Sulfur flexural

The stability and permeability of a mix are not sufficient criteria to reflect how a material will perform under the repeated loads generated by traffic. Therefore, any mix design selection process should include an examination of the material s fatigue resistance. Figure 5 shows the relationship between sulfur content and fatigue life for some SAS mixtures at two strain levels [15]. These tests were run at constant stress in third point flexure. Both curves go through a maximum at a sulfur content of 14 percent. 

Figure 27. Flexural strength and bulk density of unidirectional composites subjected to graphitizing heat treatments either for each densification cycle or after the densification cycles were completed (20,52) The matrix was a coal-tar binder pitch with 10 wt.-% sulfur the high-modulus PAN-based fiber was Sigrafil HM.

Figure 34. Comparison of the flexural strengths of unidirectional carbon/carbon composites (left-hand side) with those of hybrid composites in which the final impregnation is made with an epoxy resin (34) The composites were fabricated with high-modulus fibers rigidized with phenolic resin, and subjected to four densification cycles with coal-tar pitch plus sulfur.

Figure 35. Mechanical properties of carbon-carbon epoxy-resin hybrid composites, compared with the properties of the composite skeletons before resin impregnation (61,62). The composite skeletons were prepared from Sigrafil HM 3 PAN based fiber, rigidized with a phenolic resin, and densified by four cycles with coal-tar pitch plus sulfur the carbonization temperature was 1000 C. (b) Flexural strength. (c) Interlaminar shear stress, measured with two sample thicknesses.

In the late 1960s experiments were made again to produce sulfur concrete. Now, the emphasis was on developing a construction material (6,7). The first products had a sulfur content of about 30 wt % and had compressive and flexural strengths in the order of 250 kp/cm2 and 35 kp/cm2, respectively. These first experiments were followed by more research (8, 9,10,11). 

Figure 7. Comparison of the ratio between the flexural strength and the compressive strength of cement concrete and sulfur concrete...

Figure 12. Compressive strength vs. flexural strength of sulfur concrete samples with different DCP content in the binder...

Figure 13. Influence of the storage time on the compressive and flexural strength of DCP-modifled sulfur concrete samples.

This increase in stability, however, is accomplished at the sacrifice of mix flexibility. The data in Table IV indicate that the flexural strain at break of mixes No. 3 and 4 is reduced significantly below that of mixes No. 1 and 2 when the sulfur concentration in the binder is raised to 40 and 50 wt %, without increasing the total binder content. Flexibility is a measure of mix susceptibility to brittle fracture and is an important mix design consideration in rigid materials to prevent premature pavement cracking. 

Because of its higher rigidity at warm temperatures, sand Thermopave formulations are not as flexible as asphalt concrete mixes. A typical sand Thermopave mix (6 wt % asphalt 12 wt % sulfur) exhibits a flexural strain at break of 0.004 cm/cm under the same test conditions as indicated in Table IV. Although this is below the strain values for asphalt concrete, lower flexibility in Thermopave can be tolerated as the tensile stresses and strains developed at the underside of the pavement are lower than for an asphalt pavement of equivalent thickness and subjected to the same loading. Performance of test pavements to date, some over six years old, have not indicated flexibility to be a problem as yet. 

Mechanical Characterization of Sulfur-Asphalt. The serviceable life of a pavement comes to an end when the distress it suffers from traffic and climatic stresses reduces significantly either the structural capacity or riding quality of the pavement below an acceptable minimum. Consequently, the material properties of most interest to pavement designers are those which permit the prediction of the various forms of distress—resilient modulus, fatigue, creep, time-temperature shift, rutting parameters, and thermal coefficient of expansion. These material properties are determined from resilient modulus tests, flexure fatigue tests, creep tests, permanent deformation tests, and thermal expansion tests. 

Sulfur foams with a wide spectrum of properties can be prepared by this process. Properties generally vary with density, which may range from 3 to 45 lb/ft3. However, while density is kept constant, properties such as compressive strength, flexural strength, and closed-cell content may be altered by formulation changes. Some of the more common properties are listed in Table II. 

Properties Dimensional stability over temperature range from -40 to +71C. Attacked by nitric and sulfuric acids and by aldehydes, ketones, esters, and chlorinated hydrocarbons. Insoluble in alcohols, aliphatic hydrocarbons, and mineral and vegetable oils. Processed by conventional molding and extrusion methods. D 1.04 tensile strength about 6500 psi, flexural strength 10,000 psi, good electrical resistance, water absorption 0.3-0.4%. Combustible but slow-burning flame retardants may be added. Can be vacuum-metallized or electroplated. 

Polyester polymer concrete resists oxidizers, acids, oils, and petroleum products, but there is not enough resistance to alkaline solutions and water. The strength of polyester PC in water decreases faster than in solutions of inorganic salts and some acids therefore, resistance in acid solutions can simultaneously serve as an estimate of water resistance. For example, the flexural strength of the PC, immersed in a 10% solution of sulfuric acid or 10% sodium chloride solution is reduced by 30% after 80 days of immersion. 

PCs based on epoxy resin binder are resistant to many corrosive environments such as a concentrated solution of caustic soda at 90°C the action of alkali metal salts, alcohols, oils, gasoline and other aliphatic hydrocarbons. The flexural strength of epoxy PC is slightly affected by immersion in a 10% solutions of sulfuric acid and chloride sodium, which is an indicator of the good chemical resistance of this kind of concrete to these aggressive agents [11], However, these polymer concretes are not resistant to a sulfuric acid concentration of 60% and nitric acid concentrations above 70% [12],... 

Examination of the fractured surfaces yields a direct correlation with flexural strength. The higher strength mixes and elemental sulfur all... 

Sulfur, upon aging, tends to increase in flexural strength, as shown in Figure 14. Because of the extremely brittle nature of sulfur, reliable flexural values are difficult to obtain after 15 days. This undesirable property of sulfur points out the necessity of chemical modification to prevent or retard these brittle properties. 

Effect of Temperature on Strength. Work by Rennie et al. indicates that the flexural strength of IVz in. X 1% in. X 10 in. sulfur prisms depends markedly on the temperature at which they are equilibrated before testing (2). Other investigators (3) have noted that sulfur specimens having a substantial volume/surface area ratio may undergo thermal shock, a durability problem in which a fluctuating temperature may... 

The chemical routes to altering the properties of sulfur have been presented by Barnes (9). These techniques often result in lowering the compressive and flexural strength of the sulfur, imparting color and odor to the sulfur from by-products generated, and raising the cost of the resultant materials by the cost of the additives and the labor required... 

The sulfur method has much greater flexural strength, racking strength, and tensile or bond strength. Impact and durability tests also indicate superior performance. 

Maheshwari et al. (2007) exposed phenolic-bonded composite bipolar plates to 5% sulfuric acid solution for 5 h at 50°C. The samples were reconditioned and the differences in weight were measured. The authors also carried out water adsorption studies on several composite samples. In order to ascertain that there is no adverse effect of water adsorption on the plates, these were tested for their compressive strength, their flexural strength, and the electrical resistivity before and after water adsorption. 

Table 1. Flexural Strength and Modulus of Vulcanized Rubber Bagasse Composite as a Function of Sulfur Content...

Sample Number Natural Rubber (b) Sulfur Sundex 790 Oil(c) Bagasse (d) Iron Oxide 477(e) Flexural Strength (psi) Deflection at Break (inch)... 

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