Study On Temperature Rise Of Hydration And Impermeability Of Concrete Made Of Demolished Concrete Lumps And Fresh Concrete

To simplify the recycling process of waste concrete,the authors'research group put forward the idea of directly mixing large-scale demolished concrete lumps?DCLs?with the fresh concrete?FC?in new cast structural member.Since then,a series of experiments was carried out to investigate the mechanical and durable properties of the compound concrete made of DCLs and FC,as well as the disaster resistance performance of structural members containing DCLs.In order to better understand this new type of concrete,this paper conducted experimental studies and numerical analysis focused on the hydration temperature rise and impermeability of the compound concrete.The following work was done in this thesis:1.Twelve 300 mm edge-size cubes and four 1000mm edge-size cubes were fabricated.The test parameters include the replacement ratio of DCLs?0³0%?.The interior temperature was measured at the beginning 168 hours of the hydration process of these specimens.Additionally,the compressive strength of the cubes was tested at the ages of 2 days,7 days,14days and 28 days.It is found that:?1?when the dimension of the specimen maintains,the maximum hydration temperature and the heating rate decrease gradually as the replacement rate of DCLs increases;?2?the replacement rate of DCLs has minor influence on the time spend by the specimen reaching the highest hydration temperature;?3?The predicted combined compressive strength given by the previous linear formula agrees well with the test strength for the 300 mm cubic samples with the age large than 7 days;?4?The compressive strength of specimen made of compound concrete with a replacement ratio of 30%is,respectively,24.6%and 12.4%larger than its counterpart FC specimens when the age is 2 days and 7 days,respectively.This implies the additional of the DCLs can significantly improve the early mechanical properties.2.Numerical simulation concentrated on the hydration process of specimens made of compound concrete was carried out based on the finite element software ABAQUS/Standard.The numerical results were compared with the test data presented in chapter 2.Additionally,the effects of the replacement ratio of DCLs and the horizontal spacing of cooling water pipes on the temperature rise of massive concrete were investigated.It is found that:?1?with the same horizontal spacing of the cooling water pipes,both the maximum temperature and the maximum temperature difference between the inside and outside of the mass concrete decrease gradually as the replacement rate of the DCLs increases;?2?when the replacement rate of DCLs maintains,the maximum temperature and the maximum temperature difference between inside and outside of mass concrete specimens will increase gradually with the increasing of the horizontal spacing of the cooling water pipes;furthermore the effect of cooling water pipes will not be effective when the horizontal distance exceeds 2m;?3?as the massive concrete,when the replacement rate of DCLs is 35%,cooling water pipes cannot be laid;when the replacement ratio are 30%,25%,and 20%,the maximum allowable horizontal spacing of cooling water pipes can be increased by 100%,50%and 25%respectively when the replacement rate is 0.3.Taking the replacement rate of DCLs as the main parameter,the impermeability tests of24 standard specimens were carried out,and the influence of the replacement ratio on the seepage behavior of the specimens was analyzed.It is found that:?1?with the increasing of the replacement ratio of the DCLs,the seepage height and relative seepage coefficient of specimens made of DCLs and FC increases gradually.The seepage heights corresponding to replacement ratios of 25%,30%,and 35%increased by 2.2%,8.9%,and 12.0%,respectively,when the substitution ratio is 0;?2?when the replacement ratio is 25%,the impermeability mark of concrete made of DCLs and FC is the same as that of the FC?both S6?,and when the substitution ratio is 30%and 35%,the impermeability mark is reduced to S₄.?3?it is suggested that the replacement rate should not exceed 25%for practical projects with anti-seepage requirements.