Case Study: KBH Crusher – From Reject
Concrete to High-Value Asset
This article describes transforming concrete waste into high-quality recycled aggregate – with no screening, no additional labour costs (utilising existing plant infrastructure), and a consistent grading curve regardless of feed variation.
1 The Challenge
Hardscape manufacturing plants routinely generate significant volumes of reject material and off-cuts from splitting lines. This material is usually stockpiled on site, consuming valuable property space and incurring additional expenses for crushing and off-site transportation. While some revenue can be generated by selling this material as low-grade fill or bedding layer, far greater economic value is unlocked by re-integrating the material directly back into the concrete mix to replace the most expensive aggregate fractions. Furthermore, factory real estate can be utilised much more productively.
For producers worldwide, this challenge is compounded by:
High Raw Material Costs: Natural sand and gravel must be sourced at increasingly high prices.
Labour & Handling Overhead: Manual waste handling and intermediate storage are expensive and operationally inefficient.
The conventional attempt to avoid landfill fees relies on standard mobile jaw or impact crushers paired with screening decks. While this addresses basic volume reduction, it introduces severe operational issues: high dust emissions, elevated energy consumption (kWh/t), and extra operational labor. Crucially, integrated screens demand heavy maintenance when processing abrasive cementitious materials – especially when producing the fine gradings required for high-spec concrete product manufacturing.
Core Question: Can concrete waste be converted into a stable, high-quality recycled aggregate – with a consistent, ideal cubical geometry, zero additional labour intervention, and a payback fast enough for rapid Capex approval?
2 The KBH Crushing Solution
After years of frustration at its own production facility in Germany, KBH Maschinenbau developed a crusher system specifically designed for concrete products waste. Unlike standard crushing solutions, the KBH Recycling Crusher was engineered from the ground up to solve the specific challenges of in-plant concrete recycling and immediate re-use.
2.1 Engineered Specifically for Concrete Products –
Smart Sorting & Feeding Architecture
The Challenge Smart Sorting & Feeding Architecture: Conventional heavy crushers require massive throughput (>200 t/h) to handle large concrete units, whereas concrete plants need to process large items (e.g., kerbs, steps) at lower, energy-efficient rates (10–20 t/h).
The Challenge Advanced Secondary Crushing: Concrete scrap varies wildly: age ranges from 24-hour green concrete to fully cured 30-day product, densities differ between hollow units and dense pavers, and residual cement content alters crushing dynamics. Standard crushers produce inconsistent output curves under these changing conditions.
The Solution Smart Sorting & Feeding Architecture: A specialized sorting system manages material flow so the primary unit can digest input sizes up to 1200 x 500 x 200 mm without overloading capacity.
Mixed-Feed Capability: The feeding mechanism accepts varied scrap simultaneously – handling paving blocks, slabs, steps, retaining wall units, and kerbs together without needing pre-sorting by size or geometry.
The Solution Advanced Secondary Crushing: KBH’s patented internal features compensate for input variations. The secondary crusher delivers a reliable, constant particle size distribution regardless of whether the feed is 12-hour young concrete or fully cured heavy units. The product feeding system accommodates for a wide range of materials fed all at once. There is no need to individual feed products according to their size and geometry. The feed mechanism allows to collect product as it’s coming – Step Stones, Pavers, Slabs, Blocks, RW and SRWs all at once.
2.2 Single-Pass Operation – No Screening Required
The KBH Recycling Crusher yields a finished target grading in a single pass – eliminating screening decks and secondary circuit processing entirely. The target output grading can be tailored and fine-tuned to specific mix designs:
0-8 mm (5/16”): Maximises the fine/sand fraction (ideal for regions facing natural sand shortages).
0-11 mm (7/16”): Balanced sand/gravel split (recommended where coarse aggregate carries a higher cost).
0-16 mm (5/8”): Maximises the coarse/gravel fraction (optimal where natural stone commands a premium).
Note: The secondary crusher allows infinite mechanical adjustment of the output curve on site. Equipment specification does not lock the operation into a single grading permanently.
Direct Benefits of Eliminating Screen Decks: Drastically reduced dust emissions, zero screen mesh wear costs, and the complete elimination of screen-cleaning downtime and manual maintenance.
3 Economic Model & Value Creation Analysis
The financial justification rests on four compounding value streams:
3.1 Value-Added Leverage
Direct Sand Savings: Recycled fine fractions (0–4 mm) replace expensive natural sand.
Direct Gravel Savings: Recycled coarse fractions (4–X mm) replace virgin aggregates.
Eliminated Waste Overhead: Zero landfill fees, no transport hauling costs, and no third-party tipping charges.
Footprint Optimization: Eliminates unsightly waste stockpiles, reclaiming floor space for revenue-generating inventory or plant expansion.
Note on configuration: For sand-scarce environments (e.g., parts of Germany), a 0-8 mm (5/16”) split maximizes the fine fraction value. For other countries, where gravel commands a higher premium, a 0-11 mm (7/16”) or 0-16 mm (5/8”) configuration is recommended to increase the coarse fraction volume and maximize cost savings.
3.2 Exemplary Payback Summary
Based on an annual volume of 10,000 tonnes of concrete scrap, representative financial returns show (Table 1):
Commercial Upside: Using secondary concrete aggregate strengthens public tender competitiveness where sustainable procurement specifications and ESG credentials are required.
4 Operational & Strategic Value (Soft Factors)
In addition to the quantifiable economic benefits, the KBH Recycling Crusher system delivers a range of operational and strategic benefits that are challenging to quantify monetarily, but matter significantly in a capex business case and a long-term operational assessment.
