Sab 4163 Mix Design Intro & Eg 1

ASSOC.PROF. DR. AHMAD MAHIR MAKHTARM46-334

INSPIRING CREATIVE AND INNOVATIVE MINDS

University of Bath UK 2008 Western Michigan University USA 2010

SAB 4163CONCRETE

TECHNOLOGY


Robin Hood Castle Nottingham UK

SAB 4163CONCRETE TECHNOLOGY

PROGRAMME OBJECTIVESLEARNING OUTCOMES


COURSE LEARNING OUTCOMES


COURSE OUTLINE


Week Date Lecture Topics/Contents8 31.8.2010

1.9.201019 & 2021

Introduction to concrete mix design. Concept and background information.Design process.

9 21.9.201022.9.2010

22 & 2324

Concrete mix design examples. Modification to the mix design for pfa/ggbs mixes.

10 28.9.201029.9.2010

25 & 2627

Introduction to high strength concrete. Design for high strength concrete.Application of high strength concrete.

11 5.10.20106.10.2010

28 & 2930

Introduction to polymer in concrete. Polymer concrete, polymer impregnated concrete & polymer modified concrete.Design of polymer modified concrete. (Test 2)

12 12.10.201013.10.2010

31 & 3233

Introduction of to fibre reinforced concrete and ferrocement.Types and applications

13 19.10.201020.10.2010

34 & 3536

Introduction of repair to concrete structures. Causes of deterioration.Types of concrete deterioration.

14 26.10.201027.10.2010

37 & 3839

Diagnosis and methods of structural assessment.Repair materials and techniques.

15 1.11.2010 EXAMINATION LEAVE16 8.11.2010 EXAMINATION WEEK

COURSE OUTLINESAB 4163 CONCRETE TECHNOLOGY


DESIGNING

A CONCRETE MIX

DOE METHOD



• Constituents: cement, aggregates, water and admixtures (if necessary)

• Most widely used construction materials – abundantly available raw materials

• Versatile – can be cast into any desired shape

• Comparatively required low skill workers but knowledgeable


What is Concrete?

CONCRETE AS A CONSTRUCTION MATERIAL


• Can be designed to a desired strength

• Can be prepared to a required workability

• Can be designed to accommodate the desired environmental conditions

• Can be enhanced by using other materials


Why do we use Concrete?

• Adding the right proportion of concrete constituents:– Cement, fine & coarse aggregates & water

• Mixing the concrete thoroughly• Placing the concrete correctly• Compacting the concrete sufficiently• Cure the concrete properly


How do we cast the Concrete?

• Quality of cement is guaranteed in a similar manner as steel but concrete is the building material not cement

• Good concrete depends on good materials, design and workmanship

• Good concrete:– Satisfactory in the hardened state– Satisfactory while being transported and placed in

the formwork


Making Good Concrete

DESIGNING

A CONCRETE MIX


CONCRETE MIX DESIGN

Consists of selecting the correct proportions of cement, fine and coarse aggregate and

water to produce concrete having the specified properties


How & Why?

Concrete Mix Design

• Required for obtaining the desired proportions

• Types of mix design – standard mix design, British mix design (DOE method) etc.

• Factors governing the selection – strength, workability, durability, aggregate types and cement types.


• Based on BS 5328: Part 2: 1991

• Applicable for concrete mix design up to the strength of 25 MPa only

• Suitable for 40mm and 20 mm coarse aggregates

• Design for slump of 75 and 125 mm slump only


Standard Mix

• Specified by a designer in terms of the nature and proportions of mix ingredients

• The assessment of mix proportions is used for compliance purposes– Strength testing not being routinely used

• Is used when particular properties of concrete are required, e.g. its finish or abrasion resistance, assuming it will have the required workability, strength and durability


Prescribed Mix

• Procedure as specified in Table 1• Required some specified information

– Characteristic strength from structural engineer– Workability and the size of aggregate, based on

the nature of application– Durability, based on the condition of the

application

• Tables and figures are based on UK data• Design for 1 m3 concrete


Designed Mix (DOE)



