Quality Manual Part - II

Guidelines on

Quality Control & Quality Assurance of

Ready-Mixed Concrete

Guidelines on

Quality Control & Quality Assurance of

Ready-Mixed Concrete

Quality Manual Part - II

- 2 -

Published by Ready Mixed Concrete Manufacturers Association (RMCMA) 2008. Contact: B-5, Ground Floor, Neel Shantiniketan Co-op. Housing Society, Manipada Road, Opp. Mumbai University,Kalina, Santacruz (E), Mumbai 400 098, Tel.: 91-22-26654165, E-mail: info@rmcmaindia.org Web: rmcmaindia.org Copyright 2008 Ready Mixed Concrete Manufacturers Association (RMCMA) B-5, Neel Shantiniketan CHS, Opp. Vidyanagari, Manipada Road, Kalina, Santacruz (E), Mumbai 400 098. All rights reserved. No part of this publication should be reproduced, copied and distributed in any form or by any means or stored in a data base or retrieval system without the prior written permission of RMCMA.

- 3 -

CONTENTS

Sr. No. Description Page No.

Foreword 4 Preface 6 The Quality Team 8 Acknowledgement 10 Message from NRMCA U.S.A 11 Message from ERMCO BELGIUM 12

Section I: Guidelines 1 What is Quality? 14 2 What are QA and QC? 14 3 Complexities in providing Quality Concrete 15 4 Company Information and Quality Policy 16 5 Management Responsibility and Commitment 16 6 QA-QC Plan 16 7 Sources of Materials 18 8 Monitoring Quality of Ingredients

Cement Supplementary cementitious materials Chemical admixtures Water Aggregates

19 20 23 25 26

9 Sampling and Testing of Concrete 29 10 Process Control

Upkeep of production facility Concrete mix design

31 32

11 Control Charts 34 12 Properties of Fresh Concrete

Workability Density Temperature

35 36 37

13 Properties of Hardened Concrete Strength Standard deviation Acceptance criteria

39 40 41

14 Special QC techniques Internal quality audit report Cusum system

42 42

15 Key Personnel 43

Section II: Typical example

1 Introduction 45

2 Tables and graphs 46-61

3 Bureau of Indian Standards referred in Guidelines 62

- 4 -

FOREWORD

During the past decade, the construction industry in India witnessed remarkable growth, in which the ready-mixed concrete (RMC) industry can claim to be a proud partner. Historically speaking, India missed the benefits of RMC technology for decades. It was only in the early nineties that the industry was born, but growth really commenced from the second half of the nineties. During the past few years, housing and infrastructure have remained the major expansion areas. Faster speed and improved quality of concrete have been the two major demands of these sectors. Ready-mixed concrete was the right solution for this and it was heartening to see that the RMC industry responded positively to these demands. The result was the rapid growth of the RMC industry. This industry, which was initially confined to metropolitan cities, later spread to the two-tier and three-tier cities, vindicating the fact that RMC was a right solution for different markets. Currently, it is estimated that India produces around 20-25 million m3 of concrete annually from around 400-500 RMC facilities.

The growth of the RMC industry brought in its wake certain challenges, chief amongst which was about the quality of concrete supplied by RMC plants. In this context, we are happy that the RMC industry came forward and has tried to evolve a self-regulatory framework for this. It is our pleasure to be associated with this exercise, spearheaded by the Ready-Mixed Concrete Manufacturers Association (RMCMA). The exercise involved in-depth study of the regulatory practices in different countries, choosing the best international practices, aligning the regulatory framework with the provisions in the current codes of the Bureau of Indian Standards, evolving a system of audit of RMC facilities by external auditor, developing guidelines for the quality control and quality assurance of the final product, etc. We were happy to be actively involved during all these stages and could provide guidance to the RMCMAs Quality Sub-Committee from time to time. The Quality Scheme of RMCMA is contained in two meticulously-prepared manuals, namely Quality Manuals Part I and II, which were finalized after thorough discussion and revisions. While Quality Manual Part-I incorporates an extensive Check List to be used for auditing RMC facility, procedures of audit, etc., Quality Manual Part-II contains guidelines for QA & QC of concrete, which are based on key provisions in different BIS codes. It is noteworthy that conformity with the Quality Manual-Part I through annual external audit of RMC facility is made mandatory for obtaining a RMCMA certification.

- 5 -

It is heartening to note that the regulatory framework for quality is in place, the Quality Manual Part I and II have been finalized and that audits of nearly 50 RMC facilities located in different parts of the country have been successfully completed by external auditors til l October 2008. Improvements in quality have to be a continuous process and hence the national Experts Committee would be reviewing the performance of the present Quality Scheme from time to time and would incorporate changes in its provisions, if necessary.

We are of the opinion that a good beginning has already been made and everyone associated with construction needs to support this initiative from the RMC industry. We trust that these documents will become the cornerstone of high-quality concrete manufacturing. We are confident that alignment with these documents will ensure a healthy growth of the RMC industry in India.

For and on Behalf of the National Experts Committee

Dr. A. Ramakrishna (Advisor, Larsen & Toubro Ltd.) Dr C. S. Viswanatha (Managing Director, Torsteel Research Foundation in India, Bangalore) Mr. Jose Kurian (Chief Engineer, DT & TDC, New Delhi) Dr A K Mullick (Former Director General, National Council for Cement and Building Materials (NCB), New Delhi) Mr. A. K. Jain (Technical Advisor, Grasim/ UltraTech Cement) Mr. P L Bongirwar (Former Dy. Managing Director, MSRDC, Mumbai) Mr. C M Dordi (Customer Support Group Head (West and Exports), Ambuja Cements)

- 6 -

PREFACE

The first commercial ready-mixed concrete (RMC) facility in India was set up in Pune in 1992 and was followed by establishment of similar facilities in Mumbai, Bangalore, Chennai, Delhi, etc. The growth of the construction industry, particularly the rapid expansion of the housing and the infrastructure sectors, placed heavy demand on speed as well as quality in concrete construction. This gave an impetus to the growth of RMC industry, which took roots mainly in the urban and semi-urban areas of the country. Exact data on the growth of RMC industry is not available; however, it is estimated that India produced more than 25 million m3 of ready-mixed concrete in 2007-08 from around 400-500 RMC facilities and the number has been growing continuously. The spread of RMC facilities in urban India has brought in its wake certain challenges. Since RMC is not a finished product and the quality of the final product is dependent upon a host of factors some of which are beyond the control of the RMC producers there is likelihood of a variation in the uniformity and quality of the final product. Yet, the customer needs to be provided with some sort of quality assurance about the concrete supplied. This highlighted the need of developing a framework of quality for RMC. The Ready Mixed Concrete Manufacturers Association (RMCMA), India, which was established in March 2002 and has been striving hard to bring the Indian RMC industry at par with the industries in advanced countries, has taken up this challenge. After an in-depth study of the prevailing quality systems in different parts of world, mainly from the U.S.A.,U.K., Canada, the RMCMA decided to develop a self-regulatory framework for Quality of RMC. It formed a Sub-Committee on Quality, consisting of experienced quality personnel from member companies. Further, a committee of National Experts was also set up. The Quality Sub-Committee, which worked under the guidance of the National Experts Committee and the Managing Committee of RMCMA, put in Herculean efforts to evolve Quality Scheme for RMC in India. The Quality Scheme has been developed in two parts and the details are contained in two manuals, namely, Quality Manual Part I and Part II. Both manuals have been developed after extensive deliberations in the Quality Sub-Committee and also in the joint meetings of the entire Quality Team. The drafts of the Quality Manuals Part I and II were modified on several occasions. The first part of the scheme essentially consists of an annual audit of RMC facility by an external auditor. The audit is based on an extensive Check List included in Quality Manual Part I. While developing the Check List, it was ensured that the provisions in the same meet most of the stipulations in the Indian Standard on Ready Mixed Concrete, IS 49263 (second revision) and the other relevant codes on concrete such as IS 4561, IS 91032 and many others. In fact, the requirements of the Check List, in some cases, exceed those of the codes. Thus, RMCMA certification through the external audit would provide assurance to the users that the production facilities of the certified plant conform to the requirements of the IS code. Before the Check List was finalized, mock audits of number of RMC facilities were conducted by selected members of the Quality Sub-Committee and the Check List provisions were modified after gaining practical experience. Incidentally, the Quality Manual Part I also includes the detailed procedure of audit, detailed procedure of audit, selection criteria of auditors, sample certificate, selection criteria of auditors, sample certificate, etc. It may be Emphasized that successful completion of

- 7 -

external annual audit is mandatory for obtaining RMCMA certification However, it needs to be pointed out that availability of proper plant and equipment is only one of the factors although a very vital one that controls quality of concrete. No claim is therefore made that certification of RMCMA will necessarily assure delivery of high quality concrete. The RMCMA certificate should therefore be accepted precisely for what it is evidence that a certified production facility do possess capabilities to produce quality concrete. The existence of these capabilities is likely to reduce the incidence of deficiencies in the quality of final product. The Quality Team seriously deliberated on the issue of product certification too. It was felt that quality of the product involves contractual issues between the RMC producer and his/her clients. Further, different member companies follow different quality practices and are in competition with each other on quality parameters. The Quality Team therefore felt that product quality cannot be brought under certification at the current stage; instead, it was decided that the RMCMA should develop a Guideline document on QA and QC of Concrete for its member companies. The Quality Sub-Committee prepared the draft guidelines which were deliberated in various meetings and several improvements were made based on the guidance provided by the National Experts. It is recommended that each RMC facility should prepare its own QC Manual II following the minimum benchmarks suggested in the guideline document. Such document, which incidentally needs constant updating, would demonstrate RMC producers commitment to quality concrete.

