The chemical demolition method is a low-vibration way to separate concrete and natural stone in a controlled manner. It is used when blasting vibrations must be avoided, crack propagation controlled, and sensitive environments protected. In practice, the structure preconditioned by chemical crack induction is then usually released mechanically and separated by material type—often with concrete demolition shears and hydraulic rock and concrete splitters, powered by compact hydraulic power units. The method is relevant for concrete demolition and special demolition, building gutting and cutting, rock excavation and tunnel construction, natural stone extraction, as well as special operations.
Definition: What is meant by chemical demolition method
The chemical demolition method refers to processes in which non-explosive, chemically reactive media—typically expansive mortars (expansion grouts)—are introduced into concrete or rock via boreholes. The chemically induced volumetric expansion generates controlled tensile stresses and cracks that divide the component into defined blocks. The process is time-delayed, low-vibration, and low-noise. The released segments are then mechanically removed, crushed, and hauled away, for example with concrete demolition shears, rock splitting cylinders, multi cutters, combination shears, or steel shears for reinforcement. The method is blast-free and suitable for selective deconstruction and for areas with strict requirements regarding noise, vibration, and dust.
Operating principle and chemical fundamentals
Expansive mortar is usually based on reactive binders that undergo an exothermic hydration when mixed with water. A high, gradually increasing expansive and contact pressure develops in the boreholes. This pressure exceeds the local tensile strength of concrete or natural stone, causing cracks to form between the boreholes. The crack pattern can be controlled via hole diameter, depth, grid spacing, and the sequence of placement. Temperature and humidity influence the reaction rate; excessive temperatures can cause premature gas formation, while low temperatures slow crack formation.
The chemically induced pre-damage significantly reduces the material resistance. As a result, subsequent steps—such as secondary splitting with rock and concrete splitters or targeted biting with concrete demolition shears—can be carried out in a more controlled, quieter way and with lower energy input.
Applications and suitability
The chemical demolition method is suitable when precision and low environmental impact are paramount. Typical use cases include:
- Concrete demolition and special demolition of massive foundations, walls, and slabs
- Building gutting and cutting in existing structures with immediate neighboring use
- rock demolition and tunnel construction when vibrations must be limited
- Natural stone extraction to release blocks along defined cracks
- Special operations, for example on hard-to-access components or in areas with elevated protection requirements
Sensitive environments
In hospitals, laboratories, or listed buildings, low vibration and controlled crack guidance are crucial. The chemical approach minimizes secondary damage to adjacent components. The released pieces can then be cut off with concrete demolition shears and reduced to manageable sizes.
Massive components and rock
With very thick cross-sections or hard rock, chemical crack induction enables pre-weakening. Rock splitting cylinders and rock and concrete splitters then engage at the separation joints formed and widen them in a controlled manner. This significantly reduces the effort required for mechanical size reduction.
Workflow in practice
The typical workflow combines chemical crack formation with mechanical follow-up:
- Analysis of as-built conditions, material, reinforcement, and boundary conditions
- Planning of drilling pattern, hole diameter, depth, and grid
- Creation of boreholes and cleaning of the drill channels
- Mixing and placement of the expansive mortar in accordance with the manufacturer’s instructions
- Controlled crack formation within the intended reaction time
- Mechanical follow-up: re-splitting, biting, cutting, and sorting
- Removal, recycling, and disposal of the material fractions
Drilling pattern, dosing, and time management
The quality of the result is largely determined by the drilling pattern. Tighter grids promote uniform crack formation but increase drilling effort. Hole diameter is based on component thickness and the mortar system. Hole depth and edge distances must be chosen to enable the desired crack propagation without uncontrolled spalling. Uniform hole filling and avoiding airtight seals reduce the risk of blowouts.
Temperature management is essential: cold components slow the process, warm components accelerate it. Shading, moistening of hole walls (without standing water), and adjusting the mix water temperature help control reaction times. The time window between filling and mechanical follow-up must be defined for the project.
Reinforced concrete
In reinforced components, the reinforcement limits crack opening. After chemical pre-damage, concrete demolition shears are used to separate the concrete from the reinforcement. Steel shears or multi cutters then cut the exposed bars. This results in clean separation of concrete and steel by material type.
Combination with hydraulic tools
The greatest efficiency arises from coordinated process chains. After crack induction, hydraulic tools supplied by hydraulic power packs follow with clear roles:
- Rock and concrete splitters as well as rock splitting cylinders widen the formed separation joints and divide the material more precisely.
- Concrete demolition shears crush released segments, remove residual bridges, and finish edges.
- Combination shears and multi cutters process mixed materials; steel shears cut reinforcement; tank cutters are used for special steel tanks or pipelines.
Chemical pre-damage lowers the required cutting and splitting forces. This reduces tool loads, accelerates secondary demolition, and improves occupational safety.
Advantages and limitations
- Advantages: low vibration, low noise, precise crack control, low risk of dust and flying fragments, well-plannable sequence.
- Limitations: waiting times until crack formation, temperature sensitivity, increased drilling effort, limited effect in heavily reinforced zones without subsequent mechanical separation.
Occupational safety and environmental protection
Safe handling requires personal protective equipment, low-dust drilling, and an exclusion zone during the reaction phase. Boreholes must not be sealed airtight; this reduces the risk of blowouts. Splashes must be avoided during processing, as expansive mortars can be strongly alkaline. Good ventilation, coordinated signaling, and documented clearance before mechanical follow-up increase safety.
From an environmental perspective, pH values and potential entries into soil or water bodies must be considered. Residual mortar and rinsings must be collected and disposed of properly. Measures for dust and noise reduction, separation by material type, and recycling of fractions must be planned on a project basis and should comply with applicable codes and regulatory requirements.
Quality assurance and documentation
For reproducible results, mixing ratios, temperatures, times, drilling parameters, and crack development are documented. Before deploying concrete demolition shears or splitters, crack development is to be checked visually. Tool selection, hydraulic power, and accessibility must be aligned with the planned block size. Ongoing photo documentation facilitates verification and optimization.
Cost-effectiveness and project planning
The cost structure is determined by drilling performance, mortar consumption, reaction times, and the efficiency of the mechanical follow-up. Early alignment of the drilling pattern and the planned use of rock and concrete splitters or concrete demolition shears avoids double steps. Hydraulic power packs, shears, and cutters should be matched to site logistics in terms of output and hose lengths to minimize changeover times.
Practical application scenarios
In inner-city existing buildings, the chemical demolition method facilitates the gutting of load-bearing elements without affecting neighboring buildings. The resulting blocks are reduced to transportable sizes with concrete demolition shears. In tunnel construction and rock removal, chemical crack induction enables low-vibration loosening before rock splitting cylinders and rock and concrete splitters produce the defined separations. In natural stone extraction, controlled crack formation enables gentle block release, followed by mechanical finishing. In special operations involving mixed materials, combination shears, multi cutters, steel shears, or tank cutters are additionally used to complete separation by material type.