Chapter 3

QUESTIONNAIRE SURVEY AND ANALYSIS

1 3. 1 Introduction

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

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

38

.. __

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

39

......... ~,

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.

-10

.......

• •

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

-\I

.. ......

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.

42

........

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

43

......

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.

~~

.. _.

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

4:1

......

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

-+6

.... __

I

I

I

I

II

II

• • • • • •

\\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

47

.. __

I

I

I

I

I

I

I

I

I

I

I

I

• • • • • • • •

---------------------,----------------

. Question 13,Question 14 -

1 Question 15 !

Records of cement suppliers

I Data receive from

: suppliers(frequency) --~------------+-------' -

1 Question 16 I

--------

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

48

.. --

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

•

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

I

I Water absorption

, annually i

_ --------~~~~~ually ---~l

--- -----i 1 Fine content I annually

IG~c;se bulk density I 6 monthly ------ --------------------- __ _j__

49

.. __

I

I

• • • • • • •

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

1

- 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 ]

50

........

I

I

I

I

I

I

I

I I

I

II

II

-Ill

--• •

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

_j

51

·-·

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.

52

.. _.

_..,4

I

I

I

I

I

:-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.

53

.......

I

I

I

I

I

I

I

I

I

I

I

I

I

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_? _____ _

' . ~ I

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·• -- --- -------·-~ --------- ----

54

.. __

I

I

I

I

I

I

I

I

I

I

I

•

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.

55

.... __

I

I

I

I

I

I

I

I

I

I

• • • • • • ~ • •

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

1

, Question44 1

1

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 .

)6

.._ .

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

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

57

.. __

I

I II

II I I

• • • • •

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

:-o~~~~tiZ;n45 ---~~--~_-c-ust~:'~~ c<~npl~int~ ________________ -~

58

.. _.

3.3 Quality practices of Ready Mixed concrete suppliers

Questionnaire \vas distributed among nme Ready Mixed Concrete ' ~ . suppliers and only seven ofthem have responded. A sample questionnaire is

gin~n in annex B.

3.3 .I. Selection of materials

3.3.1.1. Cement

Almost all the RMC suppliers use Mahaweli Marine and when there

is a shortage they use Ambuja, Sanstha, L&T, ICT and Tokyo.

These brands are imported from India and Indunesia.

Clause 7.1 of SLS 1144:part 1: 1996 describes the cement which should be

used in RMC in Sri Lanka. According to the standard generally Portland

cement is used in Sri Lanka and the cement shall comply with SLS 107. For

special applications such as large concrete pours or concrete exposed to

sulphate attack or concrete for early shutter removal, other cements like low

heat Portland cement or sulphate resisting Portland cement or rapid

hardening Portland cement are to be used. And it specifies that the cement

used for RMC should comply vvith the relevant British standard.

Wherever possible, cement should be obtained from a single source to avoid

undue variation.

Results show that the RMC producers use Portland cement and check \vith

the British standards. Therefore results are acceptable.

59

.. __

I

I

I

I

I

I

I

I

I

I

I

I

• • • • • • • •

Selecting a cement supplier, majority go by the Manufacturer's certificate

.and some of them go by the SLS certificate or 31

" party certification.

QSRMC ( 1995) & ISO 9001 specify that selection of cement supplier should

be based on Manufacturer's certilicate or any other certificate equivalent to

that.

Table 3.1-Cemcnt brands used by RMC suppliers

-----~---

: M-alZ~---------- No. of

suppliers 1

!

I r--- -----------~--~------1 Mahaweli Marine -~- ---- I 1 -1 r--- -~---~---- ~----------------

1 Sanstha 1- ------1 Ambuja

---------~---

I Other (L&T, ICT, Tokyo) I

___________ ! ~-- ---·--- ----------~-- -------

Table 3.2- Selection criteria for cement suppliers

r- ------ ---- --------------------

! Selection criteria of RMC

!

I, i;,utppliers ~~---~---- ---------------- _________ j 1 Manufacturer's certificate 7 L--- ------------------ ------------

SLS ccrtilicate \ 4 ------r--------15 NBRO, Any 31l party certification 1

---- ~---~---- ---~-- ---___ l

(J()

.._ .

I I

I l I I I

--II I

-Ill II Ill

The selection criteria used by seven producers is the manufacturer's

certificate. The cement which is good for use should have the SLS

certification as well. But only 4 of them bother about the SLS certification.

They only depend on manui~1cturer's data.