The external audits of RMC facilities of member companies commenced in March 2008 and we are pleased to inform that till October 2008, more than 50 RMC facilities from different parts of the country are successful in obtaining certification. The list of these facilities as well as the names of the auditors who audited these facilities is available at www.rmcmaindia.org. The Quality Team of RMCMA will continuously review the progress in the implementation of the Quality Scheme. It would be open to constructive suggestions and based on the feedback from field, would modify the provisions in the Quality Manual Part I and II, if found necessary. The RMCMA has developed close ties with the National Ready Mixed Concrete Association (NRMCA), U.S.A and the European Ready Mixed Concrete Organization (ERMCO). We are happy to inform that these leading world organizations are supportive of the efforts being made by the RMCMA in developing the quality scheme. We are pleased to enclose the messages of appreciation from these organizations. The Quality Team of RMCMA strongly believes that the self-regulatory quality framework initiated by the RMCMA would go a long way in improving the quality of concrete produced by RMC plants and providing assurance to customers.

For and on Behalf of Quality Sub-Committee

(Vijay R. Kulkarni) Convener, Quality Sub-Committee, RMCMA

- 8 -

THE QUALITY TEAM

National Experts Committee

Dr. A. Ramakrishna- Advisor, Larsen & Toubro Ltd. Dr C. S. Viswanatha, Managing Director, Torsteel Research Foundation in India, Bangalore Mr. Jose Kurian- Chief Engineer, DT & TDC, New Delhi Dr A K Mullick, Former Director General, National Council for Cement and Building

Materials (NCB), New Delhi Mr. A. K. Jain- Technical Advisor, Grasim/ UltraTech Cement Mr. P L Bongirwar- Former Dy. Managing Director, MSRDC, Mumbai Mr. C M Dordi- Customer Support Group Head (West and Exports), Ambuja Cements

RMCMAs Sub-Committee on Quality Vijay R. Kulkarni, Convener, Quality Sub-Committee, RMCMA Mr. Rajiv Talwar, Head QA, ACC Concrete Ltd. Dr. P. Dinakar, ACC Concrete Ltd (From inception till December 2007) Mr. Harpal Singh Sehmi, ACC Concrete Ltd (From inception till June 2007) Mr. Anuj Maheshwari- Head, Technical, Grasim Industries Ltd. Mr. S. G. Bhat, Manager QC, Lafarge Aggregate & Concrete Pvt. Ltd. Mr. Hiren Joshi., QA-QC In-charge, Lafarge Aggregate & Concrete Pvt. Ltd. Mr. S. D. Govilkar, Deputy General Manager(Technical), RMC Readymix (I)

Pvt. Ltd. Mr. Girish Bonde, Head, Technical, RDC Concrete India Pvt. Ltd. Mr. Bilal Baig, Manager, Quality, Godrej & Boyce Mfg. Co. Ltd. Mr. Awadhoot Sawant- Dy. Manager RMC, Godrej & Boyce Mfg. Co. Ltd. (From inception

till Nov. 2007) Mr. D. Mohan, Manager Technical, IJM Concrete Products Pvt. Ltd.

RMCMAs Managing Committee Mr. Ganesh Kaskar, President, RMCMA & Ex. Dir. and CEO, RMC Readymix (I) Pvt. Ltd. Mr. Hans Fuchs, Vice-President, RMCMA and Managing Director, ACC Concrete Ltd. Mr. Racy Sidhu, Vice-President, RMCMA and BU Manager-RMC, Lafarge Aggregate &

Concrete Pvt. Ltd. Mr Vivek Agrawal, .Ex. President, Grasim Industries Ltd. Mr. B K Shrikhande, Former Vice-President, ACC Concrete Ltd. ( from inception till

October 2007) Mr. Sanjay Bahadur, Former Managing Director, ACC Concrete Ltd.

(from Nov. 2007 to June 2008) Mr.Akash Gonge, Secretary, RMCMA, and General Manager (RMC), Godrej & Boyce Mfg.

Co. Ltd. Mr S.R. Kumar, Immediate Past President, RMCMA ( from inception to August 2008)

- 9 -

Mr Uday Shankar, Ex. Director, RDC Concrete India Pvt. Ltd. Mr. R Krishnachander, Vice-President-Business Development, India Cements Ltd. Mr. Balaji Moorthy, President-Marketing, Madras Cement Ltd. Mr. Prakash Menon, General Manager, IJM Concrete Products Pvt. Ltd. Mr. M A Mathew, Proprietor, MC Duramix Mr. Vijay R. Kulkarni, Principal Consultant, RMCMA

- 10 -

ACKNOWLEDGMENT

We are grateful to each member of the RMCMAs Sub-Committee on Quality for carefully scrutinizing different provisions in Quality Manual Part I and II. The provisions were thoroughly discussed in the meetings of the Sub-Committee and several modifications were made after reaching broad consensus. The help rendered by Sub-Committee members is highly appreciated and we are thankful to them for their involvement and efforts.

We are also indebted to all members of the National Experts Committee and the Managing Committee of RMCMA who have provided broad guidance on different aspects of the provisions in both manuals. They not only carefully scrutinized the provisions in the Manuals but also helped the RMCMA in finalizing its approach to the Quality Scheme by offering valuable suggestions. The RMCMA would like to record its deep sense of gratitude towards the members of the Experts Committee for their valuable guidance.

The Quality Team would also like to thank the National Ready Mixed Concrete Association (NRMCA), U.S.A., particularly, Mr. Robert Garbini, President and Dr Colin Lobo, Senior Vice-President (Engineering), for the help rendered in providing guidance on the quality practices followed by NRMCA. We are also thankful to the European Ready Mixed Concrete Organization (ERMCO) for the support rendered to us.

For and on Behalf of Quality Sub-Committee

(Vijay R. Kulkarni) Convener, Quality Sub-Committee, RMCMA

- 11 -

- 12 -

- 13 -

Section I: Guidelines

- 14 -

1. What is Quality?

1.1 The term quality has been defined differently by different experts. For example, Deming defines it Meeting the customers needs; Juran says it is Fitness for use, whereas Crosby defines it as Conformance to requirements. One more definition of quality can be Satisfaction of stated and implied needs. Quality can have separate meaning. It can have subjective meaning, when it is used to indicate elegance or luxury. Quality can be relative, when the term is used to indicate grade (e.g. 5-star hotel). It can have objective meaning when it is used to indicate a specific requirement or fitness for purpose (e.g. M30/M40 grade of concrete).

1.2 The term quality has a much wider and an all-encompassing significance when applied to any multi-dimensional activities. In the context of construction industry, quality is the slated and implied needs of the users/owners who should be assured of the required serviceability and safety, without undue maintenance but also the slated and implied needs of the client/promoters who should be assured of adequate returns on their investments. Quality in construction can be said to have been achieved if it is completed without time and cost overruns, ensuring the required serviceability, durability and safety, without undue maintenance.

2. What are QA and QC? 2.1 In the literature on quality, one would often notice the use of two terms, namely, quality control

(QC) and quality assurance (QA). In day-to-day practice, there is a tendency to use these terms imprecisely. It would therefore be appropriate to have clarity about the exact meaning of these terms..

2.2 Quality control (QC), sometimes called process control, is defined as the operational techniques and activities that are used to fulfill requirements of quality. It is the sum total of activities performed by the seller (producer) to make sure that a product meets contract specifications and requirements. QC is often confused with control testing. The basic quality control concept, as promulgated by Prof. Juran, is to control the mass and not the piece. The main problem about quality control is that it is an after event operation, designed to prevent defective items from passing through the system. What happens when a product fails? The consumers risk is that a bad batch may get accepted, while the producers risk is that a good batch may be rejected. This gave rise to the concept of quality assurance (QA).

2.4 Quality assurance (QA) can be defined as all those planned activities and systematic actions necessary to provide adequate confidence that a product or service will satisfy the given contract-specific requirements. Quality assurance provides consistency and an assurance (in the form of certified records) that the established QC procedures have been carried out in full. Thus, quality control is part of quality assurance. Within an organization, quality assurance serves as a management tool; in contractual situations, quality assurance serves to provide confidence in the supplier.

