Effect of Water to Cement Ratio on Concrete

Effect of urine system to Cement Ratio on underwriteInt magnetic poleuctionIn social organization projects, cover, along with steel, wood, sparkler, etc, is one of the most essential materials that argon call fored for a successful manufacture of a structure. It one of the most common materials on a construction site and accounts for billions of pounds everywhere across the world. Due to ever-increasing machinery and technological advancementums cover shag now be made of a fluxingture of compound materials, nevertheless the necessary components of cover are course or fine heap ups, Portland Cement and piddle. In the current times, cover structures are manufactured every day and to sustain a safe environment for people, so it is vital that that the structures that are built are sturdy, durable and do not cause any hazards to people. It is therefore a wide task for construction com goat godies to guarantee that the structures that are built are done so to meet any to ld the specific safety codes, British Standards or the Euro edict Standards. The properties of concrete are very vital as they provide the necessary stability that structures are dependent on to maintain their sturdiness. As a take it is essential to research and be aware of the distinctive components of concrete and its properties, and how in this experiment these might affect the way that concrete performs when changing some variables.(Richardson, 2002).The workability of a concrete mix gives a measure of the ease with which fresh concrete seat be placed and compacted. The concrete should flow readily into the form and go around and cover the supporting, the mix should retain its congruity and the aggregates should not segregate.There are quadruple figures that can affect the workability areConsistency The degree of consistency is depended on the nature of works and type of densification.Water/cement Ratio or Water Control of a concrete Water/cement symmetry is the proport ion of pissing in a mix to the weight of cement. The quality of water that required for a mix is depended on the mix proportions, types and grading of aggregate.scoring of Aggregate The smooth and rounded aggregate exit produce a more workable concrete than the sharp angular aggregate.Cement Content The great workability can be reigned with the higher cement meat.AimsThe aim of this experiment was to establish the effectuates of water to cement proportionality on thefresh properties of concrete (workability), and its effect on the hard-bitten propertiesof concrete ( force out). Furthermore to increase the understanding in making a concrete mixture and working out the water sum that needs to be added to the mixtures. And last to expand on the understanding of the importance of fresh and hard properties of concrete.ObjectivesThe objectives of the experiment were to make three concrete mixtures by fixture their water/cement dimensions (0.47, 0.55 0.65) and to find out the w ater kernel to use for the three mixtures. To do a variety of runnings such as the slump test, compacting reckon test on fresh concrete and to carry out compressive and flexural strength tests of hardened concrete. Then 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 confused together to produce a thick agoe, to which then careful out aggregates are added to. The aggregates that are added are mainly composed of general materials such as sand, gravel and scummy rocks, however due to the latest advanced technology it has been known that another(prenominal) materials such as car tyres and crushed glass to be also used as aggregates. The cement is produced by blending limestone and clay, and burning it in a rotary kiln, this government issues in the formation of a clinker, to which gypsum is added. The mix is then ground down to fine powder cement, in which the most common is called Portland Cement. The cement/water slurry solidifies through a chemical reply called hydration, the reaction produces immense heat so fresh concrete must by no means be plentyled with unprotected bare hands. During the winter season, temperatures contrive below 2C, so the chemical hydration reaction may be very slow down as heat is needed as a particle accelerator to speed up the collision of the particles. Therefore concrete pours during these seasons are not sui control panel as the concrete result not set. Initially this reaction is slow to start with, so this allows for the concrete to be transported and poured before it is hardened, and the theory states that complete 100% hydration takes place after 28 days.Properties of Concrete There are four key properties that are desired in fresh concrete i.e.good workability, compactability, mobility and stability . The most desired properties forhardened concrete are strength and durability. The concrete should open compressive strength(resist squeezing), tensile strength (resist stretching) and flexural strength (resist hunkering).All these strengths are highly dependent on the water/cement ratio and aggregate used in themixture, the degree of compaction and the age of the concrete. Curing 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 also be writtenas 30 MPa which is adequate for use in beams, however this is solitary(prenominal) an estimation as thereare other factors (mentioned above) that affect concrete strength. In this experiment the slumptest and the compacting factor test were used to assess the workability and uniformity ofconcrete. The deflection/ flexural strength test was c arried out to evaluate the strength of theconcrete beam (mini beam sample) and find the disappointment load of the mini beam (100mm by100mm by 500mm). The compressive strength was carried out to determine the maximum misfortune load of the mental block samples (150mm by 150mm) and the cylinder samples (150mm by300mm) (Barnes 1992).MATERIALS AND EQUIPMENTCasting EquipmentConcrete sociableBucket (average size)Measuring CylinderShovelWheel BoroughScale rule 2 Shows Compaction element Apparatus. (used to determine workability of concretemixture)Figure 3 Slump Test ApparatusB.S. Slump strobile (300mm high, tapering from a 100mm diameter crystalise to a 200mmdiameter bottom)Slump rod (or steel tamping rod) (16 mm diameter, 600mm long, with rounded ends)Flat metal base plate (600 sq mm)(K0837225)Page 59. metal Rule (300mm long)10. Metal Scoop11. Levelling Trowel12. Waste rag13. Vibrating Table14. Moulds6 no. Cube Moulds (150mm by 150mm)3 no. Cylinder Moulds (150mm by 300mm)3 no. Mini beam Moulds (100mm by 100mm by 500mm)15. MaterialsCourse 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. so no considerable effect on water-cemet ratio.Striking Equipment1. Pressure pipe (for striking cubes and cylinders)2. Brushes (Soft and Hard metal brushes)3. Oil, oil brush and rugs (for cleaning moulds before storing)4. wax 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. excursion test machinery (Picture shown in figure3. Load reader/display4. Concrete samples5. Digital Camera*Personal Protective Clothing was worn on all days of the experiment (Safety boots andCoats, individuals handling concrete wore protective gloves).METHODOLOGYConcrete Producti on1. Aggregates were readily weighed and placed into buckets. Quantities (constants) used inall Concrete salmagundies are shown belowMaterial Quantitative Weight (Kg)Cement (CEM1) 6.50Fine Aggregate (Sand) 16.55Natural Course Aggregate (Stones) 26.002. The amount of water required was determined by using the formulae shown below.Water content = (water/cement ratio) x cement weight.3. Water was measured into a bucket using measuring cylinders.4. The water/cement ratio was set as the variable between 3 Concrete