Construction Materials: Chapter 4 Lecture on Concrete PDF

Adama Science and Technology University School of civil Engineering & Architecture Construction Materials Chapter 4– Mortar, Concrete Making Materials and Plain Concrete Surafel L.[Lecturer] 1...

Adama Science and Technology University School of civil Engineering & Architecture Construction Materials Chapter 4– Mortar, Concrete Making Materials and Plain Concrete Surafel L.[Lecturer] 1 Semester I, November, 2024 2  DEFINITION AND USE 3  Mortar is the name given to a mixture of sand or similar inert particles with cementing materials and water and has the capacity of hardening into a rock like mass.  In general the maximum size of the inert particles in mortar is less than 5mm, and the cementing material is Portland cement and/or lime.  In building construction, the uses of mortar are: I. Jointing medium in masonry construction  The mortar used transfers from block to block the pressure that is produced by the weight of the masonry and the supper imposed load if any.  The jointing mortar must have satisfactory strength if a durable masonry is to  DEFINITION AND USE 4 I. Jointing medium in masonry construction  CONT.… 5 II. Wall plaster  Plastering is the process of covering various surfaces of structure with a plastic material such as cement mortar, lime mortar or composite mortar, etc. to obtain an even, smooth, regular, clean and durable surface.  provides a protective coating against atmospheric effects.  It further provides a base for receiving other decorative finishes such as painting and white washing.  MORTAR MIXES 6  The traditional mortar material for building work was lime, but later to an increasing extent Portland cement replaced it.  While the use of lime results in a relatively workable mixture, rapid development of strength as well as stronger mortar is most conveniently obtained with Portland cement.  To combine the advantages compo-mortar is prepared with appropriate proportion of Portland cement, lime and sand. Lime mortar 1 part lime, 3 - 4 parts sand; low strength, poor durability but good workability. Cement mortar 1 part Portland cement, 3 - 4 parts sand. High strength, harden quickly, good durability but low workability. Should be used immediately. Lime –cement 1 part Portland cement, 1 part lime, 6 parts sand. Good strength, moderate (composite) hardening, good workability and good durability. The addition of lime mortar increases mortar workability.  PROPERTIES OF MORTAR 7 1. WORKABILITY  Properties of mortars vary greatly because they are dependant on many variables such as:  The properties of the cementitious materials,  Ratio of cementitious material to sand,  Characteristics and grading of sand, and  Proportion of mixing water.  For the same proportions, lime-sand mortar invariably gives better workability than Portland cement-sand mortar.  Mortar produced from sand of circular grains results in better workability than those produced from sand of angular grains.  At times admixtures are used in order to improve the workability of cement sand mortar.  2. STRENGTH 8  Results of tests on mortars and compo-mortars have shown that strength is affected by a following factors such as:  The quality of the ingredients,  Proportion of the ingredients,  Water/cement ratio, and  The curing method and age.  For the same proportions, lime-sand mix gives weaker mortar than cement-sand mix. This is mainly due to the following two main factors:  Difference in strength b/n Portland cement and lime pastes. For the same proportions cement gives invariably stronger paste than lime.  Portland cement is a better cementing material than lime giving a better bond b/n the paste and the inert material.  3. WATER TIGHTNESS. 11  At times mortar is used in in parts of buildings exposed to dampness or moisture and might be required to be water tight.  In such case Portland cement should be used because of its hydraulic property and the mix should be rich and dense and Such mortar can be produced by using:  higher amount of cement,  lower water cement ratio and  coarse grained size.  With the cement content, materials and workability all constant, strength and degree of water tightness increases with the density of the mix.  MATERIALS FOR MORTAR 12 1. Cementitious ingredients  Cement: Cement used for preparing masonry mortars may be:  Ordinary Portland cement  Rapid hardening cement  Blast furnace slag cement  Portland Pozzolana cement  Lime  If lime mortar is used, lime may be of hydraulic or semi hydraulic category.  Prepared lime mortar shall be kept damp and shall never be allowed to go dry.  Partly set or dried mortar shall never be remembered for use.  CONT.… 13 2. Sand  Sand used for making mortar should be well graded, that the particles should not all be fine nor all coarse.  If the sand is well graded:  The finer particles help to occupy the space (voids) b/n the larger particles.  A dense mortar which permits the most economical use of cement and/or lime can be obtained.  Sand should be clean, free from dust, loam, clay, and vegetable matter. These foreign particles are objectionable because they:  Prevent adhesion,  Reduce strength, and  Increase porosity.  CONT.… 14  Silt test should be made at the site to determine the silt content of the sand.  If the silt content is more than 6%, the sand is unsuitable for mortar work unless the excess silt is removed by washing.  In order to check the amount of organic Silt test at construction site matter, colour test could be made as described in ASTM C40. 3. Water  Water for mortar mix should be clean and free from industrial wastes. Trough for washing sand  BATCHING AND MIXING 15  Material used for making mortar should be accurately measured, especially when preparing mortar for wall plaster.  Cement is usually measured by weight in cement bags whereas wet slaked lime and sand are measured by volume.  Each cement bag contains a net weight of 50Kg which corresponds to about 35 litre loose volume.  For convenience the other material can be measured using a measuring box made to hold quantities in multiples of 35 litre.  CONT.. 17  Mortar proportions by volume for different purposes. Purpose (Mortar type) Proportions For masonry: Cement mortar 1 cem:4-5 sand Compo mortar 1 cem: 2 lime: 12 sand For brick laying: Lime mortar 1 lime: 3-4 sand (max. 4mm) Compo mortar 1 cem:3 lime: 12 sand (max. 4mm) For plastering: 1st and 2nd coat 1 cem:½ lime: 3 sand (max. 4mm) 1 cem:½ lime: 3 sand (max. 4mm) 3rd coat 1 cem:1 lime: 4 sand (max. 4mm)  What is Concrete? 