American Concrete Institute ACI Materials Journal May 2018
Can Concrete Containing High-Volume Recycled Concrete Aggregate Be Durable?
by
Seyedhamed Sadati and Kamal H. Khayat
Newswise — The use of recycled concrete aggregate (RCA) in new concrete production can minimize the environmental impact associated with the construction industry. This can also reduce the consumption of nonrenewable natural resources, and provide savings in overall costs of the project in some markets. However, the potentially marginal quality of the RCAs, stemming from the residual mortar phase of the particles (Fig. 1), and the availability of impurities and deleterious materials, can cause uncertainties in concrete durability.
In collaboration with the Missouri Department of Transportation (MoDOT), researchers at the Center for Infrastructure Engineering Studies (CIES) at Missouri University of Science and Technology focused on the development of concrete containing high-volume RCA for sustainable transportation infrastructure. The research aims at investigating the mechanical properties, volumetric stability, durability, and structural performance, as well as the determination of in-situ performance of pavement sections cast with such new generations of green concrete materials.
The overall objectives of the research include:
- Developing a fundamental understanding of the effect of RCA on concrete properties in fresh and hardened states
- Establishing and quantifying the correlations between engineering properties of the RCA materials and concrete performance
- Development of guidelines for selection of RCA sources for use in infrastructure construction
- Development of analytical methodologies and expert systems to estimate the variations in key mechanical properties of concrete given physical characteristics of RCA
- Field implementation and structural health monitoring of pavement sections made with high volume replacements of RCA
Recycled concrete aggregate materials obtained from various commercially recycled sources, along with laboratory produced RCA, were used to investigate concrete designated for transportation infrastructure. Test results highlighted the need for selective recycling to secure long-term durability. For example, it was observed that the use of RCA from residuals of air-entrained concrete can secure proper air-void system and, therefore, proper freezing-and-thawing resistance in the hardened state of RCA-made mixtures. As presented in Table 1, a reduction in spacing factor (L) from 0.0067 to 0.0028 in. (170 to 70 µm) was observed when 100 % RCA from air-entrained concrete with about 6%±1% percent air content was used. Also, the use of optimized binder systems in such a mixture reduced the sorptivity and the potential for reaching the critical saturation in a short time. Cost-effective methodologies, including the use of optimized binder compositions, proved to be effective for enhancing the durability of concrete made with high-volume (over 50 percent replacement) recycled aggregate.
Acknowledgement: The authors would like to acknowledge the financial support of the MoDOT as well as the RE-AST (Research on Concrete Applications for Sustainable Transportation) Tier-1 University Transportation Center (UTC) at Missouri S&T. The support provided by Mr. William Stone and Mr. Brett Trautman from MoDOT is highly appreciated.
Details of this research can be found in a paper entitled, “Can Concrete Containing High-Volume Recycled Aggregate Be Durable?” accepted and soon to be published in ACI Materials Journal.
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