Foaming System And Modification Of The Foamed Magnesium Oxychloride Cementitious Material

Foamed magnesium oxychloride cementitious material has the advantages of rapid hardening,good fire resistance and high mechanical strength,etc.It can be used to produce lightweight heat-insulating wallboards,building formworks and fire door boards.With the increase of application fields,more and more researchers pay attention to the problems of the FMOC,such as terrible water resistance and collapse.The key to solve these problems is to choose suitable foaming agents for the MOC system,reasonable raw material ratio and high efficiency water resistant modifiers.The types and additions of foaming agents and stabilizers were studied with the main evaluation indexes of foam expansion and half-time.The effect of foaming agents on the FMOC properties was also studied with the main evaluation indexes of dry density,compressive strength,and pore structure.The results showed that the foaming agent mixed with 1.0 wt%A1 and 1.0 wt%B3 was an ideal composite foaming agent for the MOC.The foam expansion was 16.75 and the half-time of foam was 55 min.The FMOC prepared by the composite foaming agent showed excellent properties.And the dry density was low,the pore size was uniform and the compressive strength was high.The effect of raw material ratio and the foam volume on the FMOC properties was studied with the main evaluation indexes of dry density,compressive strength,softening coefficient and water absorption.The FMOC showed excellent properties when the molar ratio of?Mg O:Mg Cl₂:H₂O was 7.5:1:16.And the dry density was 332 kg/m³,the porosity was 82.71%,the compressive strength was 0.962 MPa,the softening coefficient was 0.55,the pore size was less than 550?m.In addition,the addition of foam should not exceed 4m L/g Mg O.If not,the surface of the pores had holes and the water resistance reduced.The effect of emulsion on the FMOC properties was investigated with the main evaluation indexes of dry density,compressive strength and softening coefficient.The results showed that acid emulsion affected the stability of foam.When the addition of stearic acid emulsion was 1.0 wt%,the compressive strength of the FMOC increased to1.230 MPa and the softening coefficient was 0.70.When the addition of zinc stearate emulsion was 1.5 wt%,the compressive strength and the softening coefficient of the FMOC increased to 1.679 MPa and 0.74,respectively.Polymer emulsion had little effect on the dry density and porosity of the FMOC,but it can improve the water resistance.When the addition of silicone-acrylic latex was 1.0wt%,the compressive strength of the FMOC was1.240 MPa and the softening coefficient was as high as 0.78.When the addition of styrene-acrylic latex was 2.0wt%,the softening coefficient of samples reached 0.85.It can be seen that the crystalline phase of the FMOC modified by polymer emulsion has no significant change before or after soaking.The film appeared on the crystal surface of the FMOC modified by styrene-acrylic latex,and the crystal morphology was almost unchanged before or after soaking,which indicated that the styrene-acrylic latex can improve the water resistance of the FMOC.