EFFECTS OF EFFECTIVE MICROORGANISMS ON PROPERTIES

OF BLENDED CEMENT CONCRETE

NURUL AS’SHIKIN BINTI RAMLI

A project report submitted in partial fulfilment of the

requirements for the award of the degree of

Master of Engineering (Civil)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

JUNE 2017

iii

“Dedicated to my beloved husband Meor Shahrizan bin Zolkfle,

my son Daniyal Anaqi bin Meor Sharizan, and family for their love,

encouragement and support.”

“Special thanks to supervisor, all lecturers, and friends for their motivation, concern

and help.”

iv

ACKNOWLEDGEMENT

First and foremost, all praise and thanks to Allah the exalted for His blessing

in giving me opportunities to complete this project report.

Special appreciation goes to my supervisor, Assoc. Prof. Dr Abdul Rahman

bin Mohd Sam for his supervision and constant support. The invaluable help from

him in constructive comments and suggestions throughout the experimental and

project works have contributed to the success of this study.

I give my appreciation and thankful especially to my beloved husband Meor

Shahrizan bin Zolkfle, my parents, and my precious son Daniyal Anaqi on the

encouragement and support throughout this study. My appreciation also goes to all

the structural and material laboratory staff, who had taught on how to operate the

machine, setting up test and others.

Finally, thanks to all my friends who have happen to help me in carrying out

this project. Every single helps means a lot for this study success. Hopefully this

study will be blessed by Allah and will benefit for future.

v

ABSTRACT

Concrete is an artificial rock that is made with a mixture of cement, aggregates

and water with certain proportion. Concrete is one of the material that is most widely

used in the construction industry. Cracks that occurs in concrete structure require

regular maintenance and special type of treatment which will be very expensive,

particularly to the massive concrete structures that bear loads or main structures

members. So, to overcome this problem, EM (Effective Microorganism) concrete is

introduced to study the potential of EM concrete in filling the cracks. By mixing EM

with concrete mixture, the effect on the properties of concrete is assessed whether

this EM concrete increase the workability, strength, durability and other properties

related. In this study, understanding the function and mechanism of EM in concrete

is crucial. Several parameters and concrete properties was tested in the experimental

procedure and the effect of EM in concrete were assessed in this study. The

performance of EM were measured through its fresh and hardened properties of the

concrete. From this experimental study, the optimum EM mix to be added in the

concrete is 10%, slump of EM concrete had increase by 11.4%. Compressive

strength of the EM concrete also increase and modified compression strength is

higher than cube compressive strength by the average of 5%. UPV value were

increasing by 4%. The EM concrete had higher shrinkage and expansion strain.

Water absorption shows that concrete with dry curing condition does absorb more

water. EM concrete shows lower rate of carbonation process than control concrete by

50%. From this study, it can be concluded that the properties and behavior of EM

concrete almost similar with the normal concrete. EM concrete does have the

potential in filling the crack of concrete and further studied is crucial in

understanding the mechanism and reaction of EM in concrete.

vi

ABSTRAK

Konkrit merupakan batuan tiruan yang diperbuat daripada campuran simen,

aggregat dan air dengan nisbah yang tertentu. Konkit merupakan salah satu bahan

yang digunakan secara meluas di dalam industry pembinaan. Keretakan yang terjadi

di dalam struktur konkrit memerlukan penyelenggaraan dan pemuliharaan yang

berkala dan mahal, terutamanya kepada struktur konkrit besar yang menanggung

beban atau struktur utama. Jadi, bagi mengatasi masalah ini, mikroorganisma efektif

(EM) diperkenalkan untuk mengaji potensi EM ini dalam menutupi keretakan

konkrit. Dengan mencampurkan EM dalam campuran konkrit, kesan ke atas sifat-

sifat konkrit dinilai sama ada konkrit EM ini meningkatkan kebolehkerjaan,

kekuatan, ketahanan dan sifat-sifat lain yang berkaitan. Dalam kajian ini, memahami

fungsi dan mekanisme EM di dalam konkrit adalah amat penting. Beberapa

parameter dan sifat-sifat konkrit telah diuji dalam prosedur eksperimen dan kesan

