About

Quarry screenings (often called stone dust, cracker dust, or Otsev) are a byproduct of stone crushing, typically consisting of particles from 0 to 5 mm. While cheaper than river sand, screenings contain a high percentage of micro-fines which dramatically increase the surface area of the aggregate.

This calculator is specifically tuned for screenings-based mixes. It warns users of the increased water demand required to wet these fines. Failing to adjust for this results in a dry, crumbly mix that cannot be compacted. Conversely, adding too much water to compensate often leads to significant shrinkage cracking. This tool balances these factors for non-structural applications like paver bedding, floor screeds, or fence post backfill.

Formulas

The calculator uses an adjusted bulk density for the stone dust, which varies based on compaction state. The water demand formula incorporates a "Fines Factor" (F).

W_req ≈ C_mass × (0.5 + F)

Where F ranges from 0.1 to 0.2 for granite screenings due to high surface absorption.

Reference Data

Application	Ratio (Vol)	Cement : Dust (kg)	Water Demand	Est. Strength
Paver Bedding (Dry)	1 : 6	1 : 6.5	Low (0.4)	5-8 MPa
Floor Screed	1 : 4	1 : 4.5	Med (0.55)	15 MPa
Fence Post Fill	1 : 5	1 : 5.5	High (0.65)	10 MPa
Light Slab	1 : 3	1 : 3.5	High (0.60)	20 MPa

Frequently Asked Questions

No. Stone dust lacks the graded aggregate structure (large stones + sand) required for high compressive strength and shear resistance. It is strictly for non-structural use like bedding, screeds, or simple backfilling.

The high content of very fine particles requires more water to make the mix workable. As this excess water evaporates during curing, the volume of the concrete reduces significantly, leading to shrinkage cracks.

A "semi-dry" mix of 1 part cement to 6 parts screenings is standard. It should be moist enough to clump when squeezed in hand, but not wet enough to flow.