- 15 -

3. Complexities in providing Quality Concrete 3.1 As regards ready-mixed concrete (RMC), the problem of providing QA and QC becomes more

complex. This is because RMC is an unfinished product at the time of delivery. In its as sold condition, the product is perishable and will not remain in plastic and unhardened condition beyond a limited time. Construction materials like steel, aluminum, glass, etc are factory-produced finished products and the producers are in a position to control its final quality before delivery. This is not the case with ready-mixed concrete. The quality of finished concrete is affected by a host of factors such as:

variability in the quality of the different ingredients such as cement, aggregates, sand, water and mineral and chemical admixtures,

selection of ingredients which depends up on the end use and clients requirements, proportions of ingredients, a variety of process parameters, affecting homogeneity of mixing and other properties, conditions involving transportation, placement, finishing, curing and protection of concrete, variation in external environmental conditions such as changes in temperature, humidity and

wind speed, which can adversely affect the properties of concrete.

3.2 The main quality parameters of concrete are its workability, homogeneity and compactibility at pour site, 28-day compressive strength and long-term durability. Amongst these parameters, durability is indirectly controlled by adopting certain code-specified limiting norms, e.g. minimum cementitious content, maximum free water-binder ratio, minimum grade of concrete, etc (for example, Tables 3 and 5 of IS 456 2). The workability at pour site, which is usually measured in terms of slump, is affected by numerous factors and the RMC producer has to take proper precautions to maintain the desired values of slump at pour site, making use of his expertise and experience, especially when the weather conditions are harsh and there could be bottlenecks in transportation, involving long delays. The specified compressive strength of concrete cannot be verified at the time of sale, as an overwhelming majority of the contracts are based on the 28-day strengths.

3.3 Thus, providing quality concrete on a consistent basis is indeed a complex job. With a view to tide over this complexity, RMC producer needs to be committed to well-organized quality control and quality assurance systems. This Guideline document along with the interrelated document (QC Manual Part-I) provide necessary tools which can be used by RMC producers to produce quality concrete on a consistent basis. It may be mentioned here that QC Manual Part-I contains a comprehensive Check List, based on which audit of the production facility by external auditor should be organized each year through the good offices of RMCMA. Such audit, which provides assurance to the customers that the tools available with the RMC producer are capable of producing quality concrete, is mandatory to obtain certification from RMCMA. Since product quality is governed by contractual agreement between the producer and the client and each company follows different system of controlling quality of its own products, it was felt that audit based on the Guidelines suggested in the Part-II of this Manual would not be possible and hence not proposed. Yet, it is strongly recommended that each RMC facility should prepare its own QC Manual following the minimum benchmarks suggested in this document. Such document would demonstrate RMC producers commitment to quality concrete.

- 16 -

3.5 This Guideline document recommends a broad framework of QA and QC which is strongly recommended for adoption by RMC producers. It is believed that adoption of the guidelines would help RMC producers in establishing his own system that would provide assurance of his capabilities in producing quality concrete on a consistent basis.

4. Company Information and Quality Policy 4.1 The Guideline provides an opportunity for each Company to describe its background, organizational

structure, its products and services, mission statement, quality policy, etc. Thus, when preparing its own QC Manual, it I suggested that the following information may be incorporated in the same:

brief history of the Company growth trends of the Company including some its recent initiatives geographical locations of its production facilities description of products and services any additional information that the Company may perceive to be beneficial

4.2 Many companies have well-defined Mission and Vision, embodied in Company statements. It would be most appropriate to include such statements in the QC Manual. Further, many companies have a clear-cut Quality Policy. In case such policy has already been evolved, the same should be included in the QC Manual. In fact, incorporation such policy in the QC Manual would be welcomed by customers.

5. Management Responsibility and Commitment 5.1 The production of concrete having consistent quality demands involvement and commitment from

all those connected with the production process, either directly or indirectly. Quality is not merely the concern of the QC department; it is the concern of everyone involved in the process the marketing personnel who book orders and keep in touch with customers, the procurement personnel who procure different ingredients of concrete as well as equipment, production personnel involved in producing concrete as per the recipe agreed upon, and the QC team involved in testing, mix proportioning, monitoring and analyzing test results. Implementation of quality system often leads to reduction in the rate of failures, which can translate in to reduction in cost for the producer. However, for this to happen, everyone needs to be committed to quality. In particular, what is important is the commitment and willingness of the top management of the Company to maintain product quality regardless of the competitive pressures. The responsibilities of management personnel as well as their authorities should be clearly spelt out.

6. QA-QC Plan 6.1 This document suggests that each RMC production facility should establish its own QA-QC Plan, for

which these guidelines can serve as a basis. It is emphasized that the guidelines can be treated as minimum benchmarks. Different RMC production facilities certainly have the freedom to excel beyond the minimum benchmarks. In fact, if the publication of these benchmark guidelines results in the emergence of a true competitive spirit amongst different RMC production facilities, and they start competing with each other by excelling the given benchmarks, customers would be the final beneficiary.

- 17 -

6.2 It is suggested that the QC Plan should have the following elements:

o Management of the quality of ingredients: o Sources/location of different materials o Crucial tests and testing frequencies for different ingredients for monitoring their quality

o Process Control o Inspection and checking of different components of plant and other equipment and their

frequency o Concrete mix design: Data on laboratory and plant trials

o Sampling of concrete o Properties of fresh concrete

o Data on slump, temperature, density, o Properties of hardened concrete

o Data on compressive strengths of concrete at various ages; flexural strength (whenever specified)

o Acceptance criteria o Standard deviation

o Special QC techniques o Internal quality audit o Special techniques

o Key personnel: o Data pertaining qualification, experience, and training of all personnel involved in

production, quality control, marketing, etc.

- 18 -

7. Sources of Materials 7.1 RMC supplier would prefer to have the same source for the materials used in day-to-day production.

This is because a change in the source of the material may affect its properties and hence would warrant re-proportioning/redesigning of mixes, which is a time-consuming process. Therefore, RMC supplier would always try to avoid frequent changes in the sources of materials. However, a variety of factors such as shortage in the supply of materials, environmental restrictions on dredging and mining, transportation bottlenecks, abnormal increase in the cost of material from a particular source, etc. compel the RMC producer to make changes in the sources of input materials. Considering this, it would be advisable to document the sources of all ingredients used in production. In case of any quality problems, such documentation would be quite useful in tracking faulty materials sources, if any. Table 1 suggests the format for such documentation.

Table 1: Sources of different materials, and their period of use

Material Type/ Class

Source Name of Supplier/ Factory/ brand

Location

Cement

OPC 43 grade 53 grade

PPC PSC Other

Fly ash Siliceous Calcareous

Slag

Silica fume

Water

Ice

Fine aggregate River sand Manufactured sand

Coarse aggregate

40-mm down 25-mm down 12.5-mm down

Quarry fines W.R. Agent

H.R.W.R.A.

Retarder

Others

- 19 -

8 Monitoring Quality of Ingredients 8.1 Cement 8.1.1 RMC producers in India commonly use three types of cements, namely,

Ordinary Portland cement (OPC) o 43 grade conforming to IS 81123 o 53 grade conforming to IS 122694

Portland Pozzolana Cement (PPC) conforming to IS 14895 Portland Slag Cement (PSC) conforming to IS 4556.

8.1.2 Although cement is a factory-produced material, there may be variation in the properties between two consignments, even from the same factory. RMC producers usually prefer to have a long-term understanding with a particular cement producer. However, at times, they are constrained to use different brands from different manufacturers. Since the properties of the cement have close bearing on the properties of concrete, it would be appropriate to document the key physical properties of cement. Fortunately, most of the cement manufacturers do provide a test certificate on the properties on a regular basis, enabling documentation of such properties. Some RMC producers have facility for testing certain key physical properties of cement in their central laboratory. If such a facility is in use or in case RMC producers get the cement samples tested from a third-party laboratory, the results should be appropriately documented. Table 2 provides a format for such documentation. The table also includes the minimum and maximum provisions from the relevant Indian codes for the sake of immediate comparison.

Table 2: Selected physical properties of cement Property Manufacturer I Manufacturer II Manufacturer III

Date of testing Type of cement PPC OPC 53 grade PSC

Provisions of IS 14895

Test results*

Provisions of IS 122694

Test results*

Provisions of IS 4556

Test results*

Fineness, m2/kg 300 (min) 225 (min) 225 (min)

Min. compressive strength, MPa

3-day 16 27 16

7-day 22 37 22

28-day 33 53 33

Setting time, minute

Initial 30 (min) 30 (min) 30 (min)

Final 600 (max) 600 (max) 600 (max)

Soundness, mm 10 (max) 10 (max) 10 (max)

Loss on ignition, % 4 (max)

% of mineral admixture (fly ash or slag) in PPC or PSC

15-35 % fly ash

- 35-70 % slag

* Based on data from manufacturers certificate or in-house testing or testing done in a third-party lab.

- 20 -

8.2 Supplementary Cementitious Materials 8.21 RMC producers generally use the following three types of supplementary cementitious materials

(SCMs):

Fly ash, Ground granulated blast furnace slag (GGBS), Condensed silica fume.

