Civil Engineering Reference
In-Depth Information
25
Cements for fiber-reinforced cementitious
composites
A typical feature of hardened inorganic cement pastes is their low tensile/ compressive
strength ratio. To improve this ratio and to lower the brittleness of the material,
cementitious systems may be reinforced with suitable fibers randomly distributed within
the cement matrix (Fig. 25.1).
Figure 25.1
Schematic presentation of the distribution of fibers in a fiber-
reinforced cementitious composite material.
If such fiber-reinforced cementitious material is exposed to an external tensile stress, a
deformation of the matrix takes place, which—as long as a good bond exists between the
matrix and the fiber surface—is also transferred to the fibers embedded in the matrix.
Thus both the matrix and the fibers are put under stresses, whose magnitude is
proportional to the deformation, and—at an equal deformation—proportional to the
modulus of elasticity of the particular material (Fig. 25.2). Consequently, fibers with a
high modulus of elasticity—if introduced in sufficiently high amounts—have the capacity
to reduce distinctly the stresses existing in the matrix at a given degree of deformation
and thus increase the maximum load that the material can sustain without failure. In
general, the tensile strength of the composite material will be determined by the strength
