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Concrete and Masonry Construction. BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay. Concrete has several properties that make it well suited for a wide variety of agricultural uses. Advantages: Plastic when first mixed Durable Sanitary Low maintenance Disadvantages: Heavy
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Concrete and Masonry Construction BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay
Concrete has several properties that make it well suited for a wide variety of agricultural uses. • Advantages: • Plastic when first mixed • Durable • Sanitary • Low maintenance • Disadvantages: • Heavy • Expensive • Low insulation volume
Concrete is composed of two components: paste and aggregate. • Paste • Portland cement • Entrained air • Water • Disadvantages • Heavy • Expensive • Low insulation value Cement plant in Iola, Kansas.
Portland refers to the type of cement that is universally produced by all manufacturers. • Carefully controlled mixture of: • Lime • Silica • Alumina • Iron oxide • Burned and ground into fine powder Stone quarries on the Island of Portland.
Portland cement is available in five types as designated by ASTM.
Entrained air is important for good quality concrete. • Uses less sand and water • Reduces segregation • Improves workability • May be finished earlier • Increases water tightness • Resists freezing and thawing • Resists surface scaling One cubic yard of concrete can contain 400 to 600 billion air bubbles.
Normal portland cement is suitable for most farm and general construction work. • 1 sack = 94 lbs or 1 ft3 • Dry storage is essential • Do not use cement that contains lumps Common products for home concrete use.
Water for making concrete should be clear, free of acids, alkalis, oils, and organic matter.
Both the cost and quality of the concrete are affected by the kind of aggregate selected. • Aggregate should be: • Clean • Hard • Strong • Sharp, rough, or flat aggregate requires more cement-water paste • Fractured material severely reduces strength Gravel Quarry in Southern Ontario.
Aggregates size is determined by screening material through a Number 4 sieve. • Number 4 sieve • ¼ inch openings • 16 openings/in2 • Fine aggregate – passes through a Number 4 sieve • Coarse aggregate – does not pass through a Number 4 sieve Inclined aggregate screen.
The use of well-graded aggregates will produce an economical mixture with the least amount of cement. • “Well-graded” – a variety of materials ranging in sizes: • Fine sand • Coarse sand • Small stones • Allows small particles to fill voids between large particles • Use of aggregates from gravel banks not recommended Well-graded aggregate fit together so perfectly that a minimum of paste is required.
The maximum size of aggregate used depends on the size and shape of the structure and the distribution of rebar.
Excessive amounts of silt or organic matter prevents a secure bond between the paste and aggregate.
A silt test can determine whether aggregate should be washed. • Glass jar • 2 inches of aggregate • 6 inches of water • Shake vigorously and let stand for one hour • If more than 1/8 inch of silt has settled at the top of aggregate – wash or abandon 1/8 in Silt 2 in Aggregate The silt layer is only 1/8 in; therefore the aggregate is useable without washing.
An organic matter test can determine whether aggregate should be washed. • Glass jar • ½ pint of water • ½ pint of aggregate • 1 teaspoon lye • Stir and let stand for 3 to 4 hours • Observe color • Clear to light straw – use • Dark straw – do not use Free of OM Some OM Too much OM The samples on the left and in the middle are useable; the sample on the right is not .
Concrete strength is inversely proportional to the amount of water used. 7000 5 gallons/sack 6000 6 gallons/sack 5000 7 gallons/sack 4000 Compressive Strength (psi) 3000 2000 1000 0 7d 28d 90d Moist-cure test at 70 degrees F.
Use the specific density of materials to determine the masses of materials needed for a specific concrete mix. A 1:1.9:2.3 ratio mix = ?
The specific gravity (γ) of a substance is a comparison of its density to that of water. 1 cup water 1 cup lead Each glass contains equal volume of material; however, the glass with lead will weigh more than the glass with water.
