Multiscale assessment of asphalt emulsion as a toughening modifier for self-compacting concrete: Mechanical behaviour, microstructural analysis, and RSM-based modelling

Abstract

The development of self-compacting concrete (SCC) has revolutionized modern infrastructure by facilitating the construction of high-strength and intricate structures such as rigid pavements, bridges, tunnels, and skyscrapers since it has superior flowability and capacity for self-consolidation without external vibration. Despite all these advantages, the inherent brittleness and poor energy absorption capacity are significant shortcomings when it is subjected to impact and dynamic loading. The purpose of this investigation is to identify and ascertain the performance of an asphalt emulsion (AE) as a toughening agent on SCC to increase its energy absorption capability without significantly affecting its mechanical properties and fresh characteristics. For this study, five mixes were cast, including a reference mix and four SCC mixes containing 5, 10, 15, and 20% AE content (by weight of cementitious material). Fresh properties were measured using slump flow and J-ring tests, while hardened concrete properties included mechanical behaviour (stress-strain curve, toughness index), microstructure analysis (pore size distribution, XRD), and response surface methodology (RSM)-based modelling. This study shows that AE effectively enhances the postpeak deformation behaviour and the energy dissipation of SCC at the cost of a small reduction in compressive strength. The toughness index of the mixture with 5%, 10%, 15%, and 20% AE was improved by 5.21%, 17.00%, 24.13%, and 39.52% compared with the control, indicating an enhanced ductility and toughness with increasing AE content. In addition, the fresh properties were all within the permissible limits for SCC mixtures, suggesting that the workability of SCC was not negatively influenced by the addition of AE. Two very reliable models for predicting the slump flow, compressive strength, and flexural strength were obtained based on the RSM analysis and demonstrated a strong correlation between laboratory and predicted values. The optimum amount of AE based on both the fresh and hardened state performance of the concrete should be 10%. In addition, a suitable dosage of 10% AE can contribute to a compromise of improved toughness and energy dissipation, sufficient mechanical performance, and workability. The results suggest that AE is a promising, eco-friendly, and low-cost admixture for enhancing the toughness and impact resistance of concrete for durable and resilient transportation and civil infrastructure.