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Portland CeMent ConCrete CHAPTE r

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The minimum of the water-cement ratio for strength and exposure is chosen for proportioning the concrete. The volume of the fine aggregate is then converted to a weight using the unit weight.

Table 7.6 presents the recommended air contents for different combinations of  exposure conditions and nominal maximum aggregate sizes
Table 7.6 presents the recommended air contents for different combinations of exposure conditions and nominal maximum aggregate sizes

Mixing, Placing, and Handling Fresh Concrete

  • ready-Mixed Concrete
  • Mobile Batcher Mixed Concrete
  • depositing Concrete
  • Pumped Concrete
  • Vibration of Concrete
  • Pitfalls and Precautions for Mixing Water
  • Measuring air Content in Fresh Concrete
  • Spreading and Finishing Concrete

Agitation of the container allows the excess water to displace the air in the voids of the cement paste. The water level in the container drops as the air rises to the top of the container.

Curing Concrete

  • Ponding or Immersion
  • Spraying or Fogging
  • Wet Coverings
  • Impervious Papers or Plastic Sheets
  • Membrane-Forming Compounds
  • Forms left in Place
  • Steam Curing
  • Insulating Blankets or Covers
  • electrical, Hot oil, and Infrared Curing
  • Curing Period

Backfill can be achieved by forming soil dams around the concrete surface to retain water. Various types of liquid membrane-forming compounds can be applied to the concrete surface to reduce or delay moisture loss.

Properties of Hardened Concrete

  • early Volume Change
  • Creep Properties
  • Permeability
  • Stress–Strain relationship

It can be seen that increasing the water-cement ratio decreases both the strength and stiffness of the concrete. There are several empirical relationships between the modulus of elasticity of concrete and its compressive strength.

  • Compressive Strength test
  • Split-tension test
  • Flexure Strength test
  • rebound Hammer test
  • Penetration resistance test
  • Ultrasonic Pulse Velocity test
  • Maturity test

Thus equation 7.5 is valid as long as fracture occurs in the middle third of the specimen. The surface hardness can be correlated to a certain extent with the concrete strength.

Self-Consolidating Concrete

The most common field test used to measure flowability and stability of SCC is a modified version of the drop test discussed earlier. The cone is lifted and the expansion of the concrete is measured as shown in Figure 7.44.

Flowable Fill

Liquid fill is most commonly used as a backfill for utility trenches, retaining walls, pipe beds and building excavations. Liquid filling has become more common in recent years and is available from most ready-to-use manufacturers.

Shotcrete

For biological shields, the mass of the concrete can be increased by using heavy aggregates. Freeze-thaw resistance - the rapid drainage of the pavement limits the potential freeze-thaw resistance.

Concrete Sustainability

Calculate the required average compressive strength of the mix design if the mix installation has a standard deviation of s = 3.8 MPa. Calculate the required average compressive strength of the mix design if the standard deviation is s = 2.4 MPa. Estimate the modulus of elasticity of the concrete at the required average compressive strength (the calculated strength, not the given strength).

A masonry structure is formed by combining masonry units, such as stone, blocks or brick, with mortar. Near-uniform size bricks came into common use in Europe in the early 13th century. Over the past two centuries, bricks have been used in the construction of sewers, bridge piers, tunnel linings, and multi-storey buildings.

Masonry Units

The compressive strength of individual concrete masonry units is determined by covering the unit and applying load in the direction of the height of the unit. The gross area compressive strength is calculated by dividing the failure load by the gross cross-sectional area of ​​the unit. The net cross-sectional area is calculated by dividing the net volume of the unit by its average height.

Mortar

Grout

Plaster

Masonry sustainability

EA p2: Minimum Energy Performance Concrete masonry walls provide thermal mass to help meet minimum energy efficiency requirements. EA c1: Optimize Energy Performance Masonry concrete walls provide thermal mass to help exceed minimum energy efficiency requirements. MR c3: Material Reuse Sandblasted concrete masonry units and segmented retaining wall units can be easily stored and reused.

Before the mid-1850s, asphalt came from natural pools found in various locations around the world, such as asphalt from Lake Trinidad, which is still mined today. Tar can also be used to treat pavements, especially where fuel spills can dissolve asphalt cement, such as in parking lots and airport aprons. Some crude sources, such as Nigerian oil, produce little asphalt, while others, such as many Middle Eastern oils, have high asphalt content.