Mixes (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 Mixes 1, 2 3Concrete Mix 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 mixed for 30seconds.7. Half the water required for the mix was added to the mixture and the table of content werefurther mixed for 1 minute.8. The confine were covered and left for 8 minutes, to allow aggregates to absorb water,(because aggregates are porous therefore they should soak in water into voids to get a goodmix and bonding 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 into the mixer and thecontents were remixed for 30 seconds.FRESH CONCRETE TESTSCompacting Factor Test1. Trap doors of all hoppers were shut prior to beginning the test.2. Sample of freshly mixed concrete was scooped from the mixer into the upper hopper, theconcrete sample was change up to the brim of the upper hopper.3. The trap-door of upper hopper was opened, to enable concrete to fall into the lowerhopper.4. After 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 take of the cylinder was then cut off 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 concrete wasfilled to the brim of the cylinder.8. The now fully 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) Partially 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 cone was dampened to prevent concrete gummy 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 two sides of the mould.The mould was filled in 3 equal depth 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 motion of the rod overtop of the mold the concrete was levelled thus removing the excess concrete.The spillage was carefully removed from the sides of the mould and the base plateThe mould/cone was carefully and s lowly upraised 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) between 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, sheared slump and a true slump.The first two slump types indicate bad workability and a true slump indicates goodworkability.Concrete publicise 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 voids 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 hoursAfter which concrete was laid low(p) and placed in the curing room over 14 days.HARDENED CONCRETE TESTSConcrete Sample TestingCompressive Strength Tests were ca rried out on cube and cylinder samples.Flexural Strength Tests were carried out in the mini beams.The machines where loaded with concrete sample and load applied was set to zerobefore running the test. rump and top plates (spacers) were used to determine to provide platforms for theconcrete specimens and to also help provide even distri hardlyion of load.The load was applied by the machine work on maximum failure load was mastered.This reading was taken and the machine cleaned off concrete debris before running testsfor other samples.*Note the loading pace Rates varied for different sample cultivate as shown belowCylinders loading measure Rate was set 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 pass through when the trapdoor of the upper hopper was opened. The concrete mix wa s helped through the trap door tothe lower hopper by pushing it with a metal rod through the first trap door. The same(p) 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 due to low watercontent.Mix 2Observations The concrete mix was passed through the hopers with better ease than mix 1,however only of the contents went through, the rest was forced through some(prenominal) trap doorswith a metal rod. Therefore the flow ability and workability properties of this mix were bad,but better than mix1, owing it to the increased water content in mix 2.Mix 3Observations The obtained concrete mix was a wet mix (a bit in like manner wet) with what wouldappear to be good flowability properties as all contents went through the hopers and trapdoors with one sweep and much ease. Therefore the flowability and workability propertieswere the beat out observed for all 3 mixes, but too 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 jump out 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 too 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*Appar ent 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 varying 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 being loaded into the compressing machine and on the right,the classical cube hour glass failure mode on one of the cube specimen.Figure 9 Shows the cylinder specimen being loaded into the compressing machine and on theright, the failure mode on 3 of the cylinder specimens.Figure 10 Shows a mini beam failing 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 stres s. Hence 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 height diameter ratio. This is to just show that test conditions can also affect thedetermination of concrete strength. In BS 1881 Part 116 specifies that 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 usually applied to the cylinder strength to obtain anequivalent cube strength, it takes into account the specimen height /diameter ratio (i.e.30 0mm/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 Rates 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 results in bleeding of concretethus a weakened structure with pours in them. Again the normal distribution tailor can meexpected with extremes.DISCUSSIONOne type of test is not enough to indicate the workability of the concrete as a whole. Use of conglomerate tests pay back out various properties that determine workability, for example, thecompacting factor can indicate how workable in the concrete will be in terms of how slowcan 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 pumped 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 best indicates how workable theconcrete is in terms of its cohesive nature and segregation of its aggregates. It is valuable tocarry more than one of these tests to indicate various workability factors. These tests can alsobe carried 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 admixt ures may be added prior to transporting concrete to site,hence saving 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 befuddle same compacting factor but may not forever 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. Increasing the water cement ratio increased the compacting factortherefore the workability of the concrete. All these tests have limi ts, for example placingmore water would have resulted in decreasing compactability factor as increasing the watercontent will result in let down 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. evidenceIn 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 adequate 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 Why 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. Also this helps preventthe need to run into 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 andconsequently the energy and money that will be required when casting concrete on site.On the other hand hardened concrete properties are important in determini ng 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 bumpy 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 development and caution of a good qualitystructures and ensuring long life span. Whilst providing adequate safety to the habitats 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 reinforce 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 corrosion, due to air reacting with steel and prevent rust formation due to water.Corrosion and rust results in weakened concrete structure as may result in loss ofresilience to tensi le forces. So the concrete cove4r provides protection 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 bend and alter on site as well as provide ease of manual handling for steel fixers.