Fundamentals Of Concrete Part 2 PDF

CHAPTER 1 FUNDAMENTALS OF CONCRETE – PART 2 3.0 HARDENED CONCRETE Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 2 Cross Section of Hardened Concrete Concrete made with siliceous rounded gravel...

CHAPTER 1 FUNDAMENTALS OF CONCRETE – PART 2 3.0 HARDENED CONCRETE Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 2 Cross Section of Hardened Concrete Concrete made with siliceous rounded gravel Better workability Concrete made with crushed limestone Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 3  3.1 Curing ▪ Maintenance of a satisfactory moisture content and temperature in concrete for a suitable period of time immediately following placing & finishing so that the desired properties may develop ▪ Time ▪ Temperature ▪ Moisture Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 4 Strength of Concrete Increases if: ▪ Unhydrated cement is still present ▪ The concrete remains moist or has a relative humidity above 80% ▪ The concrete temp. remains favorable ▪ Sufficient space is available for hydration products to form Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 5 Effect Of Curing On Strength Development Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 6 3.2 Compressive Strength ▪ Defined as the measured maximum resistance of a concrete or mortar specimen to an axial load, usually expressed in MPa at an age of 28 days ▪ Most general use concrete – 20 to 35 MPa ▪ High-strength concrete by definition – 70 MPa or greater Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 7 TESTING OF COMPRESSIVE STRENGTH Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 8 Compressive Strength Test Specimen Sizes – CSA A23.1-09 ▪ Mortar — 50 mm cubes ▪ Concrete — 100 x 200 mm high cylinders (generally 150 x 300 mm in USA or a concrete mix has larger aggregates in the mix) Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 9 Approximations Of Concrete Strengths ▪ Compressive strength ( ƒc′ ) ▪ 7-day — 75% of 28-day ▪ 56 and 90-day — 10% - 15% > 28-day Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 10 3.3 Density ▪ Density Approximate Values ▪ Normal concrete — 2200 to 2400 kg/m3 ▪ Reinforced concrete — 2400 kg/m3 ▪ Low density insulating concrete — 240 kg/m3 ▪ High density concrete — 6000 kg/m3 (e.g. radiation shielding, counterweights) Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 11 3.4 Watertightness & Permeability ▪ Watertightness ▪ The ability of concrete to hold back or retain water without visible leakage. ▪ Permeability ▪ Amount of water migration through concrete when the water is under pressure or the ability of concrete to resist penetration by water or other substances (liquids, gas, ions, etc.) Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 12 Relationship Between Hydraulic Permeability, W/C- ratio, And Initial Curing Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 13 3.5 Abrasion Resistance ▪ Floors, pavement and hydraulic structures are subjected to abrasion ▪ In these applications concrete must have a high resistance to abrasion ▪ Abrasion resistance is closely related to the compressive strength of concrete Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 14 Effect Of Compressive Strength And Aggregate Type On The Abrasion Resistance Of Concrete Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 15 3.6 Volume Stability And Crack Control ▪ Concrete kept continuously moist will expand slightly ▪ Concrete that is permitted to dry will shrink ▪ Shrinkage is mostly influenced by the water content of the freshly mixed concrete. ▪ Other factors affecting shrinkage are also: ▪ Amount of aggregate used ▪ Properties of the aggregates ▪ Size and shape of the concrete mass ▪ Relative humidity and temperature ▪ Method of curing ▪ Degree of hydration ▪ Time Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 16 3.6.1 Joints ▪ Joints are the most effective method for controlling unsightly cracking ▪ The three main types of joints are: ▪ Contraction Joints - They are grooved, sawed or formed into the concrete structure to dictate where the cracking will happen. ▪ Isolation Joints – Separate a slab from other parts of a structure to permit horizontal or vertical movement of the slab. ▪ Construction Joints – Occurs where concrete work is done for the day Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 17  Construction Joint Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 18 4.0 DURABILITY Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 19 4.1 Resistance To Freezing And Thawing ▪ The most destructive weathering factor is freezing and thawing while the concrete is wet Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 20 Specimens Subjected To 150 Cycles Of Freezing And Thawing ▪ Non air-entrained ▪ High w/c ratio ▪ Air-entrained ▪ Low w/c ratio Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 21  Type GU cement Relationship Between Freeze-thaw Resistance, W/C- Ratio, And Different Concretes And Curing Conditions (1) Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 22 4.2 Alkali- Aggregate Reactivity (AAR) ▪ A reaction between the active mineral constituents of some aggregates and the sodium and potassium alkali hydroxides and calcium hydroxide in the concrete. ▪ Alkali-Silica Reaction ( ASR ) ▪ Alkali-Carbonate Reaction ( ACR ) Refer CSA A23.1-09 Annex B — Alkali-Aggregate Reaction Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 23 ALKALI-SILICA REACTIVITY ( ASR ) ▪ Mitigate ASR with use of: ▪ Non-reactive aggregates ▪ SCMs ▪ Blended cements ▪ Limit concrete alkali content (low-alkali cement) ▪ Test for effectiveness Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 24 4.3 Carbonation Corroded Steel Due To Carbonation Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 25 4.4 Chloride Resistance And Steel Corrosion Methods to reduce corrosion and embedded steel by chlorides ▪ Use low w/cm ratio concrete ▪ Moist cure ▪ Reduce permeability with SCM’s ▪ Increase concrete cover ▪ Corrosion inhibitors ▪ Epoxy-coated reinforcing steel ▪ Concrete overlays ▪ Surface treatments ▪ Cathodic protection Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 26 Reducing Corrosion By Chlorides Using Epoxy- coated Rebars Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 27 4.5 Sulphate Attack Increase sulphate resistance with the use of: ▪ Low w/cm (i.e. 0.4) ▪ Sulphate resistant cement (Type MS & Type HS) Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 28 Concrete Beams After Seven Years Of Exposure To Sulphate-rich Wet Soil Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 29 AVERAGE 16-YR RATINGS OF CONCRETE BEAMS IN SULPHATE SOILS Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 30 4.6 Concrete Exposed To Seawater ▪ A structure exposed to seawater spray is most vulnerable in the tidal or splash zone where there are repeated cycles of wetting and drying. Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 31 Questions? Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 1; 32