Ucak, Kaan; (2024) Vibration Damping and Mechanical Properties of Asphalt Emulsion-modified Concrete. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Concrete is the most widely used man-made composite material, adopted increasingly for applications such as high-speed railway, offshore and earthquake resistant structures, where vibration is encountered during the service life. Hence, attenuation of vibration in concrete structures is essential to improve their response to dynamic loads to ensure structural safety. The damping capacity of concrete is low compared to viscoelastic materials used for vibration mitigation. Modifying concrete constituents was identified as an effective way of improving the passive damping capacity of concrete. This research investigated the potential of asphalt emulsion as a cost-effective viscoelastic admixture to enhance the damping properties of both normal and lightweight concrete. The influence of replacing Portland cement (PC) binder with asphalt emulsion (AE) on the fresh, physical, mechanical, electrical, and dynamic properties of both normal and lightweight concretes were examined at 7, 28, 90, and 180 days. CEM I 52.5N PC was replaced by an anionic asphalt emulsion in steps of 10% by volume up to 40%. Damping and dynamic modulus were measured using uniaxial cyclic compression loading and impact resonance tests. The damping of normal concrete and lightweight concrete increased as more AE replaced PC, but resulted in undesirable mechanical properties such as reduction in strength, ultrasonic pulse velocity (UPV), and dynamic moduli. The results indicated that damping capacity increased by nearly 330 %, from 0.0093 to 0.031 when AE content increased up to 40 %, but at the cost of a 90 % reduction in compressive strength from 38.7 MPa to 4.1 MPa and a 17 % decrease in ultrasonic pulse velocity (UPV). The dynamic modulus also exhibited a decrease of nearly 50 % when AE content increased from 0 % to 40 %. Unexpectedly, lightweight concrete mixtures obtained similar damping as normal weight concrete mixtures. Therefore, greater damping in asphalt modified concretes was attributed to the excellent flexibility and deformation capacity of asphalt emulsion. Greater porosity in the cement-asphalt matrix and interfacial transition zone (ITZ), and increased friction between the microcracks were recognised as other principal factors leading to an improvement in damping. Increasing aggregate porosity in the form of lightweight mixtures did not improve the damping. The current study suggests that asphalt emulsion could be a potential damping enhancing binder replacement for normal and lightweight backfilling concretes.

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