The document discusses various methods for curing concrete, including maintaining moisture through ponding, immersion, fogging, or wet coverings. It also discusses methods that reduce moisture loss such as using impervious paper, plastic sheets, or curing compounds. Accelerated curing methods that provide additional heat and moisture like steam curing are also described. Proper curing is important for ensuring hydration of cement and allowing concrete to reach its desired strength and durability properties. Inadequate curing can result in reduced strength and durability in the surface layers of concrete.
Concrete permeability is a key factor in its durability. Permeability is affected by water-cement ratio, with lower ratios producing less permeable concrete. Curing also impacts permeability. Proper curing, including moist curing, produces less permeable concrete. Permeability testing involves measuring water flow through a sample over time under pressure. Sulfate attack can occur when sulfates penetrate permeable concrete and form expansive compounds that crack the material. Resistance to sulfates is improved with lower permeability concrete.
Placing and compaction of cement concretePramod GK
This document discusses placing and compaction of concrete. Placing involves depositing fresh concrete in its final position without dropping from height or piling to avoid segregation. Foundations require trenches be excavated and beds prepared before concrete is placed using chutes or tremie pipes for deep placements. Compaction removes air bubbles and improves packing using hand tools, internal vibrators like poker vibrators inserted in concrete, or external vibrators applying surface vibration. Proper placing and compaction results in dense, strong concrete.
Underwater concrete (UWC) requires special mix designs, placement techniques, and quality control due to the challenges of placing concrete underwater. The document discusses types of materials used in UWC including cement, aggregates, and admixtures. It also describes common placement methods like the tremie method, pump method, and bagwork. Construction techniques for placing UWC include the use of caissons and cofferdams to create a dry work environment. Proper production, quality control measures, and maintenance are needed to ensure the durability of underwater concrete structures.
This document discusses concrete construction in extreme hot and cold weather conditions in India. It addresses the challenges of hot weather concreting such as increased water demand, accelerated slump loss, and increased risk of plastic shrinkage cracking. Recommendations for hot weather concreting include cooling the concrete, reducing placement time, and prompt curing. Cold weather concreting risks include reduced strength if water freezes within concrete. Recommendations include protecting concrete from freezing, using accelerants, and maintaining minimum curing temperatures. Proper planning, materials, and protection methods can help produce quality concrete despite temperature extremes.
Bleeding in concrete refers to the physical migration of water to the top surface due to its lower density. While bleeding replaces water lost to evaporation and prevents cracking, it can also increase finishing time and reduce strength if not properly controlled. The document discusses the causes of bleeding including high water content and improper mixing. It also presents methods to reduce bleeding such as using pozzolans or air-entrainment and ensuring proper proportioning, mixing and compaction. Bleeding is tested using ASTM C 232, which involves measuring water released both with and without vibration.
This document discusses underwater concrete, including its production, placement methods, and quality control. It notes that underwater concrete must have proper mix design and flowability to consolidate under its own weight without vibration. The main placement methods described are tremie, pump, toggle bags, and bagwork. Quality control includes monitoring placement rate and volume. Common issues with underwater concrete include cement washout, laitance, and segregation, which mix design and proper placement seek to prevent.
This document discusses quality control and durability factors in concrete. It defines quality as conformance to requirements and durability as a concrete's ability to resist deterioration when exposed to the environment. Several factors influence concrete durability, including the materials used, water-cement ratio, compaction, curing and the physical and chemical conditions of the service environment. Common durability issues include corrosion, cracking from sulfate attack or alkali-silica reaction, and carbonation reducing alkalinity. Proper quality control of materials and construction processes is needed to produce durable concrete.
Concrete permeability is a key factor in its durability. Permeability is affected by water-cement ratio, with lower ratios producing less permeable concrete. Curing also impacts permeability. Proper curing, including moist curing, produces less permeable concrete. Permeability testing involves measuring water flow through a sample over time under pressure. Sulfate attack can occur when sulfates penetrate permeable concrete and form expansive compounds that crack the material. Resistance to sulfates is improved with lower permeability concrete.
Placing and compaction of cement concretePramod GK
This document discusses placing and compaction of concrete. Placing involves depositing fresh concrete in its final position without dropping from height or piling to avoid segregation. Foundations require trenches be excavated and beds prepared before concrete is placed using chutes or tremie pipes for deep placements. Compaction removes air bubbles and improves packing using hand tools, internal vibrators like poker vibrators inserted in concrete, or external vibrators applying surface vibration. Proper placing and compaction results in dense, strong concrete.
Underwater concrete (UWC) requires special mix designs, placement techniques, and quality control due to the challenges of placing concrete underwater. The document discusses types of materials used in UWC including cement, aggregates, and admixtures. It also describes common placement methods like the tremie method, pump method, and bagwork. Construction techniques for placing UWC include the use of caissons and cofferdams to create a dry work environment. Proper production, quality control measures, and maintenance are needed to ensure the durability of underwater concrete structures.
This document discusses concrete construction in extreme hot and cold weather conditions in India. It addresses the challenges of hot weather concreting such as increased water demand, accelerated slump loss, and increased risk of plastic shrinkage cracking. Recommendations for hot weather concreting include cooling the concrete, reducing placement time, and prompt curing. Cold weather concreting risks include reduced strength if water freezes within concrete. Recommendations include protecting concrete from freezing, using accelerants, and maintaining minimum curing temperatures. Proper planning, materials, and protection methods can help produce quality concrete despite temperature extremes.
Bleeding in concrete refers to the physical migration of water to the top surface due to its lower density. While bleeding replaces water lost to evaporation and prevents cracking, it can also increase finishing time and reduce strength if not properly controlled. The document discusses the causes of bleeding including high water content and improper mixing. It also presents methods to reduce bleeding such as using pozzolans or air-entrainment and ensuring proper proportioning, mixing and compaction. Bleeding is tested using ASTM C 232, which involves measuring water released both with and without vibration.
