AGGREGATE-INFLUENCE-CONCRETE-STRENGTH

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Civil and Structural Engineering Works THE INFLUENCE OF AGGREGATE PROPERTIES ON STRENGTH OF CONCRETE Research by : Nik Zafri Abdul Majid A Dedication to Graduates of Civil Engineering in Malaysia

© 2000 - Infringement of any forms on part(s) of this document/intellectual shall result in legal action. Prior written permission is required from the author. CHAPTER 1 1.0 INTRODUCTION 1.1 Introduction and Definition Aggregates are defined as: ‘particles of rock which, when brought together in a bound or unbound condition, form part or whole of an engineering or building structure’ Natural, sand, gravel and crushed rock aggregates are fundamental to the man-made environment and represent a large proportion of the material used in the construction industry. Despite the importance of geological material in civil engineering, design and construction, the discipline of engineering geology has traditionally been concerned more with interaction between engineering structure and its geological environment than the performance of rock aggregates in the structure itself. This imbalance is being recognized and adjusted in the fields of teaching, practice and research but an inhibiting factor is the profuse but highly open in browser PRO version


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dispersed nature of the literature on aggregate materials. There was lack of reference manuals and textbooks or even broadly based review publications, giving a comprehensive coverage of the subject. It's time to make a change. The available information is scattered through innumerable standards, specifications, research reports, professional papers & articles in the commercial press. Consequently, those who are concerned with construction, but are not material specialist, often find difficulty in identifying the literature to guide them in defining and implementing specification requirement. In the case of Malaysia, the prevalent reference would be the British Standards and Codes of Practice that lead to many difficulties of adherence due to environmental differences. For this reason, standard and codes should be thoroughly studied to suit the Malaysian environment in terms of difference properties value for local aggregate. At present, besides Information Technology, Malaysia is known to be one of the leading Asian country in the provision of construction services in civil, structural and building engineering works. The construction of highrises such as the majestic PETRONAS Twin Towers KLCC and TELEKOM KL Tower are some of the classic examples of well-balanced qualitative and quantitative application of concreting technology to suit the nature of the respective superstructure and design. Inevitably, important elements such as design and concrete mix have always been parts and parcels when discussing the topic of concrete strength. In mix design, only selection of aggregates; either crushed or uncrushed, and size/volume are considered. Care is not taken to thoroughly analyse the influence of aggregate properties on the strength of concrete which lead the researcher to conduct this research. 1.2 Objective and Scope of Work This research shall only be based on series of experiments conducted in laboratory and is limited to crushed aggregates of 20mm grade due to its’ vast application in Malaysia. The aggregates are being extracted from random quarries (averaged to 5 nos. of most accurate values) The datum of aggregate properties are based on : a. Aggregate Impact Value (AIV) open in browser PRO version


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b. Aggregate Crushing Value (ACV) c) 10 % Fine Value (10%V) d) Water Absorption (WO) e) Los Angeles Abrasion Value (LA AV) f) Polished Stone Value (PSV) shall be obtained from respective quarry owners where testings and samplings are being conducted in a lab. The concrete strength testings being conducted are based on the following: i) Crushed Cube Test using with a dimension of 150 X 150 X 150mm ii) Flexural Test with a dimension of 150 X 150 X 500mm Both of the abovementioned tests are using compression machine, The tests carried out shall be at the age of 7, 14, 28 and 56 days respectively. The selected concrete grade shall be 25 and 50 MPa. Grade 25 shall be selected due to its’ common usage in design of reinforced concrete structures while Grade 50 shall be for high performance structure such as prestressed concrete. The outcome of this research is aimed to supplement the numerous available literature works and to assist and guide the selection of appropriate specification requirement for aggregate properties value in concrete mix design. 1.3 Research Question (Expected Results) The expected results of this research proposal shall be the relationship of mechanical aggregate properties and concrete strength, which are: i. Relationship between AIV and Concrete Strength for Grade 25/50 at the age of 7, 14, 28 and 56 days. open in browser PRO version


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ii) Relationship between ACV and Concrete Strength for Grade 25/50 at the age of 7, 14, 28 and 56 days. iii) Relationship between 10% Fine Value and Concrete Strength for Grade 25/50 at the age of 7, 14, 28 and 56 days. iv) Relationship between WO and Concrete Strength for Grade 25/50 at the age of 7, 14, 28 and 56 days. v) Relationship between LA AV and Concrete Strength for Grade 25/50 at the age of 7, 14, 28 and 56 days. vi) Relationship between PSV and Concrete Strength for Grade 25/50 at the age of 7, 14, 28 and 56 days. 1.4 HYPHOTHESIS Hypothetically the results shall lead to the following conclusions : i) Lower AIV contributes to higher strength concrete ii) Lower ACV contributes to higher strength concrete iv) Higher 10%V contributes to higher strength concrete v) Lower LA AV contributes to higher strength concrete vi) Lower WO contributes to higher strength concrete vii) Higher PSV contributes to higher strength concrete Observations shall also be made to determine obvious variations of aggregate properties between Grade 25 and 50. CHAPTER 2 LITERATURE REVIEW (Aggregate for Concrete) open in browser PRO version