EM di dalam konkrit telah dinilai dalam kajian ini. Campuran optimum bagi

spesimen EM yang menyumbang kepada sifat-sifat kekuatan maksimum adalah 10%

EM dalam bahan tambah konkrit, ujian penurunan meningkat sebanyak 11.4%,

kekuatan kiub konkrit EM lebih tinggi, dan kekuatan mampatan diubahsuai adalah

lebih tinggi daripada kekuatan mampatan kiub dengan purata 5%. Bacaan UPV

meningkat sebanyak 4%, menunjukkan bahawa EM berpotensi untuk menutupi

keretakan konkrit. Konkrit EM mengalami pengecutan dan pengembangan spesimen

yang lebih tinggi. Kebolehtepalan air menunjukkan konkrit dalam pengawetan udara

menyerap lebih banyak air berbanding konkrit yang diawet di dalam air. Konkrit EM

menunjukkan kadar pengkarbonatan yang lebih rendah sebanyak 50%. Daripada

kajian ini, dapat disimpulkan bahawa sifat-sifat dan tingkah laku konkrit EM hampir

sama dengan konkrit biasa dan berpotensi digunakan dalam bancuhan konkrit.

vii

TABLE OF CONTENT

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENT vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF ABBREVIATIONS/SYMBOLS xiii

1 INTRODUCTION 1

1.1 Background of Study 1

1.2 Problem Statement 3

1.3 Objectives of the Study 4

1.4 Scope of Study 4

1.5 Significant of Study 5

2 LITERATURE REVIEW 6

2.1 Introduction 6

2.2 Causes of Cracks in Concrete Structure 8

2.2.1 Plastic Shrinkage 10

2.2.2 Plastic Settlement Cracks 11

2.2.3 Plastic Shrinkage Cracks 12

viii

2.2.4 Early Thermal Cracks 13

2.2.5 Long Term Drying Shrinkage Cracks 13

2.3 Limiting Crack Width for Self-healing 14

2.4 Self-healing Phenomena (State of Art) 15

2.5 Self-healing Mechanism 22

2.5.1 Mechanisms of Autogenic Self-healing 24

2.5.2 Mechanisms of Autonomic Self-healing 25

2.5.3 Mechanisms of Natural Healing 27

2.6 Effective Microorganism 27

2.7 Bacterial Concrete 30

2.7.1 Mechanisms of Bacterial Concrete 31

2.8 Advantages of Bacterial Concrete 32

2.9 Disadvantages of Bacterial Concrete 34

3 METHODOLOGY 37

3.1 Introduction 37

3.2 Experimental Study Plan 37

3.3 Material Used 40

3.3.1 Blended Cement 40

3.3.2 Aggregates 41

3.3.3 Water 42

3.3.4 Effective Microorganism 42

3.4 Concrete Mix Design 44

3.5 Optimum Mix Design Proportion of EM 44

3.6 Preparation of Specimen 45

3.6.1 Casting 46

3.6.2 Curing 46

3.7 Pre-Loading of Specimen 47

3.8 Experimental Test 48

3.8.1 Slump Test 48

3.8.2 Compressive Strength Test 49

3.8.2.1 Procedure for Compression Test 50

3.8.3 The Ultrasonic Pulse Velocity (UPV) Test 51

ix

3.8.3.1 Principles of Operation 52

3.8.3.2 Procedure of the UPV Test 53

3.8.4 Water Absorption Test 54

3.8.4.1 Procedure of Water Absorption Test 56

3.8.5 Flexural Test 57

3.8.5.1 Flexural Test Procedure 58

3.8.6 Modified Compression Test 59

3.8.6.2 Modified Compression Test Procedure 60

3.8.7 Expansion and Shrinkage Test 60

3.8.7.1 Expansion and Shrinkage Test Procedure 61

3.8.8 Carbonation Test 62

3.8.8.1 Carbonation Test Procedure 62

4 RESULT AND DISCUSSION 64

4.1 Introduction 64

4.2 Optimum Mix Design Proportion of EM 64

4.3 Slump Test 66

4.4 Development of Concrete Compressive Strength 67

4.5 Ultrasonic Pulse Velocity (UPV) 70

4.6 Surface Water Absorption 76

4.7 Flexural Strength Test 77

4.8 Modified Compression Test 79

4.9 Expansion and Shrinkage Test 80

4.10 Carbonation Test 81

5 CONCLUSION AND RECOMMENDATION 83

5.1 Introduction 83

5.2 Conclusions 83

5.3 Recommendations for Future Project 85

REFERENCES 87

x

LIST OF TABLES

TABLE NO TITLE PAGE

2.1 Permissible crack width for self-healing. (Source: Self-

Healing Phenomena in Cement Based Materials,

Reinhardt (2013))

