Experimental study on proportioning and properties of cemented filling material with a large mass ratio of construction demolition waste

Supply of cheap and abundant raw materials is a key factor in reducing the cost of cemented filling materials. To solve this problems of the high cost of cemented filling materials and insufficient sources of raw materials, an experimental study on cemented filling material with a large mass ratio of construction demolition waste was performed. A large amount of recycled aggregate of construction demolition waste was added to cemented material to prepare a high concentration slurry, from which the influences of aggregate/cement mass ratio, admixture/cement mass ratio, water/solid mass ratio, recycled aggregate gradation and mud content of recycled aggregate on slump, setting time and compressive strength of cemented filling material with a large mass ratio of construction demolition waste were analysed via the orthogonal test method and regression equation analysis. Finally, an industrial formula for cemented filling material with a large mass ratio of construction demolition waste was determined, and the mechanical and microscopic properties were analysed. The results indicate that the industrial formula with an aggregate/cement mass ratio of 3.0, an admixture/cement mass ratio of 1.5%, a water/solid mass ratio of 0.35, a recycled aggregate gradation of 40:30:15:15, a mud content of recycled aggregate of 0ཞ4% and a mass ratio of construction demolition waste to solid material of 75% exhibits the properties of rapid strength growth and high residual strength, and can be applied in underground coal mines conditions.

Optimisation Design and Damping Effect Analysis of Large Mass Ratio Tuned Mass Dampers

Under harmonic load and random stationary white noise load, the existing fitting formulas are not suitable for calculating the optimal parameters of large mass ratio tuned mass dampers (TMDs). For this reason, the optimal parameters of large mass ratio TMDs are determined by numerical optimisation methods, and a revised fitting formula is proposed herein based on a curve fitting technique. Finally, the dynamic time history analysis method is used to study the control effect of large mass ratio TMDs. The results show that when the mass ratio is large, the error between the existing fitting formula and the actual optimal value is quite large, and the revised fitting formula is applicable to the parameter design of the traditional small mass ratio and large mass ratio (≤1) TMDs. When the ratio of local base soil predominant frequency to structure vibration frequency is greater than 4, the optimal parameters of a TMD under white noise excitation can be calculated according to the revised fitting formula, and the remaining conditions should be determined by numerical optimisation. In addition, a large mass ratio TMD reduces the dynamic response of the main structure effectively compared with a small mass ratio TMD and reduces the relative displacement between the TMD and main structure.