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This laboratory study presents a new approach – two staged surface treatment – to treat rubber particles for improving the performance of rubber-modified cement composites. In the first stage, silane coupling agent is used to modify rubber particle surface and develop chemical bonds between rubber particles and cement paste. In the second stage, cement is used to coat the silane-treated particles. The purpose of the cement coating is to develop a “hard shell” around rubber particles after cement hydration. The proposed surface treatment was validated through a laboratory experiment. The experiment results showed that after the two-staged surface treatment of rubber particles, the compressive strength of rubber-modified cement composites could be increased by up to 110%, which could potentially increase application of rubber-modified cement composites.

The use of fly ash as an admixture results in enhancement of the electromagnetic interference (EMI) shielding effectiveness from 4 to 8 dB at 1 GHz, whereas the use of silica fume as an admixture results in negligible effect on the shielding effectiveness. The DC electrical resistivity is decreased slightly by silica fume, but is essentially not affected by fly ash. Both fly ash and silica fume cause slight increases in the reflectivity. The effectiveness of fly ash for shielding is attributed to the Fe2O3 component (15.4 wt.%) in the fly ash. D 2004 Elsevier Ltd. All rights reserved.

The shrinkage of cement-based materials during hydration is a cause of defects (such as cracks) in these materials. The extent of microstructural change (which precedes an event such as cracking) and the evolution of the microstructure as shrinkage occurs are important for understanding the shrinkage process. This article reports on a study in which the effect of shrinkage during hydration on the microstructural change in cement-based materials was evaluated by measuring electrical resistivity and shrinkage strain. Results show that the microstructural change caused by shrinkage is diminished with silica fume and increased with sand. The fractional change in resistivity per unit shrinkage strain is much larger than the fractional change in resistivity per unit compressive strain in the cured state.

Electric polarization in cement-based materials (without conductive admixture) under an applied DC electric field was found by apparent electrical resistance measurement to be faster than subsequent depolarization under a reverse field by a factor ranging from 5 to 8. The slow depolarization suggested a degree of ionic trapping. In contrast, depolarization was even faster than polarization in carbon fiber cement, due to the fast hole response. Sand addition slowed down polarization saturation, but enhanced the polarization. Silica fume addition did not slow down polarization saturation, but diminished the polarization slightly. An increase in temperature enhanced the polarization due to increase in ionic mobility.

A water-based colloid of submicron graphite particles is an effective admixture for enhancing the EMI shielding effectiveness of cement paste, though it is ineffective for lowering the electrical resistivity. As an admixture, it is more effective for shielding than 15-mm-diameter discontinuous carbon fibers, though it is less effective than 0.1-mm-diameter discontinuous carbon filaments. A shielding effectiveness of 22 dB at 1 GHz is reached by cement paste at a solid graphite content of 0.92 vol.%, compared to a value of 11 dB for a coating made from the graphite colloid and a value of 14 dB for graphite-colloid-coated cement paste (without admixture). D 2003 Elsevier Ltd. All rights reserved.

Damage evolution during freeze-thaw cycling of cement mortar was found by electrical resistivity measurement to involve damage accumulating gradually cycle by cycle until failure. The damage inflicted during cooling was more significant than that inflicted during heating. Damage infliction occurred smoothly throughout cooling from 52 to 20 C. Failure occurred at the coldest point of a temperature cycle. Electrical resistivity measurement allowed simultaneous monitoring of temperature and damage. An increase in temperature caused the resistivity to decrease reversibly, but with hysteresis, which grew with cycling. The effects of freezing and thawing on the resistivity were small compared to the effect of temperature on the resistivity. D 2002 Elsevier Science Ltd. All rights reserved.