15

2.2 Examples of Elements Belonging to each set in Figure 2.6

according to JCI TC-075B

19

2.3 Approach of Autonomous Self-Healing 26

3.1 Composition of Concrete Mixture 44

3.2 Types of Specimen 45

4.1 The Amount of Percent EM in concrete Mix 65

4.2 Slump of Specimen 66

4.3 Compressive Strength of Specimen 69

4.4 UPV Value for Concrete Specimen without Pre-Crack

(km/s)

73

4.5 UPV value for Concrete Specimen with Pre-Crack (km/s) 75

4.6 Flexural Strength Test Value 78

4.7 Modified Compression Test vs Cube Compression Test

Results

79

xi

LIST OF FIGURES

FIGURE NO TITLE PAGE

2.1 Examples of intrinsic cracks in hypothetical structure

(Source: Concrete Society, 1992)

10

2.2 Plastic Shrinkage Cracking (Source : ACI 301-05) 11

2.3 Formation of plastic settlement cracks (initial and final

state). (Source: Advanced Concrete Technology;

Concrete Properties, 2003)

11

2.4 Process of plastic shrinkage cracking (initiation and final

state) (Source: Advanced Concrete Technology; Concrete

Properties, 2003)

12

2.5 Drying shrinkage cracks on wall. Vertical lines indicate

the position of reinforcement. (Source: Advanced

Concrete Technology; Concrete Properties, 2003)

14

2.6 Venn diagram to explain terminology of self-healing

according to JCI TC-075B. (Source: Self-Healing

Phenomena in Cement Based Materials, Rooij (2011))

19

2.7 Concept of performance recovery by a healing function.

(Source: Self-Healing Phenomena in Cement Based

Materials, Rooij (2011))

20

3.1 Methodology Flow Chart 38

3.2 Blended Cement 40

xii

3.3 Course Aggregates 41

3.4 Fine Aggregates 41

3.5 Effective Microorganism (EM) 43

3.6 Curing Condition of the Specimen 47

3.7 Slump Test 49

3.8 Uniaxial Compression Load Test 50

3.9 Ultrasonic Pulse Velocity (UPV) Test 51

3.10 Schematic Diagram Water Absorption Test (source from

ASTM 1585-04 International)

55

3.11 Flexural test 58

3.12 Modified Compression Test 59

3.13 Digital Demec Gauge 61

4.1 Optimum Percentage of EM in Concrete Mix 65

4.2 Slump Test 67

4.3 Compressive Strength for Control and EM Concrete 68

4.4 Failure Mode Pattern 70

4.5 UPV Test for all Specimen 72

4.6 Water Absorption, I (mm) vs √Time (s) Graph 77

4.7 Failure Mode Pattern of Prism Specimen 79

4.8 Shrinkage and Expansion vs Age Graph 80

4.9 Carbonation Test on Fresh Fracture Concrete for both

Specimen

82

4.10 Carbonation on Control and EM Specimen in Air Curing

Condition

82

xiii

LIST OF ABBREVIATIONS/SYMBOLS

ACI - American Concrete Institute

ASTM - American Society for Testing And Material

BS - British Standard

CCRA - Cube Control Air Curing

CCRW - Cube Control Water Curing

CPRA - Cube Pre-Crack Air Curing

CPRW - Cube Pre-Crack Water Curing

ECRA - EM Cube Control Air Curing

ECRW - EM Cube Control Water Curing

EM - Effective Microorganism

EPRA - EM Cube Pre-Crack Air Curing

EPRW - EM Cube Pre-Crack Water Curing

JCI - Japan Concrete Institute

PCRA Prism Control Air Curing

PCRW Prism Control Water Curing

PEA Prism EM Air Curing

PEW Prism EM Water Curing

RILEM The International Union of Laboratories and Experts in

Construction Materials, Systems and Structures

UPV Ultrasonic Pulse Velocity

CHAPTER 1

INTRODUCTION

1.1 Background of Study

Concrete is one of the important material that is commonly used in the

construction industry. Concrete is the main material used for the infrastructure

development in every country. Concrete is made from the mixture of cement, water,

aggregate and sand with certain proportion to produce a slurry. Cement is a binder

that bind other materials together.