This document discusses underwater concrete, including its production, placement methods, and quality control. It notes that underwater concrete must have proper mix design and flowability to consolidate under its own weight without vibration. The main placement methods described are tremie, pump, toggle bags, and bagwork. Quality control includes monitoring placement rate and volume. Common issues with underwater concrete include cement washout, laitance, and segregation, which mix design and proper placement seek to prevent.
This document discusses quality control and durability factors in concrete. It defines quality as conformance to requirements and durability as a concrete's ability to resist deterioration when exposed to the environment. Several factors influence concrete durability, including the materials used, water-cement ratio, compaction, curing and the physical and chemical conditions of the service environment. Common durability issues include corrosion, cracking from sulfate attack or alkali-silica reaction, and carbonation reducing alkalinity. Proper quality control of materials and construction processes is needed to produce durable concrete.
The document discusses concrete construction in cold weather. It defines cold weather as periods when the average daily temperature is below 40°F for more than 3 days. Concrete sets more slowly at lower temperatures, taking approximately twice as long to set at 40°F compared to 70°F. Precautions are needed to prevent freezing of plastic concrete and ensure proper strength gain. Methods include using Type III cement, air entrainment, heated materials and forms left in place longer during curing to insulate concrete from cold temperatures.
1. This document describes various tests conducted on cement and concrete to determine their properties and quality, including fineness, consistency, setting time, soundness, compressive strength, and workability.
2. Tests are also described for determining water demand and the effects of admixtures on properties like setting time and strength.
3. Common admixtures include accelerators, retarders, air-entrainers, and water-reducers, which can improve concrete workability, permeability, cracking resistance and durability.
Deterioration of concrete structures can occur through various chemical, physical, and mechanical processes over time. Scaling and disintegration are forms of physical deterioration where the concrete's surface layers break down from freezing and thawing or weathering. Corrosion of reinforcement rebar can develop due to penetration of chloride ions or carbonation reducing the pH. Other causes include sulfate attack, alkali-aggregate reactions, abrasion, high temperatures, and erosion. Proper mix design and concrete quality can increase durability and prevent deterioration.
Workability refers to the ease with which fresh concrete can be mixed, placed, compacted and finished. It is affected by factors like water content, mix proportions, aggregate size and shape, grading and surface texture. Increasing water content or using admixtures improves workability by acting as a lubricant between particles. Larger, rounded aggregates require less water than smaller, angular ones. Well-graded aggregates with minimal voids also increase workability. Workability can be measured using slump, compacting factor, flow, or Vee Bee tests.
The document discusses the different types of shrinkage that can occur in concrete, including plastic shrinkage, drying shrinkage, autogenous shrinkage, and carbonation shrinkage. Plastic shrinkage causes cracks on the surface of fresh concrete due to evaporation before setting. Drying shrinkage is defined as the contraction of hardened concrete from the loss of capillary water, which can lead to cracking, warping, and deflection without any external loading. In summary, the document outlines the main types of volume changes and shrinkage that concrete undergoes both during the plastic and hardened states.
The document discusses concrete mix design according to the IS method. It covers objectives of mix design such as achieving desired strength, workability and durability economically. Basic considerations like cost, specifications, workability, strength and durability are explained. Factors influencing mix design choice like grade of concrete, type of cement, aggregate size and grading, water-cement ratio, workability and durability are outlined. Nominal and design mixes are compared. The IS method of mix design is then described which involves specifying a target average compressive strength based on the characteristic strength and standard deviation.
This document discusses the durability and permeability of concrete. It defines durability as the ability to last a long time without significant deterioration. Permeability is defined as the property that governs the rate of flow of a fluid into a porous solid. The document discusses factors that affect the durability and permeability of concrete such as water-cement ratio, cement properties, aggregate type and quality, curing methods, and use of admixtures. Maintaining a low water-cement ratio and limiting chloride and sulfate levels in concrete are important for ensuring durability.
what is polymer concrete, types, properties, material used in manufacturing process , manufacturing process, applications and their advantages. case study on polymer composite concrete.
The document discusses specifications for aggregates used in concrete from natural sources according to Indian Standard IS 383. It outlines various tests that should be performed on aggregates including aggregate crushing value, impact value, abrasion value, flakiness and soundness. The crushing value and impact value tests determine the strength of aggregates and maximum allowed values are specified based on the application of concrete. The abrasion and soundness tests evaluate durability of aggregates and maximum loss percentages are also standardized. Using aggregates that conform to these specifications and standards ensures production of high quality concrete.
Roller-compacted concrete (RCC) is a concrete that is mixed in a pugmill and placed with dump trucks and spread with bulldozers. It is compacted in lifts of 100-250mm thick using vibratory steel drum rollers. RCC does not require internal vibration and can be used for port, rail, highway, and industrial facilities. Some advantages are reduced cement, no formwork, and ability to maintain traffic flow during placement. Limitations include a rougher surface and difficulty compacting near edges.
Polymer concrete is produced by mixing mineral fillers with a synthetic or natural resin binding agent. There are three main types: latex-modified concrete, polymer-impregnated concrete, and polymer concrete. Polymer concrete has many benefits including high strength, durability, fire and heat resistance, chemical resistance, and faster cure times. It can develop high compressive strengths within hours or minutes depending on the materials used. Common applications include flooring, containment structures, trench drains, countertops, furniture, and areas with heavy traffic.
Epoxy crack injection for concrete (the basics)jbors
Epoxy injection offers a permanent repair for cracks (and delaminations) in concrete. The repair is structural, permanent and water-tight with the same lifespan as the surrounding concrete. It can be performed at temperatures as low 35°F, on cracks as narrow as 5 mils (5/1000”) and even underwater.
The cured epoxy restores the monolithic integrity of the concrete, protects the internal reinforcing steel from corrosion and is unaffected by water, chemicals and sunlight. University studies confirm that the repaired concrete matches the original strength of the uncracked concrete. A useful performance specification for the epoxy adhesive is ASTM C881, Type IV for load bearing (structural) applications. The cured high modulus epoxy generally exhibits more than 3 times the compressive strength and over 10 times the tensile strength of the surrounding concrete.
