CONCRETE CRACKING – WHO IS TO BLAME? By Christopher Stanley TECHNICAL DIRECTOR UNIBETON READY MIX. CRACKING FACTS (Concrete Society Technical Report Number 22, non-structural cracks in concrete) “If a concrete is either cooled or dried, then provided it is free. Plastic shrinkage cracking (Type A) Caused. Lack of cover. Aplikasi pembuat tema nokia e61i. Calcium chloride. Precast concrete. Excess calcium chloride. Why does concrete shrink? PLASTIC SHRINKAGE CRACKING.

After decades of building and inspecting in the Post-Tensioning (PT) concrete construction industry, we’ve seen the best and the worst of PT construction. And we keep a (long and growing) list of the mistakes we’ve encountered along the way. Knowing the ways and the extent to which problems can occur helps us implement the most cost-effective and long-lasting repairs possible. And most importantly, it helps us anticipate and avoid mistakes in our own work to create stronger, longer-lasting structures. While we’ve encountered many more, here’s a selection of the 10 most common mistakes we’ve encountered in PT construction: 10. Not considering long-term cracked deflections.

PT beams and slabs have an inherent advantage over non-PT members when it comes to deflection. But it is still critical to check and correct for long-term deflection at the design stage. It is especially critical where drainage can be an issue in cases such as roofs, parking garages, and balconies, and with flat plates where long term deflections may affect window installation. 3D software will account for instantaneous deflections but long-term deflections may not be readily evident.

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If this is the case, take the time to create a load combination for this output. 9. Using rebar for shrinkage and temperature reinforcement in parking garage slabs. Rebar reinforcement in this case is technically allowed by code but in our experience, a properly designed post-tensioned concrete slab will minimize cracking due to shrinkage. We recommend using PT for temperature and shrinkage reinforcement. 8. Neglecting to design general anchorage zones or delegating this responsibility.

PT suppliers are responsible for design of local anchorage zones, and many engineers incorrectly assume they will also take care of the general zone. And while code allows a licensed design professional (LDP) to delegate the design of the general anchorage zone to the contractor, we don’t recommend taking that route. The design of general anchorage zones is critical to the integrity of any post-tensioned concrete structure and we recommend that the LDP complete this task personally. 7. Sweeping tendons at low points without proper detailing.

If it is necessary to sweep tendons laterally – and often, it will be as a result of miss-aligned columns – make sure you are detailing these areas properly, whether at low points or at any other point in the slab. Tendons with lateral curvature at low points have a tendency to blowout the bottom of the slab – either immediately upon stressing or many years later. Refer to the PTI Manual, Sixth Edition, 2006, p. 125 for more information on proper detailing for this condition. 6. Ignoring the effect of slab folds on tendon profile. At slab folds, it is important to check tendon profile at critical points along the span to ensure the cable is positioned properly. It is not uncommon to see a theoretical tendon path falling outside of the slab at the fold – clearly a situation to be avoided.