8.22 It is well known that SCMs, possessing either pozzolanic or latent hydraulic properties, improve a host of properties of concrete, both in its fresh and hardened states. In particular, the use of these materials improves the workability and helps concrete in achieving higher long-term strength gain and improved durability leading to enhanced sustainability. However, these benefits would be achieved only when it is ensured that the SCMs possess the requisite properties; otherwise, they may just act as inert fillers. For RMC producer, the best way to ensure this is to verify as to whether the physical and chemical properties of the SCM used conform to the code-specified requirements.

While fly ash and condensed silica fume should respectively conform to IS 3812 (Part 1)7 and IS 153888, GGBS should conform to IS 12089 : 19879 and BS 6699.

8.2.1 Fly ash 8.2.1.1Fly ash or pulverized fuel ash (PFA) is a by-product from thermal power plants. Depending on the

type of coal used for burning, fly ash could either be of silicious variety (produced from bitimunous coal and having CaO < 10%) or calcareous variety (produced from lignite coal and having CaO > 10%). While finely-divided silicious fly ash has pozzolanic nature, the calcareous fly ash has both pozzolanic and hydraulic properties. However, not all fly ashes available from thermal power plants can be suitable for use in concrete. If fly ash is obtained from the same source, there will not be much variation in the chemical properties of fly ash; however the physical properties may vary depending upon the collection and separation and grinding system used. The IS 38127 has stipulated certain minimum physical and chemical requirements. RMC producer needs to ensure that the fly ash received by him has supplementary cementitious properties. It would therefore be appropriate if the fly ash supplier furnishes a test certificate along with each consignment.

8.2.1.2Before the source of the fly ash is fixed, it is essential that all the physical and chemical requirements as given in IS 38127 are complied with. Once the source is fixed, only the physical requirements of fly ash need to be monitored. Amongst the various physical requirements mentioned in Table 3, the requirement of particles retained on 45 sieve can be assessed quickly by wet sieving test. It would therefore be a good practice to carry out this test in the in-house laboratory before each consignment is accepted. It is suggested that the remaining four physical requirements, namely Blaines fineness, lime reactivity, 28-day compressive strength and soundness, should be checked once in 3 months or with the change in source.

8.2.1.3With a view to control the consignment-to-consignment variation in the quality of fly ash, IS 38127 also specifies uniformity requirements. It specifies that individual values of tests at Sr. No. 1 to 3 in Table 3 shall not vary more than 15% from average established from the tests on the 10 preceding samples or of all samples if less than 10. RMC producer should ensure that the uniformity requirements are strictly followed. The format given in Table 3 could be useful for this purpose.

- 21 -

Table 3: Physical requirements of fly ash conforming to IS 38127 and results of selected tests on samples

Sr. No.

Property IS Requirements

Frequency of test suggested by RMCMA

Sample 1 Sample 2

Date Test report Date Test report

1 Particles retained on 45 sieve *

34% (max) Each consignment

2 Blaine's fineness, m2/kg # 320 (min) 3-monthly/ change of source

3 Lime reactivity, MPa# 4.5 (min) 3-monthly/ change of source

4 28-day compressive strength, MPa #

Not less than 80% of control

3-monthly/ change of source

5 Soundness, % # 0.8 (max) 3-monthly/ change of source

* Test conducted on each consignment before acceptance # Based on data furnished by supplier by conducting tests in a third-party lab.

8.2.2 Ground-granulated blast-furnace slag (GGBS) 8.2.2.1Ground-granulated blast-furnace slag possesses latent hydraulic properties. For the use of GGBS as

a mineral admixture in concrete, no Indian code is available. However, specification for granulated slag for manufacture of Portland slag cement is available (IS 120899). It is therefore suggested that while the physical requirements of GGBS could be in accordance with BS 6699, the chemical requirements could be in line with the Indian code IS 120899. Some of the crucial properties as specified in BS 6699 and IS 120899 are given in Table 4. RMC producer needs to ensure that the supplier gives test certificate satisfying the requirements given in Table 4.

Table 4: Properties of GGBS conforming to BS 6699 and IS 120899 and results of selected tests on samples Property BS

Requirements Sample 1 Sample 2

Date

Test report*

Date Test report*

Blaine's fineness (as per BS 6691) 275 m2/kg (min)

Compressive strength, ( as per BS 6691) 7-day

28-day

12.0MPa 32.5 MPa

Initial setting time( as per BS 6691) Not less than IST of OPC

Soundness (Le-Chatellier expansion) (as per BS 6691)

10 mm (max)

Glass content (as per IS 120899) 85 % (min.)

* Based on data furnished by supplier by conducting tests in a third-party lab.

- 22 -

8.2.3 Condensed silica fume 8.2.3.1 Condensed silica fume, also known as micro silica, is a by-product of silicon and ferro-silicon

industry. It is an extremely fine material, having specific surface value greater than 15,000 m2/kg.The amorphous silica content should be more than 85%. It is a highly reactive pozzolana.

8.2.3.2 Silica fume should conform to the requirements of IS 153888, which specify the physical and chemical properties. Table 5 gives some of these crucial properties. With a view to ensure supply of good quality silica fume, RMC supplier needs to obtain test certificates from his supplier for each lot of materials that he receives and document the results in the format given in Table 5. Alternatively, it may be a good practice to send a random sample of silica fume to a third-party laboratory and cross check the results obtained with those furnished by the supplier.

Table 5: Properties of condensed silica fume conforming to IS 153888 and results of selected tests on samples Property IS 15388 8

Requirements Sample 1 Sample 2

Date

Test report*

Date Test report*

Specific surface, m2/kg 15,000 (min)

SiO2 content 85% (min.)

Pozzolanic activity index 85% at 28 days

Moisture content 3% max.

LOI 6% max.

* Based on data furnished by supplier by conducting tests in a third-party lab. 8.2.4 High reactivity metakaolin (HRM) 8.2.4.1Besides fly ash, GGBS and condensed silica fume, RMC producers can also use another SCMs,

namely high reactivity metakaolin (HRM). HRM is obtained by calcination and grinding of pure or refined clay at a temperature between 650-850O C. IS 4562 permits the use of this material as SCM. However, since no Indian standard is available on this material, it would be advisable to refer to the relevant literature on the subject and get the approval of the client/consultant about the quality of the material before use.

- 23 -

8.3 Chemical admixtures 8.3.1 Ready-mixed concrete needs to be transported over long distances and it needs to be workable to

enable proper placement, compaction and finishing. Therefore, use of chemical admixtures, which modify a variety of properties of concrete in its fresh and hardened states, becomes vital. In typical tropical weather conditions prevalent in most part of India, the commonly used admixtures are plasticizers, superplasticiser, and retarders.

8.3.2 Before selecting any brand of admixture, laboratory tests are carried out by RMC producer to establish compatibility of cement-plasticizer/superplasticiser system and also to determine the optimum dosage of admixture, initial slump, extent of slump retention with time, and compressive strengths at various ages as percent of control sample etc. Any adverse effects, e.g. abnormal slump loss, excessive retardation, increased air content, bleeding, etc., observed during these trials should be meticulously documented. Table 6 provides the format for documenting the results of laboratory trials. Incidentally, close liaison with admixture manufacturer is essential during these tests. Once the laboratory trials are over, plant trails may also be carried out. With this, the type of admixture and dosage requirements for different mixes can be frozen. Slight changes in the dosage are made by RMC producer, depending upon the conditions of placement, likely delay in transportation, etc. In case there is any change in the sources of materials, the whole exercise of laboratory trails needs to be repeated. In particular, when the source of cement is changed it may be essential to carry out compatibility trails again. The chemical admixtures used should conform to the requirements specified in IS 910310.

Cement-chemical admixture or cement-chemical-mineral admixture compatibility needs to be resolved during the selection of chemical admixture. For this purpose, help can be sought from chemical admixture manufacturer. RMC producer too can carry out certain compatibility tests (Marsh cone or mini-slump cone test) in the plant laboratory and keep the records. The latter would be useful in case certain compatibility problems are noticed.

- 24 -

Table 6: Results of initial laboratory trials* on chemical admixture Property Control

concrete Concrete with admixture Adverse effects, if any,

observed during trials Manufacturer I

Manufacturer II

Manufacturer III

Name of manufacturer Name of brand Generic type Water content, % of control sample

Slump

0 min

30 min

60 min

90 min

Setting time, minute

Initial

Final Compressive strength, % of control sample

1-day

3-day

7-day

28-day

Air content, % max over control

Observations on cement-admixture compatibility, if any

* Laboratory trials can be conducted in plant lab or in a third-party lab (in case facilities are not available in-house)

8.3.3 Admixtures are supplied in large drums. For each batch of admixture the manufacturer needs to provide certificate as per Para 10.1 and 10.2 of IS 910310, giving various properties of the material. The RMC producer should ensure that the material supplied to him matches closely with the one supplied during laboratory trails. It is quite likely that there is variation in the quality of the material being supplied from time to time. To verify this, IS 4562 recommends that the relative density of admixtures shall be checked for each batch and compared with the specified value before acceptance. This practice should be followed.

