Warm Mix Asphalts (WMAs) are asphalt concretes produced at lower temperatures than traditional Hot Mix Asphalts (HMAs). Nonetheless, the above is not enough to diminish the environmental impacts associated with the road infrastructure industry. Accordingly, incorporating Recycled Concrete Aggregate (RCA) as a partial replacement for Natural Aggregates (NAs) in WMA design has been gaining notoriety in the literature as a viable alternative to increase sustainability. However, the eco-friendly manufacturing of WMA with RCA contents (WMA-RCA) is not easy to obtain satisfactorily because the RCA causes alterations in the mix design. Thus, this research proposes three (3) methods to determine the optimal design conditions (coarse RCA content) that minimize the environmental burdens caused by WMA-RCA production. The first method is a mathematical model based on Multiple Linear Regression (MLR), which is used as a benchmark for the other two methods. The second and third methods are computational models based on Artificial Intelligence (AI), i.e., Artificial Neural Networks (ANNs) and Genetic Algorithms (GAs), respectively. Notably, the Life Cycle Assessment (LCA) was employed as the theoretical framework to support all the proposed models. Consequently, this study concludes that: (i) all the proposed methodological alternatives achieve results with a great accuracy; (ii) the GAs model is the most precise method in terms of error minimization; (iii) the MLR model is the fastest method in terms of execution time; and (iv) the ANNs model is the method that requires the longest time of running, and its exactness is at a midpoint concerning the other models. 

Environmental optimization of warm mix asphalt (WMA) design with recycled concrete aggregates (RCA) inclusion through artificial intelligence (AI) techniques

Graphene is a carbon-based nanomaterial used in various industries to improve the performance of hundreds of materials. For instance, graphene-like materials have been employed as asphalt binder modifying agents in pavement engineering. In the literature, it has been reported that (in comparison to an unmodified binder) the Graphene Modified Asphalt Binders (GMABs) exhibit an enhanced performance grade, a lower thermal susceptibility, a higher fatigue life, and a decreased accumulation of permanent deformations. Nonetheless, although GMABs stand out significantly from traditional alternatives, there is still no consensus on their behavior regarding chemical, rheological, microstructural, morphological, thermogravimetric, and surface topography properties. Therefore, this research conducted a literature review on the properties and advanced characterization techniques of GMABs. Thus, the laboratory protocols covered by this manuscript are atomic force microscopy, differential scanning calorimetry, dynamic shear rheometer, elemental analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. Consequently, the main contribution of this investigation to the state-of-the-art is the identification of the prominent trends and gaps in the current state of knowledge.

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Properties and Characterization Techniques of Graphene Modified Asphalt Binders

Effect of utilizing peanut husk ash on the properties of ultra-high strength concrete

The present paper investigates the effects of simultaneous mechanical foaming using water and fluxing with a bio-derived agent on the properties of three distinct asphalt binders: 50/70 paving-grade bitumen, 45/80–55 polymer-modified bitumen, and 45/80–80 highly modified asphalt binder. The testing involved classical tests for assessing binder consistency (penetration at 25 °C, ring and ball softening point, Fraass breaking point, and dynamic viscosity) as well as performance tests (high and low Superpave critical temperatures and multiple stress creep recovery). The tests included assessment directly after asphalt binder foaming and were repeated after a 14-day period. It was shown that bitumen foaming had only short-term effects on the asphalt binders, which did not persist in the repeated tests after 14 days. The fluxing agent that was utilized caused significant changes in the consistency of all asphalt binders. The changes in the performance characteristics of the 50/70 and 45/80–55 binders were severe and amounted to a significant decrease in high-temperature performance of these binders. On the other hand, an improvement in all performance characteristics in the case of the 45/80–80 asphalt binder was observed as a result of the applied processes, particularly when measured 14 days after foaming. This study shows that the simultaneous use of foaming and the fluxing additive decreased the dynamic viscosity of the 45/80–80 binder, while improving its properties relating the pavement performance.

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Warm Mix Asphalt Binder Utilizing Water Foaming and Fluxing Using Bio-Derived Agent

Impact of microporous γ-Al2O3 on the thermal stability of pre-cast cementitious composite containing glass waste

Crumb rubber (CR) is one of the materials most widely used in the road infrastructure industry due to its mechanical and environmental benefits as an asphalt binder modifier. Nonetheless, CR decreases the workability of mixes by increasing the viscosity of the binder, leading to an increase in the production temperatures of asphalt mixes. However, warm mix technologies can reduce the temperature demand associated with these processes. The preceding explains the growing interest in producing rubberised asphalt binders incorporating warm mix asphalt (WMA) additives. In this research, the mechanical and rheological properties of a 60/70 penetration grade asphalt binder modified with CR (at a dosage of 15, 18 and 21% by the wet process) and WMA chemical additives (Evotherm M1 and Iterlow T) were investigated. Laboratory tests included penetration, softening point, rotational viscosity, frequency sweep through dynamic shear rheometer (DSR), and multiple stress creep recovery (MSCR) tests. The results indicate that CR increases the stiffness of the asphalt binder, which is reflected in a lower penetration grade and improved softening point. It also improves its rutting resistance but decreases fatigue performance. Furthermore, it has been shown that under the conditions studied, the higher the CR content, the more elevated the degree of stiffness and performance of the asphalt binder. On the other hand, WMA technology decreases asphalt stiffness and performance at high temperatures.

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Rheological Behaviour of WMA-Modified Asphalt Binders with Crumb Rubber

Regarding the traditional Hot Mix Asphalt (HMA), Warm Mix Asphalt (WMA) with Recycled Concrete Aggregate (RCA) contents (WMA-RCA) requires lower production temperatures and diminishes the consumption of natural aggregates (NAs). Nonetheless, these environmental benefits may be counteracted by the higher optimal asphalt binder demanded by the WMA-RCAs. In this regard, this research develops a computational model to optimize the WMA-RCA design. In order to build a sufficiently accurate and adaptable model, it was decided to employ Artificial Neural Networks (ANNs). The ANN implementation was based on the postulates of the statistical learning theory, i.e., preferring to generate learning through low-complexity models. Also, a representative case study of the northern region of Colombia was assessed. In this scenario, the optimal coarse RCA content was 10%, and the sustainability savings were maintained up to an RCA's hauling distance of 200 km. 

Elvis Covilla-Valera

Papers

Rheological Behaviour of WMA-Modified Asphalt Binders with Crumb Rubber

Neural networks implementation for the environmental optimisation of the recycled concrete aggregate inclusion in warm mix asphalt