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T h e M a s t e r b u i l d e r

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Potential Use of Recycled CoarseAggregates in Concrete

Abstract: Concrete continues to be the most consumed con-struction material in the world, only next to water. This fact isdue to its appealing properties of high compressive strengthand the property of mould-ability to any conceivable shape.Due to rapid increase in construction activities, it is import-ant to assess the amount of construction and demolition

waste being generated and analyse the practices needed tohandle this waste from the point of waste management anddisposal and also with regard to waste utilization in concretefrom the sustainability aspects. Construction and Demolition(C&D) waste constitutes a major portion of total solid wasteproduction in the world, and most of it is used in landfills.Research by concrete engineers has clearly suggested thepossibility of appropriately treating and reusing such wasteas aggregate once again in concrete, especially in applica-tions such as bed concrete and in road beds for pavement i.e.where works are of less importance as regards to the strength.The use of such waste as recycled aggregate in concrete canbe useful for both environmental and economic aspects in the

construction industry. This study reports some interestingresults of the utilization of recycled coarse aggregates inconcrete from construction and demolished waste.

Due to high demand for construction activities in re-cent years in India and all over the world, the natural ag-gregates resources are remarkably waning day by day. On theother hand, millions of tonnes of C&D residues are gener-ated. Natural resources are dwindling day by day due totheir extensive use to cope with the increasing demand ofCivil Engineering Projects. Therefore, the use of C&D wasteas an alternative aggregates for new concrete productiongains importance to preserve natural resources and reduc-ing the need for disposal, (S Manzi et al. 2013). The amount

of construction and demolition waste has increased enor-mously over the last decade in the entire world, (Sami W.Tabsh et al 2009). Disposal of construction and demolitionwaste has also emerged as a problem in India. Therefore,recycling of waste concrete is beneficial and necessary forthe environmental preservation and effective utilization ofnatural resources, (Ashraf M. Wagih et al. 2013). The use ofrecycled coarse aggregate obtained from construction anddemolition waste in new concrete is a solution for effectivewaste utilization, (M. Chakradhara Rao et al.2011).

The management of construction and demolition wasteis a major concern due to increased quantity of demolitionrubble, shortage of dumping sites, increase in cost of dis-

posal and transportation and above all the concern aboutenvironment degradation. Although a substantial portion of

construction materials could be substituted by re-processedconstruction waste material, these options are not exercisedin developing countries due to lack of knowledge and insuffi-cient regulatory frameworks resulting in waste getting piledup causing disposal problems, (R.V.Silva et al. 2014). The in-creasing problems associated with construction and demo-

lition waste, have led to a rethinking in developed countriesand many of these countries have started viewing this wasteas a resource and presently have fulfilled a part of their de-mand for raw material, (Shi-Cong Kou et al. 2012).

Many developed countries have been recycling C&D wasteand using it for construction works. In Scotland about 63% ofthe C&D waste was recycled in 2000. The Government there isworking out specifications and code of practice for recyclingof C&D waste. U.K uses 49-52% of the C&D wastes and Aus-tralia reuses 54% of the wastes generated. Belgium has ahigher recycling rate (87%) and uses majority of C&D for re-cycling purposes. Japan is one of the pioneer countries thatrecycle C&D waste. 85 million tonnes of C&D waste was

generated in 2000, of which 95% of concrete was crushed andreused, (Akash Rao et al. 2007).

Using recycled concrete aggregates, will requirechecking the quality of the aggregates, since they are col-lected from different sources, grades of concrete and age,(A.K.Padmini et al. 2009). Concrete workability is more influ-enced by the shape, texture and grain size distribution of therecycled aggregates than by their total amount, (S. Manzi etal. 2013). The compressive strength primarily depends uponadhered mortar, water absorption, Los Angeles abrasion, sizeof aggregates, strength of parent concrete, age of curing andratio of replacement, interfacial transition zone, moisture state,impurities present and controlled environmental condition

(Isabel Martínez-Lage et al. 2012). Absorption of RCA is oneof the major contributing factors in the strength of concrete,(K C Panda and P K Bal 2013).

This study reports some important changes in propertiessuch as compression strength and absorption of recycledaggregate concrete.

Materials

Ordinary Portland Cement (OPC) 43 grade was used andits properties are tabulated in Table 1. Coarse aggregate wascrushed stone with a maximum size of 20 mm. Locally avail-able natural river sand conforming to zone III (IS 383-1970grading requirements) was used as fine aggregate. Physical

properties of fine and coarse aggregates are presented inTables 2 and 3 respectively. Potable quality water is used.

