The growing urgency to make industry and commerce more sustainable and efficient has also extended to the construction sector. An example of this change has been seen in an increased interest in using recycled and repurposed waste for new construction applications.
To study: Influence of waste iron filings on warm mix performance. Image Credit: senia Soboleva/Shutterstock.com
A new paper presented in the Durability assessed an example of this growing trend – the use of recycled materials in the construction of asphalt concrete pavements.
Beyond their improved durability and relative environmental friendliness, the use of recycled materials for construction projects also offers notable financial savings in terms of raw material costs and waste disposal.
The article reports specifically on the use of iron filler waste – a common mechanical grinding waste – and its use as an alternative fine aggregate for warm mix asphalt used in city pavements around the world.
This particular application is particularly important for the sustainability of the construction industry and the built environment in general, as the construction of pavements consumes a large amount of natural resources; in particular bituminous concrete, which is estimated to be used in 95% of the roads and highways in the world. Aggregates – usually natural sand – typically make up nearly 95% of the total weight of asphalt concrete.
Overall ranking for wear layer. Image Credit: Wang, Y et al., Sustainability
Their widespread use has led to a severe depletion of the natural resources needed to manufacture asphalt concrete, which has led to the demand for alternative sources of raw materials, including recycled aggregates such as ceramics, crushed concrete and slag. steel.
Waste iron filings represent another viable option for recycled aggregate, offering high strength, excellent durability and a widely available supply from local factories and workshops.
To comprehensively assess the suitability of waste iron filings as aggregate in asphalt concrete, the authors prepared five mixes by replacing specific percentages of the aggregate in the mixes with waste iron filings: 0%, 25%, 50%, 75%, and 100%. These mixes were prepared in the same way as conventional concrete mixes.
With samples in place, each blend was put through a series of tests to establish its mechanical properties and resilience; for example, the Marshall test, resilience modulus tests, permanent deformation tests, flexural fatigue and moisture sensitivity.
Scanning electron microscopy has proven to be a useful tool in analyzing both the iron filings and the natural sand components of the warm mix, with images revealing distinct morphological characteristics and crystal structures that would likely impact on the toughness and wear resistance of the resulting asphalt.
SEM images from SNSF and IFW. (a) FNS, 0.5 kx, (b) IFW, 0.5 kx, (vs) FNS, 5 kx, (D) IFW, 5 KX. Image Credit: Wang, Y et al., Sustainability
Performance analysis was carried out using VESYS modeling software, allowing the analysis of example pavements laid from the sample mixes over time.
This analysis focused mainly on roadside ruliar performance – a problem that occurs in flexible pavements where higher loads result in a densification of asphalt and shear deformation.
The study showed promising results, revealing that the use of 25% to 50% of natural sand in lukewarm asphalt with iron filing waste increased its Marshall stability by 13.7% to 18.9%.
There was also a noticeable effect of the volumetric properties of the warm mix, its concentration of air voids, and the number of voids found in the mineral aggregate.
Interestingly, the study determined that the inclusion of waste iron filings resulted in a significant reduction in fatigue cracking, with the sample containing 50% waste iron filings resulting in a marked improvement in fatigue strength asphalt under repetitive loads and wet conditions – an ideal consideration for surfaces that are intended to see heavy foot and vehicular traffic.
In terms of the extraction performance of example sidewalks, modeling showed that concrete sidewalks using scrap iron deposits demonstrated a lower level of rut compared to the control mix, potentially delivering up to 10 years of service life.
Crack index for CM and IFW compounds. Image Credit: Wang, Y et al., Sustainability
The use of recycled materials in construction applications is expected to continue to grow. As more and more materials become viable options for inclusion in materials of construction, it will be important to strike a delicate balance between ensuring that these materials provide the performance and mechanical characteristics required while striving to use the most sustainable and environmentally friendly options available.
This study opened up the possibility of using locally sourced manufacturing waste for this purpose, demonstrating that not only was it a better alternative than sending this waste to landfills, but that the optimized inclusion of waste iron filings may actually improve the properties of warm mix. asphalt.
Wang, Yu, Roaa H. Latief, Hasan Al-Mosawe, Hussein K. Mohammad, Amjad Albayati, and Jonathan Haynes. 2021. “Influence of Iron Filing Waste on Warm Asphalt Performance” Sustainability 13, no. 24:13828. https://www.mdpi.com/2071-1050/13/24/13828