Research On The Mechanical Characteristics Of Fiber Reinforced And Cement Stabilized Sludge

Every year in China,a substantial amount of dredged sludge are produced from water channel maintenance and marine construction.This wasted sludge is of poor engineering performance.Although attempts have been made to stabilize such material by various methods,one of the most practical ways is to reuse it through a proper treatment with cementitious material.However,such cement stabilized sludge often exhibits some defects like brittle failure or disintegration after soaking.It is difficult to meet the long-term strength and stability requirement of special structure under complex stress conditions(such as tension condition,flood soaking etc.).In order to overcome these defects,polyvinyl alcohol fiber was added into cement stabilized sludge to improve its mechanical properties.As unconfined compressive strength is a common reference index in the formula design of cement stabilized soil.How to estimate the compressive strength of this material is a pivotal problem in engineering.For ordinary cement stabilized sludge,many strength assessment formulas have been proposed.Most of these formulas stated that the compressive strength is primarily determined by water/cement ratio and curing time.However,for fiber reinforced and cement stabilized sludge,few strength assessment formulas have been proposed by integrating various influencing factors such as cement content,fiber content and curing time.In the present research,a series of unconfined compression tests were carried out on the fiber reinforced and cement solidified sludge samples with different fiber mixing ratio and cement mixing ratio under different curing times.As a result,a strength assessment model which takes water/cement ratio,fiber mixing ratio and curing time into account is established.The test results show that both the peak compressive strength and the residual strength are increased with fiber mixing ratio.The relationship between the strength and water cement ratio can be analyzed by Abrams equation,in which the parameter B is only between 1.23 and 1.24 regardless of water/cement ratio,curing time and fiber mixing ratio.The parameter A increases not only with the curing time but also with the fiber mixing ratio.It is proportional to a power function of curing time,in which the proportional coefficient M and the power N have a good linear fitting relationship with fiber content.Grasping the working state of material is important in the numerical analysis of structure.According to the actual situation,it requires the proper selection of the constitutive model.Duncan-Chang E-B constitutive model which can better reflect the nonlinear behavior of soil,is widely used in the numerical analysis of geotechnical engineering like foundation pit,dam etc.In the present research,several groups of drainage triaxial tests were carried out under different fiber mixing ratios and confining pressures.With consideration of the fiber inclusion influence,the Duncan-Chang E-B constitutive model of fiber reinforced and cement stabilized sludge is established.The results show that after the fiber is mixed in,the stress-strain curve of cement stabilized sludge exhibits hyperbolic characteristic,which is in accordance with Duncan-Chang model.Its cohesion dramatically increases with fiber mixing ratio while the friction angle almost remains unchanged.On the basis of experimental data and regression analysis method,the parameters of Duncan-Chang E-B model for fiber reinforced stabilized sludge are obtained.As the parameters of initial tangent modulus and bulk modulus grow in the form of power function with the increasing of fiber mixing ratio,the empirical formulas of the initial tangent modulus and bulk modulus with consideration of fiber mixing ratio are founded.