Concrete Technology Quiz: Seismic Zones & Materials

Seismic Zones and Concrete Use

• Use of Fibre Reinforced High Strength Concrete is recommended for areas with high seismic activity.

Core Sample Testing

• Core samples for testing are taken from finished structures like roads and bridges.
• Cylindrical core samples have varying height-to-diameter (H/D) ratios, commonly 1.6.
• Compressive strength of a core sample (22 MPa) is corrected using a factor of 0.95 for actual strength (20.9 MPa).
• Equivalent cube strength is derived from corrected cylindrical strength, calculated as 26.125 MPa.

Ultrasonic Pulse Velocity Test

• Conducted as per IS 516 (Part 5/Sec 1) 2018.
• Measures concrete quality through velocity, indicating homogeneity and density.
• High velocity suggests good quality; low velocity indicates voids, lower density, or cracks.
• Calibration curves must be specific to the aggregate and cement types used.

Concrete Mix Design Process

• Determine the required water/cement ratio based on strength (Abram’s Law) and durability.
• Selection involves ascertaining water and admixture content.
• Cement content is calculated using water/cement ratio and total water content.
• Adjustments are made for the volume of coarse aggregate (CA) per total aggregate (TA).
• Mix calculations utilize the Absolute Volume Method for accuracy.

M50 Grade Concrete Mix Design

• Material choices include 43 Grade Ordinary Portland Cement (IS 269-2015) and 20 mm maximum aggregate size.
• Target mean strength is calculated as 58.25 MPa and derived using statistical factors from IS guidelines.
• Required water/cement ratio established as 0.29 for strength and 0.5 for durability; lower value (0.29) is chosen.
• Water content for a 150 mm slump is set at 198.32 kg/cum after adjustments.

Final Mix Composition

• Cement content fixed at 450 kg/cum; adjusted for water content due to aggregate absorption.
• Total aggregate volume calculated, with proportions for fine aggregate (FA) and coarse aggregate (CA) as 0.318 and 0.682 respectively.
• Actual water to be added post calculations is found to be 141.19 kg/cum after accounting for absorption.

Beam Example for Quantities

• Beam dimensions (500 x 600 x 5000 mm) yield a volume of 1.5 cum, increased to 1.8 cum for wastage.
• Total material requirements from this volume include 810 kg cement, 1047.2 kg FA, and 2449.6 kg CA.

Slump Test for Fresh Concrete

• Slump test determines workability using a concrete ratio of 1:1.293:3.024:0.31.
• Unit weight of concrete estimated between 2400 to 2500 kg/cum for concrete mix calculations.

Testing of Hardened Concrete

• Both destructive and non-destructive testing methods are outlined under IS norms.
• Destructive tests involve evaluating compressive strength based on standard cube or cylinder sizes.
• Strength testing entails cyclical loading and measurement of extensometer readings until internal voids are minimized.

Stress and Strain Concepts

• Discusses linear stress proportional to strain, emphasizing linear-elastic and non-linear responses.
• Normal concrete shows limited strength capacity; hence, high strength concrete (HSC) is preferred for structural applications.

Material Preferences for Construction

• High Strength Concrete (HSC) is chosen for multi-storey buildings to reduce column size, but may compromise ductility.
• Normal Strength Concrete (NSC) maintains adequate ductility despite larger column sizes, offering safety during seismic events.