Defect dynamics, as studied by electrical resistivity measurement during repeated compression of cement mortar in the elastic regime, are characterized by defect generation, defect healing and defect aggravation. Defect generation dominates in the first compressive loading and in tensile loading in any loading cycle. Defect healing dominates in all subsequent compressive loading cycles and in tensile unloading in any cycle. Defect aggravation dominates during compressive unloading in any cycle and occurs during tensile loading in any cycle. Both the interface between sand and cement and that between silica fume and cement contribute to the defect dynamics, particularly the defect healing. The defect dynamics give similar effects to the longitudinal and transverse resistivities. Upon uniaxial compression, the resistivity decreases (except for the first cycle); upon uniaxial tension, the resistivity increases.

Cement mortar reinforced by short carbon fibers was improved by using acrylic dispersion as an admixture in the amount of 15% by mass of cement. The improvement of the tensile properties (particularly strength and ductility) was more than those attained by using methylcellulose, styrene acrylic, or latex as admixtures. Acrylic was effective whether silica fume was present or not. However, for lowering the electrical resistivity, methylcellulose in combination with silica fume was most effective.

The electrical resistance of concrete in the stress direction increased during compressive loading in the first cycle, due to defect generation. It decreased during loading in all subsequent cycles, due to defect diminution. It increased during unloading in the first and all subsequent cycles, due to defect extension. The baseline resistance and the amplitude of resistance variation increased with cycling, due to minor damage. The interface between mortar and coarse aggregate contributed to the defect dynamics, particularly defect diminution.

Degradation of the cementitious bond between steel rebar and concrete and that between old and new mortar under cyclic shear loading was observed nondestructively by measuring the contact electrical resistance of the joint. Degradation, which caused a decrease in bond strength but no visual damage, was indicated by an abrupt increase in the resistance at a small fraction of the fatigue life. Bond failure was also accompanied by an abrupt increase in resistance.

Moisture in the form of liquid water contributes little, if any, to the Seebeck effect in cement-based materials. Moisture loss has no effect on the absolute thermoelectric power, but increases the electrical resistivity.

Automatic testing software in the multi-mode terminal tester is to complete the automatic tests of multi-mode terminals so as to achieve the performance indexes and consistency condition. This paper firstly explains the multi-mode terminal tester automatic test system, and then introduces the automated testing software architecture and its design goals. Finally, it completes the overall design of the automatic testing software based on multimode terminal tester and describes the testing results.

Based on the overall introduction of the Voice Quality System in 3G core network, this paper proposes the detailed design scheme of media information processing, including the decoding analysis of RTP protocol and the generation of CDR files. The principle and algorithm of CDR synthesis are introduced and a hash dynamic synthesis method is adopted to improve the efficiency of getting CDR. After the data processing, the system accomplishes the end-to-end voice quality analysis on basis of the relevance of RTP streams and corresponding signaling processes.

The electrical resistivity of cement mortar increased monotonically during compression. An increase in strain rate caused the resistivity at any strain level to decrease, in addition to causing the resistivity at failure to decrease. This means that the microstructural change that occurred continuously during loading decreased with increasing strain rate.

Minor damage of cement mortar during cyclic compression in the elastic regime was monitored by measurement of the electrical resistivity in the stress direction. Defect generation (irreversible) resulted in an irreversible increase in the baseline resistivity as stress cycling progressed, whereas defect healing (reversible) resulted in a reversible decrease in the resistivity upon compression within a stress cycle. Defect generation was relatively significant in the early cycles and diminished upon cycling. As the cumulative damage increased, the extent of defect healing within a cycle also increased.

Degradation of the bond between steel reinforcing bar (rebar) and concrete under cyclic shear loading was observed nondestructively by measuring the contact electrical resistance of the joint. Degradation, which caused a decrease in bond strength but no visual damage, was indicated by an abrupt increase in the resistance at a small fraction of the fatigue life.

The dispersion of steel fibers in steel-fiber-reinforced mortar was improved by the use of silane as an admixture, as indicated by electrical resistivity measurement conducted at a low fiber volume fraction below the percolation threshold. The use of silane to coat the steel fibers rather than as an admixture was less effective.