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From page 125... ... 123 3.1 introduction This chapter provides essential information on materials used for constructing durable bridge structures. It focuses on durability and service life issues related mainly to concrete and steel, materials widely used in bridge construction, and provides limited information on other material types used in bridge construction. Read the entire page →
From page 126... ... 124 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Section 3.5 provides available solutions, methods, technologies, and other information helpful in developing individual strategies to mitigate factors adversely affecting service life. Section 3.6 identifies a process to select the overall material selection and protection strategy for providing materials with enhanced service life; however, much of this selection process is highly dependent on the application and is addressed in subsequent chapters. Read the entire page →
From page 127... ... 125 Chapter 3. MATERiALS In modern structures, reinforcement is common for providing tensile capacity, crack control, and ductility. Read the entire page →
From page 128... ... 126 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 3.2.1.1.2 Blended Cement Blended cements are produced by intergrinding or blending two or more types of fine material such as portland cement, ground granulated blast furnace slag, fly ash, silica fume, calcined clay, other pozzolans, hydrated lime, and preblended combinations of these materials (Kosmatka and Wilson 2011) Read the entire page →
From page 129... ... 127 Chapter 3. MATERiALS 3.2.1.1.3 Other Hydraulic Cement All portland and blended cements are hydraulic cements. Read the entire page →
From page 130... ... 128 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Magnesium phosphate cement mixtures have rapid setting time, high early strength, low permeability, and good bonding to clean, dry surfaces. They are extremely sensitive to water content, and extra water reduces their strength (NCHRP 1977) Read the entire page →
From page 131... ... 129 Chapter 3. MATERiALS Superfine fly ash is generally processed from a Class F fly ash by passing the parent ash through a classifier in which the coarse and fine particles are separated. Read the entire page →
From page 132... ... 130 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 3.2.1.2.1 Normal-Weight Aggregates Most commonly used normal-weight aggregates (NWAs) -- sand, gravel, and crushed stone -- produce concrete with a density of 140 to 150 lb/ft3. Read the entire page →
From page 133... ... 131 Chapter 3. MATERiALS water, including treated wash water and slurry water, is not used in concrete unless it produces 28-day concrete strengths equal to at least 90% of a control mixture using 100% potable water or distilled water and time of set meets the limits in C1602. Read the entire page →
From page 134... ... 132 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Admixtures help in achieving workable, low w/cm, and low-permeability concretes. Entrained air voids provide resistance to freezing and thawing, improved workability, and reduced bleeding and segregation. Read the entire page →
From page 135... ... 133 Chapter 3. MATERiALS aggregate and the air, water, and cement contents. Read the entire page →
From page 136... ... 134 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE tABLE 3.4. grAdeS oF PerFormAnce chArActeriSticS For high-PerFormAnce StructurAL concrete Performance Characteristic Standard Test Method FHWA High-Performance Concrete Performance Grade 1 2 3 4 Freeze–thaw durability (x = relative dynamic modulus of elasticity after 300 cycles) Read the entire page →
From page 137... ... 135 Chapter 3. MATERiALS Another characteristic to be considered is density. Read the entire page →
From page 138... ... 136 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 3.2.1.6.4 Ultrahigh-Performance Concrete UHPC has high strength and high ductility. A proprietary UHPC that is commonly available is discussed in this section; this UHPC is formulated by combining portland cement, silica fume, quartz flour, fine silica sand, high-range water reducer, water, and steel or organic fibers. Read the entire page →
From page 139... ... 137 Chapter 3. MATERiALS test is based on electrical conductance of concrete, and the presence of steel fibers affects the charge passed; however, the very dense matrix of UHPC isolates the steel fibers and provides very high resistance to current flow. Read the entire page →
From page 140... ... 138 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE vibration alone. In contrast, short fibers with ratios less than 50 are not able to interlock and can easily be dispersed by vibration. Read the entire page →
From page 141... ... 139 Chapter 3. MATERiALS LWA is sometimes used in combination with NWA to create structural concretes with densities between 120 and 145 lb/ft3. Read the entire page →
From page 142... ... 140 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE that of NWC (Davis 2008) Read the entire page →
From page 143... ... 141 Chapter 3. MATERiALS attributed to workmanship or improper handling of materials. Read the entire page →
From page 144... ... 142 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 3.2.1.6.9 Grout Grout is a mixture of cementitious material and water, with or without aggregate, proportioned to produce a pourable consistency without segregation of the constituents. Grout is a common material used in repairs to fill cracks, honeycombed areas, and interior voids and as a bonding agent. Read the entire page →
From page 145... ... 143 Chapter 3. MATERiALS interconnected and facilitate the intrusion of harmful solutions. Read the entire page →
From page 146... ... 144 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE determined that the best candidates were four fusion-bonded epoxy powders (Kepler et al. Read the entire page →
