Mix Design Procedure And Principles Engineering Essay

Mix instau proportionalityn Procedure And Principles Engineering Essay1. IntroductionIn the following coursework we are going to see look at the stairs that essential be taken into account for acting a cover mingle shape. When we talk close fuse design, we are going to deal with devil categories of property requirements integrity category specific for heady concrete (fresh properties of concrete) and another category specific for treated concrete (Neville 1995). The commence of this coursework is also to analyze the properties of the freshly formed concrete due to the design performed, and not of the harden concrete. As outlined in shoot the breeze 2, the two types of property categories are not independent from champion another, more likely they are directly linked, and failure in compliance with fresh properties leave behind lead to poor concrete quality in hardened state.Basic exclusivelyy, concrete mix design is performed by a careful selection of quantities f or concrete ingredients with the aim at producing cost effective concrete having a minimum set of properties such as workability, compressive strength and durability (Neville 1995).For the purpose of this coursework, we are going to design concretes which give contain mixes of tieric ingredients like so-so(predicate) Portland cement as a bonding temporal and, each speed of light% Gravel or 100% Recycled Aggregates, as a filler material. Also, we are going to design mixes by replacing a part of the Portland cement with cementitious materials such as silica Fume (10% SF) or Fly Ash (30% FA) and the reason of using these fine materials is that they depart limit the amount of energy consumed in the mixed bag process, which ordinary Portland cement is not capable of doing.Having 4 types of concrete mixes, we are going to deal with different properties amidst these mixes, each set of concrete properties being governed by the properties of the materials physical exertiond. For r epresentative, recycled pith presents an change magnitude in porosity compared with gravel, so it is no surprise that concretes with recycled aggregates all(a)ow demand more urine content than ordinary, natural aggregates. Eventually the workability testament be affected by the high uper water demand (Dhir et al. 1998). Also, as comparison betwixt the effects on concrete watch outd by SF or FA we must(prenominal) state that concretes with FA will experience a decrease in water demand, reduced bleeding and good cohesiveness, while concrete with SF will bring an extend in water measurement.Because they were 4 different types of mixes to be designed and auditioned in the lab, 4 groups, each designing their own mix, were created. Our group had the task of do the mix design for the 10% SF mix and this was done according to BS 1881 Part 125 1983 Testing concrete Methods for mixing and sampling fresh concrete in the laboratory.Silica fume has certain characteristics that make the handling, when we make the mixing of components, to be a difficult task. This is due to the small particle surface and high fineness of the silica fume, so slurry is going to be prepared, by combining silica fume with water, when performing the mixing and also we should make sure that the slurry will be amply dispersed into the mix. By having a high fineness, the SF particles will demand a large surface to be covered with water, bringing an increase in water demand as stated above.Mixes having silica fume as ingredient will give us high performance concretes., and the front of SF in the mix design process will not wholly affect the quantities of the mix proportions to be used as ingredients of concrete, but also will lead to an improvement in the fresh properties of the concrete like high cohesiveness, little to none bleeding, sui card for pumping (Neville et al. 1995).In the lab, subsequently we performed the mix, we made some essays in consecrate to bugger off quality retard over the product Slump Test, according to BS EN 12350-22000 Testing fresh concrete Part 2 Slump test, to determine the workability of the concrete and the Plastic Density Test, according to BS 12350-6, 2000 Testing concrete Method for determination of density of compacted fresh concrete, to determine the substantial charge card density of the concrete.2. Mix Design Procedure and worksheets.2.1. Procedure principles.It should be stated that this regularity is not an exact method of quantity assessment mainly, because of the disagreement of the parameters affecting the constituents of this procedure. Trial mixes are made with the purpose of guessing which combinations of ingredients will be fit for the desired concrete properties and we can modify these mixes to correspond to our requirements (Neville 1995).2.2. rendering for performing concrete mix design.Mix design follows several steps according to BRE Report 331, in which the flow chart of steps takes into considep roportionn all parameters of the mix constituents and also shows us how they are linked together. The results of the com pitchation are going to be written on a Concrete Mix Design Form.For performing this procedure a number of initial specifications must be given, specifications which includeCement type 52.5 NAggregate type Gravelupper limit aggregate size 20 mmFine aggregate grading 44%Aggregate relative densities 2600 kg/m310% Silica Fume0.45, 0.6 and 0.75 w/c, 180l/m water content, Slump of 30-60 mm (achieving S3 with SP)The stages which govern this procedure, as specified in BRE Report 331 areStage 1 water/cement ratioStage 2 water contentStage 3 cement contentStage 4 total aggregate contentStage 5 fine aggregate proportionStage 6 trial mixingHaving