Properties of Concrete With Dissimilar Treated Recycled Coarse Aggregate

The strength evaluation of concrete can be determined by destructive and Non-destructive methods. In recent years construction industry initiated using demolition waste in structural concrete and due to this action coarse aggregate cost has been reduced. By using pre-treatment method of recycled coarse aggregate (RCA), the concrete properties will increase. Thus, the RCA are treated by using mechanical scrubbing and acid treatment (H 2 SO 4 & HCl) before induced in concrete. Slump value for controlled concrete with river sand and M-sand was 110mm and 100mm. For untreated recycled aggregate concrete, the slump value reduced to 70mm and it is improved by using mechanical scrubbing treated aggregate concrete by 90mm without addition extra water. Similarly, Vee-bee consist meter test and Compaction factor test results were reduced suddenly while using untreated aggregate concrete; it was improved by all treatment methods especially by mechanically scrubbing techniques. The compressive strength for untreated aggregate concrete at 28 days is 16.83 N/mm 2 and it was improved by mechanical scrubbing by 22.68 N/mm 2 .The strength was increased by mechanically treated aggregate concrete by 25.79% on compared with untreated aggregate concrete. The rebound numbers of treated RAC were improved by 12.5-26.31% at 28 days than RAC (UN). The ultrasonic pulse velocity in different treatments of RAC was improved by 8.17 – 22.82% at 28 days than RAC (UN). Impact resistance also enhanced by using treated recycled aggregate.


INTRODUCTION
According to the survey, "Lack of awareness in recycling possibilities and techniques" was the major reason for not inducing recycled waste in the Construction industry.The quality of RCA mainly depends on where it was obtained from.The outer surface of RCA was adhered with old mortar and it's decreased the strength of concrete.The water absorption of RCA was mainly affected by old attached mortar.The density of RCA was lower than that of natural coarse aggregate (NCA) (Chakradhara Rao et al., 2011).The strength of concrete under dry curing conditions was 35% lower than that of wet curing conditions.On compared to RAC under both dry and wet curing conditions, the controlled concrete sample had 47% higher strength.In compressive strength in rebound hammer for wet curing condition of RAC had 44.9% lesser than that of controlled concrete and dry curing condition of RAC had 46.1% lower than that of controlled concrete.In the rebound hammer test, compression results of RAC under dry and wet curing conditions, early ages it increased extraordinarily but reasonable increases in older ages (MostafaKazemi et al., 2019).In the rebound hammer test, the highest number was achieved in controlled concrete.Then it's followed by rebound hammer number of heating-grinding-acid-treated RCA concrete sample was higher than that of heating -grinding treated RCA concrete respectively.H-G-A concrete sample gave enhanced surface hardness than H-G concrete samples.In Ultrasonic pulse velocity; wave velocity was high in the controlled sample due to superior glue among aggregate surface and cement paste.H-G-A treated aggregate in concrete has enhanced 5.5% of wave velocity than H-G treated aggregate in concrete.By treating with acid solvents enhance to take apart the old adhered mortar from the aggregate surface more successfully, so H-G-A shows superior performance than that of H-G (Ninyman Kencanawatiet al., 2015).At the age of 7 and 14 days, shows that results obtained by compressive test on the concrete sample are higher than that of rebound hammer test.The average difference between the two methods at age of 7&14 days were 14%&17% correspondingly.There is a reversal situation after 28 days; the rebound hammer test was got 5% higher results than that of the compression test.By maturity of concrete, results could be explained.Rebound hammers are used to evaluate the homogeneity and concrete strength.Mainly used for older concrete not for younger concretes (JedidiMalek et al., 2014).
In compressive strength at 28days, concrete inducing RCA shows somewhat lesser strength parameters relative to concrete made by virgin aggregate.When RCA is alternated for virgin aggregate the compression strength decreases.In the ultrasonic pulse velocity test, wave velocity decreases by 1-3% similar to decreases in strength.At the early stage of concrete, the ultrasonic pulse velocity distributed with results in the range of 3500-4100ms − 1 .At 28 days, the wave velocity ranges between 4100-4400ms − 1 .The overall velocity increase with the age of materials (Cho et al., 2014).The bulk density of RCA was lower than that of virgin aggregates.The speci c gravity of recycled aggregate would be increased when the water absorption of RCA is decreased.The speci c gravity of RCA ranges between 2.2 to 2.5.In compression strength, the controlled sample had the highest strength value of 41.6 Mpa.In recycled coarse aggregate concrete, the highest value is 34.3Mpa which is nearest to design compressive strength of 3 Mpa.For any concrete mixes, compression strength and ultrasonic pulse velocity are much higher for conventional concrete than recycled aggregate concrete.Eliminating the adhered mortar in recycled aggregate the water absorption ratio declines to 6.1-4.5% and the slump value of RAC is improved from 50 to 65mm.The ratio of compressive strength also improved from 0.69 to 1.13 respectively.The compressive strength assessment was enhanced from 35.6 Mpa to 45.0 Mpa (RenjieMi et al., 2020).It can be examined that replacement of virgin aggregate by recycled aggregate in concrete mixes, drops the concrete workability.In the Non-destructive test, the recycled aggregate concrete has inferior results compared to control concrete (BibhutiBhusanMukharjee et al., 2014).
The RCA properties were worst for making concrete than virgin concrete.In RCA concrete mixes extra water is added for compensation because the RCA has more absorbing capability.Due to superior porosity, density is lower and hence lowers the mechanical properties.The elongated shape of RCA tends to have low workability (Pacheco et al., 2020).High-performance concrete is better than normal controlled concrete.The recycled aggregate is incorporated into highperformance concrete, strength remained solitary at 9.0% and 6.8% respectively (C.S. Poon et al., 2004).To estimate & forecast the strength of concrete rebound hammer alone is not an appropriate method.It makes it quite di cult to judge, because high variations are obtained.When compared between pulse velocity and rebound hammer test, predicting the strength of concrete are very low in rebound test.The above methods alone didn't give a superior prediction of concrete strength.The combined method yields reliable result, than other methods ( Hisham et al ., 2000)Water cement ratio, mortar content, and aggregate properties, are used to make clear the dissimilarity of compressive strength and rebound number for each type of concrete ( Anindya Samya

