Effects Of Clay Brick Aggregate And Fine Powder On Early Shrinkage And Mechanical Properties Of Cement-Based Materials

With the advancement of urbanization,a large amount of construction waste has become an urgent problem to be solved,and if corresponding measures are not taken,it will cause serious harm to our living environment.At present,promoting the resource utilization of construction waste has become an urgent requirement for realizing ecological civilization in Chinese path to modernization,and it is of great practical significance to recycle and process it into different types of recycled materials and apply them to cement-based materials.However,China has not formed a systematic and comprehensive resource utilization system.In this paper,the recycled cement-based materials were prepared by dividing the clay brick particles into recycled brick powder,recycled brick slag and recycled bricks according to the particle size,mainly exploring the effects of alternative raw materials of clay bricks in different particle size ranges on the early shrinkage deformation,working performance and mechanical properties of cement-based materials,and explaining the effect of water absorption and discharge of clay brick particles of different particle sizes on macroscopic performance from a microscopic perspective in combination with the determination of capillary negative pressure.Compared with the different prewetting times of bricks,the changes of microstructure in the transition zone of the interface of recycled concrete were studied,which provided a theoretical basis and technical support for the rational utilization of clay brick particles in the full particle size range.After systematic experimental analysis,the main research contents and conclusions are as follows:(1)Brick powder of different particle sizes was mixed into cement slurry,and the influence of brick powder particle size and dosage on the performance of cement slurry was explored.It is found that the incorporation of brick powder will reduce the flow performance of cement slurry,the larger the particle size,the greater the impact on the fluidity,in general,when the dosage reaches more than 15%,it will significantly affect the working performance and reduce the strength of the slurry sample.In order to ensure the quality of the subsequent test,combined with the rheological constitutive parameters,the brick powder content of the subsequent cement mortar test was determined to be 10%.(2)Brick powder and brick slag were mixed into cement mortar to explore their influence on mortar performance.It is found that brick particles will have a negative impact on the working performance of cement mortar,reduce the fluidity of mortar,and increase the time-dependent loss rate of fluidity.The negative pressure accumulation rate of the capillary tube in the early stage of brick cement mortar is faster,but the negative pressure peak is smaller than that of ordinary cement mortar,indicating that the matrix is more prone to early shrinkage cracks.The incorporation of brick powder can reduce the shrinkage rate of cement mortar in the early age,and with the increase of fineness,the shrinkage rate decreases more;After brick slag is mixed into cement mortar as fine aggregate,the shrinkage rate increases linearly with the increase of its content.(3)By optimizing and comparing the properties of double-doped cement mortar prepared by brick powder and brick slag,it is found that brick slag replaces natural sand in a ratio of20%～30%,and brick powder replaces cement in a ratio of 10% to prepare double-doped cement mortar,and the mechanical properties are close to that of ordinary cement mortar,and the shrinkage rate and water absorption coefficient in early age are lower than those of ordinary mortar.(4)The early and physical mechanical properties of recycled brick concrete were studied by replacing coarse aggregate with different proportions after saturated brick treatment.It is found that the saturated bricks will slow down the agglomeration rate of negative pressure of concrete capillaries,delay the cracking time of recycled concrete,and reduce the shrinkage rate of recycled concrete at early age.Compared with ordinary concrete,recycled concrete has a smaller modulus of elasticity,a slightly higher Poisson’s ratio,and significantly reduced strength,but it can still meet the requirements of compressive strength of concrete with strength grade C30.(5)The effects of different brick pre-wetting time on working performance,early age shrinkage and microstructure of the interface region were compared,and it was found that the longer the pre-wetting time,the greater the porosity of the interface area.The shrinkage curve of the pre-wet 0.5h test group changed moderately,which could effectively inhibit the shrinkage of recycled concrete at early age,and the working performance of the mixture was closest to that of ordinary concrete;the working performance of the pre-wet 0.1h and water-saturated bricks would reduce the working performance of the mixture,and the ability to reduce the risk of cracking and shrinkage in the early age period was slightly weaker.Considering comprehensively,it is recommended to set the brick pre-wetting treatment time to 0.5h in practical applications.