On the modification of paving binder (part 3)

Abstract

Durability of asphalt pavement was enhanced by addition of a polymer in its binder. The authors studied the solubility of a polymer in the binder (Part 1), and the viscosity change of maltene by addition of a polymer (Part 2), and following equation was obtained from the experimental results.[formula omited] where, ηG is the viscosity of polymer in poise, ηm is the viscosity of maltene in poise, η is the resultant viscosity of maltene by addition of the polymer, Δ S.P. is the difference in solubility parameters between the polymer and maltene in the sample, Mwm is the average moleculer weight of maltene, Cm is the relative volume of maltene. The value of 29/(ΔS.P.×Mwm)0.43 is the swelling volume ratio of the polymer. Ductility of paving binder has an important effect on the performance of asphalt pavements, and many studies have been made on the performance derived from the ductility of its binders3)∼7). In this investigation tensile tests for four types of binders obtained from various sources and systems with addition of S.B.R. polymer were made by the ductility mold method and the Benson method9), and the results obtained by the methods were compared. As a result, it became obvious that viscosity, instantaneous elasticity and retarded elasticity of a sample could be obtained solely from the results of the ductility mold method. Test characteristics of the four binders are tabulated in Table 1, where, sample M-1 is Arabian air rectified asphalt, sample M-2 is Arabian straight asphalt, sample N-1 is Venezuelan naphthenic straight asphalt and sample C-1 is synthesized petroleum resins mixed with a flux oil. These sample contained 0, 2, 4, 6, parts of S.B.R. polymer per 100 parts by weight of sample. The S.B.R. polymer was emulsified in water. A uniform dispersion of the polymer in the sample was obtained by stirring with a propeller type stirrer at 175±5°C. The tensile tests were carried out by using an Instron tensile tester at 50cm/min and at 25°C. A sample was poured into the assembled ductility mold shown in Fig. 1 and was poured into a cylindrical cup used in the Benson method. The sample in the ductility mold and Benson cylindrical cup was tested by the tensile tester. The relation between tensile strength and strain for the Voigt model is expressed as follows. σ=Kη1+E1ε (1) for the Maxwell model the following equation was obtained. σ=Kη2(1-e-E2ε/Kη2) (2) The tensile strength of four element models is the sum of Eqs. (1) and (2), σ=Kη2(1-e-E2ε/Kη2)+Kη1+E1ε (3) where, η1 and E1 are viscosity and retarded elasticity in the Voigt model, respectively; η2 and E2 are viscosity and instantaneous elasticity in the Maxwell model, respectively; ε is strain and K is the shear rate of the sample. From Eq. (3) when tensile strength was applied to the sample the tensile stress Kη1 was generated at ε=0. Viscosity η in the Voigt model was obtained by dividing the tensile stress Kη1, which is shown at point A in Fig. 2, by shear rate K. Thus, the tensile stress in Fig. 2 is seen to increase with increasing strain, and retarded elasticity E1 is obtained from the gradient of line CD also in Fig. 2. © 1978, The Japan Petroleum Institute. All rights reserved.