18 Concrete  Is a composite material made up of inert materials of varying sizes, which are bound together by a binding medium.  Inert materials are aggregates but cement is reactive  The strength of concrete is dependent on the strength of the aggregate paste bond.  Gathering Proportioning Mixing Transporting Ingredients & finishing Compaction Placing Hardened Curing Concrete 19  Advantages of Concrete 20  Its long life and relatively low maintenance requirements increase its economic benefits.  It is not as likely to corrode, or decay as other building materials.  It has the ability to be molded or cast into almost any desired shape.  It is a non-combustible material which makes it fire-safe and able withstand high temperatures.  It is economical when ingredients are readily available.  Cont.… 21  It is resistant to wind, water and insects. Hence, concrete is often used for storm shelters.  It has high compressive strength,  Resistance to weathering, impact and abrasion.  Building of the molds and casting can occur on the work-site which reduces costs.  Disadvantages of Concrete 22  High cost of cement, steel and formwork ( in developing countries).  Difficult quality control on building sites, with the risk of cracking and gradual deterioration, if wrongly mixed, placed and insufficiently cured with water.  In moist climates or coastal regions, corrosion of reinforcement (if insufficiently protected), leading to expansion cracks.  Low tensile strength (but can be overcome with steel reinforcement).  Demolishing concrete is difficult.  Ingredients (Composition) of Concrete 23 Portland Cement Water Paste Mortar Air (entrapped or entrained) Concrete Fine Aggregate (Sand) Aggregate Coarse Aggregate (Gravel) Admixture (If required)  cont.… 24 The property of concrete depend on the characteristic of the ingredients and the proportion of the mix.  In mix proportioning workability, strength, durability and economy should be taken into consideration.  For practical concrete mixes, the ingredients should be so proportioned that the resulting concrete has the following properties.  When freshly mixed it is workable enough for economical and easy uniform placement, but not excessively fluid.  When hardened it poses strength and durability adequate to the purpose for which it is intended.  It involves minimum cost consistent with acceptable quality  I. Water 25  Water serves two purposes in Clean water is important any making concrete: impurities present will affect  It triggers the hydration of bond strength between the paste cement (only 1/3 of the water) and aggregate. and  It makes the mix fluid and workable.  Surplus/excess water = bad for o Strength, o Durability and o Permeability.  Undesirable effects of impurities in mixing water 26 Impurities in mixing water may cause any one or all of the following:  Abnormal setting time  Decreased strength  Efflorescence (white soluble salt on surface)  Corrosion of reinforcement  Some of the impurities in mixing water that cause undesirable effects in the final concrete: 27 1.Dissolved chemicals  May either accelerate or retard the set and can substantially reduce the concrete strength.  Can actively attack the cement-aggregate bond, leading to early disintegration of the concrete.  Cont.… 28 2. Seawater:  Seawater containing less than three percent salt is generally acceptable for plain concrete but not for reinforced concrete.  The presence of salt can lead to corrosion of the reinforcing bars and a decrease in concrete strength by some 10-15%.  cont.… 29 3. Algae  Can cause a reduction in the strength of concrete by increasing the amount of air captured in the paste and  Reduce the bond strength between the paste and the aggregate. 4. Sugar If sugar is present in even small amounts, it can cause rapid setting and reduced concrete strength. II. CONCRETE AGGREGATES  Aggregates 31 o Aggregates are the filler materials which make up a large portion (roughly 60-75%) of the concrete volume. o Considerable care should be taken to provide the best aggregates available.  Aggregates have 3 main functions in concrete: 1. To provide a mass of particles which are suitable to resist the action of applied loads & show better durability than cement paste alone. 2. To provide a relatively cheap filler for the cementing material. 3. To reduce volume changes resulting from setting & hardening process & from moisture changes during drying.  cont.… The properties of concrete are affected by the properties of aggregate: 1. The mineral character of aggregate affects the strength, durability, elasticity of concrete. 2. The surface characteristics of aggregate affects  the workability of fresh mass &  the bond between the aggregate & cement paste in hardened concrete.  If it is rough, workability decreases & bond increases. 3. The grading of aggregate affects the  Workability, density & economy. 4. The amount of aggregate in unit volume of concrete. It is a common practice to use as much aggregate as possible in concrete Results in less volume changes during setting & hardening or moisture changes. (increase in volume stability) Increase in strength & durability Decrease in cost 35  Classification of aggregates based on source 36 1. Natural aggregates  Are taken from natural deposits without change in their nature during production,  with the exception of crushing, sizing, grading, or during production. i.e. crushed stone, gravel, and sand are the most common. 2.Artificial aggregates: They are obtained either as a by-product or by a special manufacturing process such as heating. (blast furnace slag ) 3. Recycled Aggregate e.g. crushed concrete, clay bricks, recycled asphalt agg  Classification based on Condition Crushed o From quarry - sharp, angular particles, rough surface, o Good bond strength, low workability Uncrushed o From river – round shapes, smooth surface, o low bonding properties, high workability  According to Formation (Petrological) Characteristics: Sedimentary rock Shale Siltstone Sandstone Limestone Igneous rock Trap rock Pegmatite Granite Gabro Metamorphic rock Amphibolite Gneiss Slate Marble 38  According to Unit Weight: 1. Heavy weight of agg.:  Hematite, Magnetite  Specific Gravity, Gs > 2.8 2. Normal weight of agg.:  Gravel, sand, crushed stone  2.8 < Gs < 2.4 3. Light weight of agg.:  Expanded perlite, burned clay  Gs < 2.4  Heavyweight Aggregate ASTM C 637, C 638 (Radiation Shielding) Barite Hematite