In the undermentioned coursework we are traveling to take expression at the stairss that must be taken into history for executing a concrete mix design. When we talk about mix design, we are traveling to cover with two classs of belongings demands: one class particular for fresh concrete ( fresh belongingss of concrete ) ; and another class particular for hard-boiled concrete ( Neville 1995 ) . The purpose of this coursework is besides to analyse the belongingss of the freshly formed concrete due to the design performed, and non of the hard-boiled concrete. As outlined in Lecture 2, the two types of belongings classs are non independent from one another, more likely they are straight linked, and failure in conformity with fresh belongingss will take to hapless concrete quality in hard-boiled province.
Basically, concrete mix design is performed by a careful choice of measures for concrete ingredients with the purpose at bring forthing cost effectual concrete holding a minimal set of belongingss such as: workability, compressive strength and lastingness ( Neville 1995 ) .
For the intent of this coursework, we are traveling to plan concretes which will incorporate mixes of authoritative ingredients like ordinary Portland cement as a adhering stuff and, either 100 % Gravel or 100 % Recycled Aggregates, as a filler stuff. Besides, we are traveling to plan mixes by replacing a portion of the Portland cement with cementitious stuffs such as Silica Fume ( 10 % SF ) or Fly Ash ( 30 % FA ) and the ground of utilizing these all right stuffs is that they will restrict the sum of energy consumed in the commixture procedure, which ordinary Portland cement is non capable of making.
Having 4 types of concrete mixes, we are traveling to cover with different belongingss between these mixes, each set of concrete belongingss being governed by the belongingss of the stuffs used. For illustration, recycled aggregative nowadayss an addition in porousness compared with crushed rock, so it is no surprise that concretes with recycled sums will demand more H2O content than ordinary, natural sums. Finally the workability will be affected by the higher H2O demand ( Dhir et al. 1998 ) . Besides, as comparing between the effects on concrete determined by SF or FA we must province that concretes with FA will see a lessening in H2O demand, reduced hemorrhage and good coherence, while concrete with SF will convey an addition in H2O measure.
Because they were 4 different types of mixes to be designed and tested in the lab, 4 groups, each planing their ain mix, were created. Our group had the undertaking of executing the mix design for the 10 % SF mix and this was done harmonizing to BS 1881: Part 125: 1983 Testing concrete – Methods for blending and trying fresh concrete in the research lab.
Silica smoke has certain features that make the handling, when we make the commixture of constituents, to be a hard undertaking. This is due to the little atom size and high choiceness of the silicon oxide smoke, so slurry is traveling to be prepared, by uniting silica smoke with H2O, when executing the commixture and besides we should do certain that the slurry will be to the full dispersed into the mix. By holding a high choiceness, the SF atoms will demand a big surface to be covered with H2O, conveying an addition in H2O demand as stated above.
Mixs holding silica smoke as ingredient will give us high public presentation concretes. , and the presence of SF in the mix design procedure will non merely impact the measures of the mix proportions to be used as ingredients of concrete, but besides will take to an betterment in the fresh belongingss of the concrete like: high coherence, small to none hemorrhage, suited for pumping ( Neville et al. 1995 ) .
In the lab, after we performed the mix, we made some trials in order to hold quality control over the merchandise: Slump Test, harmonizing to BS EN 12350-2:2000 Testing fresh concrete – Part 2: Slump trial, to find the workability of the concrete and the Plastic Density Test, harmonizing to BS 12350-6, 2000 Testing concrete – Method for finding of denseness of compacted fresh concrete, to find the existent plastic denseness of the concrete.
2. Mix Design Procedure and worksheets.
2.1. Procedure rules.
It should be stated that this method is non an exact method of measure appraisal chiefly, because of the variableness of the parametric quantities impacting the components of this process. Trial mixes are made with the intent of thinking which combinations of ingredients will be suited for the coveted concrete belongingss and we can modify these mixes to match to our demands ( Neville 1995 ) .
