Electrical conductive carbon-modified cement-based composites are important multi-functional structural material. Double compounding carbon fiber and carbon black into cement-based material can improve the electrical conductive property of cement-based composites. In this paper, the influences of carbon fiber ratio and total volume fraction of carbon components on the resistivity of cement-based composites are investigated. The results show that both carbon fiber ratio and total volume fraction have great effect on the conductive behavior of carbon-modified cement-based material. At a fixed carbon fiber ratio, with the increase of total volume fraction, the resistivity of cement-based composites drops down dramatically and shows obvious percolation phenomenon. The reason is that with more and more conductive particles and fibers added into the cement material, the conductive components connect with each other gradually and at certain point reach the percolation threshold. At a fixed total volume fraction, the resistivity drops down with the increase of carbon fiber ratio. This is because that the carbon fiber has larger aspect ratio than carbon black, so carbon fiber could get lower resistivity with the same dosage according to the percolation theory. Finally, the results show that with 0.5 carbon fiber ratio and 2% total volume fraction the carbon-modified cement-based composites have relatively low resistivity, high workability and high compressive strength.
Combinning at home and abroad research results, a new method of ‘sinking ball’ was put forward to evaluate the workability of self-compacting mortar (SCM). The size of ‘sinking ball’ and the volume of mortar vessel have been optimized by experiments. The results show that: when the ball with 20mm in diameter, the mortar vessel with 60mm in diameter and 160mm in heigh, the results of sinking ball test are best; Meanwhile, results indicate that the time of curve reflects the flow ability of SCM, the slope changing of curve indicates the anti-segregate ability of SCM, the integral area of curve has great relation with self-compacting ability of SCM.
In hydraulic transmission, Hydraulic pressure can not support heavy objects long time. For the shortcoming, an electro-hydraulic lifting device is designed with mechanical structural supporting; Electric motor is the motive power. The weight is lifted by hydraulic transmission technology; the base of the device is set up a lifting rigid leg and pushing forward Casters .After hydraulic system lifting heavy objects, the lifting devices rely on the support tube, mechanical positioning tube and rigid supporting legs to lock the lifting position. In order to ensure the same high of support on different positions, a vertical fine adjustment mechanism is set. The design solves the problem that hydraulic transmission cannot lift long time. The lifting device is safe operation, easy moved, accuracy positioning, and stable support, energy-saving and environmental protection.
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