Composite cements definition

Both 6 0 and 6 C values for each end-member cement generation plot within narrow zones (Fig. 15), allowing a precise definition of the conditions under which the individual cement generations formed, albeit based on a small data set. The data show that the quantitative approach to isotope analysis provides added p cision to routine bulk-rock isotope interpretation methods in the study area. The technique used in this study may be applicable to other geological provinces, provided different cement generations do not have the same chemical composition. The image analysis technique is particularly valuable for rocks in which pure or nearly pure samples of carbonate cement end-members do not exist. 

As described in previous sections, the standard method for treating durability in EN 206 and Eurocode 2 is based on the definition of the exposure class and determining for each class, the maximum w/c ratio, the minimum cement content and the minimum thickness of the concrete cover. EN 206 provides recommended (informative, that is non-normative) values for concrete composition in terms of maximum w/c ratio, minimum strength class and minimum cement content, assuming an intended working life of 50 y, the use of Portland cement (CEM I) and maximum aggregate size between 20 and 32 mm. In national documents these values and additional requirements can be further specified as normative values, as has been done for example in NEN 8005 (nl) for The Netherlands [12]. 

Some polymers can be mixed homogeneously with others at a molecular level over a wide range of compositions in such a way that there is only one phase present, but most cannot. Immiscible polymer compositions can, however, often be induced to coexist at a variety of coarser levels of mixing, similar in some instances to the structure of cement, but on a much finer scale. In the next section the factors that determine the mixing behaviour are considered. First it is useful to give some definitions. 

The models for each property showed that the relations between the property and composition and that the relations between the properties themselves are complicated and sometimes even mutually exclusive increasing the amount of polymer increases the flexibility and waterproofness but decreases vapor permeability, increase of waterproofness by adding more fillers does not causes the increase of flexibility, the vapor permeability is not clearly disproportional to waterproofness. It was shown that some relations which had seemed to be obvious when considering the composite material such as polymer-cement coating have not worked. That is why the specific definition of the expectations is so necessary and why the desirable material properties, their importance and weights of empiric data must be defined precisely. Using elaborated material models is very helpful in designing materials. 

In the past the division of cements on the basis of phase composition was applied, as follows alite, alite-celite (Tdmebohm called brownmillerite celite), alite-aluminate and others (Fig. 1.5) [31]. Such division, although fully justified, gives few information to the user— properties of several classes are very approximate, it has no application to cements with additions and for these reasons has no practical use. However, the chemists use it frequently enough for cement kind definition, especially in the case of special cements, which are discussed in Chap. 9. 

In the above definitions, a phase is understood as a region of a material that has uniform physical and chemical properties. This means that not only are cement paste and rock aggregate grains or voids different phases in concrete when it is considered as a composite material but, for example, so also is any water or ice which fills these voids. 

The definitions and classifications of cement and concrete-like composite materials presented below are used in the chapters that follow. Various authors have put forward slightly different definitions and classifications, which can be found in Hannant (1978), Venuat (1984), Mindess et al. (2003), and others. This variety is not surprising, because concrete-like composites are produced in the largest mass and volume of any building materials in the world. They are applied in different structural and non-structural elements and are made with various constituents, used in different combinations. The term concrete-like composites is somewhat wider than cement-based composites. In fact, in this chapter a few materials are mentioned which do not contain any kind of cement and in which other binders are applied. 

Concrete-like composites are the composite materials and ordinary concrete is the most representative example of the group. They are composed of a matrix and inclusions, and possibly also of a system of reinforcement. This group of materials is by definition larger than the scope of this book, which is defined as cement-based composites. 

Thermochemical treatments, sometimes referred to as case hardening or cementation, are based on the modification of the chemical composition of the substrate material. These treatments can be succeeded by a change in the structure through heat treatment. The formal definition available in BS EN 10052 1994 reads as follows (British standard, 1994) ... 

The mechanical behavior of concrete should be viewed from the point of view of a composite material. A composite material is a three dimensional combination of at least two chemically and mechanically distinct materials with a definite interface separating the components. This multiphase material will have different properties from the original components. Concrete qualifies as such a multiphase material. Concrete is composed of hydrated cement paste (C-S-H, CH, aluminate, and ferrite-based compounds) and imhydrated cement, containing a network of a mixture of different materials. In dealing with cement paste behavior, basically it is considered that the paste consists of C-S-H and CH with a capillary system. The model of concrete is simplified by treating it as a matrix containing aggregate embedded in a matrix of cement paste. This model provides information on the mechanical properties of concrete. 

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