high performance concrete in concrete technology

high performance concrete in concrete technology

1. ADVANCED CONCRETE TECHNOLOGY BY DEEPAKMANI.K 23SE01

2. High Performance Concrete concrete meeting special combinations of performance and uniformity requirements that cannot always be achieved routinely using conventional constituents and normal mixing, placing, and curing practices. High-performance concrete (HPC) is a specialized type of concrete designed to meet specific performance requirements beyond those of conventional concrete. It typically exhibits superior strength, durability, and workability compared to traditional concrete mixes.

3. High-performance concrete (HPC) is produced by careful selection and proportioning of its constituents namely cement, sand, gravel, cementitious materials such as fly ash; silica fume; and slag, and chemical admixtures for instance high range water reducing admixtures. The strength and durability of the high-performance concrete exceed that of ordinary concrete. Therefore, the composition of high-performance concrete is almost the same as that of conventional cement concrete. However, it has many features such as high strength, smooth fracture surface, low permeability, discontinuous pore, etc. which are different from those of ordinary concrete. This is due to low water to cementitious material ratio, and the presence of cementitious materials and chemical admixtures. Curing of HPC is considerably important and critical curing period runs from placement or finishing up to 2 to 3 days later.

4. Composition of High Performance Concrete 1. Cement Chemical and physical properties of cement can help in selecting desired cement to produce high-performance concrete. For instance, cement with low C3A is the most desired type of cement to produce high-performance concrete because the C3A creates incompatibility of cement with a superplasticizer. 2. Water Water is a crucial component in high-performance concrete which should be compatible with cement and mineral/chemical admixtures. 3. Fine Aggregate Coarse fine aggregate is desired compared to finer sand to produce high-performance concrete since finer sand increases the water demand of concrete. 4. Coarse Aggregate The selection of coarse aggregate is crucial since it may control the strength of high-performance concrete. 5. Superplasticizer It is an essential component of high-performance concrete that is added into the concrete mix to reduce water to cement ratio.

5. 6. Cementitious Materials The cementitious component of high or any combination of cementitious material such as slag, fly ash, silica fume. 6.1 Silica Fume Silica fume is a waste by-product of the production of silicon and silicon alloys. Silica fume is available in different forms, of which the most commonly used now is in a densified form. In developed countries, it is already available readily blended with cement. It is possible to make high strength concrete without silica fume, at compressive strength of up to 98 MPa. Beyond that strength level, however, silica fume becomes essential. With silica fume, it is easier to make HPC for strengths between 63-98 MPa. 6.2 Fly Ash Fly ash has been used extensively in concrete for many years. Fly ash is, unfortunately, much more variable than silica fumes in both their physical and chemical characteristics. Most fly ashes will result in strengths of not more than 70 MPa. Therefore, for higher strengths, silica fume must be used in conjunction with fly ash. For high strength concrete, fly ash is used at dosage rates of about 15 % of cement content. 6.3 Ground Granulated Blast Furnace Slag (GGBFS) Slags are suitable for use in high-strength concrete at dosage rates between 15-30 %. However, for very high strengths, more than 98Mpa, it is necessary to use the slag in conjunction with silica fumes. 6.4 Others Sometimes, quartz flour and fiber are the components as well for HPC having ultra-strength and ultra ductility, respectively.

6. Composition of High Performance Concrete

7. Features of High Performance Concrete Compressive strength > 80 MPa ,even up to 800 MPa High-performance concrete is quite brittle but the introduction of fibers and can improve ductility. High durability Water binder ratio (0.25-0.35), therefore very little free water Reduced flocculation of cement grains Wide range of grain sizes Densified cement paste Low bleeding and plastic shrinkage Less capillary porosity is achieved through the use of low water to cementitious materials that produce dense microstructure, hence migration of aggressive elements would be difficult. Hence, durability improved greatly. Discontinuous pores Stronger transition zone at the interface between cement paste and aggregate Low free lime content Endogenous shrinkage Powerful confinement of aggregates Little micro-cracking Smooth fracture surface Low heat of hydration

8. Hydration of Normal Concrete Versus High Performance Concrete

9. Requirements of High Performance Concrete 1. High-early Strength 2. High Strength 3. High Durability Abrasion Resistance Blast Resistance Permeability Diffusion Carbonation Temperature Control Freeze-Thaw Resistance Chemical Attack Alkali-Silica Reactivity 4. Long Life Service 5. Toughness