Typical structures repaired using epoxy injection include: parking decks, stadiums, concrete framed buildings, residential foundations, swimming pools, airport runways and taxiways, concrete bridge decks, floor cracking and delaminations in warehouses and manufacturing facilities, concrete pipe and tanks, concrete beams and piers and port facilities including docks, piers and pilings. Facilities where crack injection is often employed include water/sewage treatment plants, industrial sites, machinery foundations, and refrigerated and frozen food storage warehouses.
Specially trained contractors should be considered to properly perform crack repair using proper surface preparation procedures and positive displacement metering pumps to properly proportion and deliver the two component epoxy.
Benefits of Epoxy Injection
• Fast cure strength — up to 5,000 psi compressive yield in less than 5 hours,
• Vibration tolerant during cure — repairs can be made while structure is open,
• Unique concrete crack injection solutions for underwater, corrosive, large void (low exotherm) and other extreme exposures,
• O VOC concrete crack repair adhesives and seals,
• Can be used in temperatures as low as 35°F,
• Restores cracked concrete and structural members including beams and columns to original monolithic strength,
• Stops water leakage through foundations,
• Prevents corrosion of embedded reinforcing steel,
• Useful in secondary containment areas to prevent leaks and
• Unlike urethane chemical grouts, the epoxy crack repair is structural and permanent.
1. Cement is made from calcining limestone and clay, and is a powder that can be mixed with water or sand and gravel to make mortar or concrete.
2. There are different types of cement classified based on their composition and properties, including rapid hardening, heat resistant, sulfate resisting, and white cement.
3. The typical composition of ordinary Portland cement includes calcium oxide, silica, alumina, iron oxide, and alkalies. The specific composition determines the cement's physical, mechanical, and chemical properties as well as its cost and applications.
This document discusses the workability of concrete. It defines workability as the ease with which concrete can be mixed, transported, placed, and compacted. Workability is associated with ease of flow, prevention of segregation, prevention of harshness, and prevention of bleeding. Several factors affect workability, including water content, aggregate size and shape, grading, porosity, admixtures, mixing time, and temperature. Workability is measured using tests such as slump testing and compacting factor testing. The document provides details on how these tests are performed and what the results indicate about a concrete mixture's workability.
The document discusses the process of manufacturing concrete. It begins by outlining the key ingredients in ordinary Portland cement - lime, silica, alumina, and iron oxide. These ingredients are heated to high temperatures in a kiln to form complex compounds. There are wet, dry, and semi-dry processes for manufacturing cement, which differ in whether raw materials are mixed dry or as a slurry. In the wet process, materials are ground into a slurry with water before being fed into a rotating kiln where they fuse at 1500°C to form clinker. The clinker is then cooled, ground, and gypsum is added to produce cement. Hydration occurs when cement mixes with water, forming hydrated compounds
Curing concrete is important to allow the cement hydration process to continue and develop strength over time. Proper curing ensures concrete reaches its designed strength and durability by controlling moisture loss. Common curing methods include water curing through ponding, sprinkling or wet coverings; membrane curing using plastic sheeting or curing compounds; and steam curing to accelerate strength gain. Curing should continue for at least 7 days for normal concrete and 14 days if blended cements are used. Inadequate curing can lead to reduced strength, increased permeability and poor durability.
The document discusses the fresh and hardened properties of concrete. It describes workability, segregation, and bleeding as important fresh properties. Workability is affected by water content, mix proportions, aggregate size and shape. The slump cone test and compaction factor test are described for measuring workability. Hardened properties discussed include compressive strength, flexural strength, and modulus of elasticity. The compression test, flexural strength test, and stress-strain relationship determination are described for evaluating hardened properties.
This document discusses sulfur infiltrated concrete (SIC), which is produced by immersing cured concrete specimens in molten sulfur to infiltrate the pores. SIC has significantly higher strength and durability compared to normal concrete. It can be used for precast elements like roofing, fences, pipes, and railway sleepers where fast curing or acid resistance is needed. The production process is simple and inexpensive, involving drying the concrete then submerging it in molten sulfur with or without vacuum. SIC shows large increases in compression and tensile strength, as well as improved elastic properties, freeze-thaw resistance, and acid resistance compared to normal concrete.
Curing concrete involves maintaining moisture and temperature conditions to allow hydration of cement to occur. It prevents premature drying out which could limit strength development and durability. Effective curing methods include ponding, fogging, wet coverings, impervious sheets, membrane compounds and steam curing. Curing should continue until the concrete reaches adequate strength, typically a minimum of 7 days, and longer periods improve concrete properties. Temperature, cement type, element size and exposure conditions influence curing needs. Inadequate curing can limit strength and durability within 30-50mm of the surface.
The document discusses concrete construction in cold weather. It defines cold weather as periods when the average daily temperature is below 40°F for more than 3 days. Concrete sets more slowly at lower temperatures, taking approximately twice as long to set at 40°F compared to 70°F. Precautions are needed to prevent freezing of plastic concrete and ensure proper strength gain. Methods include using Type III cement, air entrainment, heated materials and forms left in place longer during curing to insulate concrete from cold temperatures.
1. This document describes various tests conducted on cement and concrete to determine their properties and quality, including fineness, consistency, setting time, soundness, compressive strength, and workability.
2. Tests are also described for determining water demand and the effects of admixtures on properties like setting time and strength.
3. Common admixtures include accelerators, retarders, air-entrainers, and water-reducers, which can improve concrete workability, permeability, cracking resistance and durability.
Deterioration of concrete structures can occur through various chemical, physical, and mechanical processes over time. Scaling and disintegration are forms of physical deterioration where the concrete's surface layers break down from freezing and thawing or weathering. Corrosion of reinforcement rebar can develop due to penetration of chloride ions or carbonation reducing the pH. Other causes include sulfate attack, alkali-aggregate reactions, abrasion, high temperatures, and erosion. Proper mix design and concrete quality can increase durability and prevent deterioration.
