The Survey On The Current Situation Of Construction Wastes In Guangzhou And Investigation On The Preparation Of Recycled Concrete Small Hollow Blocks

The amount of construction wastes is huge and increases every year,and the traditional landfill treatment has many disadvantages,e.g.environment pollution,land occupation and potential safety hazards.Therefore,the recycling of construction wastes is increasingly attracted people’s attention.Meanwhile,because of the various strength grade and design structure,the demand of normal concrete small-size hollow blocks contitiously increased to meet the requirements of thermal insulation and energy conservation building material.The requirements of raw materials for concrete small-size hollow blocks is very low,thus a large amount of construction wastes can be utilized.Therefore,the survey on the current situation of construction wastes in Guangzhou and investigation on using research construction wastes to prepare recycled concrete small hollow blocks have an important application value.Firstly,on the basis of the survey on the current situation of construction wastes in Guangzhou(including saparation and collection,disposal patterns,transportation management,processing and treatment,recycling and aoolication etc.),suggestions and requirements for the industrial project layout,construction requirement,production process and equipment,recycled products and etc.of construction wastes.The estimated amount of construction wastes annually increased in the last ten years(especially the increase degree was very high in the recent few years due to the “Three Old Transformation”)and exceeded 33 million tons in 2014.The construction wastes from demolition processes the highest proportion in construction wastes,ranging from 60% to 66%.The constituent of construction wastes from demolition mainly contains waste concrete,waste brick and waste mortar.Therefore,the investigations on the recycling and application of construction wastes should be focused on waste concrete,waste brick and waste mortar in Guangzhou.Second,the properties of recycled aggregates from different sources and treatment process were investigated.The results show that the performance of recycled aggregates presented the following orders: recycled aggregates based on waste concrete had best performance,recycled aggregates based on waste bricks had worst performance;recycled aggregates from roadway had best performance,recycled aggregates from industrial architecture had better performance,recycled aggregates from dwellings of village in city had worst performance;recycled aggregates crushed by abroad mobile impact crusher had best performance,recycled aggregates domestic mobile impact crusher had better performance,recycled aggregates crushed by domestic settled jaw crusher had worst performance.Compared to natural aggregates,the apparent density of recycled aggregates reduced by 140~660 kg/m3,water absorption increased by 5.9%~14.3%,and crush index was in the range of 16% to 30%.According to the classification in national standard “Recycled Coarse Aggregates for Concrete”,for the recycled aggregates prepared in this study,the apparent density and water absorption belonged to grade Ⅲ or didn’t meet the requirement,and crush index belonged to grade Ⅱ or grade Ⅲ.Third,the mixture proportion and performance of recycled concrete based on recycled aggregates and total utilization of construction wastes were investigated,and the mechanism related to the influence of recycled aggregates on the recycled concrete was discussed.On the basis of free water cement ratio,the mixing water was designed by introducing the additional absorbed water due to the high water absorption ability of recycled aggregates.On the basis of close packing principle,natural aggregates were partially replaced by recycled aggregates by equal volume rather than equal quality.When recycled aggregates based on waste bricks were used,the strength of recycled concrete linearly decreased by the dosage of the recycled aggregates.The strength of C25 recycled concrete didn’t decrease when the mixing amount of recycled aggregates based on waste concrete was lower than 50 %,and the strength of C40 recycled concrete didn’t decrease when the mixing amount of recycled aggregates based on waste concrete was lower than 30 %.The strength reduction degree of recycled concrete with total utilization of construction wastes was larger.Compared to the recycled concrete with recycled aggregates,and the strength was significantly increased by a good gradation of recycled materials.The main reason for the reduced compressive strength of recycled concrete was the increased interfacial transition zone thickness,porosity and average pore size.The interfacial transition zone thickness was about 70μm in normal concrete,90μm in recycled concrete with 100 % recycled aggregates based on waste concrete,and 100μm in recycled concrete with 100 % recycled aggregates based on waste bricks,respectively.The porosity of recycled concrete increased by 120 %,and average pore diameter increased by one time.Finally,recycled concrete small hollow blocks were tentatively produced in factory and their performance was investigated.The results show that MU10.0 recycled concrete small hollow blocks can be prepared by using 70% recycled aggregates based on waste concrete,30% recycled aggregates based on waste bricks,or 50% mixing aggregates based on waste bricksconcrete;the performance of MU15.0 recycled concrete small hollow blocks prepared by 50% mixing aggregates based on waste bricks-concrete conformed to the requirement of national standard.In particular,the performance of recycled concrete small hollow blocks prepared by recycled coarse aggregates,recycled fine aggregates and recycled powders as raw material met the requirements of strength grade MU7.5.Therefore,the construction wastes can be 100 % used to produce one type of recycled building materials.