CIVE 320 Chapter 3.1, Spring 2016

Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering . . Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering . Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering • Concrete Quality Requirement: – Acceptable workability of freshly mixed concrete. – Durability, strength, and uniform appearance of hardened concrete. – Economy (Cost effective). • Basic Steps for Weight and Absolute Volume Methods: 1. Evaluate Strength requirement. 2. Determine the water-Cement ratio required. 3. Evaluate coarse aggregate requirements: • Maximum aggregate size. • Quantity of the coarse aggregate. Portland Cement Concrete Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete • Basic Steps for Weight and Absolute Volume Methods: 4. Determine air entrainment requirements. 5. Evaluate workability requirements of the plastic concrete. 6. Estimate the water content requirements of the mix. 7. Determine cement content and type needed. 8. Evaluate the need and application rate of admixtures. 9. Evaluate the fine aggregate requirement. 10. Determine moisture corrections 11. Make and test trial mixes. Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete • Evaluate Strength requirements: – Specified compressive strength, f’c – Variability or standard deviation s, and – Allowable risk of making concrete with unacceptable strength. The standard deviation s for a plant. Allowable risk by the American Concrete Institute (ACI) states that there should be less than 10% chance that the strength of concrete mix is less than the specified strength. f’cr= f’c + 1.34s (1) f’cr = required average compressive strength, MPa or psi f’c = specified compressive strength, MPa or psi s = standard deviation, MPa or psi Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete • Evaluate Strength requirements (cont’d): For mixes with a large standard deviation in strength, ACI has another risk criterion: f’cr= f’c + 2.33s – 3.45 (units in MPa) (2) Or f’cr= f’c + 2.33s – 500 (units in psi) The standard deviation is determined from at least 30 strength tests. If computed from 15 to 30: then s must be multiplied by a modification factor F. No. of Tests F 15 1.16 20 1.08 25 1.03 30 or more 1.00 Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete • Evaluate Strength requirements (cont’d): If fewer than 15 tests, the following adjustments are made instead: Very conservative and should not be used for large project, since concrete will be over- designed, therefore, not economical.. Specified comp. strength (f’c) MPa (psi) Required AVg. f’cr MPa (psi) < 21 (< 3000) f’c + 7.0(1000) 21 to 35 (3000 to 5000) f’c + 8.5(1200) >35 (>5000) f’c + 10(1400) Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete • Evaluate Strength requirements (cont’d): The design engineer specifies a concrete strength of 31.0 MPa (5400 psi). Determine average comp strength for: a. A new plant where s is unknown: f’cr = f’c + 8.3 = 39.3 MPa (5700 psi) b. A plant where s = 3.6 MPa (520 psi) for 17 test results: Multiply standard deviation by F, interpolate for F: F= 1.16 – [(1.16-1.08)/(20-15)]*(17-15)=1.13 S’= 3.6*1.13 = 4.1 Mpa (590 psi) f’cr= 31.0 + 1.34(4.1) = 36.5 Mpa (5300 psi) (1) f’cr= 31.0 + 2.33 (4.1) – 3.45 = 37.1 MPa (5390 psi) (2) Use f’cr= 37.1 MPa (5390 psi) Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete • Evaluate Strength requirements (cont’d): c. A plant with extensive history of producing concrete with s = 2.4 MPa (350 