Influence of cation type on deterioration process of cement paste in sulfate environment

• Influence of cation type on sulfate attack to cement paste is studied.
• Mechanical distribution based on Vickers hardness of cement paste is proposed.
• A model of compressive strength with the average Vickers hardness is established.
• The expansion of cement paste with exposure time for different sulfate is presented.
• The damage process of cement paste with attacked ratio is analyzed.

The objective of this study is to examine the influence of cation type on deterioration process of cement paste exposed to external sulfate attack. The experiment was carried out by micro-hardness test (Vickers hardness), compressive strength test and expansion test. Solutions respectively containing Na2SO4, K2SO4, (NH4)2SO4 and MgSO4 with sulfate concentration of 5.0 wt% were chosen as the sources of sulfate to attack the cement paste. The pH values of solutions containing different sulfate salts were measured to support the analysis. The deterioration process of the cement paste specimens immersed in different attacking solutions was analyzed. The results shown that, the reducing rate of Vickers hardness of cement paste samples immersed in solutions containing different sulfate salts were generally sequenced as Na2SO4 ≈ K2SO4 > MgSO4 > (NH4)2SO4. With the addition of exposure time, the deterioration process exerted at different rate with the variation of sulfate salts. The expansion of specimens immersed in solutions containing Na2SO4, K2SO4, MgSO4 and (NH4)2SO4 occurred in two stages within a certain range of exposure time. Besides, compressive strength appeared to be well correlated with Vickers hardness for different kinds of sulfate salts.