Bing Chen

Conductivity of carbon fiber reinforced cement-based composites

The conductive behavior of carbon fiber cement-based composites is presented. The influence of carbon fiber volume, size, cement-based matrix, relative humidity and curing age on the characteristic of system were studied. The relationship between conductivity and volume fraction of carbon fiber indicated that the statistical percolation theory is suitable and applicable for the change rule of conductivity of system with the volume of carbon fiber. Based on the classic percolation theory, the percolation threshold of carbon fiber cement-based composites was determined as φ=φc2 and the conductive mechanism changes from electron tunneling conduction to ohmic contacting conduction. The studies have offered basic theory for smart cement-based composites.

Effect of coarse aggregate type on mechanical properties of high-performance concrete

Tests were carried out to study the effect of the coarse aggregate type on the compressive strength, splitting tensile strength, fracture energy, characteristic length, and elastic modulus of concrete produced at different strength levels with 28-day target compressive strengths of 30, 60, and 90 MPa, respectively. Concretes considered in this paper were produced using crushed quartzite, crushed granite, limestone, and marble coarse aggregate. The results show that the strength, stiffness, and fracture energy of concrete for a given water/cement ratio (W/C) depend on the type of aggregate, especially for high-strength concrete. It is suggested that high-strength concrete with lower brittleness can be made by selecting high-strength aggregate with low brittleness.

Study of the influence of aggregate size distribution on mechanical properties of concrete by acoustic emission technique

Acoustic emission (AE) has been widely used in concrete research as a dynamic nondestructive test method. In this study, the AE characteristics of concrete with different aggregate size distributions under uniaxial compression and three-point-bending were studied. Parameters such as maximum aggregate size, compressive strain and fracture energies of different concretes were also measured and discussed. The test results show that the characteristics of AE signals from concrete can illustrate the failure process in both compression and three-point-bending. The fracture energy increases with increment of the maximum aggregate size. Moreover, there is a good relationship between AE hits and fracture energy.

Study on the AE characteristics of fracture process of mortar, concrete and steel-fiber-reinforced concrete beams

The acoustic emission (AE) signals from mortar, concrete and steel fiber reinforced concrete beams during the entire fracture process were recorded and analyzed. Different filters were set on the AE signal duration based on the characteristic of amplitude distribution. From the value of AE signal amplitude, which corresponds to the occurrence of the peak for AE hits, the AE signals from mortar, concrete and steel reinforced concrete were divided into five, seven and nine sections, respectively. The relationship between the AE signal section and the failure mechanism of these materials, analyzed on the meso-structure level was determined. Based on the experiments, the AE characteristics of each failure mechanism are given. The results show that the AE technique is a valuable tool to study the failure mechanism of concrete.

Effect of fibers on expansion of concrete with a large amount of high f-CaO fly ash

The effects of different types of fibers on expansion of cement paste, in which a large amount of high content of f-CaO fly ash (HFA) was added, were investigated and the way to prevent cement paste with HFA from expansion was proposed. The results showed that the effects of different fibers on expansion of cement paste are related to the properties of fibers. Carbon fiber and alkali-resistant glass fiber, which have high elastic modulus, can effectively restrain the expansion, while nylon fiber with low elastic modulus has no restraint effect on the expansion. In addition, the restraint effect of alkali-resistant glass fiber increases with the increase of fiber content.

Experimental Study of Effect of Fly Ash on Self-Compacting Rammed Earth Construction Stabilized with Cement-Based Composites

AbstractAs an environmentally friendly construction technique, modern rammed earth generally stabilized with portland cement has attracted growing interest recently. In this study, cement-based composites (CSCN) consisting of cement, sodium silicate, and composite promoter were used for substituting portland cement, and the effect of fly ash was investigated by unconfined compressive strength (UCS) test, thermogravimetric analysis (TG), X-ray diffraction (XRD), and scanning electron microscope (SEM). Based on the theory of pozzolanic and dispersing (P&D) effects, the contribution of fly ash was regarded as an addition of CSCN, and the quantitative analysis of P&D effects defined as P&D factors was evaluated by the clay-water/CSCN ratio hypothesis. It was found that the P&D factors for both compressive strength and secant modulus varied with CSCN content and curing age. The models of different curing ages for predicting the strength and modulus of specimens stabilized with CSCN and fly ash were developed f...

Experimental Study of Dipotassium Hydrogen Phosphate Influencing Properties of Magnesium Phosphate Cement

AbstractA magnesia-phosphate cement (MPC) paste based on magnesia and potassium dihydrogen phosphate (KH2PO4 or PDP) was prepared with the additions of dipotassium hydrogen phosphate (K2HPO4 or DHP) and borax as set-retarders. The resulting materials were characterized in terms of their setting characteristics, strength properties, hydration products, and microstructures. The replacement of PDP by DHP was found to increase the setting time and reduce the intensity of the exothermic reactions during the initial setting and hardening stages. When the replacement percentage did not reach 50%, substitution of dipotassium hydrogen phosphate for potassium dihydrogen phosphate in the MPC paste could strike a good balance between the speedy strength gains and delayed setting time. The setting time of the MPC system increased from 5xa0min (without DHP addition) to 180xa0min with PDP replaced by DHP completely. The addition of borax also led to an extension of the initial hardening period, as indicated by reductions in...