer and thecontents were remixed for 30 seconds.FRESH CONCRETE rillSCompacting Factor Test1. Trap doors of all hoppers were shut down prior to beginning the test.2. Sample of freshly mixed concrete was scooped from the mixer into the pep pill hopper, theconcrete sample was change up to the brim of the upper berth hopper.3. The trap-door of upper hopper was opened, to alter concrete to fall into the dispirithopper.4. later all concrete had been collected onto lower hopper, the trap-door of the lower hopperwas then opened and the concrete allowed to fall into the cylinder.5. Excess concrete remaining above the top level of the cylinder was then cut collide with using aplane blade.6. The concrete collected in the cylinder was then weighed. (This weight is known as theweight of partially compacted concrete).7. The concrete filled cylinder was vibrated to obtain full compaction, and more concretewas added to the cylinder as required to ensure the vibrated/compacted concr ete wasfilled to the brim of the cylinder.8. The now to the full compacted concrete in the cylinder was weighed.9. The compacting factor was then obtained using the formulae shown below.Compacting factor = (Weight of partially compacted concrete)/(Weight of fullycompacted concrete)Figure 5 Shows steps followed during the compacting factor test.1) Compacting factor equipment.2) mappingially compacted weight is taken on a scale,3) The concrete is vibrated/compactedon a vibrating table and then the contents are toped up and vibrated to the rim container and thepartially compacted weight was taken.Slump TestConcrete was thoroughly mixed in the concrete mixer.The slump conoid was dampened to prevent concrete viscid to it.The slump cone/mould was placed on the centre of the metal plate and one individual wasasked to stand on the foot pieces on both sides of the mould.The mould was filled in 3 equal attainment layers and each layer was rod 25 times using thesteel slump rod (ensuring even spread of blows covering over the whole area).Concrete was heaped over the top of the cone and with a rolling doubt of the rod overtop of the mold the concrete was levelled thus removing the overabundance concrete.The spillage was carefully removed from the sides of the mould and the base plateThe mould/cone was carefully and slowly lifted vertically upwards.The slump cone was turned upside down and placed next to the molded concrete and therod was laid across the slump cone and the distance (slump) in the midst of the underside of therod and the highest point of the moulded concrete were read using a metal rule.There are different kinds of slump a collapsed slump, cut back slump and a true slump.The first two slump types manoeuvre bad workability and a true slump indicates goodworkability.Concrete re Casting CuringConcrete was scooped out of the mixer into oiled moulds on the vibrating table (ensuringeven spread).Concrete was vibrated throughout the pour to eliminate vo ids and to enable compactionof concrete by switching on the vibrating table.The vibrating motion also levelled the concrete.The concrete was left to set on the mould for 24 hours subsequently which concrete was struck and placed in the curing room over 14 days.HARDENED CONCRETE TESTSConcrete Sample TestingCompressive dominance Tests were carried out on cube and cylinder samples.Flexural Strength Tests were carried out in the mini beams.The machines where ladened with concrete sample and load applied was set to zerobefore running the test.Base and top plates (spacers) were used to determine to picture platforms for theconcrete specimens and to also help provide even dispersal of load.The load was applied by the machine till maximum failure load was reached.This reading was taken and the machine cleaned off concrete rubble before running testsfor other samples.*Note the consignment step range varied for different sample shape as shown belowCylinders loading measure Rate was s et at 5.30 KN/sCubes loading Pace Rate was set at 6.80 KN/sMini Beams loading Pace Rate was set at 0.200 KN/sRESULTS1. FRESH CONCRETE PROPERTIES TEST RESULTSCompacting Factor Test ResultsMix 1Observations The Concrete Mix appeared to be dry and did not scat through when the trapdoor of the upper hopper was opened. The concrete mix was helped through the trap door tothe lower hopper by pushing it with a metal rod through the first trap door. The like wasdone in order to get it through the second trap door into the container. This showed that itwas a bad mix with bad flowability, mobility and workability properties referable to low watercontent.Mix 2Observations The concrete mix was passed through the hopers with wagerer ease than mix 1,however only of the contents went through, the rest was forced through both trap doorswith a metal rod. Therefore the flow ability and workability properties of this mix were bad, precisely better than mix1, owing it to the increased water content in mix 2.Mix 3Observations The obtained concrete mix was a wet mix (a atomic number 42 in any case wet) with what wouldappear to be good flowability properties as all contents went through the hopers and trapdoors with one sweep and a good deal ease. Therefore the flowability and workability propertieswere the opera hat observed for all 3 mixes, but alike much water content is not good either.The compacting factor test was worked out for all the 3 Concrete Mixes and results areshown in table 2 below.