the 3 free-water cement ratios, the low and the maximum size of the aggregates given, we can skip the starting time stage and the amount of water needed can easily be dogged.As we can see, 3 mixes will be prepared for which we can determine the amount of bonding material needed if the quantity of water is known. In this total amount of bonding material, 10% is Silica Fume, while 90% is ordinary Portland cement.In stage 4 we shall determine the total quantity of aggregate present in the mix. Because we have the grading of the fine aggregate, we can determine the quantity of the coarse aggregates by subtracting from the total quantity of aggregate the fine aggregate quantity.From the total quantity of coarse aggregate we know that 1/3 is for 10 mm Gravel and 2/3 for 20 mm Gravel. After we have determined all the mix proportions, we have to make specimens from the resulted concrete mix, specimens which will be subjected to different tests and conditions in order to determine the suitability of hardened concrete. These concrete specimens result from trial mixes for which batch system of system of weightsss are computed for a batch size of 0.02 m3. wholeness aspect hasnt been discussed so far the use of admixtures in the concrete mix design. Admixtures are regarded as secondary ingredients of concrete, and not in the same class of importance like water or cement. thither are different types of admixtures, depending on their effect on concrete, and, also their use is regarded from an economical and an increase in concrete quality point of view. For the purpose of our assignment, the admixture type which we are going to use is Superplasticizer (Glenium 51) and the British standard that regulates and controls their use is BS 5075 Part 3 1985. Superplasticizers are water reducing admixtures, and their effect on concrete is related to an improvement in fresh properties, mainly an increase in workability.4. Batch quantities allowing for denseness.4.1. Porosity, submersion and their link.Porosity and absorption are aspects concerning the aggregates, so the following discussion will take into account the way in which the presence of pores will affect the concrete. There are 2 types of p ores internal and external pores, which vary in size- the external pores, can even be seen sometimes with the naked eye. Because of its viscosity, cement paste cannot fully cover the pores of the aggregates, but water is able to do that, which eventually will lead in an increase of water demand (Neville 1995).It might seem that because its only related to aggregate, porosity and absorption will not affect concrete, but lets not forget that the weight of aggregates represents approximately 75% of the weight of concrete. Also, by doing the mixing of concrete in the lab, the moisture content of the aggregates decreases, so an adjustment for absorption of aggregates must be done we fully dry the aggregates in an oven, afterwards which we put the aggregates in water, for 24 hours. An increase in weight occurs, meaning that all the pores are fully saturated (Neville 1995). The absorption is expressed as a ratio between the moisture content increase observed in the dried aggregates to the mass of the dried aggregates. The following absorption values for aggregates are used for our designed concretesGravel 5/20 1.0%Sand 0/5 0.5%RA 5/10 3%RA 10/20 4%4.2. Adjustments for absorption.The adjustments for absorption, determined in accordance with BS 812 Part 2, are performed on the aggregate types which are going to be used in the mixture. The aggregates which we are going to use for the 10% SF mix concrete are sand 0/5 and gravel 5/20. The method allows computing the surplus quantity of water required for absorption by the following codeMaterial batch weight (kg) x absorption value (%) = additional water requiredHaving found the additional water quantity, the adjustment for absorption of aggregates can be performed byAggregate batch weight (kg) absorbed water (kg) = adjusted aggregate batch weight5. Mixing procedure and tests carried out in Lab 1.5.1. Mixing procedure.Relevant Standards BS 1881 Part 125 1983 Testing concrete methods for mixing and sampling fresh conc rete in the laboratory.The mixing procedure is the combining of all concrete ingredients, with the purpose so that the aggregates surface is covered by cement paste, and it follows 2 steps a) Sample preparation b) mixing.At the previous topic, the adjustment of aggregates for absorption was explained. Its one of the requirements for the sample preparation step, and was the last one that needed to be carried out in the lead the proper mixing of all concrete ingredients can be performed. When discussing about sample preparation, we also must take into account that we should produce at least 10% more quantity of concrete than the required quantity for the tests that have to be doneFollows a series of tasks initially, the aggregates should be added in the following order coarse aggregate, fine aggregate, sand after which we mix for 30 seconds. 