Effect Of The Recycled Powder On Cement Hydration And Concrete Performance

Using demolished concrete or clay bricks to produce recycled aggregate is an effective way to make use of recycle construction waste.However,a large amount of fine powder was generated during the production of aggregate.These fine powder need to be sieved out,otherwise,the performance of aggregate would be affected,and the powder abandoned could easily cause dust pollution.The above powder was used to prepare recycled concrete powder and recycled brick powder(general designation:the recycled powder).Based on the measurement of the basic properties of the recycled powder such as particle size distribution and chemical composition,it is used as an admixture to replace cement in concrete,in order to provide a new way for the utilization of construction waste.The main work and achievements are as follows:1.The fluidity and strength of the cement mortar and the activity index of the recycled powder were obtained through the cement mortar test.The results show that the fluidity of the mortar decreases with the increase of the amount of the recycled powder.When the amount of recycled concrete powder is not more than 10%or the amount of recycled brick powder is not more than 15%,the compressive strength of the mortar in each age group is lower than the benchmark group.The 28d activity index of recycled concrete powder and recycled brick powder is 72%and 78%respectively.2.In this study,The effect of the recycled powder on cement hydration property was investigated,and the hydration heat,hydration products and chemical bound water was measured by microcalorimeter,X-ray diffractometer and high temperature glow method,respectively.It is found that the recycled concrete powder increases the heat release rate in early age,and the appearance time of the second exothermic peak is advanced by 1.8h-3.3h.However,when the replacement percentage of the recycled brick powder is less than 10%,there is no obvious effect on the rate of heat release,and the rate of heat release reduces when the content is more than 10%,while the recycled brick powder has no effect on the second exothermic peak.Both kinds of powder can reduce the amount of heat released by hydration and the amount of chemically combined water in 72 hours,but the crystal type of cement hydration products doesn't change.3.18 groups of concrete mix ratios were designed to study various factors on the concrete for 7d.?28d and 56d compressive strength,considering recycled concrete powder or recycled brick powder(10%,15%,20%,30%);composite powder mixed with recycled concrete powder and brick powder(20%of total,ratio 7:3,5:5,3:7);composite powder mixed with recycled concrete powder or recycled brick powder with slag(20%,30%,40%of total,ratio 1:1).The results show that the compressive strength of concrete decreases gradually with the addition of recycled concrete powder or composite powder mixed recycled concrete powder with slag,When the replacement percentage of single the recycled powder was less than 15%and 30%of the composite powder,compressive strength at all ages is less different from ordinary concrete.When the recycled concrete powder and recycled brick powder are mixed,the best mix ratio of the concrete compressive strength is 3:7,and the blend ratio of 7:3 follows.4.The microscopic pore structure of concrete was measured by the mercury porosimeter,and the correlation between the microscopic pore structure and the compressive strength of the concrete was investigated through the grey correlation theory.It is found that the pore size distrubution at 20-100 nm and average pore size in 28d concrete are more related to the 28d compressive strength of the concrete.5.This paper studied the carbonation resistance performance of recycled power concrete with the accelerated carbonation experiment,and established the functional relationship between carbonization depth and carbonization time of concrete.The results show that the depth of carbonation of the concrete after single-doped and mixed-doping is less than 10mm,and the concrete anti-carbonation performance grade is T-IV except the addition to 30%of recycled power concrete.Carbonization depth and carbonization time of recycled powder concrete coincide with X=aTb function.