*The calculations were carried out on Microsoft Excel using the formula shown below.Compacting factor = (Weight of partially compacted concrete)/(Weight of fullycompacted concrete)BS 1881 Part 103 states that concrete is deemed unsuitable if its compacting factor isbelow 0.70 or above 0.98. For normal concretes the compacting factor normally liesbetween 0.80 and 0.92 (Jackson Dhir 1996).Apparent workability shown below was determined by using Compacting factor table inThere was no slump asthe mix was as well drytherefore indicatingpoor mobility,flowability andworkabilityCollapsed slump wasobtained and the slumpexceeded the allowabletolerance stated in BS5328. The slump conewas 300mm high andthe concrete mixslumped by half thatvalue to 150mm. Thisindicates that the mixwas too wet and thisaffected its cohesiveproperties.Very high*Apparent workability shown above was determined by using Slump Results Table shownin Appendix 2 (Kew 2009).(K0837225) Page 12Mix 1 Dry Mix/ Zero Slump Mix 2 Wet mix /13mm True Slump Mix3 Mix too wet/ collapsed slumpFigure 7 Shows the Slump Results Obtained for concrete mixes with change watercement ratios. (Mix 1 w/c ratio 0.45, Mix 2 w/c ratio 0.55 and Mix 3 w/c ratio 0.65).2. HARDENEDED CONCRETE PROPERTIES TEST RESULTSFigure 8 Shows the cube specimen creation loaded into the compressing machine and on the right,the important cube hour glass failure mode on one of the cube specimen.Figure 9 Shows the cylinder specimen being loade d into the compressing machine and on theright, the failure mode on 3 of the cylinder specimens.Figure 10 Shows a mini beam impuissance when subjected to Flexural Loads. This is the classical failuremode of beams. The beam undergoes tensile and flexural strain resulting in bending and snapping ofthe beam. Concrete is generally brittle and this makes it weak in tension. and then the need forreinforcement of concrete, steel is good in tension so it lends that quality to concrete, resulting inbetter stronger structures.The results above are indicative of the effects of w/c ratio on the strength of concrete. At0.45 w/c ratio the strength was 630.4(Influence of test conditions. Table above show that specimen shape and size is alsoinfluential on the compressive strength. Therefore measured strength of concrete is alsoaffected by summit diameter ratio. This is to practiced show that test conditions can also affect thedetermination of concrete strength. In BS 1881 Part 116 specifies tha t 150mm cube test areonly used for quality control purposes. Whereas BS 1881 Part 120 indicates that cylindertest specimens are used to carry out compressive strength tests for in situ concrete andprecast members. A correction factories commonly applied to the cylinder strength to obtain anequivalent cube strength, it takes into account the specimen height /diameter ratio (i.e.300mm/150mm = 2.). This explains the high compressive strength results obtained incylinder specimens than in cube specimens despite the being made off the same batch ofconcrete. It should also be considered that the loading Pace grade for cubes (and cylinderswere varied.The trend obtained from the results shown above indicates that increasing w/c ratio increasesflexural strength. Af hydration strengthens the bonding between the cementious material andthe aggregates. However like all other factors, too much of anything is not good. If the mixhas excess water it will result in reduced flexural strength and re sults in bleeding of concretethus a weakened structure with pours in them. Again the normal statistical distribution curve can meexpected with extremes.DISCUSSIONOne type of test is not enough to indicate the workability of the concrete as a whole. work ofvarious tests bring out various properties that determine workability, for example, thecompacting factor can indicate how workable in the concrete will be in terms of how easilycan the concrete be vibrated and compacted. It is also a good indicator of the mobility andflowability of concrete. It Shows how easily the concrete can be pump from a concreteskip into shutters, how easily the concrete will pass through the skip trap door when oncasting real structure on site. On the other hand the slump trounce indicates how workable theconcrete is in terms of its cohesive nature and separationism of its aggregates. It is important tocarry more than one of these tests to indicate various workability factors. These tests can alsobe carri ed out at various stages between concrete production and casting. The commonconstruction site test (In situ test) is the slump test, it serves as the last point of quality checkprior to casting, and all other workability factors are normally carried out on the concreteproduction sites. For example, the compactability factor will be most useful on production asother mobility enhancing admixtures may be added prior to transporting concrete to site,hence parsimoniousness time, money and other complications that may arise from delaying siteprogrammes. From table 2 the results obtained from all mixes had compacting factorsbetween 0.70 and 0.98 hence indicating that all the tested concrete mixes would beacceptable under the BS 