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2.1 Introduction Concrete may be defined as mixture of water, cement or binder, sand and aggregate, where the water and cement or binder from the paste and the aggregate forms the inert filler. In absolute volume terms the aggregate amounts to 6080% of the volume of concrete and is, therefore, the major constituent. The aggregate type and volume influences the properties of concrete, its mix proportion and its economy. The desirable and undesirable properties of aggregates for concrete have been thoroughly reviewed in a number of texts on concrete technology such as American Society for Testing and Materials, Murdock & Brook, Fookes, Neville 1995 and many others. In practice, difficulties are frequently encountered in translating these properties into specification requirements for aggregates, or in assessing aggregate test results to determine compliance or otherwise with already specified parameters. The essential requirement for an aggregate for concrete is that it remains stable within the concrete and in the particular environment throughout the design life of the concrete. The characteristics of aggregate must not affect adversely the performance or cost of the concrete in either the fresh or hardened state. For both technical and contractual reasons, these requirements have to be defined quantitatively. This involves the selection of relevant tests and assessment procedures and the specification of appropriate acceptance criteria. However, despite the guidance given in BS 812 and BS 882, it can be difficult to assure the long-term satisfactory performance of an aggregate combination solely by mans of a number of British or other standard tests and limits. In such cases there is a need for empirical judgement, but the specifier’s aim should always to minimize this need. For example, contract specifications often include the generalized requirements derived from previous editions of BS 882 that aggregates…be hard, durable and clean and of approved quality. These are qualitative requirements without specific acceptance limits which, therefore, necessitate judgments sometimes leading, in turn, to contractual disputes. This phrase was deleted from BS 882: 1983. It is important to avoid specifying aggregate qualities, which are contradictory, thus creating a potential for dispute. Specifications which are not relevant or which are unnecessarily superior to the needs of the particular works, thereby restricting use to unduly expensive materials should also be avoided. Thus, the specifier bears considerable open in browser PRO version


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responsibilities in these respects under a contract. Hence the need for continued vigilance despite the rare incidence or arbitrations and litigations resulting from disputes about aggregate quality. In Malaysia, the assessment of aggregate quality in both new and established deposits is not generally justified in view of the well-established characteristics for most Malaysian aggregate sources and the longstanding of the Malaysian aggregate production industry. Quality should, nevertheless be confirmed by independent testing and periodic rechecks. The ready mixed concrete industry carries out inspection and testing as part of a quality assurance precheck. This research is almost entirely concerned with density of about 24000 kg/m3. Sometimes, however, concrete is required to have either a lower or a higher density. By the use of a lightweight aggregate the concrete density can be less than 2000 kg/m3 and when a heavyweight aggregate is used the density can be greater than 3000 kg/m3 . Lightweight aggregate may be simply classified into natural or artificial aggregates. Pumice is an example of a natural lightweight aggregate and is used mostly in the production of concrete blocks. Expanding clay, shale or slate, by sintering pulverized fuel ash and by foaming molten blast-furnace slag, may form artificial lightweight aggregates. They are all capable of producing concrete strengths in excess of 25 n/mm2 with densities ranging from 1500-2000 kg/m3 . The composition of the aggregates and their properties, for example bulk density, has an influence on the resulting concrete properties (Short and Kinniburgh, 1978) Heavyweight aggregates may also be classified as natural or artificial materials. The most widely used natural materials are barytes and the iron ores such as haematite and magnetite, whereas the artificial materials are based on iron shot or lead shot. The resulting concrete strength is not of paramount importance but is usually in excess of 30 N/mm2 . The densities will vary from 3500 kg/m3 to 800 kg/m3 depending on the type of aggregate used (Miller, 1983) 1. Specification In Malaysian practice, specifications commonly only require compliance with the requirements of BS 882 for aggregates from natural sources for concrete and BS 3797 for lightweight aggregates. BS 882: 1992 contains quantitative compliance requirements for particle shape (flakiness), shell, grading, cleanliness open in browser PRO version