Limonite Iron Magnetite Steel punching or shot Produce high-density concrete up to 6400 kg/m3  Normal-Weight Aggregate ASTM C 330 Most common aggregates  Sand  Gravel  Crushed stone Produce normal-weight concrete 2200 to 2400 kg/m3  Lightweight Aggregate (1) ASTM C 330 Expanded  Shale  Clay  Slate  Slag Expanded clay expanded shale Produce structural lightweight concrete 1350 to 1850 kg/m3  Lightweight Aggregate (2) ASTM C 330  Pumice  Scoria  Perlite  Vermiculite  Diatomite Produce lightweight segregating concrete — 250 to 1450 kg/m3 According to Size: 1. Fine aggregate: d ≤4.75 mm o Sand and/or crushed stone o F.A. content usually 35% to 45% by mass or volume of total aggregate o Aggregate particles passing the No. 4 (4.75mm) sieve and retained on the No. 200 (75µm) sieve 2. Coarse aggregate: d > 4.75 mm o Gravel and crushed stone between 9.5 and 37.5 mm All-in-aggregate:-aggregate composed of both fine and coarse aggregate o Containing a whole range of particles (as “all-in” or “pit-run” aggregates. Fines- silty-clay or dust particles smaller than 75 micro m (No. 200 sieve) usually undesirable impurities in aggregates.  Properties of Aggregates 45 Important properties of aggregates include:  Gradation (grain size distribution)  Shape and surface texture  Bulk unit weight  Specific gravity (relative density)  Absorption  Hardness (resistance to abrasion or wear)  Durability (resistance to weathering)  Cleanliness (deleterious substances)  Chemical stability (i.e. Alkali-Silica aggregate) result expansion and crack on concrete  Gradation of Aggregates 46 Grading: is the distribution of particles of angular materials among various sizes  MAX SIZE OF AGG.  The maximum size of aggregate practicable to handle under a given set of conditions should be used.  It’s the smallest sieve size through which the entire amount of the agg particles can pass.  Using the largest possible maximum size will result in  Reduction of the cement content,  Reduction in water requirement, and  Reduction of drying shrinkage.  CONT…  The maximum aggregate that can be used in any given condition may be limited by the following conditions.  Thickness of section  Spacing of reinforcement  Clear cover  Mixing, placing and handling techniques  Standard Limitations for Max Agg Size  The concrete mix must be so that, it can be placed inside the molds and between the reinforcing bars easily without any segregation. So, max agg size (Dmax) should not exceed: 1) 1/5 of the narrowest dimension of the mold. d=min (d1,d2,d3) d2 d3 Dmax < d d1 5  CONT.. 2) 1/3 of the depth of the slab slab h h Dmax < 3 3) ¾ of the clear spacing between reinforcement S:-face of the distance 3 Dmax < S 4 S 4) Dmax < 40mm  Example: 4cm slab 9cm Φ=10mm Dmax=? beam 40cm 5cm 20cm 1) Dmax < 1/5 min (20,40) = 4cm 2) Dmax < 1/3(9) = 3cm Dmax < 3cm 3) Dmax < 3/4(4) = 3cm 4) Dmax < 4cm  Grading of Aggregates 53 Standard sieve sizes and square opening For Fine Aggregates For Coarse Aggregates ES Series ASTM Series Es Series ASTM Series Sieve size & Sieve size Clear opening Sieve size & clear Sieve size Clear clear opening opening opening 9.5 mm 3/8 0.375 in 75 mm 3 in 3.00 in 4.75 mm No. 4 0.187 in 63 mm 2 in 2.00 in 2.36 mm No. 8 0.0937 in 37.5 mm 1 ½ in 1.50 in - - - - 1 in 1.00 in 1.18 mm No.16 0.0469 in 19 mm ¾ in 0.75 in 600 μm No. 30 0.0232 in 13.2 mm ½ in 0.50 in 300 μm No. 50 0.0117 in 9.5 mm 3/8 in 0.375 in 150 μm No. 100 0.0059 in 4.75 mm No.4 0.187 in  ASTM Requirement for CA % Passing ASTM Requirement for Sieve 1 ½"- #4 3/4" - #4 1/2" - #4 FA 3" – – – Sieve % Passing 2 ½" – – – 3/8" 100 2" 100 – – #4 95-100 1 ½" 95-100 – – #8 80-100 1" – 100 – #16 50-85 3/4" 35-70 90-100 100 #30 25-60 1/2" – – 90-100 #50 10-30 3/8" 10-30 20-55 40-70 #100 2-10 #4 0-5 0-15 0-15 #6 – 0-5 0-5 * Changes with max aggregate size  Grading of Aggregates  The particle size distribution in an aggregate sample is known as “gradation”.  Good grading implies that a sample of aggregates contains all standard fractions of aggregate in required proportion such that the sample contains minimum voids.  A good gradation secures increased economy, higher strength, lower shrinkage and greater durability.  Types of gradation 58 Aggregates may be:  Dense Well-graded  Well graded  Gap-graded (missing one or more size )  Uniform ((one sized)  Open-graded Poorly graded  maximum density, o Particles same o Missing one  high stability, (mostly large sizes,  low permeability diameter, or more sizes, o low stability, o stable, unstable, o permeable o average high permeability permeability The terms “dense” and “well-graded” are essentially the same, as are “gap”, “uniform” and “open-graded”  Well graded aggregates: 59  Improve workability of the concrete and economy of the cement. (Such aggregate has a decreased amount of voids between the particles and consequently requires less cement paste).  Produces a stronger concrete than a poorly graded one (less water is required to give suitable workability). The cement paste requirement is related the void content of the combined aggregates.  SIEVE ANALYSIS 61 The grading or particle size distribution of aggregate is determined by sieve analysis. Dry agg. is sieved to prevent lumps. Agg. #4 ***** #8 #16 #30 Sieve Analysis #50 #100 Pan Sieve shaker Lateral & Vertical motion  SAMPLING  Tests in the lab is carried out on the samples. So, certain precautions in obtaining a sample must be taken to obtain “representative sample”. Min. Weight of Sample Max. Particle Size (kg) > 25 mm 50 25-5 mm 25 < 5 mm 13 * Details are provided in ASTM D 75 & TS 707  Determination of the Grading of Aggregate  There are two different methods for determining the agg. grading: Fineness Modulus (FM) Granulometry  The grading of the particles in an agg. sample is performed by “sieve analysis”. Requirements by ASTM C 33 o The fineness modulus (FM) must not be less than 2.3 nor more than 3.1.  Fineness Modulus (ASTM C 125) 73  The fineness modulus (FM) for both fine and coarse aggregates is obtained by adding the cumulative percentages by mass retained on each of a specified series of sieves and dividing the sum by 100.  The FM is an indexof the fineness of the aggregate.  The higher the FM, the coarser the aggregate.  FM of fine aggregate is useful in estimating proportions of fine and coarse aggregate in concrete mixtures.  Cant… 1. Fineness Modulus (FM):  For Fine Agg.→#4, #8, #16, #30, #50, #100 {practical limits→2-3.5}  For Coarse Agg.