Tag: cement

Cements Composition, Strength & Choice Factors

Cements with high alumina units, which corresponds to the higher content of calcium aluminate, grasp and harden quite quickly. However, once a certain strength is achieved during the first days it hardly increases during further solidification. Such cements are less resistant to the effects of saline water. For small values ​​of the alumina modulus, meaning when large quantities of iron oxide in the clinker, cement sets and hardens more slowly, but yield a higher final strength. Iron oxide facilitates the clinker burning, it reduces the temperature of sintering.

The limited content cements, magnesium oxide (4-4.5%), as being in a free state, it may, due to slow hydration and later, cause the appearance of stress cracks in the products. The main characteristic is its clinker mineral composition, the content of C3S, C2S, NWA and OAF. Given that each mineral of Portland cement clinker has its own characteristics (9 markers to a greater or lesser extent influenced by the general properties of the cement, builders can not only pay attention to the strength characteristics. According to Telling experts, the company specialized in architectural solutions and wide use of hydraulic lime, lime mortar and concrete technologies, alite is considered to have the best hardening strength capabilities.

The greatest intensity of strength development is the feature of C3A, but just like C4AF, it provides low strength. The last place, both in absolute terms of strength and durability of the growth rate, goes to belite. It is noted that in long periods of time curing bleaches are capable of gaining high strength/behaving similarly to mixture of these components. The greatest strength of the two-component mixture is demonstrated by alite and NWA, the smallest – in alite mixed with bleaches and alite in a mixture with C4AF. An increase in the NWA to 15% increases the strength of the first period of hardening, but further provides a reduction of strength. The contents of NWA up to 10% gives the best strength constant gain when combined with OS, although separately NWA, as noted above, provides a very low strength. In this case, the positive role is played by the presence of gypsum in the cement that is added when grinding clinker. With it in composition a complex hardening salt is formed – crystalline calcium hydro-sulfoaluminate (also known ettringite).

Deformability & no-less crucial aspects

In assessing the quality and choice of the cement it also vital to take into account the deformability, shrinkage, heat, corrosion resistance, hardiness and resistance to external conditions of the building structures and other properties. The presence of artificial mineral clinker in various quantities and combinations brings about changes in the figures of the cement.

Deformability, impact resistance and ductility, is significantly higher in aluminoferrite cement, and virtually devoid of tricalcium aluminate. Aluminoferrite cement provides almost 2 times the tensile limit than aluminate cement. The content of NWA greatly reduces the deformability of cement capacity, it increases the likelihood of cracking. NWA is the most fragile mineral, while C4AF is way less fragile.

13 Aug 2015
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