Effect Of Carbonization On The Properties Of Magnesium Oxychloride Cementitious Materials

In this paper,the compressive strength,flexural strength and apparent density of carbonization for four kinds of MOCs were studied by adding composite modifier,standard sand,fly ash and sawdust based on pure magnesium oxychloride cement（MOC）.And the TG-DTG,XRD and SEM were used to analyze the influence law of the phase and microstructure changes of the specimens,and compared with the indoor atmospheric environment,and the influence of carbonization on the properties of magnesium oxychloride cementitious materials were analyzed.The main experimental results obtained are as follows:1.The flexural strength and compressive strength of specimens with composite modifiers increased during the 28-days-old curing of indoor atmospheric environment maintenance with the increase of age,and the trend was similar with the increase of dosage;compared with indoor atmospheric environment,the flexural strength and compressive strength of the MOC specimens increased after carbonization.The flexural strength and compressive strength of the carbonized MOC specimens decreased with the increase of the blending amount,and the blending amount≤10%has better early carbonation resistance.2.The flexural strength and compressive strength of the specimens with standard sand increased during the 28-days-old curing of indoor atmospheric environment increased with the increase of age,and the trend was similar with the increase of the content;compared with the indoor atmospheric environment,the flexural and compressive strength of the MOC specimens tends to increase after carbonization.The flexural strength and compressive strength of the MOC specimens after carbonization increase first and then decrease with the increase of the blending amount.The blending amount 1:1 to 1:3 has better early carbonation resistance.3.The flexural strength and compressive strength of specimens with fly ash increased during the 28-days-old curing of indoor atmospheric environment maintenance with the increase of age,and decreased with the increase of dosage;compared with indoor atmospheric environment,the flexural strength and compressive strength of the MOC specimens increased after carbonization.The flexural and compressive strength of the carbonized MOC specimens decreased with the increase of the blending amount,and the blending amount≤5%has better early carbonation resistance.4.The flexural strength and compressive strength of the specimens with the sawdust increased during the 28-days-old curing of indoor atmospheric environment maintenance with the increase of the age,and decreased with the increase of the dosage;compared with the indoor atmospheric environment,the flexural strength and compressive strength of MOC specimens increased after carbonization.The flexural strength and compressive strength of MOC specimens after carbonization also showed a downward trend with the increase of the blending amount,and it was better in the range of≤20%that had early carbonization resistance.5.The apparent density of the specimens increased after 28 days of carbonization in the four MOC systems.The apparent density of all the specimens after carbonization increased in different degrees.The maximum ratio of increase were 5%,1:0.5,30%.and 50%.Under carbon dioxide curing,the test pieces are carbonized and decomposed to generate MgCO₃,which leads to a relative increase in apparent density.After 28d carbonization,the amount of MgCO₃ increased,but the increase was not enough to reduce the strength of the test piece.On the contrary,MgCO₃ filled the pores of the test piece,and the compactness of the test piece increased and the strength increased.6.After carbonization,the thermal stability of the composite modifier and standard sand MOC specimens increased,and the thermal stability of the fly ash and sawdust MOC specimens decreased.And the thermal stability of the test piece is increased.The needle crystals are relatively distributed in the gelatinous crystals,forming a cross-connected structure,which is the reason why the strength of the specimen after carbonization is higher than that of the air-cured specimen and its strength is higher than other blending tests.