a study on recycled concrete aggregates · a study on recycled concrete aggregates pavan p s 1,...

A STUDY ON RECYCLED CONCRETE AGGREGATES PAVAN P S

1, BABITHA RANI H

1,DEEPIKA GIRISH

1, RAGHAVENDRA K M

2,

VINOD P N1,DUSHYANTH.V.BABU.R

1,SHAIK NUMAN1

1Assistant Professor, Department of Civil Engineering, SET, Jain University.

2Student, Department of Civil Engineering, SET, Jain University.

Abstract

The amount of construction waste has been dramatically increased in the last decade, and

social and environmental concerns on the recycling of the waste have consequently been

increased. Many researchers state that recycled concrete aggregates (RCA) are only

suitable for non-structural concrete application. This research, however, shows that the

recycled aggregates that are obtained from concrete specimen make good quality concrete.

Concrete waste from demolished structure has been collected and coarse aggregate of

different percentages is used for preparing fresh concrete. In this study, for the 28th

day

cube compressive strength using OPC; the strength for 25%, 50%, 75% and 100% RCA

mixes were 23.5%, 33.5%, 32.4% and 10.7%, respectively less than 0% RCA mix whereas

for PSC, were 17.8%, 36.7%, 40.6% and 19.1% respectively less than normal concrete.

The cylinder compressive strengths at 28 days for 25%, 50%, 75% and 100% RCA mixes,

using OPC were 37.7%, 32.0%, 33.7% & 28.4% and using PSC were 20.5%, 27.5%,

25.1% & 30.3% respectively less than that of normal concrete mix. However, in split

tensile strength, a continuous decrease in strength was observed with addition of RCA. The

values obtained for 25%, 50%, 75% & 100% RCA, for OPC, were 20.6%, 33.0%, 34.9%

& 42.5% respectively less than 0% RCA concrete while for PSC, were 1.1%, 16.3%,

26.1% & 27.2% less correspondingly. This study proves that, though the strength of

concrete is affected by addition of RCA, the cost saving is upto 16% by 100% substitution

of natural aggregates. Moreover, the use of PSC instead of OPC leads upto 29% reduction

in cost.

Keywords: Recycled concrete aggregates, natural aggregates, compressive strength,

split tensile strength, Ordinary Portland cement, Portland Slag cement.

Introduction

Concrete is globally the most widely used material in the construction industry.

Basically, concrete is a manufactured product consisting of cement, aggregates, water

and admixture. The composition of aggregates forms a major portion of the mixture

consisting of sand, crushed stones and gravel which are inert granular materials.

Construction aggregates make up more than 80 percent of the total aggregate market

and are used mainly for building constructions and pavements. The word concrete

comes from the Latin word ‘‘concretus’’ (meaning compact or condensed), the perfect

passive participle of ‘‘concrescere’’, from the words ‘‘con’’ (together) and ‘‘crescere’’

(to grow). [1]

Fig. 1.1: Stress-Strain Relationship of Ordinary Concrete

International Journal of Pure and Applied MathematicsVolume 118 No. 18 2018, 3239-3263ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

3239

S

RECYCLED CONCRETE AGGREGATES

Recycled aggregates are aggregates derived from the processing of materials previously used

in construction. Examples include recycled concrete from construction and demolition waste

material (C&D), reclaimed aggregate from asphalt pavement and scrap tyres. Coarse Recycled

Concrete Aggregate (RCA) is produced by crushing sound, clean demolition waste of at least

95% by weight of concrete, and having a total contaminant level typically lower than 1% of

the bulk mass. Other materials that may be present in RCA are gravel, crushed stone,

hydraulic-cement concrete or a combination deemed suitable for pre-mix concrete production.

LITERATURE REVIEW

Sowmya.et.al. (2000), some tests were conducted using the recycled aggregates to study

and compare the results with the naturally available aggregates. The tests were conducted

International Journal of Pure and Applied Mathematics Special Issue

3240

on the aggregates which weren’t subjected to any prior treatment. The impact value for

recycled aggregate was obtained as 35% and that for natural aggregate as 29.9%. The

abrasion value for recycled aggregate was obtained as 47.4% and that for natural aggregate

as 29.6%. Water absorption of recycled aggregate (4.2%) was found to be higher when

compared to the natural aggregate (0.4%). It was found that compressive strength of

concrete made from the recycled aggregate is about 76% of the strength of concrete

made from natural aggregate for normal strength concrete (M20). Flexural strength of

the recycled aggregate concrete is almost 85% and 80% of natural aggregate concrete.