8.3.4 In addition to this, IS 910310 specifies four more uniformity tests to be carried out on admixtures, Table 7. It may be advisable to get these tests carried out by an independent laboratory and the values so obtained may be compared with those furnished by the manufacturer. IS 910310 does not specify the frequency at which the testing for uniformity can be done. The guideline document however suggests the frequency for the tests as mentioned in Table 7. A record of the test results shall be kept as per the format suggested in this Table.

- 25 -

Table 7: Uniformity requirement of admixtures conforming to IS 910310 and results of selected tests on samples Sr. No.

Uniformity test Requirements as per IS 910310 Suggested frequency

Sample 1 Sample 2

Date Test report

Date Test report

1 Relative density Within 0.02 of the value stated by the manufacturer

Every batch/ consignment

2 Dry mat. content of admixture

Liquid

Solid

0.95 T DMC 1.05 T where, T = Manufacturers stated value in % by mass DMC= Test result in % by mass

Each new batch before acceptance

3 Ash content 0.95 T AC 1.05 T

where, AC= Test result in % by mass

-

4 Chloride ion content Within 10 % of the value or within 0.2 %, whichever is greater as stated by the manufacturer

Each new batch before acceptance

5 pH 6 (min.) Each new batch

Note: While the test at Sr. No. 1 can be done on each batch/consignment of admixture, the remaining tests mentioned at Sr.No. 2 to 5 can be done in a third-party lab by the supplier and results furnished to RMC producer. 8.4 Water 8.4.1 Water used for mixing shall be potable in nature and free from oils, acids, alkalis, salts, sugar,

organic materials or any other substances that may be deleterious to steel or the concrete. Permissible limits of impurities in water are specified in IS 4562 (Table 8). Mixing and curing by sea water is not recommended because of the presence of harmful salts in sea water.

Table 8: Permissible limits for solids and results of tests on samples of fresh and recycled water

Sr. No.

Solids Permissible limits as specified in IS 4562, max., mg/l

Fresh water Recycled water Sample 1 Sample 2 Sample 1 Sample 2

Date

Test report

Date Test report

Date Test report

Date Test report

1 Sulphates as SO3 400 2 Chlorides as Cl

Reinforced concrete

500

3 pH Not less than 6 4 Organic 200 5 Inorganic 3000 6 Suspended matter 2000

Note: While the tests mentioned at Sr. No. 1, 2 and 3 can be done quickly at plant with the help of a ready-made kit, the remaining tests (Sr.

No. 4, 5 and 6) can be done in a third-party lab at the frequency suggested in IS 49261

- 26 -

8.4.2 IS 49261 specifies different testing frequencies for mains water and non-mains water. For mains water, the code specifies that testing should initially be done weekly, till six results are obtained, after which testing can be done at three-month interval. For non-mains water, once the source is found satisfactory, testing frequency should be on annual-basis, provided that the chloride ion content does not exceed 0.01%; if the value exceeds this limit, the interval of testing shall be reduced to three-monthly interval.

8.4.3 The use of recycled wash water needs to be encouraged from sustainability perspective. However, RMC producer needs to ensure that concrete having satisfying performance is produced with recycled water and that the permissible limits of total chloride and sulphate contents are not exceeded. Incidentally, the test on sulphate and chloride contents and pH can be conducted quickly with the help of a ready-made kit. Other tests (organic, inorganic matter and suspended matter) can be done in a third-party lab at the frequencies suggested in IS 49261.

8.4.4 It is suggested that documentation of test results on water should be as given in Table 8.

8.5 Aggregates

8.5.1 Aggregates, which occupy nearly 70-80% volume of concrete, need to be strong, clean, and durable. RMC producer needs large volumes of aggregates on a daily basis. Quite often, he has to depend upon more than one source of aggregates. Before selecting these sources, it is essential to conduct all routine tests on aggregates as specified in IS 38311 for ensuring quality. In addition, certain important properties of aggregates need to be monitored on a continuous basis. IS 49261 suggests testing frequency for different tests on aggregates in Annex B.

8.5.2 The basic properties of aggregate related to its mineralogical composition such as crushing value, impact value, abrasion value, soundness, potential alkali-aggregate reactivity, etc will not change much if the aggregate source is the same. Before selecting the source, all these properties are verified. RMC producers should maintain a record of such properties of aggregates obtained from different sources by getting the tests conducted in third-party lab at frequencies suggested in IS 49261. Table 9 suggests a format for such documentation.

8.5.3 Quite often, variations are likely in certain other properties such as particle size distribution, moisture content, silt content, water absorption, etc, which are related to techniques used in aggregate processing and external factors. Drawing on the experience and practice followed by some of the leading RMC producers, Table 10 suggests certain frequency of testing for these properties of aggregates. It can be seen from this table that some of the suggested frequencies are stricter when compared with those stipulated in IS 49261. All these properties of aggregates have direct bearing on some crucial properties of concrete, justifying strict frequency of testing.

- 27 -

Table 9: Physical properties of aggregates Property Frequency of

testing as per IS 49261(Low test rate)

Permissible limits, if any, as specified in IS 38311

Sample 1* Sample2*

Date

Test report

Date Test report

Impact value As specified - Not more than 30 for wearing surfaces - Not more than 45 for non-wearing surfaces

Los Angles abrasion value

Yearly/ Source change

- Not more than 30 for wearing surfaces - Not more than 50 for non-wearing surfaces

Soundness Yearly/ Source change

Chloride content Six monthly Potential AAR 5 Yearly/

Source change

* Based on tests conducted in-house or in a third-party lab.

Table10: Additional physical properties of aggregates

Property Test frequency suggested by IS 49261

Test frequency suggested by Guideline

Sample 1* Sample 2*

Date

Test result

Date Test result

Gradation Monthly Weekly or source change

Moisture content Daily twice (three times in monsoon)

Silt content for fine aggregates

Monthly Each lot

Water absorption 3 monthly Once in month; or source change

Particle density, 3 monthly 3 monthly Bulk density 6 monthly 6 monthly Flakiness 6 monthly 6 monthly Chloride content 6 monthly 6 monthly

* Based on tests conducted at plant lab.

8.5.4 Control on aggregate gradation: It is well known that aggregate grading has an impact on workability, strength and some other properties of concrete. Since RMC producers are constrained to depend upon more than one source of aggregates there is likelihood of a variation in the particle size distribution. The variation would especially be more pronounced in the particle size distribution of river sand. The Guideline therefore recommends weekly check on grading.

- 28 -

Table 11: Particle size distribution of all-in-aggregates and limits specified in IS 38311

IS sieve size Cumulative % passing for Cumulative % passing for all-in-aggregate

IS 38311 limit

20 mm 10 mm

River sand Crusher fines

Proportion of aggregate in the mix, %

36.00 12.00 31.00 21.00

40 mm 100 100

20mm 95 100

4.75 mm 30 50

600 10 35

150 0 6

8.5.4.1 With a view to verify the extent of variation in particle size distribution, it may be appropriate to carry out the sieve analysis test weekly and record the data of cumulative percentage passing for all-in-aggregates used for the main concrete mixes (for example, M20, M25, M30, M35, M40 etc.) supplied from the plant. The readings may be compared with those of the all-in-aggregate grading limits stipulated by IS 38311. Table 11 shows a typical format for recording the results of sieve analysis. Documentation of such data would be useful in tracking any large variation. If such a variation is evident, suitable corrections may be introduced in the proportions of different aggregate fractions and simultaneously the suppliers may be alerted to rectify supply.

8.5.5 Moisture content: Considerable variation is usually observed in the moisture content of river sand and crushed fines. Such variation in moisture would affect the water-binder ratio and hence strength, if appropriate corrections are not made from time to time in the water content of the mix. This would be possible if these properties are monitored regularly in accordance with the frequency of testing suggested in these guidelines. It is suggested that moisture content in fine aggregates and crushed fines should be monitored two times in a day, and the frequency may be increased to three times in monsoon. Once the moisture contents are known, appropriate correction may then be made in the water-binder ratio. It is essential to keep records of the data on moisture content, possibly in the form of an Excel table or a run chart

8.5.6 Silt content: The Guideline recommends that silt content in fine aggregates should be assessed for each lot of supply. River sand is particularly prone to have silt beyond permissible limits. Lots having excessive silt content should be rejected. Control on silt content is essential as an excessive proportion of the same may adversely affect the workability and strength of concrete. It is essential to keep records of the data on silt content. Again, this could be in the form of an Excel table or a run chart.