From page 147... ... 145 Chapter 3. MATERiALS It is apparent that stainless steel has varying properties and corrosion-resisting potential, and studies are continuing to identify them for use as reinforcement (Hartt et al. Read the entire page →
From page 148... ... 146 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE solution for repair, rehabilitation, and construction of portions of the highway infrastructure (Mertz et al. Read the entire page →
From page 149... ... 147 Chapter 3. MATERiALS have minimal defects and the matrix resists the propagation of cracks. Read the entire page →
From page 150... ... 148 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Grade 50W includes high-strength, low-alloy weathering steel shapes, plates, and bars for welded, riveted, or bolted construction, but it is intended primarily for use in welded bridges in which savings in weight and added durability are important. New high-performance steels have been added with three grades as shown in Table 3.6. Read the entire page →
From page 151... ... 149 Chapter 3. MATERiALS The steel's mechanical properties are affected by the following three factors: 1. Read the entire page →
From page 152... ... 150 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE tABLE 3.8. eFFectS And comPoSition oF ALLoying eLementS Alloy Element Advantage Disadvantage Steel Grade Typical Composition Carbon Principal hardening element in steel. Read the entire page →
From page 153... ... 151 Chapter 3. MATERiALS Alloy Element Advantage Disadvantage Steel Grade Typical Composition Molybdenum Increases strength, weldability, toughness, and corrosion resistance. Read the entire page →
From page 154... ... 152 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE higher-toughness steels with improved weldability. Improvements in these characteristics would improve the overall quality and ease of fabrication of bridge steels used in the United States. Read the entire page →
From page 155... ... 153 Chapter 3. MATERiALS temperature of –60°F, which corresponds to Zone 3, with a minimum service temperature of below –30°F to –60°F (FHWA 2002) Read the entire page →
From page 156... ... 154 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE bridge steel (FHWA 1989) Read the entire page →
From page 157... ... 155 Chapter 3. MATERiALS curing, and concrete placement) Read the entire page →
From page 158... ... 156 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE (ACI 2001a) provides guidance on tolerable crack widths for reinforced concrete exposed to different exposure conditions. Read the entire page →
From page 159... ... 157 Chapter 3. MATERiALS few hours after mixing with water (Kosmatka and Wilson 2011) Read the entire page →
From page 160... ... 158 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Sealers can be a pore blocker, forming a microscopically thin (up to 2 mm) protective layer on the concrete surface, or a penetrating liquid that acts as a hydrophobic agent (Zemajtis and Weyers 1996) Read the entire page →
From page 161... ... 159 Chapter 3. MATERiALS contributes to the expansion. Read the entire page →
From page 162... ... 160 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 3.3.1.2.5e Chlorides Chlorides that penetrate the concrete and reach the steel surface destroy the protective oxide layer, making reinforcement prone to corrosion. Without the protective layer, steel will corrode rapidly in the presence of water and oxygen. Read the entire page →
From page 163... ... 161 Chapter 3. MATERiALS Corrosion- inhibiting admixtures can be used to stabilize the passive oxide layer on the reinforcement, or viscosity-modifying admixtures can be added to improve the stability of the mix. Read the entire page →
From page 164... ... 162 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 3.3.1.2.6 Functional Considerations Functional considerations include vibrations, impact, concrete consolidation, concrete curing, and concrete placement. 3.3.1.2.6a Vibrations Vibration of fresh concrete using vibrators may cause loss of air in mixtures with a high sand content and could result in freeze–thaw damage. Read the entire page →
From page 165... ... 163 Chapter 3. MATERiALS 3.3.1.2.6d Concrete Curing Curing ensures that reactions occur and volumetric changes are minimized. Read the entire page →
From page 166... ... 164 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 3.3.2.2 Nonintrinsic Corrosion Protection of Reinforcement 3.3.2.2.1 Admixtures for Corrosion Protection Chemical admixtures that are added to concrete during batching to protect against corrosion of embedded steel reinforcement due to chlorides are available. There are two main types: corrosion inhibitors and physical barrier admixtures. Read the entire page →
From page 167... ... 165 Chapter 3. MATERiALS The wide use of cathodic protection has been hampered by the high cost and the maintenance of the power source or the protective material. Read the entire page →
From page 168... ... 166 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 3.4.1.1 Materials Material-related factors are shown in Figure 3.13. They include the ingredients of the concrete: the cementitious material, aggregates, water, admixtures, and fibers. Read the entire page →
From page 169... ... 167 Chapter 3. MATERiALS 3.4.1.2 Design The design of the structure through the selection of the geometry, detailing, and flexibility affects the performance of the concrete. Read the entire page →
From page 170... ... 168 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE The concrete mixer should be in good working order, the capacity given by the manufacturer should not be exceeded, and enough mixing time at the specified mixing rate should be maintained. Following the proper mixing guidelines will ensure a uniform, consistent concrete mixture. Read the entire page →