TREATING APPROACH FOR RCA
To improve the RCA, the following methods were adopted.
2.1 Chemical treatments: Two different kinds of acid solvents with 0.1 M are used to treat the RCA, namely sulphuric acid (H 2 SO 4 ) and hydrochloric acid (HCl) .The RCA was pre-soaked in acid solvents for 24 h at room temperature.After 24 h, the pre-soaked aggregates were washed with clean water to remove the acidic solvents.The recycled aggregate obtained after acid treatments slightly hammering action were needed to remove the loose debris on the surface of aggregate.(Revathi et al, 2015).

Mechanical treatment:
The RCA were placed in los angles abrasion machine with 12 steel spheres for 300 revolutions to remove adhered mortar content.After completion of these revolutions, the aggregate was sieved by using a 4.75 mm sieve to separate the aggregate.After sieving, the RCA was cleaned with portable water to eliminate the dust particles.(Pandurangan et al., 2016) 3. MATERIALS CHARACTERIZATION 3.1 Ordinary Portland cement OPC 53 grade cement was used for the current study con rming IS 12269 − 1987 (Rea rmed 2004).The speci c gravity is 3.15; standard consistency (%) is 29and compressive strength at 28 days is 55.5 Mpa.

River Sand &Manufacture Sand (M-sand)
River sand was used as natural ne aggregate and obtained locally.Manufactured sand obtained from crushing granite stone (quarry dust).The neness modulus of river sand is 3.0, manufactured sand is 2.75 and con rms to zone II as per IS: 383-1970.Approximately particle sizes vary in the range of 0-4.75 mm.The speci c gravity of river sand and M sand is 2.48 &2.63, water absorption (%) of river sand and M sand is 0.8 &3.51, bulk density of river sand and M sand is 1633 &1726.The physical properties of river sand and manufactured sand were determined as per IS 2386 (Part III)-1963.The sieve analysis results of river sand and M sand are presented in Fig. 1.

Natural coarse aggregate, treated and untreated Recycled coarse aggregate
The required size of granite stone was used as a coarse aggregate and obtained from Thiruvakarai near Viluppuram, India.RCA is obtained from an old demolished building.The sieve analysis of natural coarse aggregate, treated and untreated RCA con rms as per IS 383-1970 are presented in Fig. 2. The physical properties of coarse aggregates determined as per were 2386 (Part III)-1963 are presented in Table 1.All kinds of coarse aggregate used in this work are shown in Fig. 3.The elemental concentration of various aggregates are shown in Table 2 and Fig. 4,tested in National centre for earth science studies, Trivandrum, Kerala.

