and welcome once again to the series of lectures on principles of construction management and
what we have been doing in the previous few lectures is talking about issues relating
to quality control taking up a specific case studies or situations from the field and trying
to analyze them discuss them in the framework of quality control so now in that scheme of
things today the discussion is focused on quality control issues in concrete
now before we get into concrete per say lets spend some time on repeating or putting in
another way general principles of construction quality control so quality control in construction
ensures that materials and procedures used for construction comply with the intended
requirements various international agencies have laid guidelines that should be followed
in order to ensure that materials and procedures used result in a safe and durable structure
so what we are talked about is finally a structure finally it is the structure which can be broken
up and perhaps should be broken up into different systems and in order to ensure compliance
or quality of the structure we must ensure compliance from quality point of view of all
the systems and a part of ensuring compliance for all the systems what we need to ensure
is quality of the components and to ensure quality of components we need to ensure the
quality of materials nothing brings out this principle of the quality control of materials
components and systems better than discussions in concrete
because when concrete is used in the field there are so many processes which are involved
which contribute to the final quality of the product and thats something which we will
look at and discuss a little bit today these quality control standards provide the
mathematical and statistical procedures for carrying out and evaluating the results
quality control we have see before is basically linked it cannot be d linked from what is
called test methods and specifications test methods as we have repeatedly pointed out
laydown the step by step procedure exact details what temperature to carry out the test how
many times to do the tamping whether a mallet should be used or hammer should be used what
should be the size of the specimen what should be the conditions of the test those are the
details which the test methods specify based on the tests which are carried out in accordance
with a certain test method we get what we can call results
now whether these results are acceptable or not is something which the specification will
tell us in case it is acceptable so what and in case it is not acceptable what is the process
to be followed this will be laid out in the specifications and obviously the specifications
can be different for different structures they can be different for different clients
they can be different depending on different countries different environment in which the
structure is and so also the test methods the test method for example for testing of
concrete strength is not a unique method as far as the world is concerned different countries
have their own codes they have their own shapes of specimens that are tested usually it is
cubes or cylinders the size of those specimens and so on so one must specify what method
exactly is to be used as far as the testing of a certain parameters concerned
now moving forward the tests are carried out with a two fold objective the first is to
understand the performance or the characteristic or the property as a quantitative value for
example this test here shows the slump so here the objective is to find out what is
the slump of this concrete now they will be a specification whether the test carried out
in accordance to the certain test method and there are test methods which are different
as far as slump is concerned and i am leaving it to you to find out as far as that slump
is concerned whether it is acceptable or not for a particular application if you are putting
the concrete in rigid pavement or a place where there is no reinforcement the requirements
of slump will be different compared to a situation where we are trying to pump the concrete we
are not talking so much what concrete and therefore we will limit our discussion on
that and as far as the same test is concerned apart from finding out the value it can also
be used to compare two concretes just because we want a level playing field that this concrete
has more slump than this so we have to measure this value precisely
from the point of view of acceptance or for comparing two concretes as far as the testing
for quality control is concerned there is a property which is involved and the quality
control test basically evaluates that property and then there are processes which are involved
and the quality control procedure basically test the quality of the process and this part
which is process material and so on is very well covered as far as theory is concerned
in industrial processes the quality control test to evaluate the process
of construction would necessarily try to look at construction as a whole and then break
it down to a set of activities which is different processes so if you understand the test methods
before using the results of particular test for evaluation the quality control engineer
should answer the following questions what characteristic or property is required to
be measured how would the desired characteristics or property be measured and what are the factors
during the measurement that can affect the readings so if we are able to answer these
questions clearly in our mind we will not be following a particular test method blindly
usually there is no compromise the test method as prescribed should be followed but at the
same time the engineer can make an exception if there is reason to change one or the other
step but before doing that there has to be a reason for doing it and the answers to these
questions would help the engineer make the decision
even if it were the slump test the number of layers in which the concrete is placed
the type of consolidation for example the number of times the tamping is done for each
layer and the orientation in the speed of lifting the slump cone these things could
very easily change the value of slumps that is recorded
so one must keep in mind and try to follow to the extent possible the exact procedure
laid out in a particular situation now let me give you another example which is not related
