Mortar strength

Comparisons between ballistic mortar strengths and heats of detonation relative to TNT are shown in Table 1 (the mortar values were taken from Ref 5 and the heats of detonation from Vol 7, H41-42). Agreement is generally quite good... 

Comparison of Ballistic Mortar Strength with Observed - Heats of Detonation... 

Some additional mortar strengths are shown in Vol 2, B266—95... 

Type Grain shape Grain surface Grain density kg/m3 Density kg/m3 Water absorption M-% Grain strength Maximum mortar strength N/mm2... 

Compared to quartz aggregate the strength of mortars with 50 vol-% of polymer granulate is lower, as to to be expected, see fig. 4. The differences will be lower if the polymer portion is reduced. As the modulus of elasticity of the unsorted waste materials varies due to changing composition (see chapter 3), there will be a certain scatter in mortar strength, resulting from this. 

The product has a high and uniform plasticity that is developed rapidly following mixing with water (within 30 min.). It also gives high mortar strengths [20.2]. 

Fig. 4.29 Effect of retarders and accelerators on mortars strength (according to [41])...

Another method consists on the measnrement of mortars strength, composed from two parts of sand, 2.5 parts of fly ash and one part of lime, which after mixing with water are compacted in the monlds nnder the pressnre of 10 MPa and the cnbic specimens are obtained [114]. 

Fig. 7.22 Relation of mortar strength produced from cement with fly ash to the strength of reference mortar without fly ash as a function of time and temperature (according to [138]) a) compressive strength, b) flexural strength, temperature of 1-20 °C, 2-35 °C, 3-50 °C, 4-65 °C, 5-80 °C...

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. 

A bivariant linear eq uation, contain ing factors such as phase percentages, crystal sizes, morphology and cluster indexes, for predicting the 28-day mortar strength was presented by Sinha, Rao, and Akhouri (1991). The standard deviation was said to be 17.9 kg/ cm agreeing closely with the actual strength. 

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)... 

Nonprismatic dark interstitial Low mortar strength (Tsuboi and Ogawa, 1972)... 

Relatively high 28-day mortar strength Clinker burned in oxidizing atmosphere (Sylla, 1981)... 

With the use of Ono s Method and microscopy of raw feed, clinker, cement, gypsum, and kiln dust, coupled with laboratory burns and sieve analysis of the raw feed, Vanisko (1978) demonstrated the deleterious effect of belite nests in development of mortar strength. He showed that coarse quartz was correlated with numerous large belite nests and, when the raw sand was separately and more finely groimd, mortar strengths jumped to 41 MPa. 

Illustrating some of the effects of fine-grained raw feeds, mortar strengths of 44.8 MPa with a cement at approximately 400 m /kg were attained when 8.15% lime kiln dust was added to the raw feed, the burning process in the plant monitored closely with the microscope (Iany, 1986). 

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. 

Variations in predicted 28-day mortar strength among cement producers led Moir (1997) to study the burnabilities of kiln feeds from 15 cement plants in the laboratory, using a horizontal programmable tube furnace. An equation to calculate the temperature required for 1% free lime was given as ... 

Mortar Deterioration. Mortar may decay from the formation of calcium sulfoaluminate (which causes expansion and loss of mortar strength) and by the attack of pollutants in the atmosphere. Portland cement contains tricalcium aluminate, which reacts with sulfates in solution to form calcium sulfoaluminate. Exhaust gases from automobiles contain sulfur dioxide, sulfur trioxide, and nitrous oxides. These oxides react with moisture in the atmosphere to form sulfurous acid, sulfuric acid, and nitric acid, which are the attacking agents. As attack continues over the years, the mortar joints may crack, the surface of the joint may spall off, and the mortar may become softer and more crumbly. 

The parameters for the damage and restoring force models would have to be specified for a given type of masonry. To illustrate the use of these models for damage assessment, the model parameters will be determined for unreinforced brick masonry. For this purpose, the cyclic load test results reported in Zhu (1980), Ref. 7, and Xia (1986) are used. Compressive strengths of the masonry units are between 75 and 100 kg/cm, whereas the mortar strengths range from 5 to 50 kg/cm. ... 

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