Behavior of Normal Strength Reinforced Concrete Structures Incorporating Slag/Ceramic Binders

Abstract

Concrete incorporating ceramic hybrid binders is a sustainable material prepared by partial replacement of Portland cement with a proper dosage of ceramic powder and mineral admixtures or pozzolanic materials. This research was triggered by several objectives including the need to mitigate the negative environmental impact of the cement production process, as well as the need to recycle the waste of the ceramic industry. Portland cement production is currently leading to an exhaustion of natural resources, as more than 1.5 Tons of raw materials are needed to produce each Ton of Cement clinker. Furthermore, the cement production process is consuming large amounts of energy and has a significant environmental impact, since it is responsible for around 5 to 7% of the global carbon dioxide emissions. On the other hand, the ceramic industry, which produces tiles, bricks, and sanitary ware, generates 3 to 5% waste in the different production stages. Recycling ceramics waste in production plants is costing more than producing ceramics from raw materials, which makes the recycling process economically unfeasible and leads to dumping such materials in landfills and causing environmental pollution. For countries that lack proper waste management regulations, such as Lebanon, these amounts contribute to a major environmental dilemma. Recycling the ceramic waste material by integrating it in the concrete industry has been investigated in many research studies that were reported in the literature. It was found that the replacement of different percentages of Portland cement with ground ceramic powder decreased the mechanical strength properties of concrete. A recent research was conducted at the American University of Beirut to test if the negative impact of ceramic powder on concrete properties would be neutralized by the further addition of a pozzolanic material, such as slag.

Based on the previously mentioned study, the objective of this research is to extend the testing into a larger scale in order to evaluate the structural behavior of a sustainable concrete material, produced by replacing a suitable percentage of Portland cement with ceramic/slag binders. The proposed research program will be composed of two major phases: material acquisition and processing and experimental testing.

In the first phase, the required ceramic and slag materials were purchased. It is essential to understand the content of the obtained blended slag material, which is composed of 40% slag and 60% cement. Through five steps, the ceramic tiles were then processed in order to transform them into a ceramic powder. The critical part of the process is achieving a fineness that is comparable to that of the cement, in order for the replacement to be efficient and to minimize the expected reduction in strength due to replacing cement. After processing the ceramic material, the experimental testing took place. After preparing cylinders, molds and steel cages, 12 beams were tested to fail in flexure, shear and bond splitting modes. Four concrete mixes were tested, each composed of one beam for each mode of failure. With no replacements or additions, the first mix, with typical normal strength concrete, was used as the reference of the testing. In the second mix, 10% of the cement content was replaced by the ceramic powder in order to confirm the resultant reduction in strength due to the ceramic material. As for the third mix, 40% of the cement content was replaced with slag, with no ceramic content in the mix. The objective of this mix was to confirm that the slag material has the ability to enhance the strength of the concrete. In the final mix, 10% and 90% of the cement content were replaced with ceramic powder and blended slag cement, respectively. The final mix, which was composed of 10% ceramic, 36% slag and 54% cement, aimed to test if the slag material has the ability to at least neutralize the negative impact of the ceramic powder on the concrete strength. The mixes were evaluated based on ultimate load capacities, crack patterns and load deflection histories.

The results indicated that the hybrid mix was almost completely able to achieve the compressive strength of the control mix. As for ultimate loads, the flexure and shear beams of the hybrid mix did not only neutralize the negative impact of the ceramic powder, they were able to achieve an enhancement of 13% and 10%, respectively, when compared to the corresponding beams of the control mix.