Figure 2

DIFFERENT TYPES OF CEMENT


• Ordinary Portland cement (300 – 400 m2/kg)– Most commonly used– Suitable for general purpose– Lime saturation factor 0.66 – 1.02

• Rapid-hardening Portland cement (450 – 600 m2/kg)– Develop strength more rapidly– High early strength cement– Similar setting time– Higher C3S content and finer grinding


Types of Cement

• Ultra high early strength cement– Grinding to a very high fineness (700 – 900 m2/kg)– Very high C3S and very low C2S content– Deteriorates rapidly on exposure

• Low heat Portland cement– Needed due to rise in temperature in the interior of

a large concrete mass– Limiting heat of hydration to 60 cal/g at 7 days and

70 cal/g at 28 days– Limit of lime content


Types of Cement


Types of Cement

Sulfate-resisting cementTo avoid sulfate attackLow C3A content (< 3.5 per cent)

White cement and pigmentsFor architectural purposesRaw materials contain little iron oxide and manganese oxide

Portland blastfurnace cementMixture of Portland cement and ground granulated blastfurnace slag

ORDINARY PORTLAND CEMENT (OPC)

CHEMICAL COMPOSITION


Oxide % Bogue Composition % CaO 63 C3A 10.8

SiO2 20 C3S 54.1

Al2O3 6 C2S 16.6

Fe2O3 3 C4AF 9.1MgO 1.5

Alkalis (Na2O) 1

SO3 2Others 1Loss on ignition 2Insoluble residue 0.5


Typical Composition

• Four compounds are usually regarded as the major constituents of cement:– Tricalcium silicate C3S– Dicalcium silicate C2S– Tricalcium aluminate C3A– Tetracalcium aluminatoferrite C4AF

• ‘Potential’ composition calculated based on ‘Bogue composition’


Chemical Composition

• C3S = 4.07(CaO) - 7.60(SiO2) - 6.72(Al2O3) -1.43(Fe2O3) - 2.85(SO3)

• C2S = 2.87(SiO2) - 0.75(3CaO.SiO2)

• C3A = 2.65(Al2O3) - 1.69(Fe2O3)

• C4AF = 3.04(Fe2O3)


Bogue Composition

HYDRATION PROCESS OF OPC


• Reaction of cement becomes a bonding agent take place in a water-cement paste

• Main hydrates are calcium silicate hydrates and tricalcium aluminate hydrate

• Progress of hydration can be determined by:– Amount of Ca(OH)2

– Heat evolved– Specific gravity of the paste– Chemically combined water– Amount of unhydrated cement– Indirectly from strength of hydrated paste


Hydration of Cement

• 2C3S + 6H C3S2H3 + 3Ca(OH) 2

• 2C2S + 4H C3S2H3 + Ca(OH) 2

• C3A + 6H C3AH6

• C4AF + 2Ca(OH)2 + 10H C3AH6 + C3FH6


Hydration of Cement

Oxide % CaO 60 – 67

SiO2 17 – 25

Al2O3 3 – 8

Fe2O3 0.5 – 0.6MgO 0.5 – 4.0

Alkalis (Na2O) 0.3 – 1.2

SO3 2.0 – 3.5


Composition Limits

WATER FOR CONCRETE MIXES


Purpose

• Purpose: for hydration and workability• Water content – free w/c (not including

the water absorbed by the aggregates)• Water exists in capillary water,

adsorbed water, interlayer water and chemically combined water.

• Capillary water: present in voids larger than about 50A


• Quality of mixing water – should not contain undesirable chemical and physical substances in excessive proportions.

• Water with pH of 6.0 to 8.0 which does not taste brackish suitable for use but dark colour or bad smell do not necessarily mean deleterious substances present.

• Compressive strength and setting time (initial) tests used for water suitability test.