1/2 of the water quantity must be added next, mix for another minute, after which we thoroughly mix by hand. Water absorption by the aggregates takes place when we leave covered the mixer for 8 minutes. Silica fume is mixed with water for 1 minute before adding it to the mix, after which we add the cement and mix it for 1 minute. We clean the paddles we add the remaining water and superplasticizer and mix for other 4-5 minutes, after which we ensure homogeneity by mixing the sample by hand.5.2. Tests carried out in Lab 1.Before starting the discussion about what tests must be done, we should note that all these tests on fresh concrete should be carried out within 15 minutes of mixing. Two tests will be done reject test and plastic density. After the tests are carried out, we must put the used concrete in the mixer and mix for other 30 seconds.The Slump test has the aim of analysis of the workability of the fresh concrete, and it regulated by BS EN 12350-22000 Testing fresh concrete Part 2 correct test standard. When performing this test we must have some basic equipment a slump retinal cone with foot rests and a metal r od (16 mm diameter, 600 mm long). First, we must moisten the slump cone, after which we pour the concrete in the cone, while it is hold firmly into position. The pouring of the concrete must be done in 3 equal layers which are tamped 25 times with the steel road. The excess of concrete at the top and around the slump cone is removed, after which the cone is removed, inverted and placed next to the slumped concrete in order to enable us to measure the vertical distance from the top of the cone to the highest point of the slumped concrete.The deliberate vertical distance has to be reported for the nearest 5 mm, and shows us the nature of the slump that we deal with true, collapse and shear slump.Fig. 5.2 True, shear and collapse slump (Neville et al. 1987)If the shear or collapse of the sample concrete occurs, we must perform the slump test once again.Plastic Density is determined on a compacted concrete sample in the lab, and is regulated by BS 12350-6, 2000 Testing concrete Method for determination of density of compacted fresh concrete standard. When performing this test we must have some basic equipment 10 liter steel container (200 mm internal diameter, 320 mm internal height, and 4 mm wall thickness), vibrating table and 300 mm steel rule.The test is carried out as follows we measure the mass of the empty container after which we measure the mass of the container filled with 10 liter of water. The concrete is poured in the empty container, in six equal layers which will be compacted on the vibrating table and the excess concrete at the top will be removed. We record the mass of the container with the concrete in it we return the concrete to the mixer and clean the equipment.The computation can now be performed with the following formulaPlastic density, D = m / VWhere, m = mass of concrete in container(To the nearest 10 g)V = volume of container= mass of water in container (from calibration) /1000.During the mix design we have found a plastic density for each water-cement ratio. Having found that plastic density, the new lab computed plastic density must not differ by more than 20 kg/m then the demonstrable plastic density (mix design).7. Yield corrected mix proportions and differences between design/plastic and volumetric method.Because in the mix design we have taken into account only those parameters that have a major impact on concrete characteristics, and we disregarded those that have a minor role, some errors might occur during the mix design. Such errors might include faulty maneuvering of concrete ingredients, errors in performing the mixing procedure. These errors are visible when the total weight of the concrete ingredients is different than the lab computed wet concrete density (plastic density). Having computed in the lab the actual plastic density of the mix, we can make studys to the mix proportion weights so that some of the residual errors might be able to be corrected. One of the ways by which this can be done i s adjusting for yield. Yield is the ratio between the actual density and the total density, and the adjustment is performed by multiplying this ratio with the weight of each constituent, giving us corrected mix proportions.As an example we shall perform the correction of the mix proportions for the 0.45 w/c ratio mixDuring the mix design we have found that the wet density of concrete (plastic density) is 2380 kg/m3.Cement+10% SF 360+40 kg/mWater 180 kg/mSand 650 kg/m10mm Agg 385 kg/m20mm Agg 770 kg/mTOTAL engrossment 2385 kg/mACTUAL PLASTIC density 2410 kg/m (tested in labs)The correction is done with the following formulaCorrected = (Actual density/ Total Density) x each constituent = 2410/2385=1.0105Cement+10% SF (365+40) kg/mWater 180 kg/mSand 655 kg/m10mm Agg 390 kg/m20mm Agg 780 kg/mCORRECTED DENSITY 2410 kg/mAnother method by which we can adjust the mix proportions is the volumetric method. The main feature of this method is that, when performing the adjustment, we will take into consideration the particle density of each constituent taking part in the mix design. We shall also make an example for the volumetric method of correction of mix proportions.Cement 360 kg/m / 3150 kg/m = 0.114SF 40 kg/m / 2000 kg/m = 0.02Water 180 kg/m / 1000 kg/m = 0.18Sand 650 kg/m / 2600 kg/m = 0.2510mm Agg 385 kg/m / 2600 kg/m = 0.14820mm Agg 770 kg/m / 2600 kg/m = 0.296ACTUAL 1.008THEORETICAL 1.0000The correction formula Correction factor = (Theoretical/Actual) x each constituent = 0.992Cement 355 kg/m / 3150 kg/m = 0.1133SF 40 kg/m / 2000 kg/m = 0.020Water 180 kg/m / 1000 kg/m = 0.180Sand 645 kg/m / 2600 kg/m = 0.247410mm Agg 380 kg/m / 2600 kg/m = 0.146120mm Agg 765 kg/m / 2600 kg/m = 0.2932ACTUAL 1.0000THEORETICAL 1.0000The main difference between the two methods which we have shown is that the yield method requires computing the lab plastic density, and comparing it to the plastic density taken into account in the design grade of the mix, while for the volumetric me thod is not demand to make that extra effort in order to make the adjustment.As far as to which method is more appropriate to be used, from a first look at our example, we can consider that the volumetric method is more appropriate, at least from an economic point of view, because the adjustments made gave us