2.2. Description for executing concrete mix design.
Mix design follows several stairss harmonizing to BRE Report 331, in which the flow chart of stairss takes into consideration all parametric quantities of the mix components and besides shows us how they are linked together. The consequences of the calculation are traveling to be written on a Concrete Mix Design Form.
For executing this process a figure of initial specifications must be given, specifications which include:
Cement type – 52.5 N ;
Aggregate type – Gravel ;
Maximal sum size – 20 millimeter ;
All right sum rating – 44 % ;
Aggregate comparative densenesss – 2600 kg/m3 ;
10 % Silica Fume
0.45, 0.6 and 0.75 w/c, 180l/m? H2O content, Slump of 30-60 millimeter ( accomplishing S3 with SP )
The phases which govern this process, as specified in BRE Report 331 are:
Phase 1 water/cement ratio
Phase 2 H2O content
Phase 3 cement content
Phase 4 entire sum content
Phase 5 all right sum proportion
Phase 6 test commixture
Having the 3 free-water – cement ratios, the slack and the maximal size of the sums given, we can jump the first phase and the sum of H2O needed can easy be determined.
As we can see, 3 mixes will be prepared for which we can find the sum of adhering stuff needed if the measure of H2O is known. In this entire sum of adhering stuff, 10 % is Silica Fume, while 90 % is ordinary Portland cement.
In phase 4 we shall find the entire measure of aggregative nowadays in the mix. Because we have the scaling of the all right sum, we can find the measure of the coarse sums by deducting from the entire measure of sum the all right sum measure.
From the entire measure of harsh sum we know that 1/3 is for 10 millimeters Gravel and 2/3 for 20 millimeters Gravel. After we have determined all the mix proportions, we have to do specimens from the resulted concrete mix, specimens which will be subjected to different trials and conditions in order to find the suitableness of hard-boiled concrete. These concrete specimens result from test mixes for which batch weights are computed for a batch size of 0.02 M3.
One facet has n’t been discussed so far: the usage of alloies in the concrete mix design. Admixtures are regarded as secondary ingredients of concrete, and non in the same category of importance like H2O or cement. There are different types of alloies, depending on their consequence on concrete, and, besides their usage is regarded from an economical and an addition in concrete quality point of position. For the intent of our assignment, the alloy type which we are traveling to utilize is Superplasticizer ( Glenium 51 ) and the British criterion that regulates and controls their usage is BS 5075: Part 3: 1985. Superplasticizers are H2O cut downing alloies, and their consequence on concrete is related to an betterment in fresh belongingss, chiefly an addition in workability.
4. Batch measures leting for soaking up.
4.1. Porosity, Absorption and their nexus.
Porosity and soaking up are facets refering the sums, so the undermentioned treatment will take into history the manner in which the presence of pores will impact the concrete. There are 2 types of pores: internal and external pores, which vary in size- the external pores, can even be seen sometimes with the bare oculus. Because of its viscousness, cement paste can non to the full cover the pores of the sums, but H2O is able to make that, which finally will take in an addition of H2O demand ( Neville 1995 ) .
It might look that because it ‘s merely related to aggregate, porousness and soaking up will non impact concrete, but allow ‘s non bury that the weight of sums represents about 75 % of the weight of concrete. Besides, by making the commixture of concrete in the lab, the wet content of the sums lessenings, so an accommodation for soaking up of sums must be done: we to the full dry the sums in an oven, after which we put the sums in H2O, for 24 hours. An addition in weight occurs, intending that all the pores are to the full saturated ( Neville 1995 ) . The soaking up is expressed as a ratio between the wet content addition observed in the dried sums to the mass of the dried sums. The undermentioned soaking up values for sums are used for our designed concretes:
Gravel 5/20 1.0 %
Sand 0/5 0.5 %
RA 5/10 3 %
RA 10/20 4 %
4.2. Adjustments for soaking up.
The accommodations for soaking up, determined in conformity with BS 812: Part 2, are performed on the sum types which are traveling to be used in the mixture. The sums which we are traveling to utilize for the 10 % SF mix concrete are: sand 0/5 and gravel 5/20. The method allows calculating the extra measure of H2O required for soaking up by the undermentioned expression:
Material batch weight ( kilogram ) x soaking up value ( % ) = extra H2O required
Having found the extra H2O measure, the accommodation for soaking up of sums can be performed by:
Aggregate batch weight ( kilogram ) – captive H2O ( kilogram ) = adjusted aggregative batch weight
5. Blending process and trials carried out in Lab 1.
5.1. Blending process.
Relevant Standards: BS 1881: Part 125: 1983 Testing concrete – methods for blending and trying fresh concrete in the research lab.
