Cementitious materials characteristics

The essential property of a cementitious material is that it is cohesive. Cohesion is characteristic of a continuous structure, which in the case of a cement implies an isotropic three-dimensional network. Moreover, the network bonds must be attributed to attractions on the molecular level. Increasingly, recent research tends to show that cements are not bonded by interlocking crystallites and that the formation of crystallites is incidental (Steinke et al., 1988 Crisp et al., 1978). The reason is that it is difficult to form rapidly a mass which is both cohesive and highly ordered. 

The precision values are both method and material characteristics. They are valid for the tested material class, i.e. a cementitious mortar with this composition. 

Table 4.3 Physical characteristics of selected supplementary cementitious materials (SCM)...

Concrete is classified as either flexible or rigid. Mainly the cementitious materials used to bond the aggregates determine these characteristics. 

The intrinsic properties of mineral polymers are compared to the properties of organic polymers and cementitious materials. It follows that the toughness of mineral polymers can be increased by the addition of fibres, and that it is possible to incorporate a higher volume content of long fibres than is possible in cement. An application of this is presented under the form of tensile and bending characteristics of a jute reinforced laminate with mineral polymer matrix. 

BSE images reveal the different phases because of the atomic number contrast described earlier. Polished sections examined by BSE and characteristic X-rays can provide a wealth of information on length scales from millimetres to less than a micron. Nevertheless, the essential prerequisite is a well-polished sample. This is often challenging, particularly when the cementitious material contains aggregates (mortars and concretes). Aggregates are generally much harder than cement paste, so the paste component (which is the main subject of study) is frequently eroded between well-polished aggregates. 

The aim of this chapter is to illustrate the use of electron microscopy for the study of cementitious materials. Although imaging of fracture surfaces with SEs is perhaps the most commonly used technique, it is of limited use after the first day or so. The most useful technique is the study of polished sections by BSEs and characteristic X-rays. We have tried to illustrate some of the diverse applications of these methods, including the possibilities to obtain quantitative information by image analysis. However, the essential prerequisite is a well-polished sample, which is not easy to achieve. 

ISO 5725 [7] relies on a statistical analysis of variance model with two variance components "laboratory" and "repetition". Hence, a homogeneous material is assumed. Only under this homogeneity condition the calculated precision values are true method characteristics. For a heterogeneous material, like the tested cementitious mortar, the precision values are contaminated by the variance component of the material. Therefore, the precision values represent both material and method characteristics. 

Bentur A. and Kolver K. Evaluation of early age cracking characteristics in cementitious systems. Materials and Structures 2003 36(4) 183-190. 

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