Workability refers to the ease with which fresh concrete can be mixed, placed, compacted and finished. It is affected by factors like water content, mix proportions, aggregate size and shape, grading and surface texture. Increasing water content or using admixtures improves workability by acting as a lubricant between particles. Larger, rounded aggregates require less water than smaller, angular ones. Well-graded aggregates with minimal voids also increase workability. Workability can be measured using slump, compacting factor, flow, or Vee Bee tests.
The document discusses the different types of shrinkage that can occur in concrete, including plastic shrinkage, drying shrinkage, autogenous shrinkage, and carbonation shrinkage. Plastic shrinkage causes cracks on the surface of fresh concrete due to evaporation before setting. Drying shrinkage is defined as the contraction of hardened concrete from the loss of capillary water, which can lead to cracking, warping, and deflection without any external loading. In summary, the document outlines the main types of volume changes and shrinkage that concrete undergoes both during the plastic and hardened states.
The document discusses concrete mix design according to the IS method. It covers objectives of mix design such as achieving desired strength, workability and durability economically. Basic considerations like cost, specifications, workability, strength and durability are explained. Factors influencing mix design choice like grade of concrete, type of cement, aggregate size and grading, water-cement ratio, workability and durability are outlined. Nominal and design mixes are compared. The IS method of mix design is then described which involves specifying a target average compressive strength based on the characteristic strength and standard deviation.
This document discusses the durability and permeability of concrete. It defines durability as the ability to last a long time without significant deterioration. Permeability is defined as the property that governs the rate of flow of a fluid into a porous solid. The document discusses factors that affect the durability and permeability of concrete such as water-cement ratio, cement properties, aggregate type and quality, curing methods, and use of admixtures. Maintaining a low water-cement ratio and limiting chloride and sulfate levels in concrete are important for ensuring durability.
what is polymer concrete, types, properties, material used in manufacturing process , manufacturing process, applications and their advantages. case study on polymer composite concrete.
The document discusses specifications for aggregates used in concrete from natural sources according to Indian Standard IS 383. It outlines various tests that should be performed on aggregates including aggregate crushing value, impact value, abrasion value, flakiness and soundness. The crushing value and impact value tests determine the strength of aggregates and maximum allowed values are specified based on the application of concrete. The abrasion and soundness tests evaluate durability of aggregates and maximum loss percentages are also standardized. Using aggregates that conform to these specifications and standards ensures production of high quality concrete.
Roller-compacted concrete (RCC) is a concrete that is mixed in a pugmill and placed with dump trucks and spread with bulldozers. It is compacted in lifts of 100-250mm thick using vibratory steel drum rollers. RCC does not require internal vibration and can be used for port, rail, highway, and industrial facilities. Some advantages are reduced cement, no formwork, and ability to maintain traffic flow during placement. Limitations include a rougher surface and difficulty compacting near edges.
Polymer concrete is produced by mixing mineral fillers with a synthetic or natural resin binding agent. There are three main types: latex-modified concrete, polymer-impregnated concrete, and polymer concrete. Polymer concrete has many benefits including high strength, durability, fire and heat resistance, chemical resistance, and faster cure times. It can develop high compressive strengths within hours or minutes depending on the materials used. Common applications include flooring, containment structures, trench drains, countertops, furniture, and areas with heavy traffic.
Epoxy crack injection for concrete (the basics)jbors
Epoxy injection offers a permanent repair for cracks (and delaminations) in concrete. The repair is structural, permanent and water-tight with the same lifespan as the surrounding concrete. It can be performed at temperatures as low 35°F, on cracks as narrow as 5 mils (5/1000”) and even underwater.
The cured epoxy restores the monolithic integrity of the concrete, protects the internal reinforcing steel from corrosion and is unaffected by water, chemicals and sunlight. University studies confirm that the repaired concrete matches the original strength of the uncracked concrete. A useful performance specification for the epoxy adhesive is ASTM C881, Type IV for load bearing (structural) applications. The cured high modulus epoxy generally exhibits more than 3 times the compressive strength and over 10 times the tensile strength of the surrounding concrete.
Typical structures repaired using epoxy injection include: parking decks, stadiums, concrete framed buildings, residential foundations, swimming pools, airport runways and taxiways, concrete bridge decks, floor cracking and delaminations in warehouses and manufacturing facilities, concrete pipe and tanks, concrete beams and piers and port facilities including docks, piers and pilings. Facilities where crack injection is often employed include water/sewage treatment plants, industrial sites, machinery foundations, and refrigerated and frozen food storage warehouses.
Specially trained contractors should be considered to properly perform crack repair using proper surface preparation procedures and positive displacement metering pumps to properly proportion and deliver the two component epoxy.
Benefits of Epoxy Injection
• Fast cure strength — up to 5,000 psi compressive yield in less than 5 hours,
• Vibration tolerant during cure — repairs can be made while structure is open,
• Unique concrete crack injection solutions for underwater, corrosive, large void (low exotherm) and other extreme exposures,
• O VOC concrete crack repair adhesives and seals,
• Can be used in temperatures as low as 35°F,
• Restores cracked concrete and structural members including beams and columns to original monolithic strength,
• Stops water leakage through foundations,
• Prevents corrosion of embedded reinforcing steel,
• Useful in secondary containment areas to prevent leaks and
• Unlike urethane chemical grouts, the epoxy crack repair is structural and permanent.
1. Cement is made from calcining limestone and clay, and is a powder that can be mixed with water or sand and gravel to make mortar or concrete.
2. There are different types of cement classified based on their composition and properties, including rapid hardening, heat resistant, sulfate resisting, and white cement.
3. The typical composition of ordinary Portland cement includes calcium oxide, silica, alumina, iron oxide, and alkalies. The specific composition determines the cement's physical, mechanical, and chemical properties as well as its cost and applications.
