Fiber Reinforced Cement Paste Research Articles

Cement as a thermoelectric material

Cement pastes containing short steel fibers, which contribute to electron conduction, exhibit positive values (up to 68 μV/°C) of the absolute thermoelectric power. Cement pastes containing short carbon fibers, which contribute to hole conduction while the cement matrix contributes to electron conduction, exhibit negative or slightly positive values of the absolute thermoelectric power. The hole and electron contributions in carbon fiber reinforced cement paste are equal at the percolation threshold. Addition of either steel or carbon fibers to cement paste yields more reversibility and linearity in the variation of the Seebeck voltage with temperature difference (up to 65 °C).

Uniaxial tension in carbon fiber reinforced cement, sensed by electrical resistivity measurement in longitudinal and transverse directions

Uniaxial tension of carbon fiber reinforced cement paste in the elastic regime caused reversible increases in both longitudinal and transverse resistivities. Without the fibers, the resistivity increase was much smaller and less reversible.

Enhancing the Seebeck effect in carbon fiber-reinforced cement by using intercalated carbon fibers

The absolute thermoelectric power of carbon fiber-reinforced cement paste was rendered as negative as −17 μV/°C by using bromine-intercalated carbon fibers, which had a high concentration of holes. The corresponding paste with pristine carbon fibers exhibited absolute thermoelectric power as negative as −0.8 μV/°C only.

Microhardness Testing of Fiber-Reinforced Cement Paste

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Seebeck effect in carbon fiber-reinforced cement

The Seebeck effect in carbon fiber-reinforced cement paste was found to involve electrons from the cement matrix and holes from the fibers. The two contributions were equal at the percolation threshold, with a fiber content between 0.5 and 1.0% by mass of cement. The hole contribution increased monotonically with increasing fiber content below and above the percolation threshold. The fiber addition increased the linearity and reversibility of the Seebeck effect. Silica fume and latex as admixtures had minor influence on the Seebeck effect.

Ozone treatment of carbon fiber for reinforcing cement

Ozone treatment of isotropic-pitch-based carbon fiber was found to increase the surface oxygen concentration and change surface oxygen from C–O to CO, thereby causing the contact angle between fiber and water to be decreased to zero. Thus, the bond strength between fiber and cement paste was increased and the tensile strength, modulus and ductility of carbon fiber reinforced cement paste were increased. Moreover, the degree of dispersion of fibers in mortar was increased and the effectiveness of the fibers for reducing the drying shrinkage was improved. As a consequence, the strain sensing ability of carbon fiber reinforced mortar was improved in terms of increased gage factor and better repeatability. The ozone treatment did not affect the morphology, tensile strength or volume electrical resistivity of the fiber itself.

Improving the tensile properties of carbon fiber reinforced cement by ozone treatment of the fiber

The tensile strength, modulus and ductility of carbon fiber reinforced cement paste were increased by ozone treatment of the fibers prior to using the fibers. Increases were observed whether or not the paste contained methylcellulose/silica fume/latex. The ozone treatment involved exposure to O3 gas (0.3 vol.%, in air) for 10 min at 160 °C.

Glass Fiber Composites Made with a Cement Based on a Hydraulically Active CaO-SiO2-Al2O3 Glass

AbstractGlass fiber reinforced cement pastes were prepared using a cement based on a hydraulically active glass in the system CaO-SiO2-Al2O3. The properties of such composites were compared with those made with ordinary portland cement.In all the studied materials the MOR and WOF values declined with time, however for different reasons.

Evaluation of fatigue damage on the mechanical properties of fiber reinforced cement pastes

Type III Portland cement samples reinforced with 0.01 volume fraction of chopped steel fibers were subjected to cyclic loading in tension with zero minimum stress and maximum stress amplitudes varying from 0.72 to 1.38 of the first crack strength of the composite. The number of cycles-to-fracture at different stress amplitudes (S-N curve) indicated good fatigue resistance in stress amplitudes representing up to 80% of the range between first crack and ultimate composite strengths. A number of specimens cycled at a stress amplitude 38% above the first crack strength were monotonically fractured in tension following different levels of prior fatigue damage. Pre-cycled specimens exhibited a rapid drop in Young's modulus, substantial increase in ultrasonic attenuation, but insignificant decay in composite strength and post-cracking ductility. It was concluded that fatigue damages, short of propagating interface cracks to the ends of the fibers, would not adversely affect the composite strength and post-cracking fiber pull-out behavior.

Cracking processes in steel fiber reinforced cement paste

Fracture patterns produced when a crack advanced from a notch in cement paste specimens reinforced with steel fibers were studied by SEM methods. The specimens were small compact tension specimens with precast notches that could be wedge loaded within the SEM chamber in a moist environment. Steel fibers were positioned either in an array of five parallel fibers spaced 2 mm apart and across the expected crack propagation path, or else were in random orientation on the plane being observed. The cracks induced by wedge loading were found to be geometrically complex and certainly could not be described as simple straight cracks as assumed in various models. On intersection with fibers oriented perpendicularly to them, the cracks tended to displace laterally and branch into a number of microcracks; on intersection with fibers at less than perpendicular angles, the tendency was for the crack to change course and run parallel to the inclined fiber. Often at perpendicular intersections the crack appeared to be arrested in the matrix 10 to 40 μm ahead of the actual fiber interface, and then produced a “pseudo-debonding crack” parallel to the fiber but some distance away from the actual interface. These cracking patterns are considered to be influenced by the microstructure of the cement paste near the interface, which is clearly different from that of the bulk cement paste.

Crack patterns in steel fiber reinforced cement paste

Fracture patterns, produced when a crack advancing from a notch in cement paste intersected a steel fiber placed perpendicular to it, were studied by SEM methods. The specimens were small notched compact tension specimens that could be wedge loaded within the scanning electron microscope chamber using a wet cell. Three distinct cracking patterns were identified. In most cases the fiber caused a shift in the crack path, accompanied by microcracking and by separation of the main crack into several branches. Observations of the surface of the groove under the steel fiber indicated that the offsetting segment of the crack path in the matrix under the fiber was tortuous, and in many cases it was characterized by branching, discontinuities, and microcracks. The microstructure of the interface region consisted of CH-rich duplex film at the actual interface, backed by a highly porous zone consisting mainly of C-S-H. The offsetting crack segments tended to damage the preexisting interface zone microstructure under the steel fibers.