to concrete at all for example there was a situation where we want to deposit let say
two meters of soil and this had to be compacted now there are ways and means of compacting
there are different ways in which it can be compacted as far as the contract is concerned
it could simply say that the contract as responsibilities to place two meters of compacted soil now
one way of doing it is to put the entire two meters or may be little more than two meters
and compact it using some kind of a roller or hand compaction or whatever you want to
do so that you have this two meters deposit the issue really would be that how do we measure
compaction now compaction one of the methods of parameters that is quantifiable perhaps
is density now if we are able to specify that the soil
placed here has to have this density then it becomes a performance based criteria that
we have lay down a performance criteria density that has to be achieved now how it is to be
achieved is left out of the discussion for all practical purposes another way of looking
at it is that whether the density achieved or not it should be placed in a certain number
of layers there should be certain number of passes as far as the roller is concerned the
soil should have a certain amount of moisture because that will facilitate compaction if
we lay out the procedure in all the steps without is specifying acceptable density then
we are only doing a part of the job what is important to appreciate is finally
what is the parameter that we are interested in are we measuring that parameter directly
or we are doing it indirectly and if you are doing it indirectly are we concentrating too
much on the procedure or we have somehow trying to simplify the procedure and the procedure
is representative of the actual conditions so these are the kind of thought processes
which one must go through before adapting and actually using a test method
so now coming back to our discussion on concrete from the point of view of quality control
and assurance remember that quality is closely related in fact to accidents and safety and
there is a very strong element for planning for quality much as we discuss the issue of
planning for safety now before we take up an example of relation between quality and
safety lets go through this slide which says that the fact that concrete is often
placed in situ only adds to making the problem of quality control more complex in concrete
different steps involved in concrete construction are material selection proportioning mixing
transportation placing compaction and curing now each of these processes have to be carried
out in an acceptable manner in order to ensure that the final concrete construction is acceptable
we must also remember that these processes are interdependent the situation is even more
interesting because different players are involved in the different processes and the
overall quality control cannot be allowed to drop in the no mans land material selection
mixing and transportation this is done typically under the control of the ready mix concrete
manufacturer the proportioning could be done by the r m
c or it could be a part of a mix design which is given to the concrete manufacturer with
some amount of leave way the placing compaction and curing this happens directly under the
supervision of the contractor so at the end of it the contractor is using concrete and
carrying out the placing compassion and curing of that concrete which has been delivered
to the site from the r m c plant so now if at the end of the day the concrete
does not perform the weight was supposed to there is an issue r m c plant can see that
we supplied the right concrete because the contractor did not place it properly compacted
properly or cure it properly it did not reach acceptable standards and on the contractor
side they can say that the concrete was poor as far as the quality of supplies concerned
so this actually makes the quality control interesting and at the same time of course
challenging a lot of discussion today of course is not
relevant to precast concrete products where the issues are more defined uncontrollable
because after all precast concrete elements are factory made so now going back to our
discussion on relation of quality and safety we are seen this picture and seen the collapse
of these floors while the building was on construction now as is usual practice the
shuttering for a higher level slab rests on the previous lower slab
so when we are casting the slab here this shuttering is resting on the previously cast
slab this slab is cast only after this slab and this slab here supports the shattering
so something went wrong here and cause this collapse to happen in this particular case
the slabs collapsed and the accident was attributed to the fact that previously cast concrete
did not gains sufficient strength to carry the loads of construction of the slab above
so what happens is that if this slab which is caused previously does not gain enough
strength to be able to support the construction loads of the next slab this slab will give
way now if this slab gives way obviously the shattering is gone and this slab also collapses
during construction this slab here which is already cast in doing is doing fine is suddenly
subjected to the load of both these slab following on this and therefore a domino kind of in
effect likely to happen and thats what we possibly saw as far as this particular accident
is concerned so the quality of construction in terms of
strength development is one of the likely problems in this kind of a situation so the
quality of construction led to an accident and that is what is a very important matter
to appreciate investigate and learn lessons from so the use of cements that had a slower
initial strength faster cycle time one floor to another due to better equipment and mobilization
in the good old days from one slab to another the fixing of the reinforcement the fixing
of the shattering that would take a certain amount of time but with mechanization that
can be done much faster we have better and different cements where the strength development
is generally faster importance of construction loads which sometimes
ignored in the formal design process workmanship issues such as lack of curing leading to inadequate
strength development so these are some of the possible causes of the situation that