Super plasticizers
To increase the workability classic super ow SP was used.The chloride content is nil and speci c gravity is 1.20.

Compaction factor Test
The Compaction factor results were shown in gure 9.In NAC &NCMC the value was obtained as 0.94&0.92and 0.85 is obtained in RAC (UN), for RAC (MS) is 0.91, RAC (H 2 SO 4 ) is 0.90, and RAC (HCl) is 0.90, before mixing the concrete the recycled coarse aggregate must be in SSD condition.Due to old adhered mortar, the RCA absorbs more water and workability tends to be reduced.In the Compaction factor test, values from RAC (MS) have better results compared to other treatment techniques.All kinds of treatment methods improved their results in fresh properties of concrete compared to RAC (UN).

Vee-bee Consistometer Test
The Vee-bee results are exposed in gure 10.In NAC &NCMC the value was obtained as 4 & 5 sec, RAC (UN) exposed as 9 sec, for RAC (MS) is 5 sec, RAC (H 2 SO 4 ) is 6 sec and RAC (HCl) is 6 sec, before mixing the concrete the recycled coarse aggregate must be in SSD condition.Various treated aggregate shows better performance than the untreated recycled aggregate.

Compressive Strength test
The   22 and23.The correlation coe cient for impact resistance and various ages are shown in gure 24.

Photographic view of cross section and Scanning Electron Microscope
The interfacial transition zone is clearly shown in gure 25.The pores are highly in recycled aggregate concrete than controlled concrete.The untreated recycled concrete show the indication of old rebars corrosion marks on surface.The interfacial transition zone was weak in the side of old adhered mortar present in aggregate.The new cement paste and old cement paste are clearly marked in each and every photo.

CONCLUSIONS
1.A physical property of recycled aggregate was enhanced by all types of treatment methods.More effective in mechanical scrubbing treatment method.
2. In fresh concrete properties, untreated recycled aggregate concrete consumes more water for workability.The RAC (MS) consumes less water for workability requirements compared to RAC (UN). .Mechanical scrubbing treatment give better improvement compared to all other methods.This method was ecofriendly and requires no skilled labor to treat the aggregate.
7. In impact resistance, the treated aggregate enhances the concrete more signi cantly.Especially mechanical scrubbing shows better performance compared to untreated RA in concrete .The photographic and scanning electron microscope shows the surface of concrete and it gives clear observation of sample, in RAC(UN) shows old corrosion impression in aggregate and have more voids due to adhered mortar.But the treated aggregate concrete the ITZ was modi ed.

3 . 4 . 5 .
Compressive strength of RAC (MS) improved the strength by 25.79% compared to RAC (UN) at 28 days, at the same time all treated aggregate improves the strength.The rebound Number for NAC and NCMC is 23 and 20.RAC (UN) number is 14 and the rebound number enhanced in RAC (MS) is 19 at 28 days.Ultrasonic pulse velocity represented 4630 m/s and 4275 m/s for NAC& NCMC.The RAC (UN) pulse velocity was 3145 at 28 days.

Figures
Figures

Figure 3 Shows
Figure 3

Figure 4 Shows
Figure 4

Figure 5 a
Figure 5

Figure 7 Unit
Figure 7

Figure 9 Various
Figure 9

Figure 10 Various
Figure 10

Figure 11 Various Mixes Compressive Strength Figure 12 Correlation
Figure 11

Figure 15 Various
Figure 15

Figure 18 combination
Figure 18

Figure 20 Combination
Figure 20

Ran Wu et al 2018, Matias et al 2013, Xuan et al 2013, Xuan et al 2012, Guneyisi et al 2014, ZhouJZeng M et al 2019).Recycled aggregate in concrete requires more water for workability; the RCA had a huge water absorption capacity than natural aggregate. Acid-treated aggregate with 0.1 Molarities would not affect the durability of concrete(Pandurangan K et al., 2016; Shi-Cong et al., 2014; Butler et al;2011; Wang et al
., 2017).RAC bonds were improved by treating the surface of aggregate and most of the methods were eco-friendly (Cakır et al 2014, Revathi et al 2013, Saravanakumar et al 2016, Purushothaman et al 2015, Wang et al 2020, Marinkovic et al 2010, Ismail et al 2013, Wang et al 2019, Vengadesh et al 2020)