- 29 -

9. Sampling and testing of concrete 9.1 Incorrect sampling would adversely affect the results of testing; hence, extreme care should be taken

in sampling. It is imperative that the sample of concrete taken from delivery vehicle is representative. The point and time of sampling shall be at discharge from the suppliers delivery vehicle or from mixer to the site or when delivered into the purchasers vehicle. As per Annex C of IS 49261, on reaching the point of placement, the truck should re-mix its contents and allow at least the first one third of a m3 to be discharged before any samples are allowed to be taken. Four incremental samples from the remainder of the load should be then taken, avoiding the last m

3 of concrete. Then

the composite sample should be thoroughly re-mixed either in a mixing tray or in the sampling bucket and the required testing should commence only after this. A typical sample report is shown in Table 12. The report provides the time history, sampling location, truck and ticket Nos, etc. The properties of concrete in its fresh state such as slump, unit weight as well as number of cubes made should be recorded. Although filling slump cone and preparing test cubes are fairly simple procedures, the operator needs to follow the procedures meticulously. It is observed that errors in the procedures often adversely affect the test results. It is therefore essential to record the name and signature of the person involved in conducting the tests. The operators involved in carrying out these tests should be trained supervisor, Incidentally, a record of other parameters such as ambient temperature, concrete temperature can also be made in the report.

Table 12: Typical sample report of fresh concrete

Name of Company: ____________________

_____________________________________

Location: ______________________________

Name of client/project: __________________

Date: _________________

Truck No.: ______________

Ticket No.____________

Total quantity:________m3

Time history

Time batched: ___________ Time arrival at job site: _______ Time discharged: _________ Time sampled: _______ Time tested: _______

Sampled at:

End of chute End of pump hose Others

Ambient temperature: ________0C

Concrete temperature: ________0 C

Slump:_________mm

Unit weight: ___________kg/m3

No. of cubes made: __________

Cubes stored at: _____________

Cube prepared by: Mr.____________

Name of authorized person: Mr.___________

Signature: ____________________

- 30 -

9.2 IS 49261 suggests that sampling may be carried out jointly by the purchaser and the supplier with its frequency mutually agreed upon. The code further states that unless otherwise agreed between the parties involved, the minimum testing frequency to be applied by the producer in absence of recognized ready-mixed concrete industry method of production control, should be one sample for every 50 m3 of production or every 50 batches, whichever is the greater frequency. Table 13 recommends the frequency of sampling for different tests such as slump, compressive strength, density, temperature, etc. Air-entrained concrete is rarely specified in India; however, in case it is supplied, it would be essential to test air content of concrete. In many contracts, the frequency of sampling is stipulated. If the stipulated frequencies are different than what has been shown in Table 13, the former should govern. The size of the sample should generally be not less than 0.035 m3 when it is to be used for strength test. Smaller samples can be taken if used for routine slump tests.

Table 13: Frequency of sampling

QC Test on concrete Frequency

Slump Minimum of one sample for each 50m3 or every 50 batches

Compressive strength

Minimum of one sample (3 test cubes) for each 50m3 or every 50 batches for test at 28 days.

Additional sample for early age (3, 7 days) strength test, as mutually agreed

Density As agreed with customer Temperature/Air content As agreed with customer

9.3 Slump and compressive strength of concrete are two critical parameters to judge concretes quality. Carrying out slump test and preparation of compression test specimens are fairly simple procedures; however trained operators are needed to ensure that correct procedures are followed. As regards strength test, it is important to follow standard procedures described in IS 119912 and IS 51613 meticulously for making, curing and testing cube specimens. Any deviation from the procedures may adversely affect the final results, highlighting the need to employ trained operators for conducting the tests. Test cubes which are made from fresh concrete are very sensitive to method of handling and storage conditions during the fist few hours. The test specimens shall be stored in moist air of at least 90% humidity and at a temperature of 27 2OC for 24 hours from the time of addition of water to dry ingredients. The specimens shall then be marked and removed from moulds and submerged in fresh and clean water, the temperature of which shall be maintained at 27 2OC. It is essential to employ trained operators for ensuring that adequate precautions are taken during sampling and testing of specimens.

- 31 -

10. Process Control 10.1 In addition to ensuring appropriate quality of the input materials in accordance with the guidelines

described above, it is essential to exercise strict control on the production process. This can be done in two ways; firstly by ascertaining that the plant and equipment used are in good operational conditions and secondly by ensuring that sufficient efforts are taken in carrying out design of each of the concrete mixes to be supplied, following well established methods/norms.

10.2 Upkeep of production facility

10.2.1 RMCMA certification through a third-party audit certainly provides guarantee to the user that the certified production facility possesses capabilities to produce quality concrete. This certificate is however based on the commitment provided by the producer that he would adequately maintain the production facility in accordance with the provisions of RMCMA Check List (QC Manual Part-I). The producer can demonstrate this by carrying out routine maintenance of storage, handling, batching, mixing and transporting equipment as well as through regular calibration of weighing equipment at desired frequency and keeping a proper record of the same. Based on the practices followed by some of the leading RMC producers, Table 14 gives the suggested frequencies of maintenance/calibration checks for different components of plant and equipment. It may be mentioned that the frequencies suggested in this Table are either similar or stricter than those prescribed in IS 49261.

Table 14: Production control: Suggested frequencies of inspection, maintainance/calibration Items Check for Frequency

prescribed by IS 49261

Frequency prescribed by RMCMA

Plant inspection

Observation of operator, if any

Date Operator name and sign

Date Operator name and sign

Cementitious materials

Visual Inspection for weather-tightness and leaks

Weekly Weekly

Aggregate stockpile Visual Inspection for segregation and contamination

- Daily

Conveyor belts and rollers

Visual Inspection for wear and alignment

Weekly Weekly

Central mixer Visual Inspection of blades and built up

Weekly Daily

Trucks Visual Inspection of blades and built up

Weekly Weekly

Scale calibration for all weighing and measuring equipment

1.Mechanical/knife edge systems 2.Electrical/ load cell systems

2 monthly 3 monthly

Monthly Monthly

Water meters Calibration Monthly Monthly Admixture dispensers

Calibration Monthly Monthly

Gear boxes and oil baths

Oil change Quarterly Quarterly

- 32 -

10.2.1 It is essential that proper records of routine maintenance and calibration are kept by RMC producer. The records need to be updated on a regular basis. With a view to ensure accountability, it would be a good practice to include the name and dated signature of person carrying out inspection and calibration (see Table 14).

10.3 Concrete mix design

10.3.1 In India, a majority of concrete supplied by RMC producers would fall in the category of designed mixes. Most of the clients specify their requirements of workability and strength along with the requirement of pumping or otherwise. A responsible RMC producer usually ensures that the code-specified durability requirements (in terms of minimum cement content, maximum free water-cement ratio, etc.) are met with. Sometimes, durability requirements and the allowable maximum size of aggregate are specified by certain clients. Based on these requirements, the RMC producer carries out mix design in his (or third-party) laboratory, involving casting and testing trial concrete mixes and optimizing the mix proportions. It is quite likely that the RMC producer has supplied mixes with similar design earlier, in which case the producer can furnish actual field data. The details of the finalized mixes are furnished to the client, who is required to approve the same before supply can commence.

10.3.2 It is suggested that the details of the designed mixes should be maintained in a standard format as given in Table 15. These details should be furnished to the client on demand. The format is adopted from Annex D of IS 49261, which has been slightly modified to suit the requirement of these Guidelines. Besides the contents of cement and mineral additives, and free water-cement ratio, the Table also contains information on slump at pour site as well as certain additional desirable information. Separate data sheet may be kept for separate clients and for separate sites of the same client or different clients.

10.3.3 While the RMC producer is free to adopt any rational method of designing concrete mixes, it would be a good practice to adhere to the various code-specified requirements, especially those related to durability of concrete (minimum cementitious content, maximum free water-binder ratio, etc.).

- 33 -

Table 15: Concrete mix design information Name of RMC Producer: _____________________________________________________ Name of Client/Contractor:___________________________________________________ Site: ____________________________________________________________________ Mix code

Characteristic strength, N/mm2

Target strength, N/mm2

Minimum cement content, kg/m3 (if specified)

Mineral additives, kg/m3

Pulverized fuel ash Slag Silica fume Others (mention type)

Cement type and grade

Nominal maximum aggregate size, mm

Maximum free water-binder ratio

Aggregate/cement ratio

Target workability at plant, (Slump, mm)

Target workability at site, (Slump, mm)

Maximum temperature of concrete at the time of

placing

Class of sulphate resistance

( if applicable)

Exposure condition ( if applicable)

Class of finish ( if applicable)

Mix application

Method of placing

Any other requirements (if applicable)

Laboratory compressive strength, MPa

7-day

28-day

Source: Adapted from IS 49261

- 34 -

11.0 Control Charts 11.1 There is an inherent variability in the properties of various concrete ingredients, in the production

process and the testing procedures. Although RMC producers take maximum possible care to minimize variability, the same cannot be avoided. It is however important to quantify the variability and also to identify as to whether it can be attributed to the materials, the production process or the test methods. The variability could be due to chance causes or assignable causes. While chance causes can be attributed to the normal variability of the process, assignable causes can be eliminated or minimized, thereby reducing the overall variability.