In concrete, cracking is a common phenomenon due to the relatively low

tensile strength. High tensile stresses can result from external loads, imposed

deformations (due to temperature gradients, confined shrinkage and differential

settlement), plastic shrinkage, plastic settlement, and expansive reactions (e.g. due to

reinforcement corrosion, alkali, silica reaction, sulphate attack. Without immediate

and proper treatment, cracks tend to expand further and eventually require costly

repair. Durability of concrete is also impaired by these cracks, since they provide an

easy path for the transport of liquid and gasses that potentially contain harmful

substances. If micro cracks grow and reach the reinforcement, not only the concrete

itself may be attacked, but also the reinforcement will be corroded when it is exposed

2

to water and oxygen, and possibly carbon dioxide and chlorides. Micro cracks are

therefore precursors to structural failure (Tittelboom et al., 2013).

Self-healing is actually an old and well known phenomenon for concrete as it

possesses some natural autogeneous healing properties. Autogeneously crack-

healing capacity of concrete has been recognized in several recent studies. Mainly

micro cracks with widths in the range of 0.05 to 0.1 mm have been observed to

become completely sealed particularly under wet and dry condition. The mechanism

of this autogeneously healing is chiefly due to secondary hydration of non or

partially reacted cement particles present in the concrete matrix. One possible

technique is currently being investigated and developed was based on application of

mineral producing bacteria in concrete.

Although bacteria and particularly acid producing bacteria, have been

traditionally considered as harmful organisms for concrete, recent research has

shown that species such as ureolytic and other bacteria can actually be useful as a

tool repair cracks or clean the surface of concrete. Bacteria can act as catalyst for the

metabolic conversion of a suitable organic or inorganic component. The nature of

metabolically produced filler materials could be minerals such as calcite (calcium

carbonate). These minerals are relatively dense and can block cracks, thus increase

some of the concrete properties. The development of a self-healing mechanism of

concrete that is based on potentially cheaper and more sustainable material thus be

beneficial for both economy and environment.

3

1.1 Problem Statement

Concrete structures often suffers from cracking that lead to much earlier

deterioration and designed service life. To prevent such deterioration, regular

inspection of cracks in concrete structures and their repair are usually carried out by

means of some kind of human intervention. Cracks in concrete can occur in any

stage of the service life of concrete structures due to volume instabilities such as

autogenous shrinkage or drying shrinkage since concrete is composed of aggregate

of various sizes connected with the hydration process generated by mixing water and

cement. Once cracking occurs in reinforced concrete members, not only the stiffness

reduced but steel bars corrosion also occurs due to permeation of rain, harsh weather

and aggressive substances, reducing structural safety and serviceability. The

availability of self-healing concrete would make structures more reliable. For

example, if control and repair at the early stage cracks in concrete structures were

possible, permeation of factors for deterioration could be prevented, thus extending

the service life of the structures. In the meantime, sustainability is now one of the top

issues in the field of building and civil engineering from the viewpoint of global

ecology. Besides that, precipitation on calcium carbonate due to biochemical action

of bacteria has been expected to be one of the new technologies for self-healing

concrete that can be applied in the future.

From Jonkers et al. (2008), a high crack healing potential of concrete

structures is beneficial as it makes the material stronger and above all more durable.

A continuous healing of particularly surface cracks results in decreased permeability

of the material and a significantly reduced risk of premature matrix degradation and

corrosion of the embedded steel reinforcement due to ingress water and aggressive

chemicals.

4

1.2 Objectives

The main purpose of this study is to determine the effects of EM on the

properties of concrete including fresh and hardened state. Following are the

objectives of the study.

i. To determine the optimum percentage of Effective Microorganism (EM)

in blended cement concrete mix.

ii. To determine the effects of Effective Microorganism (EM) on fresh and

hardened properties of concrete.

iii. To investigate the effects of Effective Microorganism (EM) on self-

healing process of matured concrete.

