The quality of the concrete used in these structures depends entirely on how well the man standing at the concrete drum mixes the sand, gravel, cement and water. Inevitably, some batches are poor, and that leads to structural weaknesses that worsen soon after construction is completed.

In most of the world, structures more than two stories high require premixed concrete not only because of government rules but because few other places can find workers willing to hand-carry loads of concrete up more than one or two flights of stairs. In India and Bangladesh, workers routinely carry such loads up five or more flights.

Sheetal Shinde stood at a nearby tea stall with tears in her eyes looking anxiously at the rescue operation. “There are five of my relatives in that building,” she said grimly. “They are still trapped inside.”