The commixture process is the combine of all concrete ingredients, with the intent so that the sums surface is covered by cement paste, and it follows 2 stairss: a ) Sample readying ; B ) commixture.
At the old subject, the accommodation of sums for soaking up was explained. It ‘s one of the demands for the sample readying measure, and was the last 1 that needed to be carried out before the proper commixture of all concrete ingredients can be performed. When discoursing approximately sample readying, we besides must take into history that we should bring forth at least 10 % more measure of concrete than the needed measure for the trials that have to be done ;
Follows a series of undertakings: ab initio, the sums should be added in the undermentioned order: coarse sum, all right sum, sand after which we mix for 30 seconds. 1/2 of the H2O measure must be added following, mix for another minute, after which we thoroughly mix by manus. Water soaking up by the sums takes topographic point when we leave covered the sociable for 8 proceedingss. Silica smoke is assorted with H2O for 1 minute before adding it to the mix, after which we add the cement and blend it for 1 minute. We clean the paddles ; we add the staying H2O and superplasticizer and mix for other 4-5 proceedingss, after which we guarantee homogeneousness by blending the sample by manus.
5.2. Trials carried out in Lab 1.
Before get downing the treatment about what trials must be done, we should observe that all these trials on fresh concrete should be carried out within 15 proceedingss of blending. Two trials will be done: slack trial and plastic denseness. After the trials are carried out, we must set the used concrete in the sociable and mix for other 30 seconds.
The Slump trial has the purpose of analysis of the workability of the fresh concrete, and it regulated by BS EN 12350-2:2000 Testing fresh concrete – Part 2: slack trial criterion. When executing this trial we must hold some basic equipment: a slack cone with pes remainders and a metal rod ( 16 millimeter diameter, 600 millimeter long ) . First, we must wash the slack cone, after which we pour the concrete in the cone, while it is hold steadfastly into place. The pouring of the concrete must be done in 3 equal beds which are tamped 25 times with the steel route. The surplus of concrete at the top and around the slack cone is removed, after which the cone is removed, inverted and placed following to the slumped concrete in order to enable us to mensurate the perpendicular distance from the top of the cone to the highest point of the slumped concrete.
The mensural perpendicular distance has to be reported for the nearest 5 millimeter, and shows us the nature of the slack that we deal with: true, prostration and shear slack.
Fig. 5.2: True, shear and collapse slack ( Neville et al. 1987 )
If the shear or prostration of the sample concrete occurs, we must execute the slack trial one time once more.
Plastic Density is determined on a compacted concrete sample in the lab, and is regulated by BS 12350-6, 2000 Testing concrete – Method for finding of denseness of compacted fresh concrete criterion. When executing this trial we must hold some basic equipment: 10 litre steel container ( 200 millimeter internal diameter, 320 millimeter internal tallness, and 4 millimeter wall thickness ) , vibrating tabular array and 300 millimeter steel regulation.
The trial 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 litre of H2O. The concrete is poured in the empty container, in six equal beds which will be compacted on the vibrating tabular array and the extra 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 sociable and clean the equipment.
The calculation can now be performed with the undermentioned expression:
Plastic denseness, D = m / V
Where, m = mass of concrete in container
( To the nearest 10 g )
V = volume of container
= mass of H2O in container ( from standardization ) /1000.
During the mix design we have found a fictile denseness for each water-cement ratio. Having found that fictile denseness, the new lab computed fictile denseness must non differ by more than ±20 kg/m? so the existent plastic denseness ( mix design ) .
