The Development And Research On The Specialized Plastering Mortar For Aerated Concrete By Magnesium Phosphate Cement

Aerated concrete block is a kind of energy-saving and environment-friendly wall material with light weight,good thermal insulation property and so on,and has been expanded widely.However,the risk of cavity and cracking appeared frequently for the plastering mortar on the surface of aerated concrete,owning to its high water absorption,large drying shrinkage of aerated concrete.Moreover,the poor water retention and adhesive strength of traditional plastering mortar are also the main cause.Therefore,it is of great significance for the research of actually applicable plastering mortar of aerated concrete.Magnesium phosphate cement(MPC)is a new kind of cementitious material which is based on the acid-base neutralization,with short setting time,high early strength,well adhesive property,low drying shrinkage and so on.In the paper,the free water in the mortar can be effectively locked by using the characteristic of rapid hydration,short setting time and lager adhesive strength of MPC,and it wouldn't be sucked away quickly by aerated concrete block.Therefore,the poor water retention and adhesive strength of plastering mortar for aerated concrete can be improved effectively.In the paper,by using dead burned magnesia oxide,ammonium dihydrogen phosphate,fly ash,borax,floating beads and cellulose ether as raw materials,the specialized plastering mortar for aerated concrete was prepared.The influence of M/P,the variety and dosage of retarders and floating beads,the dosage of fly ash and cellulose ether was discussed.The results revealed that:(1)the addition of borax and STPP compound retarder,and fly ash could prolong the setting and hardening time of plastering mortar;(2)addition of floating beads could bring down the compressive strength of mortar to match the aerated concrete block;(3)the suitable addition of cellulose ether could have a great air entraining effect and reduce the difficulties of mixing up the mortar which was incorporated with large amount of floating beads;(4)the water absorption of aerated concrete in one minute was 5.56%,while the water retention of MPC plastering mortar was96%,which could avoid the risk of cracking caused by the water in the mortar was sucked out in a moment by the block;(5)under the optimal proportion,the plastering mortar samples whose water retention rate were96%,density were 890kg/m~3,compressive strength were 8.6MPa,adhesive strength were 1.32MPa,thermal conductivity were 0.2681W/m·K.By the comparison of traditional plastering mortar,the results show that the developed MPC plastering mortar for aerated concrete has many excellent properties,including:(1)good workability and water retention;(2)high adhesive strength;(3)low drying shrinkage and good crack resistance;(4)thermal conductivity is close to the aerated concrete block,which could effectivity solve the thermal bridge between the aerated concrete block and plastering mortar,and reduce the temperature stress caused by cold shrinkage and thermal expansion;(5)strength and shrinkage are close to the aerated concrete block,which could ensure the harmony and avoid the cracking risk between the aerated concrete block and plastering block.With the simulated analysis of the wall wiped with two kinds of plastering mortar by ANASYS,the results revealed that the wall wiped with MPC plastering mortar showed good thermal insulation performance in the winter and summer.Also,the wall wiped with MPC plastering mortar had smaller temperature stress and less temperature deformation than the wall with normal plastering mortar,thus reduced the cracking risk of wall.Therefore,the specialized MPC plastering mortar for aerated beads has a broad prospect of application.