the slab on which the shattering was resting did not gain sufficient strength
now if the design process not considering the construction loads is a failure of the
design process why i am highlighting this is to only draw your attention to the fact
that quality control or quality construction as far as concrete construction is concerned
also has a very important part in the design office so the design office has also to be
able foresee a lot of things most of the time they do it its not that its not done but its
only a matter of highlighting it its only a matter of better communication between the
site and the design the site it may happen that the temperatures maybe such or the material
may be such that the kind of assumption which the designer has male in terms of strength
development thats not happening and if that is the case then the designer has to be flagged
that well we have changed the materials here the temperature is different here the kind
of strength gain that we are getting is only this much so would you like to change or alter
some parts of the the design process the construction sequence and so on and so forth
so moving forward some of these can be identified through traditional quality control procedures
for some that may not work at all so its not easy to distinguish between the responsibility
with design or constructions so those are matters which once an accident happens there
is always going to be a tarsal and plane game and thats something which is part of our professional
life but it should be carried out in a manner that we do not repeat accidents now what is
quality construction especially in the context of concrete construction are there absolute
standards for quality now quality means it should meet the specifications
which in turn means that there should be clear specifications and appropriate test methods
for evaluation we have already talked about this consistency is another very important
dimension of quality variability in quality is a very very poor indicator as far as quality
is concerned specifications must take into account parameters such as importance of structure
nature of construction and structure and so on
now issues relating to quality control and assurance in concrete construction cannot
be looked in isolation from the stages in construction and the specifications for the
job and these specifications need to address challenges on account of using new materials
or different materials which are not traditionally used mechanization in the construction process
and the changes in the professional environment now as far as quality construction is concerned
we have talked about this considerably as far as this discussion today is concerned
that quality of concrete construction is affected by the quality of work at each step
therefore apart from the narrow view that the requirements at each step are met the
larger global picture should also not be lost sight of and given the far reaching implications
quality at each step should be seriously considered and planned for at each step as far as materials
are concerned we are routinely using blast furnace slag silica fume fly ash especially
fly ash in our cements in the concrete chemical admixtures are also routinely used whether
there air entrainers water reduces or set regulators the sometimes we use short fibres
and thats when we get fibre reinforced concrete we use different kinds of materials epoxy
coated bars fibre reinforced plastics as far as reinforcing material we have talked about
epoxy coated bars and the quality issues related to epoxy coated bars in a previous discussion
and curing and sealing compounds so these materials are routinely used they are not
new to that extent anymore and they affect the test methods they effect this specifications
as far as our efforts to ensure good quality concrete construction is concerned
so we must remember that whatever quality control standards we have set keeping in mind
the materials being used the environment in which the concrete is going to be placed and
so on so as far as mechanization is concerned that also has its own implications as far
as drawing of the right kind of standards is concerned we now are able to do concrete
construction at a much larger scale in more challenging projects we can do construction
much faster lets also now take a few examples as to how different environments the construction
being carried out in different environments how does it affect the quality control procedures
samples for concrete strength in an underwater concrete construction should be collected
underwater so it does not make any sense to collect the concrete samples in air even though
concrete is being mixed in air but its been placed underwater its going to remain underwater
and has been designed as an underwater concrete so if you want to find out the strength of
that concrete because the sampling underwater is likely to be different from sampling in
air is more challenging we must keep in mind that the cubes that we collect should be representative
of the kind of construction all the kind of member where the concrete has been placed
and in this case when its an underwater concrete the concrete has been placed under water the
member where the concrete is is underwater and therefore in order to get its representative
strength its imperative that the sampling is also done underwater for certain purposes
the cubes samples may need to be cured under conditions which are closer to the site than
under water indeed underwater curing at a certain temperature is the standard way of
curing and determining the strength at twenty eight days at times it may be important to
also have some tests some cubes which are being cured under conditions which are closer
to the site condition if for nothing but for only comparison of the strength gained under
those conditions with respect to cubes cured underwater
sampling for concrete from a roller compacted concrete is better done with coarse than with
the cubes cast now this is something which i am not going to answer here a leave it to
you to think that if we are casting a roller compacted concrete how should the sampling
first time we done its very difficult for that concrete to be cast in cubes we can do
it we can vibrate the cubes and so on but is that the way that the concrete element