Amnon.et.al (2002), concrete having a 28-day compressive strength of 28 MPa was

crushed at ages 1, 3 and 28 days to serve as a source of aggregate for new concrete,

simulating the situation prevailing in precast concrete plants. The properties of the

recycled aggregate and of the new concrete made from it, with nearly 100% of

aggregate replacement, were tested. The properties of the concrete made with recycled

aggregates were inferior to those of concrete made with virgin aggregates. Effects of

crushing age were moderate: concrete made with aggregates crushed at age 3 days

exhibited better properties than those made with aggregates of the other crushing ages.

Shailendrakumar.et.al. (2004), in this paper, the author found the relationship between

split tensile strength and compressive strength for RCA concrete as well as controlled

concrete. The recycled concrete aggregate used was that passing through IS sieve 40mm

and retained on IS sieve 4.75mm. For controlled concrete the natural stone chips of same

nominal size was used in making concrete. If required a dose of superplasticizer [Conplast

SP 430 (M)] was also added to ordinary tap water to obtain desired degree of workability.

In this study, 3 mixes were prepared i.e. replacement of natural aggregates by 0%, 50%

and 100% RCA. The strength was tested at 28 days maturity of casted concrete. It was

observed that recycled concrete aggregate has lower value of specific gravity and

moderately high values of water absorption, crushing value, impact value and abrasion

value. Furthermore, similar to concrete containing natural aggregate, tensile strength of

recycled aggregate concrete containing recycled concrete aggregate, mainly depends on

compressive strength. Chaurpagar.et.al. (2004), the author investigated physical and

mechanical properties of RCA with and without steel fibres and polymer against

controlled concrete. Specimens (cubes/beams/cylinders) were prepared by varying the

parameters like water cement ratio and volume of polymer (2.5%, 5.0%, and 10% by


3241

parts weight of cement) and constant 0.5% steel fibre by volume of concrete. Recycled

Aggregate and Natural Aggregate shows that the former has high specific gravity, high

absorption capacity and low fineness modulus. Resistance to mechanical actions such

as crushing strength, impact value and abrasion value of recycled aggregates are

significantly higher than that of conventional aggregates. There is a marginal increase

in the compressive strength due to the addition of polymer-steel fiber in recycled

concrete. There is significant increase in split tensile strength and flexure strength at 90

days in polymer steel fiber recycled aggregate concrete as compared to conventional as

well as recycled aggregate concrete. Area under stress strain curve is higher, shows the

high toughness properties of concrete that it indicates that polymer concrete is more

suitable for the earthquake resisting structures. It is observed that there is an

improvement in the ductility with addition of 10% polymer & 0.5% steel fiber in the

concrete as compared to recycled aggregate concrete as well as conventional concrete.

Limbachiya.et.al. (2004), the report aimed at examining the performance of Portland

Cement Concrete produced with natural and coarse aggregates. The study showed that

because of attached cement paste in RCA, the density of these materials is about 3-

10% lower and water absorption is about 3-5 times higher than the corresponding

natural aggregates. The results also indicate that for RCA samples obtained from four

different sources, there was no significant variation in strength of concrete at a given

RCA content. Natesan.et.al. (2005), an experimental investigation was conducted to

study the mechanical properties of concrete where natural coarse aggregate is partially

replaced with recycled coarse aggregate. It was concluded that RCA increases the

mechanical properties of conventional concrete and it was observed that a mix of 75%

RCA and 25% Natural Aggregates has good mechanical properties. RCA with rough

surface allows better bonding with cement mix. Naik.et.al. (2006), this paper throws

some light on the production of recycled aggregates, their properties and their

suitability in the production of concrete. Also, the properties and the application of

recycled aggregate concrete are discussed in detail along with bringing out the

limitations of recycled aggregate concrete. This study showed that recycled aggregates

had higher water absorption value than natural aggregates but less density and strength.

Choudary.et.al. (2006), the author investigated workability and strength properties of


3242

RCA. The recycled aggregate concrete is made by mixing 60% of recycled aggregates

with 40% of crushed stone chips. The aggregates used for concrete batching are

maintained at saturated surface dry condition. The workability of the recycled

aggregate concrete is slightly lower than that of the conventional concrete. The

compressive strength of the recycled aggregate concrete is slightly lower than that of

the conventional concrete and recycled concrete aggregate or recycled with

conventional concrete can be used in normal plain and reinforced concrete

construction. The recycled and conventional concrete containing 60% of recycled

aggregate and 40% of crushed natural stone chips occupies almost an intermediate

position is terms of workability and strength consideration between the others types of

concrete. So from economy and performance point of view, this type of concrete is

suitable only next to conventional concrete. Osei.et.al. (2013), in this study, the

compressive strength properties of concrete were investigated by completely replacing

