Three-dimensional concrete printing (3DCP) has become recognized as a possible alternative to conventional concrete construction, mainly due to its potential to increase productivity and reduce the environmental impact of the construction industry. Despite its up-and-coming popularity within the field, limited research has quantitively investigated the environmental benefits that 3DCP brings. This paper investigates the environmental tradeoff of utilizing 3DCP over conventional construction by conducting a detailed cradle-to-gate life cycle assessment (LCA) study of four case-scenarios (conventional concrete construction, 3DCP with reinforcement elements, 3DCP without any reinforcement, and 3DCP without any reinforcement and utilizing a lightweight printable concrete material.) These case-scenarios were carefully selected to quantify the environmental impact of 3DCP while emphasizing the importance of the material composition. The LCA was conducted for a 1 m² external load-bearing wall in all four scenarios. The LCA analysis showed that 3DCP significantly reduced environmental effects in terms of global warming potential (GWP), acidification potential (AP), eutrophication potential (EP), smog formation potential (SFP), and fossil fuel depletion (FFD), as compared to conventional construction methods. However, these environmental improvements diminished when 3DCP was coupled with the use of conventional reinforcement elements. Moreover, the use of an alternative concrete mixture in 3DCP showed a further decrease in the GWP, AP, EP, and FFD impact. Ultimately, the findings in this paper support the advantages of 3DCP technology and recommend the investigation of the development of (i) sustainable printable concrete materials and (ii) novel reinforcement techniques that are suitable for 3DCP rather than adopting conventional reinforcement techniques.

This paper reports a laboratory investigation aimed at evaluating the potential of polymer binders to stabilize pavement subgrades in Qatar. The conclusions regarding the impact of the polymer stabilizers are based on comparisons with selected physical, chemical, mechanical, and microstructural properties of natural Qatari subgrade soil and soils stabilized with the traditional standard, portland cement (PC). The results demonstrate that the polymer binders modify the Qatari subgrade soils resulting in more favorable engineering properties: for example, the compressive strengths of the polymer-stabilized soils are superior to those of the unstabilized soils and those stabilized using PC. The mechanical properties of the stabilized and unstabilized soils were incorporated in the analysis of asphalt pavement sections using the state-of-the-art protocol for pavement design and analysis. Results of the analysis further demonstrated the benefits of using stabilized subgrade soils in improving pavement ...

This study aims to (1) determine an optimum amount of Reclaimed Asphalt Pavement (RAP) such that its addition does not adversely impact the fracture resistance of asphalt mixtures, and (2) determine the amount of RAP binder that is active in the total mix. For this purpose, the asphalt mixtures containing three RAP contents (15, 25 and 35%) and their recovered binders were characterized. The binders were subjected to the performance grading, frequency sweep, multiple stress creep and recovery (MSCR) and linear amplitude sweep (LAS) tests. The mixtures were evaluated using dynamic modulus, Hamburg Wheel Tracking (HWT), Flow Number (FN), Semi Circular Bend (SCB), and Ideal Cracking Tolerance (Ideal-CT). The blending efficiency of the RAP binder was determined using the Hirsch model. Based on the performance results and the relatively low binder content of asphalt mixtures in Qatar, it is recommended to use up to 20% RAP in asphalt mixtures.

Aggregate particles strongly influence the behaviour and performance of asphalt mixtures. This study applies a refined version of a recently developed microstructure generator (MG) to computationally produce random aggregate particles with controlled shape parameters (i.e. angularity index [AI] and form index [FI]). These sets of aggregates were used to generate virtual microstructures of asphalt mixtures that were transferred to finite elements and subjected to mechanical loading. A main advantage of using the MG to produce several random microstructures of asphalt mixtures is that it permits to capture the heterogeneity inherent to the material and, therefore, to include the uncertainty related to its mechanical response. The results showed that virtual specimens with aggregates having low values of AI (at a constant value of FI) and high values of FI (at a constant value of AI) presented lower damaged area and smaller overall modulus of the mixture.

This paper presents results on the evolution of the macroscopic appearance and surface microstructure of asphalt binders aged in an accelerated weathering tester. Two binders used in hot mix asphalt and two binders used in warm mix asphalt were aged in the presence of UV radiation, heat, oxygen and moisture. The same binders were previously aged using the same protocol but without the presence of moisture. Analysis of images captured using atomic force microscopy showed significant differences in the microstructure of binders aged in the presence of moisture versus those that were aged without moisture. There was no consistent evolution in the microstructure features in the presence of moisture. The combined effects of moisture and UV radiation caused part of the binder to become soluble and be transported away, while the remaining part of the binder experienced cracking and discontinuities. This observation relays the vital role that these atmospheric agents play in the degradation and microstructural evolution of asphalt binders.

The use of reclaimed asphalt pavement (RAP) in road construction has become a common practice in the asphalt industry due to environmental and economic benefits. However, since RAP is an aged material, recycling agents are typically used to reduce the stiffness of the recycled asphalt mixture and make it less prone to cracking at high RAP contents. This study evaluates the effect of ageing and the use of recycling agents on the rheological, microstructural, and micromechanical properties of binder blends with high RAP contents. A total of 27 binder blends were prepared with different recycled binder ratios (0.22, 0.31 and 0.5), recycling agent doses (0%, 1.2%, 5.5% and 9%), virgin binder performance grades (PG 58-28 and PG 52-34) and ageing conditions. The microscopic properties of the binder blends were characterised using atomic force microscopy (AFM). AFM results provided an evaluation of the microstructural homogeneity of the blends, with a good correlation with the binder blends macroscopic rheological properties. The addition of recycling agents improved the homogeneity of the binder blends by reducing the variation in modulus among the different phases in the microstructure. AFM proved to be a useful tool to evaluate rejuvenated binder blends at the microscale level.