Preparation And Performance Of Foamed Cement Sandwich Panel With Fiberboard

In order to save energy,China has increased the requirements for building energy efficiency.To meet the energy saving requirements,foamed cement with excellent thermal insulation and fire resistance has been widely applied to the construction field.But it also has a lot shortcomings such as easy to take off powder dregs,easy to crack and low strength.Although metal outer skins could be used to overcome these disadvantages,they showed the defects of large energy consumption and poor recycling.In this study,wood materials were used as substitutes of metal panels to prepare new sandwich---foamed cement sandwich panel with fire-retardant medium density fiberboard(FR-MDF).The main results and conclusions are as follows:(1)Retardant treatment and optimization of the face plateDifferent proportions of compounded fire retardant with melamine cyanurate(MCA)and ammonium polyphosphate(APP)were prepared to make FR-MDF.The FR-MDF with optimal recipe that of least impact on mechanical properties and better char formation and smoke suppression performance was utilized as the surface layer of sandwich structure.The results showed that the dosage with 2.5% MCA and 7.5% APP had least impact on FR-MDF mechanical properties,which reached the requirements of standard GB/T 18958-2013.The FR-MDF with optimal proportion compounded fire retardan got good performance of char formation and smoke suppression,whose oxygen index was 40.99% and peak heat release rate and total amount of smoke reduced 31.70% and 61.98% over the contrast,respectively.(2)Performance and optimization of the core plateRelationship between density and performance of foam cement was studied to choose the lowest density foamed cement which could meet the performance requirements as the sandwich core board.The results showed that the compressive strength,tensile strength,flexural strength of foamed cements of all densities can meet the standard requirements.And the density must be no less than 330 kg/m~3 to reach JG/T 266-2011 requirement for water absorption(≤50%),no less than 380 kg/m~3 to meet the requirement of softening coefficient on foam cement slab partition by DB21/T 2353-2014(≥0.85).The foamed cement was selected whose density was 380 kg/m~3,and its weighted sound reduction(R_w)is 37.58 dB,with 58.92% strength retention rate after fired 0.5 h.(3)Preparation of the sandwich panelSandwich panels were prepared by pressing preformed fiberboard and foam core at room temperature.Three kinds of adhesive(i.e.two-component polyisocyanate emulsion,cement mixed with white emulsion(mixed glue),polyurethane foam adhesive(styrofoam))were used,and the results showed that styrofoam got the best bonding strength,followed by the mixed gule.Heat resistance of styrofoam(≤120 oC)was not as good as mixed glue,but it has met the practical demand.Furthermore,styrofoam showed better water resistance than mixed glue.When glue spread amount was 90 g/m~2,it could meet the requirement of water resistance by DB21/T 2353-2014.In conclusion,styrofoam was a superior binder to bond the foamed cement with FR-MDF,and the optimum glue spread was 90 g/m~2.(4)Properties of the sandwich panelThe facing of foamed cement with FR-MDF panel largely enhanced its mechanical properties and sound insulation.When the thickness of sandwich panel was 90 mm,lateral compressive strength,flexural strength and impact toughness of sandwich panels increased by 95.29%,260.71% and 14.50% compared with foamed cement core.The thicker the material,the better the sound insulation performance.The Rw of 50 mm and 70 mm sandwich panels approximately equal to 60 mm and 80 mm thick foam cement board owing to the better sound insulation of the FR-MDF panel.Moreover,sound insulation of the sandwich panel met the requirement of external wall insulation volume(≥45 d B)by GB 50118-2010 when the thickness of sandwich panel was 90 mm.The theoretical and calculated values of sandwich thermal conductivity got good consistency.When the thickness of sandwich panel was 90 mm,theoretical thermal conductivity was 0.108 W/m·K and close to thermal conductivity of foamed cement(0.10 W/m·K).It was indicated that when the thickness of the sandwich panel was over 90 mm,the FR-MDF face had little effect on the thermal insulation performance of sandwich.The theoretical thermal conductivity of sandwich panel with thickness of 90 mm was much smaller than the required values of sandwich composite wall with fiber cement surfaces by JC/T 1055-2007(≤0.35 W/m·K).Fire resistant strength of 90 mm sandwich panel was measured,since it showed better acoustic insulation and thermal insulation.It was found that intensity preservation rate(strength after heating for 0.5h divided by original strength)of the sandwich panel with FR-MDF face(63.64%)was greater than that of both the foamed cement(58.92%)and the MDF surface sandwich panel(52.61%).It is suggested that fire-resistance of the sandwich panel with FR-MDF face was excellent.