Abstract image of a woman sitting on books and studying on a laptop

ADMIXTURE USED IN CONCRETE.docx

Download as DOCX, PDF
N
NAUGHTYBOY9

This document provides information about a micro project completed by six students on the topic of "Admixture used in concrete". It includes the names and roll numbers of the students, certification that they completed the project, signatures of the guide and HOD, the project proposal, action plan, required resources, evaluation sheet with marks and feedback. The main body of the document defines concrete admixtures, explains the reasons for using them and classifies the main types - air entraining, accelerating, water reducing, retarding, and super plasticizing admixtures. It provides details on the chemical types, modes of action and properties of each type of admixture.

Engineering
1 of 20
Download to read offline
1
2
3
4
Most read
5
6
7
8
Most read
9
10
11
12
13
14
15
16
17
18
19
20
Y.B. PATIL POLYTECHNIC SECTOR NO. 29, AKURDI, PUNE -411044, INDIA HRISHIKESH TARANGE – Y-2070-1901340102 ATHARVA PATIL – Y-2075-1901340081 YOGESH YELAVI -Y-2083-1901340103 PRATHAMESH ROKDE – Y-2031-1901340079 AVINASH SAKHERE – Y-2058 -1901340080 DAVENDRA SUTHAR – Y-2077-1901340104 This is to certify ;has satisfactorily carried out and completed the project work entitled Admixture used in concrete This work is being submitted for the award of Diploma in civil Engineering partial fulfillment of prescribed syllabus of M.S.B.T.E Mumbai for academic Year 2020 MS.SHEETAL BANDEWAR MR,ABHIJEET PATIL GUIDE HOD CIVIL DEPARTMENT PRINCIPLE PROF.A.S KONDEKAR Micro project proposal Admixture used in concrete
1.Aims/benefits of micro project: To get knowledge about total station its objective its component use in civil engineering introduction & knowledge of total station 2 Course outcome addressed. 1 To learn about total station 2. To learn about component & it use 3. To learn about their advantage & disadvantage 3 Action plan Sr. No. Details of activity Planned Start date Planed Finished date Name of responsible team member 1) Collection of information. 20/06/2020 20/06/2020 HRISHIKESH TARANGE – Y1171 ATHARVA PATIL – Y1154 2) Working of Microsoft Word. 20/06/2020 23/06/2020 YOGESH YELAVI – Y1177 PRATHAMESH ROKDE – Y1161 3) Taking Prints of the project made in Microsoft Word & Microsoft word & binding it 22/06/2020 22/06/2020 AVINASH SAKHERE – Y1162 DAVENDRA SUTAR – Y1170 5 Resource Required Sr.no Name of resource /materials specification Qty Remark 1 Internet and reference book Collect information 1
2 laptop Working on Microsoft word 1 Name of team member with roll no HRISHIKESH TARANGE – Y1171 ATHARVA PATIL – Y1154 YOGESH YELAVI – Y1177 PRATHAMESH ROKDE – Y1161 AVINASH SAKHERE – Y1162 DAVENDRA SUTAR – Y1170 Micro project evaluation sheet Name of student HRISHIKESH TARANGE – Y1171 ATHARVA PATIL – Y1154
YOGESH YELAVI – Y1177 PRATHAMESH ROKDE – Y1161 AVINASH SAKHERE – Y1162 DAVENDRA SUTAR – Y1170 Name of programme: micro project on the topic Admixture used in concrete Semester:1st Course title: Concrete Technology Title of micro project : Admixture used in concrete Course outcome achieved 1 To learn about concrete 2. To learn about component & it use 3. To learn about their advantage & disadvantage Sr no Characteristic to be assessed Poor (mark 1-3) Average (mark 4-5) Good (mark 6-8) Excellent (mark 9-10) Sub total (A)PROCESS AND PRODUCT ASSESSMENT CONVERT ABOVE TOTAL MARK OUT OF 6 MARK 1 Relevance to the course 2 Literature review/information 3 Completion of the target as per project proposal 4 Analysis of date and representation 5 Quality of prototype/model 6 Report preparation (B)INDIVIDUAL PRESENTATION/VIVA CONVERT ABOVE MARK OUT OF 4 MARKS 7 Presentation 8 viva NAME ROLL NO (A) PROCESS AND PRODUCT ASSESSMENT (6MARK) (B) INDIVIDUAL PRESENTATIO N/ VIVA (4 MARK) TOTAL MARK (10 MARK)
HRISHIKESH TARANGE Y-2070 ATHARVA PATIL Y-2075 YOGESH YELAVI Y-2083 PRATHAMESH ROKDE Y-2031 AVINASH SAKHERE Y-2058 DAVENDRA SUTAR Y-2077 COMMENTS/SUGGESTION ABOUT TEAMWORK/LEADERSHIP/INTER-PERSONAL COMMUNICATION ( IF ANY) NAME AND DESIGNATION OF TEACHER ………………………………………………… DATED SIGNATURE……………………………… TYPES OF ADMIXTURE USED IN CONCRETE Concrete admixtures (additives) enhance the properties of concrete for applications in construction with special requirements. Concrete additives are used to achieve desired workability in case of low water cement ratio, and to enhance setting time of concrete for long distance transportation of concrete.
So, it is of much importance for a civil site engineer to know about the types of admixtures (additives) and their properties for better selection and application in concrete works. Definition of Concrete Admixtures As per BIS (IS �9103: 1999) Page No.1, Concrete Admixture is defined as a material other than water, aggregates and hydraulic cement and additives like Pozzolana or slag and fiber reinforcement, used as on ingredient of concrete or mortar and added to the batch immediately before or during its mixing to modify one or more of the properties of concrete in the plastic or hardened state. Reasons for Using Admixtures (ACI Committee Report Page �298) Admixtures are used to modify the properties of concrete or mortar to make them more suitable for the work at hand or for economy or for such other purposes as saving energy. Some of the important purposes for which admixtures are used are: To modify properties of fresh concrete, mortar and grout to: ● Increase workability without increasing water content or decrease water content at the same workability. ● Retard or accelerate time of initial setting. ● Reduce or prevent settlement.
● Modify the rate or capacity for bleedings. ● Reduce segregation. ● Improve pumpability. ● Reduce the rate of slump loss. To modify the properties of hardened concrete, mortar and grout to: ● Retard or reduce heat evaluation during early hardening. ● Accelerate the rate of strength development at early ages. ● Increase strength (compressive, tensile or flexural). ● Increase durability or resistance to severe condition of exposure. ● Decrease permeability of concrete. ● Control expansion caused by the reaction of alkalies with certain aggregate constituents. ● Increase bond of concrete to steel reinforcement. ● Increase bond between existing and new concrete. ● Improve impact resistance and abrasion resistance. ● Inhibit corrosion of embedded metal. ● Produce colored concrete or mortar When Concrete Admixtures Used? ● When properties cannot be made by varying the composition of basic material. ● To produce desired effects more economically. ● Unlikely to make a poor concrete better. ● Not a substitute for good concrete practice. ● Required dose must be carefully determined and administered How to Use Concrete Admixtures? ● Check job specification ● Use the correct admixture ● Never use one from an unmarked container. ● Keep containers closed to avoid accidental contamination. ● Add the correct dosage. ● Avoid adding ‘a little bit extra ● Use a dispenser ● Wash thoroughly at the end the day ● Best if added to the mixing water ● Manufacturer’s recommended dosage is usually adequate ● Trial mixes are important to determine most effective dosage Types of Concrete Admixtures (Additives)
Types of admixtures as per� American Concrete Institute Committee report and� IS 9103: 1999 are: 1. Accelerating admixtures 2. Retarding admixtures 3. Water-reducing and set controlling admixtures 4. Air-entraining admixtures 5. Super plasticizing admixtures 6. Admixtures for flowing concrete 7. Miscellaneous admixtures Classification of admixtures according to the book of � Concrete Admixtures: Use and Applications�edited by M. R. Rixom are given in the forward pages. 1. Air Entraining Admixture These are generally used to improve workability, ease of placing, increased durability, better resistance to frost action and reduction in bleeding. The common Air-Entraining agents are natural wood resins, neutralized vinsol resins, polyethylene oxide polymers and sulfonated compounds. Mechanism of Air Entraining Concrete Admixtures
