Flexural creep stiffness

The flexural creep stiffness of bituminous binders in the range of 30 MPa to 1 GPa is determined by the bending beam rheometer test. Apart from the flexural stiffness, the w-value and the flexural creep compliance are also determined. The flexural creep stiffness test is performed on unaged or aged bituminous binders and at low to very low temperatures, ranging from 0°C to -36°C. 

The flexural creep stiffness, or the flexural creep compliance, describes the low-temperature stress-strain time response of bituminous binder at the test temperature within the range of linear viscoelastic response. 

The low-temperature thermal cracking performance of asphalt pavements is related to the creep stiffness and the m-value of the asphalt binder contained in the mix. 

The creep stiffness and the m-value, according to ASTM D 6373 (2007) or AASHTO M 320 (2010), are used as performance-based specification criteria for bituminous binders. 

The flexural creep stiffness at loading time t, S t) [or measured flexural creep stiffness, S ,(r)], is the ratio obtained by dividing the bending stress by the bending strain. 

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With respect to crumb rubber modification, a recent study has shown that crumb rubber (size 0/0.8 mm and quantity 5%, 10% and 15% by mass of bitumen), when blended to 70/100 and 50/70 graded bitumens, results in improved penetration, softening point, flexural creep stiffness and shear modulus G. The quantity of the crumb rubber and the provenance of the bitumen directly influence the above properties of the modified bitumen (Neutag and Beckedahl 2011). 

ASTM D 6648. 2008. Standard test method for determining the flexural creep stiffness of asphalt binder using the bending beam rheometer (BBR). West Conshohocken, PA ASTM International. 

The deflection over time are automatically recorded, and the flexural creep stiffness is calculated (SJ at times of f = 8, 15, 30, 60, 120 and 240 s, as well as the m-value (m is the slope of the straight line from the IgS and Igr value pairs, where t is loading time). 

Bending beam rheometer test for flexural creep stiffness... 

CEN EN 14771.2012. Bitumen and bituminous binders - Determination of the flexural creep stiffness-Bending beam rheometer (BBR). Brussels CEN. 

The properties of PS/SBS are compared with HIPS and ABS in Tables I and II. PS/SBS is similar to HIP in color, hardness, tensile strength and flexural strength and to ABS in impact strength, stiffness, and heat resistance. PS/SBS is intermediate between ABS and HIPS in tensile creep, gloss, and chemical resistance. Normal finishing methods... 

Talc - Talc is a filler made by dry or wet grinding of mineral magnesium silicate. Talc improves stiffness, dimensional stability, flexural modulus, creep resistance, flow, surface smoothness, moisture resistance, tensile strength, and wear resistance of plastics. It also increases heat deflection temperature and decreases vapor permeability. Can be used as a film antiblock agent. Used mainly in polypropylene but also in thermoplastic and unsaturated polyesters and epoxy resins at low levels. Surface-modified grades are available. 

The advantages of WPC include increased bending strength, stiffness (flexural and tensile modulus), reduced thermal expansion and cost. Mechanical properties such as creep resistance, modulus and strength are usually lower than those of solid wood. WPC are not being nsed in applications that require considerable structural performance [53], although in early 1984, cellulose flour was used to reinforce PA to give PA 12 [54]. 

Polypropylene is a very versatile polymer. It has many properties that make it the polymer of choice for various applications (e.g., excellent chemical resistance, good mechanical properties and low cost). There are many ways in which the mechanical properties of polypropylene can be modified to suit a wide variety of end-use applications. Various fillers and reinforcements, such as glass fiber, mica, talc, and calcium carbonate, are typical ingredients that are added to polypropylene resin to attain cost-effective composite mechanical properties. Fibrous materials tend to increase both mechanical and thermal properties, such as tensile strength, flexural strength, flexural modulus, heat deflection temperature, creep resistance, and sometimes impact strength. Fillers, such as talc and calcium carbonate, are often used as extenders to produce a less-costly material. However, some improvement in stiffness and impact can be obtained with these materials. 

Talc s low cost qualifies it as a extender, for lowering the cost of the compound and extending the resin with minimal sacrifice in physical properties. Its aspect ratio qualifies it as a reinforcing fiUer, for enhancing performance properties of the compound. Polymers filled with platelike talc exhibit higher stiffness, tensile strength, and creep resistance at ambient as well as elevated temperatures. For example, when polypropylene homopolymer is filled with a 40 percent loading of talc, its flexural modulus is tripled from about 200,000 psi to about 600,000 psi. 

Tests for laminate properties indicate that the moduli and stiffness of laminates made with each type of glass are identical. Tensile, flexural, and shear strengths are generally equal or slightly higher with E-CR. Long-term behaviour (tension -creep in air) is identical. 

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