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Chapter 3
QUESTIONNAIRE SURVEY AND ANALYSIS
1 3. 1 Introduction
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3.2 Scope of the Questionnaire
3.2.1 General
3 .2.2 Selection of materials
3.2.2.1. Cement
3 .2.2.2 Aggregates
3.2.2.3 Water
3 .2.2.4 Admixtures
3.2.3 Batching and mixing
3 .2.4Delivery Facilities
3.2.5 Quality monitoring
3.2.6. Management Review
3 .2. 7 Quality Records
3 .2.8. Control of non conforming products
3 .2.9 Design control
3.2.10 Corrective & Preventive Action
3.3 Qual it;' practices of Ready Mixed concrete suppliers
3.3 .I. Selection of materials
3.3.1.1. Cement
3.3 .1.2 Aggregates '--' '--'
3.3.1.3 Water
3.3 .I .4 Admixtures
3.3 .2 Inspection and Testing
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3.3 .2.1 Test for cement
3.3 .2.2. Data from cement suppliers
3.3 .2.3 Tests for Aggregates
3.3 .3. Storage facilities provided
3.3 .4. Design control
3.3 .5 Control of Inspection, Measuring and Test equipments
3.3.6 Records
3.3. 7 Management Responsibility
3.3.8 Handling non conforming products
3.3.9 Corrective and preventive action
3.3.1 0 Delivery
3.3.11 Statistical Techniques used
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3.0 PREPARATION OF THE QUESTIONNAIRE AND ANALYSIS
3.1 Introduction
It is revealed from the personnel interviews had with few RMC
suppliers that variation in 28 day strength results has become the maJor
problem. This Questionnaire is to study the existing practices among Ready
Mixed Concrete suppliers to find the causes which atTect the quality of
concrete. Questionnaire was developed with reference to SLS 1144 part 1 &
part 2 for RMC in Sri Lanka, Q"lRMC quality and product conformity
regulations, BS 5328, ISO 9001 quality management system and Manual of
Ready Mixed Concrete. The Questionnaire were distributed among 9 Ready
Mixed Concrete suppliers. Out of these concrete suppliers three ha\ e
obtained ISO 9001 certification and others are in the process of developing
the ISO 9001 Quality Management system.
SLS 1 144 part 1:1996 - This is the Sri Lankan standard specification for
Ready Mixed Concrete. Part I of the standard covers the requirements for
supply of fresh RMC.
SLS l 144 part2: 1996 -This part of the standard specifies test methods for
determination of mass per unit volume, air content, slump, coarse aggregate
content and unit mass of air free mortar of fresh concrete, compressive
strength of concrete to determine mix proportion, water/cement ratio and
cement content.
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QSRMC 1995-This incorporate the requirements of BS EN ISO 9001 as
applicable to ready mixed concrete and in combination with BS 5328, they
provide an additional assurance that concrete will conform to the
specification agreed vvith the customer. It consist of five parts.
].Quality system requirements
2.0rdcr processing
3 .Purchase and control of materials
4.Concretc mix design '--'
5.Shipping, production and delivery
6.Control of concrete
7 .Certi !~cation and administrative procedures
BS 5328-part 1 : 1991 -This will include designated mixes, specification for
concrete provides guidance to the specifier and purchaser of concrete on the
selection of requirements for materials and concrete mixes.
There are tvventy elements that should be considered in a quality
management system. Out of these 20 elements some elements deal with the
quality control aspects. Other elements are directly relevant to the quality
management system. Since all the RMC producers do not have ISO 9001 , in
the preparation of the questionnaire only ten elements directly relevant to
quality control aspects were covered and other eleven elements were
excluded.
Elen1ents considered
1. Purchasing
1 Inspection & Testing
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3. Inspection, measuring and testing equipments
4. Handling, storage and delivery
5. Process control
6. Corrective and preventive action
7. Design control
8. Inspection test status
9. Statistical Techniques
1 O.Control of non conforming products
I 1. Management responsibility
The following elements were excluded because it directly apply to the
system.
1. Control of customer supplied product
; Quality system
3. Contract review
4. Document control
5. Purchaser supplied products
6. Traceability
7. Quality audits
8. Training
9. Services
The methodology used in the preparation of the questionnaire IS given
belO\v.
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3.2 Scope of the Questionnaire
The areas covered in the questionnaire survey are given in the
!ollmving sub sections.
3 .:?..! General
A Ready Mixed Concrete producer only supplies what is required.
The contract is to supply only exists between the purchaser and supplier.
The concrete producer completes his part of contract having produced
the concrete and delivered it to the customer's site. He has no control over
hmv the concrete is placed, compacted, finished, cured or protected.