→Fine set+3/8”+3/4”+1 ½”+3” {practical limits→5.5-8.0}  The FM of the mixture of two or more agg. is the weighted average of the FM of that two more agg.  Sieve Analysis is basically 10 steps 75 1. Quarrying method 2. Dry aggregate sample thoroughly (in ovendry temp. of 230oF). 3. Accurately weigh the dried sample (500g, 1000g, etc) 4. Record the total dry weight (ex. 506.4 grams) 5. Wash the sample over a nest of two sieves, 6. Dry the sample again (in an oven at a temperature of 230°F (110 ºC), then accurately weigh and record. 7. Separate the sample into individual sizes 8. Weigh and record the weights retained on each sieve cumulatively example below the table:  example 76  Cont.… 77 9. Calculate the cumulative percent retained on each sieve. (Answer to the nearest 0.1%)  Formula:  Example:  Weight on the No. 4 sieve = 14.8 grams  Total Dry Weight of Sample = 506.4 grams :-  Cont.. 78 10. Calculate the percent passing each sieve. (Answer to the nearest 0.1%).  To determine this figure, subtract the percent retained on each sieve from 100.  Example:  % Retained on 3/8 inch sieve = 0 100 - 0 = 100.0% passing 3/8 inch sieve  % Retained on No. 4 sieve = 2.9 100 - 2.9 = 97.1% passing No. 4 sieve  % Retained on No. 8 sieve = 9.4 100 - 9.4 = 90.6% passing No. 8 sieve  Procedure for Determining the Fineness Modulus 79  Add the Cumulative % Retained on all of the sieves except the No. 200 (75 µm) and the Pan.  Then divide by 100.  Example:  Cant… 80 FM = Cumulative of %Retained (From the above table) 100 =  sample of a Fine Agg. was sieved. Determine FM? (500g) Amount Retained Amount Retained on % Cumulative Sieve on (gr) (%) Retained on 3/8" 0 0 0 #4 30 6 6 #8 80 16 22 #16 100 20 42 #30 120 24 66 #50 125 25 91 #100 35 7 98 Pan 10 2 100 6+22+42+66+91+98 FM = = 3.25 100  Pan is not included.  Only standard sieves are included, if we were given #10 sieve you should not use that in calculations  Fine sets.→#4 (63mm), #8 (37.5mm), #16(19mm), #30(13.2mm), #50 (9.5mm), #100 (4.75mm) Grading of Coarse Agg Ex: Determine the FM for the 1000gr sample of Coarse Agg. Amount Retained Amount Retained % Cumulative Sieve on (gr) on (%) Retained on 2" 70 7 7 1 1/2" 230 23 30 3/4" 350 35 65 3/8" 250 25 90 #4 100 10 100 Fine Set+3/8”+3/4”+1 ½”+3” FM = 100 30+65+90+100+100+100+100+100+100 FM = = 7.85 100  QUIZ 2% (7min) 84  What is the Fineness Modulus? ___________  Does it meet specification? Yes _________ No _____  QUIZ 2% (7min) 85  What is the Fineness Modulus? ___________  Does it meet specification? Yes _________ No _____  Cont.… 2. Granulometry:  The FM is not always representative of the gradation of an aggregate sample and various gradation curves may give the same FM.  In the gradation curves, the vertical axis represents the % passing & the horizontal axis represents the sieve opening.  A logarithmic scale is used for horizontal axis.  Cont.…  A good aggregate gradation for a particular concrete is the one that leads to a workable, dense & uniform concrete, without any segregation of particles.  Cont.…  There is no single “ideal” grading curve. Instead, standards provide upper & lower limits.  Cont.… Ex-1 Sieve Analysis Results for Fine Aggregate (sample size = 500g) Wt. of Sieve Weight Sieve & Weight Percentage Cumulative Cumulative Lower Upper Size of Sieve Retained Retained Retained Coarser (%) Passing (%) Limit Limit (%) (mm) (g) (g) (g) (%) (%) 9.5 586 586 0 0.00 0.00 100.00 100.00 4.75 567 576 9 1.80 1.80 98.20 95.00 100.00 2.36 521 535 14 2.80 4.60 95.40 80.00 100.00 1.18 529 584 55 11.00 15.60 84.40 50.00 85.00 0.06 506 719 213 42.60 58.20 41.80 25.00 60.00 0.03 478 627 149 29.80 88.00 12.00 10.00 30.00 0.015 462 512 50 10.00 98.00 2.00 2.00 10.00 Pan 423 431 8 1.60 99.60 0.40 89 FM=2.66  Cont.… Ex-1 Gradation Curve for Fine Aggregate 90  Shape and Surface Texture of Aggregates 93  Aggregate Shapes 94 Elongated Rounded and angular Flaky and Rounded Angular Flaky Elongated (flat) PARTICLE SHAPE 95  The shape of aggregate is an important characteristic since it affects the workability of concrete.  Not only the characteristic of the parent rock, but also the type of crusher used will influence the shape of aggregates.  From the standpoint of economy in cement for a given w/c ratio, rounded aggregates are preferable to angular aggregates.  Angular aggregates give higher strength and sometimes greater durability as a result of interlocking texture in the hardened concrete.  Flat particles in concrete aggregates will have particularly objectionable influence on the workability, cement requirement, strength and durability.  In general, excessively flat aggregates make very poor concrete.  Volume of Aggregate POROSITY, ABSORPTION AND SURFACE MOISTURE  Porosity: is the ratio of the volume of the pores (small holes in aggregate through which water can go inside) in a particle to its total volume.  The porosity of aggregate is important since it affects its bulk specific gravity, permeability and absorption which in turn affect the properties of the resulting concrete.  Some of the pores are wholly within the solid, and others are on the surface.  Porosity / Absorption of Aggregates WSSD-WDry % Absorption = (Absorption Capacity) WDry WSSD WDry = (1+Abs.Cap.) Wagg-WDry Moisture Content (m) = WDry Wagg = WDry (1+m)  POROSITY, ABSORPTION AND SURFACE MOISTURE 109 The absorption capacity is the measure of the porosity of an aggregate. Material Absorption capacity % by weight Sand 0-2 Gravel 0.5-1 Basalt 0-0.5 Granite 0-0.5 Limestone (firm) 0.5-1 Sand stone 2-7 Trap rock 0-0.5  In calculating or measuring quantities for concrete mix it is important to know the state at which the aggregate is used.  If it is dry some of the mixing water will be absorbed.  If it is wet, the free moisture will become a part of the mixing water.  Specific Gravity 110  Specific gravity is the ratio of the weight of a unit volume of material to the Weight of the same volume of water.  Specific gravity is not a measure of aggregate quality but is used in making calculations related to mix design.  But if Gs increases strength increases  The specific gravity of most normal weight aggregates will range from 2.4 to 2.9 Weight of Agg. (WA) Sp.Gr.= Weight of an equal volume of water (VA*ρw)  Specific Gravity Aggregate 111 Type Specific Gravity Granite Normal weight 2.65 Gravel Normal weight 2.70 Sand Normal weight 2.60 (For normal use) Pumice Lightweight 0.75 Barite Heavyweight 4.50 (for special case e.g. heavy concrete, nuclear-radiation-shielding concrete) Bulk specific gravity Rock group Average Range Basalt 2.75 2.7-2.9 Granite 2.65 2.6-2.7 Limestone (firm) 2.65 2.6-2.7 Sandstone 2.5 2.0-2.6 Trap rock 2.9 2.7-3.0  Coarse Agg.  