1881. This certainly does not mean that all mixes had goodworkability properties. Jackson Dhir (1996) state that some of the basic assumptions forthe test are not correct and should not be solely relied upon extensively as they can bemisleading. As concrete mixes can have same compacting factor but may not always requirethe same amount of work to reach full compaction as compaction cannot be justified in thetrue sense. From the results in table 2 it shows that changing the water/cement ratio affectedthe compacting factor. increase the water cement ratio increased the compacting factortherefore the workability of the concrete. All these tests have limits, for example placingmore water would have resulted in decreasing compactability factor as increasing the watercontent will result in lowered compacting factors. (Compacting liquid materials do not resultin changes between partially compacted weight and fully compacted weight, hence if moreexcess water is added the mix will have lower differences between partially compactedweight and fully compacted weight. Hence giving rise to normal distribution curves for thecompressive tests. This also applies to flexural strength and durability of the concrete.CONCLUSIONIn conclusion it is clear that too little w/c ratio reduces the strength of concrete just as well astoo much w/c ratio will result in porous concrete. Therefore fitted amounts need to beused to gain the best results. The best way of getting accurate assumptions on concrete is toconsider various factors. Increasing the water content ratio generally increases the strengthbut may also result in shrinkage of the concrete hence altering durability and permeabilityfactors.Q1 Report all the results fresh properties (slump value and the shape of the slump) andhardened properties (strength) of the concrete and comment on the results. See ResultsSection for Answers.Q2 wherefore the need to measure the fresh and hardened properties of the concrete?Fresh properties are only of much importance in the stages of the concrete mix. Thesehelp concrete producers spot problems early on the stage before structures are cast thuspotentially saving money, time and preventing unstable structures form being built byspotting and correcting problems with concrete at an early stage. in addition this helps preventthe need to strike down newly built structures due to instability of concrete mixes used.Fresh properties can help indicate how much work labours will have to do on site and then the energy and money that will be required when casting concrete on site.On the other hand hardened concrete properties are important in determining and the lifespan of the concrete in the form of s concrete structure. The hardened properties areimportant in observing and maintaining the strength of the structure and its durability.Other hardened factors are permeability and shrinkage of the concrete structures afterbeing built due to acid weathers and conditions. The latter factors are of muchimportance in structures like dams which require high water retaining properties.Therefore both properties help in the ontogeny and maintenance of a good qualitystructures and ensuring long life span. Whilst providing adequate safety to the hab itats ofthose structures.Q3 Concrete is usually tested at 28-Days for its compression strength. why at 28-Days?The specimens should be cured under water and for normal concrete they should havereached maximum strength at 28 Days. Concrete hardening process (Hydration) isthought to reach its final strength in 28 Days as the reaction slows to a halt and addingmore water or curing concrete past that stage will sure minute or no further significantchanges in concrete strength.Q4 As for built concrete beam, describe the need to place reinforced steel inconcrete beam, the purpose of cover/spacing, the diameter of the steel used and whyconcrete beams need to be reinforced?Concrete is good in compression meaning it has high resilience to compressive forces butis very weak in tension. As noted in the results the beams failed at much lower loads thanboth cubes and cylinders, although there are other factors that play a role here that is thegeneral observation. Hence concrete reinforcement is required, it has good tensileresilience and when concrete and steel are combined they result in components strong inboth tensile and compressive properties. The purpose of concrete cover is to protect steelfrom eating away, due to nimbus reacting with steel and prevent rusting formation due to water.Corrosion and rust results in weakened concrete structure as may result in loss ofresilience to tensile forces. So the concrete cove4r provides shelter and a neutralenvironment for steel. Concrete cover usually ranges around 500mm from the steel bars.Excess cover is not good as it makes the structure more susceptible to chipping and henceweakens the cover itself and increases chances of steel corrosion taking place. Thediameter of steel used can vary according to the purpose of the structure but overreinforcement can also bring about imbalances to the structural stability and may result ina weakened structure. The normal diameter used ranges between 10-30mm, this makes iteasier to b end and alter on site as well as provide ease of manual handling for steel fixers.