I r these suppliers totally rely on the manufacturer's certification only , there

is no \Vay to check whether the batch of cement they are getting is same as

the quality implied in the certificate. Therefore it is advisable to do frequent

checks on cement parameters in a well recognised laboratory.

I suggest that it is good to carry out cement parameter tests for each new

batch arrival.

Furthermore to avoid different brands which increases the testinQ cost from '--'

time to time, one load of cement can be stored in RMC manufacturing plant

required for monthly average production.

In addition to above I have discussed how these suppliers responded to

cement parameter testing under chapter 3.3.2.1

3.3 .1.2 Aggregates

The questionnaire results show that 50 % of the RMC producers purchase

aggregates from the open market and the rest go for a selected list of

suppliers. One is having their own crusher.

vVhen aggregates buy from the open market ( from any supplier) the quality

will vary significantly.

61

.. __

I •

I

I

I

I

Since this is bulk material it is very difficult to do perfect checking.

Therefore it is not advisable to purchase material from indiscriminately.

The quality of aggregates has a significant eiTect on the quality of concrete

since they provide a rigid skeletal structure to concrete. Further it should

free from impurities from a simple test cannot identify them.

Though a very few suppliers do the screening of aggregates before using

for concrete, screening will help in improving the quality of concrete

significantly.

The importance of going for a selected supplier is the RMC producer can on

and off can do some checks on aggregates in the suppliers premises. Then

they can depend on the supplier it self.

But if the RMC producers go by any supplier in the market the problem is

with the quality which will atTect the quality of concrete.

The parameters can vary from one crusher to another. Therefore, it is

ach'isablc to carry out aggregate parameter testing when purchasing is done.

The test details are described under chapter 3.3.:2.3

From the literature it is revealed that the moisture content in aggregates have

a major effect on strength of concrete. In order to minimize this adverse

effect, \vhat I can suggest is to do moisture content checking daily. Though

temperature changes \\'ithin that particular day wi I 1 have an etTect on the

moisture content, it will be very low under normal weather conditions. If the

weather change is quite signiticant within a particular day itself , it is

advisable to do moisture content testing as and when necessary.

By adopting the above mentioned practices , quality of aggregates which is

used for RMC production can be improved.

6::?.

... _.

I

I

I

I

I

I

I

I

I

I

I

I I

I I

• • • • • •

3.3.1.3 Water

Fifty percent of the RMC suppliers take water from water board main

supply vvhere quality control is being done. Some of them take water from

wells. Since the ground water can be contaminated easily it is very essential

to check the quality of water before using for concrete. The results show that

most of the RMC suppliers do not bother about the quality of water they use

in mixing concrete as well as for washing aggregates. Presence of chemicals

in concrete will result in corrosion in reinforcement. This can be a long term

effect on quality of concrete.

Table 3.3- Water sources commonly used

; So~u~~ ---------~No. of RMC~

suppliers

:,--Water-Boa;.-d ~1~-;~1-;upply--l 4 --c--------- +------- . I I \Veils 1 4 ---1 I • I

:~)th~.----------t, ---=- j Table 3.4- Water quality tests

:- - ~No. of RMC suppliers \

11- ~ 1 ests I ___________ ---- -------- t- --- -------I Cloride 1 3 I I

f--------------------1 ---l 1 Sulphate \ :?. I I

~pll- I') I

I ~ _j i ____ - ---·~-------- --

63

... __

I

I

I

I

I

According to Clause 7.3 of SLS 1 144:part 1: 1996, Water used for mixmg

concrete shall conform to SLS 522 and water of chemical composition

acceptable for drinking, whether treated for distribution or untreated, is

suitable for concrete production. Where public supply is not available, water

may have to be obtained from natural sources which may contain

considerable organic constituents or unacceptably high contents of

inorganic salts. '-

Since surface water often carries suspended matter such as oil, clay, silt,

leaves, and other vegetable debris and may be unfit for use without physical

treatment such as filtration or impound to allow suspended matters to settle.

According to the standard water should be potable, fresh, clear, clean and

hee from acid, alkali, oiL organic impurities, lime in solution or other matter

\vhich is deleterious to concrete or steel.

The results show that less attention is paid to check whether the water is

suitable for concrete production.

3.3 .1.4 Admixtures

In general retarders are used in RMC manufacturing. In addition to

this some of them use air entraining agents and superplasticizers. Selection

of suppliers is done by the manufacturer's certification.