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(fines) and mechanical properties. The widespread use of this long-established British Standard presupposes a substantial weight of experience to justify the view that this limited number of requirements has proved adequate for most concrete construction work in Malaysia. However, experience in recent years has shown that problems can arise on overseas contracts when specifications are based solely upon BS 882 (Fookes and Collis, 1975a, b) For example, an unsound aggregate which is mechanically strong in dry state may comply with the specification, but could be unsound and impair the durability of concrete in certain environments. In contrast with the limited number of quantitative requirements given in BS 882, the related British Standard covering the testing of aggregates, BS 812, provides test methods for a wide, through not exhaustive, range of properties. However, BS 812 does not provide any guidance for interpretation of the test results. The complete chemical analysis of an aggregate is not usually considered necessary for the appraisal for suitability for use in concrete. This is due to its’ rare application in Malaysia. A thorough petrographic analysis together with some specific chemical testing may be necessary in assessing a concrete aggregate.

A good aggregate specification must be relevant to the available resources and to the characteristics required of the concrete in which the aggregates will be used. Although aggregate quality can be improved if the job so demands, sufficient flexibility for judgment should be provided in order to prevent the unintended exclusion of either superior or lower quality aggregates which, for transport reasons may be expensive. 2. Classification and Composition The provisions in BS 882, do not require a supplier to furnish a petrological classification unless it is requested by the specifier or purchaser. In the past this information has rarely been requested but with the open in browser PRO version


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concern over alkali reactive aggregates there has been an increase in this type of testing. However, even though provided, the brevity of the BS 812: Part 102:1984 classification provides little information of real value, either for engineering or materials purposes. Detailed information on the petrography of an aggregate involving field inspection can be of considerable value when assessing its potential suitability in terms of rock type and the state of geological alteration or subaerial weathering (Hammersley, 1989). Also, simple petrographic examination is particularly useful for monitoring the variability of aggregates during the course of construction. Petrographic examinations can identify, fairly rapidly and relatively inexpensively, the presence of detrimental features or potentially alkali reactive or deleterious materials, which may be present either naturally or as contaminants (Mielenz, 1955). These examinations should ideally be carried out during the feasibility study but certainly no later than the tender stage. Although the results are normally only semi-quantitative, they can indicate whether further investigations and quantitative tests are desirable. A further benefit of petrographic analysis is that, in conjunction with other physical and chemical tests, they can help to ‘fingerprint’ an aggregate or parent rock (Fookes and Collis, 1975b). This can be of value as a means of defining an approved material and can be helpful subsequently should any disputes arise as to the nature of the originally approved material. It can, however, be dangerous to infer engineering properties from a petrographic analysis. An analytical aspect of special relevance to aggregates for concrete concerns the aggregate correction factors involved in the analysis or hardened concrete to determine the original content and aggregate/cement ratio. These determinations are very common in building and civil engineering works, usually for dispute purposes, and the results are relevant to the assessment compliance with specifications and any liability issues. The aggregate correction factors can have a significant influence but representative samples of the aggregates originally used are often not available at the time of analysis. Thus, it could be of value to specify that the correction factors are determined for reference purposes at the time the materials are approved, using the procedures given in BS 1881: Part 124:1988. Basalt Group open in browser PRO version


Flint Group

Gabro Broup pdfcrowd.com

Andesite

Chrt

Basic diorite

Basalt

Flint

Basic gneiss Gabbro

Basic porphyrites Gritsone group (including gragmental volcanic rocks)

Diabase Dolerites of all kinds theralite and teschenite


including

Arcose

Hornblende-rock Norite Peridotite

Epidiorite

Greywacke

Lamprophyre

Grit

Quartz-dolerite

Sandstone

Spilite

Tuff

Granite Group

Porphyry group

Gneiss

Apline

Granite

Dacite

Quartzite group

Granodiorite

Felsite

Ganister

Granulite

Granophyre

Quartzitic sandstones

Pegmatite

Keratophyre

Re-crystallized quartzite

Quartz-diorite

Microganite

Syenite

Porphyry

Limestone group

Quartz-pprphyrite

Dolomite

Rhyolite


PicriteSerpentinite

Hornfels group Contract-altered rocks of all kinds except marble

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Limestone

Trachyte

Marble Schist group Phyllite Schist Slate All severely sheared rocks

Table 2.0 –Classification of Natural Aggregates According to Rock Type (BS 812 Part 1:1975) 3. Aggregates Properties 1. Introduction The properties of aggregates discussed in the following sections are those which are of prime concern to the concrete producer. The aggregate properties which affect the properties of fresh concrete are those which are under the control of the aggregate producer. Properties such as particle size and shape, which are influenced by selective crushing and the use of the appropriate type of crusher for the particular rock type, as well as the cleanliness in terms of fines and clay content have a great influence on the water requirement of the concrete.



