1. Frost resistance of recycled concrete
JOSEPH Miquel
BOEHME Luc, BROUCKE Ramses, FALIN, VANDEWALLE Lucie
KU Leuven – Faculty of Engineering Technology – Department of Civil Engineering, Ostend, Belgium,

2. Recycon RecyCon Mission: Sustainable building
- Recycling of Construction and Demolition Waste in Construction
Mission: Sustainable building
- Durable materials
- Energy efficiency
- Reuse of materials after “End of life”
Approach: Industrial Engineering
- focus: economic value, solutions for existing problems and industrial opportunities
- less: fundamental research
Technologiecluster Bouw
Technologiecampus Oostende
Zeedijk 101
8400 Oostende
tel

3. Introduction
Demolition
Crushing plant
Recycled aggregates
Concrete plant
Concrete
In 2012, more than 11 Mt of rubble were processed as recycled aggregates.
Currently, most recycled aggregates are used in low-grade applications such as road foundations and lean concretes.
However, research has shown that recycled debris can replace coarse natural aggregates in several concrete high-end applications
"ValReCon20: Valorisation of
recycled concrete aggregates
in concrete C20/25 and C25/30",
Oostende: Boehme Luc, 2012.
ISBN

4. Current state of the art in Flanders

5. High-end applications
Foundation
Sub foundation …
Road construction
Structural concrete ….
Precast concrete
Architectural concrete
SCC
HPC
Materials for cement ?

6. Abstract
Literature often concludes that the lower mechanical properties of recycled concrete, compared to standard concrete, is unfavourable for the durability in aggressive environments. One of these aggressive environments is frost. Belgium, with a temperate maritime climate, is a country that experiences many annual frost/thaw-cycles. Before recycled concrete can be used in outside environments, more experimental research is needed. This investigation was set up to determine the resistance of concrete made with coarse recycled concrete aggregates (0-40%), against these frost/thaw-cycles. In this research recycled concrete aggregates originating from mixed demolition containing mainly limestone aggregates and aggregates from road demolition, containing porphyry were used. A second parameter of this research was the influence of different concentrations of air entrainer. In total three reference concrete mixture and twelve different recycled concrete mixtures were made. All fifteen concretes mixtures were exposed to frost-thaw cycles in a 3% NaCl solution. Beside the frost/thaw resistance tests, the hardened density, dynamic modus of elasticity and compressive strength were tested before and after 30 frost-thaw cycles.

7. Geometrical and physical properties of aggregates

8. Aggregate Sieving Curves

9. Mixture 2: Normal Quality
Concrete mixtures
Series
[-]
Reference
Mixture 1: High Quality  
Mixture 2: Normal Quality  
Replacement
[%] 20 40
var
Cement
[kg/m³]
340
cte
w/c
0,45
Limestone
1268
976
703
906
613
RCAroad
207
398 -
RCAbuilding
167
334
Sand
645
692
739
792
779
Plasticizer 1
Air entrainer
0,44
0,88

10. Production of the test specimen
Mixing process was always the same
A two step mixing process was used
Water absorption of the aggregates was compensated
Test specimen were kept in a humidity chamber the first 28days of hardening.

11. Air content high and normal quality recycled concrete
High Quality
Normal Quality

12. Dry density of high and normal quality recycled concrete before and after frost-thaw cycles
High Quality
Normal Quality

13. Compressive Strength of high and normal quality recycled concrete before and after frost-thaw cycles
High Quality
Normal Quality

14. Modus of Elasticity of high and normal quality recycled concrete before and after frost-thaw cycles
High Quality
Normal Quality

15. Evolution of the loss of material of high and normal quality recycled concrete during frost-thaw cycles
High Quality
Normal Quality

16. Conclusions
Although recycled concrete aggregates lead to an increase in porosity of recycled concrete, compared to normal concrete using only natural aggregates, this does not automatically lead to a reduction of the resistance of recycled concrete against frost-thaw damage. On the contrary, in some cases the uses of recycled concrete aggregates can increase this resistance.
It is proven that the density and the amount of entrapped air is increased by adding normal quality recycled aggregates instead of high quality recycled aggregates.
Compressive strength and dynamic modus of elasticity are also influenced by changing the quality of the aggregates and the addition of air entrainer. On the other hand the influence of the frost-thaw cycles on these two parameters is less significant.
An important parameter when looking at the frost-thaw resistance of concrete is the scaling of concrete. According to the standards this needs to be less than 1,4kg/m². While all mixtures containing high quality recycled concrete aggregates succeeded this test, some containing normal quality aggregates did not.
After these tests we can conclude that the use of high quality recycled concrete aggregates could be beneficial to frost-thaw resistance, especially in combination with air entrainer. On the other hand, using normal of lower quality recycled concrete aggregates could give the opposite result.