Method For Early Prediction Of Strength Of Cement Solidified Mud

Large volumes of mud are produced annually from the projects of water environment management,navigation channel maintenance and port construction in China.This kind of mud has poor engineering properties and is of very low direct utilization value.Disposal of large volumes of unwanted mud into dumping sites tends to occupy very large area of land and may even produce secondary pollution.One rational solution is to solidify the mud by adding cement and utilize the cement solidified mud(referred to as CSM from hereon)as filling material of filling projects such as embankment construction and land reclamation.When CSM is used as filling material,the strength characteristics are very important.At present,post-construction strength inspection(i.e.,coring at the end of construction and measuring strength of core samples)is commonly used as the quality assurance measure in practice.However,it is not suitable for early quality control of CSM filling construction at high speed.Inspired by the early quality control technology of concrete,this thesis aims to study the strength development behavior of CSM at various curing temperatures and propose a method for early prediction of CSM strength,which can be used for early quality control of CSM filling construction.First,the strength characteristics of CSM at various curing temperatures are studied by laboratory vane shear tests(VSTs)and unconfined compression tests(UCTs).The results show that there is a setting stage in the beginning of CSM curing,followed by a hardening stage.The strength development of CSM remains almost stagnant in the setting stage but accelerates significantly after entering the hardening stage.A higher curing temperature is able to shorten the duration of the setting stage and enhance the development rate of CSM strength.Moreover,the"cross-over"phenomenon(i.e.,strength development curves at various curing temperatures intersecting with each other),which is commonly observed in concrete or mortar,does not appear in CSM;and a higher ultimate strength will be produced at a higher curing temperature.This is mainly related to the pozzolanic reactions in CSM.Second,on the basis of strength development characteristics of CSM,the hyperbolic function is selected as the characterization model of CSM strength development at standard curing temperature.Comparison results indicate that the hyperbolic model is in good agreement with the experimental data for the entire CSM strength development at the standard curing temperature.By introducing two parameters related to temperature,namely time factor and strength factor,the fundamental relation amongst the strength development curves of CSM at different curing temperatures is studied,and an innovative model is proposed to characterize CSM strength development in the entire curing period at various curing temperatures.This innovative model is able to account for both the effect of curing age and the effect of curing temperature.By using this characterization model to fit the measured strength data at various curing temperatures and curing ages,it is found that the two empirical parameters contained in the innovative model,namely time factor _T??and strength factor _T??,are dependant on the types of cement and mud,but regardless of the mix proportion(such as cement content and moisture content)of CSM.In conjunction with the innovative model proposed for CSM strength characterization and the maturity method for early prediction of concrete strength,this thesis also develops a new method for early prediction of CSM strength and provides the implementation procedure for this early prediction method in practice.This early prediction method is able to forecast the late-age(?28 d)strength of CSM cured under normal temperature by the use of the early-age(?3d)strength data of CSM cured under a high curing temperature.Verification results demonstrate that the proposed method for early prediction of CSM strength is generally of satisfactory accuracy(relative erroer is usually samller than 20%),and can be utilized as the early quality control measure for large-scale CSM filling construction.