10.  High-early Strength High early strength is an important characteristic which high performance concrete needs to possess in order to be classified as HPC. This property enables HPC to obtain its specified strength at an earlier age compared with normal concrete. The time period in which a specified strength should be achieved may range from a few hours to several days. High early strength property makes this type of concrete to be used for prestressed concrete to allow for early stressing, precast concrete for rapid production of elements, high-speed cast-in-place construction, rapid form reuse, cold-weather construction, and many other uses. High early strength can be produced using one or combination of the following materials and/or practices: High-early-strength cement High cement content (400 to 600 kg/m3) Low water-cementing materials ratio (0.20 to 0.45 by mass) Higher freshly mixed concrete temperature Higher curing temperature Chemical admixtures Supplementary cementing materials Steam curing Insulation to retain heat of hydration

11. High Strength High performance concrete can have higher compression strength compared with conventional concrete. if the compressive strength of concrete is greater than 40Mpa then it is considered as high strength in accordance with ACI Code. High compressive strength concrete is produced under careful control in concrete plants. Production of high-strength concrete may or may not require the purchase of special materials. The producer must know the factors affecting compressive strength and know-how to vary those factors for best results. Representation of Strength in Normal Strength Concrete (right) and High Strength Concrete (left)

12. High Durability Deficiencies in the durability of conventional concrete lead to many problems in aggressive environments. However, high performance concrete needs to address most of these problems due to abrasions, freezing and thawing, carbonations, sulphate attack, blasts, and alkali-aggregate reactions otherwise it does not deliver the expected performance during its life service. Bridge Structure Constructed From High Performance Concrete in Severe Environment

13. Abrasion Resistance The resistance to abrasion is associated with concrete strength that is why HPC is ideal answer for abrasive conditions. Such concrete is suitable for the construction of spillways and stilling basins, and concrete pavements or concrete pavement overlays subjected to heavy or abrasive traffic Blast Resistance As far as blast resistance requirement is concerned, the HPC should have compressive strength greater than 120MPa and contain steel fibers. Blast-resistant concretes are often used in bank vaults and military applications. Permeability Both durability and life span of concrete is dependent on the concrete cover permeability. Commonly, high performance concrete should have considerably low permeability to air, water, and chloride ions. Low permeability achieved through good compaction, low water to cement ratio, and sometimes using special types of cement. Diffusion High performance concrete possesses great resistance to diffusion on its surface due to harmful ions like chloride because water to cement ratio is low. The lower the water to cementing ratio the lower the diffusion coefficient. Supplementary cementing materials, particularly silica fume, further reduce the diffusion coefficient. Carbonation High performance concrete should have good resistance against carbonation. This can be achieved through low permeability. By and large, the resistance of high performance concrete to carbonation is well above the life span of the structure provided that adequate concrete cover is provided.

14. Advantages Increased Strength : HPC typically exhibits higher compressive strength compared to conventional concrete, allowing for the construction of more robust and durable structures. Enhanced Durability : HPC is more resistant to environmental factors such as freeze-thaw cycles, chemical attacks, and abrasion, leading to longer service life and reduced maintenance costs. Improved Workability : Despite its high strength and durability, HPC maintains good workability, allowing for easier placement and compaction, which can result in faster construction times and reduced labor costs. Reduced Permeability : HPC has lower permeability than conventional concrete, which means it is less susceptible to water penetration and corrosion of embedded reinforcement, leading to increased durability and structural integrity. Flexibility in Design : The superior properties of HPC allow for more innovative and efficient design solutions, such as longer spans, thinner sections, and reduced material usage, resulting in lighter and more economical structures. Enhanced Aesthetics : HPC can achieve smoother surfaces, sharper edges, and better color consistency, enhancing the aesthetic appeal of architectural elements and structures. Sustainability : By increasing the lifespan of structures and reducing maintenance requirements, HPC contributes to sustainability by conserving resources and minimizing environmental impact over the life cycle of a project.

15. Disadvantages Higher Cost : The materials and technologies used in HPC production often come at a higher cost compared to conventional concrete, which can increase overall project expenses. Specialized Expertise : Properly designing, producing, and placing HPC requires specialized knowledge and expertise, which may not be readily available and can lead to increased project complexity and risk. Quality Control Challenges : Achieving consistent quality with HPC can be challenging due to the precise requirements of mix design, materials, and construction practices, requiring stringent quality control measures throughout the construction process. Limited Availability of Materials : Some specialized materials used in HPC, such as high-strength aggregates and supplementary cementitious materials, may have limited availability in certain regions, which can pose logistical challenges for project implementation. Potential for Shrinkage and Cracking : HPC may be more prone to shrinkage and cracking during curing and early age hydration due to its reduced water content and higher cementitious materials content, necessitating careful attention to curing and crack prevention measures. Construction Constraints : The use of HPC may require adjustments to construction practices and equipment due to its higher strength and workability requirements, which can impact scheduling and project logistics.