is in the roller compacted concrete itself no the roller compacted concrete element is
concrete placed in a certain thickness compacted with a row vibratory roller and left there
with curing and so on moving forward there is a changing professional
environment which has its own implications as far as quality control is concerned traditional
client contractor consultant relationships has undergone a major change government participation
in public in large projects has been redefined in the role of regulatory bodys and with the
increase in the size of projects international participation has increased and private public
partnership is a new mantra basically why i am bring the subject of again
in this context is that ensuring quality construction is everybody is responsibility the issue is
there is a cost associated with quality because all these tests that are carried out are not
free they cannot be carried out for free and somebody has to bear the cost
now in the traditional system the test for simple and the cost could be worked out people
knew exactly whats going to happen and so on now in the present situation where construction
industry has gone through changes and the contractors the clients the regulators they
have their own way of looking at a certain project what happens to quality control overriding
principal is that yes nobody will subscribe to the belief that quality can be compromised
but who should bear the cost and thats why its impotent to understand that element in
drawing up the kind of plants that are required for quality assurance in construction
decision making is carried out in the framework of the contracting which is interrelationship
between the client consultant and the contractor and extra cost and whether they are admissible
or not and if so by whom these are questions that need to be built in into the contract
documents for example sampling underwater taking coarse from a roller compacted concrete
these are situations which are extremely simple but can be taken up as a case where additional
cost will be involved in even sampling and whether or not the contractor who may be charged
with the responsibility of ensuring the strength of concrete whether that additional cost should
also be borne by them in certain cases yes it is obvious but in certain cases its not
so obvious decisions relating to quality control have technical legal and financial implications
beside involvement of additional resources in terms of time manpower materials and machines
so these are kind of things which have opened an entirely different dimension to quality
control exercises as far as concrete construction is concerned importantly quality should not
only be maintained but appear to be maintained which means that they have to be records which
have to be systematically maintained so that at a later point and time they can be referred
too adequate safeguards to guard against conflict of interest misuse of discretionary interpretation
need to be built in in the provisions and stages in the construction process could
include obviously concept and planning detail design including functional architecture in
structural design construction and finally maintenance as far as we are concerned in
todays discussion we are talking primarily in detail design and the construction phases
and the quality control issues relating or arising there and as far as the design is
concerned drawings are the output that needs to be checked for quality
quality of the construction drawings is a very important issue when it comes to ensuring
quality of the final construction there has to be clarity of detail cover strength of
concrete detailing of reinforcement and so on the drawing should not be ambiguous and
they should also clearly put forward the precautions during construction we will talk about the
issues relating to the collapse of those slabs in the at the outset of this lecture today
and that is some of the things that can be addressed in the quality of the construction
planning construction drawing stage as far as the quality of concrete construction
is concerned the concrete used has issues with materials proportioning batching mixing
and transportation other than placing curing and compaction we have talked about that formwork
workmanship that is placing vibrating curing and post processing and special issues which
will be in grouting in reinforcement so these are some of the things that directly
contribute to the quality of concrete construction now coming to materials proposing batching
mixing and transportation since its not a discussion majorly on concrete engineering
i will skip some of the discussion assuming that you already know about it there are issues
relating to weigh batching and volume batching there is the issue of washing of aggregates
to be free from dust oil and dirt there is the issue of priming construction equipment
whether it is the trucks whether it is the mixers there are special situations where
mixing is allowed manually and has to be carried out and in those cases what should be the
kind of mixtures used there is a provision for nominal mixes as far as india is concerned
and moving forward there is an issue temperature in the normal construction what should be
the ambient temperature or what should not be the ambient temperature there will be a
forbidding clause that is concrete should not be caused if the temperature is below
a certain number if its higher than a certain number methods of transportation and necessary
precautions dosing of part of water and chemical admixtures during transportation or just before
placing this is a practice which is very often frowned upon by engineers and quality control
experts as far as quantifying the quality of concrete
construction is concerned we can do it in terms of properties of fresh concrete we can
do it in terms of properties of hardened concrete and we can do it in terms of properties of
the structure cast or made so what we are trying to mention here is precisely the issue
of material and component when it comes to concrete as a material we could be talking
of properties in the fresh state and we could be talking of properties in the hardened state
now as far as the fresh state is concerned the test could be slump air content temperature
at placing bleeding and setting time there could be other tests such as slump flow possibility
flowability compatibility temperature rise so the engineer has to make a decision on
