This is a presentation by Dr. Asregedew Woldesenbet of Bahir Dar University on the 3rd Annual East Africa Cement, Concrete and Energy Summit.

1. Mitiku Damtie, MSc., P.E.
&
Asregedew K. Woldesenbet, Ph.D., P.E.
3rd Annual East African Cement
Concrete & energy Summit
August 1, 2018
Recycled Concrete Aggregate
(RCA)

2. Introduction
• Concrete is the dominant and primary material in construction
• Increasing demand of concrete requires large amount of VA
• Limited methods of Construction & increased wastage
• Huge amount of con
2

3. Background
• Increased cost of
materials
• 1 bag (50 kg) of OPC
Cement cost ETB 170
($12.5) - 580% increase
from ETB 25 ($1) in
2006
• 1 m3 aggregate (size
02) cost ETB 540
($19) - 800% increase
from ETB 60 ($2.5) in
2006 3
0
100
200
300
400
500
600
2015 2016 2017 2018
Gravel Price

4. Objective
• Determine properties of RCA and influence on fresh &
hardened concrete
• Identify the economic feasibility of RAC and reasonable
percentage use in saving cost and use for construction
4

5. Prior Studies
5
Property Findings Study
Bulk Density Lower than VA
Gonzalez, F.B. and
Martinez, A.F. (2008)
Water absorption 2-10% greater than VA Hiller et al. (2011)
Specific gravity Lower than VA Anderson et al. (2009)
Workability of
concrete
Lower workability with the same
W/C
Poon, C.S. and Chan, D.
(2008)
Strength of concrete Lower strength than CC UCHE (2008)
Replacement(%) 10-30% by weight of VA Hiller et al. (2011)

6. Experimental Procedure
6
Sample Preparation Cement- CEM I 42.5 R
RCA- Sample tested Cube
VA- Basaltic
Material Testing Gradation, bulk density, specific gravity, water absorption , LAA
Mix design ACI 211.1
Concrete Casting 150*150mm cube mold
Concrete testing Tested at ages of 3, 7, 14 & 28 days
Data Analysis ANOVA and Tukey Post Hock Analysis - SPSS version 16.0

7. Concrete Mixes
Mix % 0f RCA
W/C
No of Cubes at Different Days
Total
3 7 14 28
C1 0 0.48 3 3 3 3 12
RAC-W2
25 0.52 3 3 3 3 12
50 0.52 3 3 3 3 12
100
0.48 3 3 3 3 12
0.52 3 3 3 3 12
RAC-A3
25 0.48 3 3 3 3 12
50 0.48 3 3 3 3 12
100
0.35 3 3 3 3 12
0.48 3 3 3 3 12
Sum 108 7

8. Mix
% 0f
RCA
W/C
Weight of Materials (Kg/m3)
Aggregate
Sand Cement Water Admixture
Virgin RCA
C 0 0.48 1136.45 ------ 811.10 360.00 211.31 -------------
RAC-W
25 0.52 852.34 265.23 815.17 360.00 211.34 -------------
50 0.52 568.23 530.45 819.24 360.00 211.37 -------------
100
0.48 ------ 1060.90 849.08 360.00 206.46 -------------
0.52 ------ 1060.90 827.38 360.00 211.43 -------------
RAC-A
25 0.48 852.34 265.23 818.10 360.00 210.10 10.80
50 0.48 568.23 530.45 825.09 360.00 208.89 10.80
100
0.35 ------ 1036.00 977.22 360.00 126.00 10.80
0.48 ------ 1060.90 839.08 360.00 206.46 10.80 8
Mix Proportion

9. Results & Discussion
No Property RCA Natural
1 Bulk Specific Gravity 2.65 2.8
2 Water Absorption (%) 3.54 1.89
3 Bulk density (kg/m3) 1510 1653
4 Moisture content (%) 2.34 0.22
5 Loss Angeles Abrasion (%) 15 35
9

10. Results & Discussion
10
Mix % of RCA W/C Slump(mm)
C 0 0.49 25
RAC-W
25 0.52 45
50 0.52 34
100
0.49 0
0.52 20
RAC-A
25 0.49 50
50 0.49 40.5
100
0.36 0
0.49 35

11. Results & Discussion
11
0
5
10
15
20
25
30
35
RCA-W 0% RCA-A 25% RCA-A 50% RCA-A 100%
3 Day
7 day
14 DAY
28 day

12. Results & Discussion
0
500
1000
1500
2000
2500
3000
CC RCA-W 25% RCA-W 50% RCA-W 100% RCA-A100% RCA-A 50% RCA-A25%
Cost of Concrete (ETB)
12

13. Findings & Conclusion
13
• Quality tests on RCA are satisfactory
• For normal strength concrete, sample tested RCA can replace 50% VA
• An increase amount of RCA
• The workability of RAC decreases
• Strength of RAC decreases
• Cost Analysis
• RAC –W is cheaper than CC, while RAC-A mixes are costly than CC

14. Recommendation
14
• Design engineers, practitioners & research facilities should
thoroughly study RCA
• Incorporate it in mix design and standards
• Government should advocate RCA through
• Setting of policy & standards for reuse/recycling materials
• Implementation in public projects
• Use of RCA provides economic advantage through conservation of
VA and reduction of landfills

15. 15