1.3 Scope of Study

The scope of this study is to focus on applying Effective Microorganism in

concrete as the healing agent. Cracks are formed due to plastic shrinkage, drying

shrinkage and thermal effects when the concrete are not properly cured. The porosity

of concrete produce more voids and the crack allows water and oxygen into the

concrete. The idea is that after cracking, mixed in EM on fresh concrete crack

surfaces are activated in the presence of water, and then start to multiply and

precipitate minerals, such as calcite, and close or seal the crack.

5

1.4 Significant of Research

Approach of using EM in concrete as self-healing agent makes very

beneficial compared to the conventional concrete. Based on these study, if EM

concrete does give some effects towards self-healing approach and potential through

its reaction mechanism in concrete, then EM concrete could be one of the important

material in the future construction. When EM concrete is apply in construction

industry, it may become another alternative method to repair concrete cracks

internally. The approaches of self-healing concrete can provide ways in reducing

maintenance work due to cracking and increase durability of concrete structure, high

strength buildings with more bearing capacity, retaining liquid structure which are

more detail design especially focused for preventing cracks for a long term period.

87

REFERENCES

A.M. Neville, J.J. Brooks (1987), “Concrete Technology”. Longman.

ASTM. American Society of Testing and Materials. Designation: C 1585 – 04

Dry, C.M. (2000). “Three design for the internal release of sealants, adhesive, and

waterproofing chemicals into concrete to reduce permeability.” Cement and

Concrete research 30 (12), pp. 1969-1977.

E. Schlangen, H. Jonkers, S. Qian & A. Garcia. “Recent Advances on Self-Healing

of Concrete.” Fracture Mechanics of Concrete and Concrete Structures.

(2010). Korea Concrete Institute, Seoul.

Edvardsen, C., (1999). “Water Permeability and Autogenous Healing of Cracks in

Concrete.” ACI Material Journal, 96(4), 448-454.

Ghosh, P., Mandal, S., Chattopadhyay, B. D., Pal, S. “Use of Microorganism to

Improve The Strength Of Cement Mortar.” Cement on concrete Research

35(10): 1980 – 1983 (2005).

Hall, C. “Water Sorptivity of Mortars and Concretes: A Review,” Magazine of

Concrete Rresearch, Vol 41, No. 147, June 1989. Pp 51-61.

Henk M. Jonkers, Arjan Thijssen, Gerard Muyzer, Oguzhan Coporoglu, Erik

Shlangen. “Application of Bacteria as Self-Healing Agent for the

Development of Sustainable Concrete”. Ecological Engineering 36 (2010)

230-235. Elsevier.

Higa, T., 1995, “ What is EM Technology”, College of Agriculture, University of

Ryukyus, Okinawa, Japan.

Homma, D., Mihashi H. and Nishiwaki, T. (2009). “Self-Healing Capability of Fibre

Reinforced Cementitious Composites.” Journal of Advanced Concrete

Technology, 7(2), 217-228.

88

Guim, A.; Andrade, P.; Iturrino-Schocken, R.P. and Malheiros, E.B. (1998): Aerobic

Stability of Wilted Grass Silages (Pennisetum purpureum, Schum) Treated

with Microbial Inoculant. Fundacao Moki'ti Okada and Universidade

Estadual Paulista, Jaboticabal Campus, Sao Paulo, Brazil.

John Newman, Ban Seng Choo. (2003), “Advanced Concrete Technology: Testing

and Quality”. Elsevier Ltd.

John Newman, Ban Seng Choo. (2003), “Advanced Concrete Technology: Concrete

Properties”. Elsevier Ltd.

Jonkers HM, Schlangen E. (2007).”Self-Healing Of Cracked Concrete: A Bacterial

Approach.” In Proceedings of FRACOS6: fracture mechanics of concrete and

concrete structures. Italy: Catania; 2007. p. 1821–26.

Jonkers HM, Schlangen E. (2008).”Development of a Bacteria-Based Self-Healing

Concrete.” Tailor Made Concrete Structures – Walraven & Stoelhorst (eds).

Taylor & Francis Group, London.

Jonkers HM, (2011).”Bacteria-Based Self-Healing Concrete.” Heron Vol. 56 No. ½

Jonkers HM, (2007).”Self-Healing Concrete: A Biological Approach.” Self-Healing

Materials. An Alternative Approach to 20 Centuries of Materials Science,

195-204.