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Figure 2.1 – Influence of particle size and shape on water demand for different levels of workability Figure 2.1 show the influence of particle size and shape on water demand and different levels of workability. The strength and durability properties of the hardened concrete may also be affected by any change in the water demand. The aggregate producer, however, usually has little control over aggregate properties such as strength, particle density and water absorption although these on occasions may be of some importance and be limited in concrete specifications. Processing may have some effect but, in general, these properties remain essentially the same as the parsent rock. Improvements can be sometimes made by the use of jig for the removal of low density particles which may influence the overall strength, density and water absorption of the end product or the use of special screens to extract exceptionally flaky particles. The form of production quality control applied to any aggregate will generally depend on the end use of the aggregate.

If Quality Assurance certification of the aggregates is required this should be achieved by the use of a quality system available in Malaysia such as the MS ISO 9000 quality management and assurance standards. Although products such as Portland cement, reinforcing steel and admixtures are covered by QA schemes only a few individual pits and quarries have a QA scheme for aggregates. 2.4.2 Maximum Size and Grading Where concrete of particularly high strength, uniformity or aesthetic quality is required, it is usually beneficial to specify that single-sized coarse aggregates are used; further that they are separately batched to provide continuous or noncontinuous overall gradings as appropriate. This may present problems of storage for the ready mixed concrete supplier and becomes an expensive option. In general, continuously graded aggregates tend to provide relatively straightforward and easy-to-place concretes, whereas gap-graded concretes usually require appreciably more expertise in mix design, production, handling and placing (Shacklock, 1959; Shaffler, 1979) For these reasons the labour costs of placing gap-graded concretes may sometimes be greater, but this may be justified where their special properties can be used to advantage; for example, there high mechanical stability is required immediately after open in browser PRO version


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compaction, or where increased resistance to scour is required in inter-tidal work. The maximum size of aggregate permitted by BS 882 for use in concrete is 40mm. However the size most frequently used is 20mm since consideration has to be given to the cover and bar spacing in reinforced concrete. For some situations 10mm maximum size aggregate may be used, especially when the structure size is limited or the preference is for a very cohesive concrete for use in a slipform operation. Although 40mm maximum size is permitted in pavement quality concrete it is normally only used in the bottom of the two layer construction with 20mm aggregate used in the top layer. The handling of the concrete also plays a very important part in the decision as to which maximum size to use. Of prime importance is the consistency of the maximum size within the limits of BS 882 since a change can influence the water demand of the concrete and hence affect both the strength and the durability. The inclusion of limits for the 14mm material in the 40-5mm and 20-5mm graded coarse aggregate and 20mm single sized aggregate will help the situation. The BS 882 grading limits for coarse aggregate are given in Table 2.1 below. Percentage by mass passing BS sieves for nominal sizes Graded Aggregate Sieve Size (mm)

40mm to 5mm

20mm to 5mm

14mm to 5mm

40mm

20mm

14mm

10mm

50.0

100

-

-

-

-

-

-

-

37.5

90100

100

-

100

100

-

-

-

90-100

100

85-100

85-100

100

40-80

90100

0-25

0-70

85-100

100

-

0-25

0-25

85-100

0-5

0-5

0-5

0-25

-

-

-

0.5

20.0 14.0 10.0 5.0

35-70 25-55 10-40

30-60 0-10

0-5 2.36 open in browser PRO version

Single-sized Aggregate


50-85

5mm

100 45-100

0-10 -

0-30 pdfcrowd.com

-

-

Table 2.1 – BS 882:1992 – Coarse Aggregate Grading Limits The aggregates of nominal maximum size greater than 40mm material are sometimes specified for massive placement, the aims usually being to minimize the cement content and, thereby reduce heat generation. To specify, for example a 75mm or 150mm maximum size, presumes that the physical characteristics of the larger size fractions are not inferior to those of the 40m and smaller sizes, in which case small but possibly significant reductions in cement content and cost may be achieved. This presumption is not always correct, especially in weathered rocks. The possibility of increased risks of segregation should not be overlooked, however. Certain rock types may produce crushed aggregates whose shape characteristics may be dependent on particle size and this could negate the technical and cost benefits that might otherwise be obtained. Such an effect will occur with rock materials that normally benefit from an improvement in particle shape during secondary and tertiary crushing to produce smaller aggregate sizes or with some thickly bedded or coarsely cleaved rock sources. Thus, some investigation into the likely shape characteristics should be undertaken before specifying exceptionally large nominal maximum sized aggregates for mass concrete placements (Bloem, 1959) In Malaysia, attention is rarely given to the questions of gradings, probably because of the abundant supplies of materials whose gradings have not given cause for any general concern. The specifier should investigate the grading characteristics of potential aggregate resources, in order to minimize the risk of imposing impracticable and uneconomic specification requirements. 2.4.3 Particle Shape The shape characteristics of aggregate particles are classified in qualitative terms in BS 812, but this standard only provides test methods for quantifying the proportions of ‘flaky’ or ‘elongated’ particles in coarse aggregates, and these vary according to the crushed or uncrushed nature of the aggregate. The requirements in BS 882 are that the flakiness index of the combined coarse aggregate shall not exceed 50 for uncrushed gravel and 40 for crushed rock or crushed gravel. open in browser PRO version