Natural Aggregate (NA) with recycled concrete aggregate (RCA). Densities of both

RCA concrete and NA concrete were within the range of normal weight concrete. Both

RCA concrete and NA concrete showed the similar trends in the variation of strength

and density with time. Reduction in the 28-day compressive strength of concrete due to

complete replacement of natural aggregates with recycled concrete aggregate ranges

from 11% to 33%. RCA can replace NA in the production of both non-structural and

structural concrete. Patil.et.al. (2013), this study aimed to evaluate physical properties

of concrete using recycled coarse aggregate. In this research, concrete waste from

demolished structure has been collected and coarse aggregate of different percentages

is used for preparing fresh concrete (0%, 25%, 50%, 75% & 100%). The compressive

strength of recycled coarse aggregate (RCA) is found to be higher than the

compressive strength of normal concrete when used upto a certain percentage.

Recycled aggregate concrete is in close proximity to normal concrete in terms of split

tensile strength. The slump of recycled aggregate concrete is more than the normal

concrete. At the end, it can be said that the RCA upto 50 % can be used for obtaining

good quality concrete.

MATERIALS


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Concrete is a composite material composed of water, coarse granular material (fine and

coarse aggregate) embedded in a hard matrix (cement or binder) that fills the space

among the aggregate particles and glues them together.

AGGREGATES: Aggregates used in concrete are divided into three categories:

Fine Aggregates: These aggregates passes through 4.75 mm I.S. sieve and retained on 150

micron. Coarse sand, it contains 90% of particles of size greater than 0.6 mm and less

than 2 mm .Medium sand, it contains 90% of particles size greater than 0.2 mm and less

than 0.6 mm, Fine sand, it contains 90% of particles of size greater than 0.06 mm and less

than 0.2 mm. Proper selection of sand is critical in the durability and performance of

concrete mixture

Coarse Aggregates: These aggregates passes through 63 mm I.S. sieve and retained on

4.75 micron. Coarse aggregates are particles greater than 4.75 mm, but generally range

between 9.5 mm to 37.5 mm in diameter. They can either be from Primary, Secondary or

Recycled sources.

Mixed Aggregate: Mixed aggregate is sometimes used for unimportant work without

separating into different sizes.

CEMENT: Another important material in concrete manufacture is cement. Cement is a

fine ground material consisting of compound of lime, silica, alumina and iron.

Discussions: The specific gravity of aggregates normally used in road construction ranges

from about 2.5 to 3.0 with an average of about 2.68. Though high specific gravity is

considered as an indication of high strength, it is not possible to judge the suitability of a

sample road aggregate without finding the mechanical properties such as aggregate

crushing, impact and abrasion values. Water absorption shall not be more than 0.6 per unit

by weight. From the above experiment, it is found that the specific gravity of RCA is

smaller than that of normal aggregate. Hence, RCA can be said to have less density than

normal aggregate and hence RCA is lighter. And also, it is found that water absorption is

higher in RCA than that of normal aggregates.

Fine Aggregates observations and Results

Determination of Moisture Content of Fine Aggregates by Pycnometer Method


3244

Observations and Results: Trial No.

Sl. No. Observations and Calculations 1 2

1 Mass of empty pycnometer (M1 g) 684 g 654 g

2 Mass of pycnometer + fine aggregates (M2 g) 1184 g 1185 g

3 Mass of pycnometer + fine aggregates, filled with water (M3 g) 1869 g 1871 g

4 Mass of pycnometer filled with water only (M4 g)

Specific Gravity of Sand, G

5 Mass of fine aggregates, (M2 – M1)g 500 g 500 g

6 M3 – M4 328 g

7 (G – 1) / G 0.67

8 Moisture Content,

w = [(((M2-M1)/(M3-M4))((G-1)/G))-1] x 100 1.28 % 1.28 %

9 Average Moisture Content, wavg 1.28

Discussion: For fine aggregate, it is important to determine its moisture content because if

its water content is high, there will be an excess amount of water in the mixture. The

water-cement ratio used in the mixture is 0.5 and if the fine aggregates contain a certain

amount of water, this will have a considerable impact on the mixture and this may lead to

bleeding of concrete afterwards. Therefore, there is a need to ensure that the fine aggregate

is dry or if it is not the case, then the water content of the fine aggregates needs to be

reduced.

