Influence Of Microcapsules On The Properties Of High-performance And Multi-function Concrete

To build a resource-saving and environmentally friendly society,the development of high-performance and multi-function concrete?HP-MFC?has become a hot topic and significant tendency in the modern manufacture of concrete,at the mean while,it is also an important measure to solve problems related on shortage of resource,environmental crisis,and energy conservation and emission reduction.Compared to normal concrete,HP-MFC has a much high mechanical properties and durability with functions of energy storage,antimycotic and antifungal,self-healing,high durability,etc,.During the manufacture of HP-MFC,admixtures are added to mix and cast HP-MFC together with cement and aggregates.However,side effects are induced by this direct mixing method.To overcome the side effects between admixtures and concrete matrix,microencapsulation has been regarded as a promising technology to isolate the interaction of admixtures and concrete matrix by microencapsulating admixtures into micro containers.In such a way,the side effects are avoided and the admixtures can be controllably released or triggered,thus,enhancing the properties of HP-MFC.By now,a lot of microcapsules have been developed by the physical or chemical methods,or porous materials,cincluding light-weight aggregates.However,the preparation of these containers is high cost and complex,and these containers have a much low stiffness and mechanical properties,as well as disadvantages of complicated void structure,low loading capacity,and uncontrollable release of admixtures,thus,the development of HP-MFC is limited.To promote the development and application of HP-MFC,this paper has manufactured two micro containers that perforated cenospheres and vaterite,and the following contents were studied.The method to manufacture and select perforated cenospheres based on etching by fluoric acid has been proposed,and the physical,chemical and geometrical properties of perforated cenospheres were studied by SEM,XRD,XRF,BET and LPSA.The cylinder compressive strength and densities of cenospheres and perforated cenospheres were tested.Results showed that cenospheres are commonly closed particles with single cavity,which accounts for about 51.2%of the total volume of the particle.They are mainly chemically composited by SiO₂ and Al₂O₃.Mulite,quartz and amorphous SiO₂ are the major crystals of cenospheres.The proposed method for etching and selecting perforated cenospheres is very simple,needs less equipments,and.has promising application in a large scale with extensive suitability for a variety of different cenospheres.Additionally,it has been found that the size of cenospheres plays an important role in the cylinder compressive strength and densities,both of which increase as the size of cenospheres decrease.High strength concrete has been internally cured by encapsulation of saturated perforated cenospheres.The absorption and desorption properties of saturated perforated cenospheres were investigated,and the influence of the addition of saturated perforated cenospheres on the early-age autogenous shrinkage,compressive strength,microstructure,and Cl-resistance ability of high strength concrete were studied,respectively.It was found that perforated cenospheres are excellent internal curing agents with simple structure,well-distributed voids,and much high water absorption of 120%,which is much high than the traditional internal curing agents.The incorporation of saturated perforated cenospheres in high strength concrete can effectively mitigate the self-disscation and the autogenous shrinkage.The more the incorporation of saturated perforated cenospheres in high strength concrete,the more the reduction of autogenous shrinkage,however,the 28d compressive strength was slight influenced.Since perforated cenospheres have a high mechanical strength and stiffness,they worked excellently in the microstructure of high strength concrete in a well-distributed system with good survival ability.The interface between perforated cenospheres and the surrounding cement paste is very dense.During the curing process by saturated perforated cenospheres,the hydration of unreacted cement particles was further promoted by the released internal curing water within the saturated perforated cenospheres,which eventually contributed to a denser microstructure and high Cl-resistance ability.Paraffin-based phase change microencapsulution has been fabricated with perforated cenospheres as the the container and cement paste as the coating material.The phase change behaviors of the microencapsulution were studied and the influence of incorporation of the microencapsulution in mortar on the energy storage and compressive strength were investigated.Results showed that the proposed "Four step fabrication method" for fabricating microencapsulution is very simple,and can avoid the leakage of liquid paraffin.The latent heat of this microencapsulution is about 8.135 J/g with phase change temperature of 26.25?,which is comfortable for human beings.The incorporation of this microencapsulution in mortar can effectively reduce the hydration temperature of cement and retard the happening time of the highest hydration temperature.Importantly,the compressive strength of mortar was not significantly affected.We proposed a refined C0₂ bubbling method to synthesize vaterite with high purity.The influence of final pH value of the reaction solution and CO₂ flow rates on the purity and productivity of vaterite were investigated,and the optimal synthesis condition was determined.SEM and FETEM were conducted to study the microstructure of vaterite synthesized at the optimal condition,and the influence of different relative humid environments on the crystal form of vaterite were investigated.Results showed that the a higher final pH value and CO₂ flow rate favor the formation of vaterit with high purity.When the CO₂ flow rate was 11 1/min and the final pH value was higher than 8.6,the purity of synthesized vaterite was more than 90%.Combing the results of the purity andproductivity of vaterite,the optimal synthesis condition of vaterite was determined as that CO₂ flow rate of 11 1/min and final pH value of 8.6.The proposed refined bubbling method is simple,time-saving,and cost-effective,and has the potential to enable large-scale applications of vaterite.In addition,the SEM and FETEM images of the synthesized vaterite at the optimal condition stressed the advantage of this method to prepare excellent CO₂ bubble template for producing hollow or porous vaterite particles.The successful conservation of vaterite is very sensitive to moist,it transforms into calcite gradually depending on the moist content.To avoid the metamorphism of vaterite for the potential large-scale applications,it's suggested to store vaterite without moist,N₂-protected packing may be an available approach.This study proposes a new low-cost method to integrate value-added vaterite production and CO₂ sequestration into chemical processing of RCAs for better performance in concrete.The addition of ethanol can not only prohibit the phase transformation of vaterite,but also suppress the ionization of acetic acid,leading to more vaterite produced.Experimental study confirmed that almost pure vaterite can be produced from waste solution by adding only 20%ethanol into it through CO₂ bubbling method.This new method can bring many environmental and economic benefits.It not only turns the hazardous waste solution into value-added vaterite and regenerate acid for RCAs treatment,but also permanently store CO₂ in the produced minerals.It has been estimated that 1 kg RCAs used in this study can produce 76.6 g vaterite,and store 33.7 g CO₂.One potential value-added application of the produced vaterite has also been demonstrated,which suggests that vaterite produced from the waste solution can be used as an internal curing agent for high performance concrete.