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No limits are provided in BS 882 for the percentage of ‘elongated’ particles and, indeed, limits are rarely specified for the ‘elongation index’. Flakiness and elongation are not usually specified for sands, although these characteristics are easily determined qualitatively by visual examination under low-pressure microscope. Experience suggests that the absence, until recently, of quantitative limits on the shape characteristics of concrete aggregates generally has not resulted in any undue difficulties with structural concretes in Malaysia. The probable reasons for this include the natural adequacy in respect of the majority of Malaysia gravels, and also the success with which aggregate producers have been able to control the shape characteristics of those materials which have greater tendencies on crushing to produce flaky and/or elongated particles. However, the industry is now having to consider the more marginal deposits and the difficulties that arise from producing flaky aggregates are becoming more common. The shape characteristics of coarse aggregates and sand can have marked effects on the properties of both fresh and hardened concrete (Lees, 1964), these effects tending to be beneficial where the predominant particle shape is general equidimensional, and detrimental where it is flaky and/or elongated (Kaplan, 1958, 1959, Neville, 1995) (cross referenced Figure 2.1 of this proposal showing relationship between aggregate particle shape and concrete workability) Flakiness of coarse aggregate can have an adverse influence on the workability and mobility of concrete and may cause blockages in pump pipelines due to particle interference. Experiments have shown that the workability of concrete as measured by the compacting factor is reduced by 10% when changing from a rounded to an angular shaped particle (Kaplan, 1958) The strength of concrete also tends to be reduced by increasing aggregate flakiness, with flexural strength being more affected than compressive strength (Kaplan, 1959). Flakiness in fine aggregate also affects the properties of the concrete mix. This can lead to problems of ‘bleeding’ (Barker,1983) and segregation in the fresh mix leading to reduced strength and durability of the resultant hardened concrete. Finishing of the concrete can also be affected adversely (Richards, 1982) Particle shape limits for concrete aggregates can be a major consideration when developing and designing aggregate production plant for new sources and aggregates at the limiting values can present difficulties. In some cases, the producer or the specifiers should seek to select target maxima for flaky and elongated particles in coarse aggregates. The cost-benefit of complying with relatively low target maxima is largely a matter for investigation by the aggregate open in browser PRO version


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producer and, for the work, particularly, by the consulting engineer at the earliest possible time. Improvement of aggregates particle shape usually increases production costs, but may result in an enhancement of the strength and durability potential of the concrete. Classification Rounded

Examples

Fully water-worn or completely shaped by attrition

River or seashore gravel; desert, seashore and wind-blown sand

Other gravels; land or dug flint

Irregular

Naturally irregular, or partly shaped by attrition and having rounded edges

Flaky

Material of which the thickness is small relative to the other two dimensions

Laminated rock

Angular

Possessing well-defined edges formed at the intersection of roughly planar faces.

Crushed rocks of all types; talus; crushed slag

Elongated


Description


Material; usually angular; in which the length is considerably larger than the other two dimensions

___

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Flaky and elongated

Material having the length considerably larger than the width, and the width considerably larger than the thickness.

___

Table 2.2 –Particle Shape Classification of BS 812:Part 1: 1975 2.4.4 Particle Surface Texture The main influence of particle surface texture is the effect on the bond between the aggregate and the cement paste in hardened concrete. The classification in BS 812 is generalized; it is based on subjective assessment and does not therefore lend itself to specified limitations. Indeed, the specific exclusion of material of any particular surface texture is virtually unknown. Surface texture is generally only considered in relation of concrete flexural strengths, which are frequently found to reduce with increasing particle smoothness. However, inadequate surface texture can similarly adversely affect compressive strength in high-strength concretes (say >50N/mm2 ), when the bond with the cement matrix may not be sufficiently strong to enable the maximum strength of the concrete can be realized (Kaplan, 1959; Neville, 1981). Present advances in concrete technology have made it possible to produce very high strength concrete (100-139 N/mm2 – Chow Swee Ong, 2000) with aggregate having a relatively smooth surface texture. Group

Surface Texture

Characteristics

1

Glassy

Conchoidal fracture

2

Smooth

Water-worn, or smooth due to fracture of laminated or fine grained rock



Examples Black flint, vitreous slag

Gravels, chert, slate, marble, some rhyolites pdfcrowd.com

some rhyolites 3

Granular

4

Rough

Fracture showing more or less uniform rounded grains. Sandstone, ooliete Rough fracture of fine-or medium-grained rock containing no easily visible crystalline constituents.

