At present, the global output of construction waste, particularly waste concrete, has reached alarming levels. For instance, the annual output of China’s construction and demolition waste is a staggering 1.8 billion metric tonnes, while the recycling rate is less than 10%. The consequent of this huge disparity is widespread environmental degradation coupled with immense strain on natural resources. Therefore, in view of global sustainable development, there is an increasing tendency toward the use of waste materials. Case and point, recycled aggregate concrete (RAC), that has been extensively studied for many years.
Conventionally, recycled aggregate (RA) is produced with crushed concrete, and the ordinary RAC is generally prepared with natural aggregate (NA) replaced by partial or total RA. However, RA has a layer of porous adhered mortar, a detrimental factor that inhibits its application in concrete, as it degrades compressive strength, splitting and flexural tensile, modulus of elasticity and frost resistance, and leads to the increase of chloride penetration, drying shrinkage and creep. Therefore, to enhance the practical applicability of RAC, it is imperative that a better environmentally and economically acceptable technique for preparing RAC should be devised.
Recently, Wuhan University of Technology scientists led by Professor Weiguo Shen conducted study where they revealed the influence of scattering-filling coarse aggregate (SFCA) process on the mechanical and durability properties of RAC. Specifically, they focused on applying the RA as SFCA to prepare RAC, hoping that their endeavor would result in increased coarse aggregate volume fraction in the concrete thus improving its properties. Their work is currently published in the research journal, Cement and Concrete Composites.
The researchers considered the SFCA process to prepare RAC with promoted performance. With reference of conventional concrete and the scattering-filling natural aggregate (SFNA) concrete, the influences of ratio, type, size and moisture state of RA on mechanical and durable properties of scattering-filling recycled aggregate (SFRA) concrete were investigated.
The authors observed that SFCA process had improved compressive strength, elastic modulus, and reduce the drying shrinkage and chloride penetration of RAC. In addition, they noted that the SFCA process improved the properties of the resultant concrete by increasing the homogeneity of aggregate distribution, and improving interfacial transition zone between the aggregate and cement paste in RAC. This was proved using image processing analysis and microhardness.
In summary, the study by Professor Weiguo Shen and colleagues demonstrated an efficient approach (SFCA) to prepare RAC so as to overcome the deficiencies of RA, i.e. high porosity and high-water absorption, that were responsible for detrimental shortcomings relating to the properties of convectional RAC. Altogether, SFCA process provides an economic method to produce high-quality recycled aggregate concrete and an efficiently approach to the utilization of recycled concrete aggregate from Construction and Demolition waste.
Gelong Xu, Weiguo Shen, Bingliu Zhang, Yongxin Li, Xiaoli Ji, Yongxin Ye. Properties of recycled aggregate concrete prepared with scattering-filling coarse aggregate process. Cement and Concrete Composites, volume 93 (2018) page 19–29.Go To Cement and Concrete Composites, volume 93 (2018)