Quality of Water

• In project specification, quality of water is covered by a clause “water should be fit for drinking”

• Such water rarely contains dissolved inorganic solids in excess of 2000ppm

• Potable water generally fit for mixing but some contain excessive chloride which is harmful for concrete

• Some natural mineral waters contain undesirable amounts of alkali carbonates bicarbonates which can contribute to alkali-silica reaction


Quality of Mixing Water

• Some waters not fit for drinking can be satisfactorily used in making concrete

• Quality of mixing water – should not contain undesirable chemical and physical substances in excessive proportions

• Water with pH of 6.0 to 8.0 which does not taste brackish suitable for use but dark colour or bad smell do not necessarily mean deleterious substances present



• Brackish water contains chlorides and sulphates

• Water is harmless when chlorides does not exceed 500ppm or SO3 does not exceed 1000ppm

• Compressive strength and setting time (initial) tests used for water suitability test

• Results are compared with corresponding results made with known “good” quality water



• Tolerance of 10% is permitted to allow variations in strength.

• Natural waters that are slightly acidic are harmless.

• Water containing humic or other organic acids may adversely affect the hardening of concrete.



• Sea water has total salinity of about 3.5 per cent, produces a slightly higher early strength but a lower long-term strength

• The loss of strength is no more than 15 per cent and can tolerated

• Sea water (large quantities of chlorides) tends to cause persistent dampness and surface efflorescence

• Presence of chlorides can lead to corrosion, limit the total chloride content in concrete



AGGREGATES

COARSE FINE


• The coarse aggregate is defined as containing a high proportion of particles retained on a 5mm (0.197 in.) sieve.

• Aggregates can be classified into just two types, crushed and uncrushed.

• Uncrushed aggregates are usually smoother than crushed aggregates.


Coarse Aggregates

• Crushing strength of aggregate obtained from indirect tests, eg. crushing value of aggregate

• Strength and elasticity of aggregate depend on its composition, texture and structure

• A good average value of crushing strength of aggregate is about 200MPa (but many down to 80 MPa)

• Required strength of aggregate is higher than normal range of concrete strengths


Strength of Aggregates

• The grading of the fine aggregate is characterised by the percentage passing the 600µm test sieve

• Fine aggregates should comply with the C, M or F grading requirements of BS 882: 1983


Fine Aggregates

FRESH CONCRETE


• Property of freshly mixed concrete which determines the ease and homogeneity with which it can be mixed, placed, consolidated and finished – ACI

• Tests – slump, compacting factor, vebe, flow table


Workability

• Slump test– Fill in three layers and measure the drop– Popular because of the simplicity, more of quality

assurance used rather than measuring the workability

• Compacting factor test– Fill from the top bucket, let it fill the middle bucket

and allow to fill the cylinder– Fill back the cylinder with new concrete and fully

compacted it– Determine the ratio of partially compacted concrete to

the fully compacted concrete


Workability Test

• Vebe test – Fill the cone as the slump test– Measure the time for the mix to transform from the

cone shape to the cylinder shape

• Flow table test– For mixes with high workability– Fill the cone as the slump test– Lift up the table as standard– Measure the diameter of the mix diagonally


Workability Test

• Consistency– The ease of flow

• Cohesiveness– The tendency to bleed and segregate

• Factors affecting the workability– Water content– Maximum size of aggregate– Grading, texture and shape


Attributes & Factors

• Segregation– Separation of the components of fresh

concrete

• Bleeding– Appearance of water on the surface

• Laitance– Tendency of water rising in the internal

channels within the concrete


Wet Concrete

CONCRETE MIX DESIGN

DOE METHOD


• The British method of concrete mix design, popularly referred to as the "DOE method", is used in the United Kingdom and other parts of the world and has a long established record.

• The method originates from the "Road Note No 4“ which was published in Great Britain in 1950. In 1975 the note was replaced by the "Design of Normal Concrete Mixes", published by the British Department of the Environment (DOE).

