Concrete material is currently the global preference for structural construction owing to its ease of manufacturing and durability, especially for large-scale infrastructure such as bridges which need their lifetimes in excess of a century under the sustainable design. How to ensure the quality of concrete and make the structure durable enough has become a hot and tricky problem. Concrete consists of a mixture of cement, water, minerals and chemicals in a proportion that results in improved mechanical properties. The significant difference in performance of concrete is mainly due to the ratio of its components, and the performance should be highly customizable depending on the specific application for the modern high performance concrete(HPC). Presently, different concrete mixture design methods have been developed to enhance the quality of concrete. These methods include experimental, analytical, numerical and statistical methods.
Unfortunately, several drawbacks have been encountered in the development of a universal mix design method for concrete materials. This is majorly attributed to the variation of material properties from different geographical sources, thus, a particular mixture plan obtained in one place cannot be applied in other places. This has become a major obstacle to develop the standardized methods for concrete preparation. Recently, researchers have identified packing density theory as a promising solution to developing a universal concrete design method. Generally, it decreases the void contents and thus has numerous advantages such as improved mechanical properties, reduction in permeability and reduced environmental pollution.
The packing density theory is divided into continual packing and discrete packing considering the significance of continuous gradation of aggregate in obtaining a higher packing density. However, the lack of continuous gradation in most cases resulted in the development of the discrete packing theory consisting of several discrete particles classes for further improvements. Presently, the prediction model of maximum packing density for several particle classes have attracted the attention of many researchers. Unfortunately, most of these models take into consideration the structure and interaction effects in investigating the particles mechanisms which are inadequate for providing the desired results.
In a recent research published in the research journal, Construction and Building Materials, Mr. Sun Yong(Ph.D. Candidate), Professor Wang Zonglin, Dr. Gao Qingfei and Mr. Liu Chenguang (Ph.D. Candidate) at Harbin Institute of Technology developed a mixture design method based on packing density theory consisting of the 4-parameter compressible packing model. They optimized high-performance concrete mix design for bridge construction. And proposed a novel but easy to operate and low cost experimental method and iterative algorithm to obtain the important parameter value in the theoretical model describing the degree of particle irregularity. Eventually, the mechanical properties, workability and durability of the proposed method were validated through different tests such as freeze-thaw resistance, shrinkage and compressive strength tests.
From the experimental results, the authors observed that the developed mix method resulted in concrete with high compactness and improved mechanical properties. Consequently, the key correlating parameters included aggregate volume, water binder ratio, rock strength and paste volume. For example, the concrete compressive strength was largely affected by the changes in the aggregate volume while the workability was highly affected by the changes in the paste thickness wrapped on coarse aggregate. Furthermore, the available different aggregate gradations enabled evaluation of the amount of paste used.
The study emphasizes the choice of different aggregate from various sources with different properties, which showed the potential to become a universal method for concrete design. And this is considered as a key scientific article contributing to excellence in science and engineering research. This results in enhanced accuracy and workability control. The study will thus be adopted in subsequent tests on material composition variability to further enhance its reliability. Therefore, this method is suitable for optimizing composition for high- performance concrete materials for different applications.
Sun, Y., Wang, Z., Gao, Q., & Liu, C. (2018). A new mixture design methodology based on the Packing Density Theory for high performance concrete in bridge engineering. Construction and Building Materials, 182, 80-93.Go To Construction and Building Materials