These are anionic, because the hydrocarbon structures contain negatively charged hydrophilic groups, such as COO, SO3 and OSO so that large anions are released in water. Conversely, if the hydrocarbon ion is positively charged, the compound is cation active or cationic. In other words, anionic surface active agents produce bubbles that are negatively charged, cationic charged cause bubbles to be positively charged, surface active agents of all classes can cause air entrainment in concrete, but their efficiency and characteristics of air-void system vary widely. Properties of� Air entraining Admixtures ● These are foaming agents, gas producing chemicals. It introduces millions of tiny, stable bubbles of uniform size that are uniformly distributed throughout the mix (usually about 5% of the volume). ● Improves properties of fresh concrete such as workability, cohesion and reduces segregation and bleeding. ● Improves properties of hardened concrete – For every 1% of air there is a 4% loss in strength which is minimized by the reduction in water content. It improves durability of hardened concrete. 2. Accelerating Admixtures Accelerating admixtures are used for quicker setting times of concrete. It provides higher early strength development in freshly cast concrete. Main uses of Accelerating Concrete Admixtures ● These admixtures are suitable for concreting in winter conditions ● During any emergency repair work ● In case of early removal of formwork Disadvantages of Accelerating Concrete Admixtures ● It has increased drying shrinkage ● It offers reduced resistance to sulphate attack ● CaCl2 high risk of corrosion of steel �not permitted in reinforced concrete ● It is more expensive and less effective 3. Water Reducing Admixtures Chemical Types for Water Reducing Admixtures
1. Calcium or sodium salt of lignosulfonic acid 2. Poly carboxylic acid Mode of Action The principal role of mechanism of water reductions and set retardation of admixtures are usually composed of long-chain organic molecules that are hydrophobic (not wetting) at one end and hydrophilic (readily wet) at the other. Such molecules tend to become concentrated and form a film at the interface between two immiscible phases such as cement and water, and alter the physio-chemical forces acting at this interface. The mechanism by which water reducing admixture operates is to deflocculate or to disperse the cement agglomerates into primary particles or atleast into much smaller fragments. This deflocculating is believed to be a physicochemical effect whereby the admixture is first of all adsorbed on to the surface of the hydrating cement, forming a hydration � sheath� , reduces the antiparticle separated from one another. The presence of water reducing admixture in a fresh concrete results in: 1. a reduction of the interfacial tension. 2. an increase in the electro kinetic potentials and 3. protection sheath of water dipoles around each particle i.e. mobility of fresh mix becomes greater, partly because of reduction in inter-particle forces and partly because of water freed from the restraining influence of the highly flocculated system which is now available to lubricate the mixture. Hence less water is required to achieve given consistency. Why Water Reducing Admixtures used? a) Concrete having greater workability be made without the need for more water and so strength losses are not encountered b) By maintaining some workability, but at a lower water content, concrete strengths may be increased without the need for further cement addition c) While maintaining the same w/c ratio and workability concrete can be made to a given strength as in the reference concrete at lower cement content.
Effect on durability The straight addition of admixtures of this type does not came any increase in permeability and indeed where the admixture is used to reduce the w/c, then permeability is considerably reduced. Effect on shrinkage Admixture of this type when used as workability aids on water reducers do not adversely affect the shrinkage. Effect on creep Materials of this type of admixture have no deleterious effect on the creep of concrete. Detrimental effect a) While using a water reducing agent. Care must be taken in controlling the air content in the mix. Most water-reducing agents entrain air due to their surfactant properties. b) At high doses of lignosulphonate material, retardation of the mix occurs. Applications of Water Reducing Concrete Admixtures The application of the type of admixtures are as follows � a) When concrete pours are restricted due to either congested reinforcement or these sections. b) When harsh mixes are experienced such as those produced with aggregates (crushed). Then considerable improvement in the plastic properties of concrete can be obtained. c) When required strengths are difficult to obtain within specified maximum cement content and where early lifting strengths are required. d) By addition of this admixture in concrete cement economics of about 10% can be obtained.
4. Retarding Concrete Admixtures The function of retarding concrete admixture is to delay or extend the setting time of cement paste in concrete. These are helpful for concrete that has to be transported to long distance in transit mixers and helpful in placing the concrete at high temperatures, specially used as grouting admixture and water reducers results in increase of strength and durability. Chemical type for Retarding Concrete Admixture a) Unrefined lignosulphonates containing sugar, which of course the component responsible for retardation. b) Hydroxyl carboxylic acid and their salts c) Carbohydrates including sugar d) Soluble zinc e) Soluble borates etc. Mode of action It is thought that retarding admixtures are absorbed on to the C3A phase in cement forming a film around the cement grains and presenting or reducing the reaction with water. After a while the film breaks down and normal hydration proceeds. This a simple mixture and there is a reason to believe that retards also interact with C3S since retardation can be extended to a period of many days. Why are Retarding Concrete Admixtures used? To delay in the setting time of concrete without adversely affecting the subsequent strength development. Advantage of Retarding Concrete Admixture a) The hydroxyl carboxylic acid type admixture normally produces concrete having a slightly lower aim content them that of a control mix.
b) Materials of this class (lignosulphonate containing sugar and derivatives of hydroxyl carboxylic acid) in some cases have a much higher dispersing effect and hence water reducing capacity. c) Durability increases. Detrimental effect a) When lignosulphonate based material is used, then the air content might be 0.2 to 0.3% higher unless materials of the tributyl phosphate type are added. b) As the water content increases, so there is a tendency for drying shrinkage. Applications of Retarding Concrete Admixture Retarding admixtures are used a) Where long transportation of ready mixed concrete is required then premature setting can be usefully avoided by this type admixture. b) When concrete is being placed or transported under conditions of high ambient temperature. c) In case of large concrete pours d) Concrete construction involving sliding formwork 5. Super Plasticizers or High Range Water-Reducing Admixtures in Concrete These are the second generation admixture and also called Superplasticizers. These are synthetic chemical products made from organic sulphonates of type RSO3, where R is a complex organic group of higher molecular weight produced under carefully controlled conditions. The commonly used superplasticizer are as follows: i) Sulphonated melamine formaldehyde condensate (S M F C)
ii) ii) Sulphonated naphthalene formaldehyde condensate (SNCF) iii) iii) Modified ligno-sulphonates and other sulfonic esters, acids etc., Chemical type a) formaldehyde derivatives such as melamine formaldehyde and naphthalene sulphonate formaldehyde. Mode of action of SuperPlasticizer Admixtures This admixture acts in the same way as that of a water reducing admixture acts. It disperses the cement agglomerates when cement is suspended in water and adsorbed on to the surface of cement, causing them mutually repulsive as a result of the anionic nature of super plasticizers. Why are Superplasticizer Admixtures used? a) At a given w/c ratio, this admixture increases the workability, typically by raising the slump from 75 mm to 200 mm. b) The second use of these admixtures is in the production of concrete of normal workability but with an extreme high strength (super plasticizer can reduce the water content for a given workability by 25 �35 percent compared with half that value in the case of conventional water reducing admixtures). Advantages of Superplasticizer Admixtures a) The concrete using this admixture can be placed with little or no compaction and is not subject to excessive bleeding or segregation. b) They can be used as high dosages as they do not markedly change the surface tension of water. c) It does not significantly affect the setting of concrete except that when used the cements have a very low C3A content.
