168 _______________________________________________________ DOI: https://doi.org/10.33258/birex.v2i2.875 Modeling the Influence of Surface Free Energy on Moisture Damage of Recycled Asphalt Concrete Saad Issa Sarsam 1 , Rana Khalid Hamdan 2 1 Department of Civil Engineering, University of Baghdad, Baghdad-Iraq 2 MSc student, Department of Civil Engineering, University of Baghdad, Baghdad-Iraq saadisasarsam@coeng.uobaghdad.edu.iq Abstract: Recycling is a sustainable process for restoration of the pavement quality. In this investigation, aged binder was recycled by digestion with (0.5, 1.0, and 1.5) % of polyethylene and crumb rubber. The recycled binder was implemented in the preparation of Marshal specimens. The surface free energy of the control and recycled binder was determined using the Sessile drop method. Specimens were tested under repeated indirect tensile and double punching shear stresses with the aid of pneumatic repeated load system (PRLS). Another group of specimens was tested for moisture damage, then subjected to the same loading sequence. Specimens were subjected to 1200 load repetitions under stress level of 0.138 MPa at 25 °C. The load was sustained for 0.1 second followed by 0.9 seconds of rest period. The permanent deformation was measured before and after moisture damage process for each testing technique. Regression analysis is used to develop a model for the influence of surface free energy on the deformation and the moisture damage using the SPSS Software. It was concluded that the obtained model can explain 82 % of the variation in moisture damage due to the influence of surface free energy. Keywords: recycling; asphalt concrete; repeated shear and tensile stress; moisture damage; surface free energy I. Introduction Authors all around the world have provided models to predict pavement performance both on local and on global level. Several models predicting the pavement performance have been analyzed, and it has been determined that the best predicting models are the ones formed using databases for the territory where they are intended to predict pavement properties, Matic et al, (2016). Expression and mathematical models have been obtained for the determination of cyclic tensile strength of the asphalt concrete, which considers the damage accumulation and the history of loading. Comparison of the calculation results performed under the obtained expression, and experimental tests showed that the obtained expression describes satisfactorily the cyclic tensile strength of the asphalt concrete. It was concluded that the obtained expression for determination of the cyclic tensile strength for the asphalt concrete can be used for the prediction of fatigue strength of the asphalt concrete pavement, Iskakbayev et al, (2017). A multi-objective nonlinear optimization model was established by Zhou and Chen, (2019) according to the residual sum of squares of storage modulus and loss modulus from dynamic modulus test. The results of statistical analysis indicated that the fitting curves of fractional models with fewer mechanical elements and fitting parameters were much smoother in comparison with the traditional integer model with many unknown parameters. A new nonlinear second order hyper-elastic-visco-plastic-damage constitutive model in multi dimensions was developed by Panoskaltsis and Panneerselvam, (2007) and its theoretical foundations are presented. It was concluded that the model is used to analyze experiments for asphalt concrete both in the elastic as well as in the irreversible domain of the material. Model's comparisons to experiments are very favorable. The experiments are analyzed both as homogeneous and as boundary-value problems. Sarsam and Al-Azawi, (2013) concluded that the stripping potential as indicated by the index of retained strength, is highly dependent on the