6505-10 - DURABILITY OF CONCRETE Durability of Portland...

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1 DURABILITY OF CONCRETE Durability of Portland cement concrete (according to ACI Committee 201) is its ability to resist weathering action, chemical attack, abrasion, or any other process of deterioration. A durable concrete will retain its original form, quality and serviceability when exposed to its environment. General observations: Water is the primary agent of deterioration . It can be a cause of many physical processes of deterioration, or it can be a vehicle for transport of aggressive ions which cause chemical process of deterioration. – The movement of water in concrete is controlled by the permeability of concrete. Permeability is the most important indicator of durability of concrete. – Concrete is a basic material; therefore, acidic waters are more harmful to concrete . Permeability of Concrete • Permeability is the property that governs the rate of flow of a fluid through the concrete. The rate of flow is higher when the permeability is higher. Darcy’s Law : For steady-state flow, dq/dt = K Δ H A / L where dq/dt = Rate of fluid flow (in in 3 /s or cm 3 /s) K = Coefficient of permeability (in in/s or cm/s) Δ H = Difference in pressure head (in in. or cm) A = Surface area (in 2 or cm 2 ) L = Thickness of the concrete (in in. or cm) Note: Δ H = Δ P / ρ where Δ P = Pressure difference (in lbf/in 2 or kgf/cm 2 ) ρ = Density of fluid (in lbf/in 3 or kgf/cm 3 ) Permeability of Cement Paste
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2 Comparison between Permeability of Aggregates and Cement Paste Flow of water in ft 3 per year per ft 2 of area for a unit hydraulic gradient Coefficient of Permeability Effects of w/c and Aggregate Size on Permeability Deterioration by Surface Wear Abrasion - Surface wear by dry attrition. Erosion - Wear by abrasive action of fluids containing solid particles in suspension. Cavitation - Wear due to loss of mass by formation of vapor bubbles and their subsequent collapse, due to sudden change of direction in rapidly flowing water. – In flowing water, vapor bubbles form when the absolute pressure at point is reduced to the ambient vapor pressure of water. As the vapor bubbles flowing with water enter a region of higher pressure, water will burst into the the previously vapor-occupied space with great impact, and cause severe local pitting (or scarring) of concrete. – The concrete surface affected by cavitation is irregular or pitted, in contrast to the smoothly worn surface by erosion. – The best solution against cavitation is to avoid surface misalignments and abrupt changes of slope.
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3 Test Methods to Evaluate Wear Resistance Abrasion Resistance of Horizontal Concrete Surfaces (ASTM C 779) Three test procedures to evaluate the relative resistance of concrete surfaces to abrasion. Procedure A - Revolving Disks
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This note was uploaded on 05/26/2011 for the course CGN 6505 taught by Professor Mang during the Spring '11 term at University of Florida.

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6505-10 - DURABILITY OF CONCRETE Durability of Portland...

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