ASPHALT BINDERS AND ASPHALT MIXTURES

Types of Asphalt Cement Products

The properties of the asphalt depend on the chemical composition and distribution of the molecular weight hydrocarbons. First, as oil costs have escalated, the use of these expensive solvents as a vehicle for the asphalt cement is no longer cost-effective. The electrical charge of the emulsifier causes a repulsive force between the asphalt spheres which maintains their separation in the water.

Uses of Asphalt

Although emulsions and cuts can be used for the same applications, the use of emulsions is increasing because they do not include hazardous and expensive solvents. Cold mixes are commonly used for plastering (when asphalt concrete is not available), base and subgrade stabilization, and surfacing of low-volume roads.

Temperature Susceptibility of Asphalt

1 1 Typical relationship between asphalt viscosity and temperature. hot-mix asphalt Carefully designed mix of. asphalt cement and aggregates Paving surface and base, plaster. Cold mix Mixture of aggregates and liquid. asphalt patch, low volume road. surface, asphalt stabilized base Missile Seal Spray of diluted asphalt emulsion. on existing pavement surface Seal existing pavement surface Primer Apply asphalt emulsion. binding aggregate base and asphalt concrete surface. Adhesive layer Spray asphalt emulsion. between elevators of asphalt concrete Construction of new pavements or between an existing pavement and an overlay Chip seal Spray layer of asphalt emulsion. or asphalt cement or cut-off) followed with aggregate layer.

Chemical Properties of Asphalt

The remaining maltene fraction is introduced into a chromatographic column and desorbed using solvents of increasing polarity to separate the other fractions. A third scheme [Figure 9.15(c)] is chemical precipitation, in which n-pentane is added to separate the asphaltenes.

Superpave and Performance Grade Binders

Characterization of Asphalt Cement

The aging temperature, which varies between 90°C and 110°C, is chosen according to the grade of the asphalt binder. The required amplitude depends on the value of the complex shear modulus of the asphalt binder being tested. The strain at failure is a measure of the amount of elongation the asphalt binder can sustain without cracking.

Classification of Asphalt

Three types of dilutions are produced, depending on the hardness of the residue and the type of solvent used. Cutback curing refers to the evaporation of the solvent from the asphalt residue. The viscosity of the emulsion is rated as normal flow or slow flow, based on the Saybolt-Furol viscosity (ASTM D244).

table 9.3Performance Graded Asphalt Binder Specifications (Table 1 of AASHTO M 320)
table 9.3Performance Graded Asphalt Binder Specifications (Table 1 of AASHTO M 320)

Asphalt Concrete

Asphalt Concrete Mix Design

Gmm = maximum theoretical specific weight of asphalt concrete Ps = weight percentage of aggregate. In Equation 9.17, the air voids are assumed to be 4.0%, the target air void content for a mix design. Marshall Strength and Flow Measurement - The Marshall strength of asphalt concrete is the maximum load the material can sustain when tested in the Marshall apparatus, Figure 9.30.

Figure 9.28 and Equations 9.5 to 9.7 are used to demonstrate the volumetric rela- rela-tionships used for asphalt mix design analysis
Figure 9.28 and Equations 9.5 to 9.7 are used to demonstrate the volumetric rela- rela-tionships used for asphalt mix design analysis

Characterization of Asphalt Concrete

Therefore, it is important to assess the asphalt concrete's tensile strength for the design of the layer thickness. The equipment and associated protocols for the AMPT tests are designed to capture the viscoelastic behavior of asphalt concrete. The dynamic modulus is correlated to both rutting and fatigue cracking in asphalt concrete.

Hot-Mix Asphalt Concrete Production and Constr uction

The purpose of finish rolling is to remove roller marks left on the surface from previous roller passes. Quality control during construction Long-term pavement performance requires proper construction of pavement layers. The main material parameter evaluated in the field is the density of the mat after compaction.

Recycling of Asphalt Concrete

The properties of the aggregate in each batch are evaluated following the procedures for the virgin material. Any of the previously described mix design methods can be used to design a RAP mix. This procedure minimizes the exposure time of the RAP to high temperature to reduce the hardening of the binder in the RAP.

