Frequently Asked Questions

When should MC-Injekt 640 epoxy injection be specified for a cracked concrete bridge beam, and what pre-injection preparation is required to ensure the epoxy penetrates the full depth of the crack?

Specifying the correct injection system for a cracked concrete bridge beam requires distinguishing between the crack type (active or dormant), the crack width, the moisture condition inside the crack, and the structural requirement (waterproofing only versus structural consolidation). MC-Injekt 640 epoxy injection is the correct specification when the following conditions are all met: the crack is dormant — it has been confirmed through crack monitoring (crack gauges or demountable mechanical gauges) over a minimum of 2 to 4 weeks that the crack width is not changing in response to live traffic load or thermal cycling; the crack is dry or only slightly damp — epoxy resins do not cure correctly in actively wet or water-filled cracks, as water on the crack face prevents the epoxy from bonding to the concrete. If the crack is actively seeping water, it must first be treated with MC-Injekt 2700 HV (PU foam injection) to stop the water, allowed to dry for a minimum of 2 weeks, and then re-injected with MC-Injekt 640 for structural consolidation; the structural requirement demands full strength restoration — if only waterproofing is needed (the crack is not in a high-stress zone), a flexible PU injection may be adequate and more economical than epoxy. Pre-injection preparation for correct epoxy penetration involves the following steps. Crack cleaning: The crack must be cleaned of all dust, loose concrete particles, oil, grease, and surface contamination that would prevent epoxy adhesion. For cracks in bridge beams exposed to traffic, flush the crack with clean compressed air to blow out debris. For oil-contaminated cracks (common in industrial floors and parking structures), flush with solvent and allow to dry completely before injection — oil contamination is the most common cause of poor epoxy bond. Crack sealing: The crack face (surface trace of the crack on the concrete surface) must be sealed with a rapid-setting epoxy or polyurethane surface sealant to allow pressure build-up during injection. Without sealing the surface, injection pressure simply forces the epoxy out of the crack face rather than driving it deeper into the crack. Apply the surface seal sealant along the full crack trace, leaving only the packer holes open. Packer installation and spacing: Install MC-Packer injection packers along the crack at spacing equal to one-half of the member thickness (for a 300 mm thick bridge beam, install packers at 150 mm spacing). Drill packer holes perpendicular to the member surface (90 degrees, not at an angle) — epoxy is viscosity-driven and does not require angled holes to intersect the crack plane as PU foam does. For cracks in the soffit (underside) of bridge beams, injection is performed from below, which requires higher pressure to fill the crack against gravity — increase pump pressure to 8 to 12 bar. Injection procedure: Mix MC-Injekt 640 in small batches not exceeding the pot life at the site ambient temperature — in Indian summer at 35 to 40 degrees C, the pot life may reduce to 15 to 20 minutes. Load mixed epoxy into the injection pump or cartridge. Inject from the lowest packer (for vertical members) or from one end (for horizontal members), observing for epoxy appearance at adjacent packers to confirm crack filling progress. Record the volume injected at each packer — sudden loss of pressure with no epoxy flow at adjacent packers indicates an undetected branch crack or void that must be located and injected separately.