This document discusses the workability of concrete. It defines workability as the ease with which concrete can be mixed, transported, placed, and compacted. Workability is associated with ease of flow, prevention of segregation, prevention of harshness, and prevention of bleeding. Several factors affect workability, including water content, aggregate size and shape, grading, porosity, admixtures, mixing time, and temperature. Workability is measured using tests such as slump testing and compacting factor testing. The document provides details on how these tests are performed and what the results indicate about a concrete mixture's workability.
The document discusses the process of manufacturing concrete. It begins by outlining the key ingredients in ordinary Portland cement - lime, silica, alumina, and iron oxide. These ingredients are heated to high temperatures in a kiln to form complex compounds. There are wet, dry, and semi-dry processes for manufacturing cement, which differ in whether raw materials are mixed dry or as a slurry. In the wet process, materials are ground into a slurry with water before being fed into a rotating kiln where they fuse at 1500°C to form clinker. The clinker is then cooled, ground, and gypsum is added to produce cement. Hydration occurs when cement mixes with water, forming hydrated compounds
Curing concrete is important to allow the cement hydration process to continue and develop strength over time. Proper curing ensures concrete reaches its designed strength and durability by controlling moisture loss. Common curing methods include water curing through ponding, sprinkling or wet coverings; membrane curing using plastic sheeting or curing compounds; and steam curing to accelerate strength gain. Curing should continue for at least 7 days for normal concrete and 14 days if blended cements are used. Inadequate curing can lead to reduced strength, increased permeability and poor durability.
The document discusses the fresh and hardened properties of concrete. It describes workability, segregation, and bleeding as important fresh properties. Workability is affected by water content, mix proportions, aggregate size and shape. The slump cone test and compaction factor test are described for measuring workability. Hardened properties discussed include compressive strength, flexural strength, and modulus of elasticity. The compression test, flexural strength test, and stress-strain relationship determination are described for evaluating hardened properties.
This document discusses sulfur infiltrated concrete (SIC), which is produced by immersing cured concrete specimens in molten sulfur to infiltrate the pores. SIC has significantly higher strength and durability compared to normal concrete. It can be used for precast elements like roofing, fences, pipes, and railway sleepers where fast curing or acid resistance is needed. The production process is simple and inexpensive, involving drying the concrete then submerging it in molten sulfur with or without vacuum. SIC shows large increases in compression and tensile strength, as well as improved elastic properties, freeze-thaw resistance, and acid resistance compared to normal concrete.
Curing concrete involves maintaining moisture and temperature conditions to allow hydration of cement to occur. It prevents premature drying out which could limit strength development and durability. Effective curing methods include ponding, fogging, wet coverings, impervious sheets, membrane compounds and steam curing. Curing should continue until the concrete reaches adequate strength, typically a minimum of 7 days, and longer periods improve concrete properties. Temperature, cement type, element size and exposure conditions influence curing needs. Inadequate curing can limit strength and durability within 30-50mm of the surface.
This document discusses hot weather concreting and provides guidelines and precautions. Detrimental hot weather conditions include high ambient temperature, concrete temperature, low relative humidity, and high wind speed. Precautions should be taken such as cooling concrete materials, using supplementary cementitious materials, and promptly transporting, placing, and finishing the concrete. Plastic shrinkage cracking can occur if the rate of evaporation exceeds thresholds, so fogging and windbreaks are recommended. Proper curing, including water spraying or saturated fabric, is especially important in hot weather to prevent drying of concrete surfaces.
Curing plays an important role in the strength and durability of concrete. It involves preventing moisture loss from concrete to allow the hydration process to continue and gain strength. Some common curing methods include ponding, sprinkling with water, using wet coverings like burlap or plastic sheets, sealing the surface, and steam curing. Curing should be continuous for at least 7 days for normal concrete or 10-14 days if exposed to dry, hot conditions or if blended cements are used. Maintaining moisture is especially important in cold weather to prevent freezing.
Cement concrete is a composite material consisting of a binding material (cement or lime), aggregates (fine and coarse), water, and admixtures. The cement and water form a paste that coats the aggregates and binds them together. Concrete can be classified based on its constituents, method of production, place of casting, and bulk density. Proper curing is important for concrete to gain strength and hardness through hydration. Common curing methods include water curing, membrane curing, and steam curing. The water-cement ratio significantly impacts concrete strength, with lower ratios producing stronger concrete.
This document discusses various methods of curing concrete, including water curing, membrane curing, steam curing, and electrical curing. It notes that curing allows for continuous hydration and strength gain in concrete. Proper curing retains moisture on the surface and prevents early drying out, leading to increased strength and durability. A new technique called "drip curing" is also introduced, which can reduce water consumption during curing by up to 80% through the use of multilayer sheets that drip water onto the concrete surface.
Shrinkage and plastic of concrete samples.pptGKRathod2
The document discusses various topics related to concrete, including destructive and non-destructive tests to determine concrete strength, factors affecting setting time and workability, methods to prevent issues like segregation and bleeding during concrete placement, and different curing techniques to promote strength development and durability. It provides details on tests like rebound hammer, ultrasonic pulse velocity and compression tests. It also explains concepts like slump loss, factors influencing cohesiveness, and precautions needed for hot weather concreting to prevent plastic shrinkage cracks.
The document discusses various topics related to concrete, including destructive and non-destructive tests to determine concrete strength, factors affecting setting time and workability, methods to prevent issues like segregation and bleeding during concrete placement, and different curing techniques to promote strength development and durability. It provides details on tests like rebound hammer, ultrasonic pulse velocity and compression tests. It also explains concepts like slump loss, influence of curing, and how to prevent plastic shrinkage cracks.
This document summarizes the effects of temperature on fresh and hardened concrete. It discusses how both high and low temperatures can impact concrete strength and cracking. For high temperatures, it recommends precautions like cooling materials, using retarders, and protecting from moisture loss. For low temperatures, it advises heating materials and protecting concrete to prevent freezing, which can stop hydration and cause cracking. Proper planning, curing, and temperature control of ingredients are essential to account for temperature effects on concrete properties and performance.