• In 1988 the "Design of Normal Concrete Mixes" was issued in a revised and updated edition to allow for changes in various British Standards


The History

• The DOE method utilizes British test data obtained at the Building Research Establishment, the Transport and Road Research Establishment, and the British Cement Association.

• The aggregates used in the tests conformed to BS 882.

• The cements comply to BS 12 or BS 4027


Constituents

• The DOE method is based on various assumptions and requirements:

• Mixes are specified by the weights of the different materials contained in a given volume of fully compacted concrete.

• It is assumed that the volume of freshly mixed concrete equals the sum of the air content and of the absolute volumes of its constituent materials. The method therefore requires that the absolute densities of the materials be known in order that their absolute volumes may be calculated.


Assumptions

• The absolute volume of a quantity of a material is the sum of the volumes of its particles.

• The DOE Method, assumes that the volume of fully compacted freshly mixed concrete equals the sum of absolute volumes of its constituent materials.


Absolute Volume

• It is assumed that the workability of a concrete mix depends primarily on: – The Free Water Content – The Fine Aggregate Type and, to a lesser

degree, the Coarse Aggregate Type– The Maximum Size of Coarse Aggregate


Assumptions

• The water, which is available to react with the cement, is termed the free water content of the concrete and influences the strength, durability and workability of the concrete critically.

• The free water content is generally determined by a compromise between workability requirements and strength and durability needs.

• It is the sum of – the mix water – the surface water of the aggregates

• less– the water absorbed by the aggregate in the time between the mixing

and the setting of the concrete.


Free Water Content

• Consists of the water absorbed by the aggregate to bring it to a saturated surface-dry condition, and

• The free water available for the hydration of the cement, and

• For the workability of the fresh concrete


Total Water Content

• It is assumed that the strength of a concrete mix depends on: – The Free water/Cement Ratio; – The Coarse Aggregate Type; – The Cement Properties.


Concrete Strength

• The Free Water/Cement Ratio is defined as the ratio by weight of the free water content to the cement content.

• It has been long been accepted that a low free water/cement ratio in a concrete mix is essential for the concrete’s subsequent strength and durability.

• It appears that an excessive free water content leads to the formation of capillary pores, which seriously affect the concrete strength and the concrete durability.


Free Water/Cement Ratio

• The DOE method determines the Free Water/Cement Ratio, which will provide a particular concrete strength for different cement properties and coarse aggregate types, using the results of numerous tests.


Free Water/Cement Ratio

• Characteristic strength strictly means the concrete strength , below which on average a certain proportion of test results will fall. This proportion is termed the "proportion of defectives".

• Many Standards, for example BS8110, use characteristic strengths as a basis for concrete design.

• Characteristic strength can also denote a nominal concrete strength below which a small number of results will be permitted to fall.


Characteristic Strength

• It is defined in statistics as the proportion of a set of test results, which will fail on average.

• The CIB/FIP "International recommendations for the design and construction of concrete structures“, BS 5328:1985 and BS 8110:1985, all recommend that a proportion of defectives of 5 percent

should be adopted for concrete

strength test results.


Proportion of Defectives


Characteristic and Mean Strength

1

23

4

5

• Generally a concrete mix is required to provide a specified strength.

• The most common measure of concrete strength is the compressive strength, determined in either a cube test or a cylinder test.

• Since the strength of a concrete specimen increases with time, the concrete age at testing is significant.

• It is also important to remember that the target strength of a mix will only be attained in practice, if the concrete is properly placed, well compacted and adequately cured.


Concrete Strength

• A concrete mix must provide adequate durability. However concrete mixes are not normally tested for durability directly.

• Instead concrete specifications frequently contain mix requirements, which are designed to provide durability by ensuring that the set concrete attains a minimum strength.

• It allows to specify a Maximum Free water/Cement Ratio for durability purposes.


Durability of Concrete

• Concrete strength is influenced by the coarse aggregate type used in the mix

• Generally uncrushed aggregates are smoother than crushed aggregates and so concrete made with crushed aggregates can achieve a given strength with a higher free water/cement ratio than concrete made with uncrushed aggregates.


