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.
Laboratory Testing of Modular Masonry Concrete Block-Geogrid Facing Connections
This paper describes a laboratory apparatus and test procedure that was developed by the authors to quantify the mechanical behavior of the connection between mortarless modular concrete block units and geogrid reinforcement materials. The paper illustrates that the tests should be carried out with 1-m wide samples of geogrid reinforcement in order to account for the influence of block joints and surface geometry irregularities that occur along the length of typical geogrid-reinforced concrete block walls. This paper gives recommendations for a 20 mm/min rate of loading. The interpretation of connection strength and efficiency for modular block-geogrid reinforcement connection systems is related to conventional index strengths that are routinely reported in the literature based on the ASTM D 4595 method of test. For the covering abstract see IRRD 860243.
Recycling of silicon powder waste cut by a diamond-wire saw through laser-assisted vacuum smelting
Abstract This paper proposes laser granulating technology for recycling harmful silicon powder waste cut by a diamond-wire saw. The silicon block produced by laser was easily melted in a traditional vacuum smelting furnace to form a silicon ingot with a high yield and filling rate, which could reach up to 94.7% and 65.7%, respectively. The removal efficiency of the carbon contamination was 74.2% during laser melting process and reached 86% after 30 min of vacuum smelting. In addition, laser melting process promoted the removal of most metal impurities, such as Al, Na, Ca, Mg, and so on, in the silicon powder waste without introducing any other impurities. The residual impurities could be further removed by vacuum smelting. The experiment revealed that the out capacity of the silicon block melted by a single laser gun was 1.91 kg/h, the energy consumption of laser melting was 2.63 kWh/kg, and the yield of the silicon block exceeded 97% at a laser power of 2000 W, a laser scanning interval of 5 mm, and a scanning speed of 6 mm/s. Therefore, the proposed approach is one of the most simple and efficient silicon powder waste pretreatment methods.