Curing & prefabrication of concrete structures@hemadurgarao-IIIT Nuzvidhema3366
Curing concrete is an important process to ensure proper hydration of cement and development of strength. There are various curing methods like immersion, ponding, spraying, wet covering, and membrane curing. Membrane curing uses plastic sheeting or compounds to seal in moisture. Steam curing at higher temperatures accelerates strength gain but can cause retrogression of strength with fast hydration. Prefabricated construction involves dividing construction into standardized parts that are mass produced in a plant and assembled on site. This allows for parallel production, reduced time, and standardization.
Hot weather is defined as any period with high temperatures that require special precautions for concrete. High temperatures can cause rapid drying of concrete and accelerated setting, potentially leading to cracking. It is important to account for hot weather conditions when planning concrete projects, as high heat can increase water demand and accelerate setting. To successfully place concrete during hot weather, the key is recognizing affecting factors and minimizing their impacts, such as modifying mix designs, reducing cement content, limiting water addition, starting finishing quickly, and adequately curing the concrete.
This document discusses various concrete curing methods including formwork, plastic sheeting, internal curing compounds, ponding, and sprinkling. Formwork and plastic sheeting can effectively cure concrete if kept moist, especially in hot dry weather. Internal curing compounds inhibit moisture loss to improve strength and reduce shrinkage. Ponding is effective for flat surfaces if a water supply is available. Sprinkling or fog curing can be used on most surfaces but require major water and drainage systems to prevent waste. The document provides details on properly applying the different curing methods.
Curing is the process of controlling the rate and extent of moisture loss from concrete during cement hydration. It is important to cure concrete for a reasonable period of time, such as days or weeks, to allow hydration to occur and for the concrete to achieve its potential strength and durability. There are several curing methods, including impermeable membrane curing using plastic sheeting or curing compounds to minimize moisture loss, and water curing through ponding, sprinkling, or wet coverings to continuously wet the exposed concrete surface and prevent moisture loss. The appropriate curing method depends on factors like the type of concrete member, the environment, and whether formwork can be retained.
Durability and permeability of concrete are essential for its ability to withstand weathering and chemical attacks over time. The durability of concrete depends on factors like water-cement ratio, cement and aggregate properties, use of admixtures, age of concrete, and exposure conditions. A more permeable concrete is more porous and allows more water penetration. Permeability decreases with lower water-cement ratio, finer cement, use of waterproofing admixtures, and increased age. Cracks in concrete can form due to temperature changes, drying shrinkage, chemical reactions, weathering, and poor construction practices. Reinforcement corrosion occurs via electrochemical processes and can be limited by restricting chlorides, ensuring proper concrete cover, and
Module on Special and high performance concreteErankajKumar
The document discusses different types of special concretes used in construction, including grouting, guniting, underwater concreting, and hot and cold weather concreting. Grouting involves injecting cement grout into cracks and voids to improve stability. Guniting uses a cement-sand mix applied at high pressure to repair damaged concrete. Underwater concreting requires special techniques like the tremie method and uses additives to allow placement under water. Hot and cold weather concreting require precautions like cooling or heating aggregates and protecting fresh concrete to account for temperature effects.
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concrete curing.ppt
1. Curing Concrete
Curing can be defined as a procedure for insuring
the hydration of the Portland cement in newly
placed concrete. It generally implies control of
moisture loss and sometimes of temperature.
The hydration of Portland cement is the chemical
reaction between grains of Portland cement and
water to form the hydration product, cement gel:
and cement gel can be laid down only in water-
filled space.
Hydration can proceed until all the cement reaches
its maximum degree of hydration or until all the
space available for the hydration product is filled
by cement gel, whichever limit is reached first.
2. Curing Concrete
A typical definition of curing is ‘the process of
preventing the loss of moisture from the concrete
whilst maintaining a satisfactory temperature
regime’. This particular definition adds that the
curing regime should prevent the development of
high temperature gradients within the concrete.
Curing requires adequate:
• Moisture
• Heat
• Time
If any of these factors are neglected, the desired
properties will not develop
3. Curing methods
1.Methods that maintain the presence of
mixing water in the concrete during
the early hardening period. These
include
Ponding
Immersion
Spraying or Fogging
Saturated wet coverings.
Concrete can be kept moist three curing methods:
4. Curing methods
2. Methods that reduce the loss of mixing
water from the surface of the concrete.
This can be done by covering the
concrete with
Impervious paper
plastic sheets
By applying membrane-forming curing
compounds.
Concrete can be kept moist three curing methods:
5. Curing methods
3. Methods that accelerate strength gain
by supplying heat and additional
moisture to the concrete. This is
usually accomplished with
Live steam,
heating coils
Electrically heated forms or pads.
The method or combination of methods
chosen depends on factors such as
availability of curing materials, size,
shape, and age of concrete,
production facilities (in place or in a
plant), and economics.
Concrete can be kept moist three curing methods:
6. Curing methods
-On flat surfaces, such as
pavements and floors, concrete
can be cured by Ponding. Earth or
sand dikes around the perimeter
of the concrete surface can retain
a pond of water.
-The most thorough method of
curing with water consists of total
immersion of the finished
concrete element. This method is
commonly used in the laboratory
for curing concrete test
specimens.
Ponding and Immersion
7. Curing methods
-Fogging and sprinkling with water
are excellent methods of curing
when the ambient temperature is
well above freezing and the
humidity is low. A fine fog mist is
frequently applied through a
system of nozzles or sprayers to
raise the relative humidity of the
air over flatwork, thus slowing
evaporation from the surface.
- Fogging is applied to minimize
plastic shrinkage cracking until
finishing operations are complete.
