Development And Performance Of Magnesium Phosphate Cement-based Plant Aggregate Concrete

Using crop stalks to produce building materials can enhance the sustainability of buildings.During recent years,hemp-based plant aggregate concrete(PAC)has been of great interest and prominent owing to its superior hygroscopic and thermal properties.PACs are mostly produced with lime-based and traditional cement binders.However,plant aggregate shows poor compatibility due to the high alkaline nature of these binders.This tends to cause several key issues ranging from prolonged setting time,contamination of nucleation sites,and dissolution of plant particles in alkaline environment.As a result,produced PACs show poor mechanical and durability properties and are mainly used for insulation purposes.The poor compatibility between plant aggregates and high alkaline binders urges the researchers to use expensive pretreatment methods to improve the mechanical performance of PACs.While most of the studies on the PACs explored the hygrothermal properties,durability characteristics of PACs are ignored and still need exploration.Moreover,buildings when insulated internally poses several moisture-related issues including risks of mould growth,frost damage,interstitial condensation,and other damage related problems.In addition to solving the problems of long-term durability,biocompatibility,and low mechanical properties of PAC,this thesis also studied the feasibility of PAC to regulate indoor humidity and solve moisture-related issues in internally insulated walls.Therefore,this thesis systematically studies the preparation of PAC having high mechanical properties and durability by using magnesium phosphate cement instead of traditional cementitious materials through the comparative tests and carries out numerical simulation on the heat and moisture transfer properties of the wall containing PAC as an insulation layer,to explore the feasibility of its application in indoor humidity control.To develop new biocompatible and breathable PACs,this research was carried out in six systematic phases.The first phase includes the study on the optimization of three types of binders for the preparation of plant aggregate concrete.Optimization of ordinary Portland cement(OPC),geopolymer and magnesium phosphate cement(MPC)was carried by testing the physical,and mechanical properties to find out the best mix proportion for each type of binder.Comparison of experimental results revealed that MPC binder has several technical advantages over OPC and geopolymer binders for the preparation of PAC.Experimental results were further validated by detailed microstructure analysis of all types of binders.The second phase focused on the improvement of interfacial transition zone(ITZ)between the plant particle and different cementitious materials.The influence of different types of binders(optimized in phase 1)and plant aggregate surface treatment on the interface bonding and properties of PACs were investigated.A comprehensive experimental scheme and microstructural analysis were followed to discover if OPC,geopolymer,and MPC binders show similar bio-compatibility with untreated and treated plant aggregates and if treatment can be avoided in plant concrete when using any of these types of binders.Results showed that hydrophobic treatment of plant aggregate is compulsory and effective when OPC and geopolymer are used as binders to prepare PACs.However,the influence of pretreatment was negligible on the interface bonding between the MPC binder and plant aggregate,which proved inherent bio-compatibility of the MPC binder.Comparison of results between different PACs disclosed that MPC based PACs show superior physical,mechanical and microstructural properties as compared to OPC and geopolymer based PACs.Therefore,research was further extended on the MPC based PACs containing untreated plant aggregates.In the third phase,the influence of molding method,amount of binder,size and percentage of plant aggregate on the mechanical properties,thermal performance,and hygroscopic properties of MPC based PACs were studied,and the optimal mix proportions to develop new multifunctional PACs for insulation,hygrothermal and structural purpose were proposed.It was found that mechanical and hygrothermal properties of PACs are largely influenced by the mix proportions,molding methods,and high relative humidity levels.Results also showed that MPCs based PACs fulfilled the requirement to be utilized as insulation and structural grade lightweight concrete.Comparison of newly developed MPC based concrete with the previous studies also proved its superiority in term of mechanical,thermal,and hygroscopic performance.The fourth phase of research focused on the durability study of PAC.For this purpose,PAC specimens were exposed to simulated extreme weather conditions including immersion weathering,outdoor weathering,freeze-thaw,salt attack,and fungal growth.The physical and mechanical properties of PACs were evaluated.Findings showed that PAC samples undergo cross-sectional deterioration and strength degradation under extreme weather conditions,which was associated mainly due to dissolution and leaching out of the binder resulting in weaker cohesion between the binder and plant aggregate.The use of pozzolanic materials and high compression of samples during casting could restore the properties of PACs under these conditions.In the fifth phase,a new concept of using the developed PAC as capillary active materials was proposed to address moisture-related issues inside the walls.Numerical simulation of reference wall without PACs and wall containing PAC insulation layer was performed to study the feasibility of developed PACs(a)as indoor humidity regulator material and(b)its potential to eliminate the risk of mould growth and condensation issues due to moisture accumulation inside the walls.Numerical simulation was performed through the heat and moisture transfer model under the real climatic condition of hot-humid and cold regions.Findings revealed several positive aspects of using MPC based PACs as insulation material including a high reduction in heat loss,the adjustment in indoor air temperature and relative humidity through the breathable nature of PACs,improvement in drying behavior of wall,and elimination of mould growth and condensation issue observed in reference wall.In the last phase,an artificial intelligence(AI)based gene expression programming(GEP)technique is used to develop the mathematical models for the dry density,compressive strength and thermal conductivity of PAC.A large amount of widespread database was established based on the past studies and most influential parameters were identified by the several trial analyses.Proposed mathematical models showed high correlation with the experimental results.All the models passed the statistical and performance index checks showing the strong predictability,high generalization capability and accuracy of GEP-AI models.Comparison of results with the regression analysis techniques further proved the superiority of GEP-AI models.Hence,it can be concluded that MPC based PACs are promising materials and potential alternatives to traditional PACs prepared with lime and OPC binders.MPC based PACs do not only solve the numerous performance-related issues found in traditional PACs,but their applications can be further extended to address the mould growth issues and humidity regulation in the buildings.