Updated Concrete Lecture PDF

Concrete mixtures, production, properties, behaviour, and applications in the context of Caribbean and global construction.  Objectives of Lecture Evaluation of Concrete mixtures, production and properties, behaviour Calculation of the Absolute Volume of C...

Concrete mixtures, production, properties, behaviour, and applications in the context of Caribbean and global construction.  Objectives of Lecture Evaluation of Concrete mixtures, production and properties, behaviour Calculation of the Absolute Volume of Concrete Mixtures Applications of Concrete in Different Types of Infrastructure  Concrete Most widely used construction material in the entire world Uses of concrete in construction work is huge compared to other materials that are used Moreover, no construction work will complete without using concrete Components of Concrete Concrete = Coarse aggregate (limestone or gravel)+ fine aggregate (sand)+ Portland cement paste (cement and water)+ Interfacial transition zone (ITZ) In most of the concrete, the mineral admixture – also known as supplementary cementitious materials and chemical admixtures are added Concrete can be made cast-in-place or precast or prefabricated Components of Concrete Typical size concept: Cementitious Materials Cement particle: 10 to 15 micron Pozzolan: 10-15 micron, Fly ash: 10-15 micron Interfacial Transition Zone in Concrete Interface between aggregates and cement- paste, the 'interfacial- transition zone' (ITZ), is of particular importance since it contains higher porosity and lower cement content compared to other regions Interfacial Transition Zone in Concrete This transition zone is a plane of weakness and therefore has a great influence on the mechanical behaviour of concrete. Transition zone is composed of some bulk concrete paste, the quality of paste is poorer Formation of Interfacial Transition Zone a water to cement ratio gradient develops around the aggregate particles during casting, resulting in a different microstructure of the surrounding hydrated cement paste This zone around the aggregate is called the interfacial transition zone  Aggregates in Concrete Aggregates: Sand: 0.075mm to 4.75 mm Coarse aggregate: 4.75 mm to 37.5 mm (structural applications)  Concrete Almost all concretes are reinforced concrete– but mass concrete are also used high compressive strength cost ratio, Can be cast to many complicated shape Durable if made properly Can recycle by-product or waste Has good aesthetic properties Low maintenance cost Can be used as sound, thermal, and radiation insulation Properties of Fresh Concrete 1.Workability: This refers to how easily the concrete can be mixed, placed, and finished. High workability means the concrete can be easily molded and compacted without segregation. 2.Consistency: This is the ability of fresh concrete to flow and fill the formwork completely. It is often measured using the slump test, where a higher slump indicates higher consistency. 3.Segregation: This is the separation of the different components of concrete, such as the coarse aggregates from the cement paste. Good quality concrete should have minimal segregation to ensure uniformity.  Properties of Fresh Concrete 4.Bleeding: This is a form of segregation where water rises to the surface of the concrete. Excessive bleeding can weaken the surface and lead to the formation of laitance, a weak layer of cement and water on the surface. 5.Plastic Shrinkage: This occurs when the concrete loses moisture rapidly, leading to cracks before it hardens. Proper curing and moisture control can help minimize plastic shrinkage. 6.Setting Time: This is the time it takes for the concrete to transition from a fluid state to a solid state. The initial setting time is when the concrete starts to harden, and the final setting time is when it has completely hardened.  Properties of Fresh Concrete Temperature: The temperature of fresh concrete affects its setting time and strength development. High temperatures can accelerate setting, while low temperatures can delay it.  BLEEDING in concrete is a phenomenon in which free water in the mix rises up to the Fresh surface and forms a paste of cement on the surface Properties Bleeding occurs in of Concrete concrete when coarse Bleeding aggregates tends to settle down and free water rises up to the surface. Causes of Bleeding In Concrete Excessive water cement ratio, excessive vibration, prolonged mixing, increased height of dropping of concrete, poorly graded aggregates, lean mix concrete, are the causes for segregation of concrete.  Effects of Bleeding in Concrete Causes a decrease in the strength and the durability of the concrete Segregation of Concrete Segregation of concrete is the separation of cement paste and aggregates of concrete from each other during handling and placement Segregation also occurs due to over-vibration or compaction of concrete, in which cement paste comes to the top and aggregates settles at the bottom  Slump Test Slump test is primarily used to measure the workability or consistency of freshly mixed concrete before it sets This test helps determine how easily the concrete will flow, which is crucial for ensuring proper placement and compaction. Additionally, it can indicate if a concrete batch has been improperly mixed  This test measures how easily concrete can be compacted and its ability to flow, Compaction which is crucial for Test ensuring the quality and durability of the concrete in construction projects Flow Test Measures the workability and slump height of the concrete which Measures the consistency and the setting time of the cement. This consistency allows for proper compaction which reduces the air voids in the concrete. This improves the strength and the durability of the concrete.  