Fogging and Sprinkling
8. Curing methods
-Fabric coverings saturated with
water, such as burlap, cotton
mats, rugs, or other moisture-
retaining fabrics, are commonly
used for curing. Treated
burlaps that reflect light and are
resistant to rot and fire are
available.
Wet Coverings
9. Curing methods
Impervious paper for curing
concrete consists of two sheets
of Kraft paper cemented
together by a bituminous
adhesive with fiber
reinforcement. Such paper,
conforming to ASTM C 171
(AASHTO M 171), is an
efficient means of curing
horizontal surfaces and
structural concrete of relatively
simple shapes.
Impervious Paper
10. Curing methods
-Plastic sheet materials, such
as polyethylene film, can be
used to cure concrete.
Polyethylene film is a
lightweight, effective
moisture retarder and is
easily applied to complex as
well as simple shapes
Plastic Sheets
11. Curing methods
Liquid membrane-forming
materials can be used to
retard or reduce
evaporation of moisture
from concrete. They are the
most practical and most
widely used method for
curing not only freshly
placed concrete but also for
extending curing of concrete
after removal of forms or
after initial moist curing.
Membrane-Forming Curing Compounds
12. Curing methods
-Forms provide satisfactory protection
against loss of moisture if the top
exposed concrete surfaces are kept wet.
- The forms should be left on the concrete
as long as practical. Wood forms left in
place should be kept moist by sprinkling,
especially during hot, dry weather. If this
cannot be done, they should be
removed as soon as practical and
another curing method started without
delay.
Forms Left in Place
13. Curing methods
Steam curing is
advantageous where early
strength gain in concrete is
important or where additional
heat is required to
accomplish hydration, as in
cold weather. Two methods
of steam curing are used: live
steam at atmospheric
pressure (for enclosed cast-
in-place structures and large
precast concrete units) and
high-pressure steam in
autoclaves (for small
manufactured units).
Steam Curing
14. Curing methods
Electrical, hot oil, microwave and infrared
curing methods have been available for
accelerated and normal curing of concrete for
many years. Electrical curing methods include
a variety of techniques:
(1) Use of the concrete itself as the electrical
conductor,
(2) Use of reinforcing steel as the heating
element,
(3) Use of a special wire as the heating
element,
(4) Electric blankets, and
(5) The use of electrically heated steel forms
(presently the most popular method).
Electrical, Oil, Microwave, and Infrared Curing
15. The intention of curing is to protect concrete
against:
• Premature drying out, particularly by solar
radiation and wind (plastic shrinkage)
• leaching out by rain and flowing water
• Rapid cooling during the first few days
after placing
• High internal thermal gradients
• Low temperature or frost
• Vibration and impact which may disrupt the
concrete and interfere with bond to
reinforcement.
Why cure concrete
16. The depth of the surface
zone directly affected by
curing can be up to 20 mm
in temperate climatic
conditions, and up to 50 mm
in more extreme arid
conditions. Properties of the
concrete beyond this zone
are unlikely to be affected
significantly by normal
curing.
Why cure concrete
17. The rate of evaporation of water from
the surface, taking into account the
combined influences of the ambient
temperature and relative humidity, the
concrete temperature, and the wind
velocity can be estimated from Figure
below taken from ACI 308. This
standard requires that curing measures
are taken if the predicted rate of
evaporation exceeds 1.0 kg/m2/h, to
prevent plastic shrinkage cracking, but
also recommends that such measures
may be needed if the rate exceeds 0.5
kg/m2/h.
Why cure concrete
19. The question is how early water
can be applied over concrete
surface so that uninterrupted and
continued hydration takes place,
without causing interference with
the W/C ratio.
The answer is that first of all,
concrete should not be allowed
to dry fast in any situation.
When to start curing
20. This condition should be maintained for 24
hours or at least till the final setting time
of cement at which duration the concrete
will have assumed the final volume. Even if
water is poured after this time, it is not
going to interfere with the W/C ratio.
However, the best practice is to keep the
concrete under the wet gunny bag for 24
hours and then commence water curing by
way of ponding or spraying.
When to start curing
21. This depends upon:
• The reason for curing (plastic shrinkage,
temperature control, strength, durability,
etc.)
• The size of the element
• The type of concrete (especially rate of
hardening)
• The ambient conditions during curing
• The exposure conditions to be expected
after curing
• The requirements of the specification
How long curing should be
applied?
22. Regarding how long to cure it is difficult to
set a limit. Since all the desirable properties
of concrete are improved by curing, the
curing period should be as long as practical.
For general guidance, concrete must be
cured till it attains 70% of specified strength.
At lower temperature curing period must be
increased.
Concrete keeps getting HARDER AND
STRONGER over TIME. For better strength
and durability, cure concrete for 7 DAYS.
The LONGER concrete is cured, the closer
it will be to its best possible strength and
durability.
How long curing should be
applied?
24. Cements, or combinations, containing fly
ash (pfa), blast furnace slag (ggbs),
limestone filler (>5 per cent), or condensed
silica fume react more slowly than plain
Portland cement, particularly in cold
weather. Concretes containing blended
cements should therefore be cured
thoroughly and for a longer period than for
PC concrete, particularly if the potential
durability benefits are to be obtained in the
near-surface and cover zone. Concrete
containing condensed silica fume or
metakaolin exhibits only minimal bleeding
and thus requires early protection to prevent
plastic shrinkage cracking.
The effect of cement type
25. The following circumstances warrant
particular consideration of curing needs:
• Horizontal surfaces
• Dry, hot, windy conditions (one or more
of these)
• Wear-resistant floors
• High-strength concrete (initial curing is
especially important)
When is curing of particular
importance?
26. The hardening of concrete is a chemical
reaction – the rate of this reaction increases
with temperature but so does the rate of
evaporation from an exposed concrete
surface.
The rate of reaction at 35°C is about twice
that at 20°C which is, in itself, about twice
that at 10°C. The ultimate strength of
concrete cured at low temperature (e.g. in
winter) is generally greater than that of
concrete cured at a higher temperature (e.g.
in summer); but extremes of temperature
generally have a negative effect.
