| Recycled concrete is a kind of green building material.With the need of environment and sustainable development,recycled concrete has received considerable attention.Many scholars,at home or abroad, make a lot of experimental researches on it,and have made certain theoretical achievement.But, researches of recycled aggregate mainly focus on waste concrete and waste brick,it isn't conform to the situation in our country.In beginning of 1990,the production of ceramic in china ranks first in the world. China's annual output of the waste ceramic that produced during ceramic production approximates to over 10 million tons.In addition,there are countless waste ceramic that produced during the demolition and decoration of the building and daily life.The reuse of the waste ceramic as new building materials is beneficial to a coordinated development of resources and environment.At present,there is a little literature about the waste ceramic used as aggregate to produce recycled aggregate concrete.In this situation,this paper,considers the situation that china has rich resources of ultra fine sand,but it hasn't been widely used,combines these two resources,discusses the influence to the basic properties of the recycled mortar and recycled concrete,Aiming at exploring the scientific method of utilizing those two kinds of resources. The main contents of this paper are introduced as follows.Firstly,the basic properties of materials are tested and find that recycled aggregate (produced by ceramic) differs from nature aggregate in the following points:One is that the grain type is different.The grain type of nature aggregate is usually slippery,yet recycled aggregate (produced by ceramic) is angular because of the production process;The other different is the water absorption rate.Nature aggregate is compact and has smaller water absorption rate.Yet recycled aggregate (produced by ceramic) has larger water absorption rate because of plenty of pores.Based on those points and the requirement of economy,combined the characteristics of ultra fine sand , enhancing strong points and avoiding weaknesses,the basic thought of crushing ceramic into coarse sand and using it to replace part of ultra fine sand is determined.Secondly,the suitable proportion of the coarse sand (produced by ceramic) replacing ultra fine sand is discussed by a variety of methods.That lays the groundwork for further study.Thirdly,two aspects of research are carried out in revealing the effect of recycled aggregate (produced by ceramic).One is that revealing the behavioral trait of recycled aggregate (produced by ceramic) by experimental study on same quantity of water.The results indicate:The angular grain type of recycled aggregate (produced by ceramic) is beneficial to the bite between aggregate and harden cement paste.The high water absorption rate of recycled aggregate (produced by ceramic) can improve effectively the properties of Interfacial Transition Zone (ITZ).Those have positive effect on improving strength. Another is that exploring the scientific method of utilizing recycled aggregate (produced by ceramic) by experimental study on same consistency.The recycled aggregate's shortcoming of high water demand is exposed during the study.That would increase W/B ratio to a large extent and cause a greater depression of strength.And it plays a much larger role than its positive role.However,the drawback of recycled aggregate (produced by ceramic) was improved markedly by mixing recycled aggregate (produced by ceramic) with ultra fine sand at proper ratios.Based on those researches,a better way of scientific utilizing recycled aggregate (produced by ceramic) was explored.Fourthly,based on orthogonal test,the factors influencing the workability,mechanical properties and shrinkage of the mortar,such as the recycled aggregate replacement ratio,the water-binder ratio and the fly ash replacement ratio,were investigated.The optimum conditions determined by orthogonal experiments were received.The results indicate:W/B ratio and the recycled aggregate replacement ratio are main factors which influence the properties of recycled mortar.The increasing of the fly ash replacement ratio may worsen the compression strength and tension strength of the mortar.Thus,according to the design required strength class,the fly ash replacement ratio should be determined by the design of mixed proportion of mortar.So it can reach the purpose of save energy and reuse the waste and satisfy the project request at the same time.Considered from the effects of factors on the compression strength , W/B ratio is disadvantageous to it but the effects of the recycled aggregate replacement ratio is entirely different,and the effects of W/B ratio is greater than the effects of the recycled aggregate replacement ratio.Yet,the increase of the recycled aggregate replacement ratio could increase mix water of mortar.Thus,good flow property has larger W/B ratio demands.So,to the project which request high compression strength,the recycled aggregate replacement ratio should not be too large.But the two key factors affect the flexural strength in a reverse manner.So,to the project which request high flexural strength,the recycled aggregate replacement ratio may be increased properly.That benefits the increase of mortar tenacity and the reducing of mortar crack.Finally,the effects of replacement ratio of recycled aggregate (produced by ceramic) and W/C ratio on the performance of recycled concrete are investigated by experimental study.The results indicate:With the increasing of replacement ratio of recycled aggregate (produced by ceramic),the apparent density of recycled concrete is reduced regularly.And it is lower than the apparent density of ordinary concrete.Using the methods of mixture design based on free W/C ratio,the flowability of recycled concrete is basically consistent to the flowability of ordinary concrete.Moreover,it has good retention performance and cohesiveness.The failure model and process of cubic compressive test and the splitting tensile test is similar to that of ordinary concrete.The failure surface basically comes into being between aggregate and harden cement paste.And it bellows to bonding damage.The cubic compressive strength of recycled concrete is greater than that of ordinary concrete.The using of recycled aggregate (produced by ceramic) is favorable to improve the cubic compressive strength and the splitting tensile strength.Law of W/C ratio influence on the cubic compressive strength of recycled concrete is similar to that of ordinary concrete.That is,the relation of C/W ratio and cubic compressive strength shows a good linear relationship.But the regression coefficient obtained from experiment data is different from that of ordinary concrete.Specification for mix proportion design of ordinary concrete can't be used directly for mix proportion design of recycled concrete made by recycled ceramic aggregate.The researches in the paper would provide important reference for the application of waste ceramic in recycled concrete and the effective utilization of ultra fine sand resources. |