Coarse Aggregates - Oven Dry Method: Observations and Graph:

Table : Sieve Analysis of Fine Aggregates

Observations

and Results:

Conventional Recycled

Concrete

Aggregates Aggregates

Original

sample weight

(M1 g) 880 g 780 g

Oven dried

sample weight

(M2 g)

874 g 754 g

Moisture

content, w =

[(M1-M2) /

M2] × 100%

0.68% 3.44%

Table : Determination of Moisture

Content of Coarse Aggregates by Oven

Dry Method

Sieve

Size(mm)

Weight

Retained (Kg)

Percentage

Retained (%)

Cumulative

%

Retained

Cumulative

% Passing

4.75 0 0 0 0

2.36 0.014 1.4 1.4 98.6

1 0.302 30.2 31.6 68.4

0.0006 0.24 24 55.6 44.4

0.0003 0.354 35.4 91 9

0.00015 0.062 6.2 97.2 2.8

Pan 0.028 2.8 100 N/A

TOTAL 376.8


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Graph 4.1: Particle Size Distribution Curve for Fine

Aggregates

Results: Effective size, in microns (D10,

sieve opening corresponding to 10% finer in

the graph) = 245 Microns. Uniformity

coefficient [(D60 / D10), D to be obtained

from the graph] = 310. Fineness modulus

(Sum of cumulative % weight retained / 100)

= 3.77

Discussion: According to IS 383 - 1970,

the fine aggregates belong to Zone II.

Table : Results for Effective Size, Uniformity

Coefficient and Fineness Modulus of Conventional and

Recycled Concrete Aggregates

Results:

Conventional

Recycled

Concrete


Effective Size (D10) 7.6 mm 5.1 mm

Uniformity Coefficient

(D60/D10) 1.84 2.51

Fineness Modulus 2.78 2.53

Discussion: The D refers to the size or

apparent diameter of the soil particles while

the subscript (10, 30 and 60) denotes the

percent that is smaller than that diameter, e.g.

D10 = 0.16 mm means that 10% of the

sample grains have diameter smaller than

0.16 mm. A large value of Cu indicates that

the D10 and D60 sizes differ appreciably.

SHAPE TESTS: SHAPE TESTS: Flakiness Index and Elongation Index of Coarse

Aggregates


3246

Table 4.1: Determination of Specific Gravity and Water Absorption of Coarse

Aggregates

Conventional Coarse Aggregates

Size of aggregates Weight of Thickness Weight of Length Weight of

Passing Retained Fraction gauge size, aggregates gauge Aggregates

through on IS Consisting mm in each size, in each

IS Sieve, Sieve, of at least Fraction mm Fraction

mm mm 200 pieces,

g

Thickness

gauge, mm passing

On length

gauge, mm

1 2

63 50

1 2 3 4 5 6 7

50 40 0 23.90 0 - -

40 31.5 0 19.50 0 58.00 0

31.5 25 0 16.95 0 - -

25 20 0 13.50 0 40.5 0

20 16 2000 10.80 550 32.4 220

16 12.5 850 8.55 69 25.5 175

12.5 10 500 6.75 150 20.2 98

10 6.6 110 4.89 22 14.7 0

TOTAL 3457 791 493


3247

Table 4.9: Determination of Flakiness Index and Elongation Index of Conventional

Coarse Aggregates



Passing Retained Fraction gauge aggregates gauge aggregates

through on IS Consisting size, mm in each size, in each

IS

Sieve, Sieve, of at least - fraction mm fraction

Mm Mm 200 pieces,

g

- Passing

gauge, mm

- Retained on

gauge, mm

1 2 3 4 5 6 7

63 50 0 23.90 0 - -

50 40 0 27.00 0 81.00 0

40 31.5 0 19.50 0 58.00 0

31.5 25 0 16.95 0 - -

25 20 0 13.5 0 40.50 0

20 16 1540 10.80 26 32.4 72

16 12.5 920 8.55 16 25.5 159

12.5 10 420 6.75 11 20.2 85

10 6.3 400 4.89 0 14.7 113

TOTAL W=3280 X=53 Y=429

Table : Determination of Moisture Content of Fine Aggregates by Pycnometer Method

Discussion: For fine aggregate, it is important to determine its moisture content because if

its water content is high, there will be an excess amount of water in the mixture. The

water-cement ratio used in the mixture is 0.5 and if the fine aggregates contain a certain

amount of water, this will have a considerable impact on the mixture and this may lead to

bleeding of concrete afterwards. Therefore, there is a need to ensure that the fine aggregate

is dry or if it is not the case, then the water content of the fine aggregates needs to be

reduced.