Properties of Hardened Concrete Strength: Compressive Strength: This is the maximum load per unit area that concrete can withstand. It’s typically measured using cube or cylinder specimens Tensile Strength: Although concrete is strong in compression, it is relatively weak in tension. Tensile strength is important for understanding how concrete will perform under stretching forces. Durability: Resistance to Chemical Attack: Hardened concrete must resist various chemical attacks, including those from sulfates and chlorides Frost Resistance : In colder climates, concrete must withstand freeze-th aw cycles without significant damage  Properties of Hardened Concrete Dimensional Stability: 1. Shrinkage: Concrete can shrink as it dries, which can lead to cracking if not properly managed. This includes both plastic shrinkage (early stage) and drying shrinkage (long-term) 2. Creep: This is the slow, time-dependent deformation of concrete under a sustained load Modulus of Elasticity: 3. This property measures the stiffness of concrete and its ability to deform elastically (i.e., return to its original shape) when a load is applied  Properties of Hardened Concrete Permeability: Low permeability is crucial for concrete’s durability, as it reduces the ingress of water and harmful chemicals Bond Strength: The bond strength between concrete and reinforcing materials (like steel rebar) is essential for the structural integrity of reinforced concrete  Influence of Properties of concrete High compressive strength Toughness and impact resistance Low maintenance costs Young’s Modulus  Young’s Modulus Calculation 𝐹𝑙 𝑒𝐴 F – Force acting on material E= l- length of material e- extension of material A – cross sectional area of material  Typical Engineering Properties of Concrete Compressive strength= 35 MPa (5000 psi) Flexural strength= 6 MP (800 psi) Modulus of elasticity= 28 GPa ( 4 x 10^6 psi)  Flexural Strength of Concrete Measure of an unreinforced concrete beam or slab to resist failure in bending It is measured by loading 6 x 6-inch (150 x 150-mm) concrete beams with a span length at least three times the depth.  Poisson’s Ratio (μ) Influences the speed of propagation and reflection of stress waves It measures how a concrete specimen bulges when subjected to compressive load and the ability of a material to be strained can be easily known with the value of Poisson's ratio Poisson's ratio measures the deformation in the material in a direction perpendicular to the direction of the applied force.  It is the negative ratio of the lateral strain to the longitudinal strain  Poisson Ratio “the ratio of transverse contraction strain to longitudinal extension strain in the direction of the stretching force.” Compressive deformation is considered negative Tensile deformation is considered positive. Calculati on of Poisson’s Ratio Poisson’s Ratio Poisson’s ratio=0.18, Coeff of thermal expansion= 10 x 10-6)/ degree C  Ultimate shrinkage =0.05 to 0.1 % Unit weight (normal)=2300 kg/m^3 (145 lb/ft^3) Typical Poisson’s Ratio of Concrete The Poisson’s ratio of Concrete normally varies between 0.1 to 0.25. For design calculation, in absence of data, normally 0.2 is used as Poisson’s ratio of Concrete. Sample The longitudinal strain for concrete Questi is 0.2 and its Poisson’s ratio is 0.6. on on Find the lateral strain in the concrete Poisso n’s Ratio Shrinkage of Concrete Decrease in either length or volume of a material resulting from changes in moisture content or chemical changes.  Water-Cement Ratio shrinkage is mostly influenced by the water-cement ratio of concrete. It Factors increases with the increase in the influencin water-cement ratio g the Environmental Condition shrinkage It is one of the major factors that of affect the total volume of shrinkage. concrete Shrinkage is mostly occurred due to the drying condition of the atmosphere. It increases with the decrease in humidity.  Factors influencing the shrinkage of concrete Time The rate of shrinkage rapidly decreases with time. It is found that 14-34% of the 20 years shrinkage occurs in two weeks, 40-80% of shrinkage occurs in three months, and the rest 66-85% shrinkage occurs in one year.  Type of Aggregates Factors Aggregates with moisture affecting movement and low elastic the modulus cause large shrinkage. The rate of shrinkage shrinkage generally decreases with the increase of of the size of aggregates. It concrete is found that concrete made from sandstone shrinks twice than that of concrete of limestone.  Factors affecting the shrinkage of concrete Admixtures The shrinkage increases with the addition of accelerating admixtures due to the presence of calcium chloride in it It can be reduced by lime replacement.  