Aggs are oven dried at 105±2°C for 24 hours & the weight is measured as (A)→oven dry weight (B)→saturated surface dry weight  C= Weight of the soaked specimen in water. Aggs are then weighed in water (C) B-A % Absorption = *100 A SPECIFIC GRAVITY  Bulk specific gravity: is defined as the ratio of the weight in air of a 113 given volume of a permeable material (including both its permeable and impermeable voids) to the weight in air of an equal volume of water. Bulk specific gravity = A/(B-C)  Bulk specific gravity (SSD basis): is defined as the ratio of the weight in air of a permeable material in a saturated surface dry condition to the weight in air of an equal volume of water. Bulk specific gravity (SSD) = B/(B-C) Where A= weight of the oven dry sample in air. B= weight of SSD sample in air C= weight of saturated sample in water.  Strength and Durability of Aggregates 116  One measure of the strength of an aggregate is its resistance to freeze-thaw and ability to withstand compressive stresses.  Soluble, weak material must be avoided.  Cleanliness (Deleterious Substances) 117 The cleanliness of the aggregate affects the bond between the paste and the aggregate surface. Deleterious (harmful substances) have the following effects on concrete:  Weaken bondage between cement paste and aggregates  Interfere with hydration  Reduce of strength and durability  Affect water tightness of the concrete  Modify setting action and  Cause efflorescence  Deleterıous Materıals in Aggregates  Organic Impurities in natural aggs may interfere with the setting & hardening of concrete. They can be detected by tests, ASTM C40, TS 3673  Very Fine Particles: They can appear in the form of clay and silt or in the form of stone dust → they increase the water requirement or in other words decrease workability.  They can appear as coatings on the surface of agg particles → they affect bonding properties.  TS 3527→ particles smaller than 63μm  ASTM C 117→ #200 sieve (75μm)  Cant…  Weak & Unsound Materials Light weight materials (coals, lignide): In excessive amounts may affect durability of concrete.  If these impurities occur at or near the surface, they may disintegrate & cause pop-outs & stains.  Soft particles : they are objectionable because they affect the durability adversely.  They may cause pop-outs & may brake up during mixing and increase the water demand.  Salt contamination : Most important effects are:  Corrosion of reinforcement  Effloresence: presence of white deposits on the surface of concrete.  Hardness of Aggregates 120 The hardness of aggregates is expressed in terms of their resistance to abrasion. o This characteristic is important if the aggregate is used in concrete intended for such purposes as heavy-duty floors. o Especially when concrete is used in roads or floor surfaces subjected to heavy traffic load. o Hardness, or resistance to wear (abrasion) is determined by Los-Angeles abrasion test.  131 Concrete Admixture  Cant… 132 1. Definition: Admixtures are chemicals which are added to concrete at the mixing stage to modify some of the properties of the mix. 2. Uses of admixtures:  To increase workability without changing water content.  To reduce water content without changing workability.  To adjust setting time.  To reduce segregation and/or bleeding.  To improve Pump ability.  To accelerate the rate of strength development at early ages  Cont.. 133 3. Types of admixtures : Admixtures are classed according to function.  There are five distinct classes of chemical admixtures: 1. Plasticizers (water-reducing agents) 2. Super plasticizers 3. Air entrainers 4. Accelerators 5. Retarders  3.1 Plasticizers 134  When added to a concrete mix, plasticizers (water-reducing agents) are absorbed on the surface of the binder particles, causing them to repel each other and deflocculated.  This results in improved workability and provides a more even distribution of the binder particles through the mix.  Plasticizers Reduce the water requirement of a concrete mix for a given workability by about 10%.  Concrete containing a plasticizer (water-reducing admixture) needs less water to reach a required slump than untreated concrete.  The treated concrete can have a lower water-cement ratio. This usually indicates that a higher strength concrete can be produced without increasing the amount of cement.  Uses of plasticizers 135  Increase the slump of concrete with a given water content.  Reduce the water requirement of a concrete mix for a given workability by about 10%.  The addition of a plasticizer makes it possible to achieve a given strength with a lower cement content.  Improve pump ability.  Problems associated with plasticizers 136  Some plasticizers contain chlorides which may increase the danger of corrosion of reinforcing steel.  Where plasticizers are used to increase workability, the shrinkage and creep will invariably be increased.  3.2 Super plasticizers 137  Also known as or high-range water reducers (HRWR), reduce water content by 12 to 30 percent and can be added to concrete with a low-to-normal slump and water-cement ratio to make high- slump flowing concrete.  As a result of the slump loss, super plasticizers are usually added to concrete at the jobsite.  Uses of super plasticizers 138  In areas of congested reinforcement.  Where workable concrete that can be placed with little or no vibration or compaction.  For high-strength concretes by decreasing the water: cement ratio as a result of reducing the water content by 12–30%.  Problems associated with super plasticizers 139  The effect of a super plasticizer may disappear as soon as 30-60 minutes after mixing.  They have a relatively high unit cost.  Where super plasticizers are used to produce very high workability, the shrinkage and creep will be increased.  3.3 Air entrainers 140  An air-entraining agent/manage introduces air in the form of minute swelling distributed uniformly throughout the cement paste. Uses of air-entertainers  Where improved resistance of hardened concrete to damage from freezing and thawing is required.  For improved workability, especially in harsh or lean mixes.  To reduce bleeding and segregation, especially when a mix lacks fines.  Problems of air-entertainers 141  Air entrainment may reduce the strength of concrete and overdosing can cause major loss of strength.  