## 4 Conclusions  
A micromechanics-based multiscale model for creep homogenization of polymer-modified cement pastes was developed herein. It was used to investigate the micromechanical origin of the pronounced macroscopic creep activity of such cement pastes. To this end, the microscopic polymer particles were considered to show a power-law-type creep behavior. Based on micro-to-macro-scale-transition relations, developed in the framework of continuum micromechanics, the viscoelastic behavior of the microscopic polymer particles was linked to the macroscopic creep behavior of cement paste. By means of a top-down identification approach, we exploited results from a comprehensive macroscopic early-age creep testing campaign [9], involving 168 short-term creep tests on two polymer-modified cement paste mixes. From the obtained results, the following conclusions are drawn. * The pronounced creep activity of polymer-modified cement paste can be explained by an isochoric power-law-type creep behavior of the polymers, whereby the shear creep modulus of the polymers is two orders of magnitude smaller than that of the hydrates. * The creep behavior of the polymer particles inside hydrating cement paste is not universal. The creep activity of the polymer particles decreases significantly as hydration proceeds. The underlying physical mechanism is very likely related (i) to self-desiccation resulting from the (water-consuming) hydration reaction and (ii) to the associated continuous decrease of the internal relative humidity in cement pastes [62]. * The experimentally-observed macroscopic creep behavior of hydrating polymer-modified cement pastes can be satisfactorily reproduced when considering that the power-law creep exponent of the polymer particles is age-independent and, thus, constant. In that case, the shear creep modulus of the polymer particles was found to follow a bilinear trend during the first week after production. Considering that both the shear creep modulus and the creep exponent of the polymers are age-dependent and, thus, evolving functions, the agreement between modeling results and experiments can be further improved, but at the cost of considerable additional computational efforts. * As for future research regarding the viscoelastic behavior of polymer-modified cement pastes, it is desirable to monitor the evolution of the internal relative humidity. This will provide the necessary physical background to interpret the self-desiccation-induced changes of the creep behavior of the polymers. This research is supported by the German Research Foundation (DFG) via the Research Training Group \"Evaluation of Coupled Numerical and Experimental Partial Models in Structural Engineering (GRK 1462)\" which is gratefully acknowledged. This work was further supported by a short-term scientific mission (STSM) Grant from COST Action TU 1404 \"Towards the next generation of standards for service life of cement-based materials and structures\". [PERSON] set up the overall strategies for experimental testing, measurement evaluation and the multiscale modeling within the framework of continuum micromechanics. He supervised the research progress, checked key results and supported the documentation process. [PERSON] produced the specimens and carried out the hourly-repeated three-minute-long creep tests, supported by the technical staff of the laboratory. She developed MATLAB codes for the evaluation of the measurement data, as well as for the two-scale creep homogenization of polymer-modified cementitious materials. She also carried out the model validation based on the test data and documented the research results. [PERSON] developed the Maple code for the Laplace-Carson transform, contributed to both the discussion processes and the documentation of the research results and helped with proof reading the paper. [PERSON] supervised the research process, checked key results and supported the documentation process. The authors declare no conflict of interest.