Aggregates & Strength

• The type of aggregate influences the workability.

• In comparison with concrete made with uncrushed coarse aggregate, concrete containing crushed coarse aggregate will generally have superior strength and inferior workability, although the coarse aggregate has considerably less influence on the workability than the fine aggregate.


Aggregates & Workability

• Generally uncrushed aggregates are smoother than crushed aggregates and so concrete made with uncrushed aggregates needs less free water to achieve a given workability than concrete made with crushed aggregates.

• Since the fine aggregate has a greater influence on the workability than the coarse aggregate, the DOE method assumes that the influence of the fine aggregate type on the required free water content for workability is twice that of the coarse aggregate type.


Aggregates & Workability

Mix Design Stages

• The mix design DOE Method is carried out in the following five stages.– Stage (I). Determine Free Water/Cement Ratio

Required for Strength.– Stage (II). Determine Free Water Content

Required for Workability – Stage (III). Determine Required Cement

Content – Stage (IV). Determine Total Aggregate Content – Stage (V). Determine Fine Aggregate Content


• Determine Free Water/Cement Ratio Required for Strength – Either use a specified margin or calculate a margin for a

given proportion of defectives and statistical standard deviation.

– Obtain the target mean strength by adding the margin to the required characteristic strength.

– Either accept a specified free water/cement ratio or obtain the maximum free water/cement ratio which will provide the target mean strength for concrete made from the given coarse aggregate type and from cement with the given properties.


Stage (I)

• Determine Free Water Content Required for Workability – Either use a specified free water content or obtain

the minimum free water content, which will provide the desired workability for concrete made with the given fine aggregate type, coarse aggregate type and maximum size of coarse aggregate.

– If the free water content has been determined for workability, adjust the required free water content if air entrainment is specified, and adjust further if a water-reducing admixture is specified.


Stage (II)

• Determine Required Cement Content – Obtain the minimum cement content, which is

required for strength, by dividing the free water content obtained in Stage (II) by the free water/cement ratio obtained in Stage (I).

– Check the minimum cement content, which is required for strength, against the maximum cement content, which is permitted, and give a warning if the former exceeds the latter.


Stage (III)

– Check the minimum cement content, which is required for strength, against the minimum cement content, which is allowable for durability, and adopt whichever is greater to be the cement content in the mix.

– Divide the free water content by the cement content used in the mix to obtain a modified free water/cement ratio.


Stage (III)

• Determine Total Aggregate Content – Obtain a value for the overall aggregate density. – Obtain the fractional volume of the aggregate by

subtracting the proportional volumes of the free water and the cement from a unit volume.

– Calculate the total aggregate content by dividing the volume of the aggregate by the aggregate density.


Stage (IV)

• Determine Fine Aggregate Content – Either use a specified value of the percentage of

fine aggregate, or obtain the percentage of fine aggregate, which will provide the desired workability for concrete made with the given grading of fine aggregate, maximum size of coarse aggregate and the free water/cement ratio obtained in Stage (III).

– Calculate the fine and coarse aggregate contents from the total aggregate content obtained in Stage (IV) and the percentage of fine aggregate.


Stage (V)



Characteristic and Mean Strength

1

23

4

5


EXAMPLE 1

30 282.5

8

1.96 1.96 8 16/

30 16 46

Unrestricted design

0.470.55 0.47



0.5

42

46

0.47


10 - 30

20

160



160 0.47 340

290

340


26

2400

2400 340 160 1900



70

25 – 30, say 27

1900

1900

0.27 515

515 1385


0.47

27

70


340 160 515 460 925

0.05 17.0 8.0 25.7 23 46.2

1 : 21385

Date post:	22-Oct-2014
Category:	Documents
Upload:	amirah-aziz
View:	37 times
Download:	0 times

Sab 4163 Mix Design Intro & Eg 1

Documents