Dynamic Mechanical Thermoanalysis Of Cement Asphalt Mortar

Abstract:Cement asphalt mortar (CA mortar) is an important part of the slab ballastless track structure. It’s a composite material composed of cement, emulsified asphalt, sand, water and a small amount of admixture. The dynamic mechanical properties of CA mortar are much dependent on temperature and loading frequency, by which the dynamics and durability of slab track structure will be influenced.In this paper, the dynamic mechanical thermal analysis of CA mortar is carried by DMA Q800in-40℃～60℃temperature range. The main factors influencing measured results are discussesed. The major conclusions are as follows:(1) The result of dynamic mechanical thermoanalysise relate to the choice of warm-up temperature control or cooling temperature control, speed of temperature rising, way of loading, loading frequency, shape of sample, size of sample, loading amplitude and other test parameters. According to the test result, it was determined that the parameter of CA mortar’s thermo dynamic viscoelasticity test by using dynamic mechanical thermoanalysiser is2℃/min of temperature rising rate,6Hz of loading frequence,65mm×10mm叁2.3mm of sample siz and3μ m of loading amplitude.(2)The basic thermo dynamic viscoelasticity of CA mortar is:The dynamic modulus and storage modulus is with the increasing of temperature. The loss modulus and disspation factor changes as the parabola shape when temeperature rise and the peak value appear at a particular temperature. The value of loss modulus is about one or two orders of magnitude lower than the storage modulus due to the different composition. And the value of dynamic modulus is similar with storage modulus. The value of dynamic modulus can reduce as3to10times when temperature increase from-40℃to60℃due to the different composition. We can see that the CA mortar has obvious viscoelastic characteristics. And it is mainly caused by asphalt.(3) The three component viscoelasticity mechanical model of three original model which an ideal spring and an ideal dashpot in parallet then an ideal spring in series is suitable for the description of thermo dynamic viscoelasticity change rule of CA mortar with the chang of temperature and loading frequence. This is obtained through theoretical analysis and experimental results.(4) The thermo dynamic viscoelasticity of CAmortar relate to asphalt to cement ratio, water to cement ratio and sand to cement ratio. The results from test are as fallows:1) When the asphalt to cement ratio increases, the dynamic modulus and storage modulus of CA mortar and paste decrease and disspation factor increase. The change rule of loss modulus is different in different temperature range. The loss modulus of CA mortar decrease when it is colder than-20℃or hotter than30℃and increase in temperature range of-20℃to30℃with asphalt to cement ratio increasing. The loss modulus of CA paste increase then decrease when it is colder than0℃decrease when it is hotter than10℃. On the other hand, asphalt to cement ratio can also affect the change rate of all modulus with temeperature rising and temeperature corresponding to the peak value of loss modulus and disspation factor. Analysis shows that the effect rule of asphalt to cement ratio relate to microstructure of sample, volume fraction of asphalt and the temperature dependence of asphalt molecule movement.2) The dynamic modulus, storage modulus and loss modulus increase as apparent density increasing when the asphalt to cement ratio is0.9. The dynamic modulus, storage modulus and loss modulus decrease when the asphalt to cement ratio is0.3as water to cement ratio increasing. The disspation factor of all mortar decrease when water to cement ratio increass. As the extent of variation of all the modulus is small, the dynamic mechanical properties changes little when water to cement ratio changes less than0.1. The extent of variation should be much less as asphalt to cement ratio increasing.At the same time, water to cement ratio can also affect the change rate of all modulus with temeperature rising. Analysis shows that the effect rule of asphalt to cement ratio relate to compaction rate and porosity of the mortar.3) When the sand to cement ratio increases, for the CAmortar which the asphalt to cement ratio is0.85the dynamic modulus and storage modulus increase, the loss modulus changes little, and the disspation factor dosen’t change too much in the sub-zero temperature and decrease above freezing temperature. For the CAmortar which the asphalt to cement ratio is0.3dynamic modulus, storage modulus and loss modulus increase and disspation factor dosen’t change a lot. The change rate with temperature rising of dynamic modulus, storage modulus and loss modulus is faster when the sand to cement ratio increases. Analysis shows that the effect rule of sand to cement ratio relate to the change of phase volume and interaction of organic phase and inorganic phase.To sum up, we can draw a conclusion that thermo dynamic viscoelasticity of cement asphalt mortar relate to the volume fraction of phase, interaction of organic phase and inorganic phase, microstructure (pore) and other factors. The key reason is the asphalt’s contribution of thermo dynamic viscoelasticity to the mortar and its molecular movement theory.