5

Crystalline

6

Honeycombed

Basalt, felsite, porphyry, limestone

Containing easily visible crystalline constituents

With visible cavities

pores

and

Granite gneiss

gabbro,

Brick, foamed clinker, clay

pumice, slag, expanded

Table 2.3 – Surface Texture of Aggregates (BS 812 : Part 1: 1975 with examples) 2.4.5 Bulk Density The bulk density of an aggregate, or its unit mass, reflects in part its void content and is, therefore, an indirect measure of the grading and shape characteristics. The bulk density of aggregates ranges from 1200-1800kg/m3 for normal open in browser PRO version


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aggregates and 500-1000kg/m3 for lightweight aggregates. The bulk density is most commonly used to enable concrete mixes specified by volume to be converted into gravimetric proportions, and thus enable batch masses to be determined. The use of bulk density measurements has, therefore, declined with the increasing application of designed, prescribed and standard gravimetric concrete mixes (BS 5328:1990). However, bulk density is still used for lightweight aggregates because of the difficulty in measuring particle density. More generally, the value of bulk density and void content determinations lies in providing another inference property for a material, although it is little used for this purpose. A particular use could be as a comparative measure of variations in the particle shape, characteristics of fine aggregates since no Malaysian Standard tests are available to measure these directly. However, these are not properties which should be limited in contract specifications, although they may be used by concrete producers to assist in the comparison of mix designs using alternative materials. 6. Water Absorption Water absorption is an indirect measure of the permeability of an aggregate which, in turn, can relate to other physical characteristics such as mechanical strength, shrinkage, soundness and to its general durability potential. The relationship are imprecise although in general less absorptive aggregates often tend to be more resistant to mechanical forces and to weathering. A reliable classification of water absorption values for Malaysia natural dense aggregates is not available, but a ‘low’ absorption value might reasonably be considered as less than 1%, with an acceptable range for Malaysia aggregates being less than 1% to about 5%. The effect that the water absorption values ranging from 5-20%. However, the size and the characteristics of the pores are different from natural dense aggregates and it is possible to make durable concrete from this materials. Absorption limits are rare in British Standards, although BS 8007:1987 does include a recommendation that the aggregate absorption should not ‘generally’ be greater than 3% with a maximum value of 2.5% often specified in some cases. Contract specifications do not normally include a maximum limit on the water absorption of an aggregate. Indeed, limits should not be imposed unless it has been established, for a particular material, that water absorption relates closely to some other undesirable property such as poor resistance to frost or other weathering agencies. Although an open in browser PRO version


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aggregate may satisfy a water absorption limit there is no guarantee that problem with the concrete will not occur. In such cases it may be more expedient to adopt absorption limits for control and compliance purposes, rather than specify other more time consuming and costly test procedures which cannot be carried out readily in a site laboratory.

Figure 2.2 – Diagrammatic representation of moisture in aggregates

2.4.7 Mechanical Properties BS 882 includes quantitative requirements for the mechanical properties of aggregates based upon the ten percent value test or, as an alternative, the aggregate impact value test. The various criteria, which differ according to the intended application of the concrete, are given in Table 2.3. BS 812 provides several other mechanical test procedures for the determination of the aggregate crushing value, aggregate abrasion value and polished stone value. Different American test procedures are also available, including the Los Angeles test for resistance to impact (ASTM C131), Adoption of these tests and others, which are not specified in BS 882 is a matter for judgement by individual specifiers. Some selected mechanical properties of coarse aggregates are summarized in Table 2.4. open in browser PRO version


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Type of concrete

10% fines value (kN)

Alternatively, aggregate impact value (%)

(not less than) (not exceeding) Heavy duty finishes

concrete

floor

150

25

100

30

50

45

Pavement wearing surfaces Others

Table 2.4 – BS882: 1992 – Mechanical Property Requirements for Coarse Aggregates.