The concrete producer seeks the most effective way of meeting a

specification. He may be concerned about the uniformity of distribution

through the batch and the danger of overdosing. Such concerns are only

overcome with satisfactory experience over a period of time.

64

.. _.

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

• • Ill

Admixtures do not normally contribute directly to the volume or weight of

concrete and can be conveniently ignored in yield calculations.

But the presence of air entraining and water reducing agents and

supcrplasticizers may have significant effects on either air content or water

content or both.

In that case influences on yield need to be taken into account. There can be

some adverse etTects on the strength.

Table 3.5- Type of admixtures used

No.of RMC ',Type \Make !

I

I i

I ~---------·

1 Accelerators I Fos Poe SP 430 I ~- ----------

1 Retarders I

I

I 1-----------

11 Air entrains

Pozzolith 300R, 300R Master

Builder

EA 303A, AEA 304 I ~------------

11 Supcrplasticise 1~~ heobuild 561, Reobuild l 000

~--___L

Table 3.6- Selection criteria used for admixtures

,-----------·--1 Selection criteria I I

!

i I

\

1

Manufacturer's certificate I r------

No.of RMC

suppliers

115 ---1 --l

11 Other- past experience I

_____________1----------------____J

'

65

suppliers

1

6

--2

I

13

• ..

I

I

I

I

I

I

I

I

I I

I

I

I

Clause 7.4 ofSLS 1144:Part1 :1996 specifies that the data should include

1. The typical dosage and details of the detrimental etTects of under­

dosage and over-dosage.

; The chemical names of the main active ingredients in the admixture

3. Whether or not the admixture contains chlorides and, if so, the

chloride iron content of the admixture expressed as a percentage mass

of cement in the mix.

4. Whether or not the admixture leads to the entrainment of air when

used at the admixture manufacturer's recommended dosage

5. Where more than one admixture is used, the compatibility of the

admixtures.

Since our suppliers go by the manufacturer's certificate it should satisfy the

conditions given above. Most of them rely on these data.

3.3 .:2 Inspection and Testing

3.3 .:2.1. Tests for cement

The most popular tests among the RMC suppliers are setting times,

and compressive strength. The tests such as fineness and chloride content are

not favorite among them and the alkali test is usually neglected.

They do not pay much attention to fineness, Chloride content & Alkali

content. The strength of hardened concrete will depend on the parameter

66

.. __

I

I

I

I

I

I

I

I

I

I

I I

II I I

• • I I

•

fineness, and the presence of Alkali and Chloride will help to create a

chemical environment which is conducive to corrosion.

Table 3. 7Ccment tests .

:;t I No.of RMCI

suppliers

i Type o

-·-·-----·--··

1 Fincne 4

1 Setting 1es-Initial setting time 7 I

'Final-~ 10 time b

7

[ Comp_r_ --·--··--··--·--·

ve strength-7 days( early strength 7 ------------ ~

7 1 28 days strength I ~· ·- -----------------+---------j

, Alkali content L , Chloride content 2 l_ ---~· J

Table 3.8- Test frequencies

--···--~ Once a 1· Once in 3 Once 111 6 Annually

I month ]months months -- -----

'! - 1 1 1 Fineness ----··-

Setting tim J 1 I 2

1 Compress '! - 1 - '

I

, strencrth b

·-~--~~----

l All~l~i- con

1

Chloride c

-t -r-- - - 2

~nt ] J 1-

___ L_ ··--·· i .

Every

shipment

3 I

·-

Results shmv that they pay less attention to the tests such as fineness, alkali

and chloride.

67

.......

I

I

I

I

I

I

I

I

• II

If they ahvays stick to one source of supplier the results are acceptable since

they satisfy the minimum requirements given in the SLS 1144:part1: 1996.

Sometimes it is not very practicable in Sri Lanka. Therefore they go for

different suppliers and sources. In that case the above mentioned test has to

satisfy with the given frequencies in order to achieve the quality.

And the other important factor is the place where these tests are performed ..

The test results can be vary depending on the facilities available.

Table 3.9 -Places where the above mentioned tests are being done.

\ company j NBRO \ ELS

' _ __ jlaboratory \ ---+-\ ~ i. Setting times \2 1 I 1 3

',!1S~reng~- 1 3 ___ 1 1 \ 1 \ 3

Alkali cm~ent ___ \_~--- \ 1 \I [2 Chloride content 1 11--~1~--t-\ -")-----+--

1 I I -

3.3 .2.2. Data from cement suppliers

Fairly high percentage has responded to the above question . • The results show that the normal procedure is to receive the data from

Ill suppliers when they receive a new batch of cement( every cement shipment).