what and which of these tests are relevant are they relevant and should be carried out
in toto following laydown procedure or there should be changes made
so its an important task from the point of view of quality control to identify the tests
that need to be carried out and related issues such as frequency and acceptance criteria
as far as hardened concrete is concerned strength modulus of rupture and modulus of elasticity
are is known in standard test to that list porosity permeability toughness are additional
test which are gradually creeping into our framework for quality control in concrete
construction and again here also the engineer whether its a design engineer or the field
engineer they have to decide they have to lay down the standards which are required
the test method should be followed and the specifications which would be use to accept
or reject the concrete as far as testing the structure is concerned
there have to be again clearly defined parameters such as no cracks honeycombing verticality
of the structure planeness or roughness water tightness these are some of the test of performance
requirements not from the concrete material but for the structure of course water tightness
and honeycombing would depend on the kind of concrete that has been used verticality
planeness would depend on the kind of formwork that has been used
finally we must remember that it is not the concrete which is being accepted it is the
structure which has to be accepted of course in order for the structure to be accepted
we should be placing acceptable concrete under acceptable conditions so that their performance
requirements at the structures level is met now as far as quality control for the material
in the ready mixed concrete plant is concerned we can have tests for individual materials
sampling procedures and frequency based on time and the volume of concrete mixed some
of these items need to be spelt out simply to clearly define the rules of the game and
is important from a professional and legal point of view
now continuing our discussion on the quality control test for fresh ready mix concrete
there should be test for slump air setting time and temperature we could add slump loss
or air loss as an additional test there is a location which is involved that is whether
test should be carried out at the plant or they should be carried out at the site of
placing the frequency which is involved whether it is related to time or the volume of the
pours as an illustrative example as far as testing
for compressive strength is concerned usually three specimens are taken and tested for strength
they need to yield internally consistent results and therefore we need to carry out a test
for that and create an admissible sample whether the sample itself is admissible or not obviously
only for a valid sample that is an admissible sample we will decide on the acceptance criteria
i am leaving it to you to check whether all codes require three specimen to be tested
as far as indian codes are concerned most of the time we say that they will be three
cubes which will be tested and an average will be taken and that average will be used
for further processing provided there is internal consistency in the results of these three
cubes now whether three are used by other standard as well is something which i am leaving
to you to think and determine let me ask you a question if the observed
strength of m twenty five grade concrete is found to be twenty six m p a that is the average
of the three cubes is twenty six does it mean that the concrete is necessarily acceptable
that would depend on what is the acceptance criteria being established being followed
as far as a particular project is concerned as far as this question is concerned if you
examine this question in light of provisions of i s four five six
what would be answer b similarly if the observed strength of m twenty five concrete is found
to be twenty three m p a that is the average of those three cubes is twenty three m p a
is it obvious that it does not meet the acceptance criteria i would only have you recall that
as far as the definition of characteristic strength is concerned which is important to
recall because we are talking of m twenty five grade concrete m twenty means the characteristic
strength is twenty five we talked about a normal distribution an expected
normal distribution as far as concrete is concerned we designed our concrete mix at
what is called the target mix and we define the characteristics strength here somewhere
where we said that this area here is ninety five percent that is characteristic strength
is that strength which under normal conditions would exceeded ninety five percent of the
times we are allowing five percent failure now the question really is that whether this
five percent is allowed no matter where the strength is the issue really boils down to
how much lower than the characteristic strength can an actual strength be that is something
which will depend on different standards and i am leaving it to you to identify it with
respect to i s four five six similarly to say that if the strength is just higher than
f c k n its acceptable that also has its own problems and that's something which i am leaving
to you as a homework as far as the indian standard is concerned
not more than certain amount of deviation in the three individual reading is allowed
and in that case the samples have to be discarded as far as indian codes are concerned for example
if we get twenty twenty one and thirty five as three readings there are two ways of handling
it we may say that well this guys an outlier lets work with the average of these two but
the indian codes say no if there is an outlier this sample should be rejected all together
acceptance check only for valid samples for example this sample would not be even processed
for further action examine two criteria individual average and the average of group of four in
the event of non-acceptance carry out non distractive test load test and so on before
taking a final decision on dismantling the structure
we must understand and remember all the time that quality control especially large projects
has very severe cost implications and therefore before we take a decision as far as dismantling
is concerned rejection is concerned there will be lot of pressures in terms of finances
