Gypsum matrix

However particle size is important in the durability performance of these materials. Some wood is always exposed as the material is cut to length or penetrated by fixings. This wood will respond to an inerease in moisture by swelling. This is not an issue for small partieles isolated within the plastic matrix, but would be more significant with larger partieles used in the eement and gypsum matrix produets. 

The results reported here suggest that Ancient Egyptian mortars may be characterized by two sets of pores I and ll within the gypsum matrix. 

XRD allows the determination of the actual mineral species present. The bulk coal samples resulted in an x-ray pattern with a high background due to the coal matrix. The major mineral species were easily determined, however the minor species could not be detected. As with the SEM-BSE analysis, interpretation of results in a quantitative manner (in relation to the coal) is difficult. The major minerals detected were quartz, kaolinite, gypsum and marcasite. 

Fig. 3.1.10. Phosphatic concretion from Brazos County, Texas. The large dark object is an appendage of a fossil crab, the tip of which is truncated by a calcite vein. The matrix material is essentially collophane (isotropic francolite), but contains glauconite, quartz, limonite, pyrite, gypsum, etc. in addition to fossil fragments. Magnification 27x. Reproduced with permission (McConnell, 1950).

KEY WORDS gypsum. X-ray fluorescence, thermogravimetry. analysis of gypsum, borates. Claisse fluxer, synthetic standards, matrix corrections... 

We would like to thank E>r. Bruce A. Hudgens of the U.S. Gypsum Co. Research Center, IL. for the help with the round-robin analyses of several gypsum specimens and stimulating discussions on the subject. We are also grateful to Dr. Richard Rousseau and Mr. G. R. Lachance of the Canadian Geological Survey in Ottawa, who calculated the alpha coefficients used in the matrix corrections procedure and provided many valuable suggestions. 

The effect of acid rain on mortars will depend on the particular mortar in consideration. The most susceptible mortars will be the lime-sand ones. The carbonated lime will be particularly attacked due to the small crystal size of the formed calcite (19,20). The resulting calcium sulfate can crystallize as gypsum [CaS0. 2H20] inducing mechanical stresses into the matrix of the mortar. 

Figure 4 shows the platy gypsum crystals that formed in a crack of a lime mortar. The continuing growth of these crystals will cause the crack to develop even further and thus mechanically disrupt the matrix of the mortar. 

Figure 4. SEM photomicrograph showing gypsum crystals in a crack within a lime mortar. The growth of these crystals induces mechanical stresses which progressively enlarge the crack and break up the matrix of the mortar. The extremely fine-grained calcite (formed during the setting by carbonation of the lime mortar) is especially susceptible to acid rain dissolution.

Cement is a binder that sets and hardens by itself or binds other materials together. The most widely known application of cements is in construction a second one is the area of bone cements. Cements used in construction are characterized as hydraulic or nonhydraulic and mostly for the production of mortars and concrete. Hydraulic cements set and harden after combining with water. Most construction cements are hydraulic and based on Portland cement, which consists of calcium silicates (at least 2/3 by weight). Nonhydraulic cements include the use of nonhydraulic materials such as lime and gypsum plasters. Bone cements and bone cement composites refer to compounds that have a polymer matrix with a dispersed phase of particles. For instance, polymethylmethacrylate (PMMA) is reinforced with barium sulphate crystals (for radio-opacity) or with hydroxyapatite... 

Here, an example from the Rhub-al-Khalil in the Arabian Desert shows a cyanobac-terial colony in a dolomitic zone, several cm below the surface of a large gypsum crystal embedded in a halite matrix (Figure 1-17). The Raman spectra of the biological component clearly demonstrate the presence of photoprotective pigments such as scytonemin and carotenoids. 

Based on the strong dilution trends of non-reactive species, such as chloride and sulfate, the extent of interaction of fracture condensate water with matrix pore water must have been very limited. However, reactive species, such as silica, show increasing concentrations owing to reaction with predominantly fracture-lining silica polymorphs and feldspars at higher temperatures. A precipitation zone of secondary mineral phases such as amorphous silica, calcite, and gypsum in... 

The second group consists of calcium aluminate expansive cements, in which calcium aluminate cement is a matrix and the source of aluminate ions. The latter one can originate also from the calcium aluminate hydrate C AH, added in the grinding process. Obviously, gypsum is the constituent of all these cements. 

Lifecore (US) Cal Matrix Powder 90% CaS04-/ H20 and 10% carboxymethylcellulose Solution unknown Gypsum... 

In the course of acid attack on hydrated Portland cement and related binders, inclnding blended cements, the free calcium hydroxide is dissolved together with CaO bound within the C-S-H phase. In this way the Ca0/Si02 molar ratio in this phase may be lowered below 1.0. In strong acids complete decomposition of the cement matrix may take place, leaving silica gel and gypsum as the final solid residna of the decomposition process (Ueda et al., 1997). 

Type K expansive cement is the expansive cement used worldwide in the largest amounts. It contains calcium sulfoaluminate (C4A3S) in combination with calcium sulfate as the expansive component and Portland clinker as the component producing the cementitious matrix. The expansive component is burnt separately in the form of a calcium sulfoaluminate clinker, which is subsequently interground with Portland clinker and additional calcium sulfate in the form of gypsum or anhydrite. Alternatively, the sulfoaluminate clinker may be ground separately and added to Portland cement in amounts that may vary depending in the intended use of the final expansive cement. 

The relationship between the calcium and sulphate concentrations (Figure 10) follows a 1 1 stoichiometric relationship, which indicates that the sulphate of Roces, Rozaes and El Gorgojo springs comes fiom the dissolution of gypsum. This hypothesis is coiToborated by data from the correlation matrix, previously show in Table 6. 

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