psi): Determine maxi. From Eqs. 1 and 2: f’cr= 31.0 + 1.34(2.4) = 34.2 Mpa (4970 psi) (1) f’cr= 31.0 + 2.33 (2.4) – 3.45 = 33.1MPa (4810 psi) (2) Use f’cr= 34.2 MPa (4970 psi) d. A plant with extensive history of producing concrete with s = 3.8 MPa (550 psi): Determine maxi. From Eqs. 1 and 2: f’cr= 31.0 + 1.34(3.8) = 36.1 Mpa (240 psi) (1) f’cr= 31.0 + 2.33 (3.8) – 3.45 = 36.4MPa (5280 psi) (2) Use f’cr= 36.4 MPa (5280 psi) Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete Avg. Comp. Strength at 28 days, MPA(psi) Water-Cement ratio, by wt. Non-air entrained Concrete Air-entrained Concrete 48 (7000) 0.33 - 41 (6000) 0.41 0.32 35 (5000) 0.48 0.40 28 (4000) 0.57 0.48 28 (3000) 0.68 0.59 14 (2000) 0.82 0.74 Table 7.1 TYPICAL relationship between Water-Cement ratio and compressive strength of concrete If no historical data is available. • Water-Cement Ratio Requirements: Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete Avg. Comp. Strength at 28 days, MPA(psi) Water-Cement ratio, by wt. Non-air entrained Concrete Air-entrained Concrete 17 (2500) 0.67 0.54 21 (3000) 0.58 0.46 24 (3500) 0.51 0.40 28 (4000) 0.44 0.35 31.0 (4500) 0.38 - 35 (5000) - - Table 7.2 MAXI. PERMISSIBLE Water-Cement ratio and compressive strength of concrete, when strength data from field experience or trial mixtures are NOT available. (Conservative) • Water-Cement Ratio Requirements (cont’d): Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete Exposure condition Maxi w/c for Normal wt. Concrete, by wt. Concrete protected from exposure to freezing and thawing or application of de-icer chemicals Select w/c ratio on basis of strength, workability, and finishing needs Concrete intended to be watertight exposed to: a. Fresh water b. Brackish water or seawater 0.50 0.45 Concrete exposed to freezing and thawing in a moist condition (air-entrained concrete): a. Curbs, gutters, guardrails, or thin sections b. Other elements c. In presence of de-icing chemicals 0.45 0.50 0.45 For corrosion protection for reinforced concrete exposed to de-icing salts, brackish water, seawater, or spray from these sources 0.40 (if cover is increased by 12mm, w/c may be increased to 0.45 for normal weight concrete) Table 7.3 Maxi. W/c for various EXPOSURE CONDITIONS • Water-Cement Ratio Requirements (cont’d): Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete Normal wt. concrete Lightweight concrete Sulfate Exposure Water- Soluble Sulfate in Soil % by wt. Sulfate in water, ppm Cement Type Maxi. W/C, by wt. Mini, Comp. Strength Mpa (psi) Negligible Moderate 0.00-0.10 0.10-0.20 0-150 150-1500 - II, IP(MS, IS(MS)… - 0.50 - 28(4000) Severe Very Severe 0.20-2.00 Over 2.00 1500-10,000 Over 10,000 V V plus pozzolan 0.45 0.40 31 (4500) 35 (5000) Table 7.4 Requirements for CONCRETE EXPOSED TO SULFATE-CONTAINING SOLUTIONS • Water-Cement Ratio Requirements (cont’d): Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete Situation Maxi. Aggregate size Form dimensions 1/5 of mini. Clear distance Clear space between reinforcement or prestressing tendons ¾ of mini. Clear space Clear space between reinforcement and form ¾ of mini. Clear space Unreinforced slab 1/3 of thickness MAXIMUM SIZE AGGREGATE • Coarse Aggregate Requirements: Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete Maxi. Size Agg. mm (in) Fineness Modulus 2.40 2.60 2.80 3.00 9.5 (3/8) 0.50 0.48 0.46 0.44 12.5 (1/2) 0.59 0.57 0.55 0.53 19 (3/4) 0.66 0.64 0.62 0.60 25 (1) 0.71 0.69 0.67 0.65 37.5 (1-1/2) 0.75 0.73 0.71 