11.2 Control charts can be useful in detecting and monitoring the variability. Such charts can also be useful in distinguishing chance causes from assignable causes and therefore, they can be used to decrease variability by eliminating the latter. The charts can also form a permanent record of quality. Additionally the charts can also be used as a basis for changing specification limits, if found essential.

11.3 The guidelines strongly recommend use of control charts to monitor QA and QC of concrete.

- 35 -

12.0 Properties of Fresh Concrete 12.1 Workability of concrete

12.1.1 Workability is a broad term which encompasses a range of properties of fresh concrete such as consistency (fluidity), mobility (ability of concrete to move around the reinforcement and in restricted areas), compactibility, finishibility and pumpability (for pumped concrete). Evaluating workability is therefore not easy in view the composite nature of the property. The degree of workability varies depending upon the type of construction and method of placing, compacting and finishing. The IS 4562 provides guidance on the range of workability requirements for different placing conditions and applications (Table 16). Consistency of fresh concrete is considered to be a close indication of its workability and slump test has been the most widely used test for ascertaining consistency and hence workability. However, the IS 4562 suggests that slump test is preferable only for slumps varying from 25 mm to 150mm. For applications requiring very low slumps (lower than 25mm), the code recommends use of compacting factor test. Similarly, for applications requiring very high slumps (higher than 150mm) it recommends use of flow table test. For a majority of concrete supplied by RMC producers, slump test is the most commonly-used test.

Table 16: Degree of workability for different working conditions

Placing conditions Degree of workability Slump, mm

Blinding concrete; Shallow sections; Pavement using pavers

Very low Use compacting factor test as per IS:119912

Mass concrete; lightly reinforced sections in slabs, beams, walls, columns; floors; hand placed pavements; canal linings; strip footings.

Low 25-75

Heavily reinforced sections in slabs, columns, beams, walls; slip-form work; pumped concrete

Medium 50-100 75-100

Trench fill; In-situ piling

High 100-150

Tremie concrete Very High Use determination of flow test as per IS: 910310

Source: IS 4562

12.1.2 The IS 49261 specifies the following tolerance limits of workability as criteria for acceptance:

Slump: 25 mm or 1/3rd of the specified value whichever is less Compacting factor: 0.03 for specified value 0.9;

0.04 for specified value 0.9 0.8 0.05 for specified value 0.8

Flow test: Acceptance criteria to be established between the supplier and purchaser. 12.1.3 The test for workability needs to be performed upon discharge from producers delivery vehicle

on site or upon discharge into the purchasers vehicle. On some occasions, lack of preparedness on the part of purchaser at construction site may result in delay of placement. RMC producer will

12.1.4

Fig 1

12.2 12.2.

12.2.2

12.2.

be responstarting frstates that

4 Slump tesmuch speenvironmof evapormineral agood practypical excontrol ex

Typical vari

Density o1 The plast

2450 kg/mamount oaggregatereducing t

2. Ready midetermineplastic delikelihoodvariety ofexcavatiomixes, losmonitored

3 While carthe theoreowing to process, it

nsible for marom arrival ot the respons

st is somewhecified and ental and otration, chandmixtures octice to recoxample is shxercised by R

iation in the

of concrete tic density (m3. It variesf entrapped

e and water the cement p

ixed concreted by dividiensity of cod of a discref reasons fon, miscalculss of entraind regularly.

rrying out metical densitminor adju

t would be a

aintaining thof transit misibility for de

hat a crude accepted m

ther factors snges in grador otherwise,ord the valuehown in FigRMC produc

slump of a p

(unit weight)s dependingand entrainand cemen

paste would

te is measureng the total oncrete deteepancy in thor this discrlations in for

ned air, etc. S

mix design, thty. Howeverstments thata good pract

- 36 -

e slump withixers at job selay passes o

measure ofmethod. Slumsuch as concding, batch , variation ines of slump g 1. Such gcer in contro

pumpable mi

) of conveng upon the vned air (if aint contentsincrease the

ed on the baweight of a

ermined in e concrete o

repancy. Therm volume,Such differen

he plastic der, since thert the RMC ice to measu

hin the permsite. Howeveon the purch

f workabilitymp of conccrete tempermass diffe

n air contenin Microsof

graphs wouldolling the var

x (specified v

ntional normvariation in ir-entrainingin the mix density of c

asis of volumall batched accordance

ordered and ese include deflection o

nce can be r

ensity of dee is a likeliproducer is

ure the plasti

missible ranger, after 30 m

haser.

y; yet it is qcrete is quitrature, ambi

erences, admnt, variation ft Excel formd be useful riation in wo

value: 100 m

mal-weight cthe density

g agents are . Increasingconcrete.

me. The volumaterials by

e with IS 1that actuallywastage an

or distortionseconciled if

signed mix hood of a crequired to

ic density at

ge for a periominutes, the

quick and hete sensitive ient temperamixture dosain testing, emat and drain ascertain

orkability.

mm)

oncrete variof differentused), the m

g the aggreg

ume of freshy the averag119912. Somy supplied. T

nd spillage os of forms, s

f plastic dens

is measuredchange in th carry out it regular inte

od of 30 mine IS 49261 cl

ence remainto a varie

ature, surfaceage, presencetc. It wouldaw a run chaning the lev

ies from 22t ingredientsmaximum sigate volume

h concrete cage unit weigmetimes, theThere couldof concrete, settlement osity of concr

d and talliedhe plastic dein the produerval so as en

nutes, learly

ns the ty of e rate ce of

d be a art. A vel of

50 to s, the ize of e and

an be ght or ere is d be a

over of wet rete is

d with ensity uction nsure

12.2.4

Fig 2

12.3

12.3.

that the qua containethat volumavailable delivery.

4 Many RMbefore tescubes by shows a tycertain cuthe corresdensity, th

Typical vari

Temperat

1 In most pmeasures lead to rafinishibilitimes, beadverse eprecautionhydrationand curinmix usingfor reducicovered todown the temperatulimit on th

uantities super of knownme by folloat the plan

MC producesting them fowater displaypical variat

ube compresssponding cuhe low value

iation in den

ture of conc

arts of Indiaassociated w

apid loss ofity, and craccomes a po

effects of honary measur, contractor

ng of concretg a combinaing the heato avoid diretemperature

ure of mixinghe temperatu

pplied matchn volume wiowing procednt, it would

ers prefer tofor compressacement mettion in the csive strengthube sampleses could be a

sities of cube

crete

a, tropical wewith hot wef workabilitcking of conoint of dispot weather, bres. While tneeds to takte. As far as

ation of OPCt of hydratioect exposuree. Some RMg water duriure of concre

- 37 -

h orders. Theith fully comdures detailbe a good

o measure thsive strengththod and divcube densitiehs show low s; if the denattributed to

es

eather prevaeather concrety, acceleratncrete owingpute betweenboth RMC the RMC prke a number s RMC prodC and supplon. In additie to sun and MC producer

ng hot summete at pour. D

e plastic denmpacted coned in IS 11practice to

he densities h. This can sviding the mes taken from

values, it wnsities of th

o operators s

ails, necessiteting practicted stiffening to plastic n RMC proproducer anroducer neeof well-esta

ducer is conementary ceion, the aggwater shoul

rs use chillemer months. During hot w

nsity measurcrete and tak9912. In cas

o weigh tran

of cubes (hsimply be do

mass of cubesm the record

would be advhe cubes aresampling err

ating adoptices. Absence

ng of concreand/or therm

oducer and nd the contrds to designablished precncerned, he nementitious gregate stockld be sprink

ed water or Many consu

weather cond

rement can bking the mase a weigh nsit mixers

hardened coone by findins in air by thds of a RMCisable to chee lower tharors.

on of adeque of adequaete, poor comal shrinkagcontractor/c

ractor need n a mix havcautions in pneeds to desmaterials or

kpiles in thekled on the sice flakes toultants/clienditions, it is

be done by fass of concrebridge facilbefore and

oncrete densng the volumhis volume. F

C facility. Ineck the densan the theor

ate precautioate measuresompactibilityge. The latt

clients. To ato take adeving low heplacing, finisign the conr blended cee plant shoustockpile to o bring downts stipulate u

always advi

filling ete in ity is after

sities) me of Fig 2

n case ity of etical

onary s may y and ter, at avoid quate

eat of shing

ncrete ement uld be

bring wn the

upper isable

- 38 -

to keep the temperature of concrete low. This guideline recommends 350C as the upper limit of temperature of concrete at pour.

12.3.2 It would a good practice to monitor and record both the ambient and concrete temperatures during pour. The recording of temperatures could be in the form of a run chart (see Fig 3). Such chart would give quick idea about the extent of variation of pour temperature and would be useful in the evaluation of the possible reasons for plastic shrinkage and/or thermal shrinkage cracking, if such cracking is witnessed. Such records would also be providing assurance to customers about the producers ability to control concrete temperature.