d) They do not influence shrinkage, creep modulus of elasticity or resistance to freeing to thawing. Disadvantage The only real disadvantage of superplasticizer is their relatively high cost. Applications of Super Plasticizer Admixtures a) In very heavily reinforced sections, in inaccessible areas in floor or road slabs. b) Where very rapid placing is desired. 6. Mineral Admixtures for Concrete Mineral admixtures are finely divided materials which are added to the concrete in relatively large amounts, usually of the order of 20 to 100 percent by weight of Portland cement. Source of Mineral Admixtures a) Raw or calcined natural minerals b) Industrial by products Reasons for using mineral admixtures a) In recent years�considerable efforts have been made by the cement industry world wide to reduce energy consumption in the manufacture of Portland cement. Therefore, a partial replacement of Portland cement by mineral admixtures which can be of the order of 50 � 60% by weight of total cementitious material, represents considerable energy savings. b) The ability of cement and concrete industries to consume mithions of tons of industrial byproducts containing toxic metal would qualify these industries to be classified as environmentally friendly. c) Since natural Pozzolana and industrial by-products are generally available at substantially lower costs than Portland cement, the exploitation of the Pozzolanic and cementitious
properties of mineral admixtures are used as a partial replacement of cement can lead to a considerable economic benefit. d) Possible technological benefits from the use of mineral admixtures in concrete include entrancement of impermeability and chemical durability, improved resistance to thermal cracking and increase in ultimate strength. Classification of Mineral Admixture Mineral admixtures may be classified as follows � a) Pozzolanic Silicon or siliceous and admixtures material which itself possesses little or no cementitious value but is the presence of moisture chemically reacts with CalOH2 at ordinary temperature to form compounds possessing cementitious properties. b) Pozzolanic & Cementitious �The materials which have some cementitious properties in itself. ASIM specification C618 recognizes the following three classes of mineral admixtures. a) Class N �Raw or calcined natural pozzolanic such as diatomaceous earths, clay and shales, tuffs and volcanic ashes. b) Class F �Fly ash produced from burning anthracite or bituminous coal. c) Class C �Ash normally produced from lignite or sub-bituminous coal which may contain analytical CaO higher than 10%. 7. Silica Fume as Concrete Admixture Although the use of silica fume (SF) in concrete has increased significantly in the past few years, its beneficial properties were not well realized until comprehensive research was undertaken in the late 70's and early 80's at the Norwegian Ins. of technology to study the influence of SF on concrete properties. Production of Silica Fume
Silicon, ferrosilicon or other alloys are produced in so-called � submerged are electric furnaces� . There are two types of electric furnaces one is with a heat recovery system and the other is without a heat recovery system. Types of Alloys Produced in Submerged Arc Electric Furnaces a) Ferrosilicon of various Si contents – FeSi �50% with a 43 to 50% Si content – FeSi �75% with a 72 to 78% Si content – FeSi �90% with a 87 to 96% Si content b) Calcium silicon c) Ferrochromium Silicon d) Silicomanganese Specific Gravity and Specific Surface Area of SF The specific gravity of SF is generally equal to that of amorphous silica which is about 2.20. However, depending on its chemical composition, the specific gravity of a SF particle can be as high as 2.40 and 2.55, as in the case of FeGSi. The specific surface area of SF measured by nitrogen absorption is given below. SF Calculated Surface Area (m2/kg) Measured by Nitrogen Adsorption Mean Diameter (mm) Si 20000 18500 0.18 FeCrSi 16000 – 0.18
FeSi � 50% 15000 – 0.21 FeSi � 75% 13000 15000 0.26 However, regardless of the differences in chemical composition, color and carbon content, all types of SF share a certain number of common, yet important physio chemical characteristics, which make them effective supplementary cementitious materials to cement concrete. these properties are as follows � a) SF originates from the condensed SiO vapors and generally has a high content of silica of 35 to 98% b) SF is an amorphous material c) SF is composed mostly of fine spheres with a mean diameter of 0.1 to 0.2 mm. Filler and Pozzolanic effects of Silica Fume The unique characteristics of SF that make it suitable for use as supplementary cementitious materials are its fineness, highly amorphous nature and elevated content of SiO2. The small SF spheres act as fillers since they occupy some of the space between the relatively coarse cement grains which can be otherwise occupied by water. This results also in a denser matrix with a better gradation of fine particles. Bache stated that in a super plasticized, low w/c ratio concrete, small SF spheres can displace water entrapped between the flocculated cement grains, thus increasing the amount of free water in the paste which enhances fluidity. Several researchers have studied the pozzolanic properties of SF. The resulting reactions between SF and Ca(OH)2 increases the volume of CSH and reduces the total volume of
capillary pores in the cement paste. The pozzolanic reactions of SF with Ca(OH)2 reduces the amount of Portlandite in the hydrate cement paste. Mehta explained that the absence of large Portlandite crystals in a SF mixture can be due to the fact that each SF particle can act as a � nucleation site�for precipitation of Ca(OH)2. As a result, numerous small crystals of Ca(OH)2 can form rather than a few large ones. This absence of large and weak crystals of Portlandite enhances the mechanical properties of concrete. The beneficial action of SF has also been attributed to the reduction of the porosity of the transition zone between the cement paste and aggregate which increases the strength and impermeability of the concrete. In conventional concrete, the transition zone can have large and oriented Portlandite crystals which form weak zones in the concrete. The thickness of the transition zone can be drastically produced by adding SF to the concrete since SF reduces bleeding and the amount of water accumulation under aggregate. As a result, it decreases the porosity of the transition zone and it also reduces the concentration of oriented Ca(OH)2 crystals. Selection of Concrete Admixtures Concrete admixtures shall be selected carefully as per the specifications and shall be used as recommended by the manufacturer or by lab testing report. The quantity of admixtures to be used for specific application of admixtures are recommended by the manufacturers. For use in large construction projects, the quantity of the admixture to be used shall be obtained from tests reports for concrete mixed with admixtures at various percentage admixtures used. These tests are conducted to understand the behaviour of admixtures on the desired quality and strength of concrete at different quantities of admixtures used. Thus, the optimum quantity of admixtures can be selected for specific application based on results. The selection of specific admixtures for use in concrete to alter properties of concrete should be selected carefully as per requirement of concrete works. Concrete admixtures should be
used judiciously according to specification and method of application to avoid adverse effect on concrete properties at fresh and hardened state. After selecting the admixtures product, one should carefully choose the supplier with quality product, timely service and at a competitive price. The admixture supplier should be with a good history and should possess the staff with efficient and professional experience to guide on effective application/use of admixture in the right way. Concrete admixtures should be accepted with a test certificate, manufacturing date and its chemical composition, and should comply with specifications given by the authorities.

