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Material durability

Civil engineering materials - the durability of materials. Durability generally refers to the ability of materials to maintain their performance for a long time under the conditions of use and under the action of various internal or external natural factors and harmful media.

Edited at 2023-07-27 12:21:50

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Material durability

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Outline

Civil Engineering Materials Final Edition
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basic mechanical properties
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construction mortar
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construction steel
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Technical standards and selection of construction steel
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Air-hardening cementitious materials
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BS
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Main properties of cement concrete
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asphalt
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concrete mineral admixture
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Material durability

Durability

Concept: It generally refers to the properties of materials that can maintain their performance for a long time under the conditions of use and are affected by various internal or external natural factors and harmful media.

water resistance

Concept: The material will not be damaged under the action of long-term saturated water, and its strength will not be significantly reduced.

formula:

K soft - softening coefficient. fb——The compressive strength of the material in the water-saturated state. (Mpa) fg——Compressive strength of material in dry state (Mpa)

The softening coefficient reflects the degree of reduction in strength of the material after it is saturated with water. It is one of the important characteristics of the change in properties of the material after absorbing water. The greater the softening coefficient, the better its water resistance.

The material absorbs water and its strength is reduced; K soft ≥0.85, water-resistant material

Impermeability

Concept: The resistance of materials to water penetration under the action of pressure water. Expressed by permeability coefficient or impermeability grade

×, for concrete materials, the permeability coefficient should be used to characterize its impermeability

Formula: K=Qd/AtH

K--permeability coefficient (cm/h); Q--amount of water seepage (cm3); A--water seepage area (cm2); d--thickness of specimen (cm) H--water pressure difference on both sides of the material (cm) ;t--water seepage time (h)

The smaller k is, the stronger the impermeability is.

Impermeability grade

In the concrete impermeability test, water seepage appeared on 2 surfaces of 6 specimens in each group. (i.e. no water seepage occurs on the 4 surfaces) expressed as 10 times the maximum water pressure (MPa).

For example, W2, W4, W6, w8, W10, and W12 respectively indicate that the maximum pressure that the specimen can withstand is 0.2MPa, 0.4MPa, 0.6MPa, 0.8MPa, 1.0MPa, 1.2MPa water pressure without penetration.

Factors affecting material impermeability

Material hydrophilicity and hydrophobicity

Generally, hydrophobic materials are more impermeable than hydrophilic materials.

density of material

Materials with higher density also have higher impermeability

Material pore characteristics

Materials with more open pores have poorer impermeability

main elements

Frost resistance

Concept: Refers to the material’s ability to withstand repeated freeze-thaw cycles without damage or significant reduction in strength when in a water-saturated state.

Frost resistance grade of concrete

F50, F100, F150, F200, F250, F300 level six

Note: Anti-freeze level - a standard specimen aged 28 days is subjected to repeated freeze-thaw cycles in a freeze-thaw solution of -25°C~20°C after being saturated with water, → it can withstand any one of the following standards The maximum number of freeze-thaw cycles is used to determine the frost resistance level (the relative dynamic elastic modulus drops to 60% of the initial value, or the mass loss rate reaches 5%).

Increasing the porosity of the same material will not necessarily reduce its frost resistance, which is determined by the open porosity

Factors affecting frost resistance

①Denseness of the material: The higher the density (the smaller the porosity), the smaller the frost resistance.

②Porosity characteristics of the material: The more open pores, that is, connected pores, the worse the frost resistance.

③Strength of the material: The higher the strength, the better the frost resistance.

④Water resistance of the material: The better the water resistance, the better the frost resistance.

⑤The amount of water absorption of the material: the greater the water absorption, the worse the frost resistance (water absorption saturation makes the frost resistance worse)

Weather resistance

Materials exposed to the atmosphere are often corroded by factors such as sunlight, wind, rain, dew, temperature changes, and corrosive gases (such as sulfur dioxide, carbon dioxide, ozone). The ability of a material to withstand these natural attacks is called weathering resistance.

Material composition, structure, structure and its impact on material properties

Material composition

chemical components

The chemical composition determines the chemical properties of the material and affects its physical and mechanical properties.

The chemical composition of inorganic non-metallic building materials is expressed in terms of various oxide contents. Metal materials are expressed in terms of elemental content

mineral composition

Mineral composition is the basic form of compounds present in inorganic non-metallic materials.

The elements and compounds in materials exist in specific mineral forms and determine many of the material's important properties.

micro structure

Crystal structure

amorphous structure

Colloidal structure

About crystals, amorphous and colloids, The correct one of the following statements is ().

Their microstructure is different

All amorphous materials are isotropic

Crystals have a definite melting point while amorphous crystals do not have a definite melting point

From a microstructure perspective, construction steel has a crystal structure, while fresh cement slurry has a colloidal structure.

×All crystal materials are anisotropic