As a rule-of-thumb, 1% air may cause a strength loss of 5%.  It is therefore important that mixes be specially designed for air entrainment and that the percentage of air entrained during construction must be monitored.  3.4 Accelerators 142  speed up the chemical reaction of the cement and water and so….  accelerate the rate of setting and/or early gain in strength of concrete.  Uses of accelerators  Where rapid setting and high early strengths are required.  Where rapid turnover of mould or formwork is required.  Where concreting takes place under very cold conditions.  Problems associated with accelerators 143  Certain accelerators may increase drying shrinkage, cracking and creep.  Many chloride-based accelerators promote corrosion of reinforcing steel.  Calcium chloride should not be used in reinforced concrete  Overdosing with these materials can cause marked retardation.  Accelerators work more effectively at lower ambient temperatures.  3.5 Retarders 144  These admixtures slow the chemical reaction of the cement and water leading to longer setting times and slower initial strength gain. Uses of retarders  When placing concrete in hot weather, particularly when the concrete is pumped.  To prevent cold joints due to duration of placing.  In concrete which has to be transported for a long time.  Problems associated with retarders 145  If a mix is overdosed beyond the limit recommended by the supplier, retardation can last for days.  Retarders often increase plastic shrinkage and plastic settlement cracking.  Delayed addition of retarders can result in extended retardation.  146 FRESH CONCRETE  Major properties of fresh concrete 147  Fresh concrete is also known as plastic concrete.  The major Properties of concrete in its plastic state are:  Workability  Segregation  Bleeding  Stiffening and setting  1. Workability 148  Workability is ease of placing and resistance to segregation of concrete.  Workability means how easy it is to:  Place  Handle  Compact and  Finish a concrete mix.  Concrete that is stiff or dry:  May be difficult to Handle, Place, Compact, and Finish  Will not be as strong or durable when finally hardened.  CANT…  Workability comprises three separate properties: 149  Compactability or the ease with which the concrete can be compacted and the air voids be removed.  Mobility or the ease with which concrete can flow into moulds, around reinforcing steel and be remoulded.  Stability or the ability of concrete to remain a stable, coherent homogeneous mass during handling and vibration with out the constituents segregating.  Consistency  Consistency is the term used to denote the degree of fluidity or mobility of concrete.  The degree of consistency of a concrete mixture can be described as stiff, plastic, and flowing. Note: Every job requires a particular workability.  Consistency 150  Consistency refers to ability to flow of concrete and indicates wetness of concrete, and thus workability.  Concrete could have:  Dry  Plastic: can be shaped into ball  Semi-fluid: spreads out slowly and with out segregation of aggregate  Fluid consistency: spreads out fast and results in segregation of aggregates  FACTORS AFFECTING WORKABILITY OF CONCRETE 152  Shape of aggregates:  Angular, elongated or flaky aggregates makes the concrete very harsh/exacting when compared to rounded aggregates or cubical shaped aggregates.  Surface texture: Rough textured aggregates will show poor workability and smooth or glassy textured aggregates will give better workability.  Grading of aggregates: This is one of the factor which will have maximum influence on workability. The better the grading, the less is the void content and higher the workability.  CANT… 153  Use of admixtures:  The plasticizers and superplasticizer greatly improve the workability many folds.  Effect of environmental conditions:  The workability of the concrete is also affected by the temperature of concrete and therefore, by the ambient temperature.  The amount of mixing water required to bring about certain changes in the workability also increases with temperature.  Effect of time:  Fresh concrete loses workability with time mainly because of the loss of moisture due to evaporation.  Measurement of Workability 154  Some of the methods of measuring workability that is wetness or fluidity are:  Slump test  Compacting factor test  Vebe test Slump Test Compacting factor test Vebe Time test  Slump is the subsidence of concrete cone after mold is lifted up. 155 MEASUREMENT OF WORKABILITY 156  Three types of slumps can be observed: True slump: the sample slumps evenly all around. These type of slump indicates a well proportioned concrete. Shear slump:  part of the top cone might shear off and slide down an inclined plane. Half of the cone slides, difficult to measure, and results from harsh mixes deficient in fine aggregates.  Shear slump indicates that the concrete is non cohesive and shows the characteristic of segregation. Collapse slump: the cone could completely collapse. Difficult to measure, results from very wet mixes. True slump Shear slump Collapse slump  Slump test results Degree of Slump Use for which concrete is suitable workability mm Very low 0-25 Roads vibrated by power operated machine. (Massive sections, little reinforcement) Low 25-50 Roads operated by hand-operated machines. Mass foundations without vibration or lightly reinforced sections with vibration. Medium 50-100 Manually compacted flat slabs. Normal reinforced concrete manually compacted and Limitations of slump heavilytest reinforced sections with vibration. High 100-175 For sections with congested reinforcement. Not normally suitable for vibration.  Not applicable for aggregates size greater than 40 mm  Applicable to plastic mixes only (not RCC) 15 7  Not applicable to harsh and wet mixes  Vebe Test 158  1. Compacting Factor Test 159 o Drier mixes do not give slump. Therefore, compaction factor test should be done to determine degree of compaction (compacting factor) by falling the mix through successive hoppers with standard height using a compaction factor test apparatus. Compaction factor test apparatus  Compaction factor = weight of partially compacted concrete weight of fully compacted concrete e.g.  weight of concrete partially compacted = 11.02 kg  weight of concrete fully compacted = 12.04 kg Compaction factor = 11.02 kg / 12.04 kg = 0.915 Concrete Compacting factor Uses & recommended of compaction consistency (AC)% Stiff 75 - 80 Dames-retaining walls (Vibration) Plastic 80 - 90 All mass structures (hand compaction) Flowing/fluid 90 - 95 Slabs-reinf. Structures (vibration) 160 Self compacting > 95 Thick steel renif structures(no compaction)  2. SEGREGATION 161  Segregation can be defined as the separation of the constituent materials of concrete.  