More Related Content

PPT
Admixtures , used in making of concrete in site
AryyakaSarkar
 
PDF
IRJET- Effect of Acid on Mechanical Properties of Epoxy Repaired Concrete
IRJET Journal
 
PDF
IRJET- Feasible Study on Self Compacting Concrete
IRJET Journal
 
PDF
REVIEW PAPER ON SELF-CURING CONCRETE USING BIO-ADMIXTURES
IRJET Journal
 
PDF
A Study On Self-Curing And Self-Compacting Concrete using Polyethylene Glycol
IRJET Journal
 
PDF
Experimental evaluation of the durability properties of high performance
IAEME Publication
 
PDF
Experimental evaluation of the durability properties of high performance
IAEME Publication
 
PDF
IRJET- Evaluation of Concrete Properties with Impregnated Different Polymers
IRJET Journal
 
Admixtures , used in making of concrete in site
AryyakaSarkar
 
IRJET- Effect of Acid on Mechanical Properties of Epoxy Repaired Concrete
IRJET Journal
 
IRJET- Feasible Study on Self Compacting Concrete
IRJET Journal
 
REVIEW PAPER ON SELF-CURING CONCRETE USING BIO-ADMIXTURES
IRJET Journal
 
A Study On Self-Curing And Self-Compacting Concrete using Polyethylene Glycol
IRJET Journal
 
Experimental evaluation of the durability properties of high performance
IAEME Publication
 
Experimental evaluation of the durability properties of high performance
IAEME Publication
 
IRJET- Evaluation of Concrete Properties with Impregnated Different Polymers
IRJET Journal
 

Similar to ADMIXTURE USED IN CONCRETE.docx (20)

PDF
EXPERIMENTAL STUDY ON THE EFFECT OF SAP ON CONCRETE
IRJET Journal
 
DOCX
Admixtures
Gaurang Kakadiya
 
PDF
IRJET-Experimental Investigation on Strength Characteristics of Concrete with...
IRJET Journal
 
PDF
IRJET- Experimental Study on the Behaviour of Self Healing Concrete using Sil...
IRJET Journal
 
PDF
Influence of silicone-based hydrophobic admixture on structural and mechanica...
IRJET Journal
 
PDF
Studying the Influence of Polycarboxylic Ether on Properties of Concrete
IRJET Journal
 
PPTX
Concrete Technology: Chemical and Mineral Admixture
Dr. S. GOPIKUMAR M.E, Ph.D
 
PPT
introduction to concrete
pravinakishor
 
PDF
An Analytical and Experimental Investigation of Ultimate Load Carrying capaci...
IRJET Journal
 
PDF
C046061219
IJERA Editor
 
PPTX
Role of chemicals in construction
Suhaa Chine
 
PDF
ADDITIVES_AND_ADMIXTURES[1] (3 presentation ).pdf
himanshimehta736
 
PPT
introduction to concrete
pravinakishor
 
PDF
Green concrete for sustainable construction
eSAT Publishing House
 
PDF
IRJET- Strength and Durability Studies on Concrete Made using Treated Recycle...
IRJET Journal
 
PDF
Evaluation of Performance of Geopolymer Concrete in Acid Environment
IRJET Journal
 
PDF
IRJET- Evaluation of Water Retaining Concrete Properties with Various Polymers
IRJET Journal
 
PDF
Mechanical and Statistical Study of Seawater Mixed Concrete
IRJET Journal
 
PDF
EFFECTS OF ACIDIC CURING ON THE PROPERTIES OF UNTREATED AND TREATED POLYESTER...
IAEME Publication
 
PDF
“ENHANCING CONCRETE PERFORMANCE WITH SUPERPLASTICIZER:A MIX DESIGN STUDY”
IRJET Journal
 
EXPERIMENTAL STUDY ON THE EFFECT OF SAP ON CONCRETE
IRJET Journal
 
Admixtures
Gaurang Kakadiya
 
IRJET-Experimental Investigation on Strength Characteristics of Concrete with...
IRJET Journal
 
IRJET- Experimental Study on the Behaviour of Self Healing Concrete using Sil...
IRJET Journal
 
Influence of silicone-based hydrophobic admixture on structural and mechanica...
IRJET Journal
 
Studying the Influence of Polycarboxylic Ether on Properties of Concrete
IRJET Journal
 
Concrete Technology: Chemical and Mineral Admixture
Dr. S. GOPIKUMAR M.E, Ph.D
 
introduction to concrete
pravinakishor
 
An Analytical and Experimental Investigation of Ultimate Load Carrying capaci...
IRJET Journal
 
C046061219
IJERA Editor
 
Role of chemicals in construction
Suhaa Chine
 
ADDITIVES_AND_ADMIXTURES[1] (3 presentation ).pdf
himanshimehta736
 
introduction to concrete
pravinakishor
 
Green concrete for sustainable construction
eSAT Publishing House
 
IRJET- Strength and Durability Studies on Concrete Made using Treated Recycle...
IRJET Journal
 
Evaluation of Performance of Geopolymer Concrete in Acid Environment
IRJET Journal
 
IRJET- Evaluation of Water Retaining Concrete Properties with Various Polymers
IRJET Journal
 
Mechanical and Statistical Study of Seawater Mixed Concrete
IRJET Journal
 
EFFECTS OF ACIDIC CURING ON THE PROPERTIES OF UNTREATED AND TREATED POLYESTER...
IAEME Publication
 
“ENHANCING CONCRETE PERFORMANCE WITH SUPERPLASTICIZER:A MIX DESIGN STUDY”
IRJET Journal
 
Ad

More from NAUGHTYBOY9 (20)