Therefore responsibility does not lie with the supplier for the problems due
to above causes at the site.
In the production process of Ready Mixed Concrete following activities take
place.
I. Placing an order
' Selection of materials
3. Storage of material
4. Batching and mixing
5. Delivery
6. Quality control in the above items
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Placing an order is discussed under personnel interviews. And other areas
are generally covered in this questionnaire. This questionnaire is not too
specific because the producers are most of the time try to interpret that they
are the best among others. If this is the case, the questionnaire survey results
will not ret1ect the actual situation in the concrete industry. The above facts
were observed during site visits and personnel interviews had with three
suppliers .
3 .2.2 Selection of materials
In this section purchasing of materials , Inspection & Testing aspects
and storage facilities provided are covered.
Ready Mixed Concrete is a composite material .combination of
quality materials will result in a good quality concrete.
The main constituents of concrete are
!.Cement
2.Fine aggregates(Sand)
3.Coarse aggregates(Metal)
-+.\Vater
5.Admixture
The following sections of the report describe how the material selection ts
being done in RMC manufacturing.
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3 .2.2.1. Cement
Cement is the key component of concrete. In fresh concrete,
they are the finest particles and they have the function of providing·
workability, cohesion, and stability. In the hardened concrete they
have the responsibility of providing the mechanical strength,
relatively impermeable pore structure and an internal environment to
resist chemical attack of the concrete and to protect any steel
reinforcement.
In order to achieve these benefits, the various complex components of
the cement react with water at various rates and form a new product.
This process is hydration, result in a physically boded material
structure.
Good results \Viii depend on the type and chemical composition of
cement, the amount of water, internal moisture , temperature and age
of concrete. There fore in order to produce good quality concrete
quality of the cement should be taken in to account.
The following properties of cement have the greatest relevance for the
Ready Mixed concrete producer.(Dewar and Anderson, 1992)
1 .Fineness
2.Water demand
3.Setting times
4.Strength in concrete at 28 days
5. Ratio of 7 day to 28 day concrete strength
6.Sulphate resistance
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7.Alkali content
8.Chloride content
Cement for RMC is described in the clause 7.1 of part 1 of SLS 1144.
It gives the minimum requirements and BS 5328 and QSRMC states that a
list of cement suppliers shall maintain which are authorized for use. This list
should include
1. Supplier and source
'~ Type
And cement shall be from sources (QSRMC, 1995)
1. Which hold current product conformity certification based
on product testing and surveillance of the manufacturer's
system of factory production control taking account of the
relevant clauses ofiSO 9001. or
'~ Where conform with the British Standard for the product
and the manuracturer's system of factory production control
taking account of the relevant clauses of ISO 9002. '-
And data shall be available from the supplier at a maximum of monthly
intervals.
And data shall provide the information on
1. Fineness
'~ Compressive strength (7 days) and 28 days
3. The certified average and the standard deviation of the alkali
content.
4. The chloride iron content
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\\here bulk materials are imported and held at a distributor shall be required
to
* Prevent deterioration of the product
* Ensure full traceability between the manufacturer's
certification and the distributors' documentation
* Provide certificates of tests on a weekly basis to assure the
continuing conformity of the product with British standard
I-I old certification based on product testing and surveillance of the quality
system to the relevant clauses of ISO 9001 in respect of prevention of
deterioration, traceability and testing or be subject to assessment and routine
audit by the company to ensure conformity with the product and quality
systems requirements .
To check whether the RMC producers in Sri Lanka satisfy the requirements
according to the standards the following questions were included .
1 Question number r------1 Question2 I
Purpose
The makes of cement normally used in
I concrete
I Question3- -------------·-rHo~eyselect a ceJ~ent~-pplie~-L_ , -----j
i Question4 The tests perform to check the cement
, quality
~6 ,Q7,QS,Q10, Q\1 -=- -~Frequency of' the above tests~-=~
[_<2ucstinn\2 ] Places where they do the above tests J
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. Question 13,Question 14 -
1 Question 15 !
Records of cement suppliers
I Data receive from
: suppliers(frequency) --~------------+-------' -
1 Question 16 I
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3.2.2.2 Fine and Course Aggregates
I Storage facilities
cement
Since the aggregates have two prime functions in concrete such as
(Dewar and Anderson, 1992)
!.providing a rigid skeletal structure
2.Rcducing the void space filled by the cement paste.
It is very important to select good quality aggregates which has the major
effect on quality of concrete.
There fc1re following important properties of an aggregate should be checked
in the selection.
1. Nominal maximum size
2. Grading and mean size
3. Silt, clay or tine dust content
4. Water absorption
5. Relative density
6. Moisture content
7. Chloride content
8. Alkali- silica reaction
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And the aggregate, material need to be essentially chemically inert and
physically strong and stable.