smaller weights of materials than the adjustment for yield weights. But my opinion is that the plastic density method is much more appropriate to be used, because its more reliable, and you have a superior certainty about the elimination of the errors that appear in the mixing phase and also a better control of quality of the concrete.8. Comments on fresh properties.The discussion about the fresh properties of concrete might seem to be not as important as the hardened concrete properties from a structural point of view, but as we have previously noted, there is a direct link between the two types of properties for example the strength of hardened concrete is greatly improved w hen a sufficient compaction of the fresh concrete was established (Neville 1995).The objective of this discussion is to see the stop by which different concrete components affect the fresh properties of concrete, and we shall do this by comparing the mixes presenting silica fume, go away ash and recycled aggregate with the ordinary Portland cement mix (100% Gravel).The influence of aggregate type by comparing the fresh properties of the 100% Gravel mix and 100% RA mix. Due to the fact RA have a higher porosity, a larger amount of water is needed in the mix which will eventually affect the workability of the fresh concrete. Because we have considered an absorption value for RA which was too high (RA density was larger than 2400kg/m3), the RA mix presented collapse slump, thus poor workability, also a slight bleeding, and segregation of the concrete constituents is present, leading to a poor cohesiveness. In the 30% FA and 10% SF mixes we have used as aggregate, gravel, so the infl uence of aggregate type on fresh concrete is the same in all 3 mixes, the only differences occur from the influence of other parameters.The cement type that we have used was either ordinary Portland cement (CEM I 52.5 N) or composite Portland cement, by combining the Portland cement with a cementitious material like silica fume or fly ash. As we can see from the comparison of the composite Portland cement mixes with those having only Portland cement, the 30% FA mix presents no bleeding or segregation of materials, a good cohesiveness and finishability. Fly ash reduces the amount of water to be used in the mix, having a similar effect as a superplasticizer, so at larger water cement ratios we have collapsed slump, poor cohesiveness, and a slight bleeding and segregation is present but the compactibility and finishability is still good, making it suitable for pumping . That is not the case with silica fume. Silica fume increases the water demand, and customaryly the mixes with silica fume present good cohesiveness, no bleeding and segregation, true slump giving us a good workability. The usage of both silica fume and superplasticizers has a good effect on concrete.The amount of fine material is directly linked to the cost of both silica fume and fly ash. The cost of production is quite large, so the use of silica fume and fly ash is no longer a cheap, viable solution for Portland cement replacement. As far as their consequences on fresh properties, for the 100% Gravel mix, at lower water-cement ratios we deal with a stiff mix, having less finishability and compactibility than when the amount of Portland cement is decreased, while the cohesiveness, lack of bleeding and segregation is kept the same on all mixes. We could use higher amounts of SF and FA but after a certain amount they cease to have any effect on the fresh properties of concrete.The water-cement ratio is one of the main factors affecting the concrete fresh properties, simply because water and cemen t are two of the main constituents of concrete. In the 100% RA mix, because of the use of RA, it was necessary to have a higher amount of water than in the other 3 mixes, which in return gave us a poor cohesiveness, a foldable slump resulting in a poor workability. Also some segregation and bleeding was observed, which was not present in the other mixes. As a general rule, when the w/c ratio is decreased, the ratio between the other concrete constituents is kept constant, so the workability increases (Neville 1995).The SP amount required for workability. Superplasticizers greatly affect the slump of a mix. For the 100% Gravel mix we used approximately 0.12% amount of superplasticizers for all w/c ratios, which gave us a true slump. When we look at the 30% FA and 10% SF mix we can see that we have increased the amount to about 0.31% which gave us a collapse in slump when we used FA, so too much SP, and a true slump for SF, because SF works much better with SP compared to FA.9. Concl usionsThis coursework has to be looked at as being divided in two parts a part about the concrete mix design and establishing all the mix proportions of the concrete constituents and another part relating to the fresh properties of the resulted concrete. During this coursework we have successfully designed 4 types of concrete, and as a result the fresh properties of the 4 concretes were individually established and assessed. The mix of concrete ingredients, the determination of slump and the computation of plastic density were all done in the lab according to the relevant standard governing each task.The designed concrete types were 100% Gravel, 100% RA, 30% FA and 10% SF. By assessing the concrete fresh properties we have seen which mixes had problems and were not suitable for using on site, but excluding some problems found (a high amount of superplasticizer than the one needed in the 30% FA), in general the mixes presented good workability without segregation or bleeding, were su itable for pumping so they could be used on site, in veridical conditions.