Papers by Keyword: Cement-Based Composite

Abstract: Cement-based piezoelectric composites (PECs) consist of calcium aluminate cement (CAC) and lead zirconate titanate (PZT), each accounting for 50 vol.% that can be used for structural health monitoring (SHM) due to their excellent compatibility with cementitious structures. The presence of free water inside the specimen significantly affects the polarization difficulty and piezoelectricity of PEC. Four treatment methods include vacuum drying, ethanol dehydration, non-heat treatment (untreated), and heat treatment to reduce free water in specimens. Experimental results show that reducing the free water content of PEC specimens through vacuum drying, ethanol dehydration, and heat treatment during the manufacturing process can enhance PEC performance. The free water reduction effect of PEC specimens was most with the heat treatment, followed by ethanol dehydration, and least by vacuum drying. The specimen’s dielectric loss and relative permittivity before polarization decreased if heat treatment and ethanol dehydration were applied. Heat-treated specimens provide optimal relative permittivity and piezoelectric strain constant after polarization. For the piezoelectric voltage constant, ethanol dehydration of the specimen is better than other treatments. The treatment method affects the resonance frequency value and the electromechanical coupling coefficient of the specimen. Water removal of specimens is not a suitable treatment method to increase the electromechanical coupling coefficient.

Abstract: The subject of the study presented in this paper is to quantify the effect of fiber content on the mechanical and mainly fatigue response of fine-grained cement-based composites. The reference cement-based composite was without fibers. Three types of fibers were used as dispersed reinforcement: tire cords (waste material), steel, and polypropylene. For each type of fiber, mixtures with varying reinforcement levels per volume were prepared: 0.0 % (reference composite), 0.5 %, 1.0 %, and 1.5 %. Prismatic specimens 40 mm × 40 mm × 160 mm were prepared and tested. A total of 10 composite variants were investigated. The ages of the specimens for the static three-point bending tests were 28 days, for the compression tests were 28, 120, and 275 days. While for the fatigue tests, it was approximately between 110 and 180 days. The obtained compressive strength values for the above-mentioned composite ages were approximated by a selected exponential function and the results of the fatigue tests were standardized to a nominal age of 28 days using them. All used types of reinforcement increase the strength values of the composites even from the lowest fiber doses. A positive effect of fiber dosage above 0.5 % on the fatigue behavior of composites was shown only in the case of reinforcement with commercial steel fibers.

Abstract: Graphene oxide (GO) synthesized through a modified Hummers’ method was added into cement matrix to prepare GO/cement. The microstructure, mechanical properties, and the electromagnetic shielding effectiveness (SE) at 8.2–12.4 GHz of GO/cement composite were investigated. It has been observed that incorporation of GO in the cement matrix can regulate to form flower-like hydration crystals and distinctly enhance the flexural/compressive early stage strength of GO/cement composites. Furthermore, GO sheets played a vital role in effectively improve the shielding effectiveness with the dominant shielding mechanism of absorption of electromagnetic radiation.

Abstract: Materials combined with a small amount of nanomaterials offer new possibilities in developing of multifunctional composites. Nanocarbon materials (NCMs) such as carbon nanotubes/ nanofibres, and nanographite platelets have excellent intrinsic physical properties and improvement effect to matrix materials at nanoscale. They are promising fillers for improving the mechanical property and durability of cement-based materials and introducing functional properties to cement-based materials. This paper presents a comprehensive introduction about multifuntionlities of NCMs filled cement-based composites including mechanical properties, durability, electrical properties, thermal properties, electromagnetic properties, sensing property and etc.

Abstract: Modeling of concrete failure under fatigue loading is becoming a field of interest. Possible alternative testing solutions are now being searched. In this paper, the fracture energy for a certain concrete, resulting from three traditional fracture tests, namely three point bending test, wedge-splitting test and modified compact tension test, is investigated.

Abstract: Two parameter fracture mechanics uses for description of the crack tip stress fields, not only the stress intensity factor (SIF), but the second term of Williams expansion the T-stress. In the paper, the SIF and T-stress of typical wedge splitting specimens with usual loading arrangements varying in the wedge angle are directly computed using ANSYS finite element software. The influence of the wedge angle value is quantified.

Abstract: A smart composite is fabricated from cement-matrix and spiky spherical nickel powders. The electrical resistivity of such composite decreases 69.00% under uniaxial compression. The gage factor of this composite is higher than 895.45 within the elastic regime. This ultrahigh pressure-sensitivity is attributed to the unique needle-like surface morphology of nickel powers. Comparing to the normal smooth spherical nickel particles, the needle-like features of spiky spherical nickel particles can induce field emission and tunneling effects, which leads to highly sensitive responses to strain. A constitutive model relating the change in electrical resistivity to strain of the composite is built within the elastic regime. This model incorporates the field emission effect and the inter-particle separation change of nickel powders in composite. The model is used to predict the pressure-sensitive characteristic behavior of the composite. The predicted result is compared with the experimental data obtained on the composite, and good agreement is obtained.

Abstract: As a kind of high performance cement based construction materials, because of good mechanical performance and durability, PVA fiber reinforced cement based materials have been paid more and more attention in the field of civil structure engineering. To grasp the characteristics of PVA fiber reinforced cement based composite materials and promote a better application of PVA fiber reinforced cement based composite in practical engineering, a series of research works on the mechanical properties and durability of PVA fiber reinforced cement based composite were introduced systematically.

Abstract: Cement based material are weak in flexure in comparison to compression. Fibers have been used for 100 years ago in an industrial process (i.e. Hatschek machine) to improve flexural and tensile strength of cement based materials. Many researches have been performed to define the best fiber condition such as fiber type, length, and diameter. A few investigations have been done on the effects of fiber cross section on fiber-cement bonding and flexural strength. In this research, polypropylene (PP) fibers which have diversity in cross section were selected and used as reinforcement in cementitious composites. Fibers characterized for cross sectional shape and average surface area. Flexural strength of the specimens at different fiber volume contents was evaluated. Also, the adhesion of the fibers (with different cross sections such as hollow, delta and circular) was measured using the pull-out test. Results showed that the cross section has an important effect on bonding of the fibers to cement matrix and flexural toughness of the specimens. It was observed that the hollow fiber that has the biggest lateral surface showed the highest pull-out load, and the delta fiber showed best flexural behavior.

Abstract: The microwave absorbing properties of multi-walled carbon nanotubes-reinforced cement-based composites (MWCNTs/CC) in the range of 2–18 GHz were investigated in this paper. MWCNTs with the addition of 0.08% by mass of cement were incorporated to cement mortar. It is shown that MWCNTs which act as microwave absorber reinforce the microwave absorbing properties of MWCNTs/CC. Two absorbing peaks of MWCNTs/CC appear in the range of 4–8 GHz, one lies in 4.9 GHz with the reflectivity of -29.1 dB and the other lies in 6.8 GHz with the reflectivity of - 19.2 dB, indicating that the absorbing properties of the composites are improved greatly.