Up to 8 per cent of SO3 may be incorporated into the crystalline lattice of C2S if burned in the presence of CaSO4. C3S may be formed only in the presence of F-. Under these conditions up to 5 per cent of SO3 may be incorporated. In the presence of CaSO4 and CaF2 in the raw meal portland clinkers may be formed that contain simultaneously the phases C3S and C4A3S. Clinkers of this kind yield cements with favorable strength properties at “optimum gypsum” additions.

DSP cement paste is prepared by hot-pressing technique in this study in order to improve its particle packing and chemical composition, and to investigate the relationship between its solid phase microstructure and mechanical strength at the porosity close to zero. The addition of silica fume improves strength development, although capillary porosities are not changed significantly. Results obtained indicate that the highest compressive strength reached are 800 MPa after 28 days hydration and oven drying at 200°C. The strength has better relation with degree of hydration or the physical density of C-S-H. the silicate anion polymerization closes not appear to influence strength.

There is considerable research now underway on high-performance cement-based materials, in particular on issues of processing, microstructure, strength, and related properties. However, very little research has been undertaken regarding the durability, or service performance, of these materials. Therefore the durability of high-performance cement-based materials can only be inferred from the service performance of ordinary materials or from a basic understanding of the factors affecting service performance. In this paper we review what is known about the durability of fiber reinforced concrete, high performance concrete, DSP, and MDF. Durability is discussed from the standpoint of general issues – fluid permeability, ionic diffusivity, and pore fluid composition. Much research is needed in order to predict or improve the durability of high performance cement-based materials.

In this investigation the nature and morphology of the concrete-reinforcing steel interface is studied. The effect of the partial replacement of cement by silica fume on the interface microstructure was determined. The distribution profiles of percentage porosity, calcium hydroxide and unreacted cement from the interface towards the concrete bulk were measured using the scanning electron microscope operated in the back scattering mode. The findings indicate the similarities between the morphology of the concrete-steel interface and those reported earlier in the literature for the concrete-aggregate interface. Additions of silica fume resulted in a decrease of the interface porosity and calcium hydroxide content.

The need for the rehabilitation of the infrastructure has lead to the adaptation of modem analytical methods for the characterization of concrete. These techniques are not commonly associated with evaluating concrete but promise to be very useful both as tools of quality assurance and in the determination of existing damage. This paper describes two such techniques, namely, coordinated electron-optical microscopy and gamma-ray tomography. Examples of the use and interpretation of each method are given.

The effect of carbon fibers on the uniaxial tensile strength of cement paste matrix is studied. The tensile strength values are obtained using the novel Cementitious Composites Axial Tensile Technique (CCATT) described previously [1]. The addition of 1.0, 1.5 and 2.0 volume percent of Polyacrylonitrile-based (PAN) carbon fiber results in an increase in tensile strength of 32, 41 and 48 percent respectively, as compared to the unreinforced matrix. A model based on the rule of mixtures is used to predict the tensile strength of the carbon fiber reinforced composites. Results are discussed with respect to fiber, interface bond, and cementitious matrix characteristic.