Subhash C. Yaragal , Vivek V B , M Padmini , M Jacob,

J Niveditha1, Anil Kumar Pillai2

1National Institute of Technology Karnataka, Surathkal2The Ramco Cements Limited

CONCRETE: RECYCLED AGGREGATES

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Recycled aggregates were obtained from demolished con-crete made in the laboratory with maximum size of 20 mm.

Table 4 shows the properties of recycled coarse ag-gregates and Table 5 gives mix proportions for OPC basedconcrete. The sieve analysis results of natural and recycledaggregates are shown in Table 6.

Sources and processing of RCA

In order to obtain correct assessment of strength of RCAbased concrete, it was thought necessary to produce con-struction and demolished waste from same quarry virgincoarse aggregates. To achieve C & D waste, about 30 Nos. of150 mm concrete cubes were cast and cured for a periodof 28 days. Later all these were compressed to failure, to

produce C & D waste.A common procedure adopted to recover the coarse ag-

gregates from C & D wastes is as follows. The C & D waste,was fragmented manually further, and then 10 Kg of C & Dwaste was placed in Los Angeles aggregates testing machinewith constant charge and the apparatus was run for 5 min-utes.

Later this processed material is removed, and sieveanalysis was carried out. After sieve analysis, the obtained

NO. PropertyResult ob-

tainedRequirementsas per IS code

1Specificgravity

3.12 -

2Normal con-

sistency29% -

3Setting times,

minutesInitial 65Final 270

Not less than 30Not more than

600

4Fineness,

m2/Kg330

Not less than300

5 Soundness,mm 2.50 Not more than10 mm

6Comp.

strength,Mpa

3d 7d 28d 3d 7d 28d

34 51 61 22 33 43

Table 1 Physical properties of Ordinary Portland Cement

(NCA-Natural Coarse Aggregates, RCA-Recycled Coarse Aggregates)

Table 6 Sieve analysis results of natural and recycled coarse aggregates

Table 2 Properties of fine aggregates

Table 3 Properties of coarse aggregates

Table 4 Properties of recycled coarse aggregates

Fig. 1 Compressive strength variation of OPC based concrete with RCA(Mean data)

Fig. 2 Compressive strength variation of OPC based concrete with RCA(Full data)Table 5 Composition of various mixes for OPC blended concrete

(RCA-Recycled Coarse Aggregate, C-Cement, FA- Fine Aggregates, CA-

Coarse Aggregates, W- Water)

Property Result

Specific gravity 2.62

Bulk densityLoose: 1463 Kg/m3

Compact: 1661 Kg/m3

Moisture content Nil

Property Result

Specific gravity 2.73

Bulk densityLoose: 1360 kg/m3

Compact: 1527 kg/m3

Moisture content Nil

Sl. No. Property Results

1 Specific gravity 2.59

2 Water absorption 2.69%

3 Fineness modulus 6.96

MixRCA C FA CA RCA W

(%) (kg) (kg) (kg) (kg) (kg)

Mix 1 0 400 600 1200 - 200

Mix 2 20 400 600 960 240 200

Mix 3 40 400 600 720 480 200

Mix 4 60 400 600 480 720 200

Mix 5 80 400 600 240 960 200

Mix 6 100 400 600 0 1200 200

Sieve size (mm)% Finer

NCA RCA

20 100 100

16 68.5 71.5

12.5 32.1 27.710 0.7 0.5


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RCA, was agitated and washed in a water tank to removesurface crushed rock fines (dust) and sun dried before theirbeing used as RCA to cast specimen.

Experimental Methodology

The obtained aggregates are mixed in proportions of 0%

(no RCA), 20%, 40%, 60%, 80% and 100% (all RCA) by weightof the total natural coarse aggregates in concrete. So for eachmix 3 Nos. of 150 mm cubes concrete cubes as stipulated bythe code were cast. 18 Nos. of 150 mm cubes were cast and28 days water cured before testing them for compressivestrengths. Experiments were aimed for achieving workableslump between 50-75mm without using super plasticizers.Standard slump cone apparatus is used for measuring thevalue of slump. During the slump tests it was found that theworkability of fresh concrete made with 100% replacementof RCA had slump value close to zero mm. With increase inpercentage of RCA in concrete the workability was gettinglower and lower. This was mainly due to the high absorp-tion rate (2.69%) of the RCA as compared to the fresh coarseaggregate (0.2%). Adding water to compensate for this ab-sorption was not a good option as exact amount could not beascertained. So it was decided to soak the RCA for 24 hoursbefore use, so that it does not absorb water during the processof mixing (M. Etxeberria et al. 2007), this method of soaking

helped to attain moderate workability of concrete without use ofplasticizers. The test matrix for compression test is shownin Table 7.