This implies that there can be changes in between.

68

.... _.

I

I

I

I

I

I

I

I

I

II I I

II II I I

•

The data received should be reliable and it should check frequently conforms

to a British Standard or any other standard equivalent to it.

Table 3 .I 0-Types of record receive from cement suppliers

-Rcco~·d~ I Manufacturer test reports I Production dates I SLS certificate -~

' ___ I I_ _j No.or -~5 · l1 I 1

'~-~~roducers I J

Table 3 .I I The frequency of receiving the data

Frequency No. of Producers

Weekly

tthly 1

~ ------

ually I

'Ne\

I Otht

er

~r- for every shipment 6 L__

And strength varies within an acceptable range. This also will atTect the

strength variation in concrete. Since these RMC producers depend on the

data from cement suppliers, there may be quality problems.

This part is not very satisfactory. But it satisfies the minimum requirements

in general.

69

.. __

I

I

I

I

I

I

I

Almost all of them buy cement in bulk and 50% of them blow cement

directly to the silo which is in use. The others are stored in a separate silo

and used when required.

The best method is to store them separately till they are required . It

facilitates the rejection of a load of cement if is found that it does not satisfy

the stipulated conditions.

Clause 7.5.1 of SLS 1144:partl: 1996 specifies that Bins and silos of cement

shall be weather-proof and permit free tlow and efficient discharge of

cement. Each shall be capable of being cleaned out thoroughly and inspected

I internally. Each bin or silo shall be fitted with an independent regulatory

I

I

I

I

I

I

I

• • • • •

cleaned filter, or other method of dust control, sufficient to allow the

delivery to be maintained at the correct pressure and properly maintained to

prevent interference with weighing accuracy by build up of pressure. The

store shall be managed so that the cement is used in the same order as it is

delivered.

Table 3.1:2 Storage facilities for cement

Storage facility I No. or

I producers ~------- - . ,.., : 810\v directlv to the silo which is in use _) . : Stored in a separate silo and use when it requires 4

I Other

70

.._ .

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

The results show that almost all of them store cement in silos. It satisfies the

minimum requirement in cement storage.

3.3 .2.3 Tests for Aggregates

Table 3.13- Tests for Aggregates

! Typ

:.NO! i

1

Gra

of test

1inal maximum size

ing and mean size

1

silt,

1;sh~

ty or tine dust content -·~------

md surface texture

. watc

i rela r . ' 11101

r absorption ·-.

ivc density

;ture content

Sand (No. Of Metal (No. Of

RMC Supp.) RMC Supp.)

6 6

7 7 I

·----·-~ 1------- ---~

6 ')

I _)

4 5 l 5 5

5 5

·-h---· 5 -

15 -

L~-l~loride content =r 2 J

The important factor is the storage facility. The Moisture content of

aggregates will vary significantly if the aggregates are left in open air. The

presence of moisture in aggregates affects the strength of the concrete.

71

.. __

I

I

I

I

I

I

I

I

I

I

I

• II

• • • • •

Table 3. 14 - The nominal maximum size of aggregates used

1 Size I No. of RMC suppliers l ~ --------~+ ll 1

40mm ___j_ 6

[20 111111 -1--2---------~------------11 1 5mm 7 I ~--

Clause 6.5 of SLS 1144:part I: 1996 specification for Ready Mixed Concrete

describes that the nominal maximum size is 20m. From the results it is

shown that the most popular size is 40 mm, but a few of them use 20mm as

well. Fine aggregates the size is 5mm. Size of the aggregates will vary

depending on the client's requirement.

3.3.3. Storage Facilities for aggregates

Clause 7.5.2 ofSLS 1144:part1:1996 specifies that each nominal size and

type of aggregate shall be stored separately. Storage and handling shall be

arranged to avoid contamination, minimize segregation and prevent

intermingling with adjacent material. The floor shall be constructed of

concrete and measures shall be taken for drainage as well as prevention of

foreign matter. Foil owing tables shows the results obtained from the

suppliers .

72

.. __

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

Table 3.15 Storage facilities for Aggregates

~Storage_ ·- ... f No. ofRMC suppliers~ • Inashade 11 ~-~

jbpcn air J 6 I ------- - ----'------- ____j

Table 3.16 -Frequency of checking Aggregates

!frequency of checking j No. ofRMC~~~- ··-l

! ::~~~~~- .. - j ~ . ~ sht to site . j 2 .~---··-·- . '

I Daily 1 1 l I

Since Sri Lanka has only one major aggregate supplier, almost all the RMC

producers purchase aggregates from that particular supplier because he can

give large quantities. Though there is a one major supplier he may be having

different crushers. Therefore quality can change. Therefore it is advisable to

check the aggregates when purchasing is being done.