SLS 1144:Part I: 1996 clause 7.2 specifics the requirements for aggregates
used for RMC.
And QSRMC part 3 clause 3.6.2.4 under purchasing and control of
material.
QSRMC states that a list of suppliers should be maintained and that list shall
identi Cy
I. Suppl icr and source
1 Requirement for conformity to a British standard or any other
specific quality criteria including testing
3. Description for traceability
The test frequencies should be considered as follows (BS 5328)
A ooreoate ]XOJJertv bb b ..;
i Grading- sand
- Coarse
I Chl~1-:-ide co;1tent r----- ------~---
1 flakiness
Frequency ---·~-
Monthly
3 monthly
annually
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I Water absorption
, annually i
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--- -----i 1 Fine content I annually
IG~c;se bulk density I 6 monthly ------ --------------------- __ _j__
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These standards are not directly applying to Sri Lankan conditions due to
variation in aggregate parameters from time to time which produce from
different crushers .
Therefore my suggestion is to change the frequencies of testing as follows.
Agg-regate property---~---~~ Ft:cquency 1
~ ---------------~------+- -~~~~--~-~-----------
: Grading- sand I Each new load to the plant I
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- Coarse 1
~Chloride content I
1 tlaki~1ess ____ --------------~~New load I ------------------- -~---------~--~-- - I
!_Wate~c~b~orptio~------- \\'cekly ----~--~ : Fine content Daily l ; Loo~e-bul~densit~------- Once in 3 months ~
• To check whether the RMC producers consider the above requirements in
the case of purchasing aggregates the following questions were included.
---------~--------------- --------------l
Whether they purchase aggregate from any supplier 1
__ _ __ ~hether they maintain a list of suppliers ~
:_ QL-lcstion:2~-Whe- the- r they perform the tests - [ . --------- ----------~----------------- -1 : Question:21 Type~oftes~~-performed_____ _ ______________ !
I Ques:ion:23 ~~ual standard size of aggregates _ --~
i Question15 Frequency of checking ]
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3.2.2.3 Water
Manual of Ready Mixed Concrete states that half the water requirement is
present as free moisture in the aggregates. Water fit for drinking (potable
water) is accepted as suitable for adding to concrete to supplement that in the
aggregates, but other sources may be equally acceptable.
It is possible for normally suitable ground water or stream water to
become contaminated, therefore periodic checks are necessary. This will
apply equally to the water used for washing aggregates.
According to SLS 1 144 part 1 clause 7.3
'Y../ ater shall be mains or potable or where non potable, non mains and not
recycled, conform to the requirements given in BS 3148.
Therefore it is necessary to check from where the RMC suppliers take
\Vater and what type of tests are conducted to ensure the quality.
The following questions are prepared in such a way that they cover the
general requirements for water used in RMC.
I, Question26 Water sources I
-l r- -------------. Question27 Tests are performed I
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3.2.2.4 Admixtures
Admixtures are materials added to concrete in relatively small
proportions to modify the properties of concrete.
Admixtures have important roles in
1. Enabling properties to be obtained which may be otherwise
unobtainable
'~ Enabling improvements in selected properties
3. Enabling more economic mix formulations
4. Overcoming problems in transporting, placing, compacting or
finishing.
5. Overcoming deticiencies in other materials
SLS 1144 part I clause 7.4 specities the requirements of admixtures used for
RMC.
And QSRMC part3 clause 3.6.2.5 ( 1995) ,the company shall maintain a list
of admixtures which are authorized for use. It shall identify the supplier,
type and requirements for conformity to a British standard including testing
The test certiticate shall obtain from the supplier in respect of the material
delivered.
These shall provide data on Chloride content and Alkali content.
Question 28 and Question29 generally cover the aspects of selecting
admixtures.
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:-ci~cstion28 ·-~·---· --··--~Types of admixtures you use for your
concrete - --··------
1 Question29 Selecting an admixture -- ------· ----·--------~·--------------~
3.2.3 Batching and mixing
Process control and Calibration of equipments are covered in this section.
Plant may be designed for
I. Batching
' Batching and mixing
3. Batching vvith a mixing option
The accurate vveighing of solid constituent materials has been a
fundamental requirement for producing quality concrete for many
years, but the degree of automation built into the batching process has
shown on a marked increase only in recent years. The reliability of
automatic controls has improved and computerization has enabled
more sophisticated adjustments to be incorporated.
There is a need to carry out calibration of weighing process.
SLS I 144 part I clause 8 specifics the plant and equipments which
should be used in batching and mixing ofRMC.
