Construction Materials - Material Science for Engineers - Lecture Slides, Slides of Material Engineering

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The Science and Engineering of

Materials, 4

th

ed

Chapter 17 – Construction Materials

Objectives of Chapter 17

• To present a summary of the material properties of

wood, concrete, and asphalt.

• Wood consists of four main constituents – Cellulose, hemicellulose, lignin, extractives
• Three important levels in the structure of wood:
  • The fiber structure
  • The cell structure
  • The macrostructure

Section 17.

The Structure of Wood

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Figure 17.1 The structure of the cellulose filaments in wood.

Figure 17.3 The cellular structure in (a) softwood and (b) hardwood. Softwoods contain larger, longer cells than hardwoods. The hardwoods, however, contain large- diameter vessels. Water is transported through softwoods by the cells and through hardwoods by the vessels. ( From J.M. Dinwoodie , Wood: Nature’s Cellular Polymeric Fiber- Composite, The Institute of Metals, 1989 .)

The percentage water in wood is given by:

Section 17.

Moisture Content and Density of

Wood

Example 17.1 SOLUTION (Continued)

Section 17.

Mechanical Properties of Wood

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Figure 17. The effect of the percentage of water in a typical wood on the compressive strength parallel to the grain.

Section 17.

Expansion and Contraction of Wood

The change in dimensions Δ x in wood in the radial and tangential directions is approximated by

where x 0 is the initial dimension, M (^) i is the initial water content, M (^) f is the final water content, and c is a coefficient that describes the dimensional change and can be measured in either the radial or the tangential direction.

 The anisotropic behavior of wood can be reduced, and wood products can be made in larger sizes, by producing plywood.

 Plies - The individual sheet of wood veneer from which plywood is constructed.

Section 17.

Plywood

©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 17.6 The rate of hydration of the minerals in Portland cement.

©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learninglicense. ™ is a trademark used herein under

Figure 17.7 The compressive strength of concrete increases with time. After 28 days, the concrete approaches its maximum strength.

©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.

Figure 17.8 The slump test, in which deformation of a concrete shape under its own weight is measured, is used to describe the workability of concrete mix.

©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learninglicense. ™ is a trademark used herein under Figure 17.9 The effect of the water-cement ratio and entrained air on the 28-day compressive strength of concrete.