Alite mortar strength

Using a somewhat different approach, Knbfel (1989) reliably predicted the 28-day mortar strength with a simple formula containing microscopically determined percentages of alite, belite, aluminate, and ferrite. The equation is F28 = 3(alite) + 2(belite) + aluminate - ferrite. F28 is termed the characteristic strength. The equation is designed for use within a cement plant where production conditions over the period of investigation are virtually identical. 

The microscopy of two clinkers produced within 10 seconds by electron beam radiation at 1.2 MEV was described by Handoo and others (1992). Alite and belite appear well formed, with crystal sizes of 10 to 16 pm. Mortar strength at 28 days was said to be 470 kg/cm (46.1 MPa). 

Detailed microscopical characteristics of clinkers from vertical shaft kilns, compared to laboratory burns, are presented by Ahluwalia and Raina (1992). Alite and belite crystal sizes in plant clinkers averaged approximately 21 and 19 pm, respectively, possibly accounting for high mortar strengths (44.8 MPa at 28 days). 

Diffusely reflecting alite, appearing unstable and black Decline in 28-day mortar strength by 1 % to more than 5% (Tsuboi and Ogawa, 1972)... 

Zivanovic (1995) presented a description of clinkers made with silica fume, instead of quartz sand, as the primary silica component in the raw feed. The silica fume made up approximately 3.0 percent of the feed. Alite crystal size was reported to be from 50 to 200 pm and belite grains were said to be rounded and between 50 and 60 pm. No mention of belite nests was made. The cements made with silica fume or tuff and a particular marl, compared to other cements not made with these materials, did not require as much grinding and produced higher 28-day mortar strengths. 

The studies by Kelham [149,150,154] have shown that the expansion of mortars depends on the alite and CjA content in cement and is increasing with the share of these phases, thus with the rise of early strength of mortar (Fig. 6.39). The expansion is affected also significantly by SO3 content in cement the highest expansion... 

A multiregressional equation predicting the 28-day mortar cube strength was presented by Rao, Akhouri, and Sinha (1992), the data coming from rotary and vertical shaft kiln clinkers. The prediction has a standard deviation of 17.9 kg/cm, utilizing alite and belite percentages and average crystal sizes. 

A relatively "hard-to-burn" feed from the western U.S., with a very impure dolomitic limestone, has 6.7% >125 pm and an acetic-acid insoluble residue of 9.5% >45 pm, the latter comprised of quartz, feldspar, medium to finely crystalline igneous and metamorphic rock fragments, and an abundance of ferro-magnesian minerals (mainly amphiboles and pyroxenes). = 1.6% and = 4.5%. Belite nests (many with tightly packed crystals), solitary belite, and periclase are abundant in this fine- to medium-crystalline clinker. Nevertheless, a high-compressive strength mortar (44.8 to 48.3 MPa) is made, mainly because of the small alite size and the well-scattered solitary belite. 

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