7. Output: corrected mix proportions and differences between design/plastic and volumetric method.
Because in the mix design we have taken into history merely those parametric quantities that have a major impact on concrete features, and we disregarded those that have a minor function, some mistakes might happen during the mix design. Such mistakes might include: defective maneuvering of concrete ingredients, mistakes in executing the commixture process. These mistakes are seeable when the entire weight of the concrete ingredients is different than the lab computed wet concrete denseness ( fictile denseness ) . Having computed in the lab the existent plastic denseness of the mix, we can do corrections to the mix proportion weights so that some of the residuary mistakes might be able to be corrected. One of the ways by which this can be done is seting for output. Output is the ratio between the existent denseness and the entire denseness, and the accommodation is performed by multiplying this ratio with the weight of each component, giving us corrected mix proportions.
As an illustration we shall execute the rectification of the mix proportions for the 0.45 w/c ratio mix:
During the mix design we have found that the wet denseness of concrete ( fictile denseness ) is 2380 kg/m3.
Cement+10 % SF 360+40 kg/m?
Water 180 kg/m?
Sand 650 kg/m?
10mm Agg 385 kg/m?
20mm Agg 770 kg/m?
TOTAL DENSITY 2385 kg/m?
ACTUAL PLASTIC DENSITY 2410 kg/m? ( tested in labs )
The rectification is done with the undermentioned expression:
Corrected = ( Actual density/ Total Density ) x each component = 2410/2385=1.0105
Cement+10 % SF ( 365+40 ) kg/m?
Water 180 kg/m?
Sand 655 kg/m?
10mm Agg 390 kg/m?
20mm Agg 780 kg/m?
CORRECTED DENSITY 2410 kg/m?
Another method by which we can set the mix proportions is the volumetric method. The chief characteristic of this method is that, when executing the accommodation, we will take into consideration the atom denseness of each component taking portion in the mix design. We shall besides do an illustration for the volumetric method of rectification of mix proportions.
Cement 360 kg/m? / 3150 kg/m? = 0.114
SF 40 kg/m? / 2000 kg/m? = 0.02
Water 180 kg/m? / 1000 kg/m? = 0.18
Sand 650 kg/m? / 2600 kg/m? = 0.25
10mm Agg 385 kg/m? / 2600 kg/m? = 0.148
20mm Agg 770 kg/m? / 2600 kg/m? = 0.296
The rectification expression: Correction factor = ( Theoretical/Actual ) x each component = 0.992
Cement 355 kg/m? / 3150 kg/m? = 0.1133
SF 40 kg/m? / 2000 kg/m? = 0.020
Water 180 kg/m? / 1000 kg/m? = 0.180
Sand 645 kg/m? / 2600 kg/m? = 0.2474
10mm Agg 380 kg/m? / 2600 kg/m? = 0.1461
20mm Agg 765 kg/m? / 2600 kg/m? = 0.2932
The chief difference between the two methods which we have shown is that the output method requires calculating the lab plastic denseness, and comparing it to the plastic denseness taken into history in the design stage of the mix, while for the volumetric method is non necessary to do that excess attempt in order to do the accommodation.
Equally far as to which method is more appropriate to be used, from a first expression at our illustration, we can see that the volumetric method is more appropriate, at least from an economic point of position, because the accommodations made gave us smaller weights of stuffs than the accommodation for output weights. But my sentiment is that the fictile denseness method is much more appropriate to be used, because it ‘s more dependable, and you have a superior certainty about the riddance of the mistakes that appear in the commixture stage and besides a better control of quality of the concrete.
8. Remarks on fresh belongingss.
The treatment about the fresh belongingss of concrete might look to be non every bit of import as the hard-boiled concrete belongingss from a structural point of position, but as we have antecedently noted, there is a direct nexus between the two types of belongingss: for illustration the strength of hard-boiled concrete is greatly improved when a sufficient compression of the fresh concrete was established ( Neville 1995 ) .The aim of this treatment is to see the grade by which different concrete constituents affect the fresh belongingss of concrete, and we shall make this by comparing the mixes showing silicon oxide smoke, wing ash and recycled sum with the ordinary Portland cement mix ( 100 % Gravel ) .
