Descripción: Durability Design of Concrete Structures
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Due to ever increasing quantities of waste substances and industrial by products, strong waste management is the high concern in the world. Scarcity of land filling house and because of its ever growing cost, recycling and utilization of industrial b
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Self compacting concrete can be placed and compacted under its own weight without any vibration and without segregation or bleeding. The use of mineral admixture such as fly ash, GGBS, etc. as partial replacement of cement in SCC can bring down cost.
Manual de uso del equipo slake durabilityFull description
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For a long time concrete was considered to be very durable material requiring. We build concrete Structures in highly polluted urban and industrial areas. Aggressive marine environments harmful Sub soil water in area and many other hostile conditions
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Conventional concrete used in building and civil engineering applications requires compaction to achieve strength, durability and homogeneity. The typical method of compaction, vibration, generates delays and additional costs in projects and moreover
DURABILITY PLANNING AND SUSTAINABILITY FOR NEW PROJECTS
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Chapter - I Introduction to Concrete and Concrete Material Course: Concrete Technology Level: B.E. Civil Engineering
detail report about Transparent concrete
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CHAPTER – VI CONCRETE DURABILITY Durability refers to the ability of concrete to resist weathering action, chemical attack, abrasion or any other process of deterioration, while maintaining its desired engineering properties.
6.1 Effect of Water and Permeability on Concrete Durability Water causes: i. Chemical processes of degradation ii. Physical processes of degradation Higher w/c ratio is the fundamental cause of higher permeability. Therefore, use of higher w/c ratio – permeability – volume change – cracks – disintegration – failure of concrete is a cyclic process in concrete. Therefore, for a durable concrete, use of lowest possible w/c ratio is the fundamental requirement to produce dense and impermeable concrete. It has been proved beyond doubt that low w/c ratio concrete are less sensitive to carbonation, external physical attack and other detrimental effects that causes lack of durability of concrete.
PERMEABILITY Permeability is a property that governs the rate of flow of a fluid into a porous solid. According to Darcy’s Law, for steady-state flow, the coefficient of permeability, K, is determined from: dq/dt = K.(ΔH/L).A where, dq/dt = rate of fluid flow, ΔH = pressure gradient, A = surface area and L = thickness of the solid Permeability of concrete to air or other gases is of interest in structures such as sewage tanks and gas purifiers, and in pressure vessels in nuclear reactors.
6.2 Physical and Chemical Causes of Concrete Deterioration Physical Causes of Concrete Deterioration:
Surface Wear
Cracking • Volume change due to - normal temperature and humidity gradient; crystallization pressure of salts in pores • Structural Loading overloading and impact; cyclic loading • Exposure to temperature extremes - freeze-thaw action; fire
• Abrasion • Eroson • Cavitation
Deterioration of Concrete by Chemical Reaction:
Exchange reations between aggressive fluids and components of hardened cement paste Removal of Ca++ ions as soluble products - increase in porosity and permeability
Removal of Ca++ ions as nonexpansive insoluble products increase in porosity and permeability
Substituion reactions replacing Ca++ in C-S-H
Reaction involving hydrolysis and leaching of the components of hardened cement paste Increase in porosity and permeability - a. Loss of strength and rigidity b. Increase in deterioration process c. Loss of mass d. Loss of alkalinity
Reaction involving formation of expansive products Increase in internal stresses - a. Loss of strength and rigidity b. Cracking, popouts c. Deformation
6.3 Carbonation Carbonation occurs in concrete because the calcium bearing phases present are attacked by carbon dioxide of the air and converted to calcium carbonate. Cement paste contains 25-50 wt. % calcium hydroxide (Ca (OH)2), which mean that the pH of the fresh cement paste is at least 12.5. The pH of a fully carbonated paste is about 7.
The concrete will carbonate if CO2 from air or from water enters the concrete according to: Ca (OH)2 + CO2
->
CaCO3 + H2O
When Ca (OH)2 is removed from the paste hydrated CSH will liberate CaO which will also carbonate. The rate of carbonation depends on porosity & moisture content of the concrete. The carbonation process requires the presence of water because CO2 dissolves in water forming H2CO3. If the concrete is too dry (RH <40%) CO2 cannot dissolve and no carbonation occurs. If on the other hand it is too wet (RH >90%) CO2 cannot enter the concrete and the concrete will not carbonate. Optimal conditions for carbonation occur at a RH of 50% (range 40-90%). Normal carbonation results in a decrease of the porosity making the carbonated paste stronger. Carbonation is therefore an advantage in non-reinforced concrete. However, it is a disadvantage in reinforced concrete, as pH of carbonated concrete drops to about 7; a value below the passivation threshold of steel. How do you recognize carbonation? Carbonation may be recognized in the field by the presence of a discolored zone in the surface of the concrete. The color may vary from light gray and difficult to recognize to strong orange and easy to recognize. Carbonation can be visualized by using phenolphthalein. In the optical microscope carbonation is recognized by the presence of calcite crystals and the absence of calcium hydroxide, ettringite and un-hydrated cement grains. Porosity is unchanged or lower in the carbonated zone. *(Consult a text book for “corrosion of steel in concrete”).