Coarse Aggregates - Oven Dry Method:


3248

Table 4.4: Determination of Moisture Content of

Coarse Aggregates by Oven Dry Method

Observations and Results:

Conventional

Recycled

Concrete


Original sample weight (M1

g) 880 g 780 g

Oven dried sample weight

(M2 g) 874g 754g

Moisture content, 874 g 754 g

w = [(M1-M2) / M2] × 100% 0.68% 3.44%

Discussion: From the above results, it is

found that RCA contains more water than that

of conventional aggregates because RCA has

a higher amount of cement and thus absorbs

more water than normal aggregates due to

larger pore sizes and hence, there is a need to

encounter for water absorption. Due to this,

RCA will absorb the water during mixing of

concrete and this will lead to a bad mixture as

there will be a lack of water and thus there

will be a need to add more and more water.

Fine Aggregates:

Observations and Graph:

Sieve Size Weight Percentage Cumulative

%

Cumulative

%

(mm) Retained

(Kg)

Retained

(%) Retained Passing

4.75 0 0 0 100

2.36 0.014 1.4 1.4 98.6

1 0.302 30.2 31.6 68.4

0.0006 0.24 24 55.6 44.4

0.0003 0.354 35.4 91 9

0.00015 0.062 6.2 97.2 2.8

Pan 0.028 2.8 100 N/A

TOTAL 376.8

Table : Sieve Analysis of Fine Aggregates

Graph : Particle Size Distribution Curve for Fine

Aggregates

Results: Effective size, in microns (D10, sieve opening corresponding to 10% finer in the

graph) = 245 Microns. Uniformity coefficient [(D60 / D10), D to be obtained from the

graph] = 310. Fineness modulus (Sum of cumulative % weight retained / 100) = 3.77

Discussion: According to IS 383 - 1970, the fine aggregates belong to Zone II.


3249

Graph : Particle Size Distribution Curve for Conventional Aggregates And Recycled Concrete

Aggregates

Discussion: The D refers to the size or apparent diameter of the soil particles while the

subscript (10, 30 and 60) denotes the percent that is smaller than that diameter, e.g. D10 =

0.16 mm means that 10% of the sample grains have diameter smaller than 0.16 mm. A

large value of Cu indicates that the D10 and D60 sizes differ appreciably.

Table 4.1: Determination of Specific Gravity and Water Absorption of Coarse Aggregates

Conventional Coarse Aggregates

Size of aggregates

Weight of Thickness Weight of Length Weight of

fraction gauge size, mm aggregates gauge aggregates

Passing Retained

through on IS consisting mm in each size, in each

Results:

Conventional

Recycled

Concrete


Effective Size (D10) 7.6 mm 5.1 mm

Uniformity Coefficient

(D60/D10) 1.84 2.51

Fineness Modulus 2.78 2.53

Table : Results for Effective Size, Uniformity

Coefficient and Fineness Modulus of

Conventional and Recycled Concrete Aggregates

Coarse Aggregates, Observations and Graph:

Sieve Analysis on Conventional Coarse Aggregates

Sieve

Size Weight Percentage

Cumulative

%

Cumulative

%

(mm) Retained

(Kg)

Retained

(%)

Retained Passing

40 0 0 0 100

20 0 0 0 100

10 1.56 78 78 22

4.75 0.44 22 100 0

Pan 0 0 100 N/A

Table : Sieve Analysis on Conventional Coarse Aggregates

Sieve Analysis on Recycled Concrete Aggregates

Sieve

Size Weight Percentage

Cumulative

% Cumulative %

(mm)

Retained

(Kg) Retained

(%) Retained Passing

40 0 0 0 100

20 0 0 0 100

10 1.2 60 60 40

4.75 0.66 33 93 7

Pan 0.14 7 100 N/A

TOTAL 253


3250

IS Sieve, mm Sieve, mm of at least 200 pieces, -

Fraction passing

thickness gauge,

mm mm

Fraction retained

on length gauge,

mm

1

2 3 4 5 6 7 63 50 0 23.90 0 - -

50 40 0 27.00 0 81.00 0

40 31.5 0 19.50 0 58.00 0

31.5 25 0 16.95 0 - -

25 20 0 13.50 0 40.5 0

20 16 2000 10.80 550 32.4 220

16 12.5 850 8.55 69 25.5 175

12.5 10 500 6.75 150 20.2 98

10 6.3 110 4.89 22 14.7 0

TOTAL 3457 - 791 - 493

Table : Determination of Flakiness Index and Elongation Index of Conventional Coarse Aggregates Recycled Concrete Aggregates