But moisture content, chloride content, silt, clay and dust content may vary

due to storage facilities provided and contamination problems.

Therefore more attention should be paid on the storage facilities provided.

But the results shows that these RMC producers do not pay much attention

to that. Therefore results are not up to the standard.

73

• ..... -

l

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

• • • •

3.3 .4. Design control

In general they use the standard mix proportions. In special cases where the

customer provides their specifications including grade, slump, water/ cement

ratio, minimum cement content etc. they them selves do the mix design and

get it approved by the head ot1ice design engineer.

Table 3.17-Design Control

~thods used No. of RMCI :M !

suppliers

lj ;tandard mix designs available 7 '--"

i

il )esign to suit customer specifications 5

3.3 .5 Control of Inspection, Measuring and Test equipments

The reliability of the batching results will depend on the age of the

plant and the frequency of calibration .

Half of the RMC suppliers use second hand plant and the rest use brand

new ones. Some of them have installed it in the recent past where as some

others have done the installation 9-10 years back .. The batching results may

vary due to the age of the plant.

And the most probable cause may be the calibration of scales. Results show

that only a fevv· of them do the calibration of scales in 6-12 months and they

are more concerned about the weighing scales. Pay less attention to

74

.. .....

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I I I

• • •

calibration of water meters and admixture dispencess. Only one RMC

supplier has indicated that they add admixtures manually. This may be a

cause for the variation in strengths.

Table 3.19- Equipment calibration

I lte1~ Year Production Frequency I Water Admixture

rate(m3/month) weighing I meters dispences

1-11997/second

hand l--

1 2 995/brand

5500

'2500

i 3

1

new

f\998/sccond -12900

scales

Less than 3 , -

months

6-12

months

Once a 1 Once a I Once

1

1

hand I I year or 1 year or 1 year

a

or

I ---c -1 ' I more 1 more +more ~- ~11 1997 /brand

1

. 1SOO ------- 6-1 ~-t_-- 6-12 --

\ new months \ +months

~ 5 I 1994/brand ~ 5000 3-6 months I 3-6 3-6 ---

1 I

·, I nevv I ____ ·

~-- 1991 /second rooo

hand \ 1-~-~--r-~-~-------T --1 7 \ 1994/second 4000 1

hand \

months months

6-12 3-6 3-6

months months months

6-12 6-12 6-12

months months months

I 6

L__ __ __L_~-·---____J _______ ___j__ _____ __L_ ___ _l_ ___ _

75

.. ....

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

II

II

II

It satisfies a few requirements given in the SLS standards but in general they

are not emphasized in maintenance and calibration of the batching plant.

Therefore results satisfy only the minimum requirements, but not the

desired quality standards.

3.3 .6 Records

Only a few of them adopt documental procedures and most of them

g1ve verbal or written instructions to the workers. There may be human

errors in verbal instruction system . This can be overcome by adopting a

\Vritten procedure.

Table 3.20- Way of giving instructions

Method of givi ng Instructions No. of RMC '---'

suppliers

'i Written r~"-­

'. Verbal

,.., .)

4 L I Both 3 ' c__ _____ --------

Document control is a very essential part in ISO 9001 requirements. The

results satisfy the minimum requirements and comply with ISO 9001 to a

certain extent.

76

.. __

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

II

II

II

II

3.3. 7. Management Responsibility

The concrete plant and the construction company arc two separate

sections coming under one organization structure in most of the RMC ~ '-

suppliers in Sri Lanka. Therefore it is very important to have review

meetings with the top management. In quality improvement top management

commitment adds a significant value. Though the problems are identified at

the plant stage, if it is not responded by the top management, no effective

action will be taken. Therefore input from the top management is very

important in the case of improving quality.

The results show a fairly good indication that most of the RMC producers

revicvv· the process at least once a month. Frequency is acceptable. Very few

are free to discuss the problems as and when necessary with the managing

director, v.ihich will give us a good impression on the commitment towards

the quality. According to ISO 900 I, the above results are satisfactory.

