Concrete SOG Presentation - Concrete An Overview of...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Concrete An Overview of Design & Construction Considerations Including Quality Control for Concrete Slabs-on-Grade E. Raymond DesOrmeaux 03/27/12 P.E. 1 Introduction Basic Engineering & Construction Materials Concrete Steel Wood Others Plastics, etc. Combination Use commonly called Composite Construction 03/27/12 2 This presentation will focus on the following: What is concrete? Water Cement Ratio Slump - for various Concrete Applications Joints in Concrete Types & Use Plastic Concrete Capable of being shaped or formed ACI Manual of Standard Practice Distributed Reinforcing vs. Structural Slabs 03/27/12 3 Overview Concrete is one of the most widely used building materials throughout the world The Long History of Concrete Portland Cement Various Types of Cement Type I IA II II A III III A IV V Special Properties are not required Air Entraining General moderate sulfate resistance or heat of hydration Air entraining, with Type II High Early Strength Air Entraining with Type III Low heat of Hydration Required High Sulfate Resistance Required 4 03/27/12 Acronyms SOG WWF ACI CRSI PCA ASTM W/C ASCC A word formed from the initial letters of a name (Engineers love acronyms) Slab-on-Grade Welded Wire Fabric American Concrete Institute Concrete Reinforcing Steel Institute Portland Cement Association American Society for Testing of Materials Water Cement Ratio American Society for Concrete Construction 5 03/27/12 Concrete What is It? Cement It is called "Portland" because its color resembled the stone quarried on the Isle of Portland off the British coast. Aggregates Defined by sieve size: Silts Sands Gravels Consideration of large aggregates 03/27/12 Water Other such as Admixtures 6 Water/Cement Ratio 1. More water is needed to make concrete "workable" than is needed for hydration. "Workable" is defined as the ability to place and finish concrete within acceptable tolerances and appearance". 2. W/C Ratio is not the same for all applications Slabs Formed Concrete Roadways/Highways Architectural Finishes Pre-Cast Mass Concrete 3. . To apply the W/C Ratio it is necessary to understand weights & measurements 03/27/12 7 Understanding unit measurements & dimensional quantities are absolutely critical to the success & application of most engineering principles. Weights & Measures Concrete is no exception. Water 62.4 lbs. per cubic foot 7.48 gallons per cubic foot; therefore, 8.34 lbs./gallon Cement 94 lbs. per cubic foot (Commonly called "A Bag of Cement") The industry uses cubic feet, tons, and barrels of cement for measurements Barrel of Cement = 4 cu. ft. Aggregate Weights Sand 1,400 to 2,400 pcy (dry & loose to wet & compacted) Gravel approximately the same weights Concrete Varies 3,500 4,000 lbs/cubic yard 1 cubic yard = 27 cubic foot mineral to the density of water. The SG of water = 1 Dimensional Quantities 1 cubic foot = 1' x 1' x 1' Specific Gravity - is a measure of the density of a mineral. SG compares the density of a 03/27/12 8 W/C & Slump More water is needed to make concrete "workable" than is needed for hydration. The slump number is the amount of "drop" the concrete makes out of a 12" mold (or cylinder) measured in inches (in the USA) The Cylinder is usually 6" x 12" Adding water to Concrete produces the following: 1. Higher Slump 2. Concrete with less Compressive Strength 3. Excessive water may produce unacceptable, low quality concrete, with companion problems Common Slumps for Various Concrete Applications 1. Highways 1"- 2" for certain types of machine placing (refer to DOTD Standards) 2. Formed Concrete 3" - 6" dependent on type 3. Slab-on-Grade 4" - 6" 4. Architectural dependent on application 5. Pre-Cast " " " 6. Mass Concrete Slump & Heat of Hydration Critical 03/27/12 9 W/C & Slump Continued Slab-on-Grade Slump 4" 6" (We design for 5") W/C Range 0.40 0.50 maximum Example 1 cubic yard of Concrete 5 bag Mix W/C = 0.40 Note: 5 x 94 = 470 lbs. of Cement 470 lbs. x 0.40 = 188 lbs. of Water 188 lbs. of Water = 188/8.34 = 22.5 gallons/cubic yard Most concrete delivery tickets will indicate the number of pounds of water added at the plant. It is necessary to compute the gallons that may be added at the site for workability, and within the identified slump range. Field Slump Tests !!! Review Concrete "Batch" tickets carefully for "Required" (Design) and as "Batched" Using the number of cubic yards delivered, compute how much, if any, water can be added for good workability. Therefore, in the above mix, if 7 cubic yards of Concrete are delivered, the maximum water that the mix can have is: 188 x 7 = 1,316 pounds, or 158 gallons 03/27/12 10 Slump & Admixtures Many types of Admixtures are available that alter Concrete. For Slump control (and workability), admixtures can be used to control the Slump, use less water, thereby, not negatively impacting the quality of the concrete. These are commonly called Water Reducing Admixtures Low Range Mid Range High Range commonly called Super Plasticizers, or "Super P" It is necessary for an engineer to understand the implications of using admixtures. For example, a H.R. admixture will retard "set time", and finishing characteristics. It is good practice to avoid the use of Calcium Chloride (for whatever purpose) because of its corrosive properties related to steel. 