in terms of time if for example there was that accident no matter what caused it there
is the clock being set back the project will suffer as far as time is concerned there will
be additional cost involved so cost is a very important part of quality as far as construction
is concerned and that's something which we must keep at the back of our mind when it
comes to additional tests different tests and so on
so quality of concrete construction is affected by the quality of work at each step and therefore
from a we should not work in a narrow perspective and try to have the global picture in mind
as far as possible and given the far reaching implications quality at each step should be
seriously considered and plant for this is something which have emphasized in the previous
slides also that quality reach the quality plan in fact you would recall that we are
talking of planning as far as construction project is concerned we said that has to be
a safety plan there is the quality plan there is a resource plan and so on
now testing for compressive strength as a parameter for quality control requires to
address the following issues that is sampling frequency and methods the testing method itself
and the acceptance criteria the above in a manner of speaking lay down the rules of the
game and that is critical given the nature of the activity as far as the sampling frequency
and method is concerned it could be the volume of pour it could be the day or that is time
everyday it has to be taken regardless the volume pour involved it is location of sampling
whether it is plant site agitator truck discharge pipe and so on we must remember that concrete
is likely to undergo changes depending on what location it is in
the concrete which has being made at the plant will undergo some changes by the time it is
placed in the beam or the column or the wall at site now from the point of view of quality
control what is the point in this journey of concrete where the sampling has to be carried
out we have to answer the question why we are doing it if we are doing it from the point
of view of determining what is the kind of concrete that has been actually placed in
the site then obviously the last point is the best point
but if we are also having in mind to determine whether the concrete supplied to us was good
is not then we need to sample at either the plant or at the time when it is just delivered
to the site as far as testing methods are concerned the nature and size of specimen
including tolerances in the size in the shape storage of specimens before testing that is
curing testing method which includes equipment rate
of loading the condition of specimens at the time of testing and so on these are all part
of the regime or the protocol which has to be followed when it comes to the testing method
and its suitability for determining the strength remember that we need to carry out a standard
test all efforts should be made to ensure that the provisions are followed in letter
and spirit as far as acceptance criteria as concerned these constitute the basis on which
it can be stated that the concrete meets requirement and essence accepted and as a corollary to
that feeling which the concrete is liable to be rejected so this has to be lay down
very clearly as far as contract documents are concerned as far as quality control manuals
are concerned and considerations that go in to defining an acceptance criteria could be
the definition of characteristic strength reasonableness in the criteria decision making
lay down and define unambiguous flowchartsto follow number of specimens to obtain a representative
value and how to handle non-acceptance all these have to be a part of a document of
the quality control procedures for concrete construction
similar guidelines need to be in place for testing of materials fresh concrete testing
of the finished structure and so on feedback from strength data to the construction operations
this is what we talked about right in the beginning and we are talking about that accident
or that factious accident or factious causes of that accident that if there is a problem
in strength development it has to be fed back to the design process it has to be fed back
to the design office the construction controllers and so on the importance of construction quality
records and as built drawings cannot be over emphasized in their role serving as a reference
for maintenance engineers once the structure is in service
now before we close the discussion today as far as quality control of concrete construction
is concerned i leave you with a couple of question to think about we study the quality
control parameters for concrete construction in different specifications you could use
specifications which are available for railways or nuclear power plants there will be quite
different and there will be an eye opener as far as your concerned
study the differences from the point of view of quality control in structural steel and
concrete construction find out more about the roles and responsibilities of the contractor
consultant and the owner from the point of view of quality control study sampling requirements
from different specifications how do different specifications handle noncompliance what are
the other methods to establish internal consistency and acceptance of samples as far as the indian
standards are concerned we talked about the group of four and the individual values the
individual values should not be allowed to fall below certain number and the group of
four must meet a certain requirement not necessarily just the f c k in order for the concrete to
be acceptable so those of the kind of things which if you need more specifications more
standards you will get a better handle of the those things
and details of non-destructive testings load test etcetera given in i s four five six in
case of non-acceptance on the base of strength as obtained from cubes so these are some of
the obvious questions or leads from the discussion that we had today that comprised primarily
of talking about quality control issues in concrete construction its not only related
to materials the final quality is related to so many other things including workmanship
as usual this is the list of references of some of the material that could help you understand
the topic better and i look forward to see you again in a subsequent discussion
thank you