3.3.8. Handling non conforming products.

According to the RMC producers if the incoming material fails the specified

test requirement that particular load is rejected. For fresh concrete they

perform the test for workability. If only on customer's request, the producers

perform air content as well. If the slump is less than expected ,water is

added to the mix and remixed. If it is high , dry mix is prepared and m1x

with that in order to achieve the required slump.

77

.. _.

I

I

I

I

I

3.3 .9. Corrective and preventive action.

Results shmv that most of the RMC suppliers consider customer

complaints as a measure of performance. It is a valuable source of

information for future improvements. It involves two separate elements such

as correcting customer's immediate problem and utilizing the data for long­

term improvements. And the characteristics which is very difficult to

achieve are Early strength, 28 day strength and workability.

3.3 .I 0 Delivery

The delays in delivery process are due to traffic congestion and some

times due to low capacity of the plant, breakdowns of delivery trucks and

shortage of delivery trucks.

3.3.11. Statistical Techniques used

Table 3.21- Statistical techniques used by the RMC suppliers.

1

Quality control Technique used No.of RMC

suppliers L

, Cumulative summation charts 1 '-· Control charts 6

----~------------------~

This gives an indication that six of them use control charts and one uses

cusum charts.

78

.. __

I

I

I

I

I

I

I

3.4 The current status of RMC suppliers in Sri Lanka with respect to

standards

Following table gives a summary of the results obtained from the

questionnaire survey. First column gives eleven elements which were

considered in the preparation of the questionnaire. Column 2 gives the

number of RMC producers who satisfy the ISO 9001 with respect to these

eleven elements. Third column gives the percentage of satisfaction with

respect to the number of RMC suppliers.

Table 3.22- No. of RMC suppliers who satisfy the ISO requirements for the

I given element

I

I

I

I

I

I

I

I

I

I

I

I

: Element

-------·----~-

I .Purchasing

Cement ~--~

AI..!Yregates ~b

I Water f---- --- -- ~~ I Admixtures i

! 2.Inspection and testing

I

Cement

1-! Agorecrates ! ..__o b

-

3. Calibration

~.Records I

---·--

5. Storage and Delivery ------

No of RMC suppliers o/o

satisfy IS0900 1

4 57%

4 57%

'1 43% _)

5 70%

2 28%

4 57%

3 43%

5 70%

4 157% ---- --

79

·-·

I

I

I

I

I

I

I

I

I

I

I

I

- - ---

Process control 6.

7.( 'orrective and preventive action --~--~~-

8. )esi em control b

9.S tatistical Techniques --···~~-

10 Control of non conforming

pre ~ducts --~~----·

I I Management Responsibility

5 70% I

5 70%

5 70%

7 100%

5 70%

5 70%

80

.. __

I

I

I

I

I

I

I

I

I

I

I

I

Since only few RMC suppliers have ISO 9001 certification, the elements

\vhich are directly relevant to quality control aspects were considered in the

analysis done here. And the elements which are directly connected with the

quality system \vere excluded.

Cement and aggregates has the major influence on concrete quality. Fairly

less effect from water and admixtures to the fresh concrete properties.

Purchasing of material results show that fifty seven percent of total RMC

producers satisf)' the ISO requirements. They pay less attention to inspection

and testing of cement and aggregates which will influence the properties of

concrete. Calibration of equipments results are below fifty percent.

Since records, process control, corrective and preventive action, design

control, control of non conforming products show a fairly high percentage

of the RMC producers satisf)' the condition.

All of them use some sort of statistical technique to control the process.

In the analysis given in chapter four is based on the two techniques popular

among the RMC suppliers in Sri Lanka.

The critical areas identified from this research where quality control ts

lacking can be identified as follows.

!.Inspection and testing of raw materials

2.Calibration on measuring and testing equipment

3.Storage facilities for raw materials

I suggest that testing of raw materials should be carried out to ensure that ~~ '-./

they comply with the specifications and look at the variations within the

permissible limits. There is no attempt to assess raw materials for each

81

......

batch of concrete to permit appropriate adjustments to be made. However ,

when testing is done it is a relatively long term benefit. It is very difficult to

assess these tests at an adequate level. The other important factor is the

moisture. It is very ditlicult to achieve an exact value but the value should be

representative. In modern computer controlled batching plants the

difficulties have been overcome.

For manually operated plants frequent checking should be done.

The other important area is the calibration. I suggested to do the equipment

calibration frequently. For newly installed plants frequencies given in

QSRMC 1995 can be used. For other cases (second hand or fairly old one)

testing should be done more frequently than the earlier case depending on

the age of the plant as well as the average production rate.

82

·-·