From page 171... ... 169 Chapter 3. MATERiALS vibratory screed cannot reach are finished by hand. Read the entire page →
From page 172... ... 170 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 3.4.1.5 Cracking Cracking of concrete can cause serious and costly damage to concrete structures. The cracking fault tree is shown in Figure 3.18. Read the entire page →
From page 173... ... 171 Chapter 3. MATERiALS water, cement, and paste content exhibit additional shrinkage and additional temperature rise. Read the entire page →
From page 174... ... 172 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Figure 3.18. Cracking fault tree. Read the entire page →
From page 175... ... 173 Chapter 3. MATERiALS 3.4.2.1 Load-Induced Factors Load-induced bridge-deck deterioration can be attributed to fatigue, strength and brittleness, or thermal incompatibility. Read the entire page →
From page 176... ... 174 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 3.4.2.1.3 Thermal Compatibility Thermal compatibility affects cracking potential. Temperature changes in a material result in deformations that can cause significant stress when restrained by the surrounding material. Read the entire page →
From page 177... ... 175 Chapter 3. MATERiALS 3.4.2.2.2 Coastal Climate Coastal climates introduce salt spray and high humidity, and salt and moisture accelerate the corrosion rate. Read the entire page →
From page 178... ... 176 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 3.4.2.2.3 Chemical Climate Chemical climates influence the performance of reinforcement. The main effect can be attributed to corrosion-inducing chemicals that occur naturally and can be man-made. Read the entire page →
From page 179... ... 177 Chapter 3. MATERiALS Design/Detailing Construction Inspection Production/ Operation Defects Figure 3.22. Read the entire page →
From page 180... ... 178 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE or other nonmetallic coatings that decrease bond (ACI 318-11) Read the entire page →
From page 181... ... 179 Chapter 3. MATERiALS 3.4.2.3.3 Inspection Visual inspection can indicate the condition of the reinforcement and determine if there are any gross mistakes in the reinforcement selection and placement. Read the entire page →
From page 182... ... 180 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE tABLE 3.9. technoLogy tAbLe For concrete durAbiLity Service Life Issue Solution Advantage Disadvantage Freeze and thaw Good air void system High resistance to freezing and thawing Reduction in strength due to extra air Sound aggregates Durable aggregates Availability Strength of 4,000 psi and up Used to overcome stresses Increased strength makes concrete more brittle Drainage design Minimizes saturation Ingress of water Low w/cm Reduces infiltration of water Can produce high-strength concrete that is brittle Abrasion and wear Hard aggregates Attain high concrete strengths and increased resistance to abrasion and wear Hard to obtain in some areas High-strength concrete Reduces wearing Concrete more brittle Add cover Provides new surface Extra weight Chemical reactions (ASR) Read the entire page →
From page 183... ... 181 Chapter 3. MATERiALS Service Life Issue Solution Advantage Disadvantage Corrosion of reinforcement Low permeability Reduces infiltration of aggressive solutions Can produce high-strength concrete that is brittle Membranes and coatings Reduces infiltration of aggressive solutions Difficult to apply in the field, wear of traffic Sealers for pore lining and blocking Reduces infiltration of aggressive solutions Difficult to apply in the field, concrete may be difficult to penetrate Low w/cm High strength, low permeability Excessive cracking, shrinkage Low shrinkage Minimizes cracking Low water content may adversely affect workability Low modulus of elasticity High deformation, minimizes deck cracking Reduces stiffness SCMs Reduces permeability Quality fly ash or slag missing in many areas Large maximum aggregate size Less surface area, less water, cement, and paste Less bond Well-graded aggregates Less paste Problem when good shape is missing Chemical admixtures Reduced permeability Cost, incompatibility, side effects Cover More resistance to penetration of solutions Wider cracks, extra weight and cost Overlays Creates a low-permeability protective layer over the conventional concrete Difficult to place, expensive, and prone to cracking; proper curing is critical. Read the entire page →
From page 184... ... 182 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Table 3.10 is a technology table that summarizes the solutions to reinforcement corrosion. This table includes other protective methods mentioned previously in this chapter, such as epoxy-coated, Z-bar, low-carbon chromium steel, and stainless steel. Read the entire page →
From page 185... ... 183 Chapter 3. MATERiALS 3.5.3 Structural Steel Individual strategies to mitigate factors affecting service life of structural steel are discussed in Chapter 6. Read the entire page →
From page 186... ... 184 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE • In areas with congested reinforcement or intricate formwork, high-performance concrete with high workability, such as self-consolidating concrete, would be preferred. • In bridge decks, self-consolidating concrete can lead to difficulty in maintaining the grade or the cross slope due to high flow rates; normal-weight concrete may be preferable unless durability or weight is of concern. Read the entire page →
From page 187... ... 185 Chapter 3. Read the entire page →

From page 125...

... 123 3.1 introduction This chapter provides essential information on materials used for constructing durable bridge structures. It focuses on durability and service life issues related mainly to concrete and steel, materials widely used in bridge construction, and provides limited information on other material types used in bridge construction.