Concrete Technology — Worked Examples

A concrete mixture contains $300\text{ kg}$ Portland cement, $60\text{ kg}$ fly ash, and $162\text{ kg}$ effective mixing water. Determine $w/cm$.

During a slump test, the concrete mass shears markedly to one side rather than subsiding uniformly. The technician records the largest vertical difference as 160 mm. Decide how the observation should be handled.

For $1.00\text{ m}^3$ of trial concrete: cement = 360 kg with relative density 3.15; water = 180 kg; SSD coarse aggregate = 1050 kg with bulk SSD relative density 2.65; air = 1.5%; SSD fine-aggregate relative density = 2.60. Determine SSD fine-aggregate mass.

The SSD trial proportions require 1050 kg coarse aggregate and 766 kg fine aggregate. Coarse aggregate absorption is 0.5% and total moisture is 2.0%; fine aggregate absorption is 1.2% and total moisture is 6.0%. All percentages are on an OD basis. Design mixing water is 180 kg. Determine wet aggregate masses and added water.

A trial batch uses a total batched mass of $2300\text{ kg}$ and fills a calibrated $0.0500\text{ m}^3$ measure with $118.0\text{ kg}$ of concrete. The batch was intended to produce exactly $1.00\text{ m}^3$. Estimate fresh-concrete density and actual yield.

A $150\text{ mm}$ diameter concrete cylinder fails at a maximum load of $620\text{ kN}$ during a valid cylindrical compression test. Determine measured compressive strength.

A valid project strength report is unexpectedly below the acceptance trend. Determine the investigation sequence before changing the mixture or condemning the structure.

Concrete is discharged from high above its final location, repeatedly striking reinforcement, while workers add unauthorized water to make it flow. Identify the material-quality risks and controls.