The influence of sum type: by comparing the fresh belongingss of the 100 % Gravel mix and 100 % RA mix. Due to the fact RA have a higher porousness, a larger sum of H2O is needed in the mix which will finally impact the workability of the fresh concrete. Because we have considered an soaking up value for RA which was excessively high ( RA denseness was larger than 2400kg/m3 ) , the RA mix presented prostration slack, therefore hapless workability, besides a little hemorrhage, and segregation of the concrete components is present, taking to a hapless coherence. In the 30 % FA and 10 % SF mixes we have used as sum, crushed rock, so the influence of sum type on fresh concrete is the same in all 3 mixes, the lone differences occur from the influence of other parametric quantities.
The cement type that we have used was either ordinary Portland cement ( CEM I 52.5 N ) or composite Portland cement, by uniting the Portland cement with a cementitious stuff like silicon oxide smoke or wing ash. As we can see from the comparing of the composite Portland cement mixes with those holding merely Portland cement, the 30 % FA mix presents no hemorrhage or segregation of stuffs, a good coherence and finishability. Fly ash reduces the sum of H2O to be used in the mix, holding a similar consequence as a superplasticizer, so at larger H2O cement ratios we have collapsed slack, hapless coherence, and a little hemorrhage and segregation is present but the compactibility and finishability is still good, doing it suited for pumping. That is non the instance with silicon oxide smoke. Silica smoke increases the H2O demand, and by and large the mixes with silica fume present good coherence, no hemorrhage and segregation, true slack giving us a good workability. The use of both silica smoke and superplasticizers has a good consequence on concrete.
The sum of all right stuff is straight linked to the cost of both silica smoke and wing ash. The cost of production is rather big, so the usage of silicon oxide smoke and wing ash is no longer a inexpensive, feasible solution for Portland cement replacing. Equally far as their effects on fresh belongingss, for the 100 % Gravel mix, at lower water-cement ratios we deal with a stiff mix, holding less finishability and compactibility than when the sum of Portland cement is decreased, while the coherence, deficiency of hemorrhage and segregation is kept the same on all mixes. We could utilize higher sums of SF and FA but after a certain sum they cease to hold any consequence on the fresh belongingss of concrete.
The water-cement ratio is one of the chief factors impacting the concrete fresh belongingss, merely because H2O and cement are two of the chief components of concrete. In the 100 % RA mix, because of the usage of RA, it was necessary to hold a higher sum of H2O than in the other 3 mixes, which in return gave us a hapless coherence, a collapsable slack ensuing in a hapless workability. Besides some segregation and hemorrhage was observed, which was non present in the other mixes. As a general regulation, when the w/c ratio is decreased, the ratio between the other concrete components is unbroken changeless, so the workability additions ( Neville 1995 ) .
The SP sum required for workability. Superplasticizers greatly affect the slack of a mix. For the 100 % Gravel mix we used about 0.12 % sum of superplasticizers for all w/c ratios, which gave us a true slack. When we look at the 30 % FA and 10 % SF mix we can see that we have increased the sum to approximately 0.31 % which gave us a prostration in slack when we used FA, so excessively much SP, and a true slack for SF, because SF works much better with SP compared to FA.
This coursework has to be looked at as being divided in two parts: a portion about the concrete mix design and set uping all the mix proportions of the concrete components and another portion associating to the fresh belongingss of the resulted concrete. During this coursework we have successfully designed 4 types of concrete, and as a consequence the fresh belongingss of the 4 concretes were separately established and assessed. The mix of concrete ingredients, the finding of slack and the calculation of fictile denseness were all done in the lab harmonizing to the relevant criterion regulating each undertaking.
The designed concrete types were: 100 % Gravel, 100 % RA, 30 % FA and 10 % SF. By measuring the concrete fresh belongingss we have seen which mixes had jobs and were non suited for utilizing on site, but excepting some jobs found ( a high sum of superplasticizer than the 1 needed in the 30 % FA ) , in general the mixes presented good workability without segregation or hemorrhage, were suited for pumping so they could be used on site, in existent conditions.