Research On Dissolution Characteristics And Deterioration Mechanism Of Complex Cementitious Materials

Dissolution is one of the main deterioration phenomenons for cement-based materials at late ages.The addition of mineral admixtures in the cement-based materials tends to make the dissolution process and deterioration mechanism much more complicated.Aiming at the current controversial problem of dissolution of complex cementitious materials,the macroscopic dissolution characteristics of early complex cementitious materials from dissolution depth,calcium cumulative dissolution content and compressive strength were studied by ammonium nitrate accelerated dissolution,and the deterioration microstructure characteristics were analyzed by XRD,SEM,TG and MIP.On the basis of this,the dissolution mechanism of complex cementitious materials was revealed from the three aspects of solid phase dissolution order,solid phase decalcification kinetic characteristics and pore structure deterioration.The main researching content and results are listed as follows:?1?With the increase of age,different complex cementitious materials were degraded.The admixtures had a good filling effect,which can hinder the process of dissolution to a certain extent in the early stage of dissolution.When the amount of fly ash was not more than 35%,the fly ash-cement system had the effect of dissolution resistance,and the effect was best when fly ash content was 20%;For the slag-cement system,the incorporation of slag would help to improve the dissolution resistance of the specimen when the slag hydration is sufficient;But for the limestone powder-cement system,the deterioration was aggravated with the dissolution age.The incorporation of 20% limestone powder was slightly conducive to delay the loss of calcium-containing material in the paste at the later stage of dissolution.?2?Inside the paste,the dissolution occurred first in the original pore wall area,and then gradually into the solid phase products,and the body of the increased pore volume by C-S-H and other hydration products decalcification was not all independent of small pore,but a part of the larger pore merged and expanded by the original pore.A part of the increased pore volume,also increased the connectivity of the paste whose damage to the pore structure can not be ignored.CH was more sensitive in the whole process of dissolution: first,the crystal form changed,the crystal shape was distorted and finally dissolved and disappeared.AFt,AFm,and???type C-S-H had stronger anti solubility properties than CH,???and???type C-S-H in the hydrated products of the paste.?3?The influence factors of dissolution were divided into four aspects: the ambient temperature of system,the movement state of the two mediums?water and materials?,the respective properties of the two mediums and the interface characteristics between the two mediums.The dissolution process and the C-S-H dissolution starting point were discussed from the perspective of dynamic equilibrium.It was pointed out that the dissolution starting point of C-S-H and other hydration products was the same as that of CH,just showing hysteresis in the macro scale,but the presence of CH could inhibit the dissolution of other hydration products.On the basis of the experiment,the time-varying law of dissolution depth and calcium cumulative dissolution content was numerically fitted,and the quantitative relationship between them was established.It was found that the dissolution depth and the Ca²⁺ cumulative dissolution content were proportional to the power function of time.