The concrete samples with RCA are tested for 28 daystrengths and compared with the results of the strengths ofconcrete made with virgin natural aggregates.

Results and Discussion

Compressive Strength

Table 8 presents the results of the compressive strengthtests for OPC based concrete specimen. It can be noticedthat the compressive strength of the cubes goes on decreasing

as the percentage of the RCA replacement gets increasedfrom 42.1 MPa for the control mix to 30.8 MPa in the fullyRCA replaced cubes. The drop in strength with increase inRCA proportion is attributed to the bond strength becomingweaker and weaker with RCA increase.

From Table 8, it is observed that there is a decrease instrength from 7% to 27%, when 20% of virgin aggregates isreplaced by RCA, to the case when 100% of virgin aggregatesis replaced by RCA. These findings are in agreement withother investigators. S.C.Kou et al. (2012) reports a fall in thecompressive strength. Sami W. Tabsh and Akmal S. Abdel-fatah (2009) have reported that the decrease in strength isby about 10-25%. Sumaiya Binte Huda and M. Shahria Alam(2014) have got a decrease in 15-20% when aggregateswere replaced. Figure 1 shows the normalized compressivestrength variation, with increase in RCA. These findings are

RCA (%) No. of cubes

0 3

20 3

40 3

60 380 3

100 3

Total 18

Table 7 Test matrix for compression on 150 mm cubes

Table 8 Compressive strength of cubes for OPC based concrete specimen

Table 9 Water absorption results for OPC based concrete

Fig. 3 Variation of percentage of absorption for OPC, with RCA

RCA (%)Comp.

Strength(N/mm2)

AverageComp.

Strength(N/mm2)

RelativeComp.

Strength

AverageRelativeComp.

Strength

Control 40.44

42.1

0.96

1.000 43.11 1.02

42.67 1.01

20

39.11

39.3

0.93

0.9340.89 0.97

37.78 0.90

40

37.78

37.5

0.90

0.8937.33 0.89

37.33 0.89

60

34.22

34.4

0.81

0.8134.22 0.81

34.67 0.82

8033.77

33.50.80

0.7934.67 0.82

32.00 0.76

100

30.22

30.8

0.72

0.7331.11 0.74

31.11 0.74

RCA (%)Dry weight

(kg)Wet weight

(kg)Absorption

(%)

0 8.232 8.579 4.22

20 8.080 8.470 4.8340 7.844 8.256 5.23

60 8.093 8.485 4.84

80 7.956 8.371 5.22

100 7.963 8.36 4.99


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similar to the results of Wai Hoe Kwan et. al (2012). Shi-CongKou and Chi-Sun Poon (2013) have also reported a decline intheir compressive strength. K.K.Sagoe-Crentsil et al (2001)have similar results with recycled aggregates replaced con-crete. According to the studies by Isabel Martínez-Lage et al.(2012) the estimated loss for concrete with 100% recycledaggregate was 23%, with values ranging from 20% to 31%.

There is a reduction from normalized strength factorof 1.00 to 0.73, when the natural aggregate was completelyreplaced with recycled aggregate. Hisham Qasrawi (2014)has also reported a reduction in concrete strength when re-placed with RCA. K C Panda and P K Bal (2013) have reportedthat compressive strength, flexural strength and split tensilestrength of concrete decreases with increase in the amountof RCA.

Figure 2 shows the best fit line, showing the drop instrength of concrete with increase in percentage of RCA.The proposed equation can be used to predict the normal-ized strength of concrete as a function of RCA, with maxi-

mum error in prediction of less than 2.5%.

Normalized Strength = 0.9848-[0.0026Xrca(%)] ..(1)

Water Absorption Test

Water absorption was used to determine the amount ofwater absorbed under specified conditions that indicates thedegree of porosity of a material. The results of the water ab-sorption tests are as shown in Table 9. The results indicatethat the water absorption was higher in all the cases whenthere is a replacement by recycled aggregate. The percent-age of absorption varied from 4.22% to 5.23%. It is clear thatthe concrete with RCA has more absorption rate than that of

the control mix. This is mainly due to the high absorption ofthe recycled aggregate compared to the natural aggregate(Isabel Martínez-Lage et al 2012). The residual mortar at-tached to recycled concrete particles serves as a potentialconduit for moisture transport. Figure 3 shows water ab-sorption in a graphical form. Hence we can say that the RAChas more porosity when compared to the normal concrete.Though this may not have a direct relation with the durabilityof the concrete, it is affecting the strength of the concrete.

K.K.Sagoe-Crentsil et al (2001) have got absorption ratesranging between 5-7%. The absorption rate of this investiga-tion ranges between 4-6%.

