Guides for brick and block plant investors and factory managers: clay brick kilns and extruders, sand-lime and fly ash bricks, block machines, standards and plant planning.
There is no single brick making cement ratio. India’s IS 2185 (Part 1) caps concrete blocks at one part cement to six parts combined aggregate by volume, and ASTM and EN standards set no ratio at all, only the strength and absorption the block must reach. Plants set the ratio by trial batches on their own aggregates, because grading, mix water and compaction change strength as much as cement does.
A concrete block testing machine is a compression frame with a spherically seated head that crushes capped blocks to measure compressive strength, the property every block standard grades first. A plant laboratory also needs an oven, a balance and an immersion tank for absorption and density, and gauges for dimensions and drying shrinkage. ASTM C140, the EN 772 series and IS 2185 (Part 1) set the methods.
Engineering brick vs facing brick is a choice between performance and appearance: engineering bricks are sold on strength and low water absorption, with UK Class A above 125 N/mm² and below 4.5%, and Class B above 75 N/mm² and below 7% (Wienerberger UK; Forterra). Facing bricks are sold on looks, within declared durability. For a plant, the gap lies in clay, firing and sorting.
Clay brick paving uses fired units held to tougher limits than ordinary walling brick. ASTM C902 Class SX asks for an average compressive strength of 8,000 psi (55.2 MPa) and average cold-water absorption of at most 8% (BIA TN 14, 2017), while EN 1344 grades breaking load, abrasion and slip. Reaching them takes a clean body, dense forming and thorough vitrification.
Zigzag brick kiln design forces air through a stack of bricks in a path about three times longer than a straight trench, which cuts fuel use by about 15–25% against a fixed chimney kiln (India’s BEE, 2022). A VSBK fires bricks in a vertical shaft with even less energy but small output. Tunnel kilns suit new large plants because they run all year and fire hollow units.
Fly ash bricks are made by mixing fly ash with a lime or cement binder, sand and water, pressing the damp mix in a machine, then curing the bricks. One Indian state guideline uses 70% fly ash, 10% lime, 5% gypsum and 15% sand, with about two days on pallets followed by 10–14 days of water curing.
A clay suits a brick plant if it shapes without cracking, holds its form while drying, fires strong at a workable temperature and stays free of damaging impurities. To find out, test plasticity, grain size, shrinkage, carbonates, sulfur, carbon, soluble salts and fired properties on representative samples. Results decide the forming, drying and fuel route.
Brick kiln emissions are mainly particulate matter, sulfur dioxide, fluorides, nitrogen oxides, carbon monoxide and carbon dioxide. Much of the sulfur and fluorine comes from the clay, not only the fuel. Stack limits range from 250 mg/Nm³ of particulate in India to single-digit figures for US tunnel kilns, so the target market shapes the plant design.
Hollow clay bricks are made like solid bricks, except that the clay is extruded through a die fitted with a core bridge and cores, which form the holes as the column leaves the extruder. The column is wire-cut, dried and fired. In ASTM terms a brick becomes hollow when voids exceed 25% of the gross cross-sectional area, up to 60%; the holes save clay, weight and firing energy per unit.
ASTM C62 covers building brick: solid clay or shale units for structural and non-structural masonry where appearance is not a requirement. ASTM C216 covers facing brick, where appearance is a requirement. Both grade bricks by their resistance to freezing when wet. C62 has three grades, SW, MW and NW; C216 has SW and MW, and adds types FBS, FBX and FBA that control appearance and dimensional tolerances.
