By Nidhi DhullReviewed by Susha Cheriyedath, M.Sc.Jun 24 2024A recent article published in the Beni-Seuf University Journal of Basic and Applied Sciences demonstrated the usability of industrial waste in green brick production. It specifically focused on ground granulated blast-furnace steel slag (GGBS) activated by cement kiln dust (CKD) and quicklime (QL).
Study: Producing Green Bricks Using Industrial Waste. Image Credit: Rene Notenbomer/Shutterstock.com
Background
The global production of Cement Kiln Dust (CKD), a by-product of the cement industry, is projected to exceed 220 million tons by 2030. CKD's fine particle size, cementitious properties, and high alkalinity, when combined with water, make it suitable for applications like soil stabilization. Similarly, long-term uses of industrial by-products such as Ground Granulated Blast Furnace Slag (GGBS) are being explored for soil stabilization, land restoration, and cement manufacturing. However, GGBS requires chemical modification with an alkaline activator due to its low hydration level.
Environmental and economic concerns have led countries like China to ban the use of solid-fired clay bricks. Consequently, industrial by-products are now employed as cementitious raw materials to produce stabilized, eco-friendly bricks without burning or steaming. This study aims to identify a practical and sustainable solution for managing industrial wastes by incorporating CKD and QL-activated GGBS into clay-based mixes for manufacturing stabilized green bricks.
By leveraging these materials, we can address waste management issues while creating environmentally friendly building materials.
Methods
Raw Materials: The raw materials used in this study included:
- Kafr Homied Clay (KHC): Sourced from a clay quarry in Egypt.
- Ordinary Portland Cement (OPC) and Quick Lime (QL): Commercially procured.
- Ground Granulated Blast Furnace Slag (GGBS): Obtained from a steel industry.
Mix Preparation: Five clay mixes were prepared with varying replacement ratios (5-10 wt.%) of CKD and QL, along with a control mix without CKD and QL. OPC (5 wt.%) was added to accelerate the initial setting time, and sand was included to enhance the durability of the final product.
Sample Preparation: Compacted cylinders with a diameter of 20 mm and a height of 40 mm were prepared using a conventional manual compaction apparatus. Laboratory tests were conducted on these specimens after curing periods of 7, 14, 28, and 60 days.
Analytical Methods: The raw materials and cylindrical specimens were subjected to the following analyses:
- Particle Size Analysis: To determine the distribution of particle sizes in the raw materials and mixes.
- Differential Thermal Analysis (DTA): To monitor the mineralogical and hydration products of the prepared mixes at different curing ages.
- X-ray Fluorescence (XRF) and X-ray Diffraction (XRD): To analyze the composition and crystalline structure of the materials.
- pH Measurement: Conducted at 20 ºC using a digital pH meter to assess the alkalinity of the specimens.
Physical and Mechanical Properties: The cured specimens were examined for:
- Water Absorption
- Bulk Density
- Compressive Strength
These properties were assessed according to standard specifications. Additionally, the durability of the specimens was tested against collapsibility in water by submerging them for seven days
Results and Discussion
The experimental results demonstrated the behavior of green-brick mixes with varying quantities of QL and CKD. The mixes exhibited an enhanced pH value (up to 12.5) with the addition of CKD, indicating high OH− ion activity. Conversely, the hydration products increased more significantly with the addition of QL rather than CKD as curing time increased.
A small endothermic peak was detected in the thermographs of the mix comprising 10 wt.% QL at approximately 470 °C, attributed to the formation of portlandite, resulting in lower specimen strength compared to the mix with 5 wt.% QL. Additionally, the DTA curves for these two mixes showed a small endothermic peak at about 700 °C, associated with the de-carbonation of calcium carbonate.
Distinct exothermic peaks were observed at around 800 °C in all mixes, including the control mix, indicating the devitrification effect of GGBS. Notably, the intensity of the endothermal and exothermal peaks in the control mix was the lowest compared to the other mixes.
All cylindrical specimens cured for seven days exhibited shape distortion or disintegration to varying degrees in water, making it impossible to quantify water absorption. This was explained by the insufficient hydration binding products at this early stage, which developed more fully from day 14 onwards.
As evidenced in the XRD patterns, all specimens exhibited reduced water absorption as curing time increased. Overall, the mixes containing QL or CKD cured for 14 days or more demonstrated good physical and mechanical properties. Among all, the mix comprising 5 wt.% QL demonstrated the superior properties.
Conclusion
This study demonstrated that adding QL and CKD to the stabilized green brick mixes can enhance their engineering properties with increasing curing age. The ratio of QL and CKD used significantly affected the properties of the specimens. For instance, 20% GGBS and 5% QL increased the specimen’s compressive strength while reducing water absorption.
Alternatively, when GGBS and CKD were combined, a higher content of CKD 10 wt.% gave better results than 5 wt.% CKD. Overall, the physical and mechanical properties of all specimens comprising CKD or QL met the acceptable limits of dry compressive strength (30-70 kg/cm2), water absorption (8-15%), and density (1.7-2 gm/cm3), as specified by the Egyptian building standards. Thus, the proposed stabilized green bricks incorporating waste materials provide a sustainable and eco-friendly alternative to traditional masonry bricks.
Journal Reference
El-Mahllawy, M. S. & Mohsen, S. A. (2024). Characterization and utilization capabilities of industrial wastes for green bricks production. Beni-Seuf University Journal of Basic and Applied Sciences, 13(57). https://doi.org/10.1186/s43088-024-00517-6, https://link.springer.com/article/10.1186/s43088-024-00517-6
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