Table 2
Shows the Elemental Concentration (%) of Various Coarse Aggregate found by XRF-analysis Similarly, Sulphuric acid-treated recycled aggregate concrete is abbreviated as RAC (H 2 SO 4 ), prepared with H 2 SO 4 treated coarse aggregate and M sand.Hydrochloric acid-treated recycled aggregate concrete is abbreviated as RAC (HCl), prepared with HCl treated coarse aggregate and M sand.Six different concrete mixtures and each mix 18 samples were cast in the size of 100X 100 X100 mm.Test samples were cured at room temperature for 28 days.The compression tests were conducted by destructive methods and non -destructive methods.Various concrete proportions were speci ed in Table3.Figure5a, b, cshows the experimental test setup specimen.
IS 10262:2019 Code provisions were used for mix design.The proportions of concrete mixtures were estimated for M20.The ratio used in the current study is 1:1.61:3.14.W/C ratio had arrived at 0.41.Natural aggregate concrete was abbreviated as NAC, prepared with natural river sand and crushed rock aggregate.Natural coarse aggregate & M sand concrete is abbreviated as NCMC, prepared crushed rock aggregate &M sand.Untreated recycled aggregate concrete is abbreviated as RAC (UN), prepared with Untreated recycled coarse aggregate, and M sand Mechanical scrubbing recycled aggregate concrete is abbreviated as RAC (MS), prepared with abrasion treated coarse aggregate and M sand.
By using treated recycled coarse aggregate in concrete the rebound numbers is increased.Compared to RAC (UN) the treated aggregate of RAC (MS), RAC (H 2 SO 4 ) and RAC (HCl) is enhances by 26.31%, 22.22% and 12.5% at 28days.The rebound number is increased in all kinds of treated aggregate concrete, especially increased high in mechanical scrubbing treated aggregate concrete.At the same time there is marginal difference between RAC (MS) & RAC (H 2 SO 4 ).The variations of rebound numbers of different mixes are presented in table 4 and gure 13.The correlation coe cient of rebound number with different ages is shown in gure 14.The correlation coe cient of NAC, NCMC RAC (MS), RAC (H 2 SO 4 ) and UN) has very lower compared to other mixes.After treatment of recycled aggregate the coe cient value was enhanced and still inferior when compared to natural aggregate concrete.
compressive strength of different concrete mixes was presented gure 11.The RAC (UN) reduces compressive strength of 38.75% and 28.53% compared into NAC & NCMC at 28 days.The reduction of compressive strength was more in untreated aggregate concrete.By using treated recycled coarse aggregate in concrete the compressive strength is increased.Compared to RAC (UN) the treated aggregate of RAC (MS), RAC (H 2 SO 4 ) and RAC (HCl) is enhances by 25.79%, 17.29% and 7.78% at 28days, especially the mechanical scrubbing treated RAC (MS) shows better improvement .At the same time there is marginal difference between RAC (MS) & RAC (H 2 SO 4 ).Other researchers also gave same parameters (Revathi et al, 2015 and Pandurangan et al 2016).The correlation coe cient of compressive strength with respect to different ages is shown in gure 12.The correlation coe cient of NAC, NCMC RAC (MS), RAC (H 2 SO 4 ) and RAC (HCl) was 0.8855, 0.9437, 0.9122, 0.9229, 0.8983,and 0.9088 are shown in gure 12.This show that all the concrete mixes value are in increasing trend and untreated recycled coarse aggregate concrete decline its strength due to inferior properties of aggregate surface.Then, after surface treatment the aggregate was enhanced and treated aggregate concrete values are also in increasing trend.5.3 Schmidt Rebound Hammer TestThe RAC (UN) reduces rebound numbers of 39 % and 30% compared into NAC & NCMC at 28 days.The rebound number of untreated recycled aggregate concrete represents very low compared to NAC and NCMC.