The density of a material is calculated by multiplying its specific gravity by the density of water. γsand/gravel = 2.65 ρH2O = 62.4 pcf ρsand/gravel = (2.65)(62.4 pcf) = 165.4 pcf γcement = 3.15 ρcement = (3.15)(62.4 pcf) = 196.6 pcf
Concrete Volume Example #1 Determine the volume of a one-sack batch of concrete for a storage tank. The maximum size of aggregate is ¾ inch.
Concrete Volume Example #2 Determine the amount of concrete needed for a feeding floor 35 ft by 120 ft by 4 in thick. Include 5% for error.
The actual yield of concrete is 60% of the volume of the total volume of materials.
Concrete Yield Example Determine the yield of a 7 gal/sack concrete mixed using a maximum aggregate size of 1½ inches.
The purpose of mixing is to achieve a uniform distribution of the ingredients and allow for air entrainment. • Mixing times: • One minute for ≤ 1 yd3 • One minute plus 15 s/yd3 for large batches • Mixing order (truck mixers): • Water • Little aggregate • Cement • Balance of aggregate Brand new cement mixing truck.
Forms should be ready and in place before the concrete is mixed or before the ready-mix arrives. • Form materials: • Plywood • Steel • Sheathing • Forms should be: • Clean • Tight • Tied together to prevent bulging Form for concrete column consisting of plywood and rebar.
Before pouring concrete, the job site must be properly prepared.
Remove the soft spots and fill them with soil, gravel, or crushed rock.
Excavate the site about three or more feet then backfill with compact material to prevent foundation sinking.
Wood forms should be oiled with form oil or used crankcase oil prior to concrete placement.
Immediately after the concrete is in place, it is struck off with a straight edge board, known as screeding.
Soon after screeding, the surface may be floated (smoothed) with a darby or bullfloat.
Forms may be removed from fittings or foundations in 24 hours; slabs and beams need in four to five days.
Curing is the time needed to complete the chemical reaction between portland cement and water.
Fresh concrete develops 40% of its potential strength during the first 14 days of curing; 70% during the first 28. 7000 5 gallons/sack 6000 6 gallons/sack 5000 7 gallons/sack 4000 Compressive Strength (psi) 3000 2000 1000 0 7d 28d 90d Moist-cure test at 70 degrees F.
Curing is a hydration process; therefore, concrete must not be allowed to dry out during curing. • Continuously sprinkle with water • Cover with: • Damp sand • Damp straw • Plastic film Plastic film over freshly poured slab.
Concrete must be protected from freezing or excessive heat during the curing process. • Optimum temperature ~ 75 °F • Process slows down as temperature decreases • Curing stops at 32 °F • Permanent damage if freezing occurs with first 24 hours
Reinforcing materials improve the strength of concrete structures by carrying tensile loads. • Transfer of tensile forces • Materials • Wire mesh • Reinforcing bars (rebar) • Synthetic fibers Placing rebar and wire mesh prior to pouring.
Wire mesh is a common reinforcing material for concrete. • Advantages: • Can be formed into various shapes • Tensile strength of 60,000 to 70,000 psi • Disadvantages: • Difficult to install • Expensive • High labor Wire mesh form.
Rebar is ribbed steel bars installed in foundation concrete walls, footers, and other poured structures. • Advantage: • Very high tensile strength (70,000 to 90,000 psi) • Disadvantages: • Difficult to install • Expensive • High labor • Cannot weld Rebar in sealer.
Synthetic fibers are replacing welded wire mesh, especially in residential slabs. • Advantages: • Easy to install • Reduce plastic shrinkage cracks • Disadvantages: • Very low tensile strength Nylon fibers for concrete reinforcement.
Walls constructed with concrete blocks bonded together with mortar are described as masonry construction. • Advantages: • Durable • Fire resistant • Low maintenance • Relatively inexpensive • Disadvantages: • More porous than concrete • More subject to cracking than concrete Construction of concrete block wall.
