What does harēnātum mean in Latin?

harēnātum, a noun, means “concrete, mortar made by mixing cement with sand”.

What is the genitive of harēnātum?

The genitive singular is harēnātī. harēnātum is neuter, second declension.

In classical Latin, [ha.reːˈnaː.tũː]; in ecclesiastical (church) Latin, [a.reˈnaː.tum].

noun · neutersecond declension

harēnātum n (genitive harēnātī)

Classical[ha.reːˈnaː.tũː]Ecclesiastical[a.reˈnaː.tum]

concrete, mortar made by mixing cement with sand
Quibus ratiōnibus siccīs locīs tēctōria oporteat fīerī, dīxī; nunc, quemadmodum ūmidīs locīs polītiōnēs expediantur, ut permanēre possint sine vitiīs, expōnam. Et prīmum conclāvibus, quae plāno pede fuerint, in īmō pavīmentō altē circiter pedibus tribus prō harēnātō testa trullissētur et dīrigātur, utī eae partes tēctōriōrum ab ūmōre nē vitientur.I have spoken of the methods by which stucco should be made in dry places; now I will explain how such polished finishes can be arranged in moist places so that they can last without flaws. And first, in rooms that are even with the ground, cement mixed with brick instead of with sand should be trowelled on about three feet high above the floor and made flat [with plaster] so that those parts of the plaster will not be damaged by the moisture.c. 20 BC, Vitruvius, De Architectura, section 7.4:
[In puteō fodiendō] cum ad aquam ventum est, sine harēnātō opus surgit, nē vēnae obstruantur.[In digging a well,] when you reach water, walls are built up without cement, so that the springs will not be blocked.c. 79 AD, Pliny the Elder, Natural History, section 31.17: