Frictional behaviour of segmental retaining wall units infilled with recycled concrete aggregate
The use of segmental retaining wall units as the facing column for mechanically stabilized earth (MSE) retaining walls has increased noticeably all over the world. Hollow and solid, both types of modular block units are used in dry-stacked facing columns. Nowadays, Hollow concrete units are being implicated frequently because of its cost-effectiveness and other technical advantages. The cavities of hollow concrete units are filled with natural (fresh) aggregates for better shear resistance. The use of fresh aggregates as in-fillers in retaining wall constructions is expensive and unsustainable (annihilation of natural resources). This study mainly focuses on frictional behavior of newly designed and manufactured precast “I” blocks infilled with fresh and recycled aggregates. A series of tests were performed using a specially designed & fabricated direct shear apparatus to assess the frictional behavior of infilled blocks under different normal loading conditions. The tests were executed based on the exiting ASTM and National Concrete Masonry Association (NCMA) test protocols. Test results were outlined in the form of shear stress-displacement relationship to compare the effect of recycled aggregate against the fresh aggregate. Shear capacity envelopes were also plotted using Mohr-Coulomb failure criteria to find out the angle of friction for each case. Test results revealed that the angle of friction of the blocks infilled with the recycled aggregate is almost equal to those with the fresh aggregate.
DESIGN MANUAL FOR SEGMENTAL RETAINING WALLS
The use of segmental retaining walls has increased in residence, highways, and other commercial and municipal projects. This design manual provides design methodologies, installation procedures and sample specifications for the walls. It also includes design assumptions, construction practices, reference standards for modular concrete-block retaining-wall systems and material requirements.
Robust solutions of inverse problems in electromagnetic non-destructive evaluation
Non-destructive testing (NDT) is the application of physical measurement technology based on energy interaction with the material and its nonconformities. The material's response is sensed by transducers and sensors which?in most cases?scan the component and document the results in inspection images. However, NDT measures a physically defined quantity or even an intrinsic property. The difference between non-destructive evaluation (NDE) and NDT is in the interpretation of the inspection data. NDE has to discuss the inspection results in terms of quality elements and characteristics which are relevant to describe the fitness of the material for use. In the case of macroscopic defects these are the kind of defect (cracklike, globular) and its size and orientation to the main stress directions; in the case of material property determination the parameters are mainly mechanical properties. Therefore, in NDE one has to solve inverse problems. The solution of inverse problems based on mathematical procedures such as integral equations is a strong developing discipline and most of the articles prepared for this special issue of the journal have the objective of discussing the latest state of the art in that field. However, practical NDE needs robust and quick solutions which are to be applied mainly online. Therefore, we present here inversion procedures based on multiple linear regression algorithms applied to inspection data. We describe the calibration procedure to fit the free parameters of the model functions and give examples of practical applications in industry.