Page 9 - Open-Access-Sep-2019

6.00
2%
3%
3%
5.00
5.00
5.00
Tensile strength (Mpa)
4.00
4.00
13%
4.00
3.00
Concrete
2.00
3.00
Bricks
3.00
28d
28d
1.00
Asphalt
28d
56d
2.00
56d
0.00
2.00
Tiles
56d
91d
91d
Others
1.00
79%
1.00
0.00
0.00
Control 50RCA 50RCA50FA50RCA50Slag 7d Tensile strength (Mpa) 6.00 7d Tensile strength (Mpa) 6.00 Control 50RCA 50RCA2NS 50RCA10UFFA 7d
Mix types Mix types
Mix types
TECHNICAL PAPER
recycled aggregate concretes containing 50% slag and 50%
70 fly ash with better improvement in concrete containing slag
6.00
Compressive strength (Mpa)
2% 70
3% than that containing fly ash. All SF contents show significant 70 450
60
6.00
Tensile strength (Mpa)
3% 5.00 improvement in compressive strength at all ages of recycled 6.00 400
60
60
5.00
50
50
50
4.00
40
40
13% 4.00 aggregates concrete containing 50% slag except at SF content Compressive strength (Mpa) 5.00 350
300
4.00
of 15%. Among all SF contents the 10% SF show the highest
3.00
40
7d
30
Concrete 7d 2.00 7d 7d 30 250
7d
20
28d
Bricks Tensile strength (Mpa) Compressive strength (Mpa) 3.00 28d improvement about 40% increase in 7 days compressive 28d Tensile strength (Mpa) 3.00 7d CO2 emission (Kg CO2e)
20
28d
30
1.00
28d
Asphalt 56d strength and about 10-16% improvement in compressive 56d 10 28d 200
10
56d
0.00
Tiles 2.00 strength at other ages. However, much lower improvement is 56d 2.00 56d 150
20
91d
56d
0
0
91d
Others 91d 91d
79% 1.00 observed in the recycled aggregates concrete containing 50% 1.00 100
10
fly ash, where about 5% improvement in 7 days compressive 50
0.00 0 strength and about 18-37% improvement in other ages are 0.00 Control 50RCA 50RCA2NS 50RCA10UFFA 0
Controll 50RCA 50RCA50FA50RCA50Slag observed at SF content of 5%. At other SF contents the Mix types Control 50 RCA 50 RCA+50 Slag 50 RCA+50 Fly ash
50RCA
Contro
50RCA50FA50RCA50Slag
Mix types
Mix types
Mix types
Mix types
Mix types Types of mixes
improvements in compressive strength is much lower than the
5% SF content. The higher compressive strength of recycled
(a)
aggregate concretes containing 50% slag and SF than those
500
6.00 containing 50% fly ash and SF can be attributed to the presence
3% 2% 70 450
6.00
450
3% of much higher CaO than fly ash, which helped to form
5.00 70 400 70 450
Compressive strength (Mpa)
60 60 5.00 additional hydration products e.g. Calcium Silicate Hydrate
400
5.00
350
CO2 emission (Kg CO2e)
60
Tensile strength (Mpa)
350
4.00
13% 50 Tensile strength (Mpa) 50 4.00 (C-S-H) gels and Ca(OH) 2. The presence of amorphous SF also 400
300
50
3.00
4.00
250
Concrete 7d CO2 emission (Kg CO2e) 6.00 7d reacted with Ca(OH) 2 to form additional C-S-H gels which filled 350
40
300
40
2.00
3.00
Bricks Tensile strength (Mpa) 40 3.00 7d 28d Compressive strength (Mpa) 30 200 the pores in the matrix and micro cracks in the RCA. 7d 300
250
30
7d
Asphalt Compressive strength (Mpa) 28d 20 1.00 28d 7d 28d CO2 emission (Kg CO2e) 250
150
28d
2.00
Tiles 30 2.00 56d 0.00 56d 20 200 28d 200
100
56d
56d
91d
10
Others 56d 10 91d The effects of NS and UFFA on the compressive strength of
150
1.00
1.00
79% 20 91d 0 50 0 91d recycled aggregates concretes are shown in Figure 4c. It can 56d 150
0
100
10
0.00
50
50
50
50
50
50
50
50
50
50
0.00 RCA RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 be seen that the addition of 2% NS improved the compressive 100
