The main problem in using recycled concrete aggregate (RCA) as a construction material is due to the weak adhered mortar which usually has higher porosity and water absorption. It also has lower strength compared to natural aggregate (NA), and it often forms weak interfacial transition zones in the recycled aggregate concrete (RAC). These weak zones lead to negative effects on the mechanical properties and durability performance of RAC. In order to utilize RCA in more effectively as aggregate in concrete, it is necessary to improve the quality and enhance the properties of the attached weak mortar. This paper reviews different treatment methods of RCA based on the published research, and systematically analyses the strengths and weaknesses as well as the applicability and limitations of each method. The advantages and disadvantages of each treatment method, in terms of their technical feasibility, efficiency, economic and environmental impacts, are also discussed, in view of facilitating the selection of the most suitable treatment method for RCA. Although most techniques have been examined and trialed under laboratory conditions, further investigations are required to determine the most effective approach for treating RCA, with consideration not only given to the laboratory scale, but also on a commercial production scale.

Monitoring concrete properties at a very fresh state is essential to understand the different ongoing processes. Concrete undergoes strong displacements due to different processes such as, evaporation, water migration, settlement, formation of hydrates, shrinkage, early age cracking. This early state of concrete affects the long-term concrete performance. In the present paper the displacement distribution of fresh cementitious material from plastic state up to hardened state is studied by means of the optical and contactless method of DIC. The principle of DIC realizes a full-field 3D continuous monitoring of the surface displacement. An innovative technique of speckle pattern creation allows monitoring the surface displacement few minutes after casting of cement paste and mortar. The experimental results confirmed the effectiveness and correctness of the new technique giving a global overview much more representative than point measurements with traditional displacement meters.

A novel method of adding aluminum oxide to improve the efficiency of bio-remediation was evaluated. Aluminum oxide, at various amounts, was added to the medium to obtain a change in pH and urease activity. Urea and calcium salts with various amounts of aluminum oxide, were mixed with an absorbance-fixed bacterial suspension to analyze the effect of the method on production rates for calcium carbonate. Concrete specimens in which precracking was induced were subjected to bio-remediation with different amounts of added aluminum oxide. Adding aluminum oxide can decrease the pH of the environment, providing a more suitable micro environment and improving urease activity of bacteria. Moreover, the method can increase the adsorption of germs to increase the utilization rate of urea and production rate for calcium carbonate. After repairing, those with added aluminum oxide were better repaired and their strengths were higher. Therefore, the method can accelerate the bio-remediation reaction and reduce repairing time.