PDF
MECHANICS OF STRUCTURE.pdf
NAUGHTYBOY9
 
PDF
BUILDINGTECHNOLOGY AND PLANNING.pdf
NAUGHTYBOY9
 
PDF
ENGINEERING GEOLOGY.pdf
NAUGHTYBOY9
 
PDF
Fluid mechanics unit 3.pdf
NAUGHTYBOY9
 
PDF
Engineering mathematics 3.pdf
NAUGHTYBOY9
 
PDF
FLUID MECHANICS.pdf
NAUGHTYBOY9
 
PDF
MECHANICS OF STRUCTURE.pdf
NAUGHTYBOY9
 
PDF
BUILDING TECHNOLOGY AND ARCHITECTURAL PLANNING.pdf
NAUGHTYBOY9
 
DOCX
GTE_micro_project.docx
NAUGHTYBOY9
 
DOCX
HYD MP.docx
NAUGHTYBOY9
 
DOCX
RBE MP.docx
NAUGHTYBOY9
 
DOCX
TOS MP.docx
NAUGHTYBOY9
 
DOCX
EST MP.docx
NAUGHTYBOY9
 
DOCX
GTE MP.docx
NAUGHTYBOY9
 
DOCX
BPD MP.docx
NAUGHTYBOY9
 
DOCX
TYPES OF SUPPORTS,BEAM AND LOADING.docx
NAUGHTYBOY9
 
DOCX
TRAFFIC CONTROL DEVICES AND ROAD SIGNS.docx
NAUGHTYBOY9
 
DOCX
BCO MP.docx
NAUGHTYBOY9
 
DOCX
ASU MP.docx
NAUGHTYBOY9
 
DOCX
CME MP.docx
NAUGHTYBOY9
 
MECHANICS OF STRUCTURE.pdf
NAUGHTYBOY9
 
BUILDINGTECHNOLOGY AND PLANNING.pdf
NAUGHTYBOY9
 
ENGINEERING GEOLOGY.pdf
NAUGHTYBOY9
 
Fluid mechanics unit 3.pdf
NAUGHTYBOY9
 
Engineering mathematics 3.pdf
NAUGHTYBOY9
 
FLUID MECHANICS.pdf
NAUGHTYBOY9
 
MECHANICS OF STRUCTURE.pdf
NAUGHTYBOY9
 
BUILDING TECHNOLOGY AND ARCHITECTURAL PLANNING.pdf
NAUGHTYBOY9
 
GTE_micro_project.docx
NAUGHTYBOY9
 
HYD MP.docx
NAUGHTYBOY9
 
RBE MP.docx
NAUGHTYBOY9
 
TOS MP.docx
NAUGHTYBOY9
 
EST MP.docx
NAUGHTYBOY9
 
GTE MP.docx
NAUGHTYBOY9
 
BPD MP.docx
NAUGHTYBOY9
 
TYPES OF SUPPORTS,BEAM AND LOADING.docx
NAUGHTYBOY9
 
TRAFFIC CONTROL DEVICES AND ROAD SIGNS.docx
NAUGHTYBOY9
 
BCO MP.docx
NAUGHTYBOY9
 
ASU MP.docx
NAUGHTYBOY9
 
CME MP.docx
NAUGHTYBOY9
 
Ad

Recently uploaded (20)

PPTX
Measurement Uncertainty and Measurement System analysis
jayabal subbaian
 
PPT
Chapter 1 - Introduction to Manufacturing Technology_2.ppt
garciajeremiah070
 
PDF
Abrasive, erosive and cavitation wear.pdf
nfandraden
 
PDF
UEFA_Carbon_Footprint_Calculator_Methology_2.0.pdf
tuchinad02
 
PPTX
wireless networks, mobile computing.pptx
DayaFlorance
 
PPTX
Sorting and Hashing in Data Structures with Algorithms, Techniques, Implement...
usham61
 
PDF
UEFA_Embodied_Carbon_Emissions_Football_Infrastructure.pdf
tuchinad02
 
PDF
null (2) bgfbg bfgb bfgb fbfg bfbgf b.pdf
Ramez Hosny
 
PPTX
A Brief Introduction to IoT- Smart Objects: The "Things" in IoT
KeerthanaSahadevan1
 
PDF
Soil Improvement Techniques Note - Rabbi
rahmatideal000
 
PPTX
CN_Unite_1 AI&DS ENGGERING SPPU PUNE UNIVERSITY
versetooni85
 
PDF
August 2025 - Top 10 Read Articles in Network Security & Its Applications
IJNSA Journal
 
PDF
Exploratory_Data_Analysis_Fundamentals.pdf
Ashutosh Satapathy
 
PDF
Unit I -OPERATING SYSTEMS_SRM_KATTANKULATHUR.pptx.pdf
HarshDudhatra4
 
PDF
August -2025_Top10 Read_Articles_ijait.pdf
ijait
 
PPTX
Principal presentation for NAAC (1).pptx
GMKosgiker
 
PPTX
CyberSecurity Mobile and Wireless Devices
RobinRohit2
 
PDF
Applications of Equal_Area_Criterion.pdf
Puja Gurav
 
PDF
Unit1 - AIML Chapter 1 concept and ethics
muthusamyvijay762
 
PDF
Java Basics-Introduction and program control
lohithsrikarb719
 
Measurement Uncertainty and Measurement System analysis
jayabal subbaian
 
Chapter 1 - Introduction to Manufacturing Technology_2.ppt
garciajeremiah070
 
Abrasive, erosive and cavitation wear.pdf
nfandraden
 
UEFA_Carbon_Footprint_Calculator_Methology_2.0.pdf
tuchinad02
 
wireless networks, mobile computing.pptx
DayaFlorance
 
Sorting and Hashing in Data Structures with Algorithms, Techniques, Implement...
usham61
 
UEFA_Embodied_Carbon_Emissions_Football_Infrastructure.pdf
tuchinad02
 
null (2) bgfbg bfgb bfgb fbfg bfbgf b.pdf
Ramez Hosny
 
A Brief Introduction to IoT- Smart Objects: The "Things" in IoT
KeerthanaSahadevan1
 
Soil Improvement Techniques Note - Rabbi
rahmatideal000
 
CN_Unite_1 AI&DS ENGGERING SPPU PUNE UNIVERSITY
versetooni85
 
August 2025 - Top 10 Read Articles in Network Security & Its Applications
IJNSA Journal
 