50RCA
50RCA2NS 50RCA10UFFA
Control
Control 50RCA 50RCA50FA50RCA50Slag Slag Slag+5 SF Slag+10 Slag+15 Fly ash Fly ash+5 Fly ash Fly ash strength of recycled aggregates concretes by 20-22% compared 50
0 Mix types +15 SF 0 Mix types
50 RCA
Mix types SF SF SF +10 SF to marginal improvement of about 1-6% due to addition of 10% 0
Control
50 RCA+2 NS
Control 50RCA 50RCA50FA50RCA50Slag Mix types Mix types Control 50 RCA 50 RCA+50 Slag 50 RCA+50 Fly ash
Types of mixes
Types of mixes
Mix types UFFA. The significantly higher improvement in compressive Types of mixes
strength by small amount of NS is attributed to their nano size
(b)
particles and extremely high surface area, which accelerated
the pozzolanic reaction in the concrete and formed secondary
70 500 C-S-H and filling of nano- and micro-size pores in the matrix
450
450
60 70 70 in the recycled aggregates concrete. Similar results are also
450
60
60
400
400
Compressive strength (Mpa) 40 7d CO2 emission (Kg CO2e) Compressive strength (Mpa) 40 7d CO2 emission (Kg CO2e) Compressive strength (Mpa) 40 7d aggregate concrete. The particle packing of unreacted SCMs,
observed by the author and others in the case of natural
CO2 emission (Kg CO2e)
50
400
50
50
350
350
350
300
300
nano silica and ultrafine fly ash particles to fill the micro- and
30
30
250
300
250
nano-size pores in matrix and interfacial transition zone is also
28d
20
20
28d
30
200
250
28d
200
56d
10
contributed to the improved compressive strength observed in
10
150
56d
200
91d
20
150
0
100
0
91d
50
100
10
100
0 150 56d the above concretes.
50
0 50 50 50 50 50 50 50 50 50 50 6. tEnSilE StrEngtH
RCA RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 0
Control 50RCA 50RCA50FA50RCA50Slag Slag Slag+5 SF Slag+10 Slag+15 Fly ash Fly ash+5 Fly ash Fly ash 0 Mix types Control 50 RCA 50 RCA+50 Slag 50 RCA+50 Fly ash
Mix types
SF SF SF +10 SF +15 SF The tensile behaviour of recycled aggregate concretes due to
Mix types Control 50 RCA 50 RCA+2 NS Types of mixes
Types of mixes Types of mixes addition of various SCMs and nano silica and ultrafine fly ash
(c)
are very similar to that observed in compression. It can be seen
Figure 4: Compressive strength development of concretes. in Figure 5a that the tensile strength of recycled aggregate
500 concrete is decreased by about 36-49% due to addition of 50%
450 450 The effects of addition of 5, 10 and 15% SF as partial fly ash with highest reduction of 49% at 7 days. However, in
CO2 emission (Kg CO2e) 350 CO2 emission (Kg CO2e) 350 aggregate concretes containing 50% fly ash and 50% slag at 7 days is significantly lowered to about 25% with about 7%
400
the case of 50% slag addition this reduction in tensile strength
replacement of cement on compressive strength of recycled
400
300
increase in tensile strength at 91 days. The trends are consistent
are shown in Figure 4b. It can be seen that the addition of
250
300
with those of compressive strength.
SF improved the compressive strengths at all ages of both
200
250
150
100
150
50 200 60 The IndIan ConCreTe Journal | SepTember 2019
0 100
50 50 50 50 50 50 50 50 50 50
RCA RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50
Slag Slag+5 SF Slag+10 Slag+15 Fly ash Fly ash+5 Fly ash Fly ash 0
SF SF SF +10 SF +15 SF
Control 50 RCA 50 RCA+2 NS
Types of mixes
Types of mixes