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, miquel.joseph@kuleuven.be

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 luc.boehme@bwk.kuleuven.be tel. +32 50 40 59 45

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 9789090265759.

Current state of the art in Flanders

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

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.

Geometrical and physical properties of aggregates   d/D [mm] WA24h [%] ρa [kg/m³] ρrd ρssd FI Sand 0/4 0,64 2632 2588 2645 - Limestone 4/20 0,78 2693 2638 2658 17 RCAroad 8/20 2,96 2447 2519 6 RCAbuilding 4,97 2581 2288 2402 8

Aggregate Sieving Curves

Mixture 2: Normal Quality 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

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.

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

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

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

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

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

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.