Test

Standard or country of origin

Measurement Principle

Aggregate impact value

BS 812

Fines produced by specified shock or impact loading

Aggregate value

BS 812


Crushing

BS 812

Fines produced by slowly increasing load to a specified maximum

Slowly increasing maximum load pdfcrowd.com

BS 812 Ten per cent fines falue

required to produce a specified amount of fines

Loss produced by amount of abrasion

specified

BS 812 Polished stone value

(ASTM C131) Los Angeles abrasion

Fines produced by attrition on tumbling of rock pieces with steel spheres for specified number of revolutions

(ASTM C535)

Table 2.5 – Selected Property Tests for Aggregates. The mechanical properties of coarse aggregates should be such that the material does not disintegrate or degrade (which could occur during handling, transportation, concrete mixing or compaction) and that the compressive strength and subsequent performance of the concrete is not impaired. For structural concretes, except concrete road pavements and abrasion resistant floors, the extent to which it is generally necessary to specify mechanical property requirements in addition to those given in BS 882 is limited. Any significant degradation of an aggregate prior to the concrete mixing phase should be detected more directly by routine acceptance tests for grading and fines content. During mixing, degradation of aggregate could be detected by the analysis of the fresh concrete. Furthermore, the more stringent of the BS 882 limits (for pavement wearing surfaces and heavy duty concrete floor finishes) in respect of the ten per cent value fines value should ensure that the characteristic strength of other than high strength concrete is not limited on this account (Orchard, 1976) Relationships between the mechanical properties of aggregates and their subsequent effects on the performance of concretes are generally uncertain (Bloem & Gaynor, 1963) However, the selection of a suitably high characteristic concrete strength alone is normally taken to assure a sufficient potential resistance to impact, abrasion and attrition, open in browser PRO version


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provided that sufficient attention is paid to the concrete mix design, placement and curing. The mechanical strength of the aggregate is usually not considered apart from routine compliance with BS 882 or an equivalent specification. Where the performance requirements for concrete surfaces are exceptionally rigorous and beyond what might reasonably expected of a normal structural concrete, special finishing operations (such as the use of vacuum mats, power floating, metallic surface dressings or other treatments) may have to be employed in addition to the careful selection of both coarse and fine aggregates. CHAPTER 3 RESEARCH METHODOLOGY 3.0 Introduction Random testings shall be executed in the laboratory. Samplings play a significant role as good samples are required. In preparing these samples, few important steps shall be taken into account, among others : a) Selection of concrete grade b) Concrete mix design c) Raw materials d) Measuring and mixing of concrete e) Concrete Performance test 3.1 Selection of Concrete Grade The selection of concrete grade is important in this research. Although CP 110 is limited to 9 grades only but, in this respect, the research shall only concentrate on Grade 25 and 50 to reflect the distinctions in strength from various open in browser PRO version


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types of aggregate properties being used and hence, is related to the topic of this proposal. 3.2 Concrete Mix Design During the preliminary stage prior to design process, the nature of the project and surroundings are to be considered. The design process is important to determine the quantity of materials to be used in Grade 25 and 50. The normal concrete mix design of the aforesaid grades is as per Appendices 1 & 2 respectively. The results commonly vary but statistically speaking, the variations in test results are of normal distribution to determine standard deviations. Based on statistical analysis, the strength of concrete mix is known as characteristic strength and is interpreted according to CP 110 as 5% strength (1 in 20) from test results (Figure 1.0) Thus, cubes from a concrete mix should be stronger in average from the characteristic strength. The differences between average and characteristic strength is known as permissible variation.



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Figure 3.0 – Normal Distribution for Concrete Strength 3.4 Raw Materials i. Aggregate to be used shall be granite rock extracted from 5 nos. of quarries and of 20mm graded crushed where rough and angular surfaces display variation in properties. The rocks shall be dried before testing. ii. In preparation of concrete mix, tap water from the lab shall be used. iii. Sand measuring less than 5mm shall be monitored to enable wet mix having adequate cohesiveness. The sand to be used shall be from Zone 2. To ensure well-distributed sand particles, overall tests shall be conducted. Generally, selection of zone shall be at self-discretion. The sand is then oven-dried to ensure that they are moisture-free. The sand from the oven should cool off prior usage and cannot be directly applied due to its’ affect on water contents in a mix.. vi. Cement to be used shall be only Ordinary Portland Cement. Usage of other brands may affect the results of testing obtained. 3.5 Measuring and Mixing of Concrete In general, concrete is mixed according to the appropriate batch related to work and promptness of the construction. The weight measurement method is applied in mixing raw materials such as cement, sand, aggregates and water. This method requires a stringent quality control. Appropriate weighing instrument and the weight of the raw materials shall be determined and this is implemented systematically and accurately to every batch designed. From mix design, the density obtained in weight by volume (kg/m3) Thus in order to measure material quantity, value from concrete mix design should be multiplied with value of concrete density to be mixed. Arithmetically, this can be reflect as :



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Concrete can be mixed either with hand or by using the concrete mixer. In this research, the latter technique shall apply by using lab facilities. The raw materials shall be weighed and placed into the machine. The machine shall be rotated until the materials are completely mixed. Then the mix shall be taken out and water shall be measured and poured into the mixer. Finally, the mix is shoveled back into the mixer and it shall be rotated again.