Exploratory_Data_Analysis_Fundamentals.pdf
Ashutosh Satapathy
 
Unit I -OPERATING SYSTEMS_SRM_KATTANKULATHUR.pptx.pdf
HarshDudhatra4
 
August -2025_Top10 Read_Articles_ijait.pdf
ijait
 
Principal presentation for NAAC (1).pptx
GMKosgiker
 
CyberSecurity Mobile and Wireless Devices
RobinRohit2
 
Applications of Equal_Area_Criterion.pdf
Puja Gurav
 
Unit1 - AIML Chapter 1 concept and ethics
muthusamyvijay762
 
Java Basics-Introduction and program control
lohithsrikarb719
 

ADMIXTURE USED IN CONCRETE.docx

  • 1. Y.B. PATIL POLYTECHNIC SECTOR NO. 29, AKURDI, PUNE -411044, INDIA HRISHIKESH TARANGE – Y-2070-1901340102 ATHARVA PATIL – Y-2075-1901340081 YOGESH YELAVI -Y-2083-1901340103 PRATHAMESH ROKDE – Y-2031-1901340079 AVINASH SAKHERE – Y-2058 -1901340080 DAVENDRA SUTHAR – Y-2077-1901340104 This is to certify ;has satisfactorily carried out and completed the project work entitled Admixture used in concrete This work is being submitted for the award of Diploma in civil Engineering partial fulfillment of prescribed syllabus of M.S.B.T.E Mumbai for academic Year 2020 MS.SHEETAL BANDEWAR MR,ABHIJEET PATIL GUIDE HOD CIVIL DEPARTMENT PRINCIPLE PROF.A.S KONDEKAR Micro project proposal Admixture used in concrete
  • 2. 1.Aims/benefits of micro project: To get knowledge about total station its objective its component use in civil engineering introduction & knowledge of total station 2 Course outcome addressed. 1 To learn about total station 2. To learn about component & it use 3. To learn about their advantage & disadvantage 3 Action plan Sr. No. Details of activity Planned Start date Planed Finished date Name of responsible team member 1) Collection of information. 20/06/2020 20/06/2020 HRISHIKESH TARANGE – Y1171 ATHARVA PATIL – Y1154 2) Working of Microsoft Word. 20/06/2020 23/06/2020 YOGESH YELAVI – Y1177 PRATHAMESH ROKDE – Y1161 3) Taking Prints of the project made in Microsoft Word & Microsoft word & binding it 22/06/2020 22/06/2020 AVINASH SAKHERE – Y1162 DAVENDRA SUTAR – Y1170 5 Resource Required Sr.no Name of resource /materials specification Qty Remark 1 Internet and reference book Collect information 1
  • 3. 2 laptop Working on Microsoft word 1 Name of team member with roll no HRISHIKESH TARANGE – Y1171 ATHARVA PATIL – Y1154 YOGESH YELAVI – Y1177 PRATHAMESH ROKDE – Y1161 AVINASH SAKHERE – Y1162 DAVENDRA SUTAR – Y1170 Micro project evaluation sheet Name of student HRISHIKESH TARANGE – Y1171 ATHARVA PATIL – Y1154
  • 4. YOGESH YELAVI – Y1177 PRATHAMESH ROKDE – Y1161 AVINASH SAKHERE – Y1162 DAVENDRA SUTAR – Y1170 Name of programme: micro project on the topic Admixture used in concrete Semester:1st Course title: Concrete Technology Title of micro project : Admixture used in concrete Course outcome achieved 1 To learn about concrete 2. To learn about component & it use 3. To learn about their advantage & disadvantage Sr no Characteristic to be assessed Poor (mark 1-3) Average (mark 4-5) Good (mark 6-8) Excellent (mark 9-10) Sub total (A)PROCESS AND PRODUCT ASSESSMENT CONVERT ABOVE TOTAL MARK OUT OF 6 MARK 1 Relevance to the course 2 Literature review/information 3 Completion of the target as per project proposal 4 Analysis of date and representation 5 Quality of prototype/model 6 Report preparation (B)INDIVIDUAL PRESENTATION/VIVA CONVERT ABOVE MARK OUT OF 4 MARKS 7 Presentation 8 viva NAME ROLL NO (A) PROCESS AND PRODUCT ASSESSMENT (6MARK) (B) INDIVIDUAL PRESENTATIO N/ VIVA (4 MARK) TOTAL MARK (10 MARK)
  • 5. HRISHIKESH TARANGE Y-2070 ATHARVA PATIL Y-2075 YOGESH YELAVI Y-2083 PRATHAMESH ROKDE Y-2031 AVINASH SAKHERE Y-2058 DAVENDRA SUTAR Y-2077 COMMENTS/SUGGESTION ABOUT TEAMWORK/LEADERSHIP/INTER-PERSONAL COMMUNICATION ( IF ANY) NAME AND DESIGNATION OF TEACHER ………………………………………………… DATED SIGNATURE……………………………… TYPES OF ADMIXTURE USED IN CONCRETE Concrete admixtures (additives) enhance the properties of concrete for applications in construction with special requirements. Concrete additives are used to achieve desired workability in case of low water cement ratio, and to enhance setting time of concrete for long distance transportation of concrete.
  • 6. So, it is of much importance for a civil site engineer to know about the types of admixtures (additives) and their properties for better selection and application in concrete works. Definition of Concrete Admixtures As per BIS (IS �9103: 1999) Page No.1, Concrete Admixture is defined as a material other than water, aggregates and hydraulic cement and additives like Pozzolana or slag and fiber reinforcement, used as on ingredient of concrete or mortar and added to the batch immediately before or during its mixing to modify one or more of the properties of concrete in the plastic or hardened state. Reasons for Using Admixtures (ACI Committee Report Page �298) Admixtures are used to modify the properties of concrete or mortar to make them more suitable for the work at hand or for economy or for such other purposes as saving energy. Some of the important purposes for which admixtures are used are: To modify properties of fresh concrete, mortar and grout to: ● Increase workability without increasing water content or decrease water content at the same workability. ● Retard or accelerate time of initial setting. ● Reduce or prevent settlement.
  • 7. ● Modify the rate or capacity for bleedings. ● Reduce segregation. ● Improve pumpability. ● Reduce the rate of slump loss. To modify the properties of hardened concrete, mortar and grout to: ● Retard or reduce heat evaluation during early hardening. ● Accelerate the rate of strength development at early ages. ● Increase strength (compressive, tensile or flexural). ● Increase durability or resistance to severe condition of exposure. ● Decrease permeability of concrete. ● Control expansion caused by the reaction of alkalies with certain aggregate constituents. ● Increase bond of concrete to steel reinforcement. ● Increase bond between existing and new concrete. ● Improve impact resistance and abrasion resistance. ● Inhibit corrosion of embedded metal. ● Produce colored concrete or mortar When Concrete Admixtures Used? ● When properties cannot be made by varying the composition of basic material. ● To produce desired effects more economically. ● Unlikely to make a poor concrete better. ● Not a substitute for good concrete practice. ● Required dose must be carefully determined and administered How to Use Concrete Admixtures? ● Check job specification ● Use the correct admixture ● Never use one from an unmarked container. ● Keep containers closed to avoid accidental contamination. ● Add the correct dosage. ● Avoid adding ‘a little bit extra ● Use a dispenser ● Wash thoroughly at the end the day ● Best if added to the mixing water ● Manufacturer’s recommended dosage is usually adequate ● Trial mixes are important to determine most effective dosage Types of Concrete Admixtures (Additives)
  • 8. Types of admixtures as per� American Concrete Institute Committee report and� IS 9103: 1999 are: 1. Accelerating admixtures 2. Retarding admixtures 3. Water-reducing and set controlling admixtures 4. Air-entraining admixtures 5. Super plasticizing admixtures 6. Admixtures for flowing concrete 7. Miscellaneous admixtures Classification of admixtures according to the book of � Concrete Admixtures: Use and Applications�edited by M. R. Rixom are given in the forward pages. 1. Air Entraining Admixture These are generally used to improve workability, ease of placing, increased durability, better resistance to frost action and reduction in bleeding. The common Air-Entraining agents are natural wood resins, neutralized vinsol resins, polyethylene oxide polymers and sulfonated compounds. Mechanism of Air Entraining Concrete Admixtures