Fig 3 Variation in temperature of fresh concrete

12.4 Air content of fresh concrete 12.4.1 In most parts of India, freeze-thaw conditions do not prevail; therefore it is not necessary to use

air-entrained concrete. However, in certain places in northern and north-eastern part of India, if it becomes essential to use air-entrained concrete to counter the effects of freeze-thaw conditions, it would be essential to measure and monitor the air content in concrete.

13 13.1

13.1.

13.1.2

13.1.

13.1.4

Fig 4

Propert Strengt

1 Strengthstructuracompresis the siFurthermbond strestablish

2 While thtoo longlong alsstressing

3 To overallow reuse 7-dahoweverparticula

4 A typica

chart shstrength idea abo

Typical variat

ties of Hardth of concre

h of concreteal attribute assive strengthingle most amore, many rengths, cahed.

he strength og for RMC po for contrag concrete, o

rcome this, uemedial actioay, 3-day or r important ar cementitio

al chart dephows that the

of 25 MPa.out the variat

tion of 7-day a

dened Concete

e is used as and a measurh of the cub

acceptance pproperties o

an be deduce

of concrete aproducer to

actors and spor to continu

use is madeon to be takeven 1-day to establish

ous and aggr

icting the ve actual 28- Documentation in streng

and 28-day str

- 39 -

crete

a basis for are of develoes made, cur

parameter. Tof concrete sed from com

at 28 days hawait for tak

pecifiers to we with furthe

e of the relaen quickly. strength as

h the relationregate combi

variation in 7-day strengthation of comgth values at

rengths of M2

acceptance inopment of hyred and teste

This is becausuch as elastmpressive str

as emerged aking action twait for takier constructi

ationship betFor exampla tool to est

nship betweination in us

7-day and 2hs of concre

mpressive stret a glance.

25 concrete

n civil enginydration. In ed at 28 daysuse testing otic modulusrength, after

as a basis foto rectify prng decisionsion.

tween early-e, RMC protimate the lien early-agese, and to mo

28-day strengete samples ength data in

neering conta large majos in accordanof strength i, flexural strr appropriate

r contract sproduction prs for removi

-age and 28oducers and ikely later-age and 28-daonitor the rel

gths is showare more th

n such a form

tracts. It is bority of contnce with IS s relatively rength, sheae correlation

pecificationsroblems. It iing forms or

-day strengtcontractors ge strengths

ay strengths lationship.

wn in Fig 4han the specmat gives a

both a tracts, 51613 easy.

ar and ns are

s, it is is too r pre-

ths to often . It is for a

. The cified good

- 40 -

13.2 Standard deviation

13.2.1 For the effective implementation of QA-QC programme, two main tasks before any RMC producer are: avoidance of failures and attainment of low variability in the test results. While every RMC producer would like to keep a reasonable margin of safety to avoid failures, he would also like to have the margin to be as low as possible, so as to achieve economy in production. For designed mixes, the target mean strength is kept higher than the specified strength by a certain design margin as given below:

Target strength = specified strength + k s (design margin) where,

k = a constant which depends upon the proportion of results permitted to be below specified strength

s = standard deviation. 13.2.2 In most of the contract specifications in India, the permissible percentage below which no

results are expected to lie is generally taken as 5 %. The k value derived mathematically from statistical tables for 5% failure rate is 1.64. While designing concrete mixes, when no initial data is available, code-specified values of standard deviation which are dependent on the degree of control at site as well as the grade of concrete are taken in calculations (Table 8 of IS 4562). When more than 30 strength test results are obtained, the actual standard deviation is calculated for each mix and compared with the assumed values. Higher standard deviation indicates lower levels of controls. The stricter the QA-QC at the plant, lower will be standard deviations.

13.2.3 Thus, monitoring and controlling the variation in standard deviation of compressive strength of concrete mixes could be a crucial parameter in the QA-QC of concrete. The Guideline therefore suggests that standard deviation of major concrete mixes supplied by the RMC facility should be evaluated and monitored on a regular basis. However, the standard deviation should be calculated for a minimum of 30 results.

13.2.4 The standard deviation of M20, M30 and M40 concrete mixes from a RMC facility for three consecutive months is shown in Fig 5.

Fig 5 Actual standard deviation of major mixes from a typical RMC facility

0

2

4

6

June July Aug

Stan

dard

dev

iatio

n, M

Pa

Month

M25 M30 M40

13.3

13.3.

Table

Spec

o

Source 13.3.2

Fig 6 Of 4 n

13.3.

Acceptan

1 The IS 4shall be met:

e 17: Charac

cified grade

M 15 or above

e: Table 11 of IS

2 Typical overlappchart anwould bno singl30 test r

Variation ofnon-overlapp

3 It wouldprepare

nce criteria

4562 providedeemed to

the metests co

cteristic comp

Mean of the grtest results, N/ fck + 0.825 xoff to nearest 0 Or fck + 3 N/m

S 4562 (amendme

variation inping consecund the same e easy to ime test result esults fulfill

f 28-day strenping consecu

d be a goodcharts simila

for compre

es guidance comply with

an strength omplies withpressive stren

roup of 4 non-o/mm2 x established stan0.5 N/mm2)

mm2, whichever i

ent 3 of August 2

n the 28-dayutive test recan serve a

mmediately idfalls below s the accepta

ngth of concutive test resu

d practice to ar to those in

- 41 -

essive streng

on the acceh strength re

determined h the approprngth complia

overlapping cons

ndard deviation

is greater

2007)

y strength asesults can beas record. Adentify any sthe limit of ance criteria

rete along wults.

feed the 28n Fig 6 for th

gth

ptance criterequirements

from any grriate limits oance requirem

secutive In

(rounded (

s well as thetter be montypical char

shortcoming( fck 3) (22

a set by IS 45

with the varia

8-day comprhe important

ria. Accordiwhen both

roup of four of column 2 ment

ndividual results,

( fck 3) N/mm2

he mean valunitored withrt is shown

g in the test rMPa). Thus562.

ation in the m

ressive strent concrete m

ing to the cothe followin

non-overlapin Table 17;

s, N/mm2

ues of a groh the help of

in Fig 6. Frresults. For e, it can be co

mean

ngth data in mixes supplie

ode, the conng condition

pping consec;

oup of four f an Excel-brom this graexample,in Foncluded tha

Excel sheeed by the pla

ncrete ns are

cutive

non-based aph it Fig 6, at the

et and ant.

- 42 -

14.0 Special QC Techniques In addition to whatever has been recommended above, RMC producers are free to adopt special

quality control techniques in their day-to-day work. In fact, one should welcome and encourage such efforts on the part of RMC producers. Some such techniques include: internal audit, Cusum technique, failure analysis.

14.1 Internal quality audits report

14.1.1 Many leading RMC producers have developed rigorous internal quality norms and follow well defined practices to monitor and control quality of input and output materials. In some of these companies, there is a systematic procedure of reporting quality parameters within the organization. Quite often, these reports may contain some cost-sensitive information. It is suggested that after filtering out commercially-sensitive information, the remaining information may be incorporated in the quality document and the same may be shared with the customers.

14.2 Cusum technique

14.2.1 The Cusum technique which was developed in 1960s, was applied to RMC in the 1970s. It became a widely-used technique in RMC in the UK and many other countries. The British Standard, BS 5703, published a guide on the technique in 1980 and the Quality Scheme for Ready Mixed Concrete (QSRMC), UK, adopted it in 1984.

14.2.2 The essential principle is that differences between results and their target values are calculated and added cumulatively to form a cumulative sum (cusum). When this cusum is plotted graphically against the sequence of results, a visual presentation of trends relative to the target level is produced.

14.2.3 The Cusum system can be used for monitoring trends in mean strength, standard deviation and the relationship between early-age and 28-day strengths. It assists in detection of changes in these properties and indicates when action should be taken to increase the probability of meeting the specification or to reduce the materials cost.

14.2.4 There are following three types of cusum systems:

Cusum M Mean strength Keeps track of the difference between the target mean strength and the estimated mean strength (on the basis of the 7 day result)

Cusum R Range Keeps track of the range of values of the mean strength and monitors the standard deviation.

Cusum C Correlation Keeps track of the differences between the estimated mean strength and the achieved mean strength at 28th day.

14.2.5 Some leading RMC producers have developed their own variant of the cusum system. Certain other producers use standard software packages based on cusum principles. It is recommended that some of the crucial data on monitoring cusum, which is not price-sensitive, may be included in the QC document for building confidence amongst customers.

- 43 -

15. Key Personnel 15.1.1 The success of any QA-QC system would be dependent upon the abilities of key personnel in the

production facility in particular, their level of knowledge in concrete technology, managerial ability, length of experience and training undergone. It would be a good practice to include the names and other details of key plant personnel in the QC document. Besides educational qualifications, the extent of experience in RMC sphere may also be included. Further, any recent in-house or external training undergone by the plant personnel should also be incorporated in the document. Table 18 suggests a format for such documentation.

Table 18: Names, designation and experience of key plant personnel Sr. no.

Name of personnel

Designation Educational qualification Experience Training

1 A B C Plant-in-charge BE(Civil), Dip. in Business management