Improved designed method of pervious concrete based on optimal volume ratio of paste to aggregate

An improved design method of pervious concrete was proposed to lower the deviation between the designed and actual porosity and maintain both mechanical property and permeability of pervious concrete. The improved design method is mainly based on the optimal volume ratio of paste to aggregate(VRPA), which was determined by testing the average thickness of cement paste coating aggregate. The performances of pervious concrete designed by the traditional method and the improved one were compared. The results show that with the increase of designed porosity, the reduction of compressive strength and flexural strength of pervious concrete designed by the improved method is significantly smaller than those designed by the traditional one. The maximum deviation between the designed and actual porosity of the pervious concrete by the improved method is only 1.54%, which is far less than 8.7% obtained by the traditional one. Micro-structural analysis shows that the porous distribution of pervious concrete designed by improved method exhibits better uniformity.

AN EXTENDED AGGREGATED RATIO ANALYSIS IN DEA

Data Envelopment Analysis（DEA） and Ratio Analysis（RA） are two widely used methods for measuring units＇ productivity and any other criteria that could be assessed based on the available input and output variables.A number of researchers have studied DEA and RA and noted the positive and negative differences between them.Aggregated ratio analysis（ARA） model,which provide an important linkage between DEA and RA theory,is equivalent to the CCR DEA model,and this equivalence property offers a great deal of opportunities for DEA to be interpreted and applied in different ways.This paper extends the results of ARA model and proposes an extended aggregated ratio analysis（EARA） model,similar as the development from CCR model to BCC model in DEA context.The proposed model can offer an insight into the characteristic of returns to scale,playing the corresponding role as BCC model does.The numerical example is revisited in the paper and the results are compared.

Stress-strain relationship of recycled self-compacting concrete filled steel tubular column subjected to eccentric compression

As a typical compression member,the concrete-filled steel tube has been widely used in civil engineering structures.However,little research on recycled self-compacting concrete flled circular steel tubular(RSCCFCST)columns subjected to eccentric load was reported.In this study,21 specimens were designed and experimental studies on the stress-strain relationship of were carried out to study the mechanical behaviors.Recycled coarse aggregate replacement ratio,concrete strength grade,length to diameter ratio and eccentric distance of specimens were considered as the main experimental parameters to carry out eccentric compression tests.The corresponding stress-strain relationship curves were used to analyze the influence of concerned parameters on ecentric load-bearing capacity of RSCCFCST columns.The experimental results show that the strain of the eccentric compression stress-strain curves increase with the increase of recycled coarse aggregate replacement ratio and concrete strength grade.With increase of eccentric distance,the ductility of specimens increases while the bearing capacity decreases.Moreover,a phenomenological model of RSCCFCST columns is proposed,which exhibits versatile ability to capture the process during loading.The present study is expected to further understanding the behaviors and to provide guidance of RSCCFCST columns in design and engineering applications.