  • 9. These are anionic, because the hydrocarbon structures contain negatively charged hydrophilic groups, such as COO, SO3 and OSO so that large anions are released in water. Conversely, if the hydrocarbon ion is positively charged, the compound is cation active or cationic. In other words, anionic surface active agents produce bubbles that are negatively charged, cationic charged cause bubbles to be positively charged, surface active agents of all classes can cause air entrainment in concrete, but their efficiency and characteristics of air-void system vary widely. Properties of� Air entraining Admixtures ● These are foaming agents, gas producing chemicals. It introduces millions of tiny, stable bubbles of uniform size that are uniformly distributed throughout the mix (usually about 5% of the volume). ● Improves properties of fresh concrete such as workability, cohesion and reduces segregation and bleeding. ● Improves properties of hardened concrete – For every 1% of air there is a 4% loss in strength which is minimized by the reduction in water content. It improves durability of hardened concrete. 2. Accelerating Admixtures Accelerating admixtures are used for quicker setting times of concrete. It provides higher early strength development in freshly cast concrete. Main uses of Accelerating Concrete Admixtures ● These admixtures are suitable for concreting in winter conditions ● During any emergency repair work ● In case of early removal of formwork Disadvantages of Accelerating Concrete Admixtures ● It has increased drying shrinkage ● It offers reduced resistance to sulphate attack ● CaCl2 high risk of corrosion of steel �not permitted in reinforced concrete ● It is more expensive and less effective 3. Water Reducing Admixtures Chemical Types for Water Reducing Admixtures
  • 10. 1. Calcium or sodium salt of lignosulfonic acid 2. Poly carboxylic acid Mode of Action The principal role of mechanism of water reductions and set retardation of admixtures are usually composed of long-chain organic molecules that are hydrophobic (not wetting) at one end and hydrophilic (readily wet) at the other. Such molecules tend to become concentrated and form a film at the interface between two immiscible phases such as cement and water, and alter the physio-chemical forces acting at this interface. The mechanism by which water reducing admixture operates is to deflocculate or to disperse the cement agglomerates into primary particles or atleast into much smaller fragments. This deflocculating is believed to be a physicochemical effect whereby the admixture is first of all adsorbed on to the surface of the hydrating cement, forming a hydration � sheath� , reduces the antiparticle separated from one another. The presence of water reducing admixture in a fresh concrete results in: 1. a reduction of the interfacial tension. 2. an increase in the electro kinetic potentials and 3. protection sheath of water dipoles around each particle i.e. mobility of fresh mix becomes greater, partly because of reduction in inter-particle forces and partly because of water freed from the restraining influence of the highly flocculated system which is now available to lubricate the mixture. Hence less water is required to achieve given consistency. Why Water Reducing Admixtures used? a) Concrete having greater workability be made without the need for more water and so strength losses are not encountered b) By maintaining some workability, but at a lower water content, concrete strengths may be increased without the need for further cement addition c) While maintaining the same w/c ratio and workability concrete can be made to a given strength as in the reference concrete at lower cement content.
  • 11. Effect on durability The straight addition of admixtures of this type does not came any increase in permeability and indeed where the admixture is used to reduce the w/c, then permeability is considerably reduced. Effect on shrinkage Admixture of this type when used as workability aids on water reducers do not adversely affect the shrinkage. Effect on creep Materials of this type of admixture have no deleterious effect on the creep of concrete. Detrimental effect a) While using a water reducing agent. Care must be taken in controlling the air content in the mix. Most water-reducing agents entrain air due to their surfactant properties. b) At high doses of lignosulphonate material, retardation of the mix occurs. Applications of Water Reducing Concrete Admixtures The application of the type of admixtures are as follows � a) When concrete pours are restricted due to either congested reinforcement or these sections. b) When harsh mixes are experienced such as those produced with aggregates (crushed). Then considerable improvement in the plastic properties of concrete can be obtained. c) When required strengths are difficult to obtain within specified maximum cement content and where early lifting strengths are required. d) By addition of this admixture in concrete cement economics of about 10% can be obtained.
  • 12. 4. Retarding Concrete Admixtures The function of retarding concrete admixture is to delay or extend the setting time of cement paste in concrete. These are helpful for concrete that has to be transported to long distance in transit mixers and helpful in placing the concrete at high temperatures, specially used as grouting admixture and water reducers results in increase of strength and durability. Chemical type for Retarding Concrete Admixture a) Unrefined lignosulphonates containing sugar, which of course the component responsible for retardation. b) Hydroxyl carboxylic acid and their salts c) Carbohydrates including sugar d) Soluble zinc e) Soluble borates etc. Mode of action It is thought that retarding admixtures are absorbed on to the C3A phase in cement forming a film around the cement grains and presenting or reducing the reaction with water. After a while the film breaks down and normal hydration proceeds. This a simple mixture and there is a reason to believe that retards also interact with C3S since retardation can be extended to a period of many days. Why are Retarding Concrete Admixtures used? To delay in the setting time of concrete without adversely affecting the subsequent strength development. Advantage of Retarding Concrete Admixture a) The hydroxyl carboxylic acid type admixture normally produces concrete having a slightly lower aim content them that of a control mix.
  • 13. b) Materials of this class (lignosulphonate containing sugar and derivatives of hydroxyl carboxylic acid) in some cases have a much higher dispersing effect and hence water reducing capacity. c) Durability increases. Detrimental effect a) When lignosulphonate based material is used, then the air content might be 0.2 to 0.3% higher unless materials of the tributyl phosphate type are added. b) As the water content increases, so there is a tendency for drying shrinkage. Applications of Retarding Concrete Admixture Retarding admixtures are used a) Where long transportation of ready mixed concrete is required then premature setting can be usefully avoided by this type admixture. b) When concrete is being placed or transported under conditions of high ambient temperature. c) In case of large concrete pours d) Concrete construction involving sliding formwork 5. Super Plasticizers or High Range Water-Reducing Admixtures in Concrete These are the second generation admixture and also called Superplasticizers. These are synthetic chemical products made from organic sulphonates of type RSO3, where R is a complex organic group of higher molecular weight produced under carefully controlled conditions. The commonly used superplasticizer are as follows: i) Sulphonated melamine formaldehyde condensate (S M F C)
  • 14. ii) ii) Sulphonated naphthalene formaldehyde condensate (SNCF) iii) iii) Modified ligno-sulphonates and other sulfonic esters, acids etc., Chemical type a) formaldehyde derivatives such as melamine formaldehyde and naphthalene sulphonate formaldehyde. Mode of action of SuperPlasticizer Admixtures This admixture acts in the same way as that of a water reducing admixture acts. It disperses the cement agglomerates when cement is suspended in water and adsorbed on to the surface of cement, causing them mutually repulsive as a result of the anionic nature of super plasticizers. Why are Superplasticizer Admixtures used? a) At a given w/c ratio, this admixture increases the workability, typically by raising the slump from 75 mm to 200 mm. b) The second use of these admixtures is in the production of concrete of normal workability but with an extreme high strength (super plasticizer can reduce the water content for a given workability by 25 �35 percent compared with half that value in the case of conventional water reducing admixtures). Advantages of Superplasticizer Admixtures a) The concrete using this admixture can be placed with little or no compaction and is not subject to excessive bleeding or segregation. b) They can be used as high dosages as they do not markedly change the surface tension of water. c) It does not significantly affect the setting of concrete except that when used the cements have a very low C3A content.