Additives

Scrap tires can be added to asphalt cement (wet method) or added as shredded rubber to aggregate (dry method). These modifiers have two main advantages: changing the temperature-viscosity behavior of asphalt and improving the durability of asphalt concrete. Absorption of aromatics by asphalt cement limits the amount of SBS that can be usefully added.

Warm Mix

The blend additive technologies modify the viscosity temperature properties of the asphalt in a non-linear manner as shown in Figure 9.43 (Hurley and Prowell, 2005). Hot mix can also be produced by modifying the asphalt plant to accommodate hot mix production. In the foamed state, the asphalt can flow around the aggregates and create the necessary coating.

Asphalt Sustainability

Porous pavements - evaporation of the water stored in the pavement lowers the temperature of the road surface. If the maximum theoretical specific gravity of the sample (Gmm) is 2.531, what is the vacuum content of the sample in percent. If the bulk density of the mixture is 2355 kg/m3, what is the percentage of voids in the total mixture.

Brown, Superpave Mix Design: Verifying Gradation Levels in the Ndesign Table, National Cooperative Highway Research Program Report 573. In the United States, the Forest Service of the Department of Agriculture has broad management responsibilities for harvesting timber from public lands and assisting private sources with the selection of products for harvest. Wood from endogenous trees is not generally used for engineering applications in the United States.

Structure of Wood

Most of the species used in the United States do not have decay-resistant heartwood. The anisotropic behavior of the wood is the result of the tubular geometry of the wood cells. However, a few cells in localized bundles grow radially, from the center to the outside of the stem.

table 10.1Major Sources of Hardwood and Softwood Species by Region *Chestnut is no longer harvested, but lumber from salvage timbers is available.
table 10.1Major Sources of Hardwood and Softwood Species by Region *Chestnut is no longer harvested, but lumber from salvage timbers is available.

Chemical Composition

Chemically, lignin is a poorly dissolved, insoluble material that is loosely bound to cellulose. The longitudinal shear strength of wood is limited by the boundary strength of lignin. Ash-forming materials account for 0.1% to 3.0% of the wood material and include calcium, potassium, phosphate, and silica.

Moisture Content

Assuming the green dimension is XFSP and the dimension at any moisture content below the FSP is XMC, the following equation can be used. Assume 1% swelling (relative to the green dimensions) per 5% increase in moisture content below the FSP. Assuming the green dimension is XFSP and the dimension at any moisture content below the FSP is XMC, the following equation can be used.

Figure  10.5 shows that the changes in wood dimensions vary from one direction  to another
Figure  10.5 shows that the changes in wood dimensions vary from one direction to another

Wood Production

7 An arch bridge made of structural glued laminated timber (glulam). Courtesy of the American Institute of Timber Construction). The surface (planing) of the wood surface, to produce a smooth surface, can be done before or after drying. Air drying is complete when the moisture content of the wood is in equilibrium with the air humidity.

Lumber Grades

Since wood shrinks at different rates in different directions (see Figure 10-5), the combined effects of radial and tangential shrinkage can distort the shape of pieces of wood. Based on the amount of "cutting," the wood is rated Firsts, Seconds, Selects, and Common (No. 1, No. 2, No. 3A or 3B), with Firsts being the best. In machine stress grading, each piece of wood is subjected to X-rays to measure its density, which is related to strength and stiffness.

Reaction wood causes the core to be off the center of the neutral axis of the tree. These pockets form as a result of an injury to the tree, which causes the death of a small area of ​​the cambium. Turning is the lifting of one angle out of the plane of the other three.

table 10.4Example of Design Values for Visually Graded Dimension Lumber (50 mm-100 mm thick) of Eastern White P 3   Bending values are applicable to lumber loaded on edge
table 10.4Example of Design Values for Visually Graded Dimension Lumber (50 mm-100 mm thick) of Eastern White P 3 Bending values are applicable to lumber loaded on edge

Physical Properties

Hình ảnh

Table 7.6 presents the recommended air contents for different combinations of  exposure conditions and nominal maximum aggregate sizes
table 7.8Approximate Mixing Water in kg/m3 for Different Slumps and Nominal Maximum Aggregate Sizes*
Figure 9.1Classification of bituminous materials. (Goetz and Wood, 1960)
table 9.3Performance Graded Asphalt Binder Specifications (Table 1 of AASHTO M 320)
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