Table 4
Rebound Number (RN) and Ultrasonic Pulse Velocity (m/s) at Various AgesThe ultrasonic pulse velocity of various treated RAC was improved by 9.89 -22.55% at 56 days than RAC (UN).The ultrasonic pulse velocities of NAC and NCMC at 90 days are 4815m/s& 4398 m/s .The ultrasonic pulse velocities of RAC (UN), RAC (MS), RAC (H 2 SO 4 ) and RAC (HCl) at 90 days are 3312 m/s, 4244 m/s, 3917 m/s and 3664 m/s respectively.The ultrasonic pulse velocity of various treated RAC was improved by 9.60 -21.96 % at 90days than RAC (UN).The treated aggregate improves the velocity but not exceed the NAC and NCMC.The RAC (MS) gives better improvement than other treatment methods but all kinds of treated aggregate improves their velocity compared to RAC (UN).The pulse velocity of various mix are presented in table 4 and gure 15.The correlation coe cient of ultrasonic pulse velocity with different ages is shown in gure 16.The correlation coe cient of NAC, NCMC RAC (MS), RAC (H 2 SO 4 ) and RAC (HCl) was 0.6336, 0.6042, 0.6606, 0.6402, 0.717 and0.704 are shown in gure 16.The correlation coe cient value of RCA(UN) has very lower compared to other mixes.After treatment of recycled aggregate the coe cient value was enhanced and still inferior when compared to natural aggregate concrete.5.5 Correlations between compressive strength and Schmitt rebound numberThe relationship between compressive strength and Schmitt rebound number for various mixes in this study are shown in gure 17.The correlation coe cient between compressive strength and Schmitt rebound number for various coarse aggregate mixes such as NAC, NCMC, RAC (UN), RAC (H2SO4) and RAC (HCL) was 0.946, 0.911, 0.950, 0.943, 0.927 and 0.941are shown in gure 17.The different correlation coe cient of was observed for different mixes in this study and similar to Dilbas et al.Figure18 shows the combination of all different aggregate concrete and it was very useful to determine the prediction of results.The treated aggregate concrete shows better performance than the recycled aggregate concrete.A similar observation was found in Kanellopoulos et al., Dimitriou et al 2018, Al-Bayati et al 2016.Zhen Huaet al 2014.5.6 Correlation between compressive strength and ultrasonic pulse velocityThe relationship between compressive strength and ultrasonic pulse velocity for various mixes in this study are shown in gure 19.The correlation coe cient between compressive strength and ultrasonic pulse velocity for various coarse aggregate mixes such as NAC, NCMC, RAC (UN), RAC (H2SO4) and RAC (HCL) was 0.9845, 0.9778, 0.9905, 0.9838, 0.9767 and 0.9774 are shown in gure19.The different correlation coe cient of was observed for different mixes in this study and similar to Dilbas et al.Figure20shows that the combination of all different aggregate concrete and it was very useful to determine the prediction of results.The treated aggregate concrete shows better performance than the recycled aggregate concrete.The good correlations were observed from mechanical properties of concrete, especially between compressive strength and ultrasonic pulse velocity.A similar observation was found in Kanellopoulos et al., Dimitriou et al 2018, Al-Bayati et al 2016.Zhen Huaet al 2014.5.5.Impact Resistance testAccording to ACI committee 544.1R-82, concrete disc specimens were used to nd out the resistance of impact.The size of specimen is 152.4 mm diameter and 63.5mm thick were used.Figure21(a) shows instrumental setup images for impact test of controlled concrete specimen.Figure21 (b)shows the failed pattern of various mix specimens.Each result is noted as average of three specimen values.In this current study, NAC mix at 28 days, 19 blows for initial crack occurred on the specimen and at 23 blows nal failure occurred .In NCMC mix at 28 days, initial crack appeared at 17 blows and nal failure occurred at 19 blows.But in RCA (UN) mix at 28 days, initial crack appeared at 11 blows and nal failure occurred at 13 blows.Due to old attached mortar the aggregate surface had high porous so, bonding between old mortar and new cement paste get reduced.Similarly, for RCA (MS), RCA (H 2 SO 4 ) and RCA (HCl) at 28 days, the initial crack appeared at 15, 14 & 12 blows and nal failure occurred at 18, 16 &14 blows.This shows various treated aggregate enhances the impact resistance of concrete.Especially mechanical scrubbing treated aggregate improves better resistance compared to other chemical treatment.The Impact resistance of initial crack and nal failure of various mixes are shown in Figure