Experimental study on recycled steel fiber concrete
Some basic properties of recycled steel fiber aggregate were tested, such as surface features, water absorption, apparent ensity, crushing index, cube compressive strength and so on. Recycled steel fiber aggregate were used to replace the natural aggregate by 0%, 25%, 50% and 100% proportion to make concrete. Afterward, compressive strength, splitting tensile strength and flexural strength were investigated at ages 3, 7 and 28 days. The results showed that thorn appearance of recycled steel fiber aggregate makes packing density decrease, crushing value and absorption increase. The compressive strength, splitting tensile strength and flexural strength of the recycled concrete depend on the mix proportions. Generally, the strength of recycled concrete can be 15–25% lower than that of concrete made with virgin aggregate.
Experimental research on unit water use in recycled concrete
Recyling the descasting concrete caught more attention in the world. It depends on the strength for construction bearing to utilize recyled concrete. Mixture ratio is one key factor deciding strength, which is supported by a crucial parameter: water cement ratio. So the calculation of unit water use in recycled concrete is the hot topic. In this paper, the combinations of aggregate concerning recycled concrete are discussed. It is appropriate to adopt the form of full(or part)coarse aggregate adding natural sand. In the case of mixed coarse aggregate adding natural sand, the water in each unit of recycled aggregate concrete should be increased more than it in the ordinary concrete in the mix proportion design, the calculating formula for the increased water use is put forward, the extraly increased water use coincides better with the experimental data through verification, and the formula can be used as reference for the designer in recycled concrete mixed ratio.
A New Vacuum Pressure Infiltration CFRP Method and Preparation Experimental Study of Composite
In order to prepare a carbon-fiber-reinforced polymer composite (CFRP) with ideal microstructure and properties, a new vacuum pressure infiltration CFRP method is proposed based on an analysis of existing CFRP preparation process methods. Research on composite material preparation systems was carried out by using this new method principle. The system mainly includes a fiber pre-forming module, a vacuum heating infiltration module, a hot-press curing molding module, and a data acquisition control module. Under the conditions of natural curing at 0 MPa + 6 h + 25 °C, vacuum heating curing at –0.05 MPa + 30 min + 80 °C, and hot-press curing at 0.7 MPa + 5 min + 50 °C, a two-dimensional (2D) CFRP with excellent microstructure and properties was successfully prepared. Observing the microstructure of the prepared composite material, it can be found that the inside of the composite material was sufficiently and uniformly infiltrated, and common preparation defects such as holes and delamination were effectively controlled. Through the performance test, the bending strength of the material reached 790 MPa.