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And QSRMC states that the weighing system shall be capable of
complying with the calibration requirements of these regulations both
at initial and subsequent operations.
Calibration of weighing and volume measuring equipment
(QSRMC, clause 5.11.3)
All vveighing and measuring equipment shall be tested and calibrated over its
full \Vorking range at least once every three months by a relevant specialist.
r ollm\ ing questions were prepared considering above facts
, Qu~sliot{:lO 1 wh.;, didy;;;.; install the present hatching plant0. I
· Question31 Was it brand new or second hand at the time it was
, I installed? j ',-O~~stf~n32 ____ j_l. Do~ou calib~:atethc following items_? _____ _
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r-Question-34---~ How often do you calibrate the admixture dispenses m
i I ] the plant?
1 Q~estim~35- -1-How often do you calibrate the water meters in the plant? ~
'Q~t-est-ion-33 --~-1-Io -\\;_o_f-ten-~i_o_y_o_L~-c-a-lib-t_-a-te-the weighing scales in-th-e I
I plant·• -- --- -------·-~ --------- ----
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3.2.4 Delivery Facilities
Concrete is a product as \Vel! as a service. Special types of vehicles
arc used to deliver concrete to the sites. In this research more attention is
payed to the production process not to the delivery process. Question 42 is
based on the problems with delivery of RMC.
Question42 \Vas to find the causes for delays in the delivery process.
3 .2.5 Oual itv monitoring ' . '-
The questions coming under this section are based on the statistical
Techniques used by RMC producers in Sri Lanka.
Various methods of analysis are used to monitor the results achieved with
the target. This is particularly applied to strength in the case of concrete.
Retrospective control can cover any property of materials or concrete, such
as aggregate grading, slump, or air content. But it is associated with 28 day
strengths, because by its nature it is not a property which can be measured at
the time or manufacture. There is always a delay in obtaining results, which
imp! ies that action to correct any observed departure from the intended
quality will in turn always be delayed.
Therefore it is important to monitor the production over a time period and
identify the trend of results in which the process can be improved .
from the discussions I had with the suppliers, the most used techniques are
Cusum and Control charts.
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Question40 \vas aimed at identifying the quality control techniques used by
the RMC suppliers
3 .2.6. Management Revievv·
Management Review is given in clause 4.1.3 of ISO 9001.
To verify that the top management is committed to quality and management
reviews are done at defined intervals in order to discuss the system and to
implement improvements to achieve the quality. The following questions
were included.
: C)Ct~stio~43-f-How often ~~the problems related to ready mixed concrete 1 I I I \ discussed with the Managing Director/CEO of your company? I I I c------------1---------------------------------------------------j
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, Question44 1
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What type of issues are discussed with the Managing Director 11
I_------ ____ L ______________ ----------------- ______________________ __j
3.2.7 Quality Records
In RMC industry it is very important to have the records in order to
identify the trend of results and to take necessary corrective and preventive
actions.
lt is also very important to maintain a good documented procedure to avoid
blunders .
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Clause 6.16 of QSRMC gives the following guide lines. Records of the
ro!IO\\ing activities shall be maintained.
To control test results
I. Compressive strength
1 \Vorkability
3. Density of fresh concrete
4. Temperature
5. Air entrainment
6. Aggregate loose bulk density
Other records are quality control system analysis, test equipment calibration
and control of other specified characteristics.
~ -- ~~ ~-~- ------- ----- -- --- ----~ -- l 1 Question38 I Maintaining documental procedures for each and every
~work in the plant : I 1
Question39 I Method adopted in giving work instructions --- - - ------'------ -------- ~-- ----- - --~. --- --- --
3 .2.8. Control of non conforming products
Inspection and testing is divided into three stages.(ISO 900 I)
I. Incoming inspection
1 In process inspection
3. Final inspection
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If the materials and RMC concrete do not satisfy the requirements given in
the standards there should be a method to control it. These aspects are
considered in the preparation of the following questions.
Questions 46 ,4 7 48 & 49 were aimed at controlling of non conforming
products at the incoming stage. Question 50 was based on fresh properties of
concrete.
3.2.9 Design control
The concrete m1x design for a speci fie contract and use is to select
material and their proportions \vhich will meet, economically, the properties
of the concrete in both the fresh and hardened states. For ready mixed
concrete it can be divided into three stages material selection, mix
proportioning and mix selection.
Questions 51, 52, 53 &54 were based on the procedure adopted by RMC
producers \vhen they do the mix design .
3 .2.1 0 Corrective & Preventive Action
The following questions are to check whether these RMC producers are
interested in tinding the problematic areas with regard to quality.
;()~testi;~41_T_ MostditTiZ~t parameter to achieve ----~------l I I