A good concrete is one in which all the ingredients are properly distributed to make a homogeneous mixture.  Segregation may be of three types:  The coarse aggregate separating out or settling down from the rest of the matrix.  The paste separating away from coarse aggregate.  Water separating out from the rest of the material. Problem  Reduction in concrete strength  Lack of homogeneity is also going to induce all undesirable properties in the hardened concrete  SEGREGATION 162 Causes of segregation  Badly proportioned mix where sufficient paste is not there to bind and contain the aggregates.  Insufficiently mixed concrete.  High workability (excess water content) or poor grading (excess coarse aggregate).  Dropping fresh concrete from a height  Conveyance of concrete by conveyor belt, wheel barrow, dumper, etc to a long distance.  Excessive or inadequate vibration.  3. BLEEDING  164 When a newly placed concrete sets and consolidates part of its surplus water appears on the surface when the solids settle through the body of water.  This tendency for water to rise in freshly placed concrete is known as bleeding or water gain.  It results from the inability of the constituent materials to hold all the mixing water as the relatively heavy solids settle.  The rising water tends to carry with it many fine particles which weakens the top portion and in extreme cases form a scum called “laitance” over the surface.  Bleeding is predominantly observed in a highly wet mix, badly proportioned and insufficiently mixed concrete. Note: Bleeding Cause weakness on concrete surface or develop line of weakness between pours. MIXING OF CONCRETE 16 8  Purpose of mixing 169  The purpose of concrete mixing is to provide a uniformly blended product of cement, water, and aggregates.  Basic requirement of mixing is to produce concrete of uniform consistency from beginning to end.  Mixing time 2 to 3 minutes  Methods for mixing concrete Two basic methods of mixing concrete; 1. Hand (Manual) mixing 2. Machine mixing Manually Machine mixing Drum mixer Ready mixed Pan Mixer 170  Methods for transporting concrete Concrete buggy Wheelbarrow Chute Concrete pump Bucket (through pipe) (Large & massive construction. 171 Handled by crane)  Hand Mixing 172 Adopted for small works and quantity of concrete used is small Procedure: a. Sand + cement  dry mix b. Spread the sand -cement mix on a flat platform c. Spread the measured quantity of coarse aggregate on the cement-sand mix d. Mix the cement + sand + c.agg. At least three times by shoveling from center to the side and then back to the center and again to the side e. Make a hallow in the middle of the mixed pile and pour slowly into it half to three-quarter of the total quantity of water required f. Add the remainder of the water slowly, turning the mixture over and again until the color and consistency are uniform throughout the pile Note: 1. Time of mixing should not exceed 3 minutes 2. Mixing platform is cleaned at the end of the days work, so that it is ready for use the next day  Machine mixing  173 Used in case of a large quantity of concrete is to be produced.  Concrete can be produced at a faster rate at a lesser cost and of bett quality.  Care for mixer is very important: 1. Wash the mixer every day preferably with a hose 2. Hammering or hitting of the loading skip in order to accelerate t discharge of adhering sand and cement should not be permitted 3. When the mixer is installed at one place for a loner periods, it should ensured that wheels and axle of the mixer do not get buried und accumulating materials 4. Before closing down a shift or day’s work, the interiors of the dru and blades are flushed clean 5. General upkeep and maintenance of the mixer engine be attend everyday, i.e., fuel, water, lubricant, etc.  Transporting Concrete 174 1. Pans - When quantity is small - When access to work is restricted - Method is tedious, slow and costly 2. Wheel barrows Moderate distance and medium quantities Wheelbarrow 3. Truck mixer - When place of deposit of concrete is at a very long distance from the mixer such that the concrete cannot be transported and placed in the forms within 30 minutes - Happens in case of ready-mixed concrete - Drum containing the concrete rotates continuously to prevent the concrete from being stiff and to prevent segregation  VOLUME OF FRESH CONCRETE 197 The volume of the fresh concrete is equal to the sum of the absolute volumes of its components, including the naturally entrapped or purposely entrained air. V = Va + Vw + Vc + Vfa + Vca Where: Va = Volume of the air Vw = volume of the water Vc= absolute volume of the cement Vfa = absolute volume of the fine aggregate Vca = absolute volume of the coarse aggregate  Cant… 198  Then the total volume of the fresh compacted concrete will be: V = Va + Vw + Vc +Vfa+ Vca …………………(1)  From the point of view of concrete technology it would be best to prescribe mix proportions by the "absolute volume" of the ingredients, because the volume of the resulting concrete and its properties are dependents on the, and not on their weight or bulk volume.  However, the absolute volume can easily be calculated from the relationship of the weight and specific gravity of the material: Where: V is the absolute volume in cu. m W is the weight of the material in kg.  Cont.. 199 G: is the specific gravity of the material. 1000: is the density or unit weight of fresh water in kg per cu. m.  The specific gravity of cement may be taken, for all practical purposes, equal to 3.15.  For calculating the volumes of the aggregates we use their specific gravity (bulk, saturated surface dry basis).  Substituting weight and specific gravities in equation (2) for absolute  volumes in equation (1) we get the volume of concrete in cu. m as follows:  Cant…. 200  If the cement, water, and air contents per cu. m. of fresh concrete are known, then the required weight of the aggregates for a cubic meter of fresh concrete can easily be calculated from Eq. (3). Example:1  Cont… 201  Cont… 202  Cont.. 203  If the proportion of the fine to coarse aggregate by weight is 1:2, then the quantities of aggregates will be:  Example 2  If the loose/slack unit weights of the surface dry materials in example 1  Cement = 1,300kg, per m3 (under the given condition of measurement)  Sand (S. S. D) = 1, 600 kg, per m3  C.A (S.S.D) = 1,400kg per m3  Then the total amount of dry materials in loose volume per cu. m of concrete are: ___________  Cont… 204   Cont.. 205 Wv = 190-(609*0.03)=172L= 0.172m3.  