Effect of temperature
27. The slow rate of reaction at low
temperatures means the concrete must be
cured for a longer period to achieve the
desired degree of reaction.
The fast rate of reaction at high
temperatures gives relatively high early
strengths but the long-term strength and
durability are generally reduced.
The optimum temperature required to
produce the maximum 28-day strength,
based on small laboratory specimens, is
said to be approximately 13°C (Neville and
Brooks, 1987) and ambient temperatures of
15–25°C are generally considered to be
most suitable for concreting operations.
Effect of temperature
29. Hydration will proceed, to some extent, at
temperatures down to as low as –10°C.
Nevertheless, little strength will develop
below 0°C, and below 5°C the early
strength development is greatly retarded
(ACI 308). Even in the temperature range
5–10°C conditions are unfavorable for the
development of early strength. These
effects will be most prevalent in thin
sections, in the near surface of larger
sections, and in concrete made with slow
hydrating cements. The bulk strength of
larger sections will be less affected
because, generally, the internal
temperature will be elevated by the heat of
hydration.
Effect of temperature
30. Concrete should not be allowed to freeze
before it has gained sufficient strength to
resist damage. According to ACI 308 this
strength is approximately 3.5 MPa. Air
entrained concrete should not be allowed to
undergo any freeze–thaw cycles until it has
reached a strength of approximately 25
MPa. Non air-entrained concrete should, of
course, never be allowed to undergo
freezing and thawing while saturated. The
temperature of concrete during curing
depends on:
Effect of temperature
31. • The dimensions of the element
• The weather (ambient conditions)
• cement type cement content
• Admixtures (accelerators, retarders)
• The fresh concrete temperature
• Formwork type/insulation
• Formwork stripping time
Mostly, temperature control of in-situ concrete
during hardening is only attempted at
temperature extremes where, for example,
there is:
• A risk of freezing
• A risk of an excessive peak temperature or
an excessive temperature difference across
the section.
Effect of temperature
32. The peak temperature in a section should
generally be kept below about 65–70°C to
minimize the effect on compressive
strength. Measures to reduce peak
temperatures are beyond the scope of
normal curing techniques and may include
cooling of the fresh concrete by various
means or cooling of the placed concrete by
means of cooling pipes within the section.
Effect of temperature
33. Concrete allowed to freeze before a certain
minimum degree of hardening has been
achieved will be permanently damaged by the
disruption from the expansion of the water
within the concrete as it freezes. This will
result in irretrievable strength loss.
Excessive evaporation from an exposed
horizontal surface within the first
approximately 24 hours after casting will result
in plastic shrinkage cracking and a weak,
dusty surface. An excessive temperature
difference through the cross-section of an
element will result in early thermal cracking
due to restraint to contraction of the cooling
outer layers from the warmer inner concrete.
What happens if concrete is not
cured properly?
34. Inadequate curing will result in the
properties of the surface layer of concrete,
up to 30–50 mm, not meeting the intentions
of the designer in terms of durability,
strength and abrasion resistance.
What happens if concrete is not
cured properly?
35. -The effect of curing on strength development
is limited to the near-surface of concrete so
its effect on strength will depend on the
element size and type of loading that will be
applied.
-The effect on large elements loaded in
compression will be much less than on
slender elements loaded in flexure. It is
unlikely that the structural capacity of most
elements would be significantly reduced by
poor curing.
The effect of curing on strength
36. -Required curing duration is sometimes
expressed in terms of the maturity of the
concrete.
-The maturity concept is used to predict the
rate of strength development at different
temperatures; it is mostly used for the
determination of formwork stripping time
and for structural considerations such as
time at loading.
The maturity concept for estimation
of required curing duration
37. -Maturity allows the strength of a concrete of
known temperature-time history to be
predicted from laboratory specimens cured
under standard conditions. The maturity is
the sum of the product of temperature
(above a datum level, usually –11°C, the
temperature at which hydration is said to
cease) and the time over which the
temperature prevails:
M = Σ (T ・ Δt) [°C.h]
The maturity concept for estimation
of required curing duration
38. Equal maturity should mean equal strength; but
the relationship between maturity and strength
depends on the actual cement type and
strength class used, the water/cement ratio
and whether any significant water loss occurs
during curing. The maturity concept cannot, at
the current state of knowledge, be directly
related to durability aspects rather than
strength. Thus where curing is required for
properties such as abrasion resistance,
permeability, freeze–thaw resistance, etc. it
may be necessary to extend curing beyond
the period predicted by maturity at which a
certain strength develops.
The maturity concept for estimation
of required curing duration
39. -Practical applications of accelerated curing
include:
1- Ensuring a daily cycle with, for example,
apartment formwork systems.
2 -Speeding construction in winter
conditions.
3 -Ensuring multiple daily use of moulds
used for precast concrete.
4 -Reducing the time between production
and delivery of precast concrete elements.
Applications of accelerated curing
40. 1-Steam in pipes (precast technique
mainly).
2- Gas heating. This system is common for
in-situ construction.
3- Electric heating
4- Turbo heaters
Methods of accelerated curing
41. Accelerated curing has the following effects
on the properties of concrete:
1- Reduces the ultimate strength by up to 30
per cent depending on the peak temperature
reached.
2- A significant increase in coarse porosity
depending on the temperature reached.
3- If the curing temperature is high, there is a
significant risk of delayed ettringite formation.
4- For in-situ construction, accelerated curing
will increase the risk of early-age thermal
cracking caused by external restraint.
Effect of accelerated curing on
concrete properties
42. -The reason for the loss of strength and
increase in coarse porosity is believed to be
due to the hydration products forming close
to the original cement grains and not
spreading uniformly throughout the space
between the cement grains. If the peak
temperature during accelerated curing does
not exceed 65°C, the effect on long-term
properties is not significant.
Effect of accelerated curing on
concrete properties