K.A. Shahid, M.F.M. Jaafar & F.M. Yahaya. “Self-Healing Behaviour of Pre-

Cracked Pofa-Concretes in Different Curing Conditions.” Journal of

Mechanical Engineering and Sciences (JMES), Vol. 7, pp. 1227-1235,

December 2014.

Klass van Brugel. “Self-Healing Material Concepts as Solution for Aging

Infrastructure.” 37th

Conference on Our World in Concrete & Structure. 29-

31 August 2012. Singapore.

Li, V. C., Sakulich, A. R., Reinhardt, H. W., Shlangen, E. (2013). Recovery Against

Mechanical Action : Self Healing Phenomena in Cement based Materials.

RILEM.

Khaliq, W. Basit, ehsan. (2016). “crack healing in concrete using various bio

influenced self-healing techniques.” Construction and Building Materials

Journals 102, 345-357

Mario, d. R., Kim, V. Tittelboom, Nele, d. B., Erik, Schlangen. (2014). “Self-

Healing Phenomena in Cement-Based Materials – State-of-the-Art Report of

89

RILEM Technical Committee 221-SHC: Self-Healing Phenomena in Cement

Based Materials. Vol.11”

Na, S. H., Hama, Y., Taniguchi, M., Katsura, O., Sagawa, T., Zakaria, Mohamad.

“Experimental Investigation on Reaction Rate and Self-Healing Ability in Fly

Ash Blended Cement Mixtures.

Patel P., (2016). “Helping Concrete Heal Itself”.Chemical & Engineering News.

Volume 94 Issue 6. Pp. 29 – 30 (online article)

http://cen.acs.org/articles/94/i6/Helping-Concrete-Heal-Itself.html

Ramakrishnan, S.K., Panchalan, R. K., Bang, S.S. (2001). “Improvement of Concrete

Durability by Bacterial Mineral Precipitation.” 11th

International Conference

on Fracture, Turin. Italy

Ramm, W. and Biscoping, M., (1998). “Autogenous Healing and Reinforcement

Corrosion of Water-Penetrated Separation Cracks in Reinforced Concrete.”

Nuclear Engineering and Design, 179(2), 191-200.

Reinhardt H.W., Jonkers, H., Tittelboom, V. K., Snoeck, D. (2013). Recovery

Against Environmental Action. “self – Healing Phenomena in Cement- Based

Materials. RILEM

Rooij, M. R., Shlangen, E. and Joseph, C. (2013). “Self-Healing Phenomena. Self-

Healing Phenomena in Cement Based Bacteria.” RILEM.

Salmabanu Luhar, Suthar Gourav. “A Review Paper on Self-Healing Concrete.”

Journal of Civil Engineering Research 2015, 5(3): 53-58.

Sangadji, S., “Can Self-healing Mechanism Helps Concrete Structures Sustainable?”.

Procedia Engineering 171 (2017) 238 – 249.

Talaiekhozan, A., Kevyanfar, A., Shafagat, R. Andalib, R. Majid, M. A., Fullazaky,

and Marwar, N. F. (2014). A Review of self-healing concrete research

development. Journal Of Advanced Concrete Techology 2012, Vol 10, 240-

253..

Th. A. BIER. (1987). “Influence of Type of Cement and Curing On Carbonation

Progress and Pore Structure of Hydrated Cement Paste, Materials Research

Society Symposium.” 85, pp. 123–34

Van Tittelboom K. & Nele De Belie. (2013). “Self-Healing in Cementitious

Materials: A Review. Materials 2013, 6, 2182-2217.

Victor C. Li & Emily Herbert. “Robust Self-Healing Concrete for Sustainable

90

Infrastructure. Journal of Advanced Concrete Technology. Vol. 10,207-218,

June 2012.

Wasim Khaliq, Muhammad Basit Ehsan. “Crack Healing in Concrete Using Various

Bio Influenced Self-Healing Techniques.” Journal on Construction and

Building Materials. 102 (2016) 349-357. Elsevier.

Yongzhen N, Waijiong L (1994) Report on the Deodorizing Effect of Effective

Microorganisms (EM) in Poultry Production. Beijing, China. 402 - 440.

Zhong, W., Yao, W. (2007). Influence of Damage Degree on Self –healing of

Concrete. Journal on Construction and Building Materials. 22 (2008) 1137-

1142. Elsevier.