Passing Retained fraction gauge aggregates gauge Aggregates

through on IS consisting size, mm in each size, mm in each

IS Sieve, mm Sieve, mm of at least200 pieces, g -

Fraction passing

thickness gauge, mm

fraction retained on

length gauge, mm

1 2 3 4 5 6 7

63 50 0 23.90 0 - -

50 40 0 27.00 0 81.00 0

40 31.5 0 19.50 0 58.00 0

31.5 25 0 16.95 0 - -

25 20 0 13.50 0 40.5 0

20 16 1540 10.80 26 32.4 72

16 12.5 920 8.55 16 25.5 159

12.5 10 420 6075 11 20.22 85

10 6.3 400 4.89 0 14.7 113

TOTAL W = 3280 - X = 53 - Y = 429


3251

Table 4.10: Determination of Flakiness Index and Elongation Index of


Results:

Conventional

Recycled

Concrete


Flakiness Index = [(X1+ X2+…..) / (W1 + W2

+….)] × 100 22.88% 1.62%

Elongation Index = [(Y1 + Y2 +…) / (W1 + W2

+….)] × 100 14.26% 13.10%

Discussions: Flaky and elongated

particles should be avoided in

pavement construction, particularly

in surface course. If such particles

are present in appreciable

proportions, the strength of

pavement layer would be adversely

affected due to possibility of

breaking under loads. Workability is

reduced for cement concrete. As per

IRC recommendations, the

conventional aggregates tested

proved to be within permissible

limits for use in all types of

pavements except for bituminous

macadam and WBM base course

and surface course ones. The

recycled concrete aggregates are

within limits for all types of

pavements and may be used for

anyone based on its flakiness index.

Results for Flakiness Index and Elongation Index of

Conventional and Recycled Concrete Aggregates

Angularity Number

Observations and Results : Conventional

Recycled

Concrete


W = Mean weight of

aggregates in the cylinder, g 4310 g 4225 g

C = Weight of water required

to fill the cylinder, g 3000 g 3000 g

G = Specific gravity of aggregate 2.73 2.46

Angularity number = 67-100

W/CG 14 10

Discussion: From the values obtained

above, it is found that the angularity number

of conventional aggregates is higher than

that of RCA. Thus, higher the angularity

number, more angular and less workable is

the aggregate mix.In cement concrete mix,

rounded aggregates may be preferred

because of better workability, lesser specific

surface and higher strength for particular

cement content. In addition, the more

angular shape of the RCA and its rougher

surface texture are also what contribute

AGGREGATE IMPACT TEST


3252

Table : Determination of Aggregate Impact Value for Conventional

and Recycled Concrete Aggregates

Results:

Conventional

Recycled

Concrete


Original weight of aggregates, W1 g 320 g 300 g

Weight of fraction passing

through 2.36mm IS sieve, W2 g 100 g 100 g

Aggregate Impact Value = (W2 / W1) ×

100% 31.30% 33.30%

Discussion:10% →

Exceptionally strong.10–20%

→ Strong.20–30% →

Satisfactory for road surfacing. >

35% → Weak for road surfacing.

STANDARD CONSISTENCY OF CEMENT

Portland

Cement

(OPC)

Slag

Cement

(PSC)

Weight of empty dry bottle,

W1 g 66.3 g 80.3 g

Weight of empty bottle +

water, W2 g 176.9 g 178.8 g

Weight of empty bottle +

kerosene, W3 g 153.4 g 157.6 g

Weight of cement, W4 g 57.6 g 49.3 g

Weight of bottle + cement +

kerosene, W5 g 196.5 g

193.9 g

Specific gravity of kerosene,

‘g’ 0.79

0.79

Specific gravity of cement,

G = {W4 (W3-W1)} /

{(W4+W3-W5)(W2-W1)}

3.15 3.00

Table: Determination of Specific Gravity of Cement

SPECIFIC GRAVITY OF A CEMENT

Discussion :

The specific gravity of Ordinary Portland

Cement (OPC) varies from 3.1 to 3.15

and that of Portland Blast Furnace Slag

Cement varies from 3.0 to 3.05.


3253

Observations and Results:

Ordinary Portland Portland Slag

Cement (OPC) Cement (PSC)

Weight of cement

taken (W1 g) 400 g 400 g

Quantity of water

added to cement

(W2 ml)

150 ml 116 ml

Depth of penetration

(mm) 5 mm 8 mm

Normal Consistency =

(W2/W1) X 100 % 37.5 % 29.0 %

Table : Determination of Normal Consistency of Cement

Discussion:

The basic aim is to find out the water

content required to produce a cement

paste of standard consistency as

specified by the IS: 4031 (Part 4) –

1988. From the above results, normal

consistency of OPC is more than that

of PSC. It is seen that more water is

required to produce a cement paste in

OPC and hence OPC requires more

water to be able to produce a reliable

cement paste whereas with lesser

amount of water in PSC, depth of

penetration is more and thus, more

workable is the paste.