0.69 50 (2) 0.78 0.76 0.74 0.72 75 (3) 0.82 0.80 0.78 0.76 150 (6) 0.87 0.85 0.83 0.81 Table 7.5 Volume of Coarse Agg. Per unit of volume of concrete for different Fineness Moduli of Fine aggregate • Coarse Aggregate Requirements (cont’d): Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete 9.5mm (3/8 in) 12.5mm (1/2 in) 19mm (3/4in) 25mm (1 in) 37.5mm (1- 1/2in) 50mm (2 in) 75 mm (3 in) 150mm (6 in) Non-air ent. Conc, ~entrapped % 3 2.5 2 1.5 1 0.5 0.3 0.2 Air-ent. Mild exposure Moderate Severe 4.5 6.0 7.5 4 5.5 7.0 3.5 5.0 6.0 3.0 4.5 6.0 2.5 4.5 5.5 2.0 4.0 5.0 1.5 3.5 4.5 1.0 3.0 4.0 Table 7.6 Approximate Target Air Requirements for Maxi. Sizes of Aggregates • Air Entrainment Requirements: Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete Table 7.7 Recommended slumps for Various types of Construction Concrete Construction Slump mm (in) Maxi.1 Mini. Reinforced foundation walls and footings 75 (3) 25 (1) Plain footings, caissons, substructure wall 75 (3) 25 (1) Beams and reinforced walls 100 (4) 25 (1) Buildings columns 100 (4) 25 (1) Pavement and slabs 75 (3) 25 (1) Mass concrete 50 (2) 25 (1) 1.May be increased 25 mm (1 in) for consolidation by hand methods, such as rodding and spading. • Workability Requirements: Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete Slump mm Maxi. Aggregate Size mm 9.5 12.5 19 25 37.5 50 75 150 Non-Air Entrained Concrete 25 to 50 207 199 190 179 166 154 130 113 75 to 100 228 216 205 193 181 169 145 124 150 to 175 243 228 216 202 190 178 160 - Air Entrained Concrete 25 to 50 181 175 168 160 150 142 122 107 75 to 100 202 193 184 175 165 157 133 119 150 to 175 216 205 193 184 174 166 154 - Table 7.8. Approximate mixing water for different slumps and Maximum. Aggregate Sizes in Kg/m3. FOR ANGULAR AGG. (CRUSHED STONE) • Water Content Requirements: Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete The recommendations of table 7.8 are reduced for other aggregate shapes: • Water Content Requirements (cont’d): Aggregate Shape Reduction in Water content Kg/m3 Sub-angular 12 Gravel with crushed particles 21 Round Gravel 27 Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete Minimum Cement Requirements for Normal weight Concrete Used in Flatwork • Cement Content Requirements: Maxi. Size Aggregate, mm Cement, Kg/m3 37.5 280 25 310 19 320 12.5 350 9.5 360 Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete If one or more are used, the quantity should be considered in proportioning. Manufacturers provide specific information on the amount required to achieve the desired results. • Admixture Requirements: • Fine Aggregate Requirements: At this point the: water, cement, and coarse agg. Are known per cubic meter; and the volume of air is estimated. The only remaining is fine agg. Table 7.10. Estimate of Mass (Weight) of Freshly Mixed concrete: Maxi. Agg. Size. mm Non-Air entrained kg/m3 Air Entrained Concrete kg/m3 9.5 2276 2187 12.5 2305 2228 19.0 2347 2276 25.0 2376 2311 37.5 2412 2347 50.0 2441 2370 75.0 2465 2394 150 2507 2441 Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete A trial batch is mixed to check the design. Three 0.15m x 0.30m cylinders are made, cured for 28 days, and tested for comp strength. In addition to slump and air content measured. • Trial Mix Requirements: • Moisture Content Corrections: Need to adjust water content to account for moisture content (MC). • If MC > SSD moisture content: mixing water is reduced by an amount equal the free weight of the moisture on agg. • If MC < SSD: mixing water is increased. Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete • Design Problem (Volume Method): Design Environment: Bridge pier exposed to freezing and subjected to de-icing chemicals Required Design strength = 24.1 Mpa (3500 psi) Mini dimension = 0.3m Mini. Space between rebars = 50 mm Mini. Cover over rebars = 40 mm S = 2.4 Mpa (350 psi) (more than 30 samples) Only air entrained is allowed Available Materials: CEMENT: select type V due to exposure AIR ENTRAINER: Manufacture specification 6.3 ml/1% air/100Kg cement COARSE AGGREGATE: 25 mm maxi size, river gravel (round), Bulk oven dry specific gravity = 2.621, Absorption 0.4% Oven dry rodded density = 1681 kg/m3, moisture content = 3% Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete • Design Problem (Volume Method): FINE AGGREGATE: Natural sand, Bulk oven-dry specific gravity = 2.752, Absorption = 0.8% Moisture content = 4%, Fineness Modulus = 2.60 1. Strength Requirement: f’cr= 31.0 + 1.34(2.4) = 27.3 Mpa (3960 psi) (1) f’cr= 31.0 + 2.33 (2.4) – 3.45 = 26.2 MPa (3810 psi) (2) f’cr= 27.3 Mpa (3960 psi) • Solution 2. Water Cement Ratio: Strength Requirement Table 7.1: w/c = 0.48 by interpolation Exposure requirement Tables 7.3 and 7.4: w/c = 0.45 Water-cement ratio = 0.45 Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete 3. Coarse Aggregate Requirement: 25 mm < (1/5) 300 mm mini. Dimensions 25 mm < (3/4) 50 mm rebar spacing 25 mm < (3/4) 40 mm rebar cover Aggregate Size OK for Dimensions Table 7.5: 2 mm maxi. Size coarse agg. And 2.60 FM fine agg. Coarse agg. Factor = 0.69 Oven Dry wt. coarse agg. = 1681 * 0.69 = 1160 kg/m3 Coarse Agg. = 1160 kg/m3 4. Air Content: Table 7.6: Sever exposure, Target air content = 6.0% Job range = 5 to 8% base Design on 7% Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete 5. Workability: Table 7.7: Pier Best fits the column requirement in the table Slump range = 25 to 100 mm Use 75 mm 6. Water Content: Table 7.8: 25 mm agg. With air entrainment and 75 mm slump Water = 175 kg/m3 for angular agg. Since we have round agg. Reduce by 27 kg/m3 Required Water = 148 kg/m3 7. Cement Content: w/c = 0.45, water = 148 kg/m3. Cement = 148/0.45 = 328 kg/m3 for exposure Cement = 334 kg/m3 8. Admixture: 7 % air, cement = 334 kg/m3. Admixture = 6.3 * 7 * (334/100) = 147 ml/m3 Admixture = 147 ml/m3 Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete 9. Fine Aggregate Requirements: Find fine agg. Content; use the absolute volume method. Water Vol. = 148/(1 x 1000) = 0.148 m3/m3 Cement Vol. = 334/(3.15 x 1000) = 0.106 m3/m3 Air Volume = 0.07 m3/m3 Coarse Agg. Vol. = 1160/ (2.621 x 1000)= 0.443 m3/m3 Subtotal Volume = 0.767 m3/m3 Fine agg. Vol. = 1 – 0.767 = 0.233 m3/m3 Fine agg. Wt. = 0.233 x 2.572 x 1000 = 599 kg/ m3 Fine agg. Wt. = 599 kg/ m3 10. Moisture Corrections: Coarse agg.: Need 1160 kg in SSD condition, so increase by 1.5 for excess moisture Moist coarse agg. = 1160 x 1.015 = 1177 kg/m3 Fine agg.: Need 599 Kg in SSD condition, so increase 4% for excess moisture Moist Fine agg. = 599 x 1.04 = 623 kg/m3 Water: Reduce for free water on aggregates = 148 – 1160(0.015 – 0.004) – 599(0.04 – 0.008) = 116 kg/m3 Faculty of Engineering and Architecture American University of Beirut Dept. of Civil and Environmental Engineering Portland Cement Concrete • Summary Bath Ingredients Required 1 m3 PCC Water 116 kg Cement 334 kg Fine Aggregate 623 kg Coarse aggregate 1177 kg Admixture 147 ml