About

Enriched Sand-Gravel Mix (often abbreviated as OPGS in industrial contexts or Premium Ballast) differs significantly from standard pit-run gravel. It undergoes processing to achieve a consistent particle size distribution, typically maintaining a rigid ratio of gravel (approx. 70%) to sand (approx. 30%). This optimization reduces the void ratio within the aggregate matrix, requiring less cement paste to fill gaps compared to standard ballast.

This calculator determines the precise cement dosage required for structural applications using enriched aggregates. Unlike standard ballast tools, this algorithm adjusts for the higher bulk density (approx. 1600-1700 kg/m³) and lower void fraction of enriched mixes. Using standard ratios on enriched material often results in excessive cement consumption or unworkable mixes due to the lack of fines.

Formulas

The calculation relies on the Absolute Volume Method, adjusted for the specific specific gravity of enriched aggregates. The basic mass balance equation for a cubic meter of concrete is:

M_cρ_c + M_aggρ_agg + M_wρ_w + V_air = 1000

Where M represents mass in kg and ρ represents specific gravity. Enriched aggregates typically allow for a reduction in V_air and M_w due to better packing density.

Reference Data

Target Grade	Comp. Strength (MPa)	Cement Grade	Ratio (C:Agg)	Water/Cement
M15 (General)	15	42.5	1 : 6.0	0.65
M20 (Foundations)	20	42.5	1 : 4.8	0.55
M25 (Structural)	25	42.5	1 : 4.0	0.50
M30 (Heavy Duty)	30	52.5	1 : 3.5	0.45
M35 (Pre-cast)	35	52.5	1 : 3.0	0.42

Frequently Asked Questions

Enriched aggregate (or OPGS) has a guaranteed ratio of gravel to sand, usually artificially blended or screened to remove excess fines and oversized stones. Standard ballast is often "pit-run", meaning it is used exactly as dug from the ground, leading to unpredictable void ratios and strength.

Enriched mixes contain fewer "fines" (dust and clay) than standard pit sand. Fines absorb significant water. With fewer fines, enriched mixes require less water to achieve the same workability (slump), which inherently increases the final strength of the concrete.

It is not recommended for high-load structural elements like columns or beams. Grade 32.5 cement has slower strength development and requires a higher cement content to match the 28-day strength of 42.5 grade. Using 42.5 or 52.5 is more efficient for structural work.