INITIAL AND FINAL SETTING TIME OF CEMENT

Results :

Ordinary Portland

Cement Portland Slag Cement

(OPC) (PSC)

Initial Setting

Time 156 mins 160 mins

Final Setting

Time 194 mins 215 mins

Discussion: From the above values,

OPC takes lesser time than PSC to

set. Hence, once the mixing is done,

the concrete has to be used quickly

compared to PSC which takes more

time to set.

METHODOLOGY

SOURCES OF MATERIALS

Different materials were obtained from different sources and the laboratory tests were

performed. The recycled aggregates were obtained from a demolished house which was

about 30 years old. The concrete used in Mauritius is usually M20 grade one. The slab,

columns and beams of the demolished building were made of this grade of concrete and

the walls were made of concrete hollow blocks.


3254

SCHEDULE OF WORK

The time plan prepared for casting of concrete and also for testing of the concrete cubes

and cylinders after acquiring all the required materials is as shown below

Monday Tuesday Wednesday Thursday Friday Saturday Sunday

17-Mar 18-Mar 19-Mar 3/27/2014 -

75%

3/28/2014

- 0%

22-Mar 23-Mar

3/24/2014 3/25/2014 /26/2014 - 50% 3/29/2014

4 - 100% RPC

(OPC)

25% RCA RCA (OPC) RCA (OPC) RPC (OPC) RPC (OPC) 30-Mar

4/1/2014 4/2/2014 - 50%

RCA (PSC) +

4/3/2014 - 25%

RCA (PSC)

+

4/4/2014 - 75%

RCA

(PSC) +

4/5/2014 - TEST 0%

RCA

6-Apr

31-Mar

(PSC) + TEST

4/9/2014 - TEST

TEST 50% TEST 75% (PSC) -

100% RCA OPC) RCA (OPC RCA (OPC)

7-Apr 8-Apr 100% RCA

(PSC)

TEST 50%

RCA (PSC)

TEST 25%

RCA (PSC)

TEST 75%

RCA (PSC) 13-Apr

14-Apr 15-Apr 16-Apr 17-Apr 18-Apr 4/19/2014 TEST 0%

OPC

20-Apr

21-Apr

4/22/2014 –

TEST

100% RCA

(OPC)

4/23/2014 – TEST

25% RCA

(OPC)

4/24/2014 –

TEST 50%

RCA (OPC)

4/25/2014 –

TEST 865

% RCA (OPC)

TEST 0%

RCA (PSC) 27-Apr

28-Apr 29-Apr

4/30/2014 –

TEST 100% RCA (PSC)

5/01/2014 –

TEST 50% RCA (PSC)

5/02/2014 –

TEST 25%

RCA (PSC)

5/03/2014 –

TEST 75% RCA (PSC)

4-May


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- Casting of Concrete

- 7th

Day Test on Cubes and Cylinders

- 28th

Day Test on Cubes and Cylinders

Table 5.1: Work Schedule

MIX DESIGN AND CALCULATIONS

For each mix specimen, the quantity of materials required for concrete mixing has been

calculated and tabulated. The water/cement ratio is kept constant but however, the water

content may vary for the slag cement due to its property to improve workability. For each

mix specimen, the following are to be cast for the basic tests:

6 cubes for compressive strength test - 3 at the age of 7 days

- 3 at the age of 28 days

6 cylinders for compressive strength test




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6

cylinder

s for

split-

tensile

strength

test



Quantity of Materials

Type of

Cement Ratio

Mix Specimen Cement

(kg)

Water

(L)

Fine

Aggregates

(kg)

Coarse Aggregates (kg)

