Study On Performance Of Cement-Based Materials With Seawater And Sea-Sand

With the rapid development of urban construction all over the world,concrete structures are widely used.As the main raw materials of concrete,the annual consumption of river sand and fresh water reaches billions of tons,causing many serious problems,such as the shortages of river sand and fresh water,breaching of dyke and instability of river bed.At then same time,due to the reduction in land resources for development,the trend of reclamation of coastal cities and construction of island cities has intensified.For the purpose of protecting freshwater and river sand,as well as launching marine engineering,people gradually turned their attentions to the vast marine resources and try to use the adundant marine water resource and sea-sand resource to make cement-based materials.Because using seawater and sea-sand to produce cement-based materials can bring significant economic benefits and environmental protection value,as well as solve the problems,such as the difficulty of material transportation during the construction of islands.The application of the marine material has been extensively studied.However,most scholars use self-made seawater and desalinated sea-sand for experimental research.At present,research on the application of intact seawater and sea-sand to make cement-based materials is still very scarce.In view of the above research background,this research project used intact seawater(SW),tap water(TW),river-sand(RS),continental shelf sea-sand(SS)and coral-sand(CS)(sea-sand contains continental shelf sea-sand and coral-sand in this abstract)as raw materials.A total of 2 groups of cement paste with fixed water/cement(W/C)ratio,6groups of mortar with fixed W/C ratio,and 54 groups of mortar with different W/C ratio were designed for the tests of mini slump cone,cube strength,mercury intrusion porosimetry(MIP),SEM analysis,XRD analysis,fresh properties and dry shrinkage etc.The main research work and conclusions covered in this thesis are as follow:(1)In order to study the effect of seawater on the strength,microstructure and hydration productions of hydrated Portland cement paste.Two groups of fresh water paste and seawater paste with fixed W/C ratio were made for carrying out the mini slump cone test,cube strength test,MIP test,SEM test and XRD test.The results show thatseawater would reduce the workability of Portland cement paste,but increase the strength of paste,reduces the porosity of the hydrated cement and improve the compactness of the hardened paste.Meanwhile,a new hydration product,called Friedel's salt,has been found in the seawater cement paste.(2)To study the effects of seawater and/or sea-sand on the strength and durability of cement-based materials,a batch of seawater and/or sea sand mortar with fixed W/C ratio were prepared for the tests of mini slump cone,cube strength,MIP,SEM,XRD and dry shrinkage.The results are presented as followed.The early strength of the mortar made with seawater and sea-sand is higher than that of the mortar made with fresh water and river sand.However,as the age increased,the strength of SS mortar and RS mortar tended to be closed,but the strength of CS mortar was relatively low due to defects in coral sand.Generally,the strength of mortars made with seawater is higher than that made with tap water.The dry shrinkage strain of SW mortars are higher than that of TW mortar.By using the same water,the dry shrinkage strains of mortar with different aggregates are in the order of CS mortar> SS mortar> RS mortar.In terms of microstructure,the pore structure of SW mortar is better than that of TW mortar,leading to higher compactness of hardended mortar.By using the same water,the use of SS and CS effectively reduces the peak pore size of mortar and improve the pore structure in the case of TW mortar,but in SW mortar,the pore structure of three different aggregates is similar.The interface between river sand,coral sand and cement paste is better than that between sea sand and cement paste,but coral sand was easier to crack under pressure.Meanwhile,a new hydration product called Friedel's salt was found in the mortar contaning seawater,sea sand or coral sand.(3)Investigate the effects of W/C ratio,water types,aggregate types on the fresh properties and cube strength of mortar by carrying out mini slump-flow test,mini V funnel test,sieve segregation test,stone rod adhesion test and cube strength test.The findings indicates that with the increase of W/C ratio,the static flowability and dynamic flowability of mortars increased,while the cohesiveness decreased,and the adhesiveness increased first and then decreased.The use of seawater in mortar caused the decrease in static flowability and dynamic flowability of mortars,but improvement in thecohesiveness and the andhesiveness.By using the same water,SS mortar's static flowability and dynamic flowability were lower than that of RS mortar,whereas the cohesiveness and the adhesiveness of SS mortar were higher.The CS mortar's static and dynamic flowability and adhesiveness were lower than that of RS mortar,whereas the cohesiveness of CS mortar was higher than that of RS.Overall,the influence degree of each parameters on the fresh properites of mortar are in the order of W/C ratio> water types> aggregate types.On the other hand,the cube strength of mortars increased first,and then decreased with the increase of W/C ratio.SW mortar has lower strength due to low workability at low W/C ratio,but higher strength at high W/C ratio than that of TW water.By using the same water,the strength of mortars with different aggregates are in order of RS mortar> SS mortar> CS mortar at low W/C,but the strength of mortars with different aggregates are in order of SS mortar> RS mortar>CS mortar at high W/C.(4)By measuring the packing density of mortar mix under wet packing test,the effects of seawater and sea-sand on the packing density,total solid spcific surface area of mortar were investigated.Meanwhlie,the water film thickness(WFT)of mortar was calculated,and then,the combined effects of WFT on fresh properties of seawater and/or sea-sand mortar were evaluated by using regression analysis.The results demonstrates that the use of seawater and sea-sand in mortar caused the decrease of packing density.With the increase of W/C ratio,the WFT increased;whereas with the use of seawater and sea-sand,the WFT of fresh mortar decreased.Based on the numerical modelling,the combined effects of WFT,seawater and sea-sand on fresh properties of mortar were quantitatified,it has been proved that the WFT,water types and aggregate types are the key factors affecting the fresh properties of seawater and/or sea-sand mortar.