Other factors affecting shrinkage of concrete The type and quantity of cement Granular and microbiological composition of aggregates The strength of concrete The method of curing The dimension of elements  Creep Increased strain or deformation of a structural element under a constant load Concrete can alter shape if it is subjected to prolonged strain or stress. This deformation occurs most often in the direction of the applied force. A concrete column compressing or a beam bending are examples of this. Difference between shrinkage and creep in concrete Creep: It is the effect due to which concrete undergoes continuous deformation under sustained loading applied for a considerable time (Sustained Applied Load) Shrinkage: It is drying of concrete and is independent of applied loads. Difference in the relative humidity of the concrete and the environment  Factors affecting Creep in Concrete Magnitude of the sustained loading Age and strength of the concrete when the stress is applied Total amount of time that the concrete is stressed.  Factors affecting creep in concrete When the aggregate volume is increased, creep will be less as the aggregate is more rigid than the cement paste. When the water/cement ratio is increased, the higher water/cement ratio will result in a more porous and weaker cement paste which will deform more under a given load. When the natural aggregate is replaced by a lightweight artificial aggregate, the lightweight aggregate will be more porous and less rigid than the natural aggregate. If the applied load is increased, the creep also increases.  Creep coefficient refers to the ratio of the concrete Creep creep amplitude value to the instantaneous. Coefficie compressive strain of the concrete. nt Concrete shrinkage refers to the shrinkage of the volume that. occurs during the initial setting or hardening of concrete Comparison between Creep and Shrinkage of Concrete  Freezing and Thawing of Concrete occurs Freeze-thaw damage occurs when water fills the voids of a rigid, pores and then freezes and expands. When concrete is saturated with water and the temperature drops The accumulative effect of successive freeze-thaw cycles and disruption of paste and aggregate can eventually cause expansion and cracking, scaling, and crumbling of the concrete.  Durability of Concrete Freeze-Thaw Resistance is the property of concrete to sustain its strength and surface properties under repeated F-T cycles. Air void structure is crucial in obtaining f-t resistant concrete. Air entraining agents are the only means of getting a good air void structure (4-7% disconnected micro bubbles at uniform spacing) Low W/C ratio also increases f-t resistance  Absolute Volume Used when units of density is in lbs/ft3 Units of density : kg/m3 or lbs/ft3 Absolute Volume The absolute volume method is used to work out the necessary quantities of materials for developing the desired quantity of concrete based on the specified mix ratios. This method follows the principle that the volume of fully compacted concrete is equivalent to the absolute volume of all the materials of concrete like cement, sand, coarse aggregates and water. Absolute Volume Calculations Volume of Concrete Components  Residentia l Houses concrete is best because concrete is not burned and it is fire-resistant material. Commercial Building Construction wide range of material and it is available in many colors or finishes.. Energy and cost are effective Sewers and Culverts Durable and strong and it has a long life, so the concrete is commonly used for the construction of sewers and culverts.  Construction of Bridges Structure which allows the traffic from one place to another on the obstacle like a river, valley Concrete is the best material for the bridge construction because concrete has a different type like high-performance concrete or precast concrete  Concrete Dams Capability and the extreme strength of the concrete (concrete takes some extreme strength to stop the flow of the water body) Gravity and the Buttress dam is constructed with concrete, so the weight of the concrete gives strength to the dams to resistant the different loads. Concrete attaches with reinforcement and gates, tunnel liners, rubber water stops, and electric control or the plastic compound to get Concrete Flooring Concrete floor in the residence is attractive and low maintenance  In residences concrete surface is made rough because plain concrete is slipped when the soapy water is on it.  Concrete Countertops Unique look to the kitchen or bathrooms. It also used to make durable and attractive finishes to the outdoor kitchen. It is a good choice for outdoor if you are planning to spent a lot of time outdoors in the warmer months. Concrete Sinks Molded as a single unit It is a very durable and heavy item It has a long life In the maintenance, parts will need to seal occasionally.  Decorative Walls and Beams Wall and beam the concrete is the best option in replace of the stone  Floating Docks and Beams Made with precast concrete. It is a good material option instead of the wood which not have succumbed to the weather or water for a long time  It also gives attractions and low in maintenance  Transparent Concrete Panel Passes the light from it is also made of concrete  All the panels are independently constructed with design as per your wish  High Performance Concrete Used to describe concrete with special properties not attributed to normal concrete High-performance means that the concrete has one or more of the following properties: low shrinkage, low permeability, a high modulus of elasticity, or high strength.  Uses of High Performanc e Concrete Construction of bridges, hydropower structures, pavements, bridges, high-density radiation shielding, mass concrete projects, offshore platforms noise and vibration dampening, tunnels, and high-rise