When water and materials are thoroughly mixed, it shall be formed into cube specimens after conducting slump test to suit the selection of the concrete mix design. 3.6 Concrete Test One of the concrete characteristics that has made it been widely used is due to its’ high compressibility in withstanding burden. The concrete performance test has always been referred to the compressibility in withstanding concrete cube load with a dimension of 150 X 150 X 150mm at the age of 28 days. There are many techniques known to be applied in order to obtain compressive strength of concrete whether directly or indirectly, non-destructive test etc. In this research, the methods applied shall be non-destructive which is the Cube Compressive Test with a dimension of 150 X 150 X 150mm and the Flexural Test with a dimension of 150 X 150 X 500mm and tested at the age of 7, 14, 28 & 56 days respectively. 3.6.1 Compression Test open in browser PRO version


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The main objective of this test is to obtain the concrete strength. Observations shall also be made on factors of cube density and failures. The concrete mix shall be placed into the mould, which has been applied with mould oil to ease opening. Concrete shall be compacted into three layers using steel rods 25mm in size with 35 blows per layer and the surface shall be leveled using trovel. After 24 hours, the mould shall be opened and the cubes shall be treated in a pond. All tests shall comply to the requirements of BS : 1881, Part 4, and MS 26 : 1971. Prior to the test, the cubes/specimens shall be weighed to obtain density and placed onto the lower steel platen plate with both smooth surfaces facing the top and bottom platen plates. The load weight constantly applied shall be 4.5-9.0 KN/sec. until the specimen fails. The load failure shall be recorded according the reading meter. By ascertaining the load failure and surface area, the concrete strength can be obtained. Observations shall also be made to the modes of failure and the aggregate arrangements of the concrete.



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Figure 3.1 – Cube Test 3.6.2 Flexural Test The concrete mix shall be placed into the mould. Concrete shall be compacted into two layers using steel rods 25mm in size with 50 blows per layer. All tests and methods shall comply to the requirements of BS : 1881, Parts 3 & 4. Concrete beams taken out from the curing tanks shall be left to dry and later weighed to obtain density. Then the beam shall be placed on the supporting points and load of 0.9-1.35 KN/sec. shall be applied. The load value until the beam failed shall be recorded.



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Figure 3.2 – Flexure Test For a £ 133 mm, flexural strength = 3Pa X 9.81 X 1000 = N/mm2 BD2

4.0 WORK SCHEDULE Work Schedule (Compression Test) open in browser PRO version


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Grade 25

Grade 50

Age

Age

Aggregate Samples

7

14

28

56

S

7

14

28

56

S

Quarry 1

2

2

2

2

8

2

2

2

2

8

Quarry 2

2

2

2

2

8

2

2

2

2

8

Quarry 3

2

2

2

2

8

2

2

2

2

8

Quarry 4

2

2

2

2

8

2

2

2

2

8

Quarry 5

2

2

2

2

8

2

2

2

2

8

40 40 open in browser PRO version


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Amount of concrete required = 0.15 X 0.15 X 0.15 X cube nos. = 0.003375 m3 X 80 nos. = 0.27 m3 + 15% wastage = 0.31 m3 / 5 sources of aggregates = 0.062 m3 per batch Work Schedule (Flexural Test) Grade 25

Grade 50

Age

Age

Aggregate



Samples

7

14

28

56

S

7

14

28

56

S

Quarry 1

2

2

2

2

8

2

2

2

2

8

Quarry 2

2

2

2

2

8

2

2

2

2

8

Quarry 3

2

2

2

2

8

2

2

2

2

8

Quarry 4

2

2

2

2

8

2

2

2

2

8

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Quarry 5

2

2

2

2

8

2

2

2

2

8

40 40 Amount of concrete required = 0.15 X 0.15 X 0.5 X cube nos. = 0.01125 m3 X 80 nos. = 0.9 m3 + 15% wastage = 1.035 m3/ 5 sources of aggregates = 0.207 m3 per batch



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AGGREGATE-INFLUENCE-CONCRETE-STRENGTH

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