03/27/12 11 Joints in Concrete Joints in Concrete Slabs-on-Grade are constructed to allow the concrete slab to move slightly, and, to a degree, provide a crack-free appearance for the slab. Slab movements are caused primarily by: (from ACI 224.3R-95) Shrinkage of the concrete, a volume change due to drying Temperature changes Direct or flexural stress from applied loads Settlement of the slab Types of Joints Contraction (sometimes erroneously called "Control Joints") Sawed Joints Hand Tooled Formed (keyway) Inserts Expansion Including Isolation Joints Construction Construction joints are placed in the slab where the concreting operations are terminated. Special Item Dowels Joints may include or exclude Dowels, which may be "smooth" or deformed bars Dowels are used as "Load Transfer Devices" 03/27/12 12 Joints in Slabs-on-Grade Continued Factors to Consider in Joint Spacing Thickness of Slab Base thickness & type, load capacity Subgrade General Guidelines 1. "Panels" to be as "square" as possible 2. If panels are rectangular keep length to width ratio less than 1.5:1 3. For Parking Lots & Drives - spacing 15' or less (length) (15' x 10') (A 15' x 15' panel is likely to crack at mid-point in one direction) 4. 5. 6. 7. 8. 9. Do not "stagger" joints Building Slabs concrete covered or uncovered? WWF Re-Bar or plain concrete? Avoid acute angles at joints (obtuse angles o.k.) Re-entrant corners Joint Sealing Sub-Grade Drag Theory 13 03/27/12 Concrete Drive Joint Layouts 03/27/12 14 Joints in Slabs-on-Grade Continued Joint Sealing 1. 2. 3. 4. Prevent Water Infiltration base failure, then concrete failure Embedded Objects joint not performing as designed Prevent "raveling" of concrete at edges unsightly Extends design life of pavements or slabs-on-grade ACI Selected References ACI 302.1 - R 5 ACI 224.3R - 95 ACI 330 R - 01 Floor Classifications Table 2.1 Joints in Concrete Construction Guide for Design & Construction of Concrete Parking Lots 03/27/12 15 Reinforcing Steel WWF or Re-Bar 1. Anticipated loads, Floor Classification, Design Thickness 2. Quality of Base 3. Punching Shear 4. Unexpected cracking holding crack to a minimum reduce failure Distributed Steel Reinforcement Welded-wire fabric or bar mats used in pavement to hold the concrete together. This type of reinforcement does not contribute to the structural capacity of slabs on grade. Structural Slab A Concrete Slab with sufficient reinforcing (either a 1 way or 2 way design) that satisfactorily resists all calculated loads for the unsupported span width and length. A Structural Slab can also be a slab-on-grade with significant loads requiring substantial steel reinforcing for its intended use. 03/27/12 16 Reinforcing Steel WWF Welded Wire Fabric (temperature or shrinkage control) 6 x 6 W4.0 x W4.0 Wires are spaced 6" apart in each direction W4.0 - the wire size is a Wire 4 (not a re-bar # 4) Re-Bar Reinforcing Steel (either Grade 40 or 60) (ksi) The size of a bar is the diameter of the bar in 1/8" increments # 3 Bar 3/8" #4 4/8" = " #5 5/8" Bars are available from # 2 up to # 18 S, although the most commonly used bars are # 4 through # 9 03/27/12 17 Concrete General Comments Is a Joint an Engineer's method of hiding a crack? Use the proper amount of Cement. Remember it is the Cement that causes concrete to crack. Using more than the required amount is not only wasteful, but will probably cause you to take additional precautions with joints. construct properly. Use care in design and construction. Plan accordingly. Expansion Joints are the most difficult type of joint to Concrete can expand and contract approximately " per 100' ACI & PCA are your authoritative sources for Concrete info 03/27/12 18 Summary Important Elements of Quality Concrete Mix Design Slump Joints Finishing Curing Large Aggregates, Cement Content, Water Type of Work, Workability Issues Proper Type & Location Broom, Hard Trowel Water, Wet Mats, Liquid Compounds Joint Sealants, Sealing of Concrete Surfaces Durable Concrete requires careful attention to all design & construction elements 03/27/12 19 Author Permissions This document is the personal work of its author, E. R. DesOrmeaux. It may not be copied, reproduced, or edited in part or in whole by any other individual without the expressed written consent of the author. It may be used as a guide, or reference material in further studies of Concrete Slabs-on-Grade. It is noted that this presentation consists of general information related to quality concrete, and is not intended as a sole source of information for the design or construction of slabs. Design, construction and use of concrete is a complex engineering discipline. Civil Engineers with an interest in concrete rely on related education and professional training, along with significant research available in published works. P.E. 03/27/12 E. Raymond DesOrmeaux , 20 ...
View Full Document

  • Spring '12
  • desormeaux
  • ACI, American Concrete Institute Concrete, Concrete Institute Concrete, various concrete applications, Concrete Applications Joints

{[ snackBarMessage ]}

Ask a homework question - tutors are online