SOILS & MATERIALS

Soils & Materials

Soils & Materials

Answer 1

Wood is an orthotropic and anisotropic material. Because of the orientation of the wood fibers and the manner in which a tree increases in diameter as it grows, properties vary along three mutually perpendicular axes: longitudinal, radial, and tangential (Fig. 1). The longitudinal axis is parallel to the fiber (grain) direction, the radial axis is perpendicular to the grain direction and normal to the growth rings, and the tangential axis is perpendicular to the grain direction and tangent to the growth rings (Bodig, 1982). Although most wood properties differ in each of these three axis directions, differences between the radial and tangential axes are relatively minor when compared to differences between the radial or tangential axis and the longitudinal axis. Property values tabulated for structural applications arc often given only for axis directions parallel to groin (longitudinal) and perpendicular to grain (radial or tangential).

Fig. 1: Three principal axes of wood with respect to grain direction and growth rings.

Answer 2

Viscosity of Tar and Bitumen

A 300PEN, bitumen will be such that a standard needle having a 100g. Load on it will penetrate a standard sample cup of bitumen 300 tenths of a millimeter, at 25 degrees centigrade in 5 seconds.

With a 200SECS, cut-back bitumen, it is so called because it will take 200 seconds for 50 ccs. Of bitumen to run through a standard hole at 40 degrees centigrade. Be Careful The smaller the number with penetration (PEN.) grade bitumens the stiffer the material i.e. 50PEN. Is stiffer than 100PEN. bitumen.

The stiffer bitumens resist penetration giving a low number.

The smaller the number with "time" (SECS.) grade cut-back bitumens the more lively it will be, i.e. 100SECS. bitumen will be more lively than 200SECS bitumen. The stiffer bitumens take longer to flow through the standard orifice giving a high number.

This standard sets out the procedure for determining the viscosity of cutback bitumen using the Standard Tar Viscometer. This British Standard is identical with IP 72/86(92).

Although this piece of apparatus is called the Standard Tar Viscometer it is more commonly used for testing the viscosity of Cutback Bitumen these days, (there's not a lot of TAR about).

The Standard Tar Viscometer measures viscosity in time, i.e. seconds. E.g. the common viscosity for Cutback Bitumen for Surface Dressing is 100 seconds.

This is the time it takes for 50cc's of the BINDER under test, held at 40 degrees centigrade in a ...