Concrete Inspection Construction Inspection for Field Office Activities

Objectives Review and define terms related to quality concrete Review typical specification requirements Discuss testing procedures and results based on specification

Terms Related to Quality Concrete Durability – Long lasting Permeability – Ability to hold fluids Water to cement ratio (w:c) – Affects durability and permeability –Low w:c results in higher durability and lower permeability (Good) –Determined from weight of total water in the mix (includes water in aggregates) divided by total weight of cement-like material (cement and fly ash)

Terms Related to Quality Concrete Slump – Measure of workability Air – Amount of entrained air in mix Compressive Strength – Strength of design mix or actual specimens after 28-day curing period Curing – Time period when exposed concrete surfaces are not allowed to be dry

Concrete Specifications and Testing Review the concrete specification in the Mortality Facility Example Plans Compressive Strength – 4000 psi at 28 days Water to cement ratio – 0.50 Air Content – 5-8 percent Slump – 3-5 inches Curing – 7 days without drying Temperature – degrees F What testing is required?

Concrete Class Problem The specification in the mortality facility example requires a w:c of 0.50 or less. 1.Does the design mix meet the specification? Found in Class Problems Section. Refer to Happy Hogmeister Mortality Facility Design packet to answer questions 1-4 at your tables.

Concrete Class Problem 2. What is w:c of batch? Weight of water = 242 gal x 8.33 lb/gal = 2024 lbs Weight of cement = 5076 w:c = 2024/5076 = Can water be added? 4.If water is added how many revs required?

Concrete Class Problem 3. How many gallons of water can be added? Max water weight = 0.45 x 5076 = 2284 lbs Max water gallons = 2284/8.33 = 274 gallons Additional gallons = = 32 gallons

Steel Reinforcement for Concrete Construction Inspection for Field Office Activities

Objectives - Develop an Understanding Of: The purpose and use of steel reinforcement The materials used for steel reinforcement The placing of steel reinforcement The tolerances for placement of steel reinf

Basic Principals Concrete is strong in compression and shear strength Concrete is weak in tensile strength Compressive strength 4000 psi Shear 80% ~ 3200 psi Tensile 10% ~ 400 psi

Steel is strong in compressive, tensile and shear strength Structural grade steel: –Tensile strength ~ 18,000 psi –Compressive strength ~ 90,000 psi Steel bars in compression tend to buckle Will not support substantial compressive loads alone

Concrete bonds well with steel Both have nearly the same coefficient of expansion –1 inch per 100 feet between winter and summer Concrete and steel stick together and act, together, to make reinforced concrete R/C is strong in both: –Compression, and –Tension

Main Tensile Reinforcement Loaded beam supported at each end tends to sag

Convex bottom of beam is in tension Concave top is in compression Without steel reinforcement near the bottom of the beam the concrete cannot withstand the tension Wooden Craft Sticks Demonstration!!

Temperature and Shrinkage Reinforcement ( T & S) Temperature changes can cause –Expansion, or –Contraction Shrinkage causes contraction Expansion induces compressive forces in concrete & is not normally a problem Contraction induces tension which must be counteracted

T & S Reinforcement (cont) Steel bars used for contraction reinforcement are usually #3 or #4 bars spaced 12” to 18” apart with cross bars as needed for tying Some concrete is reinforced (for T&S) with steel or plastic fibers added to the concrete during mixing

Reinforcement Location in Typical Sections Location of structural steel reinforcement is crucial to the construction of any concrete structure Steel placed near the center of a wall is usually T & S reinforcement unless it goes into a foundation, wall base, or floor

Reinforcement Location in Typical Sections Tension is greater on the surface opposite of the forces (earth or stored material) Steel reinforcement for tension needs to be placed as close to the tension surface as possible There is a minimum cover to maintain to protect steel from corrosion & to insure adequate bond of concrete to steel

Materials Bar Reinforcing Steel –Smooth - used for dowels –Deformed – the standard type of reinforcement Protrusions or deformation conform to ASTM A615 Concrete bond with the steel is dependent on deformation

Three grades of steel –S–Stuctural 40,000 psiGrade 40 –I–Intermediate 60,000 psiGrade 60 –H–Hard 75,000 psiGrade 75 Bar sizes from #2 (smooth) to #18 Nominal diameter of bar = bar size/8 – #4 bar = 4/8 or ½ inch diameter

(From ASTM A615)

How to Read Bar Markings

Example Rebar # 4 bar = ½” Producing Mill S = Billet (ASTM A615) 1 extra rib = Grade 60

Example Rebar # 5 bar =5/8” Producing Mill S = Billet (ASTM A615) Grade 60

Welded Wire Reinforcement (WWR) Rolls –Difficult to flatten and position correctly –May be used for slabs on grade Sheets –Delivered in flat sheets –Easier to position correctly –Heavier gauges available

WWR Example of poor positioning in slab

WWR continued WWR generally comes in 6, 8 or 10 gage wire Rectangular grid pattern - 6” by 6” is most common

Typical Bar Types

Placing Surface condition of steel – no loose, flaky, scaly rust –Light covering of tight, yellow brown rust is beneficial in increasing the adhesion of concrete to steel –Remove oil from re-bars if excessive –Remove any mud from bars Reinforcement - accurately positioned and secured as shown on the drawings

Placing - continued Supports should hold bars firmly –Sufficient strength to carry the loads –Not displace too much concrete –Eliminate any opportunity for leakage or rusting –Close enough together that bars will not sag appreciably

Placing – Examples of supports

Placing - continued Splices – dependent upon –Bar diameter –Location in structural member –Location to other laps Splice location typically not shown on the drawings No lap length less than 12 inches –Typical lap = 30D (D = bar diameter)

Cover Construction Plans will show min cover Cover = distance between concrete edge and reinforcing edge or between rebar edges Typical cover distances –#4 bars in footings, ends exposed to earth = 3” –#4 bars, slab, exposed to earth or weather = 2”

Example Tolerances (Location) Minimum cover shown on drawings: ±3/8” Location in wall or floor section: ±3/8” of position shown on drawings Lap or splice location: ±1”, minimum splice length of 12” From NEH 645, Appendix E

Example Tolerances (Spacing) Minimum spacing shown on drawings: ±1/4” Uniform spacing shown: ±2” from theoretical location From NEH 645, Appendix E

Tolerances for Placement

Interpreting Steel Drawings Refer to composter drawings sheet 4

Interpreting Steel Drawings

Review Questions (Use sheet 4 of the Composter drawings to answer) 1.What shape is a type 21 bar? 2.What shape is a Mark W2 bar? 3.What is the spacing for the Mark W4 bars? 4.What is the tolerance for that spacing? 5.What is the nominal diameter for the Mark W4 bars?