Conclusions

(1) RCA exhibits similar behaviour like fresh aggregatein concrete; therefore, RCA could be incorporated intomany concrete structures. However, RCA that has anunknown origin should be tested to ensure that the RCAwas not from a structure that was suffering from alka-li-silica reaction, alkali-aggregate reaction, sulphate at-tack, or some other harmful reaction. Such RCA couldaffect adversely the strength and durability of the con-crete and may be harmful.

(2) A maximum reduction of about 27% was noticed in com-pressive strength when the entire coarse natural aggre-gate was replaced with RCA. Moreover, environmental

benefits may be able to compensate for the negativeeffect of loss in strength to some extent due to the use

of recycled coarse aggregate in concrete leading us tosustainable development.

(3) Absorption for RCA concrete was more than that for con-trol mix. This may affect the durability of the concrete.

(4) As the degree of processing gets higher the RA tends to

be more similar to NA. Hence RA after processing showsbetter results than unprocessed RA.

References

[1] A.K.Padmini, K.Ramamurthy, M.S.Mathews (2009), Influence ofparent concrete on the properties of recycled aggregate concrete.Construction and Building Materials, 23, 829-836.

[2] Akash Rao, Kumar N. Jha, Sudhir Misra, (2007), Use of aggregatefrom recycled construction and demolition waste in concrete, Re-sources Conservation and Recycling, 50, 71-81.

[3] Ashraf M. Wagih , Hossam Z. El-Karmoty , Magda Ebid , Samir H.Okba (2013), Recycled construction and demolition concrete wasteas aggregate for structural concrete, HBRC Journal , 9, 193–200.

[4] Hisham Qasrawi (2014), The use of steel slag aggregate to enhance

the mechanical properties of recycled aggregate concrete and re-tain the environment, Construction and Building Materials, 54, 298–304.

[5] Isabel Martínez-Lage, Fernando Martínez-Abella, Cristina Vázquez-Her-rero, Juan Luis Pérez-Ordóñez (2012), Properties of plain concretemade with mixed recycled coarse aggregate , Construction andBuilding Materials ,37 ,171–176.

[6] K C Panda, P K Bal (2013), Properties of self-compacting concreteusing recycled coarse aggregate, Procedia Engineering, 51, 159 – 164.

[7] K.K.Sagoe-Crentsil, T.Brown, A.H.Taylor (2001), Performance ofconcrete made with commercially produced coarse recycled con-crete aggregate, Cement and Concrete Research, 31 , 707-712.

[8] M. Chakradhara Rao , S.K. Bhattacharyya , S.V. Barai (2011), Be-haviour of recycled aggregate concrete under drop weight impact

load, Construction and Building Materials, 25 ,69–80.[9] M. Etxeberria , E. Vázquez, A. Marí, M. Barra (2007), Influence of

amount of recycled coarse aggregates and production process onproperties of recycled aggregate concrete, Cement and ConcreteResearch, 37, 735–742.

[10] R.V. Silva, J. de Brito, R.K. Dhir (2014), Properties and composition ofrecycled aggregates from construction and demolition waste suit-able for concrete production, Construction and building materials,65, 201-217

[11] S. Manzi , C. Mazzotti, M.C. Bignozzi (2013), Short and long-termbehavior of structural concrete with recycled concrete aggregate,Cement & Concrete Composites , 37 , 312–318

[12] S.C. Kou, C.S. Poon (2012), Enhancing the durability properties ofconcrete prepared with coarse recycled aggregate, Constructionand Building Materials, 35, 69–76.

[13] Sami W. Tabsh ,Akmal S. Abdelfatah (2009), Influence of recycledaggregate concreteon strength properties of concrete, Constructionand Building Materials ,23, 1163–1167.

[14] Shi-Cong Kou, Chi-Sun Poon (2013), Long-term mechanical and du-rability properties of recycled aggregate concrete prepared with theincorporation of fly ash, Cement & Concrete Composites, 37, 12–19.

[15] Shi-Cong Kou, Chi-Sun Poon, Hui-Wen Wan (2012), Properties ofconcrete prepared with low-grade recycled aggregates, Construc-tion and Building Materials, 36, 881–889.

[16] Sumaiya Binte Huda, M. Shahria Alam (2014), Mechanical behaviorof three generations of 100% repeated recycled coarse aggregate,Construction and Building Materials, 65, 574-582.

[17] Wai Hoe Kwan , Mahyuddin Ramli, Kenn Jhun Kam, Mohd ZailanSulieman (2012), Influence of the amount of recycled coarse aggre-

gate in concrete design and durability properties, Construction andBuilding Materials, 26, 565-573. w


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