W/C

Ratio RCA

Conventio

nal

Mix1 0% RCA 38.2 19.1 76.4 0 112.6 0.5

Ordinary Mix 2 25% RCA 38.2 19.1 76.4 28.1 84.4 0.5

Portland Mix 3 50% RCA 38.2 19.1 76.4 56.3 56.3 0.5

Cement

(OPC) Mix 4 75% RCA 38.2 19.1 76.4 84.4 28.1 0.5

Cement Mix 5 100% RCA 38.2 19.1 76.4 112.6 0 0.5

(OPC) Mix 6 0% RCA 38.2 19.1 76.4 0 112.6 0.5

Portland Mix 7 25% RCA 38.2 19.1 76.4 28.1 84.4 0.5

Slag Mix 8 50% RCA 38.2 19.1 76.4 56.3 56.3 0.5

Cement Mix 9 75% RCA 38.2 19.1 76.4 84.4 28.1 0.5

(PSC) Mix 10 100%RCA 38.2 19.1 76.4 112.6 0 0.5

Total for 6 cubes

and 12 OPC 191 95.5 382 281.4 281.4

Cylinders PSC 191 95.5 382 281.4 281.4

Table : Determination of Slump Values of Concrete using OPC and PSC


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Table : Quantity of Materials Required Slump Values for Concrete

with Water Cement Ratio = 0.5

0 %

RCA

25 %

RCA 50 % RCA

75 %

RCA 100 % RCA

Using OPC 100 mm 110 mm 115 mm 110 mm 110 mm

Using PSC 100 mm 100 mm 90 mm 115 mm 100 mm

Discussion: The standard slump values for normal RCC work

ranges from 80-150 mm. If the concrete mixture is too wet, it

will have a greater slump and the coarse aggregates will settle at

the bottom of concrete mass, i.e. it will collapse and as a result

concrete becomes a non-uniform composition. If the concrete

mixture is too dry, it will have a lesser slump value

Results: Compaction Factor for Concrete with Water

Cement Ratio = 0.5 Using OPC

0 % 25 %

50

%

75

%

100

%

RCA RCA RCA RCA RCA

Weight of empty

cylinder (W,g) 11,980 g 11,980 g 11,980g 11,980 g 11,980 g

Weight of cylinder

with

partially compacted

concrete

(W1g)

23,180 g 23,320 g 23,420g 23,160 g 23,200 g

Weight of cylinder

with fully compacted

concrete (W2 g)

24,520 g 24,140 g 23,960g 23,900 g 24,110 g

Compaction Factor

= (W1-W / W2-W) 0.89 0.93 0.95 0.93 0.92

Compaction Factor for Concrete with Water Cement

Ratio= 0.5 Using PSC

0 % 25 %

50

%

75

% 100 %

RCA RCA RCA RCA RCA

Weight of empty

cylinder (W,g) 11,980 g 11,980 g 11,980g 11,980 g 11,980 g

Weight of cylinder

with

partially compacted

concrete

(W1g)

23,440 g 23,480 g 22,700 g 23,480 g 22,660 g

Weight of cylinder

with fully

compacted concrete

(W2 g)

24,700g 24,460g 24,260g 24,160g 23,780g

Compaction Factor

= (W1-W / W2-W) 0.9 0.92 0.87 0.94 0.91

Discussion: Following is a table showing the standard limits

for compaction factor of concrete: Table : Standard Values for Compaction Factor

Degree of

workability

Compacting factor

Small

apparatus

Large

apparatus

Very low 0.78 0.80

Low 0.85 0.87

Medium 0.92 0.935

High 0.95 0.96

Very high - -

Vee-Bee Degrees for Concrete with Water Cement Ratio = 0.5

Table : Determination of Vee-Bee Degrees for Concrete with

Different Percentage of RCA using OPC and PSC

0 % 25 % 50 % 75 % 100 %

RCA RCA RCA RCA RCA Using 9.3 7.1 6.8 7.2 7.0

OPC VB-

degrees

VB degrees VB Degrees

Using 9.1 9.5 11.3 6.9 8.9

PSC VB-

degrees

VB-

degrees

VB-

degrees

VB-

degrees

VB-degrees

Discussion:Following is a table showing the standard limits of Vee-Bee test on concrete:

Workability description Vee-Bee time, in seconds

Extremely dry 32-18

Very stiff 18-10

Stiff 10-5

Stiff plastic 5-3

Plastic 3-0

Flowing -

Table : Standard limits for Vee - Bee test on concrete

RESULTS AND DISCUSSIONS In this chapter, the results obtained by performing tests on hardened concrete

are displayed and explained. These tests have been explained in detail in . Firstly, compressive strength tests were

performed on concrete cubes and cylinders after 7 and 28 days of curing. Secondly, split tensile strength test was

performed on concrete cylinders at 7 and 28 days of curing as well. The tests were done on concrete with RCA

proportions using both Ordinary Portland Cement (OPC) and Portland Slag Cement (PSC).


3258


3259

ACKNOWLEDGMENT

This Research work was supported by DST FIST(No: SR/FST/ETT-378/2014,Dated 24/11/2015) in SET-JU. We

are thankful to our organization that provided expertise that greatly assisted the research

Reference

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