  • 15. d) They do not influence shrinkage, creep modulus of elasticity or resistance to freeing to thawing. Disadvantage The only real disadvantage of superplasticizer is their relatively high cost. Applications of Super Plasticizer Admixtures a) In very heavily reinforced sections, in inaccessible areas in floor or road slabs. b) Where very rapid placing is desired. 6. Mineral Admixtures for Concrete Mineral admixtures are finely divided materials which are added to the concrete in relatively large amounts, usually of the order of 20 to 100 percent by weight of Portland cement. Source of Mineral Admixtures a) Raw or calcined natural minerals b) Industrial by products Reasons for using mineral admixtures a) In recent years�considerable efforts have been made by the cement industry world wide to reduce energy consumption in the manufacture of Portland cement. Therefore, a partial replacement of Portland cement by mineral admixtures which can be of the order of 50 � 60% by weight of total cementitious material, represents considerable energy savings. b) The ability of cement and concrete industries to consume mithions of tons of industrial byproducts containing toxic metal would qualify these industries to be classified as environmentally friendly. c) Since natural Pozzolana and industrial by-products are generally available at substantially lower costs than Portland cement, the exploitation of the Pozzolanic and cementitious
  • 16. properties of mineral admixtures are used as a partial replacement of cement can lead to a considerable economic benefit. d) Possible technological benefits from the use of mineral admixtures in concrete include entrancement of impermeability and chemical durability, improved resistance to thermal cracking and increase in ultimate strength. Classification of Mineral Admixture Mineral admixtures may be classified as follows � a) Pozzolanic Silicon or siliceous and admixtures material which itself possesses little or no cementitious value but is the presence of moisture chemically reacts with CalOH2 at ordinary temperature to form compounds possessing cementitious properties. b) Pozzolanic & Cementitious �The materials which have some cementitious properties in itself. ASIM specification C618 recognizes the following three classes of mineral admixtures. a) Class N �Raw or calcined natural pozzolanic such as diatomaceous earths, clay and shales, tuffs and volcanic ashes. b) Class F �Fly ash produced from burning anthracite or bituminous coal. c) Class C �Ash normally produced from lignite or sub-bituminous coal which may contain analytical CaO higher than 10%. 7. Silica Fume as Concrete Admixture Although the use of silica fume (SF) in concrete has increased significantly in the past few years, its beneficial properties were not well realized until comprehensive research was undertaken in the late 70's and early 80's at the Norwegian Ins. of technology to study the influence of SF on concrete properties. Production of Silica Fume
  • 17. Silicon, ferrosilicon or other alloys are produced in so-called � submerged are electric furnaces� . There are two types of electric furnaces one is with a heat recovery system and the other is without a heat recovery system. Types of Alloys Produced in Submerged Arc Electric Furnaces a) Ferrosilicon of various Si contents – FeSi �50% with a 43 to 50% Si content – FeSi �75% with a 72 to 78% Si content – FeSi �90% with a 87 to 96% Si content b) Calcium silicon c) Ferrochromium Silicon d) Silicomanganese Specific Gravity and Specific Surface Area of SF The specific gravity of SF is generally equal to that of amorphous silica which is about 2.20. However, depending on its chemical composition, the specific gravity of a SF particle can be as high as 2.40 and 2.55, as in the case of FeGSi. The specific surface area of SF measured by nitrogen absorption is given below. SF Calculated Surface Area (m2/kg) Measured by Nitrogen Adsorption Mean Diameter (mm) Si 20000 18500 0.18 FeCrSi 16000 – 0.18
  • 18. FeSi � 50% 15000 – 0.21 FeSi � 75% 13000 15000 0.26 However, regardless of the differences in chemical composition, color and carbon content, all types of SF share a certain number of common, yet important physio chemical characteristics, which make them effective supplementary cementitious materials to cement concrete. these properties are as follows � a) SF originates from the condensed SiO vapors and generally has a high content of silica of 35 to 98% b) SF is an amorphous material c) SF is composed mostly of fine spheres with a mean diameter of 0.1 to 0.2 mm. Filler and Pozzolanic effects of Silica Fume The unique characteristics of SF that make it suitable for use as supplementary cementitious materials are its fineness, highly amorphous nature and elevated content of SiO2. The small SF spheres act as fillers since they occupy some of the space between the relatively coarse cement grains which can be otherwise occupied by water. This results also in a denser matrix with a better gradation of fine particles. Bache stated that in a super plasticized, low w/c ratio concrete, small SF spheres can displace water entrapped between the flocculated cement grains, thus increasing the amount of free water in the paste which enhances fluidity. Several researchers have studied the pozzolanic properties of SF. The resulting reactions between SF and Ca(OH)2 increases the volume of CSH and reduces the total volume of
  • 19. capillary pores in the cement paste. The pozzolanic reactions of SF with Ca(OH)2 reduces the amount of Portlandite in the hydrate cement paste. Mehta explained that the absence of large Portlandite crystals in a SF mixture can be due to the fact that each SF particle can act as a � nucleation site�for precipitation of Ca(OH)2. As a result, numerous small crystals of Ca(OH)2 can form rather than a few large ones. This absence of large and weak crystals of Portlandite enhances the mechanical properties of concrete. The beneficial action of SF has also been attributed to the reduction of the porosity of the transition zone between the cement paste and aggregate which increases the strength and impermeability of the concrete. In conventional concrete, the transition zone can have large and oriented Portlandite crystals which form weak zones in the concrete. The thickness of the transition zone can be drastically produced by adding SF to the concrete since SF reduces bleeding and the amount of water accumulation under aggregate. As a result, it decreases the porosity of the transition zone and it also reduces the concentration of oriented Ca(OH)2 crystals. Selection of Concrete Admixtures Concrete admixtures shall be selected carefully as per the specifications and shall be used as recommended by the manufacturer or by lab testing report. The quantity of admixtures to be used for specific application of admixtures are recommended by the manufacturers. For use in large construction projects, the quantity of the admixture to be used shall be obtained from tests reports for concrete mixed with admixtures at various percentage admixtures used. These tests are conducted to understand the behaviour of admixtures on the desired quality and strength of concrete at different quantities of admixtures used. Thus, the optimum quantity of admixtures can be selected for specific application based on results. The selection of specific admixtures for use in concrete to alter properties of concrete should be selected carefully as per requirement of concrete works. Concrete admixtures should be
  • 20. used judiciously according to specification and method of application to avoid adverse effect on concrete properties at fresh and hardened state. After selecting the admixtures product, one should carefully choose the supplier with quality product, timely service and at a competitive price. The admixture supplier should be with a good history and should possess the staff with efficient and professional experience to guide on effective application/use of admixture in the right way. Concrete admixtures should be accepted with a test certificate, manufacturing date and its chemical composition, and should comply with specifications given by the authorities.