The total volume of aggregates needed will be =0.869 + 0.523 = 1.33m3  The mix proportions by volume (with damp sand)  0.172 : 0.27 : 0.523 : 0.869  0.27 0.27 0.27 0.27 0.638 : 1 : 1.94 : 3.22 Or cement to aggregates : 1: 5. 16  Cont.. 206  Failure to allow for the building of sand when batching volumetrically with reduce yield of concrete and result in an under sanded and harsh mix, which is difficult to place as may be seen from the following calculation:  If only 0.38 cu. m. sand is taken then the actual weight of sand in the mix will be: (0.38 x 1200 ) - 3% (0.38x1200) = 456 - 14 = 442 kg  Cont… 207  There are more factors involved like the shape the size of the measuring device and the person who fills it.  From the above results it is possible to calculate the cement factor (CF) and the yield (y)/income of the concrete.  The cement factor for a concrete mix is the cement content expressed in terms of sacks of cement per cubic meter of concrete.  In example 5.1 350 kg of cement is used to produced 1m3 of concrete; taking 50 kg as the weight of one sack of cement we have:  Cont… 208  The yield of concrete is the amount of fresh concrete in m3produced per sack of cement.  QUIZ 5% (10min) 209 Exercises: 1. a) Determine a mix proportion for 120 liters of concrete with the following. Data:  Water = 175 kg/m3  Cement = 300 kg/m3  Specific gravity of cement = 3.15  Specific gravity of aggregates = 2.65  Moisture content of the fine aggregate = 2.4% by Wight  Use ratio of fine aggregate to coarse aggregate = 1:1.8 by weight.  Assume air content to be at 1.6% by volume b) Calculate the yield & the cement factor of the above mix proportion.  MIX DESIGN 210  The purpose of a concrete mix design is to have economical mix proportions for the available concreting materials which complies with the contract specification in all respects and has adequate workability to be placed in it’s final position on site.  Basic Relationship 211 Workability   Consistency  Strength  Water-cement (w/c) ratio  Durability  Density  Generation of heat Background Data To the extent possible, selection of concrete proportions should be based on test data or experience with the materials actually to be used. The following information for available materials will be useful: 212 213 214 215 216  Mix Design Example: 217  Concrete is required for a portion of a structure that will be below a ground level in a location where it will not be exposed to severe weathering or sulfate attack.  Structural considerations require it to have an average 28-day compressive strength of 24 MPa with slump of 75 to 100 mm.  The coarse aggregate has a nominal maximum size of 37.5 dry-rodded mass of 1600 kg/m3.  Ordinary Portland cement will be used and its specific gravity is assumed to be 3.15. the coarse aggregate has a bulk specific gravity of 2.68 and an absorption of 0.5 percent.  The fine aggregate has a bulk specific gravity of 2.64, an absorption of 0.7% and a fineness modulus of 2.8.  Moisture in coarser aggregate is 2% and in fine aggregate 6% respectively.  Solution: 218 Step 1 :The slump is required to be 75 to 100 mm. Step 2 : The aggregate to be used has a nominal max size of 37.5mm Step 3 : The concrete will be non-air entrained since the structure is not exposed to severe weathering. From table 2 the estimated mixing water for a slump of 75 to 100 mm in non air entrained concrete made with 37.5 aggregate is found to be 181 kg/m3. Step 4: The water-cement ratio for non-air entrained concrete with a strength of 24 MPa is found from table 3 to be 0.62. Step 5 : From the information developed in step 3 and 4. the required cement content is found to be 181/0.62 = 292 kg/m3.  Cont.. 219 Step 6 : The quantity of coarse aggregate is estimated from 5. For a fine aggregate having a finesse modulus of 2.8 and 37.5 mm nominal maximum size coarse aggregate, the table indicated that 0.71 m3 of coarse aggregate, on a dry-rodded basis, may be used in each cubic meter of concrete.  The required dry mass is therefore, 0.71*1600 = 1136 kg. Step 7.1 Mass basis: The mass of a cubic meter of non-air-entrained concrete made with aggregate having a nominal maximum size of 37.5 mm is estimated to be 2410kg. Mass already known are:  Cont… 220  The mass of fine aggregate, therefore, is estimated to be 2410-1609 = 801 kg.  Step 7.2 Absolute volume basis: with the quantities of cement, water and coarse aggregate established, and the approximate entrapped air content (as opposed to purposely entrained air) of 1 percent determined from table 2 the sand content can be calculated as follows:  Volume of entrapped air = 0.01 * 1 = 0.010 m3  Total solid volume of ingredients 0.708 m3 except fine aggregate  Cont.. 221  Cont.. 222  Cont… 223  Cont… 224  225 HARDENED CONCRETE Definition:  Hardened concrete is a concrete which developed the required strength and changed to solid state.  Properties of Hardened concrete 226  The properties of Hardened concrete are properties which change with time.  In its hardened state the various properties which need consideration are 1. Strength Permeability 2. Durability 3. Dimensional Change (elasticity shrinkage, thermal expansion, creep) 4. Fire Resistance  227 Strength  Significance :- The strength of concrete is the most important property as far as structural designs are concerned.  Nature and Kind :- Strength of concrete is defined the ability to resist force which might cause rupture by the following kinds of stresses.  Compressive stress  Tensile stress  Flexural stress  Shear stress  229 DURABILITY  Property of concrete to withstand factors, which reduces the life of concrete by their disintegrating effects.  Mechanisms that affect durability: 1. Freeze-thaw damage (physical effects, weathering). 2. Alkali-aggregate reactions (chemical effects). 3. Sulfate attack (chemical effects). 4. Corrosion of reinforcing steel embedded in concrete 5. Abrasion (physical effects). 6. Mechanical loads (physical effects). 230 231  Factors affecting properties of hardened concrete 239  Water cement ratio  Cement content  Temperature  Age  Aggregates properties  Curing  Frost  Entrained Air 240 Testes for Hardened Concrete  Cont.. 255 thank you